Adsorption of methylene blue dye in the thiol-norbornene crosslinked polyvinyl alcohol hydrogel surface: a molecular dynamics study.

Methylene blue, a widely used dye in various industries, poses significant environmental and health risks when released into water bodies. The experimental methods, while effective for studying the adsorption of dye on a macroscopic level, lack the atomic-level insights necessary to fully understand the process which can be studied using molecular dynamics simulations. This study investigates the adsorption mechanism of methylene blue on thiol-norbornene crosslinked polyvinyl alcohol (PVA) hydrogel surfaces using MD simulations for the first time. This adsorption behavior is characterized by analyzing hydrogen bonding, radial distribution function (RDF), mean square displacements, and dye removal efficiency. The hydrogen bonding analysis shows consistent stability of the hydrogel network across different pH conditions. The RDF analysis indicates dissociation of the methylene blue molecule, with the cationic part adsorbing onto PVA's hydroxyl groups and the chloride ion exhibits preferential association with the ions in the pH medium. The mean square displacement result suggests a lower diffusion of methylene blue in pH 12.0 which can enhance the rate of adsorption. These findings provide crucial insights into the molecular-level interactions governing dye adsorption on crosslinked PVA hydrogels.