Co3O4 Nanosheets Decorated with In2O3 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 In 2 O 3 nanocubes with exposed {001} facets to couple with MOF-derived porous Co 3 O 4 nanosheets (NSs) forming p–n heterojunction for trace CO detection. Benefiting from the vacancy storing effect of the sub-valent band on In 2 O 3 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 °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 Co 3 O 4 NSs and the high-index facet effect of In 2 O 3 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.