Molecular dynamics simulation of Sunset Yellow dye removal from water using hydrochar adsorbent.

Water pollution by synthetic dyes poses a serious environmental threat, necessitating effective and sustainable remediation technologies. This study explores the molecular mechanisms of Sunset Yellow (SSY) dye removal using hydrochar adsorbents via molecular dynamics simulations. Three hydrochar models were designed representing standard (with mixed functional groups), pure aromatic, and hydroxyl-enriched. All exhibited high SSY adsorption, with the standard model achieving adsorption capacities of 74-460 mg/g depending on SSY concentration, and 90% average efficiency. Adsorption increased with hydroxyl group density and decreased in their absence. Molecular analysis revealed that van der Waals interactions and π-π stacking are the dominant mechanisms, with van der Waals forces being the strongest and scaling linearly with concentration. Hydroxyl functionalization enhanced adsorption by 35% compared to non-functionalized surfaces, while mixed functional groups offered the best balance of capacity and efficiency. The results demonstrate that functional group engineering critically influences adsorption performance, offering quantitative design principles for optimized hydrochar materials. These findings provide molecular-level insights to guide the development of advanced, sustainable adsorbents for water treatment.