Snail-shell-derived biochar for the adsorption of petroleum pollutants from wastewater: Perspective from computational studies

Para-chlorophenols (PCPs) are toxic and persistent, chlorinated aromatics that are prevalent in industrial and petroleum-contaminated wastewater, which has serious environmental and health impacts because of their bioaccumulative and recalcitrant properties. The study aims to design and test chemically activated snail shell biochars (SSB) as an effective PCP remedial material, combining the molecular understanding of the material with the predictions of adsorption efficacy. To study both electronic, structural, and dynamic interactions of PCP with a series of biochar analogs (KOH@SSB, H2SO4@SSB, AMS@SSB, Mg@SSB, Zn@SSB), both Density Functional Theory (DFT) calculations and Monte Carlo (MC) simulations were used. Findings indicate that chemisorptive behavior is observed on all biochar surfaces, with Mg@SSB and Zn@SSB having the highest adsorption (Eads = -1.96 and -1.17 eV, respectively). The adsorption is confirmed to be stabilized by highly polarized closed-shell interactions, which are mostly non-covalent, plus partial covalent character in systems with metals, but these are confirmed through non-covalent interaction and QTAIM analyses. Collectively, this study provides a mechanistic understanding of PCP adsorption at the molecular level and demonstrates that chemically and metal-activated snail shell biochars offer sustainable, high-affinity platforms for the removal of chlorophenols from contaminated aqueous environments, supporting circular economy principles and guiding experimental adsorbent design.