Water Permeation through Conical Nanopores: Complex Interplay between Surface Roughness and Chemistry

Abstract

Inspired by biological water channels (e.g., aquaporin with an hourglass shape), there is a growing interest in the use of conical nanopores for water purification; however, the surface roughness of conical nanopores has not been considered in the literature. In this work, a molecular dynamics simulation study is conducted to investigate water permeation through conical nanopores by considering both surface roughness and chemistry. In hydrophilic alumina nanopores, water permeability is found to increase with increasing surface roughness; however, a reverse trend is observed in hydrophobic carbon nanopores. Comprehensive microscopic analysis reveals that surface roughness in the carbon nanopores induces multiple high-energy barriers and frequent forming/breaking of hydrogen bonding network, which impedes water permeation. In the alumina nanopores, water becomes more bulk-like with increasing surface roughness, thus enhancing water permeation. The molecular insights from this simulation study provide quantitative understanding of water permeation in hydrophilic and hydrophobic conical nanopores and unravel the complex interplay between surface roughness and chemistry, facilitating the design of new materials for water purification.

Membrane Fouling: Microscopic Insights into the Effects of Surface Chemistry and Roughness

“…[ 27 ] Along the z ‐axis, the alumina surface consisted of two layers of aluminum (Al) and oxygen (O) atoms underneath hydrogen (H) atoms. [ 23,25 ]…”

“…For rough alumina and graphene surfaces, the roughness was introduced onto a flat surface by using a sinusoidal function [ 25 ] were A is the wave amplitude, x is the atomic position along the x ‐axis. For each type of surface, three different amplitudes ( A = 0, 3, and 5 Å represented by A0, A3, and A5, respectively) were examined.…”

“…demonstrated a membrane distillation process for water desalination through a graphene membrane, which showed antifouling capability superior to commercial distillation membranes against saline water containing oils and surfactants. [ 21 ] In general, the surface roughness of alumina and graphene membranes has been revealed to significantly affect water transport and separation performance; [ 22–25 ] however, the effect on fouling is less clear.…”

Molecular modeling of thin-film nanocomposite membranes for reverse osmosis water desalination

“…A significant effort has been devoted to understanding the mechanisms behind water transport through hourglassshaped pores in either tubular or nanosheet structures. [163][164][165][166][167][168][169][170][171][172][173][174] These studies have provided important insights into the structure, chemistry, material, and operational conditions required for fast water transport across membranes with hourglassshaped pores. However, to the best of our knowledge, there has been limited molecular modeling devoted to studying the ability of hourglass-shaped pores to reject salt ions.…”