Improving the desalination performance through conical nanochannels of multilayer oxidized graphene membranes by making a trade-off between the water permeability and salt rejection

Reverse osmosis (RO) desalination, renowned for its exceptional energy efficiency and superior purification efficacy, has emerged as a pivotal technology for mitigating freshwater deficits. Graphene-based membranes are recognized as prime candidates for RO desalination implementation due to its remarkable water permeability characteristics. Herein, we propose a conical nanochannel of multilayer oxidized graphene membranes to improve desalination performance by balancing water permeability and salt rejection. Molecular dynamics (MD) simulations were conducted to investigate the effects of nanochannel geometry and oxidation positions on water flux and water molecular transport. The results demonstrate that conical nanochannels exhibit lower energy barriers of approximately 3.2 kJ/mol for water molecule permeation compared to cylindrical nanochannels, with a maximum increase in water flux of approximately 80 %. Oxidized graphene not only attracts water molecules but also reduces the energy barriers for water entry/exit from the channels, while simultaneously exerting ion rejection effects. Specifically, the conical nanochannel with the last-layer oxidized graphene (CyC-LGO) maintains high water flux while improving ion rejection rates. These findings provide critical insights into regulating ion and water molecular transport, offering significant implications for improving the water permeability and salt rejection of reverse osmosis membranes.