Designed formation through a metal organic framework route of ZnO/ZnCoO hollow core-shell nanocages with enhanced gas sensing properties.

The rational design of nanoscale metal oxides with hollow structures and tunable porosity has stimulated tremendous attention due to their vital importance for practical applications. Here, we report the designed synthesis of ZnO/ZnCoO hollow core-shell nanocages (HCSNCs) through a metal-organic framework (MOF) route. The strategy includes the synthesis of a zeolite imidazolate framework-8 (ZIF-8)/Co-Zn hydroxide core-shell nanostructure precursor and subsequent transformation to ZnO/ZnCoO HCSNCs by thermal annealing of the as-prepared precursor in air. Various techniques were employed for characterization of the structure and morphology of the as-prepared ZnO/ZnCoO HCSNCs. When applied as a gas sensing material, the ZnO/ZnCoO HCSNCs show enhanced sensitivity to xylene when compared with ZnCoO shells as well as ZnO nanocages (NCs). In addition, excellent reversibility and superior selectivity of the sensor were observed. The remarkable enhancement in the gas-sensing properties of the ZnO/ZnCoO HCSNCs is attributed to their unique structure and a synergistic effect of ZnO and ZnCoO.