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 °C in Ar, which were subsequently converted to Co3O4 nanowires by oxidative annealing at 600 °C. The reactions at 500 and 550 °C in 0.5% O2 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.