Mixed-matrix membranes based on semi-oxidation MXene modified g-C3N4 nanosheet for enhanced CO2 separation

While mixed matrix membranes (MMMs) containing two-dimensional (2D) layered materials (such as, GO, g-C3N4 and MXene, etc.) have revealed potential application prospects for gas separation applications, it still faces a serious challenge to enhance the performance of CO2 separation. Owing to the structural defects of g-C3N4 nanosheets produced during the exfoliation process, which has greatly reduced the gas selectivity. Herein, we describe the construction of g-C3N4-MXene/Pebax MMM composed by MXene modified the structural defects in g-C3N4 nanosheets to surmount the low gas selectivity of g-C3N4 membrane. However, the stacking of nanosheets on each other hinder the gas transport channels. The TiO2 nanoparticles derived in-situ from MXene semi-oxidation can support an intermediate layer between g-C3N4 nanosheet and MXene nanosheet to expand the gas transport channels. Eventually, a novel g-C3N4-TiO2@MXene/Pebax MMM was obtained that exhibited maximum CO2 permeability of 1673.69 Barrer in separation of CO2/CH4, CO2/N2 selectivity of 45.13, and CO2/CH4 selectivity of 47.76, exceeding the bond 2008 limit on Robeson. What's more, the MMM within 100 h (1 bar and 298 K) are measured to have outstanding separation performance. Overall, this concept offers a novel strategy to enhance CO2 separation by MXene modified defects in g-C3N4 nanosheets.