Photocatalytic Degradation Of Simulated Dye Wastewater With Polyoxometalate/Titanium Dioxide Composite

The homogeneous photocatalytic reaction of azo dye solutions(Reactive Black 5, Reactive Red 24 and Acid Brilliant Scarlet 3R) under solar irradiation with polyoxometalate K6ZrW11O39Sn·12H2O(ZrW11Sn) were studied. The effects of the initial concentration of dye solution, the pH value, the photolysis time and the photocatalyst dosage on the photocatalytic reaction were also considered. The kenetics and mechanisms of the photocatalytic degradation of dye solutions under solar irradiation were researched. The results showed that the main influence factors of the photocatalytic reaction are the dosages of photocatalyst, the initial pH values and the initial concentrations of dye solution. When catalyst dosage in the dye solution was 1.0 g/L, and the dye solution was irradiated for 4 h under the sunlight, the decoloration rates of Reactive Black 5(6 mg/L, 20 mL, pH=6), Reactive Red 24(8 mg/L, 20 mL, pH=6) and Acid Brilliant Scarlet 3R(6 mg/L, 20 mL, pH=6) were 65.9%, 45.1% and 40.6%, respectively. The process of photocatalytic degradation of the dye solutions all followed pseudo first-order reactions, which could be described by Langmuir-Hinshelwood kinetics equation. However, the holes oxidation was much more predominant in photo-oxidation process.A novel composite photocatalyst, ZrW11Sn/TiO2, was synthesized by sol-gel method which was characterized by UV-vis diffuse reflectance spectroscopy(UV-vis DRS), X-ray diffraction(XRD), scanning electron microscope(SEM), transmission electron microscope(TEM), fluorescence spectrophotometer(PL), Brunauer-Emmett-Teller surface areas analysis(BET), and X-ray photoelectron spectroscopy(XPS). The optimal synthetic conditions of Zr W11Sn/TiO2 including the doping concentration of ZrW11 Sn and the calcination temperature were investigated. The photocatalytic activity of ZrW11Sn/TiO2 and the influence factors on its photocatalytic degradation of Reactive Black 5 solution with Xenon lamp illumination were also researched. Experimental results showed that ZrW11 Sn /TiO2, has the character of high activity and well stability. Its photocalytic efficiency was superior to the commercial anatase Ti O2. When there are 0.02 g(1.8 wt%) ZrW11 Sn in ZrW11Sn/TiO2 and the calcination temperature was 400℃, the composite photocatalyst has the highest photocatalytic activity. The photocatalytic degradation rate of Reactive Black 5 solution(200 mL, 10 mg/L, pH=6) was 98.5% with 0.04 g ZrW11Sn/TiO2 photocatalyst with Xenon lamp illumination for 60 min.