Investigations on adsorptive performance of pomegranate peel-derived biochar for the removal of sulfamethoxazole: A kinetics, isotherm, and thermodynamics study

Rapid industrialization and increasing use of pharmaceuticals have led to the growing problem of pharmaceutical contamination worldwide. Among these contaminants, antibiotics are of particular concern, as their un-prescribed use and overdosing can cause significant environmental and health impacts, including the rise of antimicrobial resistance. Sulfamethoxazole (SMX) is a widely used antibiotic for many bacterial infections in humans and animals. In the present work, a chemical-free biochar developed using pomegranate ( Punica granatum ) peel (PP) was used for the adsorption study of SMX. The PP biochar was prepared using a mechanical blending process followed by pyrolysis at 700°C. The prepared biochar has been studied to adsorb SMX under various adsorption parameters including solution pH, agitation time, adsorbent dose, initial concentration of adsorbate, and temperature. Batch adsorption studies suggested that adsorption of SMX follows the Langmuir and Freundlich models (with R 2 values of 0.995 and 0.972, respectively). The maximum adsorption capacity of SMX was evaluated as 4.85 mg/g using Langmuir isotherm. The kinetics study reveals that the adsorption followed the Pseudo-second order kinetics model with R 2 of 0.994 and the Elovich kinetic model with R 2 value of 0.932. The adsorption is also governed by the intra-particle diffusion model ( R 2 of 0.918), which dominates the porous structure of the biochar. The thermodynamic study indicates that the reaction is endothermic and proceeds spontaneously for the sorption of SMX over the temperature range of 25 to 45°C. The Gibbs free energy was shifted from 0.12 to -1.26 kJ/mol. This study shows the feasibility of utilizing waste biomass to mitigate emerging contaminants and provides insights towards achieving sustainable development goals and circular economy.