Facile MOF-on-MOF isomeric strategy for ZnO@Co3O4 single-shelled hollow cubes with high toluene detection capability

Abstract

A facile metal–organic framework (MOF)-derived isomeric strategy to prepare ZnO@Co3O4 single-shelled hollow cubes (HCs) is described. The crystallinity, morphology, and microstructure of the as-synthesized ZnO@Co3O4 HCs are characterized in detail by X-ray diffraction, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and thermo gravimetric analysis. The results confirm that ZnO@Co3O4 HCs with porous surfaces are successfully synthesized via a self-templating strategy followed by an annealing process, in which bimetal self-assembled MOF are used as a sacrificial template. The formation mechanism of single-shelled ZnO@Co3O4 HCs is discussed. Gas sensors based on ZnO@Co3O4 HCs not only possess high response, fast response-recovery capability, and good selectivity for toluene at 290 °C, but also show a good linear range from 10 to 100 ppm, good repeatability, and long-term stability. The improved toluene sensing performance compared with the ZnO or Co3O4 components is mainly attributed to their single-shelled hollow structure, which provides larger surface area, more active sites for gas diffusion, catalytic effect of Co3O4, and the synergistic effect of p-n heterojunctions between ZnO and Co3O4.