| Because of the light stability and high photocatalysis propertie, titanium dioxide as a new photocatalyst for environmental protection has become a hotspot of domestic and international study at present. But, only the ultraviolet light which wavelength less than 387nm can be used by TiO2. The utilization efficiency of solar energy is very low. So researchers make a lot of changes to expand the light absorption range of TiO2 to visible region.H2O2 has a crucial role in the photocatalytic process. On one hand, it is decomposed into HO·in the UV irradation and generates HO·though the reaction with light born electronic as an excellent electron acceptor. On the other hand, H2O2 itself is a strong oxidant, which usually oxidize organic substance directly; as a homogeneous photocatalyst, H2O2 can also occur photocatalytic degradation in the absence of TiO2; and third, the system can generate H2O2 in the photocatalytic process under the ultraviolet light which can accelerate the reaction. At present, the study of TiO2-H2O2 photocatalytic system mainly focus on UV light conditions, although the photocatalytic efficiency has been improved greatly, it's still unable to use the sunlight which limites industrialization and industrial applications. For the reasons, it is necessary to modify TiO2 which can enhance the visible light absorption and further aceletate the utilization of the visible light and the efficiency of degradate pollutants in the TiO2-H2O2 photocatalytic system.Atrazine is a selective translocated pre-and post-emergence herbicide. Because of excellent weeds control efficiency and low price, atrazine is widely used and popularized in the world as one of the most widespread herbicide. As it is diffcult to be degradated in natural media, has a long time of residue, can be bioaccumulation, it not only has a potential threat to grain and food security and pollutes water and soil, but also impacts human's health. So the study of atrazine degradation is significant for bioremediation and environmental protection.In this paper, the photocatalyst (denoted Fe-R)-rutile TiO2 modified by Fe (III) is prepared and characterized. We study the catalytic activity, impact factors and reaction mechanism of the photocatalytic degradation of atrazine with H2O2 by Fe-R under visible irradiation. Key contents and conclusions are as follows:(1) Rutile TiO2 modified by Fe (Ⅲ) is made by soakage when FeC2O4 is used as Fe source. The photocatalyst is characterized and tested by XRD, Laser particle size analyzer, BET and UV-Vis, the impact of calcined temperature on the catalysts' structure and photocatalytic activity is also studied. Rusults show that Fe is loaded on surface of rutile TiO2 in the form of Fe2O3; the visible light absorption range of Rutile TiO2 modified by Fe (Ⅲ) is expanded significantly. The calcined temperature has an important influence on the catalytist particle size and photocatalytic activity. As the calcined temperature raising, the particle sizes of Fe-R are increased because the catalyst crystals have serious reunion phenomenon, while the photocatalytic properties are reduced because the form of Fe come into TiO2 has changed, for which, the content of Fe2O3 decreases while the content of FeTiO3 increases constantly. Comprehensive survey shows that the catalyst calcined at 400℃has the best performance on degradating atrazine and the structure of size.(2) The factors of the photocatalytic degradation of atrazine with H2O2 by Fe-R under visible irradiation are studied when atrazine is used as model contamination, as well as the repeat efficiency of photocatalytic. The experimental results show that the removal of atrazine is up to 95.7% while the removal of TOC is up to 75% when Fe-R-400℃with 1% content of Fe is used as photocatalytic, reaction initial pH is 3, dosage of photocatalytic is 1g/L, initial concentration of H2O2 is 1mmol/L, initial concentration of atrazine is 10mg/L. The rate of dissolved iron and the cycle test of photocatalytic show that Fe is loaded on the surface of rutile TiO2 firmly and the photocatalytic has a good repeat performance and stability.(3) With terephthalic acid as probe material, the generation of hydroxyl radical situation in the (Fe-R)-H2O2 photocatalytic system process is analyzed and determined by fluorescence technology. The degradable rate of atrazine is reduced significantly when add the free radical reaction inhibitors (sodium carbonate and sodium bicarbonate) into the photocatalytic reaction system, moreover, the trend is more obvious as the concentration of inhibitor increases.GC-MS and HPLC are used to trace the intermediate metabolite during the degradation of atrazine. The reaction mechanism is liquid-phase oxidation reaction mechanism:hydroxyl radicals generates from adsorption structure between H2O2 and rutile TiO2 excitated under visible light, which reacts with atrazine in solution and finaly atrazine could be completely mineralized to CO2,H2O and NO3-. |
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