Mesoporous Co3O4 nanowires decorated with g-C3N4 nanosheets for high performance toluene gas sensors based on p-n heterojunction

Mesoporous cobalt oxides nanowires (Co3O4 NWs) were synthesized by nanocasting pathway, and then g-C3N4 nanosheets were anchored on the surface of Co3O4 NWs to form g-C3N4/Co3O4 nanocomposites. The introduction of g-C3N4 nanosheets exists on the surface of Co3O4 NWs, and the specific surface area decreases from 64.19 m2/g for Co3O4 NWs to about 30 m2/g for g-C3N4/Co3O4 nanocomposites. The experimental results indicate that g-C3N4 nanosheets greatly affect the toluene gas-sensing performance of g-C3N4/Co3O4 sensors. The 100 ppm toluene gas response increases with the increasing g-C3N4 content from 2.84 for Co3O4 sensor to 15.05 for (C3N4)0.07Co3O4 sensor, up to the maximum of 17.02 for (C3N4)0.12Co3O4 sensor, and then decreases to 13.33 for (C3N4)0.15Co3O4 sensor at the operating temperature of 220 °C. Although g-C3N4/Co3O4 nanocomposites possess the lower specific surface area to decrease the adsorption oxygen, p-n heterojunctions at the interface of g-C3N4 and Co3O4 greatly increase the resistance in toluene gas. In this way, g-C3N4 nanosheets greatly improve the toluene gas-sensing performance of g-C3N4/Co3O4 sensors due to p-n heterojunctions.