Clorazepate and Diclofenac adsorption mechanisms on Al-coated açaí biochar: Insights from statistical physics and DFT calculations

Pharmaceutical contamination in water underscores the need for efficient, sustainable agro-industrial waste-based adsorbents for wastewater treatment. This study investigated the adsorption mechanisms of the drugs clorazepate (CLZ) and diclofenac (DFC) on açaí biochar modified by aluminum (Al) deposition. The research combined adsorption experiments, physicochemical characterization, physical-statistical modeling, and Density Functional Theory (DFT) calculations to elucidate the mechanism. The biochar was obtained by conventional pyrolysis and modified by magnetron sputtering at powers of 100, 150, and 200 W for 15 min. The material treated at 200 W showed the best performance, with higher adsorption capacities (CLZ = 260.00 mg g −1 ; DFC = 277.00 mg g −1 ) while the unmodified biochar exhibited lower values ​​(CLZ = 84.0 mg g −1 ; DFC = 100.0 mg g −1 ). Physical-statistical modeling indicated that the process is predominantly physical, with adsorption energies between 1.51–8.22 kJ mol −1 (CLZ) and 14.87–23.76 kJ mol −1 (DFC). The increase in Al content promoted the formation of multilayers and greater surface heterogeneity, as well as changes in molecular geometry and the number of molecules adsorbed per active site. DFT calculations confirmed the experimental results: CLZ exhibited greater electronic reactivity (µ = –4.26 eV; ΔE = 4.87 eV), whereas DFC showed greater stability and electrophilicity ( ω = 26.3 eV; η = 3.93 eV), resulting in a higher adsorption capacity. The Fukui index shows that the heteroatoms N and Cl act as regioselective centers that interact with Al-coated biochars. Thus, Al modification enhanced the efficiency of the biochar and bolstered its potential, providing a basis for the development of advanced adsorbents for the removal of emerging pollutants from contaminated water.