Different upconversion properties of β-NaYF4:Yb3+,Tm3+/Er3+ in affecting the near-infrared-driven photocatalytic activity of high-reactive TiO2.

Double-shell-structured β-NaYF4:Yb(3+),Tm(3+)/Er(3+)@SiO2@TiO2 upconversion photocatalysts have been successfully synthesized by a simple hydrothermal method. It is found that the double-shell-structured photocatalyst consists of uniform β-NaYF4:Yb(3+),Tm(3+)/Er(3+) nanocrystals, SiO2 as the media shell, and anatase TiO2 nanocrystals exposed with the high-reactive {001} facets as the outer shell. The TiO2 shell is modified to absorb both the UV and visible light in order to make sufficient use of the upconverted light from β-NaYF4:Yb(3+),Tm(3+)/Er(3+) for photocatalysis. Effective energy transfer from β-NaYF4:Yb(3+),Tm(3+)/Er(3+) to TiO2 and its importance are confirmed. The photocatalytic activity in the degradation of Rhodamine B (RhB) under the near-infrared (NIR) (980 nm laser) irradiation suggests that the NIR-driven photocatalytic activity of the double-shell-structured photocatalyst is significantly dependent on the properties of the upconversion materials and the irradiated NIR power density. Moreover, the NIR-driven photocatalyst shows stable photocatalytic degradation of RhB in the recycled tests. This study suggests a promising system and a new insight to understand the application of appropriate upconversion materials to effectively utilize the NIR for photocatalytic applications of TiO2-based photocatalysts, which may advance the application of solar energy in the future.