A Study On The Preparation Of Composite Photocatalysts And Its Applications In Pesticide Wastewater

As poisonous and complicated of chemical composition of pesticide wastewater, the degradation and treatment of them is a very difficult problem in the field of wastewater treatment. So it has attracted much attention of the society. In recent years, the semiconductor photocatalysis oxidation technique applied in degradation of environment pollution is one of the researching hotspot by environmental investigator in the whole world. TiO2 has been the focus of the investigations, particularly because of its advantages of stability, low cost, high photocatalysis efficiency and extensive application. The TiO2 photo-oxidation process, however, has not been widely applied due to, for instance, low electron transfer rate to oxygen and high recombination rate of electron–hole pairs and, thus, low photo-oxidation rate of organic compounds on the catalyst surface. Several attempts have been made to enhance the photocatalytic activity of TiO2, such as combination of TiO2 with other semiconductors, covering of the surface with dyes in order to extend the light absorption to the visible range, doping, and partially coating with noble and transition metals. In order to improve the photocatalytic activity and extend energy range of photo-excitation of TiO2, the composite photocatalysts have been prepared by doping the noble metal(Ru and Pt) in TiO2 coated float pearls(FP) in this paper. As the model pollutant of Beta-cypermethrin(BEC) and deltamethrin(DM) to evaluate the photocatalysis activity of composite photocatalysts, the experimental results were as follows:1. Preparation and structural characterization of composite photocatalysts As float pearls(FP) to carrier, RuO2/TiO2/FP and Pt(Ⅳ)/TiO2/FP composite photocatalysts were prepared by Sol-gel-immersion method. The structure, morphology, and element of composite photocatalysts were characterized by the techniques such as SEM, XRD, IR, XPS and the power spectrum. The results showed that the surface of composite photocatalysts is smooth, and the transformation from anatase TiO2 to rutile TiO2 by increase of heat-treated temperature. The composite photocatalyst RuO2/TiO2/FP at the heat-treated temperature of 500℃for 2h, TiO2 mainly was anatase; the composite photocatalyst Pt(Ⅳ)/TiO2/FP at theheat-treated temperature of 250℃for 3h, TiO2 mainly was unformed structure.2. Photocatalytic degradation experimentsThe photocatalysis activities of composite photocatalysts were evaluated by the photodegradation of BEC and DM, and the effects of various conditions on the photocatalytic characteristics were investigated. The experimental results were as follows:(1) Photocatalysis system of RuO2/TiO2/FP: doping 0.3%(molar fraction)RuO2, heat-treated temperature of 500℃, used 5g/L RuO2/TiO2/FP composite photocatalyst, the best air flow rate was 200mL/min, initial pH6.5, 125W mercury lamp as light source, 45 mg/L BEC was degraded 88.1% in 60min. The results showed that the degradation reaction of the BEC almost followed Langmuir-Hinshehwood model, and the photocatalysis reaction is a first-order reaction at lower concentration (≦ 90mg·L-1). The reaction rate constant k0 and the absorption constant K were determined to be 4.94×10-3mg·(L·min)-1 and 14.22L·mg-1, respectively. 8W ultraviolet lamp and 8W fluorescent lamp as light sources, the BEC degradation rate respectively achieves 82.8% and 75.1% in 1 hour.(2) Photocatalysis system of Pt(Ⅳ)/TiO2/FP:①Degradation of BEC(45mg/L): initial pH6.5, doping 1.8%(weight fraction)Pt(Ⅳ), used 4g/L composite photocatalyst, heat-treated temperature of 250℃, the film layers of 5, the best air flow rate was 200mL/min, 8W fluorescent lamp as light source, the BEC degradation rate nearly 90% in 1 hour. The results showed that the degradation reaction of the BEC almost followed Langmuir-Hinshehwood model, and the photocatalysis reaction is a first-order reaction at lower concentration (≦90mg·L-1). The reaction rate constant k0 and the absorption constant K were determined to be 3.04×10-3 mg·(L·min)-1 and 19.5 L·mg-1, respectively.②Degradation of DM(2mg/L): initial pH5.5, doping 1.8%(weight fraction)Pt(Ⅳ), heat-treated temperature of 250℃, composite photocatalyst, the best air flow rate was 200mL/min, the film layers of 5, used 5g/L, 8W fluorescent lamp as light source, DM degeneration rate achieves 84.4% in 1 hour.(3) Degradation of simulated pesticide wastewater:The simulated pesticide wastewater made from BEC45mg/L, DM 2mg/L and parathion 25mg/L has been handled by using two kinds of RuO2/TiO2/FP and Pt(Ⅳ)/TiO2/FP composite photocatalysts, respectively. The results showed that both of composite photocatalysts have all good degeneration activeities. Under the same conditions, Pt(Ⅳ)/TiO2/FP photocatalyst has better photocatalytic activity than that of Pt(Ⅳ)/TiO2/FP, the degeneration rate may be obtained nearly 90% in 2 hour for the simulated pesticide wastewater.