Controlled transformation of ZnO nanobelts into CoO/Co ₃O ₄ nanowires

Highly crystalline CoO and Co ₃O ₄ 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 CoCl ₂ at 700 °C in Ar, which were subsequently converted to Co ₃O ₄ nanowires by oxidative annealing at 600 °C. The reactions at 500 and 550 °C in 0.5% O ₂ led to the formation of well-defined oxide p-n junction nanostructures such as Co ₃O ₄-decorated ZnO nanobelts and ZnO-ZnCo ₂O ₄ 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.