Adsorption behavior and mechanism of typical antibiotics by chitosan and biochar in single and complex solutions
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 CH1BC(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 CH1BC 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 CH1BC 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,p Ka 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 and π-π interaction were proved to be the main mechanisms of antibiotic adsorption on chitosan biochar by re-characterizing the adsorbed biochar.
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