Adsorption properties, kinetics & thermodynamics of tetracycline on carboxymethyl-chitosan reformed montmorillonite

This paper describes a modification method of Na-montmorillonite (Na-Mt) with carboxymethyl-chitosan (CMC). The as-prepared samples were analyzed by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analyzer and thermogravimetric analysis (TGA). Two common tetracycline antibiotics, tetracycline (TET) and chlortetracycline (CTC), were selected as the represented pollutants and adsorbed by CMC-Mt under different experimental conditions. The intercalation of CMC obviously amplified the basal spacing of the interlayers confirmed by XRD measurements and improved the adsorption capacities of montmorillonite to some degree. The results showed that the tetracycline antibiotic sorption onto CMC-Mt was mainly dependent on pH and was not affected by temperature. Besides, the removal of TET and CTC rapidly attained an equilibrium within 2 h of contact time. The kinetic data of adsorption was determined by first-order, second-order kinetics and intraparticle diffusion models. The kinetic study indicates that the TET and CTC adsorption processes obeyed the second-order kinetics. The Freundlich isotherm study was in agreement with the practical data, suggesting a heterogeneous sorption process. Furthermore, the thermodynamic studies revealed that the removal process was more spontaneous at a lower temperature, implying it an exothermic reaction. The synthesized adsorbent CMC-Mt can be widely used in the treatment of wastewater.