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

G-C₃N₄ nanosheets were synthesized by hydrothermal method and then were anchored on the surface of mesoporous Co₃O₄ nanowires (NWs) to from g-C₃N₄/Co₃O₄ heterojunctions. After calcination, the influence of calcined temperature on the microstructures and gas-sensing performance is investigated in detail. All results show that g-C₃N₄ nanosheets affect the microstructure of Co₃O₄ NWs and are decorated on the surface of Co₃O₄ NWs. With the increasing calcination temperature, the specific surface area decreased from 64 m²/g for Co₃O₄ NWs to about 20 m²/g. The responses of g-C₃N₄/Co₃O₄ sensors are improved from 11.01 for Co₃O₄ 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-C₃N₄/Co₃O₄ heterojunctions exhibit the low specific surface area, the p-n heterojunctions at the interface of g-C₃N₄ and Co₃O₄ greatly increase the resistance in toluene gas. As the result, g-C₃N₄ nanosheets greatly improve the toluene gas-sensing performance of g-C₃N₄/Co₃O₄ sensors due to p-n heterojunctions. [ABSTRACT FROM AUTHOR]