Activate the filtration capability of 3.5 nm ultra-large pores and eliminate the requirement of pore homogeneity for carbon nanotube array membranes

Abstract

Vertical array carbon nanotube (VACNT) membrane is considered as one of the most promising materials for seawater desalination due to its excellent porosity, strong mechanical properties and atomic smoothness of the inner wall. However, in practical applications, the synthesis of highly oriented VACNT arrays with uniform pore sizes (< 1.1 nm) needs to be strictly controlled, and achieving high permeability-retention for large pores (> 1.1 nm) is a great challenge. Here, we use molecular dynamics simulations to introduce the oscillation paradigm into VACNT filtration membranes with a heterogeneous pore network with a wide pore size distribution (ranging from 1 nm to 3.5 nm). Notably, the oscillating heterogeneous VACNT membrane achieved ultra-high permeability of 1421.8 L/cm²/day/MPa (~5 times speed increase in comparison with homogeneous VACNT and ~ 2 times over state-of-the-art CNT membranes), while maintaining a selectivity of 97.5 %. This method activates the filtration capacity of 3.5 nm ultra-large pores, eliminating the requirement for pore homogeneity in VACNT, and achieves the effect of “killing two birds with one stone”. In addition, the filtration performance of specific heterogeneous VACNT membrane was successfully predicted by water permeability curve fitting, which provided valuable theoretical guidance for the design of high-performance VACNT reverse osmosis desalination system.