Adsorption selectivity of water-ethanol mixtures on organosilica surfaces: Role of hydrophilicity

<ns3:p>Background The competition between hydrophilic and hydrophobic interactions in water-ethanol mixtures gives rise to abnormal properties, such as the formation of an ethanol-rich surface layer at non-polar interfaces like graphite. This phenomenon, resulting from the balance between solid-liquid and liquid-liquid interactions, could benefit the development of microporous membranes for separating water-alcohol mixtures. Methods We used molecular dynamics simulations of water-ethanol mixtures near planar organosilica surfaces, focussing on the role of surface properties in interfacial ethanol enrichment. Surface hydrophobicity was controlled by adjusting the ratio of methyl to hydroxyl groups. We analyzed the impact of surface composition, roughness, and the spatial distribution of functional groups on ethanol adsorption. Results Our simulations reveal that ethanol preferentially adsorbs onto hydrophobic organosilica surfaces functionalized with methyl groups, similar to previous findings for graphite. Ethanol enrichment is strongly influenced by mixture composition and surface properties, including roughness and functional group distribution. Hydrophobic surfaces consistently exhibit enhanced ethanol affinity, whereas hydroxylated surfaces show weaker adsorption. Conclusions These findings demonstrate the ability of organosilica materials to preferentially adsorb ethanol over water. Overall, this work identifies a cost-effective alternative to carbon-based materials for the fabrication of filtration membranes.</ns3:p>