SnO2 nanocrystals with abundant oxygen vacancies: Preparation and room temperature NO2 sensing

Abstract SnO 2 oxide nanocrystals were synthesized by annealing the precursor powders at 550 °C in vacuum and air environment, respectively. The nanocrystals were characterized by using techniques including X-ray diffraction, transmission electron microscopy, UV-Vis diffuse reflectance spectra, and X-ray photoelectron spectroscopy. It was found that the SnO 2 nanocrystals obtained in vacuum contained more oxygen vacancies than the SnO 2 nanocrystals prepared in air. When used as gas sensors, the SnO 2 nanocrystals prepared in vacuum showed much enhanced room temperature sensing performance to NO 2 gas relative to the SnO 2 nanocrystals prepared in air. This result confirms the important role of oxygen vacancies in improving gas response of the oxide nanocrystals. The oxygen vacancies make the grain surface possess special chemistry state thereby improving the NO 2 adsorption at low operating temperatures and enhancing the charge transfer from the surface to the adsorbate. It suggests that the vacuum annealing is a valid method to generate oxygen vacancies in SnO 2 nanocrystals. Such synthetic method with the merits of simplicity and no using any surfactants or additives may pave the way to acquire other oxides with oxygen vacancies thereby being used as advanced materials.