ZnO Nanorods with Doubly Positive Oxygen Vacancies for Efficient Xylene Sensing

Because of their structural flexibility, earth abundance, and environmental friendliness, ZnO nanomaterials have been widely utilized for gas sensors. ZnO-based sensors showed a high gas response performance, which can be essentially attributed to the effect of oxygen vacancies. However, rare research has focused on the type of oxygen deficiency for regulating gas sensing properties. In this work, we first synthesized ZnO nanorods with a low BET surface area of 6.8 m2/g, presenting superior normalized gas sensitivity toward 200 ppm xylene. This was attributed to very high amounts of doubly positively charged oxygen vacancies forming in these nanorods by creating a highly anoxic environment for oxygen-deficient ZnO growth. In contrast, Ga doping can serve as active sites that are beneficial for adsorbing more oxygen into the lattices of ZnO, resulting in a reduced number of doubly positively charged oxygen vacancies, lower oxygen vacancy-related photoluminescence intensity, and worse xylene sensing performance. Therefore, the doubly positively charged oxygen vacancies play an important role in the gas sensing performance of metal-oxide semiconductors. The results obtained can provide a strategy and facilitate research on the design of other metal-oxide semiconductors with gas sensing properties.