Orderly Stacked Multilayer Carbon Nitride Nanosheets as Membranes for Efficient Hydrogen Separation.

Two-dimensional polymeric carbon nitride (2D PCN) nanosheets with well-defined nanopores are promising for constructing high-performance gas separation membranes. Membranes originated from monolayer nanosheets often suffer from defect formation, low yield, and complex preparation procedures. Multilayer nanosheets offer an alternative to eliminate these defects and enable effective gas separation through intrinsic nanopores; however, disordered stacking during membrane assembly leads to nonselective nanochannels and accordingly reduces separation efficiency. Herein, inspired by the construction of irregular stone walls, we present a novel strategy in which a polymer (poly(vinyl alcohol), PVA) acts as the cement for regulating the ordered stacking of multilayer PCN nanosheets through hydrogen bonding. The resultant PVA/SPCN membrane exhibited an H2 permeability of ∼15,744 Barrer and exceptional selectivity, outperforming the previously reported defect-repaired PCN membrane constructed by monolayer nanosheets and most other 2D membranes. This study provides a scalable and simple approach for constructing 2D membranes via polymer-regulated ordered stacking of multilayer nanosheets.