Mesoporous Co3O4/In2O3 nanocomposites for formaldehyde gas sensors: Synthesis from ZIF-67 and gas-sensing behavior

Mesoporous In2O3 nanowires (NWs) were synthesized with nanocasting method, and then Co3O4/In2O3 nanocomposites were prepared through calcining ZIF-67. All results indicate that Co3O4 nanoparticles greatly affect the microstructures and gas-sensing properties of Co3O4/In2O3 sensors. The response to 10 ppm (formaldehyde) HCHO gas exhibits a significant improvement though the loading of Co3O4. The response values soar from 26.16 for In2O3 NWs to 92.94 for 6%Co3O4/In2O3 and up to maximum 113.6 for 8% Co3O4/In2O3, then decreases to 25.76 for 10% Co3O4/In2O3. 8% Co3O4/In2O3 sensor possesses the excellent HCHO gas-sensing performance with the highest response (113.6) and shortest response time of 20 s. The working temperature of Co3O4/In2O3 sensors is 30 °C lower than that of In2O3 sensor due to Co3O4 catalysis. P-n heterojunctions between p-type Co3O4 and n-type In2O3 affect the interfacial carrier distribution, improving the gas-sensing behavior of Co3O4/In2O3 sensors. Furthermore, oxygen vacancies also play a important role to improve the gas-sensing performance of Co3O4/In2O3 sensors.