Controlled transformation of ZnO nanobelts into CoO/Co3O4 nanowires

Highly crystalline CoO and Co3O4 nanowires were prepared by vapor-phase conversion of ZnO nanobelts. The ZnO nanobelts were successfully transformed into highly crystalline CoO nanowires by thermal evaporation of CoCl2 at 700 degrees C in Ar, which were subsequently converted to Co3O4 nanowires by oxidative annealing at 600 degrees C. The reactions at 500 and 550 degrees C in 0.5% O-2 led to the formation of well-defined oxide p-n junction nanostructures such as Co3O4-decorated ZnO nanobelts and ZnO-ZnCo2O4 core-shell nanocables, respectively, as the reaction intermediates. The evolutions of phase and residual Zn component during the conversion were investigated in relation to the reaction temperature and oxygen partial pressure.