In-Depth Study of Captopril Adsorption on a Biosourced Adsorbent: Statistical Physics Approach and Pore Characterization, with Modeling of Adsorption Isotherms, Energetic and Steric Analysis

Abstract

This current research implements statistical physics principles to microscopically elucidate and interpret the retention mechanism of Captopril onto the activated carbon derived from Butia catarinensis (ABc-600) for water decontamination. The empirical points were modeled exploiting four different statistical isotherm frameworks: the single-energy monolayer, dual-energy monolayer, trienergetic monolayer and dual-energy bilayer. Supported by an error quantification approach (R², Reduced Chi-Square, RSS and R_adj²) the single-energy monolayer was identified as the most rigorous scenario. Stereographic analysis revealed that the adsorption sites consistently capture a fraction of the adsorbed species with n < 1 across all tested temperatures indicating a multianchorage mechanism without aggregation. The decrease in the monolayer adsorbed amount with incrementing temperature highlights the endothermic nature of the Captopril/ABc-600 retention mechanism. Moreover, the energetic assessment corroborates the predominance of physisorption (<40 kJ/mol) indicating that van der Waals forces primarily govern the docking operation. PSD examination revealed a predominantly macroporous structure (0.7 μm) with a discernible shift toward smaller pore radii at elevated temperatures. The AED curves consistently displayed physisorption within the 22–29 kJ/mol energy range across all temperature conditions.