壳聚糖-生物炭对典型抗生素在单一和复合溶液中的吸附行为与机理

Adsorption behavior and mechanism of typical antibiotics by chitosan and biochar in single and complex solutions

本研究选择壳聚糖作为改性剂对水稻秸秆生物炭进行改性,通过批量吸附试验探究了原始生物炭(BC)和壳聚糖-生物炭复合材料(CHBC)对溶液中单一或复合存在的典型抗生素四环素(TC)或磺胺甲噁唑(SMX)的吸附性能,并结合多种表征技术探究其对抗生素的吸附机理。结果表明:壳聚糖增加了生物炭表面氨基(-NH2)、羟基(-OH)和羧基(-COOH)等活性官能团,显著提升了生物炭对抗生素的吸附能力,其中CH_(1)BC(即壳聚糖与生物炭初始质量比为1∶1)展现出最佳的吸附性能,它对TC和SMX的最大吸附量较BC提升了2.63倍和3.74倍。随着溶液pH的增加,生物炭对抗生素的吸附量逐渐下降,这是由于随pH增加,生物炭和抗生素表面负电荷增多,使它们之间的静电排斥作用增大所导致的。此外,随着溶液温度的升高,生物炭对抗生素的吸附量也增加,热力学分析表明CH_(1)BC吸附抗生素的过程是自发吸热易发生的。生物炭对抗生素复合溶液的吸附试验结果表明,BC和CH_(1)BC对复合溶液中TC与SMX的吸附量较单一溶液中有所下降,其中,TC的吸附量下降较少,而SMX的吸附量下降尤为显著,说明TC与SMX在生物炭上的吸附存在竞争关系,且TC的吸附优先级更高,这主要是TC与SMX自身的分子结构、pKa和溶解性不同造成的。通过对吸附后的生物炭再次表征证明了氢键作用和π-π作用是壳聚糖生物炭吸附抗生素的主要机理。

In this study,chitosan was selected as a modifier to modify rice straw biochar,and the adsorption performance of pristine biochar(BC)and chitosan-biochar composites(CHBC)on typical antibiotics tetracycline(TC),or sulfamethoxazole(SMX)present singly or compositely in solution was investigated by batch adsorption tests,and the adsorption mechanisms of antibiotics was also explored by combining various characterization techniques.The results showed that chitosan increased the active functional such as amino(NH2),hydroxyl(−OH),and carboxyl(COOH)on the surface of the biochar,which significantly enhanced the adsorption capacity of the biochar for antibiotics,with CH_(1)BC(i.e.,the initial loading ratio of chitosan to biochar was 1∶1)showing the best adsorption performance,and its maximum adsorption of TC and SMX was enhanced by 2.63 times and 3.74 times compared with BC.The adsorption of antibiotics by biochar gradually decreased with the increase of solution pH,which was caused by the increase of negative charges on the surfaces of biochar and antibiotics with the increase of pH,which led to the increase of electrostatic repulsion between them.In addition,the adsorption of antibiotics by biochar increased with the increase of solution temperature,and thermodynamic analysis showed that the process of antibiotics adsorption by CH_(1)BC was prone to occur by spontaneous heat absorption.The results of the adsorption test of biochar on antibiotics composite solution showed that the adsorption of TC and SMX by BC and CH_(1)BC decreased compared with that in single solution,in which the adsorption of TC decreased less,while the adsorption of SMX decreased significantly,indicating that there is a competitive relationship between the adsorption of TC and SMX on the biochar,and that TC has a higher adsorption priority.This is mainly caused by the difference in molecular structure,pKa and solubility between TC and SMX itself.The present study clarified the adsorption differences and mechanisms of chitosan-biochar on typical antibiotics in single and binary pollution,which provided a theoretical reference for improving the removal efficiency of antibiotics in real wastewater.Hydrogen bonding andπ-πinteraction were proved to be the main mechanisms of antibiotic adsorption on chitosan biochar by re-characterizing the adsorbed biochar.