Synthesis and calcination–temperature-dependent gas-sensing performance of g-C3N4/Co3O4 heterojunctions for toluene gas sensors

G-C 3 N 4 nanosheets were synthesized by hydrothermal method and then were anchored on the surface of mesoporous Co 3 O 4 nanowires (NWs) to from g-C 3 N 4 /Co 3 O 4 heterojunctions. After calcination, the influence of calcined temperature on the microstructures and gas-sensing performance is investigated in detail. All results show that g-C 3 N 4 nanosheets affect the microstructure of Co 3 O 4 NWs and are decorated on the surface of Co 3 O 4 NWs. With the increasing calcination temperature, the specific surface area decreased from 64 m 2 /g for Co 3 O 4 NWs to about 20 m 2 /g. The responses of g-C 3 N 4 /Co 3 O 4 sensors are improved from 11.01 for Co 3 O 4 sensor to about 20–100 ppm toluene gas, and CNC-500 presents excellent response values of 25.8 at the operating temperature of 220 °C. Although g-C 3 N 4 /Co 3 O 4 heterojunctions exhibit the low specific surface area, the p-n heterojunctions at the interface of g-C 3 N 4 and Co 3 O 4 greatly increase the resistance in toluene gas. As the result, g-C 3 N 4 nanosheets greatly improve the toluene gas-sensing performance of g-C 3 N 4 /Co 3 O 4 sensors due to p-n heterojunctions.