Synthesis Of Ytterbium-Doped Titania/Diatomite Photocatalyst And Its Photocatalytic Activity

Titanium dioxide?TiO₂? is one of the most promising photocatalyst due to its biological and chemical inertness, high photocatalytic activity, environmental friendliness, and low cost. However, a serious disadvantage of TiO₂ nanoparticles is its large band gap energy?3.2eV?, thus it is activated only by ultraviolet?UV? light irradiation???370nm?, where only 3–5% solar energy is effective. In order to enhance the utilization of solar energy,many researchers have synthesized RE?rare earth? irons doped TiO₂, the photocatalysts exhibited wider absorption region and higher photocatalytic activity compared to undoped samples.In addition to the large band gap energy, there are some draw-backs such as agglomeration, low adsorption capacity, and difficult separation that limit the practical application and commercial benefits of TiO₂. To overcome these limitations, extensive efforts have been devoted to the immobilization of the TiO₂ onto natural minerals, such as diatomite, kaolinite, zeolite, and attapulgite. Among various porous supporting materials, diatomite has attracted significant attention due to its chemical stability, low density?2000²500kg/m3?, highly porous structure?80%⁹0%?, large specific surface area?10⁸0m2/g?, and low cost. The photocatalytic performance of TiO₂/diatomite photocatalyst is obviously improved compared to that of TiO₂.TiO₂/diatomite photocatalytic materials were prepared by sol–gel method. The phase structure was characterized by X-ray diffraction?XRD?, the photocatalytic activity of synthesized samples was investigated by the degradation of methylene blue?MB? under UV light irradiation, and the influencing factors of photocatalytic performance were also investigated. The results shows the amount of diatomite can influence the distribution of TiO₂ on the surface of diatomite. The crystalline was improved with the increasing of calcination temperature and holding time. However, with the increasing of holding time, the sample particles will be sintered and aggregated. With the increased of the initial concentration of the dye solution, the photocatalytic activity of the photocatalyst would decrease; while with the increase of catalyst dosage, the degradation rate also will increase; and the lower pH is beneficial to photocatalycal reaction. The optimized initial concentration of methylene blue solution,amount of photocatalysts, and pH are 5mg/L, 2.5g/L and 2, respectively.Combined with the diatomite and RE doping, Yb³⁺-doped titanium dioxide(Yb³⁺-TiO₂)/diatomite photocatalytic materials with different Yb³⁺ concentrations were prepared by sol–gel method. The phase structure, morphology, and chemical composition of the as-prepared composites were well characterized by X-ray diffraction?XRD?, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy?SEM?, and ultraviolet–visible?UV–vis? diffuse reflection spectroscopy. The XRD and Raman spectroscopy analysis indicated that the TiO₂ existed in the form of pure anatase in the photocatalysts. The SEM images exhibited the well deposition and dispersion of TiO₂ nanoparticles with little agglomeration on the surfaces of diatoms. The UV–vis diffuse reflection spectra showed that the band gap of TiO₂ could be narrowed by the introduction of Yb³⁺ ions, which was further affected by doping concentration of Yb³⁺. Compared to pure TiO₂ and TiO₂/diatomite, the Yb³⁺-doped TiO₂/diatomite photocatalysts exhibited higher photocatalytic performance for methylene blue under UV irradiation. The MB decoloration rate by 0.75%Yb³⁺-TiO₂/diatomite photocatalyst finally reached up to 99.8%. And the photocatalytic activity of 0.75%Yb³⁺-TiO₂/diatomite was 6.29 and 2.87 times higher than that of the pure TiO₂ and TiO₂/diatomite samples, respectively. This was attributed to the synergistic effect of diatomite and Yb³⁺ ions. Diatomite was beneficial to form hydroxyl radicals, provided more active sides, and inhibited the agglomeration of TiO₂ nanoparticles. In contrast, the specific 4f-electron configuration of Yb³⁺?six 4f electronics? makes it a need to trap one electron to reach half-filled state. The photogenerated electrons released by TiO₂ under UV irradiation could be captured by Yb³⁺ions?turn into Yb2+?, and then Yb2+ ions inclined to release them to O₂ adsorbed on the surface of the catalyst to form superoxide anion radicals?O₂-?, which could further accelerate the photocatalytic reaction. Furthermore, the introduction of Yb³⁺ ions could extend the absorption region and narrow the band gap, leading to an improvement in the photocatalytic activity...