Porous ZnO/ZnCo ₂ O ₄ hollow spheres: synthesis, characterization, and applications in gas sensing

Dispersed porous ZnO/ZnCo2O4 hollow spheres were successfully prepared by annealing the precursor, which was obtained via a facile one-step solvothermal method without any templates or surfactants. The X-ray powder diffraction (XRD) measurement showed that the crystal phase of the sample was a mixture of ZnO and ZnCo2O4. The field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images revealed that the as-synthesized porous ZnO/ZnCo2O4 hollow spheres had an average diameter of about 850 nm and were constructed from a large number of primary nanoparticles. To demonstrate the potential applications of such porous ZnO/ZnCo2O4 composites, the as-prepared products were used to fabricate a gas sensor that was then investigated for gas-sensing performances. Results of the test showed that this sensor had fast response kinetics to acetone at the operating temperature of 275 °C, and a high response to 100 ppm acetone, one that was about 4 times higher than that of sensors based on ZnO/ZnCo2O4 nanoparticles. The remarkable enhancement in the gas-sensing properties of the porous ZnO/ZnCo2O4 hollow spheres was attributed to their unique structure.