Influence of the oxidation rate on the dielectric properties of water confined in graphene bilayers

Abstract In recent years, numerous studies have focused on enhancing water permeability and ion retention by oxidizing pristine graphene membranes. Despite advanced modification and successful applications, the physical properties involved in the separation processes by graphene oxide nanochannels, such as the dielectric constant are not fully understood. A series of molecular dynamics simulations are carried out in this work to investigate the dielectric properties of aqueous solution in both pristine and oxidized bilayer graphene membranes. Results show that the dielectric constant decreases with the increase of the oxidation ratio as the oxidation ratio of the channel is less than 20%. However, the dielectric properties violate the previous trend as the oxidation rate continues to increase up to 40%. We show that the former is due to the formation of hydrogen bonds between water and graphene oxide substrate, leading to the decrease of water dipole fluctuation and the dielectric constant and the latter is caused by the formation of hydrogen bonds between adjacent OH groups on the graphene sheets at high oxidation rate, thus reducing the ability to attract water and formation of water-substrate hydrogen bonds.