Crystalline phases and photocatalytic activities of hydrothermal synthesis Ag3VO4 and Ag4V2O7 under visible light irradiation Original Research Article

Visible-light-driven silver vanadate photocatalysts were successfully synthesized using a low-temperature hydrothermal synthesis method. Under various hydrothermal conditions, the structures of silver vanadates were tuned by changing the hydrothermal time and with the assistance of a surfactant. X-ray diffraction (XRD) results reveal that the hydrothermal synthesis powders consisted of three kinds of phase: pure Ag4V2O7 or pure α-Ag3VO4 or mixed phases of Ag4V2O7 and α-Ag3VO4. UV–vis spectroscopy indicated that silver vanadate particles had strong visible light absorption with associated band gaps in the range of 2.2–2.5 eV. The powder synthesized at 140 °C for 4 h (HT4) exhibited the highest photocatalytic activity among all samples. The reactivity of HT4 (surface area, 2.04 m2 g−1) on isopropanol and benzene was 16.6 and 16.2 times higher than those of P25 (surface area, 49.04 m2 g−1) under visible light irradiation. The enhanced photocatalytic activity of HT4 is attributed to mixed crystalline phases of Ag4V2O7 and α-Ag3VO4, where α-Ag3VO4 is the major component. In addition, the highest large amount of hydroxyl groups on the surface of α-Ag3VO4, detected by the in situ FT-IR diffuse reflectance (DRIFT) technique, was considered as the other factor. Detailed DRIFT experiments also revealed that the stability of Brønsted acid sites of HT4 was excellent, as confirmed by NH3 adsorption. Studies of crystalline phase and surface property showed that the photocatalytic activities of the hydrothermal synthesis of silver vanadates are strongly affected by hydrothermal time. Besides, the amount of surface hydroxyl groups and the crystallinity of α-Ag3VO4 phase were verified to be the key factors influencing photocatalytic activity.