Graphitic carbon nitride (g-C3N4) is a family of compounds with a general formula near to C3N4 and structures based on heptazine units which, depending on reaction conditions, exhibit different degrees of condensation, properties and reactivities.
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Preparation
Graphitic carbon nitride can be made by polymerization of cyanamide, dicyandiamide or melamine. The firstly formed polymeric C3N4 structure, melon, with pendant amino groups, is a highly ordered polymer. Further reaction leads to more condensed and less defective C3N4 species, based on tri-s-triazine (C6N7) units as elementary building blocks.
Graphitic carbon nitride can also be prepared by electrodeposition on Si(100) substrate from a saturated acetone solution of cyanuric trichloride and melamine (ratio =1: 1.5) at room temperature.
Well-crystallized graphitic carbon nitride nanocrystallites also can be have prepared via benzene-thermal reaction between C3N3Cl3 and NaNH2 at 180–220 °C for 8–12 h.
Recently, a new method of syntheses of graphitic carbon nitrides by heating at 400-600 °C of a mixture of melamine and uric acid in the presence of alumina has been reported. Alumina favored the deposition of the graphitic carbon nitrides layers on the exposed surface. This method can be assimilated to an in situ chemical vapor deposition (CVD).
Characterisation
Characterisation of crystalline g-C3N4 can be carried out by identifying the triazine ring existing in the products by X-ray photoelectron spectroscopy (XPS) measurements, photoluminescence spectra and Fourier transform infrared spectroscopy (FTIR) spectrum (peaks at 800 cm−1, 1310 cm−1 and 1610 cm−1).
Properties
Due to the special semiconductor properties of carbon nitrides, they show unexpected catalytic activity for a variety of reactions, such as for the activation of benzene, trimerization reactions, and also the activation of carbon dioxide (artificial photosynthesis).
Uses
A commercial graphitic carbon nitride available under the brand name Nicanite® can, in its micron-sized graphitic form, be used for tribological coatings, biocompatible medical coatings, chemically inert coatings, insulators and for energy-storage solutions. Graphitc carbon nitride is reported as one of the best hydrogen storage material. In 2016, graphitic carbon nitride is being commercialised by Fairland Technology in the UK. www.fairlandtech.com
To date, the main applications are all research based, but include:
Photocatalytic splitting of water to produce hydrogen. Multiple locations are working on this, including KAUST in Saudi Arabia:
Use of the material's semiconducting properties to develop future replacements for silicon in electronics: