Dual-Functional Green Facile synthesis of graphene doped CuO-SnO2:F sprayed thin film as an efficient photocatalyst and ammonia gas sensor at low concentration

Undoped and graphene-doped CuO-SnO2:F thin films were synthesized using spray pyrolysis technique with varying graphene ratios (Gr/(Gr + Cu)) of 2 %, 4 %, and 6 %. These thin films were thoroughly characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), UV–Vis–NIR spectrophotometry, and impedance spectroscopy. Their performance was evaluated for photocatalytic degradation of various pollutants, including Green Malachite (GM), Rhodamine B (RdhB) and Methylene Blue (MB) dyes under sunlight irradiation, as well as for gas sensing of ammonia (NH3) in the concentration range of 5–25 ppm at 250 °C.The photocatalytic activity was significantly enhanced in the case of the 6 % graphene-doped CuO-SnO2:F thin film. This improvement is attributed to the substantial reduction in the bandgap energy, from 3.092 eV to 2.238 eV for SnO2:F and from 1.500 eV to 1.450 eV for CuO, upon graphene doping. These bandgaps narrowing facilitate to improve absorption of sunlight, resulting in higher photocatalytic efficiency. Similarly, the 6 % graphene-doped CuO-SnO2:F sensor demonstrated superior gas sensing performance, which can be explained by the increase of the porosity and conductivity introduced by graphene. These changes promote efficient charge transfer and improve the adsorption of ammonia molecules on the sensor's surface, leading to higher sensitivity and faster response and recovery times.Based on the advantages indicated above and the benefits of its simple structure, cost-effective fabrication, and the inherent advantages of the p-type semiconductor properties, the 6 % graphene-doped CuO-SnO2:F thin film presents a promising dual-functional material. It offers a high photocatalytic performance for pollutants degradation under sunlight and an excellent gas sensing capability for detecting low concentrations of ammonia (5–25 ppm), making them highly suitable for environmental and industrial applications.