Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs (SpringerBriefs in Environmental Science) [1st ed. 2023] 9789819964338, 9789819964345, 9819964334

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SpringerBriefs in Environmental Science Ken Sun

Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs

SpringerBriefs in Environmental Science

SpringerBriefs in Environmental Science present concise summaries of cuttingedge research and practical applications across a wide spectrum of environmental fields, with fast turnaround time to publication. Featuring compact volumes of 50 to 125 pages, the series covers a range of content from professional to academic. Monographs of new material are considered for the SpringerBriefs in Environmental Science series. Typical topics might include: a timely report of state-of-the-art analytical techniques, a bridge between new research results, as published in journal articles and a contextual literature review, a snapshot of a hot or emerging topic, an in-depth case study or technical example, a presentation of core concepts that students must understand in order to make independent contributions, best practices or protocols to be followed, a series of short case studies/debates highlighting a specific angle. SpringerBriefs in Environmental Science allow authors to present their ideas and readers to absorb them with minimal time investment. Both solicited and unsolicited manuscripts are considered for publication.

Ken Sun

Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs

Ken Sun College of Water Resources North China University of Water Resources and Electric Power Zhengzhou, Henan, China

ISSN 2191-5547 ISSN 2191-5555 (electronic) SpringerBriefs in Environmental Science ISBN 978-981-99-6433-8 ISBN 978-981-99-6434-5 (eBook) https://doi.org/10.1007/978-981-99-6434-5 © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore Paper in this product is recyclable.

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Current Progress of Antibiotics Contamination and Treatment . . . . 1.1.1 The Concept and Classification of Antibiotics . . . . . . . . . . . . 1.1.2 Current Progress of Antibiotic Contamination . . . . . . . . . . . . 1.1.3 Effects of Antibiotics on Environment and Health . . . . . . . . . 1.1.4 Treatment Techniques of Antibiotics . . . . . . . . . . . . . . . . . . . . 1.2 Research Progress on the Adsorption of Clay Minerals to Antibiotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 Structural Characteristics of Common Natural Clay Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Research Progress on the Adsorption of Natural Clay Minerals to Antibiotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Research Progress in the Application of Organically Modified Clay Minerals to Antibiotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Preparation of Organically Modified Clay Minerals . . . . . . . 1.3.2 Characterization Techniques of Organically Modified Clay Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3 Study on the Surface Reaction Between Modifier and Clay Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.4 Study on the Adsorption of Organic Modified Clay Minerals to Antibiotics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Preparation and Adsorption Methods of Four CTAB Modified Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Adsorption and Mechanism of CTAB Modified Zeolite for DS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 1 2 2 5 12 13 19 21 21 22 24 25 28 31 35 35 35

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2.2.2 Adsorption and Mechanism of CTAB Modified Kaolinite for DS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 Adsorption and Mechanism of CTAB Modified Montmorillonite on DS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Adsorption Characteristics of Modified Illite on DS . . . . . . . 2.3 Chapter Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Study on the Adsorption of Anionic Antibiotics on Natural Clay Minerals Modified by Ionic Liquids . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Preparation and Adsorption Experimental Methods of Three Cationic Modified Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Adsorption and Mechanism of CAP on Ionic Liquid Modified Zeolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Adsorption Characteristics of Modified Montmorillonite to CAP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Adsorption Characteristics of Modified Illite to CAP . . . . . . 3.3 Summary of this chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Molecular Dynamics Simulation of Adsorption of Anionic Antibiotics on Organic Modified Natural Clay Minerals . . . . . . . . . . . 4.1 Modelling with the Materials Studio . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Modeling Clay Mineral Structures . . . . . . . . . . . . . . . . . . . . . . 4.1.2 Modeling Structure of Surfactant . . . . . . . . . . . . . . . . . . . . . . . 4.1.3 Modeling Structure of Antibiotics . . . . . . . . . . . . . . . . . . . . . . 4.2 Molecular Dynamics Simulation of Cationic Surfactants and Antibiotics Adsorbed on the Surface of Zeolite . . . . . . . . . . . . . . 4.2.1 Setting Molecular Force Field, Molecular Dynamics Module and Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Outcomes and Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Molecular Dynamics Simulation of the Adsorption of Cationic Surfactants and Antibiotics on the Surface of Kaolinite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Setting Molecular Force Field, Molecular Dynamics Module and Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Outcomes and Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Molecular Dynamics Simulation of the Adsorption of Cationic Surfactants and Antibiotics on the Surface of Montmorillonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Setting Molecular Force Field, Molecular Dynamics Module and Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Outcomes and Discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Summary of This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 5 Dynamic Adsorption Experiment of Modified Zeolite and Montmorillonite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Experimental Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Adsorption Experiments of CTAB Modified Zeolite and Montmorillonite on DS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Adsorption of CAP on Zeolite and Montmorillonite Modified by Ionic Liquid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Summary of This Chapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

105 107 107 110 112 113 114

6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Chapter 1

Introduction

Abstract The pollution of PPCPs had become a global environmental problem. How to efficiently and deeply control the pollution of PPCPs in the water had become a hot spot and a difficult issue in the global environmental field. Therefore, it was very urgent and necessary to study the efficient PPCPs pollution control and removal technologies. This chapter introduced the concept and pollution status of PPCPs as well as treatment technologies at home and abroad, the research progress of adsorption of PPCPs by clay minerals, and the research progress of organic modified clay minerals on PPCPs. It also introduced the purpose, significance, main content and technical route of this book. Keywords PPCPs · Natural clay minerals · Organic modified clay minerals

1.1 Current Progress of Antibiotics Contamination and Treatment 1.1.1 The Concept and Classification of Antibiotics Antibiotics are a class of secondary metabolites, which are produced in the process of life with anti-pathogen or other activities in the microorganisms (including bacteria, fungi, actinomycetes) or higher flora and fauna and can interfere with the development of other living cell functions of chemical substances. According to the chemical structure, antibiotics can be divided into quinolone antibiotics, β-lactam antibiotics, macrolides, aminoglycoside antibiotics, etc. According to its use, antibiotics can be divided into anti-bacterial antibiotics, antifungal antibiotics, anti-tumor antibiotics, antiviral antibiotics, livestock antibiotics, agricultural antibiotics, and other microbial drugs (such as ergotine produced by ergot with pharmacological activity of alkaloids, which has the effect of contracting the uterus), et al. According to the different types, antibiotics have many ways of

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 K. Sun, Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-981-99-6434-5_1

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production, such as penicillin by microbial fermentation for biosynthesis. Sulfonamides, quinolones, and other antibiotics can be produced by chemical synthesis. There are semisynthetic antibiotics, whose molecular structures are modified by chemical, biological or biochemical methods.

1.1.2 Current Progress of Antibiotic Contamination As the population grows, so does the need for animal protein, and so does the need for antibiotics. In 2018, the production of antibiotics in China was 205,000 t. And it grew to 218,000 t in 2019 (Beijing Zhongjing Vision Information Consulting Co., LTD, 2020). China has a problem of an excessive amount of antibiotics for both human and animal use. Humans and animals metabolize antibiotics very slowly, and more than 70% of antibiotics are excreted into the environment same as before (). In addition, China also consumes a lot of antibiotics. Among China’s prescription drugs, antibiotics accounted for 70%, while western countries do not half as much as China. In addition to being used as medicine to treat human diseases, antibiotics are also widely used in animal breeding. One is the application of antibiotics in the prevention and treatment of diseases, and the other is to improve the animal production performance. According to relevant data, about 70% of antibiotics are used in animal husbandry. In animal husbandry, the amount of antibiotic additives in the feed eaten by animals accounts for 45.8%. More than 70% of antibiotics will be eliminated in their original form, and some of them will be disposed into sewage plants along with the domestic wastewater. At present, there is no standard for antibiotic discharge and environmental acceptance criteria. Due to lack of effective treatment, the vast majority of antibiotics will enter surface water, pollute drinking water sources and pollute groundwater through water circulation. Additionally, antibiotics retained by the medical waste in landfills will seep down into groundwater and pollute water supplies. Long-term use of antibiotics in fish pond silt, the presence of antibiotics in animal excrement and sewage sludge, can be used as organic fertilizer for agricultural production. If antibiotics enter the farmland through this route they will pass through the food chain, accumulate in the human body, and be harmful to human health.

1.1.3 Effects of Antibiotics on Environment and Health Antibiotics are usually characterized by environmental persistence, bioaccumulation, and toxicity. They can migrate freely in the environment, disperse in soil, water and atmosphere, or accumulate in animals and plants, causing different degrees of damage to human health and ecological environment. Since August 2012, when the

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Ministry of Health implemented the “Strictest Restriction on Antibiotics” (Administrative Measures on Clinical Application of Antibiotics), antibiotics have been subject to increasingly strict supervision in hospitals and pharmacies. The agricultural sector also constantly issued a list of banned certain antibiotics, However, due to the dispersed farmers, supervision is difficult and ineffective. The situation in the use of antibiotics reflects the difficulties of treatment: there is a lack of comprehensive investigation of the pollution situation, and there are numerous toxic and harmful chemicals; the related scientific research is still relatively weak and the applications of new monitoring methods are less; the cost of “treatment after pollution” is extremely high and there is a lack of effective removal technology. At present, antibiotic residues are commonly detected in soil, water, animal, plant samples, and in surface water and even in groundwater several hundred meters below the surface. Haihe River and Zhujiang River basin are the two most seriously polluted rivers with average concentrations dozens of times higher than those in western basins such as Brahmaputra River. About 46% of the antibiotics that were seen going into the water, and 54% went into the soil. Sacher et al. (2001) collected 108 underground water samples from Germany and found that there were 60 kinds of antibiotics in the water samples at the level of μg/L. Tong et al. (2009) found that groundwater and surface water in Hubei Province contained a variety of typical quinolone antibiotics, and the content of quinolone antibiotics in surface water (0.01 μg/L) was significantly higher than that in groundwater (0.001 μg/L). Sun’s study (2009) on surface water quality analysis in Xiamen also showed that surface water was polluted by antibiotics. In addition to detecting antibiotics in surface water in areas with high human activity, antibiotic contamination has also been detected in surface water in some scenic areas. Golet et al. (2001) detected ng/L quinolone antibiotics in the streams of the watershed in the valley of Grat, Switzerland. Tang et al. (2018) tested 12 kinds of sulfonamides from 14 sampling points in the water in the Nanjing section of the Yangtze River, and the results showed that 8 kinds of sulfonamides were detected in the surface water of the southern section of the Yangtze River, with a concentration range of 13.2–21.0 ng/L, with an average value of 16.2 ng/L. Liu et al. (2020) found that the concentration of antibiotics in Qingshan Lake, Taihu Lake in China, ranged from 0.05 to 940 ng/L, and the concentration of antibiotics in groundwater ranged from 0.57 to 503 ng/L. Li (2020) found that the average concentration of antibiotics in the sediments of Jiaxing and Shangyuna sewage areas was 48,180.7 ng/L, and the average concentration of antibiotics in the sediments was 34.8 ng/g and 74.67 ng/g, respectively. Half of China’s antibiotics go to the farming industry. And a large amount of sewage treatment equipment for antibiotic treatment is inadequate. Untreated sewage from many cultivation enterprises is discharged directly into rivers or used to irrigate fields. China has yet to establish a clear standard for antibiotics in sewage. The overuse of antibiotics in humans and animals is believed to be a major cause of the development of drug-resistant bacteria. During the breeding cycle of animals in China, farmers and farmers have been feeding them a small number of drugs., these drugs are not used to cure the sick animals, but to promote growth, and suppress from close contact with each other’s waste caused by disease, animals eat antibiotics,

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after only a few is absorbed, most with faeces. The resistant bacteria can spread to humans through the environment, eating the meat of the animals, or in some cases becoming “superbugs” making it difficult even impossible to treat the infection with conventional antibiotics without the development of new drugs. The threat has been exposed in humans. The abuse and resistance of antibiotics in animals has become one of the major public health problems worldwide. Doctors are faced with fewer choices and less time to make decisions. They are often troubled by the agonizing choice of how to save a patient’s life. Antibiotics can save lives, but the threat of abuse is even direr. Zhang (2005) also detected a high content of antibiotics (1.57– 6.29 mg/kg) in chicken, cow, and pig manure. After the usage of antibiotic-containing sludge or livestock manure, the soil was seriously polluted by antibiotics, and the pollution was persistent. Ma (2007) found that the total concentration of antibiotics in pig manure was up to 10.83 mg/kg. Zhou et al. (2007) surveyed antibiotics in northern farmland soil, showing that the antibiotic content in common soil was at μg/kg level, while the antibiotic content in the soil-applied organic fertilizer was relatively high and varied widely, fluctuating between μg/kg level and mg/kg level, among which the content of sulfamethazine in the soil was as high as 900 mg/kg. Chu et al. (2021) established an estimation model of the carrying capacity of livestock and poultry manure polluted farmland based on the ecological risk value of antibiotics in farmland soil and studied aquaculture and planting production system in Heilongjiang Province and Xinjiang Production and Construction Corps. The results showed that high ecological risk antibiotics such as sulfadiazine and enoxacin should be the main measures to prevent the ecological risk of antibiotics in farmland soil of Heilongjiang Province and Xinjiang Production and Construction Corps. Antibiotics can also enter the farmland soil system through the agronomy of sludge, the application of organic fertilizer and irrigation water, causing the pollution of antibiotics in the soil, leading to the absorption and accumulation of antibiotics in vegetables, and thereby threatening human health through the food chain. Different plant varieties had different effects on the accumulation of antibiotics in soil, and the accumulation of antibiotics in plants increased with the increase of soil antibiotic content. The soil of a vegetable base in the south where organic fertilizers were used contained antibiotics. Li et al. (2008) found that the content of antibiotics in the soil of vegetable base reached the level of several hundred micrograms per kilogram. The study of antibiotics in the soil in the pearl river delta led by Tai et al. (2010) showed that quinolone, tetracycline and sulfa antibiotics were widely detected in the pearl river delta and even high-grade vegetable base soil (such as pollution-free vegetable production base, green vegetable production base, and organic vegetable production base), levels in dozens to hundreds of micrograms per kilogram. Lillenberg et al. (2010) found that cucumber, barley, and lettuce could all absorb and accumulate antibiotics, ciprofloxacin, and enrofloxacin. Wu (2011) in Guangzhou and Dongguan vegetable quinolones, according to a study by 4 kinds of quinolones compounds (ciprofloxacin, norfloxacin and maintain, and grace of sand) the detection rate of not less than 90%, melon kind of antibiotic content in different kinds of vegetable averages (including 91.29 g/kg, in all kinds of vegetable products the first place, and the average content of antibiotics in leaf vegetables was 52.30 μg/kg, which was

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the least in all kinds of vegetables; The content of antibiotics in green vegetables was the highest, with an average of 104.49 μg/kg, and the content of antibiotics in common vegetables was the lowest, with an average of 61.23 μg/kg. Li et al. (2021) investigated and analyzed the pollution of antibiotics in vegetables in eastern Hebei and found that the types of antibiotics and vegetables in vegetables in eastern Hebei were important factors affecting the distribution characteristics of antibiotics.

1.1.4 Treatment Techniques of Antibiotics At present, the treatment technology of antibiotics mainly includes physical treatment technology, chemical treatment technology, biological treatment technology, and the combination of many methods. (1) Physical processing technology The wastewater from antibiotic production is a kind of organic wastewater that is difficult to degrade, especially the strong inhibitory effect of the residual antibiotics on microorganisms, which makes the wastewater treatment process more complicated and expensive, and the effect is not stable. Therefore, physical methods can be used to reduce suspended solids in water and biological inhibitory substances in wastewater. At present, the commonly used physical methods include coagulation, precipitation, air floatation, adsorption, reverse osmosis, filtration, and so on. Coagulation method is a method of forming a flocculent which has lost its electric charge contact each other after adding coagulant and through stirring, which is convenient for its precipitation or filtration to achieve the purpose of separation. Coagulation method can effectively reduce the concentration of pollutants and improve the biodegradability of wastewater. Coagulants commonly used are polymerized FeSO4 , FeCL2 , ferrite salt, poly aluminum chloride sulfate, polyaluminum chloride, polyaluminum chloride ferric sulfate, PAM, etc. Sedimentation is the method of separation or removal from the suspended particles that are denser than water. Air floatation is the method of solid–liquid or liquid–liquid separation by using tiny bubbles to absorb pollutants in wastewater. Generally, it includes the methods of inflatable air flotation, dissolved air flotation, chemical air flotation, and electrolysis air flotation. Adsorption method is the method in which porous solids are used to adsorb certain or several pollutants in wastewater to recover or remove pollutants and make the wastewater be purified. The adsorbents commonly used are activated carbon, active coal, humic acid, adsorption resin, and so on. This method has the advantages of small investment, simple process, convenient operation, and easy management, and it is suitable for improving the process of the original sewage treatment plant. The reverse osmosis method is the method in which can achieve the purpose of concentration and purification of wastewater. With pressure difference as a driving

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force, it’s to use a semi-permeable membrane to separate the concentrated and dilute solution, and it applies pressure beyond the osmotic pressure of the solution, so that it changes the natural osmosis direction, pushes the water from a strong solution into a dilute solution side, When the concentration of ammonia nitrogen greatly exceeds the allowable concentration of microorganisms, microorganisms are inhibited, and it is not easy to obtain good results. (2) Chemical treatment technology 1) Application of photocatalytic technology in the treatment of antibiotic wastewater Antibiotic wastewater has unstable water quality and many inhibitory substances, so it is difficult to remove the pollutants completely by conventional treatment. Therefore, the treatment of antibiotics in wastewater by using new photocatalytic oxidation technology has become a new research direction. Foreign scholar Emad (2010) conducted related photocatalytic studies on amoxicillin and cloxacillin, etc. Under ultraviolet conditions, titanium dioxide photocatalysis has low removal efficiency for several antibiotics in wastewater, and it is not cost-effective. There are also many related types of research in China. Ye (2014) made Si-ZnO nanomaterials, and the photocatalytic degradation rates of Si-ZnO materials for TC (tetracycline), OTC (oxytetracycline) and DC (doxycycline) under UV radiation were 96.44%, 77.83% and 84.83%, respectively. Shi (2013) prepared Ki-I2-doped TiO2 catalyst and studied tylosin, norfloxacin, sulfadiazine sodium and tetracycline hydrochloride. Under the conditions of simulated sunlight, optimum pH value, initial solution concentration of 0.1 mmol/L and catalyst dosage of 1 g/L. The results showed that the maximum removal rates of norfloxacin, tetracycline hydrochloride, sulfadiazine sodium, and tylomycin were 98.2, 96.7, 91.8, and 90.7%, It was also pointed out that pH was an important factor affecting degradation in photocatalytic reactions (Wang 2011; Yang et al. 2009). Wang et al. (2021) reviewed the mechanism and research progress of photocatalytic degradation of sulfonamides (SAS) in water, they gave a detailed introduction of TiO2 Modified materials, and graphite-phase carbon nitride (G-C3 N4 ) based materials were used as photocatalysts to degrade SAS. Researchers have demonstrated the feasibility of photocatalytic technology for degrading antibiotics in wastewater, but the removal of antibiotics at low concentrations has been less studied. There has been little research into the degradation of antibiotics by FeOOH. Most semiconductor materials are conventional titanium dioxide or related doping modified materials. How to improve the catalytic efficiency of FeOOH materials and explore the optimal degradation conditions and degradation mechanisms of different antibiotics have become the focus of research. Photolysis is the main degradation way to antibiotics in feces, because tetracycline, quinolone, and sulfonamides antibiotics, as well as toxins and nitrofurans and other antibiotics, are sensitive to light and easy to decompose under sufficient light conditions. This photolysis mainly exists in places with sufficient light, such as soil, sewage, and silt. It is mainly divided into direct degradation and indirect degradation, among which the main factors affecting photolysis mainly include light frequency

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and light intensity. In addition, the photolysis efficiency of antibiotics is influenced by various environmental conditions, factors such as pH and hardness of the water all affect the photolysis. Werner et al. found that at different pH values and ion concentrations (Ca2+ and Mg2+ ), the photolysis first-order rate constant of tetracycline can vary by an order of magnitude. 2) α-FeOOH with graphene loading Graphene is a two-dimensional carbon nanometric material, which is composed of a single layer of carbon atoms packed tightly. Each carbon atom exists in a hexagonal sp2 hybridized orbital. In the remaining one p orbital, electrons form conjugated π–π bonds with good mobility, and the lattice is honeycombed. Graphene is extremely hard, it far exceeds the hardness of diamonds and existing steel, but its thickness does not exceed 0.5 nm. Its thermal conductivity is better than that of carbon nanotubes and diamonds. Its thermal conductivity is more than 10 times that of copper at room temperature, making it the carbon material with the highest thermal conductivity at present. Graphene has a unique electronic structure and electrical performance, the moving speed of the electrons in graphene is much higher than another normal conductor of movement speed. It has high electron mobility. At room temperature, the electrons and holes can co-exist in a row, and its carrier concentration is extremely high, little affected by temperature, graphene carrier mobility can be up to 4 × 104 cm2 /(V S) under ideal conditions, and the carrier concentration is as high as 1013 /cm2 . Graphene Oxide is a kind of Graphene derivatives. Its surface contains rich oxygen-containing groups such as hydroxyl group, carboxyl group, and epoxy group, which enhance the hydrophilicity of Graphene materials. The GO dispersion system is easy to form film and has a high monolayer rate. The oxygen-containing groups are conducive to the in-situ composite of GO and other materials and enhance the role of chemical and ionic bonds between composites. Other derivatives of graphene include graphane, nitrogen-doped graphene, etc. When α-FeOOH was loaded with graphene, the crystal structure remained unchanged. By XRD detection, no characteristic peak of GO was detected in the spectrum, indicating that α-FeOOH was evenly distributed on the surface of the graphene and successfully loaded. Compared with normal α-FeOOH/GO, the particle size of α-FeOOH/GO decreases to a certain extent, and there is no large cluster structure on the surface of α-FeOOH/GO, which improves the surface agglomeration phenomenon, and the crystal plane spacing is about 0.27 nm. The specific surface area of α-FeOOH/GO was significantly increased by graphene loading, reaching about 133 m2 /g for both 0.2 m-α-FeOOH/GO and 0.4 m-α-FeOOH/GO, Compared with 0.2 M and 0.4Mα-FeOOH samples, the increase was about 71.8 m2 /g and 34.5 m2 /g, respectively. There are more contact opportunities between the material and the degradation substrate, which enhances the photocatalytic efficiency; The average pore size of α-FeOOH/GO decreases, and the minimum pore size is about 4.7 nm, but the overall pore volume of α-FeOOH/GO material increases, increasing the total adsorption capacity. Through characterization, the defect density of GO is higher, and the electron conduction on α-FeOOH/GO composite material is easier, which speeds up the photocatalytic reaction rate.

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1 Introduction

Using GO as a substrate greatly increases the specific surface area of α-FeOOH/ GO, making it have more contact area with the catalytic substrate, enhancing the adsorption capacity of α-FeOOH/GO, and increasing the total adsorption capacity of the composites. Through kinetic fitting, it is found that the second-order kinetics is more suitable to describe the whole process of α-FeOOH/GO adsorption of tetracycline. There is chemisorption in the adsorption process, which can adsorb tetracycline in water solution faster. (3) the combination of biological treatment and a variety of methods 1) Aerobic treatment method Aerobic biological methods commonly used include: ordinary activated sludge method, pressurized biochemical method, deep well aeration method, biological contact oxidation method, biological fluidized bed method, sequential batch activated sludge method, etc. At present, activated sludge process is a mature method to treat antibiotic wastewater at the domestic and foreign. The activated sludge method improves the aeration method due to enhanced pretreatment and stable operation of the device. However, the disadvantage of the ordinary activated sludge process is that the wastewater needs a lot of dilution, the operation of the foam, easy to occur sludge bulking, the residual sludge amount is large, the removal rate is not high, and it often adopts two or multi-stage treatment. Therefore, it has become an important content in the research and development of activated sludge process to improve aeration method and microbial immobilization technology to improve the treatment effect of wastewater. Compared with the ordinary activated sludge process, the pressurized biochemical method can increase the concentration of dissolved oxygen and provide sufficient oxygen, which is not only conducive to accelerating biodegradation but also conducive to improving the ability of biological impact load resistance. Deep well aeration is a method of high speed activated sludge system. Compared with the common activated sludge process, the deep well aeration has the following advantages: High oxygen utilization rate, equivalent to 10 times of the common aeration; High sludge load, 2.5–4 times higher than ordinary activated sludge process; Small area, less investment, low operating cost, high efficiency, the average COD removal rate can reach more than 70%; Strong resistance to hydraulic and organic load impact; There is no sludge bulking problem; Good heat preservation effect. The biological contact oxidation has the characteristics of both the activated sludge process and the biofilm process. It has a higher treatment load and can treat the organic wastewater which is easy to cause sludge bulking. In the treatment of pharmaceutical production wastewater, biological contact oxidation method, or anaerobic digestion, acidification as pretreatment process is often used to treat pharmaceutical production wastewater. However, in the treatment of pharmaceutical wastewater by contact oxidation method, prevention and treatment measures should be taken during the operation, if the influent concentration is high because a large amount of foam is likely to appear in the pool. The biological fluidized bed combines the advantages of the ordinary activated sludge method and the biological filter method, so it has the

1.1 Current Progress of Antibiotics Contamination and Treatment

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advantages of high volume load, fast reaction speed, small occupation area, and so on. Sequential batch activated sludge process (SBR) has the advantages of homogenizing water quality, no need of sludge reflux, impact resistance, high sludge activity, simple structure, flexible operation, less area, less investment, stable operation, substrate removal rate is higher than that of ordinary activated sludge process, etc., which is more suitable for the treatment of wastewater with intermittent discharge and large fluctuation of water quantity and quality. However, the SBR method has the disadvantages of long sludge sedimentation and slurry separation time. In the treatment of high concentration wastewater, it is required to maintain a high sludge concentration, at the same time, it is easy to occur high viscosity expansion. Therefore, it is often considered to add powdered activated carbon to reduce aeration tank foam, improve sludge settling performance, liquid–solid separation performance, sludge dehydration performance, etc., to obtain a higher removal rate. The direct application of aerobic treatment of antibiotic wastewater still needs to consider the residual antibiotics in the wastewater to the existence of the toxicity of aerobic bacteria, so it is generally necessary to pretreatment the wastewater. 2) Anaerobic treatment Anaerobic biological treatment is a method that refers to the process of decomposing various complex organic substances in wastewater into methane and carbon dioxide by anaerobic microorganisms (including facultative microorganisms) in the absence of molecular oxygen. It is also called anaerobic digestion. Main metabolism due to anaerobic treatment process of acid-producing bacteria and methane-producing bacteria have relatively different biological characteristics. Therefore, different environmental conditions suitable for its growth can be constructed separately, and acidproducing bacteria can grow fast and have poor sensitivity to poisons as the first stage of the anaerobic process to improve the biodegradability of wastewater and reduce the complex components and toxicity of wastewater. Inhibition of methanogenic bacteria, improve the impact load resistance of the treatment system and ensure the stability of the treatment effect in the methane production stage of the subsequent composite anaerobic treatment system. Anaerobic processes used in antibiotic wastewater treatment include up-flow anaerobic sludge bed, anaerobic composite bed, etc. The key to the efficient and stable operation of UASB is whether the granular sludge with suitable microorganisms, high methane-producing activity, and good settling performance can be formed in the reactor. UASB reactor has the advantages of high anaerobic digestion efficiency and simple structure. However, when using the UASB method to treat pharmaceutical production wastewater, it is usually required that SS content should not be too high to ensure the COD removal rate. Upflow anaerobic sludge bed filter is a new type of composite anaerobic reactor developed in recent years. It combines the advantages of UASB and anaerobic filter and improves the performance of the reactor. The composite reactor can effectively intercept the sludge, accelerate the granulation of the sludge, and has a good bearing capacity to the fluctuation of volume load and temperature pH value during the start-up operation.

10

1 Introduction

3) Compound anaerobic reactor The compound anaerobic reactor has both the characteristics of sludge and membrane reactor. The results show that the COD volume loading rate of the reactor is 8–13 kg/ m3 d for the treatment of Ethylhelicase production wastewater, satisfactory effluent water can be obtained. When the pressurized up-flow anaerobic sludge bed (PUASB) is used to treat wastewater, the oxygen concentration is significantly increased, the degradation rate of the matrix is accelerated, and the treatment effect can be improved. The lower part of the reactor has the characteristics of a sludge bed, with a huge surface area per unit volume, which can maintain a high concentration of microbial biomass, fast reaction speed, and high sludge load. The top of the reactor is hung with a fibrous composite filler, and the microorganisms mainly exist in the form of an attached biofilm. On the other hand, the gas-producing bubbles rise and contact with the filler and attach to the biofilm, making the surrounding cellulose float. When the bubbles become larger and leave, the fibers droop, which not only plays the role of stirring but also stabilizes the water flow. The COD of the effluent treated by a single anaerobic method is still high, so it is difficult to achieve the standard of effluent. Aerobic treatment is generally adopted to further remove the remaining COD. 4) Photosynthetic bacteria treatment (PSB) Many strains of rhodopseudomonas in photosynthetic bacteria (PSB) can use small molecules of organic matter as hydrogen donor and carbon source and have the ability to decompose and remove organic matter. Therefore, photosynthetic bacteria treatment can be used to treat wastewater from certain industries such as food processing, chemical, and fermentation. PSB can metabolize organic matter under aerobic micro-aerobic and anaerobic conditions, and anaerobic acidification pretreatment can often improve the treatment effect of PSB. PSB treatment process has the advantages of higher organic load, no biogas production, less temperature influence, nitrogen removal ability, small equipment occupation, less power consumption, low investment, the bacteria produced in the process of treatment can be recycled, etc. 5) Anaerobic and aerobic treatment methods and their combination with other methods Single aerobic or anaerobic treatment often can not meet the requirement of the wastewater treatment, and anaerobic–aerobic treatment methods and its combination with other methods of technology in improving wastewater treatment can be biochemical resistance, impact resistance, reduce the cost of investment, improve the effect of processing, etc. is better than a single treatment, make it become the main treatment of pharmaceutical wastewater. Flocculation sedimentation + hydrolytic acidification + SBR process is an effective method to treat pharmaceutical wastewater, which is economical and reasonable and suitable for our country. The anaerobic hydrolysis treatment is used as the pretreatment of various biochemical treatments, this is widely used in the treatment of high concentration organic industrial wastewater which is difficult to biodegrade,

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such as chemical, papermaking, and pharmaceutical because this greatly reduces the production and operation cost, improves the biodegradability of sewage, reduces the load of subsequent biological treatment, greatly reduces the aeration amount of subsequent aerobic treatment process, and reduces the project investment and operation cost. But, in the process of the cultivation of sludge domestication, the aerobic sludge, and anaerobic sludge contains bacteria are sensitive to the environment, although the system has a certain impact resistant ability, if long time in the overload operation conditions, there will be nitration become slow, lead to NO2 –N accumulation on the high side, make the system run in the nitrosation stage, As a result, the quality of effluent water is difficult to be guaranteed. Although at present the biochemical process is the most common way to treat pharmaceutical wastewater. However, with the strengthening of environmental awareness at home and abroad and the continuous improvement of environmental standards, the traditional biochemical method is difficult to achieve the goal. The combination of electrolysis and SBR is feasible for the treatment of pharmaceutical wastewater containing antibiotics. In the pretreatment of pharmaceutical wastewater by electrolysis, the higher the electrolytic voltage is, the faster the removal of COD and chroma of wastewater will be, and the higher the removal rate will be. Electrolytic voltage has a great influence on COD removal. After electrolytic pretreatment, the biodegradability of wastewater is greatly improved, but too long electrolytic time can decrease the biodegradability of wastewater. The influence of pH value on the electrolysis effect exists. Too high or too low pH value is adverse to the removal of COD in wastewater. When the pH value is about 7, the electrolysis effect is relatively good. The effect of pH value on chromaticity removal is small. The COD removal rate of electrolytic pretreatment is 37–47%, and the COD removal rate of the SBR biochemical treatment system can reach 80–86%. To sum up, among all antibiotic removal technologies, the adsorption method has irreplaceable advantages. The removal of antibiotics by adsorption method mainly refers to the adoption of natural clay minerals and some synthetic functional adsorption materials for the adsorption and curing of antibiotics, and the functional modification of some clay minerals with strong adsorption performance can also be carried out to achieve the effect of efficient curing (Lyu et al. 2016). Compared with natural migration, solid-phase adsorption has the advantage of high curing efficiency due to its special adsorption structure and functional adsorption groups. In addition, due to the immature development of advanced oxidation degradation technology, high cost and poor application, and the fact that curing is an important prerequisite for complete degradation, solid-phase adsorption is still the most commonly used antibiotic treatment method at present (Caldas et al. 2016; Kyzas et al. 2013). Was at the beginning of the study, taking advantage of the activated carbon adsorption of antibiotics in sewage, however, activated carbon for natural hydrophobic organic contaminants (NOM) has high removal efficiency, and for some antibiotics removal effect of polarity is still limited (Wang et al. 2015), combined with the regeneration of activated carbon materials technology is not mature and limits its application. In addition, the immature regeneration technology of activated carbon material limits its application (Dawood and Sen 2012). Clay minerals adsorb antibiotics better than

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1 Introduction

sandy soil with low content of organic solvents. This is because the surface of clay minerals often contains some organic substances, which have similar compatibility with antibiotics of organic pollutants (Doretto et al. 2014; Teijon et al. 2013). Therefore, no matter polar or non-polar antibiotics, clay minerals will have a certain adsorption effect on them. On the other hand, the surface electrical properties of natural clay minerals promote the adsorption of anionic or cationic antibiotics. In addition, the clay minerals with expandable structure or large pore structure have obvious curing effect on some antibiotics with moderate size, and the clay mineral adsorption method is simple, low cost and no secondary pollution. Moreover, the adsorption characteristics of clay minerals can be further improved by surface modification and modification. Therefore, clay mineral adsorption has become the most promising antibiotic treatment method at present (Polubesova et al. 2006). Through the adsorption of natural clay minerals, the diffusion of antibiotics in the environment can be controlled, the absorption of antibiotics in plants can be reduced, and the effect of antibiotics on underground organisms can be reduced (Kan et al. 2011).

1.2 Research Progress on the Adsorption of Clay Minerals to Antibiotics Natural clay minerals can be divided into crystalline and amorphous types. Crystalline clay minerals can be divided into two types of structures: layered and interlayered. Layered clay minerals are generally composed of [SiO4 ] tetrahedral lamellae and [Al(Mg)O8 ] octahedral lamellae in a certain proportion and manner to form structural unit layers, which are periodically stacked along the C-axis. The distance between the lamellae is determined by the content of cations and water molecules between the lamellae (Martin et al. 1991). The layered clay minerals can be divided into two structural types according to the proportion of the basic structural layers in the structural unit layers and the way of superposition: (1) 1:1 structural layer: composed of a layer [SiO4 ] tetrahedral lamellae and a layer [Al(Mg)O8 ] octahedral lamellae are combined into basic structural unit layers, which are arranged periodically along the C-axis, such as kaolinite group minerals (White et al. 2011); (2) 2:1 Structure layer: the basic structural unit layer is composed of two [SiO4 ] tetrahedral lamellae sandwiched by one [Al(Mg)O8 ] octahedral lamellae, which are periodically arranged along the C-axis, (Fang 1985). On the other hand, according to the difference of interlamellar substances and unit chemical formula charge (X), stratified clay minerals can be divided into kaolinite group (X = 0), montmorillonite group (0.2 < X < 0.6), illite group (0.6 < X < 1), and chlorite group (X Tianjin) (Fang 1985). The structure of chain-layered clay minerals is also composed of [SiO4 ] tetrahedron and [Al(Mg)O8 ] octahedrons, but tetrahedrons and octahedrons are eventually linked to each other into a shelflike structure with pores, such as zeolite and sepiolite, etc.

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(Alessandro 2006). The composition of amorphous clay minerals is not fixed and does not have a certain crystal structure, such as hydroaluminite and ferrosilicate.

1.2.1 Structural Characteristics of Common Natural Clay Minerals (1) the structural characteristics of zeolite Zeolite is a frame structure of aqueous aluminum silicate minerals, pure zeolite is colorless or white, but can be mixed with impurities into a variety of light color, Morse hardness medium, specific gravity 2.0–23.0. The basic structure of the skeleton is tetrahedron [SiO4 ] and aluminum oxide tetrahedron [AlO4 ]. In this tetrahedron, there are Si or Al atoms at the center, and each Si or Al atom is surrounded by four oxygen atoms. Due to the different connection modes of [SiO4 ] and [AlO4 ] tetrahedrons, many holes and channels are formed in the zeolite structure. They can be one-dimensional (a specially developed channel in one direction), twodimensional (two directions connected), or three-dimensional (three directions of space connected). Among them, [AlO4 ] tetrahedrons itself cannot be connected, and there must be a [SiO4 ] tetrahedron in the middle, while [SiO4 ] tetrahedron can be connected (Bare et al. 2005). The chemical composition of zeolite is complex, and there are great differences due to different types. The channels mainly contain Na and Ca and a few metal ions such as Sr, Ba, K and Mg. The structural formula is Am/q [(AlO2 )x (SiO2 )y ]nH2 O, where A is the cations such as Ca, Na, K, Sr, Ba, q is the price of cations, m is the number of cations, n is the number of water molecules, x is the number of Al atoms, y is the number of Si atoms, y/x is usually between 1 and 5, (x + y) is the number of tetrahedrons in the unit cell (Shan 2007). Therefore, due to the presence of exchangeable cations in zeolite pores, zeolite has a strong adsorption performance for cationic antibiotics, and there is pore adsorption for antibiotics whose molecular size is smaller than the zeolite pore size. The common zeolites include pyroxenes (Fig. 1.1a), clinoptilolite (Fig. 1.1b), etc. The structure of pyroxenes is composed of [SiO4 ] tetrahedron and [AlO4 ] tetrahedron with a common angular apex connected to form a frame structure, the chemical composition of Na7.67 Ca4.84 (Al17.35 Si54.65 O144 )(H2 O)16.56 , space group: Amma, orthogonality system, Si-Al ratio of about 3:1. Xinhui zeolite crystal cell parameters are: a = 13.7200 (5) Å, b = 17.6808 (8) Å, c = 17.4461 (8) Å, a/b = 0.7760, b/c = 1.0135, c/a = 1.2716, (31) V = 4232.08 Å3 , Z = 1 (ICSD-83469). The structure of clinoptilolite is a frame structure composed of [SiO4 ] tetrahedrons connected by a con angular top. The chemical composition of clinoptilolite is Ca3.16 Si36 O72 (H2 O)21.80 , space group is C12/m1, monoclinic system. Crystal cell parameters of clinoptilolite are: a = 17.646 (5) Å, b = 17.898 (15) Å, c = 7.397 (5)Å, β = 116.37°, (3) V = 2093.09 (239) Å3 , Z = 1 (ICSD-4349). Figure 1.2 shows the standard XRD diffraction patterns of pyroxenes (Fig. 1.2a) and clinoptilolite (Fig. 1.2b). By comparing the actual XRD patterns of zeolite

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1 Introduction

Fig. 1.1 Crystal structure of pyroxenes (a) and clinoptilolite (b)

(a) Intensity(a.u.)

Intensity(a.u.)

(b)

10

StilbitePDF#89-8589 20 30 40 50 2Th (Degree)

10

Clinoptilolite PDF#25-1349 20 30 40 50 2Th (Degree)

Fig. 1.2 Standard XRD patterns of pyroxenes (a) and clinoptilolite (b)

samples in the experimental study with the standard patterns of pyroxenes and clinoptilolite, the contents of pyroxenes, clinoptilolite, and other phases in the experimental zeolite samples can be characterized. (2) Structural characteristics of kaolinite Kaolinite is a common and important clay mineral (Yu et al. 1996; Jin 1992), its structure is 1:1 type layered silicate, mostly white or light gray color, earlike luster, specific gravity 2.60–2.63, Mohs hardness 2.0–2.5. The basic structural unit layer of kaolinite is composed of a [SiO4 ] tetrahedral lamellar and an [AlO8 ] octahedral lamellar, which are periodically arranged along the C-axis (Fig. 1.3) (Bougeard et al. 2000). There are no water molecules and exchangeable cations between the layers, so the surface is electrically neutral and the unit chemical formula charges X = 0 (Fang 1985). The layer spacing of kaolinite is relatively small, about 7 Å. Since there are no cations or water molecules between the layers, strong hydrogen bonds strengthen the connection between the structural layers, giving kaolinite weak cation exchange properties (Mackay and Seremet 2008; Carrasquillo et al. 2008; Li et al. 2010), so its adsorption behavior is mostly surface adsorption. The adsorption of organic compounds, heavy metals and other pollutants by kaolinite have important effects on migration. Using acid–base titration and surface complexation theory, some researchers have established a theory of proton adsorption on kaolinite surfaces

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Fig. 1.3 Crystal structure of kaolinite

(Brady et al. 1996; Huertas et al. 1998). For example, Xie Zhipeng conducted a study to develop the adsorption properties of organic molecules carboxymethyl sesbania gum kaolinite and montmorillonite, he found that there was no significant change before and after the kaolinite clay layer, which indicate adsorption on the outer surface rather than the inner layer. The chemical composition of kaolinite is Al2 [Si2 O5 ] · (OH)4 , the space group is C1 , triclinic system, Si: Al = 1:1, so it is called 1:1 type clay minerals. Kaolinite crystal cell parameters for a = 5.1400 Å, b = 8.9100 Å, c = 7.2600 Å, α = 91.6700°, β = 104.6700°, gamma = 90.0000°, V = 321.50 Å3 , Z = 2 (ICSD-20593). Since the length of the unit cell on-axis c in the standard card is just the length of the period of a structural unit (Fig. 1.3b), the vertical distance of c in plane a and plane b can be calculated to approximate the inter-layer distance of kaolinite. According to the formula: d = c × sin β (1), where d is the layer spacing of kaolinite, c is the distance of the unit cell of kaolinite along the C-axis, and β is the Angle between Axis a and Axis c in the unit cell. It can be calculated that the layer spacing of kaolinite d = 7.02a (Malek and Ramli 2015). Figure 1.4 shows the standard XRD patterns of kaolinite. It can be seen that the three diffraction peaks of kaolinite are located at 2Th = 12.6°, 21.4°, and 25.3° respectively, and the corresponding surface network indices are 0 01, −1−11, and 0 02, respectively. 2Th = 12.6° and the spacing between the surfaces and the net index of 0 01 is the spacing between the layers of kaolinite, d = 7.02 Å. By comparing the actual XRD pattern of kaolinite samples with the standard XRD pattern of kaolinite, the content of the kaolinite phase in kaolinite samples in the experiment can be characterized. (3) Structural characteristics of montmorillonite Montmorillonite is the main component of bentonite. According to the types of exchangeable cations, bentonite can be divided into four types: sodium-based, calcium-based, magnesium-based, and aluminum (hydrogen) based bentonite. Its structure is 2:1 type layered silicate, mostly soil-like blocks, white, with a relative density of 2.6–2.7 and a Mohlite hardness of 2.0–2.5. The structural unit of montmorillonite is composed of two [SiO4 ] tetrahedral lamellae sandwiched by

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1 Introduction

Fig. 1.4 Standard XRD patterns of kaolinite

Inte nsity (a.u.)

(001)

(00 2) (-1-11)

Kaolinite PD F#80-885

5

10

15 2 0 25 30 2Th (Degree)

35

40

one [Al(Mg)O8 ] octahedral lamellae, and interlamellar domain-containing hydrated cations are often formed between adjacent structural layers (Fig. 1.5) (Schmidt et al. 2005; Tambach et al. 2006; Ebrahimi et al. 2012). In [SiO4 ] tetrahedron of crystal structure, Si4+ can be replaced by Al3+ and Fe3+ , and in [AlO8 ] octahedron, Al3+ can be replaced by Mg2+ , so that the electricity price of the original coordination oxygen is not completely neutralized so that the surface of the montmorillonite becomes negative, and water molecules and exchangeable cations are adsorbed between the layers of the montmorillonite, mainly Na+ and Ca2+ . Since the unit chemical formula charge X of montmorillonite is between 0.2 and 0.6 (Fang 1985), and the intensity of charge is moderate, the cations between the layers of montmorillonite are exchangeable cations, which is the origin of the expandable adsorption property of montmorillonite (Boek et al. 1995). Thermal analysis: the first endothermic valley appears between 80 and 250 °C, removing interlayer water and adsorbed water. Due to the presence of interlaminar water and exchangeable cations, the interlaminar spacing of montmorillonite is larger than that of kaolinite without interlaminar cations, so its cation exchange and adsorption properties are superior. Therefore, montmorillonite is widely used in edible oil refining, decolorization and detoxification, petroleum purification, nuclear waste treatment, and sewage treatment. The chemical composition of montmorillonite is Nax (H2 O)4 {(Al2−x Mgx )[Si4 O10 ](OH)2 , the main components of which are oxides of Si, Al, Fe and Mg, the space group is P1, triclinic crystal system, and the Si-Al ratio is about 2:1, so it is called 2:1 type clay mineral. Montmorillonite crystal cell parameters for a = 5.1800 Å, b = 8.9800 Å, c = 15.0000 Å, α = 90.0000°, β = 90.0000°, γ = 90.0000°, V = 697.75 Å3 , Z = 2 (ICSD-161171). Since the length of the unit cell on-axis c in the standard card is just the length of the period of a structural unit (Fig. 1.5b), the vertical distance of c in the plane a and b can be calculated to represent the interlayer distance of montmorillonite. According to the formula: d = c × sin β (1) Where d is the layer spacing of montmorillonite, c is the distance of the unit cell of montmorillonite along the c axis, and β is the Angle between Axis a and Axis c in the unit cell. The interlayer spacing of montmorillonite can be calculated as d = 15 Å (Wu 2016).

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Fig. 1.5 Crystal structure of montmorillonite

Figure 1.6 shows the standard XRD diffraction pattern of montmorillonite. It can be seen that the strongest diffraction peak of montmorillonite is located at 2Th = 5.8°, and the corresponding surface network index is 001. The spacing between surfaces and networks corresponding to the index of 001 is the spacing between layers of montmorillonite, d = 15 Å. The content of the montmorillonite phase in the experimental samples can be characterized by comparing the actual XRD pattern with the standard pattern of the montmorillonite. (4) Structural characteristics of illite Elite is a clay mineral with a layered structure similar to mica, also known as water white mica. It is mostly white but often dyed yellow, green, brown, and other colors due to impurities. The Morse hardness is 1–2, and the specific gravity is 2.6–2.9. The structure of illite is similar to that of montmorillonite, both of which are composed of two [SiO4 ] tetrahedral lamellae sandwiched by one [Al(Mg)O8 ] octahedral lamellae as the basic structural units, and the adjacent structural units are arranged along the periodic C-axis. However, because the Si in [SiO4 ] hedral in illite is largely replaced by Al, Instead, a large number of [AlO4 ] tetrahedrons appeared in the tetrahedral Fig. 1.6 Standard XRD patterns of montmorillonite

Intensity (a.u.)

(001)

Montmorillonite PD F#2-37

10

20

30 40 50 2Th (Degree)

60

70

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1 Introduction

Fig. 1.7 Crystal structure of illite

layer of [SiO4 ] (Fig. 1.7) (Benedicto et al. 2014). The content of cations between the layers was significantly higher than that of montmorillonite, and the electronegativity of the surface was also higher than that of montmorillonite. The interlaminar cation of illite is K+ , the surface is electronegative, and the unit chemical form charge X is between 0.6 and 1 (Fang 1985). The bonding force between cations and layers of illite is strong, so illite has weak cation exchange characteristics. Due to the strong electrostatic attraction between cations and laminate, the layer spacing will not be larger because of more cations than montmorillonite. The adsorption behavior of illite is similar to that of kaolinite, and the adsorption behavior is mainly surface adsorption. However, compared with kaolinite with the electronegative surface, illite has a stronger surface electronegativity, which has obvious advantages for the adsorption of cationic antibiotics. The chemical composition of illite is K(Al4 Si2 O9 (OH)3 ), the space group is C12 / c1 Si: Al = 1:2 in the monoclinic system. Unit cell parameters of illite is: a = 5.2226 (12) Å, b = 9.0183 (23)Å, c = 20.143 (5) Å, β = 95.665° (21), V (40) = 944.08 Å3 , Z = 4 (ICSD-90144). Since the length of the unit cell in the standard card on the c-axis is exactly the length of 2 structural unit periods (Fig. 1.7b), therefore can be made of illite in the crystal cell parameters to calculate the distance between layers, according to the formula: d = c/2 × sine beta), (2) d to the layer spacing of illite c for illite unit cell along with the c axis distance, beta for the unit cell of a shaft with c axis Angle, can be calculated illite layer spacing d = 10 a (Chang et al. 2012). Figure 1.8 shows the standard XRD diffraction pattern of illite. It can be seen that the strongest diffraction peak of illite is located at 2Th = 25.7°, and the corresponding surface network index is − 1 1 4. By comparing the actual XRD pattern of illite samples in the experimental study with the standard pattern of illite, the content of the illite phase in the experimental study samples can be characterized.

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Intensity (a.u.)

Fig. 1.8 Standard XRD patterns of illite

illitePDF#26-911 20

30 2Th (Degree)

40

1.2.2 Research Progress on the Adsorption of Natural Clay Minerals to Antibiotics Natural clay minerals are generally characterized by [SiO4 ] tetrahedron and [Al(Mg)O8 ] layered or shelflike silicate formed by the combination of octahedrons in a certain proportion and manner. The adsorption of unmodified clay minerals to antibiotics mainly includes two aspects: one is structure adsorption, the other is surface adsorption. (1) Structural adsorption Structural adsorption is a kind of adsorption, which is the interlayer adsorption of antibiotics by clay minerals with expandable structure or by clay minerals with large pores. For example, the adsorption capacity of expandable clay mineral montmorillonite on tetracycline antibiotics reaches 300 mg/g (Lv et al. 2013). Tetracycline has weak cationic properties in an aqueous solution, while the content of organic material on the surface of montmorillonite is limited. Therefore, the adsorption of montmorillonite on tetracycline is mainly interlayer adsorption, which is affected by structure. Because the adsorption of structure or pore is an inherent characteristic of clay minerals. Only clay minerals with expandable structure or pore diameter larger than pollutant molecules can adsorb and remove pollutants due to structural characteristics. Some clay minerals experts have tried to regulate the interlayer bonding force and pore adsorption by artificially doping or replacing the electrical properties in mineral structures without changing the mineral structure, This technology is more advanced, and requires a low content of doping substances to maintain the inherent structure of the mineral itself is not destroyed, but often due to the low content of doping, the improvement of clay minerals in the structural adsorption performance is limited. (2) Surface adsorption Si in [SiO4 ] tetrahedron can be replaced by Al. After the Si ion itself becomes + 4 valence and is replaced by + 3 valence Al, the electricity price of coordination oxygen

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1 Introduction

is not completely neutralized, and the whole [AlO4 ] tetrahedron is electronegative, which makes the surface of clay minerals show a negative charge. Conversely, when there is no phenomenon of Al3+ replacing Si4+ in the structure, The surface of the clay mineral is electrically neutral. The unmodified clay mineral surface has a good adsorption effect on cationic antibiotics, but a poor adsorption effect on neutral or anionic antibiotics. This is because, on the one hand, unmodified clay minerals itself adsorbed on the surface of some organic material, The surface of electrically neutral clay minerals can adsorb antibiotics largely due to antibiotics are generally organic pollutants antibiotic organic chain end compatible with an organic matter similar on the surface of the clay mineral and it is not affected by antibiotics charged situation, however, due to the limited organic matter content on the surface of natural clay minerals, the adsorption capacity is limited due to the interaction between the surface organic matter and neutral antibiotics (Li et al. 2010). On the other hand, in addition to the adsorption of organic matter, the electronegative clay mineral surface also has an electrostatic attraction to cationic antibiotics, while the adsorption effect to neutral or anionic antibiotics is weak. Therefore, the natural electronegative properties of the clay mineral surface have limitations on the adsorption of neutral and anionic antibiotics. After surface modification and modification, the content of surface organic matter and the electrical property can be changed, so that the adsorption capacity and range of natural clay minerals to antibiotics will be greatly improved (Lu et al. 2014). Zeolite layer with exchangeable cations, the surface is electronegative, the cationic antibiotic has surface adsorption, there is pore adsorption for antibiotics which the molecular size is less than the zeolite pore structure. In addition, due to the structure of zeolite types, different zeolite adsorption performance is different. For example, the adsorption of common zeolite for sulfonamides with smaller molecular size (200–1000 mmol/kg) includes both surface adsorption and pore adsorption, while the adsorption of antibiotics with the larger molecular size is only surface adsorption (Braschi et al. 2010; Blasioli et al. 2014; Mavrodinova et al. 2015). The unit chemical charges of the layered clay minerals kaolinite (X = 0), montmorillonite (0.2 < X < 0.6) and illite (0.6 < X < 1) gradually increase, which indicates that the interlaminar charges of the three minerals gradually increase, the interlaminar cation content gradually increases, and the surface electronegativity also gradually increases. The kaolinite layer does not contain water molecules and metal cations, the surface is electroneutral, so the adsorption of kaolinite to antibiotics is mainly surface adsorption, and the adsorption performance is poor, for example, the adsorption performance of kaolinite to tetracycline and chloramine typical antibiotics is only 9–20 mmol/kg (Li et al. 2010; Lv et al. 2014a, b). There are exchangeable alkali metal cations and water molecules between the layers of montmorillonite, and the surface is electronegative. Therefore, the adsorption of montmorillonite on antibiotics usually includes both surface adsorption and structural adsorption. Compared with montmorillonite, due to more substitutions in illite structure, illite contains a large number of metal cations, which is significantly higher than montmorillonite, However, due to the effect of electrostatic attraction, the bonding force between the cations and laminates is too strong, so that the interlamellar distance and expansibility

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are lower than montmorillonite. In the case of comparing surface adsorption only, illite with strong electronegativity will be the most superior for cationic antibiotics adsorption and absorption energy, but taking into account the influence of structural expansion factor, natural montmorillonite generally has better adsorption performance than illite. Therefore, the order of the three natural layered clay minerals in terms of the adsorption capacity of antibiotics is Montmorillonite > illite > kaolinite. For example, the saturated adsorption capacities of natural montmorillonite, illite, and kaolinite for enrofloxacin were about 600 mmol/kg, 200 mmol/kg, and 20 mmol/ kg, respectively, and the order of their adsorption properties was consistent with the theoretical analysis (Wan et al. 2013). However, due to the limited organic matter content on the surface of natural clay minerals, the adsorption capacity generated by the similar compatibility of surface organic matter and antibiotics is limited. In addition, the electronegativity of the surface of natural clay minerals for the adsorption of anionic antibiotics is still limited. After surface modification and modification, the content of organic matter on the mineral surface and the electrical property can be changed, and the adsorption capacity and range of natural clay minerals to antibiotics can be greatly improved.

1.3 Research Progress in the Application of Organically Modified Clay Minerals to Antibiotics 1.3.1 Preparation of Organically Modified Clay Minerals Due to the influence of surface organic matter content and electronegativity of natural clay minerals, the main modifiers of natural clay minerals are cationic organic modifiers. One end of the cationic organic modifier acts directly with the mineral surface, the other end is non-extreme, and the number of C atoms is 10–24, to ensure that the obtained modified minerals have better lipophilic properties. There are two kinds of common preparation of organically modified clay minerals by wet method and dry method. (1) wet method Wet modification is a method that usually by clay mineral is added to a certain concentration of modifier in the solution (the dosage of the modifier in the adsorption capacity of clay mineral of modifier, the clay minerals of the CEC (Zhu et al. 2011), the different structure of clay mineral because of its surface electrical and organic matter content is different for different adsorption capacity of modified agents, In general, when preparing organic modified clay minerals, the amount of modifier added should be slightly greater than the adsorption capacity of minerals to it so that the adsorption capacity of minerals to modifier can reach saturation in the modification process). After the adsorption balance of minerals to modifier reaches, the

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minerals are centrifuged and cleaned. Finally, it is dried at a certain temperature (generally between 50 and 70 °C) (Yang et al. 2016). (2) Dry method The steps of dry preparation of organically modified clay minerals are relatively simple, that is, the clay minerals and an appropriate amount of modifier are fully mixed, and the reaction is 5–30 min in anhydrous temperature and higher than the melting point of the modifier. After the reaction, the organically modified clay minerals can be prepared by grinding and screening.

1.3.2 Characterization Techniques of Organically Modified Clay Minerals Various characterization techniques of structure, morphology, and surface electrical properties can be used to characterize whether modified clay minerals are successfully prepared, whether the modification is an interlayer modification or surface modification, the distribution and morphology characteristics of modifier on the mineral surface, and the amount of modifier adsorption by minerals. In general, Xray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), specific surface area (BET), Zeta potential test (Zeta), etc. (1) XRD By comparing the XRD diffraction patterns of clay minerals before and after modification, the structure changes of clay minerals before and after modification can be characterized. For example, natural Na-montmorillonite was modified by cetyltrimethyl ammonium bromide, and the diffraction peak of d (001) crystal plane was shifted to a low Angle in the XRD diffraction pattern after modification, and the layer spacing was expanded from about 1.19 nm to about 1.4 nm (Lu et al. 2014), which indicated that the modifier not only adsorbed on the surface of the montmorillonite but also adsorbed into the interlayer of the montmorillonite. In this case, the adsorption of modified montmorillonite on antibiotics will also include the dual action of surface and interlayer. Because both surface and interlayer are organic, the adsorption capacity of unmodified montmorillonite on antibiotics is greatly improved. However, if the XRD pattern of the mineral before and after modification does not change, it indicates that the modifier only adsorbed on the surface of the mineral and did not enter into the interlayer. If the XRD diffraction peak intensity of the mineral decreases before and after modification, and some diffraction peaks disappear, it indicates that the modification process destroys the crystal structure of the mineral, and the structure of this kind of mineral is unstable, and it is not suitable to be used as a modifier. (2) SEM

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By comparing the SEM images of clay minerals before and after modification, the adsorption form and content of modifier on the mineral surface can be directly characterized. The adsorption saturation point of clay minerals with the same structure to modifier can be characterized by SEM. Different clay minerals with different structures have different adsorption capacities for modifiers due to their surface electrical properties and organic matter contents. SEM characterization technology can be used to visually compare the adsorption content of modifiers and characterize the adsorption properties of clay minerals with different structures. (3) IR Using infrared spectrum test technology, the mineral can be characterized before and after the modification of the change of surface functional groups, if the modified mineral more before the infrared spectra of the modified some functional groups of absorption peak, and the same position of the absorption peak is just the infrared characteristic absorption peak modifier itself, suggesting that modifier to the success of the adsorption on the surface of the mineral. For example, Na-montmorillonite was modified with C45 H80 N2 Br2 , and it was found that the IR of the modified product showed infrared absorption peaks at 2926, 2851, 1643, 1467 cm−1 , etc., which were all characteristic absorption peaks of C45 H80 N2 Br2 . But not the infrared absorption peak of the original montmorillonite, indicating that the C45 H80 N2 Br2 -modified Na montmorillonite was successfully prepared (Yang et al. 2016). (4) BET The specific surface area test technique can be used to characterize the adsorption properties of clay minerals before modification. The adsorption properties of clay minerals with different structures and minerals with different sizes of the same structure are also different. This is because the specific surface area of minerals increases with the decrease of size, which will make more mineral surfaces contact with the organic modifier and greatly improve the adsorption of the modifier on the mineral surface. BET analysis is specially applied to the study of particle surface adsorption capacity. The larger the specific surface area of the same mineral is, the stronger the surface adsorption capacity of the modifier is. (5) Other test technologies Some modified clay minerals with fluorescence properties can be characterized by fluorescence electron microscopy. In the fluorescence micrograph, in general, clay minerals are dark in color. However, if the modifier with fluorescence and luminescence properties is adsorbed on the mineral surface, fluorescent spots will appear in the image, and the positions of these spots are the positions of modifier (Castillo et al. 2016). In addition, through Zeta potential test can also characterize the content of the modifier adsorbed on the surface of the mineral, this is because, with cationic modification agent for natural electronegative modified clay minerals, the mineral surface electrical changes from negative to positive, theoretically, when the positive electrical properties of the mineral surface no longer increase, it indicates that the adsorption capacity of the mineral to the modifier reaches saturation.

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1.3.3 Study on the Surface Reaction Between Modifier and Clay Minerals (1) Mechanism and model of surface reaction between modifier and clay minerals The adsorption process of cationic organic modifier on the surface of montmorillonite was used as a model to simulate the reaction mechanism between the modifier and clay mineral surface (Zhu et al. 2011). The formation of the bimolecular layer is a recognized mechanism of mineral modification by cationic organic modifier. This is due to the cationic organic modifier, one end is the alkyl chain hydrophobic group, the other end is the cationic polar group. In the modification process, with the increase of the amount of modifier, because the cationic polar end of the modifier is absorbed with the electronegativity of the mineral surface, a monolayer modifier adsorption is firstly formed on the mineral surface (Fig. 1.9a). And when the amount of modifier is more than one layer, the mineral surface will form a transition from one to two layers of bilayer adsorption, modifier organic end of the first layer and the second modification agent of organic side alkyl bilayer formation, the second end of cation modifier exposed until the bilayer covered the entire mineral surface (Fig. 1.9b). When the amount of modifier is increased, the maximum adsorption amount of modifier on the mineral surface remains unchanged, and the modifier forms micelles in the solution. (2) Influencing factors of the reaction between clay mineral surface and modifier

Fig. 1.9 Mechanism and model of surface reaction between modifier and clay minerals

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1) Ionic strength The change of ionic strength is not consistent with the mineral adsorption on modifier, but it can be determined that the change of ionic strength mainly affects the electrostatic attraction between mineral surface and modifier and has little influence on the non-electrostatic adsorption. For example, for some expandable clay minerals, modification experiments under acidic pH conditions can improve the modification effect. This is because acidic conditions are conducive to the protonation of polar groups of the modifier, improving the cation exchange performance between the layer and the clay minerals, and improving the effect of interlayer adsorption modification (Daitx et al. 2015). 2) Influence of alkyl carbon chain length The length of the alkyl chain of the modifier mainly affects the lipophilicity of the mineral surface. In the process of forming a biolayer, the modifier with a long carbon chain has a stronger binding force than the short carbon chain, and the longer the carbon chain is, the more hydrophobic it is. Therefore, increasing the length of the carbon chain has a promoting effect on the modification effect. However, too long of the carbon chain will affect the stability of the modifier on the mineral surface, so the length of the carbon chain of the modifier is generally 10–24 carbon. 3) Modification temperature Wet modification can be done after a certain time of reaction at a general temperature (30–80 °C). Modified clay minerals with high crystallization properties or certain morphologic characteristics are expected to be formed by stirring modification with additional high-temperature calcination (Olutoye et al. 2016).

1.3.4 Study on the Adsorption of Organic Modified Clay Minerals to Antibiotics (1) Adsorption mechanism and model of organically modified clay minerals for antibiotics Due to the limited organic matter content on the surface of natural clay minerals, the adsorption capacity caused by the similar compatibility between the surface organic matter and antibiotics is limited. In addition, the electronegativity of the surface of natural clay minerals for the adsorption of anionic antibiotics is still limited. After surface modification and modification, the content of organic matter on the mineral surface and the electrical property can be changed, and the adsorption capacity and range of natural clay minerals to antibiotics can be greatly improved (Yang et al. 2016). The adsorption mechanism of organically modified clay minerals on antibiotics was simulated by using cationic alkyl chain modifier to modify naturally electronegative montmorillonite and the adsorption process of anionic antibiotics as the

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model, as shown in Fig. 1.10. In the modification process, with the increase of the amount of modifier, monolayer modifier adsorption is firstly formed on the mineral surface, and the organic end of the modifier is exposed outside. At this time, the adsorption of antibiotics on the mineral surface is mainly caused by the similar compatibility effect of the organic molecular layer formed by the modifier on the organic chain of antibiotics (Fig. 1.10a). The amount of modifier is added. The first layer of organic modifier in the end and the second layer of modifier form alkyl bilayer organic end, the polar end of the second modifier exposed, then mineral surface adsorption of anionic antibiotics, which is mainly due to the mineral surface bilayer of anode side and antibiotic Yin polarity of the electrostatic attraction (Fig. 1.10b). (2) The factors affecting the adsorption of antibiotics by organically modified clay minerals 1) Influence of PH values The pH value of the solution affects the ability of organic clay minerals to adsorb antibiotics. This is because antibiotics usually present different valence states in aqueous solutions. When the amount of H+ in the solution increases, the polar end of antibiotics will be qualitative and the price will rise. As the amount of OH− in the solution increases, the polar end of the antibiotic will be alkalized, reducing the price of electricity. For example, in an aqueous solution, chlorpheniramine maleate has a positive valence, chlorpheniramine maleate’s pka1 = 4.0 and pka2 = 9.2. chlorpheniramine maleate will have positive bivalence when the pH in the solution is less

Fig. 1.10 Adsorption mechanism and model of organically modified clay minerals for antibiotics

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than 4.0. Chlorpheniramine maleate is electrically neutral when the solution pH > 9.2. (Lv et al. 2014a, b; Wang et al. 2010). Then, the adsorption of culminating by unmodified natural surface electronegative clay minerals will be optimal under acidic conditions and greatly reduced under alkaline conditions. However, the adsorption performance of clay minerals modified by organic cationic surfactants to antibiotics will reach the best under alkaline conditions. Another example is that the neuron antibiotic nalidixic acid is electronegative in neutral aqueous solution. When the pH of the solution is acidic, the surface price of nalidixic acid is neutral. Only when the pH value is less than 0, its surface is positively electrically active (Wu et al. 2013). Therefore, the change of the surface electrical property of antidiabetic acid with the pH value will also affect its adsorption behavior on the clay surface. 2) Influence of different modification proportions According to the adsorption mechanism of modified clay minerals to antibiotics, when monolayer modifier adsorption is formed on the mineral surface, the adsorption of antibiotics is mainly due to the similar and compatible adsorption of the organic molecular layer formed by the modifier to the organic end of antibiotics. When the alkyl bilayer is formed on the mineral surface, the adsorption or repulsion of antibiotics is mainly due to the electrostatic attraction or repulsion between the polar end of the mineral surface bilayer and the polar end of the antibiotic. Due to electrostatic attraction at higher strengths than alkyl chain similar compatible, taking the adsorption of cationic modified clay minerals to anionic antibiotics as an example, when the adding amount of modified agents reaches the bilayer, in the same mineral surface using electrostatic attraction than monolayer formation to adsorption manner is high to the effect of alkyl chain. In addition, the adsorption stability of antibiotics is poor when the alkyl chain compatible adsorption method is used, and it is easier to desorb antibiotics in an aqueous solution compared with the electrostatic adsorption method. Therefore, the change of different modification ratios will also affect the adsorption capacity of the modified minerals to antibiotics. 3) Influence of modifier types The types of modifiers for natural clay minerals can be divided into four types: anionic, cationic, neutral and amphoteric. Because the surface of natural minerals is mostly electronegative, the modification of natural minerals is mainly cationic and amphoteric modifiers, while the modification effect of anionic and neutral modifiers is poor. The modification effect of anionic and neutral ion modifiers has little effect on the electrical properties of mineral surfaces, therefore, the anionic and neutral ion modifiers are mainly used to improve the organic properties of mineral surfaces, make up for the inadequacy of unmodified clay mineral surface organic matter content, the best suitable for the adsorption of cationic antibiotics. But the application is limited because of the poor modification effect. The use of cationic modifier not only improves the organic properties of mineral surface but also changes the electrical properties of the natural mineral surface, which breaks the limitation of natural mineral adsorption on anionic antibiotics (Ma et al. 2016). Compared with modifiers

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with single electrical properties, zwitterionic modifier for a particular situation has certain advantages, this is because, compared with cationic modification agent, when the amphoteric modifier is adsorbed into the clay mineral layers, on the one hand, by cation exchange effect, on the other hand, modifier of the electronegativity to modifier to positively charged layer between aggregation, This makes the expansion of the final layer spacing stronger (Ma et al. 2016). In addition, in the adsorption of cationic antibiotics, the interlayer and surface adsorption is contributed by the alkyl chain lipophilicity, and the adsorption of anionic, cationic and non-ionic antibiotics on the surface or between the layers of amphoteric ion modified minerals is stronger. However, the adsorption and modification of clay minerals at home and abroad mainly focus on the modification effect and influencing factors, and lack research on the modification and adsorption mechanism. In this study, the modification, and adsorption mechanism of the reaction system were systematically investigated by combining various test characterization, The molecular dynamics simulation of typical clay minerals and their adsorption process of anionic antibiotics is carried out for the first time, proved the surfactant molecules on the surface of the mineral distribution, simulates the organic modification of clay mineral adsorption antibiotic molecular configuration form.

References Bare SR, Kelly SD, Sinkler W, Low JJ, Modica FS, Valencia S, Corma A, Nemeth LT (2005) Uniform catalytic site in Sn-â-zeolite determined using X-ray absorption fine structure. J Am Chem Soc 127:12924–12932 Beijing Zhongjing Vision Information Consulting Co., Ltd. (2020) 2020 China antibiotic market analysis report Benedicto A, Missana T, Fernández AM (2014) Interlayer collapse affects on cesium adsorption onto illite. Environ Sci Technol 48:4909–4915 Blasioli S, Martucci A, Paul G, Gigli L, Cossi M, Johnston CT, Marchese L, Braschi I (2014) Removal of sulfamethoxazole sulfonamide antibiotic from water by high silica zeolites: a study of the involved host–guest interactions by a combined structural, spectroscopic, and computational approach. J Colloid Interface Sci 419:148–159 Boek ES, Coveney PV, Skipper NT (1995) Molecular modeling of clay hydration: a study of hysteresis loops in the swelling curves of sodium montmorillonites. Langmuir 11:4629–4631 Bougeard D, Smirnov KS, Geidel E (2000) Vibrational spectra and structure of kaolinite: a computer simulation study. J Phys Chem B 104:9210–9217 Brady PV, Cygan RT, Nagy KL (1996) Molecular cont rols on kaolinite surface charge. J Colloid Interface Sci 183(2):356–364 Braschi I, Blasioli S, Gigli L, Gessa CE, Alberti A, Martucci A (2010) Removal of sulfonamide antibiotics from water: evidence of adsorption into an organophilic zeolite Y by its structural modifications. J Hazard Mater 178:218–225 Caldas SS, Rombaldi C, Arias JLO, Marube LC, Primel EG (2016) Multi-residue method for determination of 58 pesticides, pharmaceuticals and personal care products in water using solvent demulsification dispersive liquid-liquid microextraction combined with liquid chromatographytandem mass spectrometry. Talanta 146:676–688

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Carrasquillo AJ, Bruland GL, Mackay AA, Vasudevan D (2008) Sorption of ciprofloxacin and oxytetracycline zwitterions to soils and soil minerals: influence of compound structure. Environ Sci Technol 42:7634–7642 Castillo SZ, Armenta JLR, Cinco MYC, Cruz BAS, Martínez AMM (2016) Physical and rheological properties of asphalt modified with SEBS/ montmorillonite nanocomposite. Constr Build Mater 106:349–356 Chang PH, Li AH, Jean JS, Jiang WT, Wang CJ, Lin KH (2012) Adsorption of tetracycline on 2:1 layered non-swelling clay mineral illite. Appl Clay Sci 67–68:158–163 Daitx TS, Carli LN, Crespo JS, Mauler RS (2015) Effects of the organic modification of different clay minerals and their application in biodegradable polymer nanocomposites of PHBV. Appl Clay Sci 115:157–164 Dawood S, Sen TK (2012) Removal of anionic dye Congo red from aqueous solution by raw pine and acid-treated pine cone powder as adsorbent: equilibrium, thermodynamic, kinetics, mechanism and process design. Water Res 46:1933–1946 Doretto KM, Peruchi LM, Rath S (2014) Sorption and desorption of sulfadimethoxine, sulfaquinoxaline and sulfamethazine antimicrobials in Brazilian soils. Sci Total Environ 476:406–414 Ebrahimi D, Pellenq RJM, Whittle AJ (2012) Nanoscale elastic properties of montmorillonite upon water. Adsorpt Langmuir 28:16855–16863 Fang Y (1985) Classification of clay minerals. Marine Geol Quat Geol 5(2):125–127 Huertas FJ, Chou L, Wollast R (1998) Mechanism of kaolinite dissolution at room temperature and pressure: Part 11 surface speciation. Geochim Cosmochim Acta 62(3):417–431 Kan TT, Jiang XH, Zhou LM, Yang M, Duan M, Liu PL et al (2011) Removal ofmethyl orange fromaqueous solutions using a bentonitemodifiedwith a newgemini surfactant. Appl Clay Sci 54(2):184–187 Kyzas GZ, Kostoglou M, Lazaridis NK, Lambropoulou DA, Bikiaris DN (2013) Environmental friendly technology for the removal of pharmaceutical contaminants from wastewaters using modified chitosan adsorbents. Chem Eng J 222:248–258 Li ZH, Schulz L, Ackley C, Fenske N (2010) Adsorption of tetracycline on kaolinite with pHdependent surface charges. J Colloid Interface Sci 351:254–260 Lu LF, Gao ML, Gu Z, Yang SF, Liu YN (2014) A comparative study and evaluation of sulfamethoxazole adsorption onto organo-montmorillonites. J Environ Sci 26:2535–2545 Lv GC, Pearce CW, Gleason A, Liao LB, Williams MPM, Li ZH (2013) Influence of montmorillonite on antimicrobial activity of tetracycline and ciprofloxacin. J Asian Earth Sci 77:281–286 Lv G, Li Z, Jiang WT et al (2014) Removal of Cr(VI) from water using Fe(II)-modified natural zeolite. Chem Eng Res Des 92(2):384–390 Lv GC, Wu LM, Li ZH, Liao LB, Liu MT (2014) Binding sites of chlorpheniramine on 1:1 layered kaolinite from aqueous solution. J Colloid Interface Sci 424:16–21 Lyu B, Gao JJ, Ma JZ, Gao D, Wang HD, Han XW (2016) Nanocomposite based on erucic acid modified montmorillonite/sulfited rapeseed oil: preparation and application in leather. Appl Clay Sci 121–122:36–45 Ma LY, Chen QZ, Zhu JX, Xi YF, He HP, Zhu RL, Tao Q, Ayoko GA (2016) Adsorption of phenol and Cu(II) onto cationic and zwitterionic surfactant modified montmorillonite in single and binary systems. Chem Eng J 283:880–888 Mackay AA, Seremet DE (2008) Probe compounds to quantify cation Exchange and complexation interactions of ciprofloxacin with soils. Environ Sci Technol 42:8270–8276 Malek NANN, Ramli NI (2015) Characterization and antibacterial activity of cetylpyridinium bromide (CPB) immobilized on kaolinite with different CPB loadings. Appl Clay Sci 109–110:8–14 Martin RT, Bailey SW, Eberl DD, Fanning DS, Guggenheim S, Kodama H, Pevear DR, Srodon J, Wicks FJ (1991) Clays and clay mineral 39(3):333–335 Mavrodinova V, Popova M, Yoncheva K, Mihály J (2015) Solid-state encapsulation of Ag and sulfadiazine on zeolite Y carrier. J Colloid Interface Sci 458:32–38

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Chapter 2

Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay Minerals

Abstract This chapter described the successful preparation of modified zeolite, kaolinite, montmorillonite and illite by CTAB organic reagents and characterization of the materials by XRD, SEM, contact angle measurements and IR, and drew six conclusions. (1) SEM characterized the successful preparation of zeolite, kaolinite, illite, and montmorillonite modified by CTAB. (2) The contact Angle test indicated that the surface lipophilicity of the four clay minerals increased after CTAB modification, which was conducive to the adsorption of organic antibiotics. (3) Zeta potential test characterized the process of surface electrical properties of four clay minerals from neutral and negative to positive. (4) Adsorption experiments showed that the adsorption capacity of unmodified clay minerals to DS was weak, and the adsorption capacity of modified minerals with different dosages of modifier to anionic DS was greatly improved. (5) The adsorption behavior of porous zeolite, non-expansive kaolinite and illite for CTAB and DS was mainly surface adsorption, while the adsorption behavior of expansive montmorillonite with exchangeable cation for CTAB and DS included not only surface adsorption but also interlayer adsorption. (6) IR characterized the successful preparation of CTAB modified zeolite, kaolinite, illite and montmorillonite. The characteristic functional group of CTAB appeared on the surface of modified zeolite, kaolinite, illite, and montmorillonite. Keywords CTAB · DS · RD · SEM · Contact angle measurements · IR

Diclofenac Sodium (Diclofenac Sodium, DS) is a new type of potent antiinflammatory non-steroidal anti-inflammatory drug. As a typical antibiotic, its analgesic, anti-inflammatory, and antipyretic effects are 26–50 times stronger than aspirin and 2–215 times than indomethacin, it is one of the best-selling drugs in the world, but its oral plasma half-life is short (t1/2 is about 1–2 h), and it can usually cause a short and rapid increase in plasma DS concentration and a rapid decrease, which brings pain to the patients (Xu 2005). According to relevant reports, DS has been widely seen in sewage treatment plants and river water, lake water and other environmental water bodies, causing concern at home and abroad. The sources of diclofenac

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 K. Sun, Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-981-99-6434-5_2

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2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Fig. 2.1 Chemical structure formula of DS

in the environment include three ways: human drug discharge, wastewater treatment in sewage plants, sludge reuse and landfill residues. Conventional water treatment processes (activated sludge or anaerobic fermentation process) are difficult to completely degrade and mineralize, resulting in the cumulative concentration of chlorogenic in the effluent and receiving water of some sewage treatment plants reaching g/L (Stulten et al. 2008), which hurts the growth of land animals and aquatic organisms and brings potential harm to human health. Antibiotics attack specific metabolic pathways and molecular pathways in humans or animals and may affect the same or similar target organs, tissues, cells, and biomolecules in animals when they enter the environment. Cleuvers (2004) Studies by Cleavers et al. have shown that typical anti-inflammatory drugs also have different degrees of toxicity to Daphnia Magna. In addition, the study of Flippin et al. also showed that anti-inflammatory drugs could affect the egg-laying rate and the changes of COX enzyme activity in the body of Japanese medaka. PKA (Bui and Choi 2009) and Logkow (Bui and Choi 2009) of diclofenac were 4.15 and 4.51, respectively, as shown in Fig. 2.1 for their chemical structure. The current treatment methods of diclofenac mainly include adsorption, advanced oxidation, and membrane bioreactor. The adsorption method is simple and fast, adsorption materials include silica, resin, natural zeolite, and so on. Because DS is an anionic anti-inflammatory drug, its adsorption effect in all kinds of clay minerals is limited. In recent years, studies on the environmental behavior of anti-inflammatory drugs at home and abroad mostly focused on the adsorption behavior of cationic antiinflammatory drugs in soil. Oranuj (Oranuj et al. 2006; Oranuj et al. 2007) Oranuj (Oranuj 2006; Olanuj et al. 2007) studied the adsorption of acetaminophen in aquifer sand with low organic matter content. Silicate and bauxite with different charge properties and a hydrophobic material Porapak P were selected as adsorption media to conduct experiments on behalf of the aquifer. It was found that the above media did not adsorb acetaminophen in the initial concentration range of 1.0–10.0 mg/L in the static experiment, and the further dynamic adsorption experiments showed that the above media also had no obvious blocking effect on acetaminophen. Angela et al. (Angela 2010) collected water samples and sediment samples from the Ji-lung River in Taiwan and studied the biodegradation and adsorption of acetaminophen in a simulated water environment in the laboratory, showing that although biodegradation is the main mechanism of acetaminophen degradation, the sediment also absorbed 30% of the acetaminophen, indicating that the sediment adsorption of

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acetaminophen is not negligible While Hiroshi Yamamoto et al. (Hiroshi 2009), studied the adsorption behavior of acetaminophen on the sediments of Akui River, Tamiya River, and Tatara River, they found that there were significant differences in the amount of acetaminophen adsorption on different sediments. The adsorption capacity of the same concentration solution in the three sediments was the largest difference of about 800 μg/kg. Zhao et al. (2013) studied the adsorption characteristics of acetaminophen in Weihe River sediments. The adsorption process basically reached equilibrium after 24 h, which was in line with the pseudo-first-order kinetic model. When the pH of the system changed in the range of 3.0–9.0, there was no significant effect on the adsorption capacity of acetaminophen on sediments. When pH was greater than 9.0, the adsorption capacity showed a decreasing trend. Ternes et al. (2002) used FeCl3 as a coagulant to conduct laboratory coagulation and precipitation tests on diclofenac and found that its removal rate was less than 10%. Bender (2006) found that diclofenac generated at least five kinds of by-products after chlorination, one of which was chloramine, but the mineralization and degradation degree of diclofenac was not high. Based on the research status at home and abroad, it can be found that the studies on the adsorption of anti-inflammatory drugs in the environment mainly focuses on cationic anti-inflammatory drugs such as acetaminophen, and there are few studies on DS. The existing studies have low DS removal rate and adsorption rate. Due to the differences in the properties of different adsorbents, the main factors affecting the adsorption of DS are still uncertain, and the adsorption of Diclofenac Sodium in the soil is not systematic enough. The study on the mechanism of DS adsorption is only at the preliminary conjecture level. Therefore, four representative clay minerals were used as adsorbents to systematically study the adsorption characteristics of DS in minerals, which is helpful to further understand the adsorption mechanism of DS in soil and provide basic data for the correct evaluation of the risk of DS in the environment. Natural clay minerals have a certain adsorption capacity for DS, but the adsorption capacity is small. The adsorption saturation of the four unmodified minerals zeolite, kaolinite, montmorillonite, and illite for DS is about 20 mmol/kg, 10 mmol/kg, 80 mmol/kg and 10 mmol/kg, respectively (Fig. 2.2). The surface of kaolinite is electrically neutral, the surface of zeolite, montmorillonite, and illite are electrically negative. Therefore, the surface electrostatic attraction of the four unmodified clay minerals to the anionic DS is weak. Zeolite, kaolinite and illite are all non-inflatable clay minerals, and because the molecular size of DS is larger than the pore size of the zeolite, it fails to enter the pore of zeolite. Therefore, the weak adsorption of DS by zeolite, kaolinite, and illite is due to the similar compatibility effect between the trace organic matter on the surface of clay minerals and the organic end of DS. Therefore, it is necessary to modify the natural clay mineral organically and change the charge on its surface to adsorb the anionic anti-inflammatory drug DS effectively. CTAB is the abbreviation of cetyl trimethyl ammonium bromide, its molecular formula is C16 H33 (CH3 )3 NBr, and its structural formula is shown in Fig. 2.3. It is usually white or light yellow crystal to powder, with an irritating odor, easily soluble

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a

20 10 Zeolite/DS 0 -10

0 1 2 3 4 5 6 Equilibrium concentration (mmol/L)

100 80

c

60 40

Montmorillonite/DS

20 0

Adsorption amount (mmol/Kg)

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Adsorption amount (mmol/Kg)

Adsorption amount (mmol/Kg)

Adsorption amount (mmol/Kg)

34

30

b 20

10 Kaolinite/DS 0

20

0 1 2 3 Equilibrium concentration (mmol/L)

d

10

0 1 2 3 4 5 6 7 Equilibrium concentration (mmol/L)

0 illite/DS 0.0

0.5

1.0

1.5

Equilibrium concentration (mmol/L)

Fig. 2.2 Adsorption of DS by four unmodified minerals

Fig. 2.3 Structure of CTAB

in isopropanol, soluble in water, and produces a large amount of foam when it oscillates. It can have good coordination with anionic, non-ionic and amphoteric surfactants, and is a typical cationic organic modifier (Zhao et al. 2011a, b). It has excellent permeability, softening, emulsification, antistatic, biodegradability, and sterilization properties. This product has good chemical stability, heat resistance, light resistance, pressure resistance, strong acid, and alkali resistance. Therefore, In this study, CATB was used to modify natural clay minerals to adsorb anti-inflammatory drug DS in water, the adsorption capacities of four typical modified clay minerals were evaluated by thermodynamics and kinetics of adsorption, and used the X-ray diffraction (XRD), infrared spectroscopy (FTIR), surface contact angle, scanning electron microscope (SEM), and other test methods to study the adsorption mechanism.

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

35

2.1 Preparation and Adsorption Methods of Four CTAB Modified Minerals The CEC of zeolite, kaolinite, montmorillonite, and illite used in the experiment was 100 mmol/kg, 60 mmol/kg, 1200 mmol/kg and 70 mmol/kg, respectively. Four kinds of clay minerals were modified by different dosages of CTAB, and the clay minerals modified by different dosages of modifier were prepared. First, according to their CEC, CTAB with different qualities was weighed and dissolved, and then the corresponding quality of clay minerals was added and shaken at room temperature for 24 h, centrifuged and filtered, washed several times for natural drying, and finally, CTAB modified clay minerals were prepared. Adsorption test: prepared 0.5 mmol/L–5 mmol/L DS solution of different concentrations of 10 mL and added to 0.5 g zeolite, 0.5 g CTAB modified zeolite with 0.5 g 200% CEC dosage, 0.5 g kaolinite and 0.5 g CTAB modified kaolinite with 0.5 g 200% CEC dosage, respectively; 0.5–5 mmol/L DS solutions of different concentrations of 20 mL were added to 0.07 g of montmorillonite, 0.07 g of 200% CEC dosage of CTAB modified montmorillonite. 0.5 mmol/L–1.7 mmol/L DS solutions with different concentrations of 10 mL were added to 0.2 g illite and 0.2 g 200% CEC modified illite by CTAB, respectively. After oscillating adsorption for 24 h, centrifuge filtration was carried out at 5000 r/min. The absorbance of DS was measured at λ = 276 nm, and the maximum adsorption capacity of the four unmodified clay minerals to DS was calculated. The experiment was repeated twice.

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals 2.2.1 Adsorption and Mechanism of CTAB Modified Zeolite for DS (1) Characterization of modified zeolite by scanning electron microscopy (SEM) SEM test results of unmodified zeolite, 75% CEC, 150% CEC, 200% CEC dosage of CTAB modified zeolite are shown in Figure 2.4. The experimental results showed that the surface of the unmodified zeolite was smooth and there were micropores on the surface. The surface of zeolite modified by 75% CEC, 150% CEC, and 200% CEC contains a large number of tiny adsorbents, which indicated that CTAB had been adsorbed to the surface of zeolite, and the preparation of cationic modified zeolite was successful. (2) Contact Angle test of modified zeolite The contact angle of unmodified zeolite, 75% CEC, 150% CEC, 200% CEC CTAB modified zeolite with the aqueous solution was tested. The experimental results

36

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Fig. 2.4 Unmodified zeolite, 75% CEC, 150% CEC, 200% CEC dosage of CTAB modified zeolite SEM

showed that the contact angles of unmodified zeolite, 75% CEC, 150% CEC, and 200% CEC were 39.5°, 57°, 59.5°, and 60.5°, respectively. When the amount of modifier was in the range of 0–200% CEC, the contact angle of the modified zeolite gradually increased with the increase of the amount of modifier. This was because the modification of alkyl chain CTAB containing hydrophobic alkyl chain can increase the hydrophobicity of the surface of the zeolite, thus increasing the contact angle of the surface of the zeolite (Fig. 2.5). This indicated that the lipophilicity of natural zeolite increased after CTAB modification to the zeolite surface. (3) Zeta potential test of modified zeolite Figure 2.6 shows the Zeta potential curves of the original zeolite and the CTAB modified zeolite with different dosage. The surface of the original zeolite has a negative charge, which is related to the –OH on the surface of the original zeolite. It is also the reason for the low adsorption capacity of the original zeolite on diclofenac sodium, and the root of the electrostatic adsorption mechanism of the organic zeolite on diclofenac sodium. With the increase of modified concentration, the surface of zeolite changed from negative charge to positive charge. The order of positive charge on the surface of four CTAB modified zeolite and original zeolite is: 150% > 200% > 50% > original zeolite. This is because, in the test process of Zeta potential, after the modification and cleaning of cationic CTAB, the surface of the zeolite exposed to the outside is one end of the positive base of CTAB, with the increase of the amount of CTAB, the positive electrical properties of the surface gradually increase, and the

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

37

Fig. 2.5 Contact angle test of unmodified zeolite, 75% CEC, 150% CEC, 200% CEC dosage of CTAB modified zeolite

surface of the zeolite raw ore into natural electronegativity. Therefore, the surface electrical properties of natural zeolite can be changed from negative to positive by CTAB modification. In theory, the amount of modifier used when the surface of zeolite is electrically neutral can approximately represent the amount of monolayer adsorption of zeolite to the modifier.

Fig. 2.6 Zeta potential of zeolite samples before and after modification

38

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

(4) The equilibrium adsorption of DS by modified zeolite Experimental steps: Prepared 0.5 mmol/L–5 mmol/L of different concentrations of DS (C14 H10 Cl2 NNaO2 ) solution and added to 0.5 g of zeolite original sample and CTAB modified zeolite with 75%, 150%, and 200% CEC, respectively. After vibration adsorption for 24 h, the absorbance of DS was measured by centrifugation at 5000 r/min. The absorbance of DS was measured by supernatant at λ = 276 nm, and the maximum adsorption capacity of CTAB modified zeolite with the dosage of 0.5 g zeolite original sample and 75% CEC, 150% CEC and 200% CEC were calculated. The experiment was repeated twice. The maximum adsorption capacities of 75% CEC, 150% CEC, 200% CEC modified zeolite and original zeolite for DS were studied by equilibrium adsorption of different concentrations of DS. The experimental results showed that the adsorption capacity of the unmodified zeolite sample to DS was weak, because the surface of the modified zeolite had surface electronegativity, so it was not easy to adsorb anion antibiotics. However, the maximum adsorption capacity of CTAB modified zeolite with 75%, 150%, and 200% CEC modified by cationic modifier for DS was about 80 mmol/kg, 110 mmol/kg, and 120 mmol/kg, respectively (Fig. 2.7). (5) X-ray diffraction analysis (XRD) of modified zeolite

Fig. 2.7 Adsorption equilibrium curves of CTAB modified zeolite with the dosage of 0.5 g zeolite, 75% CEC, 150% CEC and 200% CEC for DS

Adsorption amount (mmol/Kg)

XRD patterns of zeolite modified by CTAB are shown in Fig. 2.8. The XRD spectra show that the phase diagram of zeolite before and after modification is very similar, and the position of peak and diffraction Angle are basically the same, no diffraction peaks of other impurities were found, The modified zeolite still retains the characteristics of the original zeolite diffraction peaks, This indicated that CTAB modification did not change the crystal structure of the original zeolite, that was, most of the CTAB molecules did not enter the internal crystal lattice of the zeolite, but were coated on the surface of kaolinite particles. The XRD of modified zeolite before and after adsorption did not significantly change, indicating that the adsorption of DS did not destroy 140 120 100 80 60

Raw Raw/75% CTAB Raw/150% CTAB Raw/200% CTAB

40 20 0 0

1 2 3 4 5 Equilibrium concentration (mmol/L)

6

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

Zeolite/DS/CTAB

Intensity (a.u)

Fig. 2.8 XRD patterns of unmodified zeolite, CTAB modified zeolite with 200% CEC dosage and 200% modified zeolite after adsorption of 5 mmol/L DS

39

Zeolite/CTAB

Zeolite

10

20

30

40

50

60

2 Theta (degree)

the structure of the zeolite, therefore, the adsorption of CTAB modified zeolite on DS was mainly surface adsorption. (6) IR spectrum analysis of modified zeolite The IR spectra of diclofenac sodium adsorption by zeolite and modified zeolite before and after modification (Fig. 2.9) were analyzed and found that: Natural zeolite had typical Si(Al)–O stretching vibration characteristic peak and Si(Al)–O bending vibration characteristic peak, it belonged to the typical scaffold structure silicate mineral, the zeolite modified by CTAB still appeared several strong characteristic peaks in 950–1200 cm−1 and 400–550 cm−1 . These characteristic peaks were the characteristic absorption peaks of natural zeolite, which indicated that the properties of modified zeolite had not changed basically. At the same time, it can be seen from the chromatograms that the modified zeolite had an obvious absorption band at 2800–2900 cm−1 , and the absorption peak there was the characteristic absorption peak of the modifier CATB, which indicated that the organic chain of CTAB quaternary ammonium salt exists in the pore and silicate crystal layer of zeolite, or was adsorbed to the surface of zeolite. In addition to the addition of the characteristic absorption band of quaternary ammonium salts, there was no significant change in the zeolite after organic modification, indicating that quaternary ammonium salts had no significant influence on the bond type of zeolite structure after entering the zeolite void or crystal layer through exchange or adsorption.

2.2.2 Adsorption and Mechanism of CTAB Modified Kaolinite for DS (1) Characterization of modified kaolinite by scanning electron microscopy (SEM)

40

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Fig. 2.9 IR spectra of unmodified zeolite and 200% CEC modified zeolite

Zeolite/CTAB/DS

Transmittance(%)

Zeolite/CTAB

3630

Zeolite

1055 DS

CTAB

2920

2850

4000 3500 3000 2500 2000 1500 1000 -1 Wavenumber(cm )

500

SEM test results of unmodified kaolinite, 50% CEC, 100% CEC, and 200% CEC modified kaolinite are shown in Fig. 2.10. The results showed that there were a lot of small adsorbents on the surface of CTAB modified kaolinite by 50% CEC, 100% CEC, and 200% CEC, which indicated that CTAB had been adsorbed to the surface of kaolinite and the preparation of cationic modified kaolinite was successful. (2) Contact Angle test of modified kaolinite The contact Angle of unmodified kaolinite, 50% CEC, 100% CEC, 200% CEC CTAB modified kaolinite with the aqueous solution was tested. The experimental results showed that the contact angles of unmodified kaolinite, 50% CEC, 100% CEC, and 200% CEC were 31°, 47°, 58°, and 55°, respectively. In the range of 0–200% CEC of Fig. 2.10 CTAB modified kaolinite SEM with the dosage of unmodified kaolinite, 50% CEC, 100% CEC and 200% CEC

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

41

Fig. 2.11 Contact angle test of CTAB modified kaolinite with unmodified kaolinite, 50% CEC, 100% CEC, and 200% CEC

modifier dosage, the contact Angle of modified kaolinite tended to increase with the increase of modifier dosage. This is because the modification of alkyl chain CTAB containing hydrophobic alkyl chain increases the hydrophobicity of kaolinite surface, thus increasing the contact Angle of kaolinite surface (Fig. 2.11). This indicated that CTAB modification to the surface of kaolinite can increase the lipophilicity of natural kaolinite. (3) Zeta potential test of modified kaolinite Figure 2.12 shows the Zeta potential curves of original kaolinite and CTAB modified kaolinite. The negative charge on the surface of the original kaolinite is related to the – OH on the surface of kaolinite, which is also the reason for the low adsorption capacity of the original kaolinite on diclofenac sodium. Meanwhile, it is further proved that organic kaolinite has an electrostatic adsorption mechanism on diclofenac sodium. With the increase of modification concentration, the surface of kaolinite changed from negative charge to positive charge. The order of positive charge on the surface of the four kinds of CTAB modified kaolinite and original kaolinite was 200% > , 100% > and 50% > the original kaolinite. This is because the cationic modification of CTAB and after cleaning, the surface of the kaolinite is exposed CTAB positive side, increase the amount of CTAB surface electropositive increases gradually, and the surface of the kaolinite ore approximation is electrically neutral, thus modified CTAB has realized the natural kaolinite positively charged surface gradually rise, in theory, when the positive charge on the surface of zeolite tends to be stable with

42

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Fig. 2.12 Zeta potential of kaolinite samples before and after modification

the increase of CTAB, the amount of modifier used can be used to approximate the biolayer adsorption capacity of zeolite to the modifier. (4) Equilibrium adsorption of modified kaolinite on DS Experimental steps: Preparation of 0.5–5.0 mmol/L DS solutions with different concentrations of 10 mL were added to 0.5 g kaolinite, 50% CEC, 100% CEC, and 200% CEC CTAB modified kaolinite, respectively. After oscillating adsorption for 24 h, centrifuge filtration was carried out at 5000 r/min. The supernatant was taken to measure the absorbance of DS at λ = 276 nm, and the maximum adsorption capacity of CTAB modified kaolinite with 0.5 g of original kaolinite sample, 50% CEC, 100% CEC, and 200% CEC were calculated. The experiment was repeated twice. The maximum adsorption capacity of CTAB modified kaolinite (50% CEC, 100% CEC, 200% CEC) and original kaolinite (50% CEC, 100% CEC, 200% CEC) for DS was investigated by equilibrium adsorption of different concentrations of DS. The experimental results showed that the unmodified kaolinite sample had a weak adsorption capacity for anion antibiotics, while the maximum adsorption capacity of the modified kaolinite with 50%, 100%, and 200% CTAB for DS was about 15 mmol/ kg, 20 mmol/kg and 42 mmol/kg, respectively (Fig. 2.13). (5) Adsorption kinetics of modified kaolinite to DS Figure 2.14 shows the relationship between the adsorption amount of kaolinite on diclofenac sodium and the time. As can be seen from Fig. 2.14, the adsorption rate of kaolinite on diclofenac sodium increased rapidly at first, and the removal rate reached about 95% within 50 s, then increased slowly and gradually approached equilibrium.

Adsorption amount (mmol/Kg)

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

40

43

200% 100% 50% Raw

20

0

0 1 2 Equilibrium concentration (mmol/L)

3

Fig. 2.13 Adsorption equilibrium curve of 0.5 g kaolinite, 50% CEC, 100% CEC, and 200% CEC modified kaolinite for DS

The quasi-second-order kinetic model was used to collimate the adsorption data of DS in montmorillonite at different times. The linear model of the quasi-second-order kinetic equation was expressed as: 1 1 t = + t qt ks qe2 qe qt =

K 0 − Ct V M

where, qt is the adsorption capacity at time t, mmol/kg; ks quasi-second-order kinetic rate constant, mmol/(kg h); Ct is the concentration of DS at time t, mmol/L. Take t as the abscissa and t/qt as the ordinate, draw Fig. 2.14a. The results showed that the second-order kinetic model can fit the adsorption data well, and the correlation coefficient was above 0.9996. (6) X-ray diffraction analysis (XRD) of modified kaolinite XRD patterns of CTAB modified kaolinite are shown in Fig. 2.15. XRD spectrum showed that the montmorillonite modified before and after the phase diagram of extremely similar, the position of the peak and the diffraction Angle of basic same, did not find other diffraction peaks of the impurities, modified kaolinite is still keeping the original characteristics of kaolinite and the diffraction peak, that CTAB modification did not change the crystal structure of the original montmorillonite, namely the vast majority of CTAB molecules into the interior of the montmorillonite lattice, it was coated on the surface of kaolinite particles. The phase diagram peak position and diffraction Angle of modified kaolinite adsorbed by 5 mmol/L DS were basically the same as those before adsorption, indicating that modified kaolinite adsorbed by

44

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

b Absorption amout(mmol/Kg)

50

40

7

30

6

a

5 4

20

3 2

10

1

R=0.9996

200%

0 0

50

100

150

200

250

300

350

400

0 0

50

100

150

200

250

300

350

400

Time/s Fig. 2.14 Adsorption kinetics curve of 0.1 g 200% CEC modified kaolinite for DS

DS was surface adsorption. Since kaolinite was a non-swelling clay mineral, the experimental results were consistent with the theoretical results. (7) IR spectrum analysis of modified kaolinite In the infrared spectrum of kaolinite, the absorption peak with a wavenumber of 3000–4000 cm−1 was caused by the stretching vibration of –OH, and the absorption peak at 950–1300 cm−1 was caused by the stretching vibration of Si–O. As can be seen from Fig. 2.16, CTAB modified kaolinite still has the characteristic absorption peak of natural kaolinite, which indicates that the properties of modified kaolinite

Kaolinite/CTAB/DS

Intensity (a.u)

Fig. 2.15 XRD patterns of unmodified kaolinite, 200% CEC modified kaolinite with CTAB and 200% modified kaolinite after 5 mmol/L DS adsorption

Kaolinite/CTAB

Kaolinite

10

15

20

25

30

2 Theta (degree)

35

40

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals Fig. 2.16 IR spectra of unmodified kaolinite with 200% CEC dosage of CTAB modified kaolinite

45

Kaolinite/CTAB/DS

Transmittance(%)

Kaolinite/CTAB Kaolinite

3694

3653 DS

CTAB

2920

2850

4000 3500 3000 2500 2000 1500 1000

500

-1

Wavenumber(cm )

have not changed basically. At the same time, it can be seen from the chromatograms that the modified kaolinite has an obvious absorption band at 2800–2900 cm−1 , which is the characteristic absorption peak of CTAB, indicating that the organic chain of CTAB quaternary ammonium salt exists on the surface of kaolinite, that is, the preparation of CTAB modified kaolinite is successful.

2.2.3 Adsorption and Mechanism of CTAB Modified Montmorillonite on DS (1) Characterization of modified montmorillonite by scanning electron microscopy (SEM) SEM test results of unmodified montmorillonite, 50% CEC, 100% CEC, and 200% CEC modified montmorillonite are shown in Fig. 2.17. The experimental results showed that there were a lot of small adsorbents on the surface of CTAB modified montmorillonite by 50% CEC, 100% CEC, and 200% CEC, which indicated that CTAB had been adsorbed to the surface of montmorillonite, and the cationic modified montmorillonite was successfully prepared. (2) Contact Angle test of modified montmorillonite The contact Angle between CTAB modified montmorillonite and aqueous solution with the dosage of unmodified montmorillonite, 50% CEC, 100% CEC, and 200% CEC was tested. The experimental results showed that the contact angles of unmodified montmorillonite, 50% CEC, 100% CEC, and 200% CEC were 51.5°, 53.5°, 60.5°, and 76.5°, respectively. In the range of 0–200% CEC of modifier dosage, the contact Angle of modified montmorillonite tends to increase with the

46

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Fig. 2.17 CTAB modified montmorillonite SEM with the dosage of unmodified montmorillonite, 50% CEC, 100% CEC and 200% CEC

increase of modifier dosage. This is because the modification of alkyl chain CTAB containing hydrophobicity increases the surface hydrophobicity of montmorillonite, thus increasing the contact angle of the surface of montmorillonite (Fig. 2.18). (3) Zeta potential measurement of modified montmorillonite Figure 2.19 shows the Zeta potential curves of original and CTAB modified montmorillonite. The surface of montmorillonite has a negative charge, which is related to the OH on the surface of montmorillonite, which is also the reason for the low adsorption capacity of montmorillonite on diclofenac sodium, and further proves that organic montmorillonite has an electrostatic adsorption mechanism on diclofenac sodium. With the increased modification concentration, the surface of montmorillonite changed from negative charge to positive charge. The order of positive charge on the surface of four kinds of CTAB modified montmorillonite and original montmorillonite was 100% > , 200% > and 50% > original montmorillonite. (4) The equilibrium adsorption of modified montmorillonite on DS Experimental steps: 0.5 mmol/L–5 mmol/L DS solutions of different concentrations of 20 mL were prepared and added to 0.07 g montmorillonite, 50% CEC, 100% CEC, 200% CEC dosage of CTAB modified montmorillonite, respectively. After vibration adsorption for 24 h, the montmorillonite was centrifugally filtered at 5000 r/min. The supernatant was taken to measure the absorbance of DS at λ = 276 nm, and the maximum adsorption capacity of 0.07 g CTAB modified montmorillonite with the

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

47

Fig. 2.18 Contact angle test of CTAB modified montmorillonite with unmodified montmorillonite, 50% CEC, 100% CEC and 200% CEC

Fig. 2.19 Zeta potential of montmorillonite samples before and after modification

dosage of 50% CEC, 100% CEC and 200% CEC were calculated. The experiment was repeated twice. The maximum adsorption capacity of CTAB modified montmorillonite and original montmorillonite with the dosage of 50% CEC, 100% CEC and 200% CEC

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Fig. 2.20 Adsorption equilibrium curves of 0.07 g montmorillonite, 50% CEC, 100% CEC and 200% CEC modified montmorillonite for DS

1000

Absorption amout(mmol/Kg)

48

raw 50% 100% 200 %

800 600 400 200 0

0

1

2

3

Equilibrium concentration

4

5

mmol/L

for DS was investigated by equilibrium adsorption of different concentrations of DS. The experimental results showed that the unmodified montmorillonite sample had a weak adsorption capacity for anion antibiotics, while the maximum adsorption capacity of the modified montmorillonite with 50%, 100%, and 200% CTAB was about 450 mmol/kg, 580 mmol/kg, and 1000 mmol/kg for DS, respectively (Fig. 2.20). (5) Adsorption kinetics of modified montmorillonite on DS Figure 2.21 shows the relationship between the adsorption amount of montmorillonite on diclofenac sodium and the time. As can be seen from Fig. 2.21, the adsorption rate of montmorillonite on diclofenac sodium increased rapidly at first, and the removal rate reached about 95% within 0.5 h, then increased slowly and gradually approached equilibrium. In general, chemical adsorption and complexation reaction are relatively fast, ion exchange and physical adsorption are relatively slow. The quasi-second-order kinetic model was fitted for the adsorption data of DS in montmorillonite at different times. The linear model of the quasi-second-order kinetic equation was expressed as follows: 1 1 t = + t 2 qt k s qe qe qt =

K 0 − Ct V M

where, qt is the adsorption capacity at time t, mmol/kg; ks quasi-second-order kinetic rate constant, mmol/(kg·h); Ct is the concentration of DS at time t, mmol/L. Take t as the abscissa and t/qt as the ordinate, draw Fig. 2.20a. The results showed that the pseudo-second-order kinetic model can fit the adsorption data well, and the correlation coefficient was above 0.9997. (6) X-ray diffraction analysis (XRD) of modified montmorillonite

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

49

b

Absorption amout(mmol/Kg)

800 700 600 500

0.030

a

0.025

400

0.020

300

0.015 0.010

200%

200

R=0.9997

0.005

100

0.000 0

5

10

15

20

25

0 0

5

10

15

20

25

Time/h Fig. 2.21 Adsorption kinetics curve of 0.1 g 200% CEC modified montmorillonite for DS

XRD patterns of CTAB modified montmorillonite are shown in Fig. 2.22. The XRD spectra showed that the d (001) value of CTAB modified montmorillonite increased with the increase of the amount of modifier and gradually moved to a lower Angle. The above results indicated that CTAB cations can enter into the interlamellar montmorillonite through cation exchange and lead to the increase of interlamellar spacing of montmorillonite, that is, part of CTAB molecules enter the internal crystal lattice of montmorillonite, rather than just coating on the surface of montmorillonite particles. The phase diagram peak position and diffraction Angle of modified montmorillonite adsorbed 5 mmol/L DS were basically the same as that before the adsorption, so it was speculated that there was interlayer adsorption of modified montmorillonite adsorbed diclofenac sodium. (7) IR spectrum analysis of modified montmorillonite In the infrared spectrum of sodium montmorillonite (Fig. 2.23), there are two obvious absorption bands in the high-frequency region: One is near 3620 cm−1 , which belongs to the stretching vibration absorption zone of Al–O–H bond in the montmorillonite 2:1 type element layer. The other one is near 3420 cm−1 , which belongs to the stretching vibration of water molecules between the H–O–H bond layers. This absorption band is relatively wide, reflecting the adsorption of water between the layers of montmorillonite. It corresponds to the bending vibration of the H–O–H bond of water molecules near 1636 cm−1 , indicating that there is crystal water between the layers of montmorillonite. In the intermediate frequency region, there is a relatively high absorption peak near 1450 cm−1 , which is the main difference between sodium montmorillonite and calcium montmorillonite. All above are the characteristic absorption peaks of montmorillonite, and there is no obvious change before

50

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Intensity (a.u)

Montmorillonite/DS/CTAB

Montmorillonite/CTAB

Montmorillonite

10

20

30

40

50

60

70

2 Theta (degree) Fig. 2.22 XRD patterns of unmodified montmorillonite and 200% CEC modified montmorillonite by CTAB and 200% modified montmorillonite after 5 mmol/L DS adsorption

and after modification. At the same time, it can be seen from the chromatograms that the modified montmorillonite has two new sharp absorption peaks at 2920 and 2850 cm−1 , which indicates that the organic chain of CTAB quaternary ammonium salt exists in the pore and silicate crystal layer of montmorillonite or is adsorbed to the surface of montmorillonite, that is, the CTAB modified montmorillonite was successfully prepared.

Montmorillonite/CTAB/DS

Transmittance(%)

Montmorillonite/CTAB

Montmorillonite

3620

1450 1032 DS CTAB

2920

2850

4000 3500 3000 2500 2000 1500 1000 -1 Wavenumber(cm ) Fig. 2.23 IR spectra of unmodified montmorillonite with 200% CEC

500

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

51

2.2.4 Adsorption Characteristics of Modified Illite on DS (1) Characterization of modified illite by scanning electron microscopy (SEM) SEM test results of unmodified illite, 50% CEC, 100% CEC, and 200% CEC modified illite by CTAB are shown in Fig. 2.24. The experimental results showed that there were a lot of tiny adsorbents on the surface of illite modified by CTAB with 50% CEC, 100% CEC, and 200% CEC, which indicated that CTAB had been adsorbed to the illite surface and cationic illite had been successfully prepared. (2) Contact Angle test of modified illite The contact Angle of unmodified illite, 50% CEC, 100% CEC, 200% CEC CTAB modified illite with the aqueous solution was tested. The experimental results showed that the contact angles of unmodified illite, 50% CEC, 100% CEC, and 200% CEC were 21.5°, 42.5°, 43°, and 57°, respectively. In the range of 0–200% CEC of modifier dosage, the contact Angle of illite modified gradually increased with the increase of modifier dosage. This is because the modification of the alkyl chain CTAB containing hydrophobic alkyl chain can increase the hydrophobicity of the illite surface, thus increasing the contact Angle of the illite surface (Fig. 2.25). (3) Zeta potential test of modified illite Figure 2.26 shows the Zeta potential curves of original illite and CTAB modified illite. Proto-illite surface has a negative charge, which is related to the OH on the

Fig. 2.24 CTAB modified illite SEM with the dosage of unmodified illite, 50% CEC, 100% CEC and 200% CEC

52

2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Fig. 2.25 Contact angle test of CTAB modified illite with unmodified illite, 75% CEC, 150% CEC, and 200% CEC

surface of illite, and it is also the reason why the adsorption capacity of proto-illite on diclofenac sodium is low. The surface charge of illite did not change obviously with the increase of modification concentration. (4) The equilibrium adsorption of modified illite to DS

Fig. 2.26 Zeta potential of illite samples before and after modification

2.2 Adsorption and Mechanism of DS by Four CTAB Modified Minerals

53

Experimental steps: 10 mL of DS solutions with different concentrations of 0.5 mmol/ L–1.7 mmol/L were prepared and added into 0.2 g illite, 50% CEC, 100% CEC, and 200% CEC modified illite, respectively. After oscillating adsorption for 24 h, centrifuge filtration was carried out at 5000 r/min. The supernatant was taken to measure the absorbance of DS at λ = 276 nm, and the maximum adsorption capacity of CTAB modified illite to DS was calculated with the dosage of 0.2 g original illite, 50% CEC, 100% CEC, and 200% CEC. The experiment was repeated twice. The maximum adsorption capacity of CTAB modified illite and original illite with the dosage of 50% CEC, 100% CEC, and 200% CEC for DS was studied by equilibrium adsorption of different concentrations of DS. The experimental results showed that the unmodified illite sample had a weak adsorption capacity for anion antibiotics, while the modified CTAB with 50%, 100%, and 200% dosage had a maximum adsorption capacity of about 17 mmol/kg, 30 mmol/kg, and 52 mmol/kg for DS, respectively (Fig. 2.27). (5) Adsorption kinetics of modified illite to DS

Absorption amout(mmol/Kg)

Figure 2.28 shows the relationship between the adsorption amount of illite on diclofenac sodium and the time. As can be seen from Fig. 2.28, the adsorption rate of illite on diclofenac sodium increased rapidly at first, and the removal rate reached about 95% within 13 min, and then grew slowly and approached equilibrium gradually. In general, chemical adsorption and complexation reaction are relatively fast, ion exchange and physical adsorption are relatively slow. The quasi-second-order kinetic model fitting was performed for the adsorption data of DS in illite at different times. The linear model of the quasi-second-order kinetic equation was expressed as:

50

raw 50% 100% 200 %

40 30 20 10 0 0.0

0.2

0.4

0.6

0.8

1.0

Equilibrium concentration

1.2

1.4

1.6

mmol/L

Fig. 2.27 Adsorption equilibrium curves of 0.2 g illite, 50% CEC, 100% CEC and 200% CEC modified illite for DS

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2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

t 1 1 = + t 2 qt k s qe qe qt =

K 0 − Ct V M

where, qt is the adsorption capacity at time t, mmol/kg; ks quasi-second-order kinetic rate constant, mmol/(kg h); Ct is the concentration of DS at time t, mmol/L. Took t as the abscissa and t/qt as the ordinate, drew Fig. 2.28a. The results showed that the pseudo-second-order kinetic model can fit the adsorption data well, and the correlation coefficient reaches 0.1. (6) X-ray diffraction analysis (XRD) of modified illite XRD patterns of CTAB modified illite are shown in Fig. 2.29. XRD spectrum showed that the phase diagrams of illite before and after modification were very similar, and the position of peak and diffraction Angle were basically the same, did not find other diffraction peaks of the impurities, modified illite was still keep the original features of each diffraction peak of illite and that CTAB modification did not change the crystal structure of the original illite, namely the majority of CTAB molecules not enter the internal lattice of illite, It was coated on the surface of illite grains. The peak position and diffraction Angle of phase diagram after 5 mmol/L DS adsorption of modified illite were basically the same as that before adsorption, indicating that the adsorption of diclofenac sodium by modified illite was surface adsorption. (7) IR spectrum analysis of modified illite

b

55

Absorption amout(mmol/Kg)

50 45 40 35 30

7

25

6

a

5

20

4

15

3 2

10

1

5

R=0.1

200%

0 0

0 0

50

20

100

150

200

40

250

300

350

400

60

80

100

Time/min Fig. 2.28 Adsorption kinetics curve of 0.1 g 200% CEC modified illite for DS

120

2.3 Chapter Summary

55

Intensity (a.u)

DS/200%CTAB/illite

200%CTAB/illite

illite

20

30

40 50 2 Theta (degree)

60

70

Fig. 2.29 XRD patterns of unmodified illite and 200% CEC modified illite with CTAB and 200% modified illite after adsorption of 5 mmol/L DS

In the study of the organic modification of illite, by comparing the changes of infrared absorption spectra (IR) between CTAB modified illite and natural illite, The changes of organic ions entering illite layers in local microenvironment, the intermolecular or intermolecular interactions and the configuration of molecular alkyl chain can be understood. Figure 2.30 shows the infrared absorption spectra of natural illite and CTAB modified illite. The spectra are basically the same, indicating that the structure of illite has not changed after CTAB modification. The stretching vibration peak of the R-OH structure appeared at 3621 cm−1 , the absorption peak of 1 082 cm−1 was the stretching vibration peak of Si–O–R in the crystal lattice, and the bending vibration absorption peak of Si–O–Si and Si–O–Al at 519 cm−1 were all characteristic absorption peaks of illite, and there was no obvious change before and after modification. New absorption peaks and two sharp strong absorption peaks were added at 2920 cm−1 and 2850 cm−1 , which were attributed to the symmetric and antisymmetric strain vibration generated by –CH3 and –CH2, indicating that a certain amount of cetyltrimethylammonium bromide entered the illite structure, that is, the modified illite was successfully prepared.

2.3 Chapter Summary This chapter introduces the successful preparation of modified zeolite, kaolinite, montmorillonite, and illite using CTAB organic reagents, and characterized the materials by a series of characterization methods: XRD, SEM, contact Angle test, and IR test, etc., and the characterization results were studied and analyzed. The adsorption capacity of DS on four kinds of natural minerals was weak, and the adsorption on

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2 Adsorption of Anionic Antibiotics by CTAB Modified Natural Clay …

Transmittance(%)

Illite/CTAB/DS Illite/CTAB Illite

3621

1028 DS

CTAB

2920

2850

4000 3500 3000 2500 2000 1500 1000 -1 Wavenumber(cm )

500

Fig. 2.30 IR spectra of unmodified illite with 200% CEC dosage of CTAB modified illite

four kinds of CTAB modified clay minerals was mainly electrostatic, and the distribution of DS on minerals also played a certain role. The adsorption of DS in the interlayer of montmorillonite had an important effect on it, and DS can enter the interlayer to form monolayer adsorption. In addition, intermolecular hydrophobicity may also exist, because the DS adsorbed on the mineral may affect the adsorption of itself and other organic pollutants as the organic matter of the mineral. Based on the experimental results, the following conclusions were drawn: (1) SEM characterized the successful preparation of zeolite, kaolinite, illite, and montmorillonite modified by CTAB. (2) The contact Angle test indicated that the surface lipophilicity of the four clay minerals increased after CTAB modification, which was conducive to the adsorption of organic antibiotics. (3) Zeta potential test characterized the process of surface electrical properties of four clay minerals from neutral and negative to positive. (4) Adsorption experiments showed that the adsorption capacity of unmodified clay minerals to DS was weak, and the adsorption capacity of modified minerals with different dosages of modifier to anionic DS was greatly improved. The maximum adsorption capacities of zeolite, kaolinite, montmorillonite, and illite modified with 200% CEC for DS were about 120 mmol/kg, 42 mmol/kg, 1 000 mmol/kg, 52 mmol/kg, respectively. Among them, the adsorption effect of organo-modified montmorillonite on DS was obviously better than that of the other three, because the adsorption of organo-modified montmorillonite on DS does not exist surface adsorption but also includes interlayer adsorption, and the interlayer adsorption made a great contribution, while the adsorption of other three modified minerals on DS was mainly surface adsorption, and the effect was similar. Kaolinite had the worst adsorption effect. In addition, the

References

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adsorption kinetics models of the four modified clay minerals can be well fitted by the second-order kinetics model. (5) XRD diffraction analysis characterized whether the modifier and adsorbent destroyed the crystal structure of the mineral before and after modification and adsorption, whether it was a surface modification or adsorption or interlayer modification or adsorption. The results showed that the adsorption behavior of porous zeolite (pore size is smaller than the molecular size of CTAB and DS), non-expansive kaolinite and illite for CTAB and DS was mainly surface adsorption, while the adsorption behavior of expansive montmorillonite with exchangeable cation for CTAB and DS included not only surface adsorption but also interlayer adsorption. (6) IR characterized the successful preparation of CTAB modified zeolite, kaolinite, illite and montmorillonite. The characteristic functional group of CTAB appeared on the surface of modified zeolite, kaolinite, illite, and montmorillonite.

References Bui TX, Choi H (2009) Adsorptive removal of seleceted pharmaceuticals by mesoporous silica SBA-15. J Hazard Mater 168(2–3):602–608 Cleuvers M (2004) Mixture toxicity of the anti-inflammatory drugs diclofenac, ibuprofen, naproxen and acetylsalicylic acid. Ecotoxicol Environ Saf 59:309–315 Stulten D, Zuhkle S, Lamshoft M et al (2008) Occurrence of diclofenac and selected metabolites in sewage effluents. Sci Total Environ 405(1–3):10–316 Ternes TA, Meisenheimer M, Mcdowell D et al (2002) Removal of pharmaceuticals during drinking water treatment. Environ Sci Technol 36(17):3855–3863 Zhao YF, Zhao L, Wang GC, Han Y (2011a) Fabrication of the tricontinuous mesoporous IBN-9 structure with surfactant CTAB. Chem Mater 23:5250–5255 (2011a) Zhao YP, Geng JJ, Wang XR (2011b) Tetracycline adsorption on kaolinite: pH metal cations and humic acid effects. Ecotoxicology 20:1141–1147 (2011b)

Chapter 3

Study on the Adsorption of Anionic Antibiotics on Natural Clay Minerals Modified by Ionic Liquids

Abstract Firstly, the preparation and adsorption experimental methods of the three characteristics of cationic minerals were introduced. Secondly, the adsorption and mechanism of the three ionic liquid-modified minerals on CAP were described, and the following six conclusions were reached. (1) SEM characterized the successful preparation of ionic liquid modified zeolite, montmorillonite, and illite. (2) The contact angle test characterized that the lipophilicity of the surface of zeolite, montmorillonite, and illite was increased through ionic liquid modification, which was conducive to the adsorption of organic antibiotics. (3) The Zeta potential test characterized the transition process of the surface electrical properties of the three clay minerals from neutral and negative to positive. (4) The adsorption experiment showed that the adsorption capacity of unmodified clay minerals to CAP was weak, and the adsorption performance of modified minerals with different modifier dosages to anionic CAP was greatly improved. (5) The adsorption behavior of pore structure zeolite (pore size smaller than the molecular size of ionic liquid and CAP) and nonexpandable illite on ionic liquid and CAP were mainly surface adsorption. (6) The characteristic functional groups of ionic liquid appeared on the surface of modified zeolite, montmorillonite, and illite. Keywords Ionic liquid organic reagents · CAP · XRD · SEM · Contact angle measurements · IR

Preliminary experimental studies have proved that CTAB modified clay minerals had a good adsorption effect on the anionic anti-inflammatory drug DS. However, CTAB has a high saturated vapor pressure and is easy to volatilize into the gas phase. This will cause secondary pollution to the environment during clay modification and subsequent use. To solve this problem, a new type of environmentally friendly modifier-ionic liquids was found, which is a salt compound that is a combination of organic cations and inorganic anions, which is liquid at room temperature or low temperature. Ionic liquids have the following characteristics: © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 K. Sun, Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-981-99-6434-5_3

59

60

3 Study on the Adsorption of Anionic Antibiotics on Natural Clay …

Fig. 3.1 Comparison of DS adsorption performance between CTAB modified minerals and ionic liquid modified minerals

➀ Colorless, odorless, and almost no vapor pressure; ➁ It has high thermal and chemical stability, and has a large temperature range in a liquid state; ➂ No flammability, no ignition point, large heat capacity, and low viscosity; ➃ The ion conductivity is high, and the decomposition voltage (also known as the electrochemical window) is generally as high as 3–5 V; ➄ It has strong Bronsted, Lewis, and Franklin acidity and super acid properties, and the acidity and alkalinity can be adjusted. The maximum adsorption effect of the CTAB modified mineral to the anionic anti-inflammatory drug DS is similar to that of the ionic liquid modified mineral (Fig. 3.1). However, compared with general organic cationic modifiers, such as CTAB, ionic liquids are salt compounds that are liquid at room temperature or low temperature. They have the advantages of low vapor pressure, high stability, acid and alkali resistance, and relatively cheap prices. It can avoid secondary pollution in the process of mineral modification or use, so it is also called “green solvent”. To verify the universality of organically modified clay minerals for the adsorption of antibiotics, this chapter intends to use ionic liquid-modified clay minerals to adsorb anionic antibiotics-chloramphenicol. Antibiotics are organic substances that are produced by organisms during their life activities or obtained by other methods, it can selectively inhibit or affect other biological functions at low concentrations. The effect on microorganisms is the initial form of action of antibiotics. At present, antibiotics mainly include β-lactams, quinolones, macrolides, sulfonamides, and tetracyclines. Compared with the traditional organic pollutants that are highly toxic and easy to bioaccumulate, the existence, behavior, and possible negative effects of antibiotics widely used in human daily life in the environment have not attracted people’s attention. It is not until the emergence of super-bacteria that people begin to pay attention to antibiotics that are widely used in daily life.

3 Study on the Adsorption of Anionic Antibiotics on Natural Clay …

61

With the development of large-scale animal husbandry, epidemic diseases have gradually become an important link restricting the development of animal husbandry. Antibiotics play an important role in the animal husbandry industry. Approximately 70% of antibiotics worldwide were used for this (Heilig et al. 2002). The production of veterinary antibiotics increased rapidly from 91 t in 1950 to 9 300 t in 1999. According to reports, about 16,000 tons of antibiotics were used in the United States in 2000, 70% were used for non-disease treatment purposes (Mellon et al. 2000). A large number of antibiotic drugs enter the environment in the form of female parent or metabolites, causing a huge load to the environment and a potential threat to the ecological environment. Long-term low-dose exposure of microorganisms in the soil to residual antibiotics can induce drug resistance and cause potential harm. Especially when the residual antibiotics in the environment migrate from the soil to rivers, lakes, and even groundwater through rainwater and percolation, its harm is even greater. In China, the production and use of antibiotic drugs are huge. According to statistics, the total consumption of antibiotics in my country in 2012 was about 162,000 tons, which was 4.9 times the consumption of antibiotics in 2000 (Yu 2015). Relevant data shows that the use of antibiotics in my country is increasing year by year in recent years. The density of antibiotic emissions in the east was more than 6 times that of the western basin. At present, people still have many misunderstandings in the use of antibiotics. Antibiotics for any disease that can be treated with antibiotics. They have not realized the harm of antibiotics. The lack of scientific guidance on drug supervision and drug use has led to a very serious problem of antibiotic abuse in my country. After antibiotic pollutants enter the environment, they will migrate, transform, distribute, degrade, and die in environmental media such as water bodies, suspended solids, soil, sediments, and organisms, and some of them will also have biological effects. Because the migration, transformation, and biological effectiveness of pollutants in the environment are largely affected by adsorption, and this adsorption has a great correlation with the physical and chemical properties of the pollutants themselves, climatic conditions, soil characteristics, and other environmental factors. Therefore, people have successively carried out a series of research work on the adsorption effect and mechanism of organic pollutants including antibiotic drugs on environmental media. Antibiotics as ionic organic pollutants can be divided into cationic (such as tetracycline, ciprofloxacin, tylosin, etc.) and anionic (such as CAP, etc.).

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Because of its different properties, the mechanism of action of clay minerals in the soil is different. Tolls made an important review of the adsorption mechanism of several antibiotics on soil in 2001 (Tolls 2001). Tetracycline antibiotics all contain a naphthacene structure skeleton, mainly including chlortetracycline, oxytetracycline, tetracycline, chlortetracycline, and so on. Bao Yanyu reported that the adsorption capacity of tetracycline antibiotics in cinnamon soil was in the order of chlortetracycline > tetracycline > oxytetracycline, and physical adsorption was the main adsorption mechanism of tetracycline antibiotics in soil (Bao et al. 2010). Sassman et al. studied the adsorption of several different tetracycline antibiotics (tetracycline TC, oxytetracycline OTC, chlortetracycline CTC) on different soils. By analyzing the relationship between the adsorption amount of tetracycline antibiotics on the soil and soil pH, clay content and type, cation and anion exchange capacity, and soil organic carbon, the main factors affecting the adsorption of tetracycline in the soil were found. The results showed that all soils had a very strong adsorption effect on tetracycline antibiotics, especially in soils with high acidity and clay content (Sassman and Lee 2005). The adsorption of tetracycline on montmorillonite was much stronger than that on kaolinite. And with the increase of pH value and ionic strength, the adsorption capacity of tetracycline on minerals decreased. The higher the cation valence, the greater the reduction in adsorption capacity (Figueroa et al. 2004). The results showed that ion exchange was the main mechanism of tetracycline adsorption on clay minerals. Wu et al. (2010) showed that the main reason for the adsorption of ciprofloxacin on montmorillonite was cation exchange. The cations in the solution, especially Ca2+ , had a great influence on its adsorption on montmorillonite. Due to the competition of Ca2+ , the higher the concentration, the smaller the adsorption capacity of ciprofloxacin on montmorillonite (Mo et al. 2011). The adsorption capacity of tylosin in bentonite and montmorillonite could reach 190 and 65 g/kg, while the adsorption capacity in illite and kaolinite could only reach 22 and 6.5 g/kg (Lee et al. 2010; Bewick 1979). Ter Laak et al. studied the adsorption of tylosin on soil and found that as the pH value (6–9) increases, the adsorption capacity of soil to tylosin decreases. This trend was related to the ionic form of antibiotics. Under low pH conditions, tylosin had a net positive charge and was easily adsorbed on clay minerals. With the increase of ionic strength, the adsorption of tylosin showed a trend of first increasing and then decreasing.

3 Study on the Adsorption of Anionic Antibiotics on Natural Clay …

63

Fig. 3.2 The molecular structure of CAP

This was because under the condition of low ionic strength, the pH decreased slightly with the increase of ionic strength, resulting in a slight increase in the adsorption of tylosin. However, when the ionic strength was high, the positive metal cations in the solution competed with the positive tylosin for adsorption, so that the adsorption of tylosin decreased with the increase of ionic strength (Ter Laak et al. 2006). The adsorption capacity of tylosin on montmorillonite was significantly higher than that of illite and kaolinite. Essington et al. (2010) studied the effects of pH and ionic strength on the adsorption of tylosin on montmorillonite and kaolinite. CAP (Chloramphenicol, CAP) is a broad-spectrum antibiotic (its chemical structure is shown in Fig. 3.2). Because of its low price, excellent antibacterial properties, and stable efficacy, it is often used to treat various infectious diseases of animals and various diseases of humans, and it has a relatively strong inhibitory effect on many kinds of pathogenic bacteria. Especially in the treatment of various inflammations in dairy cows and laying hens, it can also promote animal growth. However, CAP had serious toxic and side effects. Residual CAP in water not only had direct harm to animals and humans but also induced drug resistance of pathogenic bacteria, which was easy to cause human blood poisoning. It could cause irreversible aplastic anemia, posing a huge threat to human health (Hu and Shen 2001; Robert et al. 1994). The European Union stipulated that the detection limit of CAP residues is 0.1 μg kg−1 , and the United States stipulated the detection limit of 0.3 μg kg−1 (Li et al. 2002). Announcement No. 193 issued by the Ministry of Agriculture in 2002 clearly stipulated the content of CAP in edible animal tissues.

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China is a big meat product country. In recent years, importing countries have frequently detected CAP residues in meat products exported from China. CAP residues had become a major obstacle to the international trade of Chinese aquatic products. In response to this situation, the Ministry of Agriculture of our country relisted CAP in the safety evaluation system in 2000. In addition, my country stipulated that CAP must not be detected in the edible parts of animals in the “Regulations on Residues of Animal Food and Veterinary Drugs.” In the daily inspection of exports, once the CAP is found to exceed the standard, the export is prohibited. Therefore, there is an urgent need for a high-efficiency adsorbent to treat CAP and minimize the harm of CAP. The surface of typical natural non-metallic minerals is mostly negative and has good adsorption performance for cationic antibiotics. Based on the current research status in China and abroad, it can be found that the research on the adsorption of antibiotics in the soil mainly focuses on cationic antibiotics, while the research on anionic antibiotics is less, and the research on its adsorption characteristics and mechanism in the soil is still immature. It is worth noting that although the abuse of drugs and personal care products in my country is very serious, environmental behavior in the soil has not attracted enough attention. Research on the anionic antibiotic CAP is even rarer. Therefore, it is very necessary to develop an efficient, non-pollution-free anionic antibiotic treatment technology to protect the environment and people’s health. The three unmodified clay minerals all have a certain amount of adsorption to CAP, but the adsorption amount is significantly smaller than that of modified minerals. The three unmodified minerals, zeolite, montmorillonite, and illite, have adsorption saturation of approximately 4 mmol/kg, 2 mmol/kg, and 5 mmol/kg for CAP, respectively (Fig. 3.3), and the adsorption effect is almost zero. Therefore, this chapter intends to use ionic liquids to modify natural clay minerals to adsorb chloramphenicol in water. Through adsorption thermodynamics and kinetics, the adsorption capacity of typically modified clay minerals is evaluated. And using X-ray diffraction (XRD), infrared spectroscopy (FTIR), surface contact angle, scanning electron microscope (SEM), and other test methods to study the adsorption mechanism.

3.1 Preparation and Adsorption Experimental Methods of Three Cationic Modified Minerals mmol/kg and 70 mmol/kg. The CECs of zeolite, montmorillonite, and illite used in the experiment were 100 mmol/kg, 1200 mmol/kg, and 70 mmol/kg, respectively.

a 4 3 Zeolite/CAP

2 1

0 1 2 3 4 5 Equilibrium concentration (mmol/L)

Adsorption amount (mmol/Kg)

5

Adsorption amount (mmol/Kg)

Adsorption amount (mmol/Kg)

3.1 Preparation and Adsorption Experimental Methods of Three Cationic …

65

8

b 6

Montmorillonite/CAP

4 2 0

0 1 2 3 4 Equilibrium concentration (mmol/L)

10

c illite/CAP

5

0

0 1 2 3 4 5 Equilibrium concentration (mmol/L)

Fig. 3.3 Adsorption of CAP by three unmodified minerals

The three types of clay minerals were modified with different amounts of ionic liquids to prepare clay minerals modified with different amounts of modifiers. First, weighed ionic liquids of different masses to dissolve them according to their CEC. Then added the clay mineral of the corresponding quality, shaking at room temperature for 24 h, centrifuge and filter, washed it several times, and then dried it naturally. Finally, the ionic liquid-modified clay mineral was prepared. Adsorption experiment steps: Weighed 0.5 g zeolite, 0.5 g ionic liquid modified zeolite containing 200% CEC, 0.1 g montmorillonite, 0.1 g ionic liquid modified montmorillonite containing 200% CEC, 0.5 g illite, and 0.1 g containing 200% CEC dosage of ionic liquid modified illite. And added 0.5–5 mmol/L of different concentrations of DS solution 10, 10, 20, 20, 10, 10 mL. After vibrating and adsorbing for 24 h, performed centrifugal filtration at 5000 r/ min.

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Took the supernatant liquid to measure the absorbance of CAP at λ = 278 nm, and calculated the maximum adsorption capacity of the three unmodified clay minerals for CAP, and compared the adsorption performance of the modified clay minerals.

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified Minerals 3.2.1 Adsorption and Mechanism of CAP on Ionic Liquid Modified Zeolite (1) Scanning electron microscope characterization (SEM) of modified zeolite The SEM test results of ionic liquid modified zeolite with unmodified zeolite, 50% CEC, 100% CEC, and 200% CEC were shown in Fig. 3.4. The experimental results showed that the unmodified zeolite has a smooth surface and micropores on the surface. The surface of the ionic liquid modified zeolite with 50% CEC, 100% CEC, and 200% CEC contained a large number of tiny adsorbents, which showed that the ionic

Fig. 3.4 SEM of ionic liquid zeolite with unmodified zeolite, 50% CEC, 100% CEC, and 200% CEC

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified …

67

Fig. 3.5 Contact angle test of unmodified zeolite, 50% CEC, 100% CEC, 200% CEC ionic liquid modified zeolite

liquid has been adsorbed to the surface of the zeolite and the cationic modified zeolite has been successfully prepared. (2) Contact angle test of modified zeolite Tested the contact angle of unmodified zeolite, 50% CEC, 100% CEC, and 200% CEC of ionic liquid modified zeolite with an aqueous solution, as shown in Fig. 3.5. The experimental results showed that the contact angles of unmodified zeolite, 50% CEC, 100% CEC, and 200% CEC of ionic liquid modified zeolite were 38°, 59.5°, 64°, and 65°, respectively. When the amount of modifier was in the range of 0–200% CEC, the contact angle of the modified zeolite gradually increased with the increase of the amount of modifier. This was because as the amount of ionic liquid increased, the amount of ionic liquid adsorbed on the surface of the modified zeolite also increased. The more ionic liquid on the surface, the stronger the hydrophobicity, which increased the contact angle of the zeolite surface. (3) Zeta potential measurement of modified zeolite Figure 3.6 shows the zeta potential curves of the original zeolite and the modified zeolite with different concentrations of ionic liquid. The negative charge on the surface of the original zeolite is related to the OH on the surface of the zeolite, which is also the reason for the low adsorption capacity of the original zeolite to CAP. It also further proves that the organic zeolite has an electrostatic adsorption mechanism for CAP.

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Fig. 3.6 Zeta potential before and after modification of zeolite sample

As the modification concentration increases, the surface of the zeolite turns from negatively charged to positively charged. The order of the positive charges on the surface of the four ionic liquid modified zeolite and the original zeolite is 200% > 100% > 50% > original zeolite. (4) IR spectrum analysis of modified zeolite Analyzing the adsorption CAPIR chart 3.7 of zeolite before and after modification and modified zeolite, it is found that: Natural zeolite has typical Si(Al)–O stretching vibration characteristic peaks and Si(Al)–O bending vibration characteristic peaks. It belongs to a typical framework silicate mineral. The zeolite modified by ionic liquid has several strong characteristic peaks at 800–1000 cm−1 and 500–650 cm−1 . These characteristic peaks correspond to those of natural zeolite. This indicates that the properties of the modified zeolite are basically unchanged. At the same time, it can be seen from the spectrum that the modified zeolite has a weak absorption band at 2800–2900 cm−1 . The characteristic absorption peak of the zeolite modified by the ionic liquid is consistent with that of the original zeolite. The spectrum also shows the absorption bands caused by the CH3 and CH2 C–H vibrations at 2916 and 2852 cm−1 , which indicates that the ionic liquid has been loaded on the surface of the zeolite (Fig. 3.7). (5) Equilibrium adsorption of CAP by modified zeolite Experimental procedure: Prepared 10 mL of CAP solution with different concentrations of 0.5–5.0 mmol/L respectively.

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified … Fig. 3.7 IR spectra of ionic liquid, unmodified zeolite, 200% CEC dosage of ionic liquid modified zeolite

69

200% 2852

Transmittance(%)

2916

Zeolite

1015

797

Ionic liquids

4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumbers (cm )

Added 0.5 g of zeolite, 50% CEC, 100% CEC, 200% CEC of ionic liquid modified zeolite. After vibrating and adsorbing for 24 h, performed centrifugal filtration at 5000 r/ min. Took the supernatant liquid and measured the absorbance of CAP at λ = 278 nm, and calculated the maximum adsorption capacity of CAP on the ionic liquid modified zeolite with the amount of 0.5 g zeolite, 50% CEC, 100% CEC, and 200% CEC. Repeated experiment 2 Times. Through the equilibrium adsorption of different concentrations of CAP, the maximum adsorption capacity of 50% CEC, 100% CEC, 200% CEC modified zeolite and original zeolite for CAP was discussed. The experimental results showed that the original unmodified zeolite has a weak adsorption capacity for CAP. This was because the surface of the modified zeolite has surface electronegativity, so it was not easy to adsorb anionic antibiotics. The maximum CAP adsorption capacity of ionic liquid modified zeolite with 50%, 100%, and 200% CEC dosage modified with cationic modifier was about 13 mmol/ kg, 17 mmol/kg, 25 mmol/kg, respectively (Fig. 3.8). (6) Adsorption kinetics of CAP on modified zeolite Figure 3.9 shows the relationship between the amount of CAP adsorption by zeolite and time. It can be seen from Fig. 3.9 that the adsorption rate of zeolite to CAP increases rapidly at first, and the removal rate reaches about 95% within 30 min and growth then slowed and came closer to equilibrium. The quasi-second-order kinetic model of the adsorption data of CAP in the zeolite at different times is quasi-matched, and the linear model of the quasi-second-order kinetic equation is expressed by the formula:

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Absorption amout(mmol/Kg)

Fig. 3.8 The adsorption equilibrium curve of CAP on the ionic liquid modified zeolite with 0.5 g zeolite, 50% CEC, 100% CEC, and 200% CEC

raw 50% 100% 200 %

25 20 15 10 5 0 0

1 2 3 4 5 Equilibrium concentration mmol/L

26

Absorption amout(mmol/Kg)

24 22 20 18 16 14

5

12

4

10

3

8

2

6

1

4

R=0.9997

200%

0

2 0

b

0

0

20

20

40

60

40

80

100

120

60

80

100

120

Time/min Fig. 3.9 Adsorption kinetic curve of CAP on 0.5g 200% CEC modified zeolite

t 1 1 = + t 2 qt k s qe qe K 0 − Ct V qt = M In the formula, qt is the adsorption amount at time t, mmol/kg; ks is the quasisecond-order kinetic rate constant, mmol/(kg h); Ct is the concentration of CAP at time t, mmol/L. Used t as the abscissa and t/qt as the ordinate to draw Fig. 3.9b.

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified …

Zeolite/CAP/Ionic liquids

Intensity (a.u)

Fig. 3.10 XRD patterns of unmodified zeolite, ionic liquid modified zeolite with 200% CEC dosage, and 200% modified zeolite after adsorption of 5 mmol/LCAP

71

Zeolite/Ionic liquids

Zeolite

10

20

30 40 50 2 Theta (degree)

60

70

The results showed that the two-stage kinetic model can fit the adsorption data well, and the correlation coefficient is above 0.99. X-ray diffraction analysis (XRD) of modified zeolite The XRD pattern of the ionic liquid-modified zeolite is shown in Fig. 3.10. The XRD pattern shows that the phase diagrams of the zeolite before and after modification are very similar, the peak positions and diffraction angles are basically the same, and no diffraction peaks of other impurities are found. The modified zeolite still retains the characteristics of the diffraction peaks of the original zeolite, indicating that the ionic liquid modification does not change the crystal structure of the original zeolite, which means that most of the ionic liquid molecules do not enter the internal crystal lattice of the zeolite, but are coated in the surface of the zeolite particles. The peak position and diffraction angle of the phase diagram of the modified zeolite after adsorbing 5 mmol/LCAP is basically the same as those before the nonadsorption, indicating that the adsorption of CAP by the modified zeolite is surface adsorption.

3.2.2 Adsorption Characteristics of Modified Montmorillonite to CAP (1) Scanning electron microscope characterization (SEM) of modified montmorillonite The SEM test results of ionic liquid modified montmorillonite of unmodified montmorillonite, 50% CEC, 100% CEC, and 200% CEC are shown in Fig. 3.11.

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Fig. 3.11 Unmodified montmorillonite, 50% CEC, 100% CEC, 200% CEC dosage of ionic liquid modified montmorillonite SEM

It can be seen from the Fig. that the morphology of Na-montmorillonite particles is different in size and agglomerate or flocculent aggregate. The aggregate is formed by stacking extremely thin wafers, and the particle size of some aggregates is greater than 10 μm. There are wrinkles on the edges of the aggregates of particles, irregular in appearance and relatively loose. Comparing with the unmodified montmorillonite surface, the ionic liquid modified montmorillonite with 50% CEC, 100% CEC, and 200% CEC adds a lot of tiny adsorbents. This shows that the ionic liquid has been adsorbed on the surface of the montmorillonite, and the cationic modified montmorillonite has been successfully prepared. (2) Contact angle test of modified montmorillonite The contact angle of unmodified montmorillonite, 50% CEC, 100% CEC, and 200% CEC of ionic liquid modified montmorillonite with the aqueous solution was tested. The experimental results showed that the contact angles of modified montmorillonite for unmodified montmorillonite, 50% CEC, 100% CEC, and 200% CEC were 32.5°, 71.5°, 62°, and 74°, respectively. In the range of 0–200%, CEC of modifier dosage, the contact angle of modified montmorillonite tended to increase with the increment of modifier dosage.

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified …

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This was due to the modified ionic liquid containing hydrophobic alkyl chains increases the hydrophobicity of the montmorillonite surface and increases the contact angle of the montmorillonite surface (Fig. 3.12). (3) Zeta potential measurement of modified montmorillonite Figure 3.13 shows the zeta potential curves of original montmorillonite and ionic liquid modified montmorillonite with different concentrations. The surface of the original montmorillonite is negatively charged, which is related to the OH on the surface of the montmorillonite. This is also the reason why the original montmorillonite has a low adsorption capacity for CAP. At the same time, it further proves that organic montmorillonite has an electrostatic adsorption mechanism for CAP. When the concentration of the ionic liquid is small, Monolayer is formed by the adsorption of cations in ionic liquid on the surface and between layers of montmorilloniter, which gradually reduces the negative charge of the montmorillonite until it is not charged. Although the montmorillonite at this time has been modified, the adsorption effect of CAP is still not good. When the concentration of the modifier continues to increase, the cations in the ionic liquid form a bilayer on the surface and between the layers of the montmorillonite due to the action of micelles, which reverses the charge on the surface of the montmorillonite, thereby being positively charged.

Fig. 3.12 Contact angle test of unmodified montmorillonite, 50% CEC, 100% CEC, 200% CEC dosage of ionic liquid modified montmorillonite

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Fig. 3.13 Zeta potential of montmorillonite samples before and after modification

As the modified concentration increases, the surface of montmorillonite turns from negatively charged to positively charged. The order of the positive charges on the surface of the 4 kinds of ionic liquid modified montmorillonite and the original montmorillonite is 200% > 100% > 50% > original montmorillonite. (4) IR spectrum analysis of modified montmorillonite In the infrared spectrum of sodium-based montmorillonite (Fig. 3.14), there were two obvious absorption bands in the high-frequency region: One was near 3620 cm−1 , which belonged to the stretching vibration absorption zone of the Al–O–H bond in the 2:1 montmorillonite unit layer. The other was near 3420 cm−1 , which was attributed to the stretching vibration of water molecules between the H–O–H bond layers. This absorption band was relatively wide, reflecting the adsorbed water between the montmorillonite layers. It corresponded to the bending vibration of the H–O–H bond of water molecules near 1636 cm−1 , indicating that the montmorillonite layers contain crystal water. In the middle-frequency region, there was a relatively high absorption peak near 1450 cm−1 , which was the main difference between sodium-based montmorillonite and calcium-based montmorillonite. The above was the characteristic absorption peaks of montmorillonite, and there was no obvious change before and after modification. At the same time, it can be seen from the spectrum that the modified montmorillonite has added 3 sharp strong absorption peaks at 1471, 2916, and 2852 cm−1 .

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified … 200% 3621

Transmittance(%)

Fig. 3.14 IR spectra of ionic liquid, unmodified montmorillonite, 200% CEC dosage of ionic liquid modified montmorillonite

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It showed that the organic chain of ionic liquid quaternary ammonium salt has existed in the pores and silicate crystal layer of montmorillonite, or adsorbed to the surface of montmorillonite. This indicated that the preparation of ionic liquid-modified montmorillonite was successful. Equilibrium adsorption of modified montmorillonite to CAP Experimental procedure: prepared 20 mL of CAP solution with different concentrations of 0.5 mmol/L–5 mmol/L respectively. Added 0.1 g montmorillonite, 50% CEC, 100% CEC, and 200% CEC to the ionic liquid modified montmorillonite in the solution. After vibrating and adsorbing for 24 h, performed centrifugal filtration at 5000 r/ min. Took the supernatant and measured the absorbance of CAP at λ = 278 nm. The maximum adsorption capacity of ionic liquid modified montmorillonite for CAP with the amount of 0.07 g montmorillonite, 50% CEC, 100% CEC, and 200% CEC was calculated, and the experiment was repeated twice. Through the equilibrium adsorption of different concentrations of CAP, the maximum adsorption capacity of the ionic liquid modified montmorillonite and the original montmorillonite with the dosage of 50% CEC, 100% CEC, and 200% CEC was discussed. The experimental results showed that the adsorption capacity of CAP on modified montmorillonite and unmodified montmorillonite increases with the increase of the equilibrium concentration of CAP. The unmodified montmorillonite had weak adsorption capacity for anionic antibiotics, while the maximum adsorption capacity of modified montmorillonite for CAP with 50%, 100%, and 200% ionic liquids was about 135, 173, 311 mmol/ kg (Fig. 3.15).

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Fig. 3.15 The adsorption equilibrium curve of 0.07 g montmorillonite, 50% CEC, 100% CEC, 200% CEC modified montmorillonite for CAP

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For organic montmorillonite modified with ionic liquid, the adsorption capacity of CAP on this type of organic clay mineral was higher than that of unmodified montmorillonite, because the ionic liquid was exchanged into the interlayer of montmorillonite. The distance between the montmorillonite layers increased, and the adsorption sites increased; in addition, the hydrophobicity of the mineral surface will also increase. This means that when the amount of ionic liquid is increased, the ionic liquid can not only enter the montmorillonite mineral layer through the exchange but also can be adsorbed by the mineral surface to enhance the hydrophobicity of the mineral surface. (6) Adsorption kinetics of CAP on modified montmorillonite Experimental steps: Prepared 10 mL of 5 mmol/L CAP solution, added 0.1 g 100% ionic liquid modified montmorillonite respectively and repeated the experiment twice. After shaking and adsorbing for 0.5, 1, 5, 30 min, 1, 2, 6, 9, 24 h, centrifuged and filtered at 3500 r/min. Took the supernatant to measure the absorbance of CAP at λ = 278 nm, and calculated the maximum adsorption capacity of 0.1 g ionic liquid to CAP. Figure 3.16 showed the relationship between the amount of CAP adsorbed by montmorillonite and time. It can be seen from Fig. 3.16 that the adsorption rate of montmorillonite to CAP initially increases rapidly. Within 10 min, the removal rate reached about 97%, and then increased slowly and gradually approached equilibrium. Generally speaking, chemical adsorption and complexation reactions were relatively fast, while ion exchange and physical adsorption were relatively slow.

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Absorption amout(mmol/Kg)

180 170 160 150 0.7

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Time/min Fig. 3.16 Adsorption kinetics curve of CAP on 0.1 g 100% CEC modified montmorillonite

The CAP adsorption data in montmorillonite at different times were fitted with a pseudo-second-order kinetic model. The linear model of the pseudo-second-order kinetic equation was expressed as: t 1 1 = + t qt ks qe2 qe K 0 − Ct V qt = M In the formula, qt is the adsorption amount at time t, mmol/kg; ks is the quasisecond-order kinetic rate constant, mmol/(Kg h); Ct is the concentration of CAP at time t, mmol/L. Use t as the abscissa and t/qt as the ordinate to draw Fig. 3.16b. The results showed that the quasi-second-order kinetic model can fit the adsorption data well, and the correlation coefficient is above 0.9999. (7) X-ray diffraction analysis (XRD) of modified montmorillonite The XRD pattern of ionic liquid-modified montmorillonite was shown in Fig. 3.17. The XRD pattern showed that the d (001) value of the ionic liquid modified montmorillonite had a corresponding change compared with the sodium-based montmorillonite, and the diffraction peak angle shifted to a lower angle. The above results indicated that ionic liquid cations could enter the interlayer of montmorillonite through cation exchange, and caused the increase of the interlayer spacing of montmorillonite.

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Fig. 3.17 XRD patterns of unmodified montmorillonite, ionic liquid modified montmorillonite with 200% CEC dosage, and 200% modified montmorillonite after adsorption of 5 mmol/ LCAP.

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This meant that part of the ionic liquid molecules has entered the internal lattice of the montmorillonite instead of just covering the surface of the montmorillonite particles. The peak position and diffraction angle of the phase diagram of the modified montmorillonite after adsorbing 5 mmol/LCAP was basically the same as before. Therefore, it was speculated that the modified montmorillonite adsorbed CAP with interlayer adsorption.

3.2.3 Adsorption Characteristics of Modified Illite to CAP 1) Scanned electron microscope characterization (SEM) of modified illite The SEM test results of ionic liquid modified illite with unmodified illite, 50% CEC, 100% CEC, and 200% CEC were shown in Fig. 3.18. The experimental results showed that the surface of illite modified with 50% CEC, 100% CEC, and 200% CEC ionic liquid contains a large number of tiny adsorbents. This showed that the ionic liquid has been adsorbed on the surface of illite, and the cationic modified illite has been successfully prepared. (2) Contacted angle test of modified illite The contact angle of unmodified illite, 75% CEC, 150% CEC, and 200% CEC of ionic liquid modified illite with an aqueous solution was tested. The experimental results showed that the contact angles of ionic liquid modified illite for unmodified illite, 75% CEC, 150% CEC, and 200% CEC were 0°, 53.5°, 62°, and 63.5°, respectively. The amount of modifier was in the range of 0–200% CEC. With the increase of the amount of modifier, the contact angle of modified illite gradually increased.

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Fig. 3.18 Unmodified illite, 50% CEC, 100% CEC, 200% CEC dosage of ionic liquid modified illite SEM

This was because the modified ionic liquid containing hydrophobic alkyl chains could increase the hydrophobicity of the illite surface and increase the contact angle of the illite surface (Fig. 3.19). (3) Zeta potential test of modified illite Figure 3.20 showed the zeta potential curve of original illite and ionic liquid modified illite. The surface of the original illite was negatively charged, which was related to the OH on the surface of the illite, which was also the reason for the low adsorption rate of CAP on the original illite. As the modified concentration increased, the surface charge of illite gradually changed from negative to positive. The order of the charge on the surface of the four kinds of ionic liquid modified illite and original illite was: 200% > 100% > 50% > original illite. IR spectrum analysis of modified illite In the study of the organic modification of illite, by comparing the changes of infrared absorption spectra (IR) of ionic liquid modified illite and natural illite, it was possible to understand the changes in the local microenvironment of the organic ions entering the illite layers, the interactions within or between molecules, and the configuration of molecular alkyl chains. Figure 3.21 showed the infrared absorption spectra of ionic liquid, natural illite, and ionic liquid modified illite.

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Fig. 3.19 Contact angle test of unmodified illite, 50% CEC, 100% CEC, 200% CEC dosage of ionic liquid modified illite Fig. 3.20 Zeta potential of illite samples before and after modification

The spectra were basically the same, indicating that the structure of illite had not changed after being modified by the ionic liquid. The absorption peak at 1055 cm−1 was the Si–O–R stretching vibration peak in the lattice, and the 460 cm−1 was the Si–O–Si and Si–O–Al bending vibration absorption peak. They were the characteristic absorption peaks of illite, and there was no obvious change before and after modification. New absorption peaks appeared in the modified illite at 2916 and 2852 cm−1 , and two sharp and strong absorption peaks were added, indicating that a certain amount

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified … Fig. 3.21 IR spectra of ionic liquid, unmodified illite, and ionic liquid modified illite with a dosage of 200% CEC

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of ionic liquid has entered the illite structure. It showed that the modified illite is successfully prepared. (5) Equilibrium adsorption of modified illite to CAP Experimental procedure: Prepared 10 mL of CAP solution with different concentrations of 0.5–5.0 mmol/L respectively. Added 0.5 g of illite, 50% CEC, 100% CEC, 200% CEC of ionic liquid modified illite. After vibrating and adsorbing for 24 h, performed centrifugal filtration at 5000 r/ min. Took the supernatant liquid and measure the absorbance of CAP at λ = 278 nm, and calculated the maximum adsorption capacity of CAP by ionic liquid modified illite with 0.5 g original illite, 50% CEC, 100% CEC, and 200% CEC. Repeated Experiment 2 times. Through the equilibrium adsorption of different concentrations of CAP, the maximum adsorption capacity of the ionic liquid modified illite and the original illite with the dosage of 50% CEC, 100% CEC, and 200% CEC for CAP was discussed. The experimental results showed that the unmodified illite had a weaker adsorption capacity for anionic antibiotics. The maximum adsorption capacity of CAP modified by 50%, 100%, and 200% ionic liquids was about 14 mmol/kg, 17 mmol/kg, and 25 mmol/kg, respectively (Fig. 3.22). Adsorption kinetics of CAP on modified illite Figure 3.23 showed the relationship between the adsorption capacity of illite on CAP and time. It could be seen from Fig. 3.23 that the adsorption rate of illite to CAP initially increased rapidly.

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Fig. 3.22 Adsorption equilibrium curve of 0.2 g illite, 50% CEC, 100% CEC, 200% CEC modified illite for CAP

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Fig. 3.23 Adsorption kinetic curve of CAP by 0.5 g 200% CEC modified illite

Within 30 min, the removal rate reached about 95%, after which it increased slowly and gradually approached equilibrium. Generally speaking, chemical adsorption and complexation reactions were relatively fast, while ion exchange and physical adsorption were relatively slow. The quasi-second-order kinetic model was fitted to the adsorption data of CAP in illite at different times. The linear model of the quasi-second-order kinetic equation was expressed by the formula:

3.2 Adsorption and Mechanism of CAP by Three Ionic Liquid Modified …

CAP/Ionic liquids/illite

Intensity (a.u)

Fig. 3.24 The XRD pattern of unmodified illite, 200% CEC dosage of ionic liquid modified illite, and 200% modified illite after adsorption of 5 mmol/LCAP

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illite

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t 1 1 = + t qt ks qe2 qe K 0 − Ct V qt = M In the formula, qt is the adsorption amount at time t, mmol/kg; ks is the quasisecond-order kinetic rate constant, mmol/(kg h); Ct is the concentration of CAP at time t, mmol/L. Using t as the abscissa and t/qt as the ordinate to draw Fig. 3.23b. 4° The results showed that the quasi-second-order kinetic model can fit the adsorption data well, with a correlation coefficient of 0.9994. (7) X-ray diffraction analysis (XRD) of modified illite The XRD pattern of ionic liquid modified illite was shown in Fig. 3.24. The XRD pattern showed that the phase diagrams of illite before and after modification were very similar, the peak positions and diffraction angles were basically the same, and no diffraction peaks of other impurities were found. The modified illite still retained the characteristics of the diffraction peaks of the original illite, indicating that the ionic liquid modification did not change the lattice structure of the original illite, that is, most of the ionic liquid molecules did not enter the internal crystal lattice of the illite but Coated on the surface of illite particles. The peak positions and diffraction angles of the phase diagram of the modified illite after adsorbing 5 mmol/LCAP were basically the same as those before the nonadsorption, indicating that the adsorption of CAP on the modified illite was surface adsorption.

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3.3 Summary of this chapter This chapter introduced the successful preparation of modified zeolite, montmorillonite, and illite using ionic liquid organic reagents, and characterized the materials through a series of characterization methods: XRD, SEM, contact angle test, and IR test, etc., to study the characterization results analysis. The adsorption effect of unmodified zeolite, montmorillonite, and illite on CAP was almost zero. The adsorption of CAP on the three organic modified clay minerals was mainly electrostatic, and the anionic CAP also had a certain effect on the distribution of the surface and between layers of the organic minerals. The difference in the specific surface area of different minerals led to the difference in the adsorption capacity and time of CAP on different minerals. The adsorption of CAP in zeolite only existed on the surface. The reason was that the size of the pores in the pore structure of the zeolite was much smaller than the size of the organic molecules themselves. CAP had interlayer adsorption in montmorillonite, and CAP could enter the interlayer to form monolayer adsorption. In addition, there may also have intermolecular hydrophobic interactions. This was because CAP adsorbed on minerals may affect the adsorption of itself and other organic pollutants as the organic matter of minerals. The following conclusions could be drawn from the experimental results: SEM characterized the successful preparation of ionic liquid modified zeolite, montmorillonite, and illite. The contact angle test characterized that the lipophilicity of the surface of zeolite, montmorillonite, and illite was increased through ionic liquid modification, which was conducive to the adsorption of organic antibiotics. The Zeta potential test characterized the transition process of the surface electrical properties of the three clay minerals from neutral and negative to positive. The adsorption experiment showed that the adsorption capacity of unmodified clay minerals to CAP was weak, and the adsorption performance of modified minerals with different modifier dosages to anionic CAP was greatly improved. The maximum adsorption capacity of CAP modified by ionic liquid modified zeolite, montmorillonite, and illite with a dosage of 200% CEC was about 25 mmol/ kg, 311 mmol/kg, and 25 mmol/kg, respectively. Among them, the adsorption effect of ionic liquid modified montmorillonite on CAP was significantly better than the other, which was consistent with the adsorption law of DS on montmorillonite modified by CTAB. This was because the adsorption of organically modified montmorillonite to CAP not only existed on the surface adsorption, but also existed in the interlayer adsorption, and the interlayer adsorption had a huge contribution, while the adsorption of CAP by the other two modified minerals was based on the surface adsorption. Mainly, the effect was equivalent.

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In addition, the adsorption kinetic models of the three modified clay minerals could be well fitted by the second-level kinetic model. XRD diffraction analysis characterized whether modifiers and adsorbents damaged the crystal structure of minerals before and after modification and adsorption, whether it belonged to surface modification or adsorption, or included interlayer modification or adsorption. The results showed that the adsorption behavior of pore structure zeolite (pore size smaller than the molecular size of ionic liquid and CAP) and non-expandable illite on ionic liquid and CAP were mainly surface adsorption. The adsorption behavior of ionic liquid and CAP by expansive montmorillonite with exchangeable cations included not only surface adsorption, but also interlayer adsorption. IR characterized the successful preparation of ionic liquid modified zeolite, montmorillonite, and illite. The characteristic functional groups of ionic liquid appeared on the surface of modified zeolite, montmorillonite, and illite.

References Bao Y, Zhou Q, Wan Y et al (2010) Adsorption and desorption of three tetracycline antibiotics on cinnamon soil. China Environ Sci 30(10):1383–1388 Bewick MWM (1979) The adsorption and release of tylosin by clay and soils. Plant Soil 51(3):363– 372 Essington ME, Lee J, Seo Y (2010) Adsorption of antibiotics by montmorillonite and kaolinite. Soil Sci Soc Am J 74(5):1577–1588 Figueroa RA, Leonard A, Mackay AA (2004) Modeling tetracycline antibiotic sorption to clays. Environ Sci Technol 38(2):476–483 Heilig S, Lee P, Breslow L (2002) Curtailing antibiotic use in agriculture: it is time for action: this use contributes to bacterial resistance in humans. West J Med 176(1):9 Hu DF, Shen JZ (2001) Analysis of residual fenicol antibiotics. Chinese J Veterinary Drug 35(5):55– 57 Lee J, Seo Y, Essington M (2010) Adsorption of antibiotics by montmorillonite and kaolinite. Soil Sci Soc Am J 74(5):1577–1588 Li XC, Kong YQ, Leng KL et al (2002) Analysis of determination methods of chloramphenicol residues in aquatic products. Marine Fisherries Res 23(4):76–81 Mellon MG, Benbrook C, Benbrook KL et al (2000) Hoggig it: estimates of antimicrobial abuse in livestock. UCS Publications, Cambridge, MA Mo X, Huang X, Wu X et al (2011) Adsorption equilibrium and kinetic characteristics of montmorillonite on quinolone antibiotics. J Hunan Univ: Nat Sci Ed 38(6):64–68 Robert K, David C, Holiand JE (1994) Gas chromatographic determination of chloramphenicol residues in shrimp: interlaboretory study. Jaoac Int 77(3):596–601 Sassman SA, Lee LS (2005) Sorption of three tetracyclines by several soils: assessing the role of pH and cation exchange. Environ Sci Technol 39(19):7452–7459 Ter Laak TL, Gebbink WA, Tolls J (2006) The effect of pH and ionic strength on the sorption of sulfachloropyridazine, tylosin, and oxytetracycline to soil. Environ Toxicol Chem 25(4):904– 911

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Tolls J (2001) Sorption of veterinary pharmaceuticals in soils: a review. Environ Sci Technol 35(17):3397–3406 Wu Q, Li Z, Hong H et al (2010) Adsorption and intercalation of ciprofloxacin on montmorillonite. Appl Clay Sci 50(2):204–211

Chapter 4

Molecular Dynamics Simulation of Adsorption of Anionic Antibiotics on Organic Modified Natural Clay Minerals

Abstract The adsorption behavior of personal care products on the surface/interface of clay minerals was investigated using molecular dynamics simulation. The adsorption processes of surfactant molecules cetyl trimethyl ammonium bromide and chlorinated 1-hexadecyl-3-methylimidazole on the surfaces of kaolinite, zeolite, and montmorillonite, and adsorption of personal care products DS and CAP on organically-modified clay minerals with different concentrations were respectively investigated. Keywords Molecular dynamics simulation · Organic modified clay minerals · DS · CAP

With the rapid development of material science and computer technology and the improvement of various calculation methods, molecular simulation technology based on computer hardware has developed into an effective tool for scientific innovation. In recent years, the adsorption of organic modified clay minerals on environmental pollutants has attracted the attention of many researchers in the field of science with its superior properties. Since the adsorption of clay minerals often occurs in their nanoscale space, it is difficult to characterize their microstructure and mechanism from an experimental point of view. Therefore, the method of computer simulation can be used as a tool to explore materials and microstructure and composition mechanism, which can play an important role in guiding experiments. Molecular dynamics simulation is the third scientific research method for human beings to understand the objective world (Zhu and He 2003), which can calculate the process and result of the change of objective things by reasonable molecular configuration and physical principles. We can also intuitively observe the changes of matter at the molecular level by molecular dynamics simulation. With the rapid development of computer software and hardware technology, computer simulation technology is also widely used in material structure and material science (Wen and Zhou 2002; Zeng et al. 1998; Faux 1998; Wen et al. 2003). Regarding the research on the preparation of organoclay minerals, scholars at home and abroad have developed many results. There are also many studies on the structure of organic modified clay © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 K. Sun, Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-981-99-6434-5_4

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minerals and the arrangement of organic surfactants on the surface and interlayer of clay minerals in molecular dynamics simulation. However, the mechanism of organic modified clay minerals and their adsorption of antibiotics is not very clear so far. With the wide application of clay minerals, the study of the microstructure and properties of the surface and interlayer of clay minerals from the molecular level has attracted more and more attention. In recent years, based on in-depth research on the structure of silicate minerals, some scientists have begun to expand and combine the original classical force field and its parameters, and explore a force field that is more suitable for clay and more in line with experimental results. Heinz et al. (2005) first improved the charge of atoms in silicate mineral systems and applied to a new force field suitable for pyrophyllitetype clay (such as montmorillonite, mica, etc.). They also used the newly modified force field to study the structural and kinetic properties of octadecyl ammonium modified montmorillonite, the results were in good agreement with the experimental data, which proved the applicability of the force field to layered silicate minerals.In addition, Professor Lu Xiancai of Nanjing University firstly used the CLAYFF force field to study the organic modification of montmorillonite (Zhou et al. 2010). Based on the molecular dynamics simulation of the Clayff-CVFF combined force field, they studied the monolayer, bilayer and transition structures of quaternary ammonium salts with three different alkyl chain lengths between montmorillonite layers, the co-intercalation of cetyltrimethylammonium and acetate ions was also investigated, the results were in good agreement with the experiments. These newly developed and modified force fields will provide a solution for the simulation of organic clay mineral composites. Wei et al. (2009) et al. also used molecular dynamics simulation methods to simulate the molecular environment and the arrangement of long alkyl chains in the interlayer domain of modified organic montmorillonite with long-chain cationic surfactants. The effects of modifier loading and interlayer water content on the arrangement and activity of the alkyl chain and the distribution of N and C atoms in surfactant ions were investigated. Organic clay usually uses organic ammonium cations to interact with the negatively charged clay surface through electrostatic interaction to make it organic and become hydrophobic, reduce the surface energy of the clay, enhance the interaction with organic molecules, and improve its performance. Zeng et al. had completed a series of studies on the structure and dynamics of organic clay, by using isothermalisobaric (NPT) simulations to study the basic spacing of organic clay and compare their results with experimental data, they found that their simulation results were very consistent with the experimental results. Gardebien et al. (2004) used molecular dynamics simulations to study the structure and energy of polymers (ε-caprolactone), where the PCL chain was confined between two kaolinite clay flakes modified with organic matter. The interaction of various components in organic clay was considered to be an important factor affecting the structure and properties of composites, therefore, this aspect was also a hot spot of research. Tanaka and Goettler (2002) studied the binding energy of each component in nylon 66 nanocomposites by using molecular dynamics and energy minimization simulation. The results showed that as the volume fraction of the surfactant increased, the binding energy of nylon 66

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and the montmorillonite flakes decreased, while the binding energy of nylon 66 and the surfactant increased. If there were polar functional groups on the organic ammonium chain, such as hydroxyl groups are present, their binding energy was greater. Titiloye and Skipper (2000) also used MD and MC methods to simulate the structure and dynamics of CH4 in the aqueous sodium bentonite system. The results showed that CH4 was encapsulated by 12–13 H2 O and forms coordination with the six-membered ring of siloxane on the surface of the clay mineral. The calculated diffusion coefficients were in good agreement with the experimental data. Organosilicate composite materials have attracted the attention of researchers in the fields of science and technology due to their excellent properties. However, it is difficult to accurately characterize its microstructure and formation mechanism only from experiments and existing test levels, and only the overall structure and macroscopic properties of the material can be obtained. Therefore, computer molecular dynamics simulation can play an important role in exploring the microstructure and composite mechanism of materials and guiding experiments. The main purpose of this study is to simulate the distribution and arrangement of different surfactants between zeolite, kaolinite and montmorillonite layers and surfaces by molecular dynamics simulation, Combined with the experimental data, the mechanism of the increase of the adsorption capacity of organic modified clay minerals on antibiotics was explained, which provided theoretical guidance and technical support for the preparation of organic modified clay minerals. Materials Studio is a software developed by Accelrys, an American company, for research in Materials science. Materials Studio molecular simulation software uses quantum mechanics, molecular mechanics, molecular dynamics, dissipative particle dynamics, Monte Carlo, mesoscopic dynamics, and other advanced algorithms and X-ray diffraction analysis, and other instrumental analysis methods. The application fields include surface chemistry, polymer materials, and soft materials, solid-state physics, chemical reaction, nanomaterials, crystals, and crystallization, etc. It can also support 32 with 64.bit Windows and Linux operating platforms. In this paper, a molecular dynamics simulation method was used to study the distribution and arrangement of different surfactants CTAB and 1-cetyl-3methylimidazole chloride in the layers and end surfaces of typical clay minerals by Materials Studio software. The adsorption of different antibiotics on the surface of typical organic clay minerals is simulated. Combined with the change of surface charge after organic modification and the previous experimental data, the mechanism of organic modification of different clay minerals and the adsorption of antibiotics were obtained by using the simulation calculation method, which provided theoretical guidance for the relevant experimental research and subsequent application.

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4.1 Modelling with the Materials Studio 4.1.1 Modeling Clay Mineral Structures (1) Modeling Structure of Kaolinite The structural model of kaolinite was established by using modules in Materials Studio 6.1. The simulated supercell consisted of 8 unit cells of 4 a × 2 b × 1 c, the space group was P1, and the horizontal size was 2.640 nm × 4.319 nm. The steps to build the model were as followed: 1) Inputted the spatial group and symmetric type of the kaolinite model. 2) Inputted the cell parameters of kaolinite and established the cell unit. 3) Added various atoms through the spatial coordinates of atoms and connected each bonding atom. 4) Established 4 a × 2 b × 1 c supercell on unit cell (Fig. 4.1). 5) Distributed the charges of kaolinite supercell, after that, the net charges of kaolinite supercell were—3. (2) 1) 2) 3)

Modeling Structure of Zeolite. Inputted the spatial group and symmetric type of the zeolite model. Inputted the cell parameters of zeolite and established the cell unit. Added various atoms through the spatial coordinates of atoms and connected each bonding atom. 4) Established 4 a × 2 b × 1 c supercell on unit cell (Fig. 4.2). 5) Distributed the charges of zeolite supercell, after that, the net charges of zeolite supercell were—4. (3) Modeling Structure of Montmorillonite. The structural model of montmorillonite was established by using modules in Materials Studio 6.1. The simulated supercell consisted of 8 unit cells of 4 a × 2 b × 1 Fig. 4.1 Initial model of kaolinite

4.1 Modelling with the Materials Studio

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Fig. 4.2 Initial model of zeolite

c, the space group was P1, and the horizontal size was 2.092 nm × 1.812 nm. The steps to build the model were as followed: 1) Inputted the spatial group and symmetric type of the montmorillonite model. 2) Inputted the cell parameters of montmorillonite and established the cell unit. 3) Added various atoms through the spatial coordinates of atoms and connected each bonding atom. 4) Established 4 a × 2 b × 1 c supercell on unit cell (Fig. 4.3). Fig. 4.3 Initial model of montmorillonite

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Fig. 4.4 Molecular model of surfactant

5) Distributed the charges of zeolite supercell, after that, the net charges of montmorillonite supercell were—4.

4.1.2 Modeling Structure of Surfactant The modules in Materials Studio, 6.1 software are used for structural modeling of organic surfactant molecules. Firstly, the molecular formula of the surfactant is understood, and each anion and cationic surfactant model is constructed according to the molecular formula (Fig. 4.4). First sketched each surfactant molecule. The molecular mechanics and molecular dynamics of the obtained molecules were optimized to obtain the structure with the smallest energy. Table 4.1 The chemical structure, abbreviation, and name of the modifiers used in this chapter.

4.1.3 Modeling Structure of Antibiotics To use the modules in the Materials Studio 6.1 software to model the structure of antibiotic organic molecules, firstly, the molecular formula of the antibiotics must be understood, and then, various cationic antibiotic models could be constructed according to the molecular formula (Fig. 4.5). First sketched each antibiotic molecule. The molecular mechanics and molecular dynamics of the obtained molecules were optimized to obtain the structure with the smallest energy. Table 4.2 The chemical structure, abbreviation, and name of the modifiers used in this chapter

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Fig. 4.5 Molecular model of antibiotics

4.2 Molecular Dynamics Simulation of Cationic Surfactants and Antibiotics Adsorbed on the Surface of Zeolite 4.2.1 Setting Molecular Force Field, Molecular Dynamics Module and Parameters Combined the model into a binary system with Materials Studio 6.1, namely a zeolite surface layer, a surfactant molecular layer and antibiotic molecules. Firstly, the binary system model should be combining optimized and energy minimized to obtain the equilibrium structure of the system, and then the molecular dynamics calculation was carried out at 298 K by NVT canonical ensemble on CLAYFF force field, with a step size of 1 fs, a simulation time of 1ns, and every 300 ps as a frame for sampling storage.

4.2.2 Outcomes and Discussions (1) Molecular dynamics simulation of the distribution of CTAB at different concentrations on zeolite surface and its adsorption of DS The morphology and configuration of different concentrations of organic cationic surfactant (CTAB) on the surface of zeolite were simulated, and the equilibrium configuration of the simulated system was intercepted for analysis. The simulation

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Fig. 4.6 Distribution of CTAB with different concentrations on the zeolite surface

results showed that the surface simulation of zeolite modified by different concentrations of organic cationic surfactants was significantly different. Figure 4.6a, b respectively show the arrangement of 100% CTAB and 200% CTAB on the surface of the zeolite. It can be seen from the figures that CTAB molecules with N groups in 100% CTAB modified zeolite tends to adsorb on the zeolite surface, which was due to the variable charges of zeolite. This system simulated the negative charges on the zeolite surface in an aqueous solution. CTAB molecules were adsorbed on the surface by electrostatic interaction, thereby neutralizing the negative charges on the surface of the zeolite (100% CTAB modified zeolite system is theoretically neutral). The modifier was added to 200% CEC, and the modifier molecules were adsorbed to the zeolite surface by the interaction between the long chains. At that time, some CTAB molecules with N groups deviated from the zeolite surface, and the outer layers of the system showed positive electricity. Molecular dynamics simulation of adsorption of DS about organically modified zeolite with different concentrations is shown in Fig. 4.7. The 100% CTAB modified zeolite system is theoretically electrically neutral, and there is no electrostatic interaction on the anionic antibiotic molecules, which resulted in a small adsorption capacity of the system. From Fig. 4.7a, it can be directly observed that the DS molecule is far away from the 100% CTAB modified zeolite system. The interaction between organic groups was the main reason for the adsorption effect of the system. The outer layer of the 200% CTAB modified zeolite system (Fig. 4.7b) was positive and had a strong electrostatic attraction to anionic DS molecules. From the figure, it can be observed that DS molecules are adsorbed to the surface of the system, further verifying that the 200% CTAB modified zeolite had a strong adsorption effect on anionic antibiotic molecules.

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Fig. 4.7 Distribution of DS adsorbed by CTAB modified zeolite with different concentrations

(2) Molecular dynamics simulation of the distribution and the adsorption of CAP of ionic liquids with different concentrations on the zeolite surface Simulated the morphologies and configurations with different concentrations of organic cationic surfactants (ionic liquids) on the zeolite surface and intercepted the equilibrium configuration in the simulated system for analysis. It was found that the surface simulation of modified zeolite with different concentrations of organic cationic surfactant had a significant difference. Figure 4.8a, b respectively show the arrangement of 100% ionic liquid and 200% ionic liquid on the surface of the zeolite. From the figure, it can be seen that the imidazole groups in the ionic liquid molecules in the 100% ionic liquid modified zeolite tend to be adsorbed on the surface of the zeolite, which was due to the variable charges of zeolite. This system simulated the negative charges on the zeolite surface in an aqueous solution. The molecules in the ionic liquid were adsorbed on the surface by electrostatic action, thereby neutralizing the negative charges on the surface of the zeolite (100% CTAB modified zeolite system is theoretically neutral). When the amount of modifier was added to 200% CEC, the modifier molecules were adsorbed to the surface of zeolite through the interaction between chains. At this time, the imidazole groups of some ionic liquid molecules deviate from the surface of zeolite, and the outer layer of the system showed positive electricity. Molecular dynamics simulation of adsorption of CAP about organically modified zeolite with different concentrations is shown in Fig. 4.9. The 100% ionic liquid modified zeolite system is theoretically electrically neutral, and there is no electrostatic effect on anionic antibiotic molecules, which resulted pin a small adsorption capacity of the system. From Fig. 4.9a, it can be directly observed that the CAP

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Fig. 4.8 Distribution of ionic liquids with different concentrations on the zeolite surface

molecule is far away from the 100% ionic liquid-modified zeolite system. The interaction between organic groups is the main reason for the adsorption effect of the system. The outer layer of the 200% ionic liquid-modified zeolite system (Fig. 4.7b) was positive and had a strong electrostatic attraction to anionic CAP molecules. From the figure, it can be observed that CAP molecules are adsorbed to the surface of the system, further verifying that the 200% ionic liquid modified zeolite had a strong adsorption effect on anionic antibiotic molecules. Fig. 4.9 Distribution of CAP adsorbed by ionic liquid modified zeolite with different concentrations

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4.3 Molecular Dynamics Simulation of the Adsorption of Cationic Surfactants and Antibiotics on the Surface of Kaolinite 4.3.1 Setting Molecular Force Field, Molecular Dynamics Module and Parameters Using Materials Studio 6.1 software, the model was combined into a binary system, namely a kaolinite surface lamellar, surfactant molecular layer, and antibiotic molecule. First, the established binary system model was combined with optimization and energy minimization to obtain the equilibrium structure of the system. Then, the NVT canonical ensemble was selected to conduct molecular dynamics calculation under the condition of 298 K. Cliff force field was adopted, the step length was 1 fs, the simulation time was 1 ns, and every 300 ps was used for sampling and preservation.

4.3.2 Outcomes and Discussions (1) Molecular dynamics simulation of the distribution of CTAB at different concentrations on kaolinite surface and its adsorption of DS Simulated the morphologies and configurations with different concentrations of organic cationic surfactants (CTAB) on the kaolinite surface and intercepted the equilibrium configuration in the simulated system for analysis. It was found that the surface simulation of modified kaolinite with different concentrations of organic cationic surfactant had a significant difference. Figure 4.10a, b show the arrangement of 100% CTAB and 200% CTAB on the surface of kaolinite. It can be seen from the figures that CTAB molecules with N groups in 100% CTAB modified kaolinite tend to adsorb on the kaolinite surface, which is due to the variable charges of kaolinite. This system simulated the negative charges on the kaolinite surface in an aqueous solution. CTAB molecules were adsorbed on the surface by electrostatic interaction, thereby neutralizing the negative charges on the surface of the kaolinite (100% CTAB modified kaolinite system is theoretically neutral). When the amount of modifier was added to 200% CEC, the modifier molecules were adsorbed to the surface of kaolinite through the interaction between chains. At this time, some groups with N in CTAB molecules deviate from the surface of kaolinite, and the outer layer of the system showed positive electricity. Molecular dynamics simulation of adsorption of DS about organically modified kaolinite with different concentrations is shown in Fig. 4.11. The 100% CTAB modified kaolinite system is theoretically electrically neutral, and there is no electrostatic interaction on the anionic antibiotic molecules, which resulted in a small adsorption capacity of the system. As can be directly observed from Fig. 4.11a, the

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Fig. 4.10 Distribution of CTAB with different concentrations on kaolinite surface

distance between the DS molecule and the 100%CTAB modified kaolinite system is relatively far. The interaction between organic groups is the main reason for the adsorption effect of the system. The outer layer of the 200% CTAB modified kaolinite system (Fig. 4.11b) was positive and had a strong electrostatic attraction to anionic DS molecules. From the figure, it can be observed that DS molecules are adsorbed to the surface of the system, further verifying that the 200% CTAB modified kaolinite had a strong adsorption effect on anionic antibiotic molecules. (2) Molecular dynamics simulation of the distribution and the adsorption of CAP of ionic liquids with different concentrations on kaolinite surface Simulated the morphologies and configurations of different concentrations of organic cationic surfactants (ionic liquids) on the kaolinite surface and intercepted the equilibrium configuration in the simulated system for analysis. It was found that the surface simulation of modified kaolinite with different concentrations of organic cationic surfactant had significant difference. Figure 4.12a, b respectively show the arrangement of 100% ionic liquid and 200% ionic liquid on the surface of kaolinite. From the figure, it can be seen that the imidazole groups in the ionic liquid molecules in the 100% ionic liquid modified kaolinite tend to be adsorbed on the surface of the kaolinite, which was due to the variable charges of kaolinite. This system simulated the negative charges on the kaolinite surface in an aqueous solution. The molecules in Fig. 4.11 Distribution of DS adsorbed by CTAB modified kaolinite with different concentrations

4.3 Molecular Dynamics Simulation of the Adsorption of Cationic …

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Fig. 4.12 Distribution of ionic liquids with different concentrations on kaolinite surface

the ionic liquid were adsorbed on the surface by electrostatic action, thereby neutralizing the negative charges on the surface of the kaolinite (100% CTAB modified kaolinite system is theoretically neutral). When the amount of modifier was added to 200% CEC, the modifier molecules were adsorbed to the surface of kaolinite through the interaction between chains. At this time, the imidazole groups of some ionic liquid molecules deviated from the surface of kaolinite, and the outer layer of the system showed positive electricity. Molecular dynamics simulation of adsorption of CAP about organically modified kaolinite with different concentrations is shown in Fig. 4.13. The 100% ionic liquid-modified kaolinite system is theoretically electrically neutral, and there is no electrostatic effect on anionic antibiotic molecules, which resulted in a small adsorption capacity of the system. From Fig. 4.13a, it can be intuitively observed that the distance between the CAP molecule and the 100% ionic liquid-modified kaolinite system is relatively far. The interaction between organic groups is the main reason for the adsorption effect of the system. The outer layer of the 200% ionic liquid-modified kaolinite system (Fig. 4.13b) was positive and had a strong electrostatic attraction to anionic CAP molecules. From the figure, it can be observed that CAP molecules are adsorbed to the surface of the system, further verifying that the 200% ionic liquid modified kaolinite had a strong adsorption effect on anionic antibiotic molecules. Fig. 4.13 Distribution of CAP adsorbed by ionic liquid modified kaolinite with different concentrations

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4.4 Molecular Dynamics Simulation of the Adsorption of Cationic Surfactants and Antibiotics on the Surface of Montmorillonite 4.4.1 Setting Molecular Force Field, Molecular Dynamics Module and Parameters Materials Studio 6.1 software was used to assemble the model into a binary system, namely a montmorillonite surface layer, surfactant molecular layer, and antibiotic molecular layer. First, the established binary system model was combined with optimization and energy minimization to obtain the equilibrium structure of the system. Then, the NVT canonical ensemble was selected to carry out molecular dynamics calculation under the condition of 298 K. Clayff force field was adopted, the step length was 1 fs, the simulation time was 1 ns, and every 300 ps was used as a frame for analysis and sampling preservation.

4.4.2 Outcomes and Discussions (1) Molecular dynamics simulation of the distribution of CTAB at different concentrations on montmorillonite surface and its adsorption of DS Simulated the morphologies and configurations with different concentrations of organic cationic surfactants (CTAB) on the montmorillonite surface and intercepted the equilibrium configuration in the simulated system for analysis. It was found that the surface simulation of modified montmorillonite with different concentrations of organic cationic surfactant had a significant difference. Figure 4.14a, b show the arrangement of 100% CTAB and 200% CTAB on the surface of montmorillonite. It can be seen from the figures that CTAB molecules with N groups in 100% CTAB modified montmorillonite tend to adsorb on the montmorillonite surface, which was due to the variable charges of montmorillonite. This system simulated the negative charges on the montmorillonite surface in an aqueous solution. CTAB molecules were adsorbed on the surface by electrostatic interaction, thereby neutralizing the negative charges on the surface of the montmorillonite (100% CTAB modified montmorillonite system is theoretically neutral). The modifier was added to 200% CEC, and the modifier molecules were adsorbed to the montmorillonite surface by the interaction between the long chains. At that time, some CTAB molecules with N groups deviated from the montmorillonite surface, and the outer layers of the system showed positive electricity. Molecular dynamics simulation of adsorption of DS about organically modified montmorillonite with different concentrations is shown in Fig. 4.15. The 100% CTAB modified montmorillonite system is theoretically electrically neutral, and there is no electrostatic interaction on the anionic antibiotic molecules, which resulted in a

4.4 Molecular Dynamics Simulation of the Adsorption of Cationic …

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Fig. 4.14 Distribution of CTAB with different concentrations on montmorillonite surface

small adsorption capacity of the system. From Fig. 4.15a, it can be directly observed that the DS molecule is far away from the 100% CTAB modified montmorillonite system. The interaction between organic groups was the main reason for the adsorption effect of the system. The outer layer of the 200% CTAB modified montmorillonite system (Fig. 4.15b) was positive and had a strong electrostatic attraction to anionic DS molecules. From the figure, it can be observed that DS molecules are adsorbed to the surface of the system, further verifying that the 200% CTAB modified montmorillonite had a strong adsorption effect on anionic antibiotic molecules. Fig. 4.15 Distribution of DS adsorbed by CTAB modified montmorillonite with different concentrations

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(2) Molecular dynamics simulation of the distribution and the adsorption of CAP of ionic liquids with different concentrations on montmorillonite surface Simulated the morphologies and configurations with different concentrations of organic cationic surfactants (ionic liquids) on the montmorillonite surface and intercepted the equilibrium configuration in the simulated system for analysis. It was found that the surface simulation of modified montmorillonite with different concentrations of organic cationic surfactant had a significant difference. Figure 4.16a, b show the arrangement of 100% ionic liquid and 200% ionic liquid on the surface of montmorillonite. From the figure, it can be seen that the imidazole groups in the ionic liquid molecules in the 100% ionic liquid modified montmorillonite tend to be adsorbed on the surface of the montmorillonite, which was due to the variable charges of montmorillonite. This system simulated the negative charges on the montmorillonite surface in an aqueous solution. The molecules in the ionic liquid were adsorbed on the surface by electrostatic action, thereby neutralizing the negative charges on the surface of the montmorillonite (100% CTAB modified montmorillonite system is theoretically neutral). Added the amount of modifier to 200% CEC, the modifier molecules were adsorbed to the surface of the montmorillonite through the interaction between the organic long chains. At that time, part of the imidazole groups of the molecules in the ionic liquid was away from the surface of the montmorillonite, and the outer layer of the system was positively charged. Molecular dynamics simulation of adsorption of CAP about organically modified montmorillonite with different concentrations is shown in Fig. 4.17. The 100% ionic liquid-modified montmorillonite system is theoretically electrically neutral, and there is no electrostatic effect on anionic antibiotic molecules, which resulted in a small adsorption capacity of the system. From Fig. 4.17a, it can be directly observed that the CAP molecule is far away from the 100% ionic liquid-modified montmorillonite Fig. 4.16 Distribution of ionic liquids with different concentrations on montmorillonite surface

4.5 Summary of This Chapter

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Fig. 4.17 Distribution of CAP adsorbed by ionic liquid modified montmorillonite with different concentrations

system. The interaction between organic groups is the main reason for the adsorption effect of the system. The outer layer of the 200% ionic liquid-modified montmorillonite system (Fig. 4.17b) was positive and had a strong electrostatic attraction to anionic CAP molecules. From the figure, it can be observed that CAP molecules are adsorbed to the surface of the system, further verifying that the 200% ionic liquid modified montmorillonite had a strong adsorption effect on anionic antibiotic molecules.

4.5 Summary of This Chapter In this chapter, molecular dynamics simulation was used to investigate the adsorption behavior of antibiotics at the surface/interface of clay minerals. The results are as follows: The adsorption processes of surfactant molecules hexadecyltrimethylammonium bromide and 1-hexadecyl-3-methylimidazole on kaolinite, zeolite, and montmorillonite were investigated by molecular dynamics simulation. The simulation results showed that surfactant molecules could spontaneously adsorb to the outer surface of clay minerals by electrostatic interaction. When the system was adsorbed on a monolayer, one end of the surfactant molecule with positive charge adsorb to the clay mineral surface, while the organic chain deviated from the mineral surface in reverse. The positive end of the partially modified molecules deviated from the surface of the clay minerals, and the outer system was positively electric. The molecular dynamics simulation method was used to study processes that the antibiotics DS and CAP were adsorbed by organic modified clay minerals with different concentrations. Simulation results showed that 200% CEC organic modified

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clay minerals exhibited strong adsorption capability to antibiotic molecules. The reason was that the positive charges of the outer layer of the system had a strong electrostatic effect on the anionic molecules at double-layer adsorption. Secondly, the volume and density of organic phase on clay mineral surface also enhanced the adsorption force of the system to some extent. The surface of the 200% CEC modified organoclay formed an organic phase with a larger volume and a denser structure, which can effectively fix organic pollutants through distribution, and exhibited a synergistic adsorption effect on the macroscopic level. The calculated results were consistent with the experimental data.

References Faux DA (1998) Molecular dynamics studies of sodium diffusion in hydrated Na-Zeolite-4A. J Phys Chem B 102:10658–10662 Gardebien F, Gaudel-siri A, Bredas JL, Lazzaroni R (2004) Molecular dynamics simulations of intercalated poly(epsilon-caprolactone)-montmorillonite clay nanocomposites. J Phys Chem B 108:10678–10686 Heinz H, Koerner H, Anderson KL (2005) Force field for micatype silicates and dynamics of octadecylammonium chains grafted to montmorillonite. Chem Mater 17(23):5658–5669 Tanaka G, Goettler LA (2002) Predicting the binding energy for nylon6, 6/clay nanocomposites by molecular modeling. Polymer 43:541–553 Titiloye J, Skipper N (2000) Computer simulation of the structure and dynamics of methane in hydrated Na-smectite clay. Chem Phys Lett 329(1):23–28 Wei JM, Yang HM, Zhu JX (2009) Molecular simulation of the interlayer microstructure of organic montmorillonite. Miner Rocks 29:33–37 Wen YH, Zhou FX (2002) Molecular dynamics simulation of unidirectional tensile deformation of nanocrystalline copper. J Mech 34(1):29–36 Wen Y, Zhu R, Zhou F (2003) Main techniques of molecular dynamics simulation. Adv Mech 33(1):65–71 Zeng P, Zajac S, Clapp PC (1998) Nanoparticle sintering simulations. Mater Sci Eng, A 252:301 Zhou Q, Lu X, Liu X (2010) Molecular dynamics simulation of influencing factors of methane hydrate stability in sodium montmorillonite interlayer domain Zhu J, He H (2003) Study on the spatial geometry of HDTMA+ pillared ions and the interlayer arrangement of pillared montmorillonite. Miner Rocks 23(4):1–4

Chapter 5

Dynamic Adsorption Experiment of Modified Zeolite and Montmorillonite

Abstract The experimental method of dynamic adsorption was applied to investigate the adsorption behavior of DS or CAP from CTAB, modified zeolite and doped with modified montmorillonite. The following conclusions were obtained: (1) Compared with the CTAB modified zeolite, the modified montmorillonite had a larger adsorption capacity and a longer adsorption time to reach saturation. (2) Compared with the ionic liquid modified zeolite, the modified montmorillonite had a larger adsorption capacity, which extended the time to reach adsorption saturation. Further verifying the modified montmorillonite had a strong adsorption capacity for anions in the water. Keywords Dynamic adsorption · CTAB · DS · CAP

Dynamic adsorption experiment (hereinafter referred to as dynamic experiment) is an experiment which will first reaction medium material (modified zeolite, montmorillonite) in a bulk density loading in 2 cm in diameter, high 10 cm plastic column, the column vertically, and then from the bottom of the cylinder by peristaltic pump fluid into the simulation pollution, make good contact with pollution liquid and reaction medium in the cylinder, reaction, And regularly take the liquid from the top of the cylinder to detect the concentration of pollutants in each component. By comparing the changes in the content of pollutants in the outflow liquid and through the liquid, the adsorption and removal effect of the cylinder on pollutants is investigated. Zeolite surface modification can adsorb anions directly, or by reducing oxygencontaining anions, allowing the conversion of ion exchange to the zeolite itself in drug combinations (Figueiredo and Quintelas 2014). Liu et al. (2004) studied the thermodynamic properties, regeneration performance and influencing factors of ammonia nitrogen adsorption by natural clinoptilolite through static test, dynamic test and regeneration test, The results show that the static saturated adsorption capacity of clinoptilolite for ammonia nitrogen is 20 times, 23 times and 27.5 times of that of powdered activated carbon, granular activated carbon and diatomite, respectively, and can be reused for three times. He et al. (2009) studied the dynamic fluoride removal performance of the modified zeolite prepared by the method of nitric acid © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 K. Sun, Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-981-99-6434-5_5

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activation and immersion of aluminum potassium sulfate, aluminum sulfate, and ferric chloride. The dynamic fluoride removal capacity of the modified zeolite was about 5 times that of the static fluoride removal capacity of the natural zeolite, and the fluoride removal capacity increased with the increase of fluoride content in the water sample. Jin et al. (2010) studied the dynamic adsorption of methylene blue by zeolite, and the study showed that the column size was 2.6 cm × 20 cm, the peristaltic pump speed was 7.0 mL/min, the zeolite dosage was 20 g, the packing height was 7 cm, and the mass concentration of methylene blue was 100 Under the experimental condition of mg/L, the dynamic adsorption effect of zeolite on methylene blue is the best, and the saturated adsorption capacity reaches 42.12 mg/g. Lu et al. (2014) conducted adsorption experiments on Cr (VI) with unmodified zeolite and Fe (II) modified zeolite (Fe EZ). The Fe (II) modified zeolite (Fe EZ) led to the increase of Cr (VI) adsorption, which was proportional to the ionic strength of the solution and had good mechanical stability with the increase of pH value of the solution. Chen and Wang (1996), obtained the modification method of natural montmorillonite clay and the method to improve the effectiveness of the adsorbent of montmorillonite clay on the treatment of printing and dyeing wastewater through experiments and elaborated the mechanism of the modification of montmorillonite clay and the adsorption of organic pollutants. The adsorption capacity of natural montmorillonite clay to organic pollutants has been greatly improved after the modification of natural montmorillonite by sodium and inorganic polymer. He et al. (2001) studied the adsorption capacity of montmorillonite, illite, and kaolinite for heavy metal ions such as Cu2+ , Pb2+ , Zn2+ , Cd2+ , Cr3+ by increasing the adsorption liquid volume and then increasing the content of heavy metal ions in the system, and found that the mineral adsorption capacity was closely related to its cation exchange capacity. Lu et al. (2011) studied the adsorption characteristics of natural clinoptilolite zeolite particles for ammonium ions, and the experimental results showed that these factors, such as zeolite particle size, bed height, flow rate, ammonia nitrogen concentration, and influent water quality, had obvious adsorption effects on the NH4+ of zeolite particles. Xu (2002) studied a new adsorbent, aluminum sand-loaded zeolite P 1 (Al SZP 1), and prepared an effective and inexpensive system for removing arsenic ions from water. Chen et al. (2012) studied the removal effect of hexadecyltrimethylammonium chloride (CTAC) modified activated carbon on pentavalent arsenic As (V) in water. In this study, Rapid small-scale column test (RSSCT) was used to investigate the adsorption capacity of CTAC modified activated carbon for arsenic, the factors affecting the adsorption capacity and the regeneration method of activated carbon. The modified performance of CTAC can effectively improve the adsorption capacity of activated carbon to As (V). The results of the column test on the effluent CTAC show that the combination of CTAC and activated carbon is very stable, and can effectively remove arsenic from the water. Li et al. (2015) modified zeolite with cetyltrimethylammonium bromide (CTAB) as adsorbent, The adsorption behavior of methyl orange (Mo) in an aqueous solution was studied. The dynamic adsorption experiments showed that the adsorption kinetics of Mo by CTAB modified zeolite could be described by a

5.2 Experimental Methods

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Fig. 5.1 Dynamic experimental reaction device

quasi second-order kinetic equation, which indicated that the adsorption mechanism of Mo was a physical and chemical adsorption process. Based on the results of static experiments, two minerals, organically modified zeolite, and montmorillonite, were selected in this chapter. Considering the good permeability of zeolite, the adsorption experiments of CTAB modified zeolite on DS solution and ionic liquid modified zeolite on CAP solution were carried out. In addition, considering that the adsorption capacity of organically modified montmorillonite is the largest, this chapter also carried out the adsorption experiments of the mixed reaction medium (modified zeolite and combination of montmorillonite) to Cap and DS solutions respectively.

5.1 Experimental Setup The reaction device for dynamic experiments is shown in Fig. 5.1. The peristaltic pump can control the liquid flow rate by adjusting its speed; DS solution and CAP solution were respectively contained in a 2 L glass beaker. The black line represents the plastic conduit that carries the liquid, and the arrows next to it indicate the direction in which the liquid is flowing. The plastic column was 2 cm in diameter and 10 cm in height, and the reaction medium was modified zeolite or montmorillonite.

5.2 Experimental Methods (1) Installation of cylinders

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First, one end of the cylinder is blocked with a rubber plug, and quartz sand between 0.5 and 1.0 mm in diameter is filled, and the height is controlled at about 2 cm. Then fill the cylinder with medium raw materials, every increase of 1 cm will light the cylinder 15–20 times to ensure that the medium in the cylinder is evenly distributed, tightly arranged. After loading to the specified height, add the quartz sand with a height of about 2 cm again, lightweight, and record the height of the cylinder and the quality of the medium raw material. (2) Determination of cylinder void volume After the installation of the cylinder is completed, the total mass of the cylinder is weighed with a balance, which is recorded as m1 . Then the column was placed vertically on the bracket, and then deionized water was slowly passed through the bottom of the column with a peristaltic pump to make the column filled with water. The weight of the column was weighed once every 5h. When the mass of the column stopped changing, it was indicated that the column had reached saturation, and the mass of the column at this time was recorded as m2 . The porosity (P) of the cylinder can be calculated by the following formula: p=

m2 − m1 × 100% pV

(5.15)

where, p is the porosity, m2 (g) is the mass of the cylinder after water saturation, m1 (g) is the mass of the cylinder when water saturation is not present, ρ is the density of deionized water (g/cm3 ), and V is the total volume of the cylinder charge (cm3 ). (3) Determination of permeability coefficient Permeability coefficient refers to the flow rate per unit cross-sectional area under a unit hydraulic gradient, which represents the degree of difficulty for fluid to pass through the pore skeleton. Its value is related to both the size of pore volume and the state of interconnection between pores and is an important groundwater parameter. The permeability coefficient of the material can be according to the determination of darcy’s law, the experimental method for installing a certain thickness (L) of dielectric materials in a glass column, the water saturation is bubbled into water material, from bottom to top and from top to bottom at a certain velocity (v) water, to water and water speed phase at the same time, the determination of the thickness of the pressure difference of H for L material, by the following formula to calculate the permeability coefficient k: v = k(

H ) L

(5.16)

where V represents the seepage flow rate (cm/h), H represents the water pressure difference (cm), and L represents the thickness of the medium (cm). (4) Determination of concentration of DS solution

5.2 Experimental Methods

109

The concentration of DS solution was determined by an ultraviolet spectrophotometer. The principle is that many substances have characteristic absorption peaks in the UV–visible region, so ultraviolet spectrophotometry can be used to determine these substances respectively (quantitative analysis and qualitative analysis). Ultraviolet spectrophotometry is based on the Lambert–Beer law. Lambert–Beer law is the basic law of light absorption, commonly known as the law of light absorption, is the basis and basis of quantitative analysis of spectrophotometry. When the wavelength of the incident light is fixed, the absorbance of solution A is a function of the concentration of the absorbent substance C and the thickness of the absorbent medium L (absorption path). The measurement steps were as follows: DS stock solution with a concentration of 5 mmol/L was prepared and diluted to different concentrations respectively. When the wavelength was 276 nm, the absorbance of the solution to be tested was measured with distilled water as the reference solution, and the working curve was drawn. The absorbance of the solution to be tested was measured with distilled water as the reference solution. When the absorbance value is converted into the concentration value, the standard DS curve can be drawn according to the good linear relationship between the concentration and the absorbance when the concentration of DS is between 0.01 and 0.20 mmol/L, and then the concentration value corresponding to the absorbance can be calculated. The standard curve was drawn by adding 0, 0.04, 0.06, 0.08, 0.10, 0.12, and 0.14 mL DS standard solutions (5 mmol/L) into 7.20 mL sample vials and diluting them to 10 mL, and measuring the absorbance. The corrected absorbance is obtained by deducting the blank value of the reagent (zero concentration) from the absorbance measured in the above series of standard solutions. Then, the calibration curve was plotted using the DS concentration as the abscissa and the correction absorbance as the ordinate. The DS working curve obtained in this experiment is shown in Fig. 5.2, with r2 = 0.9947. The relationship between DS concentration and absorbance is as follows: DS concentration = absorbance/10.624

0.8

Fig. 5.2 DS working curve

0.7 0.6

吸光度

0.5 0.4 0.3 0.2 0.1 0.0 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

双氯芬 酸钠溶液浓 度(mol/L)

110

5 Dynamic Adsorption Experiment of Modified Zeolite and Montmorillonite

(5) Determination of CAP concentration The concentration of CAP solution is determined by an ultraviolet spectrophotometer. The principle is that many substances have characteristic absorption peaks in the UV–visible region, so ultraviolet spectrophotometry can be used to determine these substances respectively (quantitative analysis and qualitative analysis). Ultraviolet spectrophotometry is based on the Lambert–Beer law. Lambert–Beer law is the basic law of light absorption, commonly known as the law of light absorption, is the basis and basis of quantitative analysis of spectrophotometry. When the wavelength of the incident light is fixed, the absorbance of solution A is a function of the concentration of the absorbent substance C and the thickness of the absorbent medium l (absorption path). The measurement steps are as follows: the concentration of 5 mmol/L Cap solution was prepared and diluted to different concentrations. When the wavelength was 278 nm, the absorbance of the solution to be tested was measured with distilled water as the reference solution, and the working curve was drawn. The absorbance of the solution to be tested was measured with distilled water as the reference solution. When the absorbance value is converted into the concentration value, the DS standard curve can be drawn according to the property that when the concentration of CAP is between 0.01 and 0.20 mmol/L, its concentration has a good linear relationship with the absorbance, and then the concentration value corresponding to the absorbance can be calculated. The standard curve is drawn by adding 0, 0.06, 0.08, 0.10, 0.12, 0.14, and 0.16 mL DS standard solutions (5 mmol/L) to 7.20 mL sample vials and diluting them to 10 mL, and measuring the absorbance. The corrected absorbance is obtained by deducting the blank value of the reagent (zero concentration) from the absorbance measured in the above series of standard solutions. Then, the calibration curve is plotted using the DS concentration as the abscissa and the correction absorbance as the ordinate. The DS working curve obtained in this experiment is shown in Fig. 5.3, with R2 = 0.998 5, and the relationship between DS concentration and absorbance is: DS concentration = −absorbance 0.008 5)/9.4086

5.3 Adsorption Experiments of CTAB Modified Zeolite and Montmorillonite on DS One column containing 9 g CTAB modified zeolite and one column containing 0.5 g montmorillonite and 8.5 g CTAB modified zeolite was installed. The column parameters are shown in Table 5.1. The DS solution with a concentration of 5 mmol/ L was added, and water samples were collected from the exits of the two columns at regular intervals for testing. The variation of DS concentration with running time was investigated.

5.3 Adsorption Experiments of CTAB Modified Zeolite …

111

Fig. 5.3 CAP working curve

Table 5.1 Parameter table of CTAB modified zeolite and montmorillonite column Column type

Stacking density (g/cm3 )

Void volume (cm3 )

Porosity (%)

Hydraulic retention time (h)

Modified zeolite (9.0 g)

1.4283

7.5190

37.59

10

Modified zeolite (8.5 g), montmorillonite (0.5 g)

1.3764

7.3224

36.61

10

As can be seen from Fig. 5.4, the dynamic adsorption of CTAB modified zeolite column on DS reached adsorption saturation at 6 h, while the dynamic adsorption of CTAB modified zeolite and montmorillonite column mixture on DS reached adsorption saturation at 16 h. The modified zeolite and montmorillonite were positively charged, while DS was negatively charged in water. The CEC of modified montmorillonite was 1200 mmol/kg, and that of modified zeolite was 100 mmol/kg. The adsorption capacity of the column was increased by adding modified montmorillonite, and the adsorption equilibrium time was delayed. The data show that the modified montmorillonite has a higher adsorption capacity than the CTAB modified zeolite.

5 Dynamic Adsorption Experiment of Modified Zeolite and Montmorillonite

Fig. 5.4 a Dynamic adsorption curve of DS on CTAB modified zeolite column; b dynamic adsorption curves of CTAB modified zeolite and montmorillonite DS mixture

5

a

4 c(mmol/L)

112

3 2 1 0

0

10

20 Time(h)

30

40

5 b

c(mmol/L)

4 3 2 1 0

0

10

20 30 Time(h)

40

5.4 Adsorption of CAP on Zeolite and Montmorillonite Modified by Ionic Liquid A zeolite column with 9 g ionic liquid modification and a zeolite column with 0.5 g montmorillonite and 8.5 g ionic liquid modification was installed. The column parameters are shown in Table 5.2. Cap solution with a concentration of 5 mmol/ L was added, and water samples were collected from the exits of the two columns at regular intervals for testing to investigate the variation of DS concentration with running time. Table 5.2 The column parameters of the ionic liquid modified zeolite, montmorillonite column Types

Bulk density (g/ cm3 )

Void volume (cm3 )

Porosity (%)

Hydraulic dwell time (min)

Modified zeolite (9.0 g)

1.4533

7.3203

36.60

10

Modified zeolite (8.5 g), montmorillonite (0.5 g)

1.4492

8.1695

40.84

10

5.5 Summary of This Chapter

5

a

4 c(mmol/L)

Fig. 5.5 a Dynamic adsorption curve of CAP on ionic liquid modified zeolite column; b Dynamic adsorption curve of the mixture of zeolite and montmorillonite column modified by ionic liquid for CAP

113

3 2 1 0

0

10

20 30 Time(h)

40

5

50

b

c(mmol/L)

4 3 2 1 0

0

10

20 30 Time(h)

40

50

As can be seen from Fig. 5.5, the dynamic adsorption of the ionic liquid modified zeolite column on CAP reached adsorption saturation at 2 h, while the dynamic adsorption of the mixture of ionic liquid modified zeolite and montmorillonite column on CAP reached adsorption saturation at 8 h. The modified zeolite and montmorillonite were positively charged, while DS was negatively charged in water. The CEC of modified montmorillonite is 1200 mmol/kg, and that of modified zeolite is 100 mmol/ kg. The addition of modified montmorillonite increases the adsorption capacity of the column and delays the adsorption equilibrium time. The desorption process of modified montmorillonite is slower than that of modified zeolite. It further explains its large adsorption capacity and strong adsorption effect on anions. The data show that the modified montmorillonite has a higher adsorption capacity than the ionic liquid-modified zeolite.

5.5 Summary of This Chapter The adsorption behavior of DS or CAP by CTAB, modified zeolite, and modified montmorillonite was investigated by a dynamic adsorption experiment. The conclusions were as follows:

114

5 Dynamic Adsorption Experiment of Modified Zeolite and Montmorillonite

(1) According to the dynamic adsorption data, compared with the CTAB modified zeolite, the modified montmorillonite has a larger adsorption capacity and a longer adsorption time to reach saturation. (2) According to the dynamic adsorption data, compared with the ionic liquid modified zeolite, the modified montmorillonite has a larger adsorption capacity, which extends the time to reach adsorption saturation, further verifying the modified montmorillonite has a strong adsorption capacity for anions in water.

References Chen T, Wang J (1996) Experimental study on treatment of printing and dyeing wastewater with montmorillonite clay modified adsorbent. China Environ Sci (1):60–63 Chen W, Cheng M, Zhang D (2012) Adsorption and regeneration of arsenic (V) in water by CTAC modified activated carbon in column experiment. J Environ Sci 32(1):150–156 Figueiredo H, Quintelas C (2014) Tailored zeolites for the removal of metal oxyanions: overcoming intrinsic limitations of zeolites. J Hazard Mater 274(12):287–299 He G, Lei L (2009) Experimental study on dynamic defluoridation of modified zeolite. China Sci Technol Inf (17):35–36 He H, Guo J, Zhu J et al (2001) Experimental study on the adsorption capacity of montmorillonite, kaolinite and illite to heavy metal ions. J Petrol Mineral 20(4):573–578 Jin X, Lu Z, Wang Q-p et al (2010) Dynamic experimental study on treatment of methylene blue by zeolite. Ind Saf Environ Prot 36(4):18–20 Li K, Yan Y, Pan Y et al (2015) Modified zeolite adsorbents for dye adsorption: mechanism and functional characterization. Ion Exch Adsorpt (5) Lu FH, Zhang XY, Wu ZC (2011) Study on ion-exchange characteristics in the dynamic adsorption process of NH4 + by natural granulated zeolite. Oalib J 795–800 Lu LF, Gao ML, Gu Z, Yang SF, Liu YN (2014) A comparative study and evaluation of sulfamethoxazole a dsorption onto organo-montmorillonites. J Environ Sci 26:2535–2545 Xu YH, Nakajima T, Ohki A (2002) Adsorption and removal of arsenic(V) from drinking water by aluminum-loaded Shirasu-zeolite. J Hazard Mater 92(3):275–287

Chapter 6

Conclusion

Abstract Two typical anionic PPCPs in the environment were taken as the research objects, and four conclusions, three research features and three future prospects were drawn in the book. The surface of natural clay minerals was generally negatively charged, and this structural feature determined that they had better adsorption effects on cationic PPCPs. While, their adsorption effects on anionic PPCPs were poorer, and they needed to be organically modified. Keywords Conclusions · Features · Prospects

Adsorption of antibiotics on clay minerals is one of the most important environmental behaviors of their migration and transformation in the environment. At the same time, the use of the clay mineral adsorption method is also an important method to control antibiotic pollution. The surface of natural clay minerals is generally negatively charged, which determines that they have a good adsorption effect on cationic antibiotics, but a poor adsorption effect on anionic antibiotics, so it is necessary to carry out the organic modification. This study focuses on the following: (1) The adsorption properties of diclofenac sodium (DS) by organically modified zeolite, kaolinite, montmorillonite, and illite with cationic surfactant cetyltrimethylammonium bromide (CTAB) were systematically studied; (2) The adsorption properties of organically modified zeolite, montmorillonite, and illite for chloramphenicol (CAP) with cationic surfactant 1-cetyl-3-methyl imidazole (ionic liquid) were systematically studied; (3) The molecular dynamics simulation of organic modification of typical clay minerals and their adsorption on antibiotics was carried out. The changes of surface charge and microstructure during the modification and adsorption of clay minerals were analyzed from the microscopic level; (4) The adsorption and removal effect of organic modified zeolite and montmorillonite mixed medium (layered accumulation and mixed accumulation) cylinder on DS and CAP was studied, and its potential application value was discussed. The following main conclusions were drawn: © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 K. Sun, Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-981-99-6434-5_6

115

116

6 Conclusion

The saturated adsorption capacity of the four kinds of natural clay minerals for the anionic anti-inflammatory drug DS is small, and the saturated adsorption capacity of montmorillonite is the largest, reaching 80 mmol/kg. The application of anionic antibiotics adsorbed by natural clay minerals is limited by the low saturated adsorption capacity. Therefore, organic modification of natural clay minerals must be carried out to regulate the surface charge. Organic modified zeolite, kaolinite, montmorillonite, and illite were successfully prepared by cationic surfactant CTAB. The materials were characterized by a series of characterization methods, and the characterization results were analyzed. The adsorption capacity of the four modified clay minerals for DS is followed by that of the montmorillonite > zeolite > illite > kaolinite, and the saturated adsorption capacity of the CTAB modified montmorillonite for DS is about 1000 mmol/ kg. This depends on the structural characteristics and adsorption mechanism of the mineral. The adsorption of DS on the four clay minerals is mainly electrostatic. The different specific surface area of zeolite and kaolinite leads to the difference in the adsorption effect of DS in the two minerals. The adsorption of DS on the interlayer of montmorillonite has an important influence on the final adsorption effect. The modified zeolite, montmorillonite, and illite were further prepared by using the environmentally friendly ionic liquid. The adsorption behavior of the modified zeolite, montmorillonite, and illite on the anionic antibiotic CAP was studied, and the materials were characterized by a series of characterization methods. The results show that the adsorption effect of unmodified zeolite, montmorillonite, and illite on CAP is almost 0. The adsorption capacity of ionic liquid-modified minerals is slightly lower than that of CTAB modified minerals, but the adsorption mechanism is similar. The difference of charge, specific surface area, and crystal structure on the surface of different modified minerals lead to the difference of adsorption capacity of CAP on different minerals. The adsorption of CAP in zeolite only exists on the surface, the reason is that the pore size in the pore structure of zeolite is much smaller than the size of the organic molecule itself. There is interlayer adsorption of CAP in montmorillonite, and CAP can enter interlayer to form monolayer adsorption. (3) The adsorption behavior of antibiotics on the surface/interface of clay minerals was investigated by molecular dynamics simulation. The adsorption process of surfactant molecule cetyltrimethylammonium bromide and chloride 1-hexadecyl-3-methylimidazole on kaolinite, zeolite, and montmorillonite was investigated by the molecular dynamics simulation method. The simulation results show that the surfactant molecules can spontaneously adsorb to the outer surface of clay minerals through electrostatic interaction. When the system is adsorbed in a monolayer, the positive side of the surfactant molecule is adsorbed to the surface of the clay mineral, while the organic chain is reversed away from the mineral surface. With the increase of modification concentration, the surfactant molecules get close to each other through interaction between chains until the system reaches adsorption equilibrium, that is, double-layer adsorption. The positive charge end of some modifier molecules deviates from the surface of clay minerals. At this time, the outer layer of the system shows a positive charge.

6 Conclusion

117

The molecular dynamics simulation method was used to investigate the adsorption process of antibiotic pollutants DS and CAP by organically modified clay minerals at different concentrations. The simulation results show that 200% CEC organically modified clay minerals exhibit strong adsorption capacity for antibiotic molecules, which is due to the positive electric properties of the outer layer of the system on the anionic molecules have a strong electrostatic effect. Secondly, the volume and compactness of the organic phase on the surface of clay minerals also enhanced the adsorption capacity of the system to a certain extent. The organic phase with a larger volume and more compact structure was formed on the surface of 200% CEC modified organic clay, which could effectively be fixed the organic pollutants through the distribution effect, and exhibited synergistic adsorption effect on the macro level. The calculated results are in good agreement with experimental data. (4) based on the above static adsorption tests, two modified minerals, zeolite (good permeability) and montmorillonite (high adsorption capacity), were optimized, and the two modified minerals were used in combination. The dynamic adsorption results show that with the increase of the content of modified montmorillonite in the system, the dynamic system has a larger adsorption capacity and a longer saturated adsorption time, but the increase of the content of montmorillonite will lead to the decrease of the permeability of the system, so the mixed structure of 0.5 g montmorillonite and 8.5 g zeolite is the optimal dynamic adsorption column structure.

Appendix

Name

Ken Sun

Nationality

China

Date of birth

May 1982

Gender

Male

Native place

Dengzhou, Henan Province

Main resume

Start and end date (fill in Study or work place from university)

Position and title

Degree awarded

1999.09–2003.06

North China University of Water Resources and Electric Power

Student

Bachelor

2003.07–2004.07

Huanghuai University

Teaching assistant

Bachelor

2004.09–2007.06

North China University of Water Resources and Electric Power

Student

Master

2007.07–Now

North China University of Water Resources and Electric Power

Lecturer

Master

2011.09–2016.07

China University of Geosciences (Beijing)

Student

Ph.D. candidate

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 K. Sun, Organic Modification of Natural Clay Minerals and Its Adsorption on Anionic PPCPs, SpringerBriefs in Environmental Science, https://doi.org/10.1007/978-981-99-6434-5

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