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

Abstract The β –NaYF 4 : Yb 3+ , Tm 3+ @ TiO 2 nanocomposite has been prepared by a facile hydrothermal method followed by the hydrolysis of TBOT, and then NaYF 4 : Yb 3+ , Tm 3+ @ TiO 2 , HAuCl 4 and sodium citrate were put into an oil bath for reaction to obtain the β –NaYF 4 : Yb 3+ , Tm 3+ @ TiO 2 @ Au core–shell nanocomposite. XRD and HRTEM show that the samples exhibit the hexagonal phase NaYF 4 , anatase TiO 2 and cubic Au, indicating that the core–shell phases of NaYF 4 −TiO 2 or NaYF 4 −TiO 2 −Au coexist in these samples. EDS and XPS results show the presence of Na, Y, F, Ti, O and Au elements. When TiO 2 was coated on the surface of upconversion nanomaterials of NaYF 4 : Yb 3+ , Tm 3+ , the photocatalytic activity was improved significantly, and the β –NaYF 4 : Yb 3+ , Tm 3+ @ TiO 2 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 –NaYF 4 : Yb 3+ , Tm 3+ @ TiO 2 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 –NaYF 4 : Yb 3+ , Tm 3+ @ TiO 2 @ Au core–shell nanocomposite does not exhibit the better photocatalytic activity, and the optimal research will be carried out in the future.