Poly(triazine imide) with Intercalation of Lithium and Chloride Ions [(C₃N₃)₂(NH_xLi_1−x)₃⋅LiCl]: A Crystalline 2D Carbon Nitride Network

Abstract

Poly(triazine imide) with intercalation of lithium and chloride ions (PTI/Li(+)Cl(-)) was synthesized by temperature-induced condensation of dicyandiamide in a eutectic mixture of lithium chloride and potassium chloride as solvent. By using this ionothermal approach the well-known problem of insufficient crystallinity of carbon nitride (CN) condensation products could be overcome. The structural characterization of PTI/Li(+)Cl(-) resulted from a complementary approach using spectroscopic methods as well as different diffraction techniques. Due to the high crystallinity of PTI/Li(+)Cl(-) a structure solution from both powder X-ray and electron diffraction patterns using direct methods was possible; this yielded a triazine-based structure model, in contrast to the proposed fully condensed heptazine-based structure that has been reported recently. Further information from solid-state NMR and FTIR spectroscopy as well as high-resolution TEM investigations was used for Rietveld refinement with a goodness-of-fit (χ(2)) of 5.035 and wRp=0.05937. PTI/Li(+)Cl(-) (P6(3)cm (no. 185); a=846.82(10), c=675.02(9) pm) is a 2D network composed of essentially planar layers made up from imide-bridged triazine units. Voids in these layers are stacked upon each other forming channels running parallel to [001], filled with Li(+) and Cl(-) ions. The presence of salt ions in the nanocrystallites as well as the existence of sp(2)-hybridized carbon and nitrogen atoms typical of graphitic structures was confirmed by electron energy-loss spectroscopy (EELS) measurements. Solid-state NMR spectroscopy investigations using (15)N-labeled PTI/Li(+)Cl(-) proved the absence of heptazine building blocks and NH(2) groups and corroborated the highly condensed, triazine-based structure model.

Pharaoh's Serpents: New Insights into a Classic Carbon Nitride Material

“…These spectra more closely resemble the 15 N CP-MAS measured for the Pharaoh's serpent material than those of PTI·LiCl, [41] PTI·LiBr, [42] or PTI·HBr. [37] We note that Lotsch et al [11] prepared a 15 N-enriched sample of Liebig's melon that allowed them to observe of a small signal at approximately -225 ppm (δ =156 ppm relative to MeNO 2 ) that could be unambiguously assigned to the central N c atom of the heptazine structural unit.…”

Dendritic Tip-on Polytriazine-Based Carbon Nitride Photocatalyst with High Hydrogen Evolution Activity

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4 DFT calculations were used to describe the copolymerization effects on the structure and optical properties. The CN was modeled by the incompletely polymerized PTI-0 structure proposed by Lotsch and coworkers, 57 from which LiCl was removed, thus leading to the composition g-C 6 N 9 H 3 . Refining the P6 3 cm structure proposed in the literature yielded a local minimum with P6 3 /mcm symmetry.…”

Graphitic Carbon Nitride Materials for Energy Applications

“…Scanning electron microscopy (SEM) examination (Figure 2b) indicated that gCNM exhibits a latticework of interlocking planar microstructures with individual layer thicknesses on the order of 2-3 nm that give rise to porous aggregates with pore sizes on the order of a few nm. This material is not very highly condensed, and its structure could be close to that of Liebig's melon or melem that are built from "ribbons" of PH polymeric units (56,60,61), but with the possibility that PTI units may also be contained within the structure derived from the melamine precursor. The aggregates are fused together to give rise to much larger pores (1-2 µm) within the resulting solid.…”

“…The aggregates are fused together to give rise to much larger pores (1-2 µm) within the resulting solid. BET measurements revealed a surface area of 28 m ) was prepared using an ionothermal route (56,57). This method allowed us to obtain a highly crystalline carbon nitride using relatively mild conditions.…”