Molecular simulations of the tunable pore structure models elucidate the adsorption of sulfamethoxazole on biochar.

Biochar is an environmentally friendly adsorption material that can effectively adsorb sulfamethoxazole (SMX) in water. However, the relationship between the pore structure characteristics of biochar and the SMX adsorption process remains unclear. In this study, molecular dynamics (MD) simulations combined with complementary experiments was employed to investigate SMX adsorption on four biochar models: isolated mesopores (BC1), micropores (BC2), hierarchical pores (BC3), and amorphous carbon (BC4). A remarkable concordance was observed between the MD simulations and experimental results. MD simulations revealed that porous structures facilitate SMX adsorption, leading to the fastest adsorption equilibrium rate for BC4. Additionally, a correlation between pore size and the SMX adsorption kinetics was observed. Within micropores, SMX achieves adsorption equilibrium at a slower rate, exhibiting a diffusion coefficient 62 % lower than that observed in mesopores. Noncovalent interaction (NCI) analysis and energy decomposition demonstrated that both π-π interactions and hydrogen bonds jointly stabilize SMX adsorption on biochar, with van der Waals interaction (contributing 59 %) playing a dominant role. Experimental results showed that the adsorption of SMX onto BBC-800 conformed to the Langmuir isotherm and pseudo-second-order kinetic model. Both simulations and experiments jointly elucidated the adsorption mechanism of SMX onto biochar, primarily involving pore filling, π-π stacking, and hydrogen bonding interactions. These findings provide atomic-scale insights for designing biochar with optimized pore structures for antibiotic removal.