A simple grinding-calcination approach to prepare the Co3O4–In2O3 heterojunction structure with high-performance gas-sensing property toward ethanol

Abstract

The development of gas sensing devices with high sensitivity, good selectivity and excellent stability is becoming increasingly important since toxic or harmful gases are a threat to human health. Herein, we report a simple grinding-calcination method to prepare high-performance gas sensing materials based on a novel Co₃O₄–In₂O₃ heterojunction structure. Particularly, morphological and structural analyses indicate that the n-type In₂O₃ and p-type Co₃O₄ semiconductors are successfully combined and form a stable heterojunction structure through only a simple grinding-calcination process, in which electrons transfer from n-type In₂O₃ to p-type Co₃O₄ and then combine with holes belonging to Co₃O₄ nanoparticles, which can explain the formation mechanism of the electron depletion layer or the unique heterojunction structure. Interestingly, the sensing materials based on the Co₃O₄–In₂O₃ heterojunction exhibit excellent sensing properties to ethanol. This enhanced sensing performance can be attributed to the electron depletion layer formed at the interface between n-type In₂O₃ and p-type Co₃O₄. Particularly, the sensing device based on the Co₃O₄–In₂O₃ heterojunction structure with 1 wt% Co₃O₄ (labeled Co₃O₄–In₂O₃ (1%)) in the composite system shows a very high gas response to ethanol (approximately 62.13 at 240 °C, which is 1.36 times higher than that of pure In₂O₃ and 11.4 times higher than that of pure Co₃O₄). Moreover, the Co₃O₄–In₂O₃ (1%) sensing device shows an extremely low detection limit to ethanol (the gas response value can reach up to 4.4 to 5 ppm of ethanol, which is 1.43 times higher than that of pure In₂O₃). Furthermore, the fast response and recovery time (42 and 92 s, respectively), high selectivity and high stability presented by the Co₃O₄–In₂O₃ heterojunction display its great potential in the design of excellent gas sensing materials for practical gas detection.