Synthesis of g-C3N4-based NaYF4:Yb,Tm@TiO2 ternary composite with enhanced Vis/NIR-driven photocatalytic activities

Upconversion (UC) NaYF4:Yb,Tm nanocrystals (NCs) are capable of converting low-energy near-infrared (NIR) photons to high-energy ultraviolet (UV) and visible (Vis) photons. Integration of NaYF4:Yb,Tm with graphitic carbon nitride (g-C3N4) can extend the spectral response of g-C3N4 to the NIR range. However, photocatalytic activity of NaYF4:Yb,Tm/g-C3N4 is still severely limited by the high recombination rate of photo-generated (PG) electrons and holes (e-/h+) in the g-C3N4. Herein, we report a facile approach to fabricate a ternary nanocomposite consisting of NaYF4:Yb,Tm, TiO2 and g-C3N4. When NaYF4:Yb,Tm NCs were coated with a TiO2 shell and sequentially assembled with g-C3N4 nanosheets (NSs), a semiconductor heterojunction can be fabricated on the UC particles. The as-prepared nanocomposites possess an enhanced photocatalytic activity under Vis and/or NIR lights due to the formation of heterojunction and UC effect. The ternary nanocomposites have been characterized in detail and their photocatalytic mechanism is proposed. Such kind of ternary nanocomposites may provide a new scenario for the design and synthesis of composite photocatalysts for efficiently utilizing the Vis/NIR lights in environmental remedy.