NiO/ZnO heterojunction microspheres for methane detection at room temperature

Low working temperature CH4 gas sensors are necessary to explore to obtain intrinsic safety. In this work, NiO/ ZnO microspheres were synthesized through facile hydrothermal methods and the strategy of photo-activation was used to develop room-temperature CH4 gas sensors. The characterizations of as-prepared samples were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, photoluminescence spectra, and electrochemical impedance spectroscopy. The results indicated that NiO/ZnO is a microsphere structure assembled with porous nanosheets. NiO/ZnO composite had good optical properties to use light energy. The methane gas-sensing performances were systematically investigated at room temperature. It shows that the prepared sensors exhibit good CH4 gas sensing performances at room temperature under UV illumination. NiO/ZnO microspheres exhibited enhanced response values. In particular, NiO/ZnO-2 sensor exhibited the highest response (8.61-5000 ppm CH4), which is 3.42 times of pure ZnO, low detection limit, good selectivity, and repeatability under UV light. The excellent gas sensing performances may be related to the UV light and the formation of heterojunction, which widens the depletion layer and increases the amount of valid carriers. This work gives a sight to explore photo-activated CH4 gas sensors.