The Effect of Surface Heterogeneities on Water Dynamics in Functionalized Carbon Nanopores

Transport properties of guest molecules within the nanoconfinement of the host are important for the tuning of nanoporous materials to various technological applications. In particular, the presence of water as an impurity can cause serious performance degradation of these materials. Hence, understanding water transport in nanoconfined space is important. Although it is well documented that water displays fast diffusion in pristine carbon pores, various trends in diffusivity as a function of loadings have been observed for different types of activated carbons, whose pore surfaces contain various functional groups. In this study, we performed molecular dynamics simulations to elucidate the role of functional groups, which act as surface heterogeneities, in the transport of water. We compared diffusivities of water in slit-shaped pores composed of homogeneous or functionalized layers at different pore sizes and loadings. It is found that the dynamics of water in functionalized carbon pores ranges from individual hopping of water molecules between neighboring localized clusters around the functional groups to a facilitated motion along the liquid bridges formed between neighboring clusters. There is a noted difference in the trends of diffusivities versus loadings for different pore sizes because of the presence of functional groups.