Preparation Of YF₃:Ho³⁺@TiO₂ Photocatalyst And Their Photocatalytic Activity

TiO₂ is a kind of environmental functional material with excellent performance, which is friendly to environment, stable in quality and cheap in price. However, due to the wide band gap of TiO₂, it can only be excited by ultraviolet light, so the utilization rate of solar light is very low, so that the wide application of TiO₂ has been affected and restricted. On the basis of the analysis of the existing photocatalyst modification technologies, it is considered that the combination of "upconversion luminescence technology" and "TiO₂ photocatalytic technology" is a promising treatment technology. Upconversion luminescence technology can absorb visible light and convert it to UV light, so as to stimulate TiO₂ to produce highly efficient photocatalytic effect, so the target pollutant can be degraded by TiO₂ under the visible light.The study starts with the development of the rare earth ions single doped upconversion material YF3:Ho3+, then the basic physical and chemical properties were characterized and analyzed. Using the characteristics of it can absorb visible light and emit ultraviolet light, an upconversion luminescent material doped TiO₂ photocatalyst was synthesized. And the photocatalyst's structure, morphology and photocatalytic properties were studied.The main contents and conclusions of the paper are as follows:?1? Ho3+ single-doped YF3 nanoparticles were successfully synthesized by a hydrothermal method. X ray diffraction?XRD? result showed that the prepared upconversion material is orthorhombic YF3. The Scanning Electron Microscope?SEM?and Energy Dispersive Spectrometer?EDS? results showed that upconversion material YF3:Ho3+ exhibited rice-like morphology with an average length of approximately 100 nm and an average diameter of approximately 50 nm. UV-visible diffuse-reflectance spectroscopy?DRS UV-Vis? analysis revealed that YF3:Ho3+ absorbed light in the visible light and UV light region, and the strongest absorption peak was around 450 nm. Ultraviolet upconversion luminescence around 288 nm was observed clearly in YF3:Ho3+ nanoparticles under excitation at 450 nm. Combined with double-logarithmic plot of the dependence of excitation power on luminescence intensity for the YF3:Ho3+ nanoparticles and energy level diagram of Ho3+ analysis revealed that ultraviolet upconversion occurred via a three-photon process or a combination of three-photon and two-photon processes.?2? The best performance of the UV upconversion luminescence of YF3:Ho3+ was selected to synthesize an upconversion luminescent material doped photocatalyst YF3:Ho3+@TiO₂ by a sol-gel process. X ray diffraction?XRD? test result showed that the photocatalyst was anatase TiO₂. The Transmission Electron Microscope?TEM? results showed fine TiO₂ nanoparticles were attached to the surface of large granular YF3:Ho3+ nanoparticles, and the samples displayed spherical morphology with an average size of approximately 10 nm and showed marked aggregation. In the preparation process of photocatalyst, the size and morphology of YF3:Ho3+ nanoparticles remained unchanged after introducing TiO₂. Upconversion luminescence spectra results revealed that upconversion luminescence properties of YF3:Ho3+@TiO₂ and YF3:Ho3+ were similar. Ultraviolet upconversion luminescence around 288 nm was observed clearly in YF3:Ho3+@TiO₂ photocatalyst under excitation at 450 nm, but the intensity of UV emission around 288 nm decreased significantly.?3? Rhodamine B, as a model pollutant, was used in a series of degradation experiments to evaluate the photocatalytic activity of YF3:Ho3+@TiO₂ under visible light excitation. The results showed that there was an optimum value of the dosage and the hydrolysis reaction time of TBOT in the preparation of the photocatalyst YF3:Ho3+@TiO₂, which were 6.0 mL and 60 min, respectively. The photocatalytic activity of YF3:Ho3+@TiO₂ was the highest at the optimal value of the two parameters. Degradation rate of RhB up to 94% within 10.5 h when the photocatalyst dosage is 0.15 g, the initial concentration of RhB is 4.0 mg/L, and the light intensity is 141500 lx. YF3:Ho3+@TiO₂ has the highest catalytic efficiency with such conditions. RhB degradation consistent with Langmuir-Hinshelwood kinetic equation photocatalyzed by YF3:Ho3+@TiO₂. Considering the factors of the photocatalyst dosage, the initial concentration of RhB and light intensity, the dynamic model is:...