title: Insights into tetracycline adsorption onto kaolinite and montmorillonite: experiments and modeling.
abstract: Adsorption of tetracycline (TC) on kaolinite and montmorillonite was investigated using batch adsorption experiments with different pH, ionic strength, and surface coverage. As a result, pH and ionic strength-dependent adsorption of TC was observed for the two clay minerals. The adsorption of TC decreased with the increase of pH and ionic strength, and high initial TC concentration had high adsorption. In addition, a triple-layer model was used to predict the adsorption and surface speciation of TC on the two minerals. As a result, four complex species on kaolinite (≡X(-)∙H3TC(+), ≡X(-)∙H2TC(±), ≡SOH(0)∙H2TC(±), and ≡SOH(0)∙HTC(-)) and three species on montmorillonite (≡X(-)∙H3TC(+), ≡X(-)∙H2TC(±), and ≡SOH(0)∙HTC(-)) were structurally constrained by spectroscopy, and these species were also successfully fitted to the adsorption edges of TC. Three functional groups of TC were involved in these adsorption reactions, including the positively charged dimethylamino group, the C=O amide I group, and the C=O group at the C ring. Combining adsorption experiments and model in this study, the adsorption of TC on kaolinite and montmorillonite was mainly attributed to cation exchange on the surface sites (≡X(-)) compared to surface complexation on the edge sites (≡SOH) at natural soil pH condition. Moreover, the surface adsorption species, the corresponding adsorption modes, and the binding constants for the surface reactions were also estimated.
authors.affiliation: Jiangsu Key Laboratory of Environmental Change and Ecological Construction, Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, School of Geographical Science, Nanjing Normal University, 1, Wenyuan Road, Xianlin University District, Nanjing, 210023, China. yanping-zhao@163.com.
authors.forename: Yanping
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China. xueyuangu@126.com.
authors.forename: Xueyuan
authors.initials: X
authors.lastname: Gu
authors.affiliation: Jiangsu Key Laboratory of Environmental Change and Ecological Construction, Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, School of Geographical Science, Nanjing Normal University, 1, Wenyuan Road, Xianlin University District, Nanjing, 210023, China. Lishiyin88@126.com.
authors.forename: Shiyin
authors.initials: S
authors.lastname: Li
authors.affiliation: Jiangsu Key Laboratory of Environmental Change and Ecological Construction, Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, School of Geographical Science, Nanjing Normal University, 1, Wenyuan Road, Xianlin University District, Nanjing, 210023, China. hanruiming12@126.com.
authors.forename: Ruiming
authors.initials: R
authors.lastname: Han
authors.affiliation: Jiangsu Key Laboratory of Environmental Change and Ecological Construction, Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application, School of Geographical Science, Nanjing Normal University, 1, Wenyuan Road, Xianlin University District, Nanjing, 210023, China. wangguoxiang@njnu.edu.cn.
authors.forename: Guoxiang
authors.initials: G
authors.lastname: Wang
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D007616:Kaolin / Q000737:chemistry*; D008956:Models, Chemical; D013752:Tetracycline / Q000737:chemistry / Q000302:isolation & purification
chemical_list: D001546:Bentonite; D007616:Kaolin; D013752:Tetracycline
keywords: Adsorption; Kaolinite; Montmorillonite; Surface complexation model; Tetracycline