State of Art and recent trends in bulk carbon nitrides synthesis

Light element-based materials are of relevant interest because of their specific physico-chemical properties mainly dependent on the involved strong chemical bonds. Among them, diamond and c-BN are still today the most representative materials especially concerning super hardness property. Nevertheless, since the prediction by Liu and Cohen (on the basis of ab initio calculation) of theoretical materials with C3N4 composition exhibiting low compressibility, many efforts have been devoted to the synthesis of carbon nitrides. The first part of this review deals with the brief description of the different predicted C3N4 polymorphs exhibiting either a dense network or a graphitic one. In addition, predicted carbon nitrides with different stoichiometry are also described. The second part presents the analysis of the processing routes described in the literature for the synthesis of carbon nitrides as bulk materials. If many attempts have been devoted to high-pressure processes (direct synthesis, direct conversion from the graphitic form, flux-assisted conversion or solvothermal processes), some experiments performed in moderate experimental conditions have also been investigated and appear as really promising. A comparison with the different processes developed for diamond and c-BN is associated. As a conclusion, a discussion about the promising routes related to bulk carbon nitrides synthesis is given. (C) 2007 Elsevier B.V. All rights reserved.