Mechanism of permeance enhancement in mixed-matrix reverse osmosis membranes incorporated with graphene and its oxides

Fabricating mixed-matrix reverse osmosis (RO) membranes via incorporating nanocomposites is a promising strategy to enhance permeance performance without sacrificing the ion rejection. To better design such mixedmatrix membranes (MMMs), the transport mechanism of water molecules through them is urgently desired. Compared to the stiff inorganic nanoparticles, the flexible graphene (Gr) and its oxides (GO) attract much attention due to their better compatibility with aromatic polyamide (PA) matrix. In this work, nonequilibrium molecular dynamics simulations of water passing through highly cross-linked PA membranes, Gr/PA and GO/PA MMMs are performed to reveal the transport mechanism. The simulation results show that the MMMs exhibit higher permeance compared to the pure PA membranes. After analyzing the transport details of water molecules, we discovered that the permeance enhancement for two types of MMMs result from distinct factors. While the Gr/PA MMMs have lower interior transport resistance because of the hydrophobic nature of Gr, the permeance enhancement of GO/PA MMMs should be attributed to the higher solubility of water molecules into MMMs. Therefore, a proper hydrophilicity of RO membrane, which has lower interior transport resistance while having higher solubility, is expected for the optimized performance.

Automated summary

Fabricating mixed-matrix reverse osmosis (RO) membranes by incorporating nanocomposites is a promising strategy to enhance permeance performance without sacrificing ion rejection. The study reveals that the permeance enhancement in mixed-matrix membranes results from distinct factors related to the characteristics of graphene and graphene oxides, providing insights into the transport mechanism of water molecules through the membranes.