Investigation On The Regulation Of The Structure Of GO Laminar Channels And The Mechanism Of Confined Mass Transport

The graphene oxide(GO)stack structure has attracted extensive attention in many separation systems due to its precise separation and molecular sieve separation capabilities.However,there is still a lack of understanding of the mass transfer process in the confined channel at the micro level.The neglect of the interaction between GO and guest molecules may be the main reason for the slow progress of the study on the mechanism of mass transfer in the confined domain of GO Channels.Therefore,in this paper,we explore the the influence law confined by channel size and interaction object molecules(gas,water and ions)by experiment and the combination of molecular dynamics(MD)simulation method,from the size sieving and the interface potential synergies,in order to reveal the GO cascade channel confined and mass transfer mechanism of composite membrane preparation for high performance GO stack state provide theoretical guidance.In order to explore the confined transfer characteristics of GO stack structure to molecules,reduced graphene oxide(r GO)prepared by hydrothermal reduction method in this paper has a fold structure,and the higher the reduction degree,the larger the fold,the size of stacked interlayer channel also increases.The larger the interlayer channel size is,the higher the gas molecular permeability is,but the larger the channel size is,the lower the gas selectivity is.In addition,GO has a strong adsorption effect on carbon dioxide,and a sub-strong adsorption effect on nitrogen and methane,and the weakest adsorption effect on hydrogen.This adsorption inhibits mass transfer of carbon dioxide,nitrogen and methane in GO interlayer channels.MD simulation further found that this adsorption is an inherent property of graphene sheets,independent of functional groups,but the steric hindrance of functional groups can inhibit the adsorption to a certain extent.Therefore,the optimization of reduction degree is particularly important for the interaction between r GO and guest molecules.In view of this,this paper restores the temperature-regulated r GO fold structure to regulate its stack channel size.We found that 120 ℃ after processing of r GO nanoscale fold,with its diameter size close to the gas molecular dynamics,so show obvious hydrogen to carbon dioxide,nitrogen,methane permeability difference,selective hydrogen/carbon dioxide as high as 584,hydrogen/nitrogen selectivity is as high as 353,hydrogen/methane selectivity is as high as 672.In order to further explore the transfer characteristics of GO stack structure to molecules with hydration structure,the cross-linking method was used to control the layer spacing and inhibit its swelling.It was found that under the condition of the same layer spacing,the mass transfer rate of water molecules in GO cascade channel was lower than that of r GO,and much lower than that of graphene.This indicates that GO channel has an obstructing effect on the transfer of water molecules.Further analysis showed that this blocking effect was caused by a large number of oxygen-containing functional groups on the GO surface.Take cations as an example,they are not transferred in a complete hydration structure in the channel.As the polarity of oxygen-containing functional groups on the surface of GO has an attractive effect on cations,the hydration structure of ions can be destroyed.Therefore,the sieving effect of the confined channel cannot be judged by the diameter of hydration ions.It can be seen that the ionic transfer process of GO cascade channel is determined by the interaction of size screening and interface potential energy.It is found that sieving size determines whether guest molecules(gas,water,ions)can enter the channel,and interfacial interaction determines the mass transfer rate of guest molecules in the channel.Therefore,the synergistic control of size screening and interface interaction is expected to achieve high selective permeability of GO membrane.