Synthesis, Structure and Electronic Properties of Graphitic Carbon Nitride Films

Dark-colored shiny flakes of graphitic carbon nitride materials produced by reacting dicyandiamide C2N4H4 in a KBr/LiBr molten salt medium were determined to have a C/N ratio near 1.2:1. The compounds also contained 2.3–2.5 wt % H incorporated within N–H species identified by Fourier transform infrared spectroscopy. One recent study revealed analogous results for thin films produced by an similar synthesis method, while a previous investigation instead reported formation of crystalline gC3N4 flakes with a triazine-based graphitic carbon nitride (TGCN) structure. The structures of the materials produced here were studied using a combination of high resolution transmission electron microscopy, X-ray diffraction, IR and Raman and X-ray photoelectron spectroscopy, along with series of density functional theory (DFT) calculations carried out for a range of model layered structures. The results indicate the graphitic layered gCxNy materials contain a mixture of sp2-hybridized C–N and C–C bonded structures, with TGCN to graphene-like domains existing within the layers. Paramagnetic centers localized on the C3N3 rings revealed by electron paramagnetic resonance spectroscopy correspond to potential defect structures within the graphitic layers predicted by DFT calculations. Our results combined with those of previous researchers indicate that a range of graphitic carbon nitride materials could exist with different C/N/H ratios leading to tunable electronic properties for catalysis, semiconducting, spintronics and energy applications, that could be targeted by controlling the synthesis and thin film deposition procedures.