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

Highly dispersed and thermally stable TiO 2 quantum dots (TiO 2 -QDs) were achieved in the pore channels of SiO 2 foams with large pore size (14–20 nm) via in-situ hydrolysis of Ti-alkoxide. Owing to the anchoring effect between TiO 2 -QDs and the pore-wall of SiO 2 foam, both the TiO 2 phase transformation from anatase to rutile and the aggregation of TiO 2 -QDs were effectively prohibited. The anatase TiO 2 -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 TiO 2 -QDs/SiO 2 photocatalysts (molar ratio of Ti/Si = 60%, 900 °C) still exhibited a high H 2 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 TiO 2 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 TiO 2 -QDs. This proposed route offered an effective platform for fabricating highly active metal oxide QDs with high thermal stability, greatly prolonging the recyclability.