Adsorption of non-steroidal anti-inflammatory drug (NSAID) by agro-industrial by-product with chemical and thermal modification: Adsorption studies and mechanism

Abstract

Abstract Because Diclofenac potassium (DCF-p) is a drug that is easily accessible and widely consumed worldwide, it is often identified in water monitoring samples. Wastewater treatment has not been able to remove it completely, and for this reason traces reach the surface and groundwater, causing an impact on non-target organisms. In this sense, adsorption is highlighted as a simple and usually efficient process. Soybean hulls are residues generated in large quantities, often disposed of in landfills. For this reason, their use as adsorbent becomes interesting. However, no study to date has evaluated modifications of such residue in order to remove drugs from water. Thus, the objective of this study was to evaluate the adsorption capacity of the soybean hulls after chemical and thermal treatment in the removal of DCF-p. In the adsorption tests, it was found that the increase in pH from 5 to 9 caused a small reduction in the adsorption capacity, however the effect of the ionic strength showed that the dissolved salt ions acted as co-adsorbents, favoring adsorption. Kinetic data demonstrated rapid adsorption, with equilibrium at 180 min and adsorption capacity of 17.27 mg g−1. The experimental data adjusted to the pseudo-first-order model, and the intraparticle diffusion model suggested a multi-stage process. The adsorption isotherms were adjusted to the Sips model, revealing a maximum adsorption capacity of 96.88 mg g−1 at 308 K. The thermodynamic parameters indicated a spontaneous and favorable process for all temperatures studied, with an exothermic reaction controlled by physisorption. Lastly, it was found that the adsorption of DCF-p occurred by π-π interaction and hydrogen bonds.