Effects of Co3O4 nanocatalyst morphology on CO oxidation: Synthesis process map and catalytic activity

This study focuses on drawing a hydrothermal synthesis process map for Co3O4 nanoparticles with various morphologies and investigating the effects of Co3O4 nanocatalyst morphology on CO oxidation. A series of cobalt-hydroxide-carbonate nanoparticles with various morphologies (i.e., nanorods, nanosheets, and nanocubes) were successfully synthesized, and Co3O4 nanoparticles were obtained by thermal decomposition of the cobalt-hydroxide-carbonate precursors. The results suggest that the cobalt source is a key factor for controlling the morphology of cobalt-hydroxide-carbonate at relatively low hydrothermal temperatures (≤ 140 °C). Nanorods can be synthesized in CoCl2 solution, while Co(NO3)2 solution promotes the formation of nanosheets. Further increasing the synthesis temperature (higher than 140 °C) results in the formation of nanocubes in either Co(NO3)2 or CoCl2 solution. The reaction time only affects the size of the obtained nanoparticles. The presence of CTAB could improve the uniformity and dispersion of particles. Co3O4 nanosheets showed much higher catalytic activity for CO oxidation than nanorods and nanocubes because it has more abundant Co3+ on the surface, much higher reducibility, and better oxygen desorption capacity.