Permselective H₂/CO₂ Separation and Desalination of Hybrid GO/rGO Membranes with Controlled Pre-cross-linking

Covalent bonding is widely adopted in graphene oxide (GO) membrane to improve structural integrity and restrict swelling, while it comes with a price of enlarged d-spacing and sacrifices membrane selectivity. This work offers a facile strategy to break the trade-off between membrane stability and selectivity. Specifically, graphene oxide (GO)/reduced graphene oxide (rGO) hybrid membranes were fabricated by a controlled pre-cross-linking method. With this method, restricted swelling by cross-linking and reduced d-spacing by GO reduction can be achieved simultaneously by controlling reaction time. Membranes were prepared on porous alumina support by vacuum filtration method. Two different d-spacing values (∼12.0 and ∼7.5 Å) were found in the hybrid membrane, representing the layer structures of expanded GO interspacing with inserted cross-linker and reduced layer spacing after GO reduction. The presence of such mixed layer structures enables restricted swelling, excellent mechanical strength, and unique separation property. The hybrid membrane shows excellent permselective H₂/CO₂ separation with a separation factor of 22.93 ± 1.57 and H₂ permeance of 2.46 ± 0.01× 10^-8 mol m^-2 s^-1 Pa^-1. In desalination test with 3.5 wt % sea salt solution, the hybrid membrane shows high ion (Na⁺, K⁺, Mg²⁺, Cl^-, and SO₄^2-) rejection rate of above 99%, as well as excellent durability.