Synergistic effects of UV activation and surface oxygen vacancies on the room-temperature NO2 gas sensing performance of ZnO nanowires

The room-temperature detection of NO2 by metal oxide nanostructures has been a long-term hot topic. The utilization of UV illumination and introducing surface oxygen vacancies (V-o) have been demonstrated as effective strategies for enhancing the NO2 sensing performance of metal oxides. Herein, we demonstrated the synergistic effects of UV activation and surface V-o on the room-temperature NO2 sensing performance of ZnO nanowires, which were hydrothermally grown and treated in NaBH4 solution to introduce rich surface V-o. The room-temperature NO2 sensors based on V-o-rich ZnO nanowires showed significantly higher responses and faster response/recovery rates under UV illumination compared with the V-o-deficient untreated sample. In addition, the sensors exhibited excellent reversibility, high selectivity and good stability. The synergistically enhanced NO2 sensing performance of ZnO nanowires could be attributed to their improved optoelectronic properties as well as the UV and V-o co-modulated surface chemisorption and reactions of O-x(-) and NOx- species. O-2 temperature programmed desorption analysis (O-2-TPD), in-sintElectron paramagnetic resonance (EPR) and in-situ Fourier transform infrared spectroscopy (IR) spectroscopy studies suggested that surface V-o could act as active centers for the ionized adsorption of oxygen to generate highly-active O- species under UV illumination, which would subsequently promote the formation of NO3- species, leading to the enhanced NO2 adsorption and electron transfer at room temperature.