C3N4 nanocrystals were synthesized by the reaction Of C3N3O3 with NaN3 in DMF through a constant-pressure solvothermal method, using mesoporous silica SBA-15 microparticles (SMP) as the promoter. The key steps in our approach are as follows: (1) by stirring at room temperature for 12 h, the starting materials are adsorbed on SMP, facilitating the reaction of the starting materials and (2) at higher temperature, the intermediates on SMP decompose to form the CNx nanocrystals with higher crystallinity. The crystallinity, morphology and composition of the samples were examined. Both the content Of beta-C3N4 and the crystallinity of the samples were improved in the presence of SMP. A preliminary model for the formation of CNx involving a six-member ring transition state on SMP is suggested. (c) 2007 Elsevier B.V. All rights reserved.