Removal of polycyclic aromatic hydrocarbons from water by sugarcane bagasse: explanation of the possible adsorption mechanism by theoretical calculations

This study aimed to remove a mixture of the EPA’s 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) using sugarcane bagasse as an adsorbent. Initially, the bagasse fibers were characterized by scanning electron microscopy and energy-dispersive spectroscopy for elemental analysis, Fourier transform infrared spectroscopy, and Brunauer-Emmett-Teller (BET). The highest loading capacity was observed for PAHs with two to three aromatic rings. Meanwhile, the highest removal percentages occurred at the highest concentration level in a contact time of approximately 40 min. Adsorption equilibrium data fitted well to the Temkin and Elovich isotherm models, suggesting a multilayer chemical adsorption process. Additionally, Density Functional Theory (DFT) revealed that the primary adsorption mechanisms of PAHs onto bagasse were driven by van der Waals forces, π-π stacking, and hydrogen bond interactions, with lignin facilitating adsorption through its encapsulating behavior. This paper combined experimental and theoretical approaches to investigate the adsorption of PAHs onto sugarcane bagasse, with a novel focus on lignin-PAH interactions using DFT. The theoretical simulations revealed for the first time that lignin encapsulated PAHs, explaining the interactions and adsorption mechanism.