Effect of hydrophilicity on water transport through sub-nanometer pores

Abstract

Pore hydrophilicity is crucial parameter for water transport through nanopores. However, the effect of pore hydrophilicity on water permeance at the sub-nanometer scale remains unclear because it cannot be described by the conventional fluid mechanics. Herein, to determine the separate relationship between water permeance and pore hydrophilicity at the sub-nanometer scale, an equation derived from interfacial friction is obtained to exclude the effects of other variables. Using non-equilibrium molecular dynamics, we investigate water transport through a series of nanopores which is constructed from 12 types of functionalized covalent organic frameworks (COFs) with various degrees of hydrophilicity but similar skeletons and sub-nanometer pore sizes. The variable-excluded permeance has a linear relationship with contact angle. However, this linear relationship is not applicable to the hydrophobic and extremely hydrophilic nanopores under experimental pressure drops. For experimental predictions, the final relationship is corrected by considering the combined effect within all-range degrees of hydrophilicity. Therefore, a range of moderate pore hydrophilicity is suggested for the application of sub-nanometer pores in water transport. This study reveals the quantitative effect of pore hydrophilicity on water permeance at the sub-nanometer scale, which can be useful for the screening of nanomaterials for various applications.