Regulation of Water Molecule Filling in Carbon Nanochannels via Oxidation

Abstract

Carbon-based materials play a crucial role in water treatment, and their oxidation significantly enhances their potential applications. Understanding the behavior of water molecules in carbon materials with varying degrees of oxidation is crucial for optimizing their performance. Experimental studies have demonstrated that mixed functional groups form on the surface of graphene oxide, and the presence of these mixed groups limits the application performance of graphene oxide. Loading graphene with a single functional group can expand its application range. In this study, we investigate the water retention characteristics of carbon nanochannels under varying degrees of oxidation by using molecular dynamics simulations. We find that the degree of oxidation directly modulates the distribution of water molecules adjacent to the nanochannel walls. Specifically, as the number of single functional groups generated by surface oxidation increases, the number of water molecules near the surface initially decreases and then increases with a critical coverage rate of 40%. This behavior can be attributed to the increase in the coverage rates at higher degrees of oxidation. For the formation of pure hydroxyl functional groups on the surface, water molecules preferentially form hydrogen bonds with the oxygen atoms of the hydroxyl groups at low coverage. However, once the coverage exceeds the critical threshold, water molecules interact primarily with the hydrogen atoms of the hydroxyl groups, leading to a transition in the local distribution of water molecules. The single functional groups on the surface of graphene exhibit distinct properties compared with mixed functional groups, which will expand the application of graphene and promote the development of single-oxidation technology.