Thermodynamics of sorption of drugs on chitosan: low- and high-concentration analysis.

The presence of pharmaceuticals in effluents, which are wastewater discharges from various sources, has emerged as a significant environmental concern in recent years. Among the various methods available to address this challenge, adsorption stands out as one of the most effective, both technically and economically. In this study, we investigate the potential of cross-linked chitosan (C-CHIT) as an adsorbent for sodium cromoglicate (CG) and sodium diclofenac (DF). Both CG and DF were found to spontaneously adsorb onto C-CHIT, a sorbent with a positively charged surface when dispersed in water (as confirmed by zeta potential measurements). The adsorption of these anionic drugs resulted in a change in the polarity of the surface charge. Thermodynamic analysis was conducted using a standard approach, wherein parameters from Redlich–Peterson and Frumkin isotherms at the low-concentration limit were utilized to calculate the enthalpy and entropy of adsorption. This analysis suggested that CG was more effectively adsorbed onto C-CHIT. Additionally, a novel approach was proposed in this study for adsorption under surface saturation conditions, which deviate from ideal solution conditions. Interestingly, thermodynamic data indicated a reversal of behavior, with DF being more effectively adsorbed by C-CHIT. This finding was supported by geometric parameters calculated using MarvinSketch 23.12, along with a more repulsive Frumkin's lateral interaction parameter for CG. [ABSTRACT FROM AUTHOR]