Thermally stable TiO2 quantum dots embedded in SiO2 foams: Characterization and photocatalytic H2 evolution activity

Abstract

Highly dispersed and thermally stable TiO2 quantum dots (TiO2-QDs) were achieved in the pore channels of SiO2 foams with large pore size (14–20 nm) via in-situ hydrolysis of Ti-alkoxide. Owing to the anchoring effect between TiO2-QDs and the pore-wall of SiO2 foam, both the TiO2 phase transformation from anatase to rutile and the aggregation of TiO2-QDs were effectively prohibited. The anatase TiO2-QDs anchored on the surface of silica foams could be well maintained with a ultrafine crystal size (<7.0 nm) even after high temperature (up to 1000 °C) calcination in air, suggesting a high thermal stability. The sample of TiO2-QDs/SiO2 photocatalysts (molar ratio of Ti/Si = 60%, 900 °C) still exhibited a high H2 evolution rate (HER, 10399 μmol g−1 h−1) for reducing water with a quantum efficiency of 17.8% under UV light irradiation (λ = 365 nm), slightly lower than that of the sample treated at 500 °C. In the absence of the silica foam, the pure TiO2 crystals calcined at 900 °C crystals nearly cannot exhibit an obvious HER value. Such excellent photocatalytic hydrogen evolution performance was ascribed to the short electron-transfer distance, high anatase crystallinity, uniform dispersity in silica foam, and excellent stability of the TiO2-QDs. This proposed route offered an effective platform for fabricating highly active metal oxide QDs with high thermal stability, greatly prolonging the recyclability.