Diclofenac Removal by Alkylammonium Clay Minerals Prepared over Microwave Heating

Diclofenac is an emerging contaminant widely detected in water and has had adverse effects on the biota. In this study, the adsorbents were prepared by reacting tetradecyl-(C₁₄), hexadecyl-(C₁₆), and octadecyltrimethylammonium (C₁₈) bromides with sodium vermiculite (Na-Ver) and used for the removal of the first time for diclofenac sodium from aqueous solution. Synthesis was carried out in a microwave-assisted reactor operating at 50 °C for 5 min, using proportions of organic salts in 100 and 200% of the phyllosilicate cation exchange capacity. The stability of loaded alkylammonium solids was evaluated under drug adsorption conditions. Adsorption was mainly influenced by the amount of surfactant incorporated into the clay mineral according to the thermogravimetric and CHN elemental analysis data. Samples prepared with 200% CEC presented lower stability at pH 6.0 and 8.0. Drug adsorption was more effective for C₁₄-Ver-200%, C₁₆-Ver-200%, and C₁₈-Ver-200% samples, with a maximum retention of 97.8, 110.1, and 108.0 mg g^-1, respectively. The adsorptive capacities of C₁₄-Ver-200%, C₁₆-Ver-200%, C₁₈-Ver-200%, C₁₄-Ver-100%, C₁₆-Ver-100%, and C₁₈-Ver-100% were reduced to 29.0, 36.8, 41.0, 61.0, 50.4, and 58.0%, respectively, compared with their initial value after three adsorption cycles. X-ray diffraction (XRD) patterns revealed that diclofenac was adsorbed into the interlayer region of organovermiculites. Fourier transform infrared spectroscopy (FTIR), Zeta potential results, and the pH study of adsorption indicated that van der Waals interactions are dominant in the adsorption mechanism.