Co3O4 Nanosheets Decorated with In(2)O(3 )Nanocubes with Exposed {001} Facets for ppb-Level CO Sensing

To selectively detect trace carbon monoxide (CO typically lower than 100 ppb) at low temperature is still a great challenge for chemiresistive gas sensors. In this work, we introduce In2O3 nanocubes with exposed {001} facets to couple with MOF-derived porous Co3O4 nanosheets (NSs) forming p-n heterojunction for trace CO detection. Benefiting from the vacancy storing effect of the sub-valent band on In2O3 nanocube {001} facets and the p-n heterojunction effect, the electron-hole recombination is effectively inhibited, and the carrier lifetime is prolonged. As a result, the prepared CoIn0.1-based gas sensor shows a good selectivity and ultralow detection limitation of 25 ppb toward CO at relatively low temperature of 175 degrees C. In addition, the CoIn0.1-based CO sensor also exhibits high response (272.89%) and ultrafast response/recovery time (2 s/13 s) to 100 ppm CO, which can be ascribed to the fast gas diffusion in the porous Co3O4 NSs and the high-index facet effect of In2O3 nanocubes. This work provides a method to design and synthesize trace CO gas sensors via modulating the band structure of p-n heterojunctions constructed by two-dimensional metal oxide NSs and oxide-exposed high-index facets.