High-Performance Room-Temperature NO₂ Gas Sensor Based on Au-Loaded SnO₂ Nanowires under UV Light Activation

Optical excitation is widely acknowledged as one of the most effective means of balancing sensor responses and response/recovery properties at room temperature (RT, 25 °C). Moreover, noble metals have been proven to be suitable as photosensitizers for optical excitation. Localized surface plasmon resonance (LSPR) determines the liberalization of quasi-free electrons in noble metals under light irradiation, and numerous injected electrons in semiconductors will greatly promote the generation of chemisorbed oxygen, thus elevating the sensor response. In this study, pure SnO₂ and Au/SnO₂ nanowires (NWs) were successfully synthesized through the electrospinning method and validated using XRD, EDS, HRTEM, and XPS. Although a Schottky barrier led to a much higher initial resistance of the Au/SnO₂ composite compared with pure SnO₂ at RT in the dark, the photoinduced resistance of the Au/SnO₂ composite became lower than that of pure SnO₂ under UV irradiation with the same intensity, which confirmed the effect of LSPR. Furthermore, when used as sensing materials, a detailed comparison between the sensing properties of pure SnO₂ and Au/SnO₂ composite toward NO₂ in the dark and under UV irradiation highlighted the crucial role of the LSPR effects. In particular, the response of Au/SnO₂ NWs toward 5 ppm NO₂ could reach 65 at RT under UV irradiation, and the response/recovery time was only 82/42 s, which far exceeded those under Au modification-only or optical excitation-only. Finally, the gas-sensing mechanism corresponding to the change in sensor performance in each case was systematically proposed.