Enhanced photocatalytic activity of TiO₂ in visible and infrared light through the synergistic effect of upconversion nanocrystals and quantum dots

The synergy of up-conversion luminescence nanocrystals NaYF₄:Yb,Tm and CdS quantum dots(CdS QDs) is used to improve the photocatalytic activity of TiO₂ in visible and infrared light. The photocatalyst was fabricated with the water-soluble NaYF₄:Yb,Tm nanocrystals as the core and anatase-TiO₂ as the shell. Then CdS QDs were deposited on the surface of shell TiO₂ by hydrothermal method. The photocatalytic activity of the prepared NaYF₄:Yb,Tm@TiO₂/CdS QDs composite was investigated by photodegration of Rhodamine B under white, visible light and near-infrared light. When compositing TiO₂ with the upconversion NaYF₄:Yb,Tm, the photocatalytic activity of the NaYF₄:Yb,Tm@TiO₂ was 6.8 times to TiO₂ under white light and 2.5 times to TiO₂ under visible light. After coupling the upconversion effect and the quantum dots sensitization effect with TiO₂, the photocatalytic activity of the NaYF₄:Yb,Tm@TiO₂/CdS QDs composite was significant 11.2 times to TiO₂ under white light, and 6.5 times to TiO₂ under visible light, respectively. Even more considerable enhancement was discovered under the near-infrared light. The NaYF₄:Yb,Tm@TiO₂/CdS QDs composite showed 1590 times relative to almost no activity of TiO₂. The photocatalytic enhancement is attributed to two effects. First, the sensitization of CdS QDs can extend the absorption region of TiO₂ to 490 nm. Secondly the upconversion NaYF₄:Yb,Tm can absorb near-infrared light and emit ultraviolet (348 nm and 366 nm) absorbed by anatase-TiO₂ and visible light (476 nm) absorbed by CdS QDs. (paper)