A study on upconversion UV-vis-NIR responsive photocatalytic activity and mechanisms of hexagonal phase NaYF₄: Yb³⁺,Tm³⁺@TiO₂ core-shell structured photocatalyst

A new core-shell structured composite consisting of upconversion hexagonal phase NaYF₄:Yb³⁺,Tm³⁺ (simply named NaYF₄) microrods and UV-vis-NIR driven anatase TiO₂ nanosheets with exposed high-reactive {001} facets has been prepared and shown to be an advanced NIR and sunlight activated photocatalyst. To understand the nature of NIR-driven photocatalysis of NaYF₄@TiO₂, various analysis methods are conducted. Structure analysis proved that TiO₂ is closely attached on the surface of NaYF₄ and can absorb all the converted NIR light (980nm laser) for photocatalysis. As a result, the new photocatalyst gives higher photocatalytic activity in decomposing phenol and Rhodamine B (RhB) than their physical mixture and pure TiO₂ under the NIR and simulated sunlight irradiation. High-reactive hydroxyl radicals (OH) analysis confirmed the superiority of the core-shell structure and the significant role of the upconversion material in using the NIR light to improve the photocatalytic activity of as-prepared TiO₂. Finally, a mechanism for NIR driven photocatalysis is proposed which will help to improve the structure design and functionality of new type of photocatalysts.