Enhanced relatively low-temperature carbon monoxide sensing properties of cupric oxide/porous graphitic carbon nitride p–n heterojunction

Abstract In the present study, heterojunctions of cupric oxide (CuO)/porous graphite-like carbon nitride (g-C3N4) with different g-C3N4 loading amounts were synthesized and employed as sensitive layers to study gas sensing response towards carbon monoxide (CO). X-ray photoelectron spectroscopy revealed the successful formation of the heterojunction through the interaction between Cu and N atoms. Moreover, scanning electron microscopy offered insights into the morphology of these materials. At the low content of g-C3N4, CuO nanoparticles only decorated g-C3N4 nanosheets. Upon increasing the amount of g-C3N4, the morphology was transformed into a flower-like structure with petals of g-C3N4 nanosheets connected well with CuO. Therefore, the porous structure of g-C3N4 nanosheets with a pore size distribution of 2–200 nm and a high specific surface area of 9.1 m2 g−1 is convenient for the growth of CuO nanoparticles. The sensor with an appropriate ratio of g-C3N4 (8%) exhibited good characteristics toward CO, including high response in a wide detection range, a rapid response/recovery process, and good repeatability at a relatively low operating temperature of 150 °C. Anchoring the CuO nanoparticles onto the large surface area of g-C3N4 nanosheets provides sufficient p-n heterojunction and active sites to adsorb reactants which significantly improves the sensing activity. Moreover, the intimate interface between the CuO nanoparticles and g-C3N4 promotes the charge transfer kinetics, which benefits the sensing performance. The present results open an avenue to synthesize various novel metal oxide semiconductor/g-C3N4 heterojunctions with intriguing characteristics for sensing applications.