Synthesis of β-NaYF4: Yb3+, Tm3+ @ TiO2 and β-NaYF4: Yb3+, Tm3+ @ TiO2 @ Au nanocomposites and effective upconversion-driven photocatalytic properties

The β-NaYF4: Yb3+, Tm3+ @ TiO2 nanocomposite has been prepared by a facile hydrothermal method followed by the hydrolysis of TBOT, and then NaYF4: Yb3+, Tm3+ @ TiO2, HAuCl4 and sodium citrate were put into an oil bath for reaction to obtain the β-NaYF4: Yb3+, Tm3+ @ TiO2 @ Au core-shell nanocomposite. XRD and HRTEM show that the samples exhibit the hexagonal phase NaYF4, anatase TiO2 and cubic Au, indicating that the core-shell phases of NaYF4−TiO2 or NaYF4−TiO2−Au coexist in these samples. EDS and XPS results show the presence of Na, Y, F, Ti, O and Au elements. When TiO2 was coated on the surface of upconversion nanomaterials of NaYF4: Yb3+, Tm3+, the photocatalytic activity was improved significantly, and the β-NaYF4: Yb3+, Tm3+ @ TiO2 nanocomposite gives the highest photodegradation efficiency for MB and RhB, and decomposes about 73% of MB or 80% of RhB within 4.5 h under simulated solar light irradiation respectively. When the ultraviolet light from simulated sunlight irradiation was removed by the addition of a UV filter, the β-NaYF4: Yb3+, Tm3+ @ TiO2 nanocomposite decomposes about 42% of MB or 48% of RhB within 4.5 h. It means that the upconversion-driven photocatalytic performance (decomposes 42% of MB or 48% of RhB) is more effective than UV light-driven photocatalytic performance (31% of MB or 32% of RhB) in the photodegradation process. In addition, the β-NaYF4: Yb3+, Tm3+ @ TiO2 @ Au core-shell nanocomposite does not exhibit the better photocatalytic activity, and the optimal research will be carried out in the future.