Preparation, Characterization And The Study On The Photocatalytic Efficiency Of Visible Light Photocatalysts

Organic pollutants in water environment (Such as phenols, halogenated hydrocarbons, aromatic hydrocarbons and their derivatives, heterocyclic compounds, etc.) with the characteristics of complicated composition, toxicity are difficult to treat by the traditional environmental controlling technology. Photocatalytic chemistry has a strong oxidbillity, so it plays a very important role in the degradation of organic pollutants. Current researches about catalyst are mainly TiO2.The limitations of the catalyst is its wide band gap, so it has no photocatalytic activity in the visible light. The photocatalytic efficiency is lower because of difficult separation of electron and holes. It is difficult to recycle this catalyst.In this paper, new catalysts with high efficiency photocatalytic activity in the visible light, TiO2 modification and immobilization, magnetic carrier catalyst were studied. A series of new visible light catalysts were designed and synthesized. The catalytic activity of the degradation of toxic organic pollutants was tested. It was focused on the catalyst surface structure and the active component of the degradation activity of organic pollutants. And the principle was analyzed. The main research contents and results are as follows:(1) The new nano visible light photocatalysts, BiVO4 and Bi2WO6 were prepared with the Bi contained precursor. And the photocatalytic activity of BiVO4 was improved by the surface modification with Ag. The MoS2 NAno-tube mingled Nano-TiO2 micro-sphere catalyst and loaded fly ash micro-sphere photo-catalyst were prepared by sol-gel method.The new coated magnetic photocatalysts TiO2/SrFe12O19 and TiO2/SiO2/γ-Fe2O3 were prepared by sol-gel method.(2) The MB degradation by Ag-BiVO4 was examined under the UV irradiation and visible light irradiation using the O2 in the atmosphere. The compare experiments show that:The presence of Ag significantly enhanced the MB degradation and the optimal content of Ag was 3 wt%. It is confirmed that the calcination temperature on Ag-BiV04 is very important for the photocatalytic activity and the highest removal of MB was obtained by calcination at 100℃. The MB degradation is 95% after 2h. The UV-Vis spectral analysis showed that blue shift resulting from N-demethylation of MB occurred accompanied with oxidative degradation. On the same time, the MB degradation by Bi2WO6 was researched. The results demonstrated that the activity of catalyst which were prepared by hydrothermal process much better than prepared by solid-state reaction method. In the MB/ Bi2WO6 system, MB was effectively degraded by about 80% within 4 h, when the dosage of catalyst was 0.2 g/L, the initial concentration of MB was 10 mg /L and pH was 9.30.(3) The photocatalytic activity of the MoS2 NAno-tube mingled Nano-TiO2 micro-sphere catalyst and loaded fly ash micro-sphere photo-catalyst was examined in different conditions, such as loading volume, catalyst volume, temperature of the heat treatment, and so on. The experimental results show that:The MB degradation ratio is 70% after 2h while the loading volume is 0.4wt%, the catalyst volume is 0.02wt%, the original concentration is 15mg/L, pH>7, the aeration is 1L/min. The MB degradation ratio with TiO2 loaded fly ash micro-sphere photo-catalyst is 80% while it is loaded one time and prepared in 500℃(4) The catalysts, the ferrite coated by a layer of nano-anatase TiO2 (TiO2/SrFe12O19) still had excellent magnetic property and showed strong absorptive property under visible light irradiation. At the conditions of the doped content of barium ferrite of the photocatalyst, initial concentration of MB and pH value being 20 wt%,1.5 g·L-1,10 mg·L-1 and 6.8, respectively, the degradation of MB reached to above 95% in five hours under visible light. Furthermore, the degradation of using the two photocatalysts followed the first-order reaction kinetic model at different conditions in the reaction system. Finally, after magnetic separation of the catalysts for four times, the recovery rate of the catalyst was above 90%, the photocatalytic degradation rate of MB was around 90%. So the magnetic photocatalyst is very easy to recycle. The composite material of TiO2/SiO2/γ-Fe2O3 was synthesized via sol-gel technology, and theγ-Fe2O3 was the magnetic core. The characterization results indicate thatγ-Fe2O3 was red-brown, and the spectrum lines position of X-ray diffraction of TiO2 were in agreement with the standard spectrum of anatase TiO2. VSM results show that the composite has good magnetic property after loaded. The degradation of MB reached to above 98% under UV light, while the degradation is above 65% under visible light. After magnetic separation of the catalysts for two times, the recovery rate of this catalyst was above 97%. After magnetic separation of the catalysts for three times, the photocatalytic degradation rate of MB was around 95 %. Based on it s properties of high photocatalytic activity and easy separation and recovery, the photocatalyst will have a promising application.