Enhancing adsorptive removal of diclofenac from aqueous solution: Evaluating organic and inorganic acid treatment of zeolite

Abstract

This study examined the adsorption capacity of natural zeolite (ZN) and zeolite treated with citric acid (ZCA) and nitric acid (ZNA) to evaluate their effectiveness in removing the pharmaceutical compound diclofenac (DCF) from water in batch experiments. Fourier Transform Infrared Spectroscopy (FTIR) and textural properties (BET) were used to investigate the changes in zeolite resulting from chemical modifications. The findings demonstrate a significant enhancement in surface area, pore volume, and the presence of acidic sites, resulting in an improved adsorption capacity for DCF. The observed increase in the Si/Al ratio following acid treatment suggests the de-alumination of the zeolite. Results have shown an increase in the percentage of DCF adsorbed to 76.8 % from 11.2 % using nitric acid-treated and untreated zeolites, respectively. In comparison, citric acid zeolite achieves 48.9 %. The adsorption kinetic was assessed using pseudo-first and pseudo-second-order models, and it was observed that the pseudo-second-order provided the best fit for all adsorbents. Furthermore, the BET model exhibited the best fit for the adsorption isotherm data. The maximum adsorption capacities were found to follow the order: ZNA (85.9 mg/g) > ZCA (33.6 mg/g) > ZN (14.4 mg/g). These results indicate that the acidic treatment enhances the adsorption capacity of the zeolite, and nitric acid treatment shows the most significant improvement.