Comparative adsorption of diclofenac sodium and losartan potassium in organophilic clay-packed fixed-bed: X-ray photoelectron spectroscopy characterization, experimental tests and theoretical study on DFT-based chemical descriptors

Abstract

Diclofenac sodium (DS) and losartan potassium (LP) are pharmaceuticals extensively used worldwide and contaminants of emerging concern. This work aims to examine the monocomponent continuous adsorption of DS and LP in fixed-beds packed with the organophilic clay, Spectrogel. The external surface of Spectrogel was studied by X-ray photoelectron spectroscopy (XPS) prior and post application as adsorbent. Continuous tests were conducted for the effects of flow rate (0.4–1.0 mL/min) and inlet concentration (0.05–0.15 mmol/L). Both DS- and LP-systems best operated at 0.4 mL/min and 0.15 mmol/L condition, which provided the highest breakthrough adsorption capacities (0.0047 mmol/g for DS and 0.0013 mmol/g for LP) and the lowest mass transfer zones (4.3 cm for DS and 4.4 cm for LP). Five different models were applied to describe the breakthrough curves and Dual site diffusion approach showed high suitability (R2 > 0.97). The DS adsorption performance by Spectrogel was contrasted with other materials. Density functional theory (DFT) computations were combined with experimental findings to clarify the particularities of DS and LP adsorption. Greater hydrophobicity, lower water solubility, reduced steric hindrance effects and greater chemical molecular reactivity were some of the factors attributed to the enhanced DS adsorption onto Spectrogel compared to LP.