Bimetallic MOF-derived CeO2/Co3O4 microflowers with synergy of oxygen vacancy and p-n heterojunction for high-performance n-butanol sensors

In this work, CeO2/Co3O4 microflowers have been prepared by a facile bimetallic metal-organic framework (MOF) derivatization method. By optimizing the calcination temperature, the CeO2/Co3O4-350 with the calcination temperature as 350 ℃ has been prepared with the optimal morphology and gas sensing performance. The microflowers composed of nanosheet subunits can fully expose the surface-active sites of CeO2/Co3O4-350, expanding its contact surface with the detected gas. Moreover, for the larger atomic radius and polyvalent state of Ce, more oxygen vacancies can be generated on the surface of CeO2/Co3O4-350 composites. And the p-n heterojunction formed at the junction of CeO2 and Co3O4 can expand the depletion layer at the interfaces, increasing the amount of adsorbed oxygen, which conduce to heighten the response of CeO2/Co3O4-350. Benefiting from the synergy of oxygen vacancy and p-n heterojunction, CeO2/Co3O4-350 exhibits excellent sensing properties toward n-butanol. At the operating temperature of 190 °C, CeO2/Co3O4-350 can make a fast response/recovery (63 s/11 s) to 100 ppm n-butanol with a response value of 87.96, and the lowest limit (LOD) of detection is 2 ppm. Moreover, the theoretical detection limit of CeO2/Co3O4-350 to n-butanol has been evaluated to be 105 ppm, which means that it can respond to ppb-level n-butanol. After 15 days long-term test, the response still maintains about 94%, showing good stability of CeO2/Co3O4-350, which is of great significance to the practical application of gas sensors. Our work uses simple MOF-derived method to construct sensing materials with larger active surface and optimized internal electronic structure, providing a facile and practical strategy to design gas sensing materials.