| Heteropoly acid is a new type of environment-friendly acid catalyst and selective oxidation catalyst. However, the recycling issue mainly hinder its use. In addition, most applications as photodegradation catalyst were investigated under ultraviolet. This thesis focuses on the possibility of photocatalytic degradation of dyeing wastewater with phosphotungstate under visible light.In this paper, phosphotungstate (K3PW12O40·xH2O, (NH4)3PW12O40·xH2O and Cs3PW12O40·xH2O) was prepared and the application as photocatalytic degradation of dyeing wastewater was studied. The physical and chemical properties of phosphotungstate catalyst were characterized by infrared spectroscopy (IR), X-ray diffraction analysis (XRD), thermogravimetric analysis (TG), scanning electron microscope (TEM) and so on. The photocatalytic degradation of organic dyes, such as disperse blue 130, Rhodamine B and Rhodamine 6G was studied by prepared phosphotungstate as photodegradation catalyst.Three phosphotungstate catalysts, K3PW12O40·xH2O, (NH4)3PW12O40·xH2O and Cs3PW12O40·xH2O, were first prepared from phosphotungstic acid and soluble salts such as potassium chloride, ammonium chloride and cesium carbonate with a simple dropping method, followed by calcination at 200℃,300℃and 450℃. IR analysis showed that the freshly synthesized and calcined phosphotungstate, has vibration absorption peak of POa vibration, W=Ot, W-Ob-W, W-Oc-W and vibration peak of bridge oxygen bond of W-O-W, O-P-O, and its infrared spectrum is consistent with phosphotungstic acid's. IR spectra indicated that the introduction of cation does not change the Keggin structure of heteropoly acid anion, and the Keggin structure is stable in activated phosphotungstate. The 2θposition of phosphotungstate's X-ray diffraction peak mainly concentrated at 21-23°,25-28°,29-32°and 35-37°, which verifies the accuracy of the above conclusion. TG analysis showed that the combination of the cation and anion of heteropoly acid improves the stability of bound water and crystal water. TEM analysis showed that (NH4)3PW12O40·xH2O, which was freshly prepared and calcined at 450℃, had particle size of about 500nm, and the particles were well dispersed.The photocatalytic degradation of Disperse Blue 130 with three phosphotungstates was studied. The effects of calcination temperature, catalyst dosage, hydrogen peroxide dosage, visible light irradiation time and recovery times of repeated use on degradation rate were discussed. The results showed that the best activation temperature of K3PW12O40·xH2O, (NH4)3PW12O40·xH2O and Cs3PW12O40·xH20 was 300℃, RT and RT, respectively. The optimal dosage of phosphotungstate was 6 g/L, and the best concentration of hydrogen peroxide was 0.048%. It was found that the catalyst can be recycled with good performance, indicating that it will not cause secondary pollution to the environment. Phosphotungstate can be reused after simple treatment, greatly improves the efficiency and costs of the catalyst, indicating a potential practical application.The photocatalytic degradation properties of cationic dye (Rhodamine B and Rhodamine 6G) with three phosphotungstates were also studied. The experiment was performed under visible light without adding strong oxidant H2O2. The results showed that Cs3PW12O40-xH2O was significantly better than the other two kinds of salt on the photocatalytic degradation activity of Rhodamine B. When the dosage of 300℃activated Cs3PW12O40·xH2O was 6 g/L and visible light irradiation time was 2.5 h, the degradation rate of Rhodamine B was up to 80%. The photodegradation of Rhodamine 6G with three phosphotungstates which were activated at 200℃was the best, and when the amount of Cs3PWi2O40-xH2O which was activated at 200℃was 6 g/L and visible light irradiation time was 2 h, the degradation rate was at 39.1%.
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