Nanosized sheelite- and zircon-type BiVO4: Active sites and improved sensitivity to H2S and acetone in comparison to V2O5

Bismuth-related mixed-metal oxides are of interest as gas sensitive materials with improved selectivity. Bismuth vanadate is an n-type semiconductor widely explored as a photocatalyst. Less is known on gas sensing behavior, active sites, and sensing mechanism of different polymorphs of BiVO4. In this work, we synthesized nanocrystalline monoclinic sheelite ms-BiVO4 and tetragonal zircon tz-BiVO4 polymorphs and comparatively studied the surface acidity, oxidation reactivity, electric conduction, and gas sensing performance, using V2O5 as a reference. It was found that tz-BiVO4 and V2O5 had close concentrations of acid sites, while a lower surface acidity was observed for ms-BiVO4. Higher oxidative reactivity of BiVO4 than that of V2O5 was revealed by temperature programmed reduction. The improved sensitivity and selectivity of BiVO4 sensors to H2S and acetone were observed depending on temperature. Sensors responses were 21.5–1 ppm H2S at 100 °C, and 7.4–20 ppm acetone at 300 °C. By in situ diffuse reflectance infrared (DRIFT) spectroscopy, it was shown that the sensing mechanism of BiVO4 relies on oxidation of target gases by vanadate ions. Distinct effects of humidity on the sensitivity of ms-BiVO4 and tz-BiVO4 to H2S and acetone were rationalized by different surface acidity of the polymorphs.