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

• Upconversion material (NaYF4:Yb,Tm) is used for photocatalysis.
• UV–vis–NIR driven high-reactive TiO2 can absorb the upconverted light efficiently.
• Core–shell structure is very important for efficient energy transfer.
• Photocatalytic activity of TiO2 is enhanced by using the NIR light.

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 {0 0 1} 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 (980 nm 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.

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