Large-scale synthesis of crystalline g-C₃N₄ nanosheets and high-temperature H₂ sieving from assembled films

Poly(triazine imide) (PTI), a crystalline g-C₃N₄, hosting two-dimensional nanoporous structure with an electron density gap of 0.34 nm, is highly promising for high-temperature hydrogen sieving because of its high chemical and thermal robustness. Currently, layered PTI is synthesized in potentially unsafe vacuum ampules in milligram quantities. Here, we demonstrate a scalable and safe ambient pressure synthesis route leading to several grams of layered PTI platelets in a single batch with 70% yield with respect to the precursor. Solvent exfoliation under anhydrous conditions led to single-layer PTI nanosheets evidenced by the observation of triangular g-C₃N₄ nanopores. Gas permeation studies confirm that PTI nanopores can sieve He and H₂ from larger molecules. Last, high-temperature H₂ sieving from PTI nanosheet-based membranes, prepared by the scalable filter coating technique, is demonstrated with H₂ permeance reaching 1500 gas permeation units, with H₂/CO₂, H₂/N₂, and H₂/CH₄ selectivities reaching 10, 50, and 60, respectively, at 250°C.