Synthesis of self-supported ordered mesoporous cobalt and chromium nitrides

Herein, we demonstrate an ammonia nitridation approach to synthesize self-supported ordered mesoporous metal nitrides (CoN and CrN) from mesostructured metal oxide replicas (Co3O4 and Cr2O3), which were nanocastly prepared by using mesoporous silica SBA-15 as a hard template. Two synthetic routes are adopted. One route is the direct nitridation of mesoporous metal oxide nanowire replicas templated from SBA-15 to metal nitrides. By this method, highly ordered mesoporous cobalt nitrides (CON) can be obtained by the transformation of CO3O4 nanowire replica under ammonia atmosphere from 275 to 350 degrees C, without a distinct lose of the mesostructural regularity. Treating the samples above 375 degrees C leads to the formation of metallic cobalt and the collapse of the mesostructure due to large volume shrinkage. The other route is to transform mesostructured metal oxides/silica composites to nitrides/silica composites at 750-1000 degrees C under ammonia. Ordered mesoporous CrN nanowire arrays can be obtained after the silica template removal by NaOH erosion. A slowly temperature-program-decrease process can reduce the influence of silica nitridation and improve the purity of final CrN product. Small-angle XRD patterns and TEM images showed the 2-D ordered hexagonal structure of the obtained mesoporous CoN and CrN nanowires. Wide-angle XRD patterns, HRTEM images, and SAED patterns revealed the formation of crystallized metal nitrides. Nitrogen sorption analyses showed that the obtained materials possessed high surface areas (70-90 m(2) g(-1)) and large pore volumes (about 0.2 cm(3) g(-1)).