Solvothermal synthesis of the graphitic form of C3N4 as macroscopic sample

The ab initio calculations of the stability of unknown materials present new developments in solid state chemistry and can improve the research of new superhard materials. The compound C3N4 is an interesting illustration of such a new route for predicting original materials. During approximately the past 10 years five different structures have been predicted: one is two-dimensional (the graphitic form of C3N4) and four are three-dimensional (alpha, beta, a zinc-blende-type with carbon vacancies, a cubic-type isostructural of the high-pressure variety of Zn2SiO4). Different routes have been investigated for preparing one of the previous C3N4 forms (involving PVD, chemical vapour deposition and high pressures processes). Unfortunately, due to the strong stability of the N-2 molecule, carbon nitrides - deficient in nitrogen - have been obtained in most of the cases. In several attempts, small microcrystallites attributed to a crystallized C3N4 form embedded in an amorphous phase have been isolated. Recently using a solvothermal process: the pyrolysis of melamine in presence of a nitriding solvent (NH,NH,) in high pressure conditions (P=3 GPa, 800 less than or equal to T less than or equal to 850 degrees C), the graphitic form of C3N4 has been prepared and characterized (X-ray diffraction, scanning electron microscopy, electron probe micro-analysis, ESCA, infrared spectroscopy). (C) 1999 Elsevier Science S.A. All rights reserved.