Visible-light-enhanced room-temperature methane sensing using a SnO₂/WO₃/graphene composite structure

Room-temperature methane sensing remains challenging because CH₄ is chemically stable and most chemiresistive metal-oxide sensors require thermal activation. Here, a visible-light-enhanced SnO₂/WO₃/graphene (SnO₂/WO₃/G) composite sensor is developed by integrating a porous SnO₂/WO₃ adsorption-photocatalytic layer with a highly conductive graphene transduction layer. Under 450 nm illumination at 25 °C and 60%RH, the sensor exhibits a response of 70.82% to 2000 ppm CH₄, with response and recovery times of 46 and 86 s, respectively. The concentration-dependent response yields a theoretical limit of detection of 27.31 ppm. The device also demonstrates excellent cycle repeatability, with a relative standard deviation of 0.82%, and stable response during the current 30-day observation period, with a relative standard deviation of 3.49%. Comparative analysis indicates that the proposed sensor combines heater-free room-temperature operation, rapid response kinetics, and a high response in a single platform. The improved sensing behavior is attributed to the porous SnO₂/WO₃ surface, visible-light-assisted generation of reactive oxygen species, and interfacial charge transfer to graphene. These results provide a promising route for room-temperature CH₄ monitoring.