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.