Large-scale synthesis of crystalline g-C ₃ N ₄ nanosheets and high-temperature H ₂ sieving from assembled films

Abstract

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.

Understanding spontaneous dissolution of crystalline layered carbon nitride for tuneable photoluminescent solutions and glasses

“…The presence of water in a solvent has been shown to prevent effective LiCl•PTI exfoliation in DMAc solutions previously. 12 To monitor the impact of water on solvated PTI, water was added to a pre-exfoliated LiBr•PTI DMSO solution to give a 75:25 DMSO/water mixture. The PL signature changed immediately and dramatically (Fig.…”

“…The synthetic mechanism is currently the subject of ongoing debate. 12 The resultant product consists of 1,3,5-triazine rings linked with NH bridges to give slightly buckled 2D sheets of intrinsic porosity with C 6 N 9 H 3 unit cells, termed polytriazine imide (PTI, Fig. 1).…”

“…28 Further, we have previously shown that spontaneous exfoliation and dissolution is possible without agitation for solid intercalated LiBr•PTI when exposed to polar, aprotic (i.e., without exchangeable H atoms) solvents such as dimethyl sulfoxide (DMSO), N,N-dimethyl formamide (DMF) Nmethyl-2-pyrrolidone 24 and N,N-dimethyl acetamide. 12 Solutions have been shown to be capable of exfoliation down to monolayer thicknesses in the solvated state, 12,24 and examination of the nanomaterials formed after evaporation of the solvent using high resolution transmission electron microscopy (HRTEM) and high-speed atomic force microscopy (HS-AFM) revealed hexagonal nanoparticles with the same (30 -165 nm) external dimensions and crystalline layered structure as the starting PTI phase, with 2 -25 layer thickness maximized at around 9 layers. 24 The steady-state photoluminescence (PL) spectra of DMF solutions of LiBr•PTI exhibited a peak near 380 nm with a width that broadened slightly towards the blue-green range with longer wavelength excitation.…”

Efficient Kr/Xe separation from triangular g-C3N4 nanopores, a simulation study

“…[20][21][22] Among them, g-C 3 N 4 is rapidly emerging for application in catalysis, 23,24 energy storage, 25 sensors, 26 and molecular separations. 27,28 The in-plane structure of g-C 3 N 4 hosts either a 1,3,5-triazine or a heptazine (1,3-,4,6,7,9,9bheptaazaphenalene) building unit. 29 In particular, poly(triazine imide) or PTI is quite attractive for gas separation because of its highly ordered nanoporous structure, composed of imide-bridged triazine units which form a triangular sub-nanometer-sized pore (Fig.…”

“…1). 27 A remarkable aspect of the mesh-like two-dimensional (2d) structure of PTI is its high pore density, 1.6 Â 10 14 pores per cm 2 , much larger than those typically realized in other 2d nanoporous membranes (such as nanoporous single-layer graphene), 30 making it promising for obtaining large permeances. The chemical and thermal robustness of PTI is also attractive for separation under harsh conditions.…”