Adsorption of nimesulide and paracetamol on aluminum-coated biochar: insights from statistical physics modeling

Abstract

Pharmaceutical contaminants in water bodies pose significant environmental and health risks, necessitating efficient removal technologies. This study investigated the adsorption of two widely used pharmaceuticals, nimesulide (NMS) and paracetamol (PCM), onto aluminum-coated biochar. Equilibrium adsorption isotherms were obtained at different temperatures (298–328 K) and analyzed using advanced statistical physics models, particularly a double-layer model, to elucidate the underlying adsorption mechanisms. The highest adsorption capacities were 113.48 mg/g for NMS and 76.40 mg/g for PCM at 298 K under the optimized adsorption conditions (pH 5, adsorbent dosage of 0.50 g/L, and contact time of 8 h). These results indicated that the biochar exhibited higher adsorption capacity for NMS than for PCM, mainly due to stronger intermolecular interactions. Adsorption occurred predominantly via physisorption mechanisms involving hydrogen bonding, hydrophobic interactions, and van der Waals forces. Steric analysis showed temperature-dependent adsorption configurations, especially for PCM, which transitioned from non-parallel to parallel orientation as the temperature increased. Thermodynamic parameters indicated that the adsorption processes were spontaneous and favored at lower temperatures. Overall, this work provides valuable insights into the molecular-level behavior of pharmaceutical adsorption on metal-modified biochar, supporting its potential application in water treatment. Classical Langmuir and Freundlich isotherm models were also applied and compared with the double-layer model to provide complementary insights into the adsorption behavior.