High-Pressure Bulk Synthesis of Crystalline C₆N₉H₃·HCl:  A Novel C₃N₄ Graphitic Derivative

Abstract

A novel carbon nitride compound, structurally related to the proposed graphitic phase of C(3)N(4), has been synthesized in a bulk well-crystallized form. The new material, with stoichiometry C(6)N(9)H(4)Cl, was prepared through a solid-state reaction of 2,4,6-triamino-1,3,5-triazine with 2,4,6-trichloro-1,3,5-triazine at 1.0-1.5 GPa and 500-550 degrees C and also through a self-reaction of 2-amino-4,6-dichloro-1,3,5-triazine at similar conditions. X-ray and electron diffraction measurements on the yellowish compound indicate a hexagonal space group (P6(3)/m) with cell parameters of a = 8.4379(10) A and c = 6.4296(2) A. This new compound possesses a two-dimensional C(6)N(9)H(3) framework that is structurally related to the hypothetical P6m2 graphitic phase of C(3)N(4), but with an ordered arrangement of C(3)N(3) voids. The large voids in the graphene sheets are occupied by chloride ions with an equivalent number of nitrogen atoms on the framework protonated for charge balance. The composition of the sample was determined by bulk chemical analysis and confirmed by electron energy loss (EELS) spectroscopy. The chemical and structural model is consistent with bulk density measurements and with the infrared and (13)C NMR spectra. This work represents the first bulk synthesis of a well-characterized and highly crystalline material containing a continuous network of alternating carbon and nitrogen atoms.

Modulation of the crystallinity of hydrogenated nitrogen-rich graphitic carbon nitrides

“…The IR spectrum of rawsample ( Fig. 3a) is classical of that observed for graphitic carbon nitrides [15][16][17][20][21][22][27][28][30][31][32][33][34][35][36][37]. The absorptions between 1100 and 1700 cm -1 are typical for molecules that contain CN heterocycles (stretching vibrations of triazine ring).…”

“…The overstoichiometry in nitrogen can here be explained by the presence of C 3 N 3 voids accompagnied by a protonation of the bridging nitrogen atoms surrounding the void (hydrogen being here provided by the starting reagent) [16,19].…”

“…Although nitrogen deficiency is common in carbon nitrides because of the stability of the easily-formed N 2 molecules, it was evidenced that mild experimental conditions involved in processes such as solvothermal reactions or thermal decomposition are favorable to retain nitrogen in the material, leading then to nitrogen-rich materials [9,[15][16][17][18]. The presence of hydrogen in raw-sample is not surprising as it is usually evidenced in carbon nitrides [9,[15][16][19][20][21][22][23]. Finally, the presence of oxygen, although in low content, should be noticed as well as the absence of sulfur in raw-sample.…”

Tackling the stacking disorder of melon—structure elucidation in a semicrystalline material

“…18,41 For nearly all cases hydrogen contents well above 1.6 wt-% were observed, which indicates the presence of oligo-or polymeric melon-type materials rather than of binary carbon nitride. 4,29,30,35,[42][43][44] The acquisition of accurate data beyond stoichiometry and composition remains largely elusive due to an inherent poor crystallinity and a high degree of disorder. X-ray powder patterns usually indicate a pronounced stacking disorder of neighboring layers with an interlayer distance amounting to about 3.2 Å .…”

Reexamination of Solvothermal Synthesis of Layered Carbon Nitride

“…In the past few decades, g-C 3 N 4 attracted considerable attention in industrial applications such as photocatalyst (e.g., [4]), hydrogen storage (e.g., [5]), semiconductor (e.g., [6]), and a starting material for synthesizing potential superhard carbon nitride phases (e.g., [7]). A number of reports have been published for the synthesis of g-C 3 N 4 and even other graphitic forms with nonstoichiometric compositions on the basis of various techniques such as CVD [8][9][10], solid reaction [11][12][13][14][15][16][17], solvothermal method [18][19][20][21][22], and thermal decomposition of compounds [23][24][25][26]. Among these, one of the easiest and simplest ways to obtain a nanocrystalline powder of g-C 3 N 4 is the solvothermal method, in which the synthesis is achieved through the reaction of chemical sources in a solvent such as benzene and acetonitrile at high temperatures.…”