Room-temperature gas sensors based on ZnO nanorod/Au hybrids: Visible-light-modulated dual selectivity to NO₂ and NH₃

Gas sensors play vital roles in air pollution monitoring. Despite considerable progress in improving the room-temperature gas sensing sensitivities and rates of materials, comparably less attention is paid to the sensor selectivity. Here, ultrathin ZnO nanorods (˜15 nm) were synthesized by a nanoseed-assisted wet chemical approach and subsequently functionalized by Au nanoparticles by a photoreduction method. The hybrid material exhibited visible-light-activity owing to the surface plasmon resonance (SPR) effects of Au nanoparticles. The ZnO/Au hybrids were assembled into a high-performance, optically-controlled gas sensor operating at room temperature, which was found to be more selective to NH₃ in dark but showed high selectivity to NO₂ under visible-light illumination (λ = 532 nm). Moreover, the sensors exhibited high response and short response and recovery times as well as excellent reversibility and selectivity at room temperature. Such visible-light-modulated dual gas selectivity could be mainly attributed to the opposite direction of electron transfer between ZnO and Au nanoparticles in dark and under visible-light illumination, which led to the different surface depletion characteristics of the ZnO nanorods. In addition, the ultrathin diameters of nanorods also synergistically contributed to the light-controlled dual gas selectivity. The presently developed light modulation strategy provides an alternative approach to highly-selective and dual-functional gas sensors operating at room temperature.