Tuning the C/N Ratio of C-Rich Graphitic Carbon Nitride (g-C 3 N 4 ) Materials by the Melamine/Carboxylic Acid Adduct Route.

C-rich graphitic carbonitride materials (CN _x ) with a large range of compositions have been prepared thanks to the self-assembly, in different ratios, of melamine (M) and a panel of polycarboxylic acids (A) such as oxalic, tartaric and citric acid. The thermal conversion of the formed adducts (MA _y ), led to CN _x phases, with x ranging from 0.66 to 1.4 (x=1.33 for g-C ₃ N ₄ for comparison). The properties of these materials were examined by different techniques (XRD, Raman spectroscopy, TEM, TGA, XPS and DRIFT). It appears that the increase in the C content is associated with the disappearance of the long-range order of heptazine units and an increase in the sub-nanometer carbon-rich cluster size within the graphitic g-C ₃ N ₄ structure. This trend is followed by a significant increase in the interlayer spacing and a lower proportion of N=C-N bonds compared to C=C bonds. The thermal stability under an inert atmosphere of these phases and their UV-Visible absorbance properties were also investigated.
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