Synergism Of Ultrasound, Ozone And Photocatalysis With Composite Oxide System

To overcome the issue that operating costs of advanced oxidation processes for bio-refractory organic wastewater treatment are high, a growing number of advanced oxidation technology has been developed in order to produce maximum quantities of strong oxidizing hydroxyl free radicals. But the effect of combined techniques has to be improved nowadays. There are many to study in the synthesis and surface modification of BiVO4, Bi2WO6 and other binary or multi-oxide. Meanwhile, surface complex of the composite oxide and titanium dioxide (TiO2) needs to be studied further. Treatment of dye wastewater is very difficult, also current researches have many difficulties in the removal of the color and the presence of toxic organics.The new advanced oxidation treatment of ultrasound, ozone and photocatalysis is the ideal combination in the development of advanced oxidation technology. At present, exploration of synergism of ultrasound, ozone and photocatalysis with composite oxide system photocatalysts "Ag-BiVO4/Bi2WO6-TiO2" in the degradation of methylene blue and methyl orange wastewater is expected to achieve new breakthroughs.This paper studies the degradation process, degradation effect and the mechanism of synergism in the degradation of methylene blue and methyl orange using different combinations of advanced oxidation methods: ultrasound, ozone and photocatalysis with composite oxide system photocatalysts "Ag-BiVO4/Bi2WO6-TiO2".Ag-TiO2 was prepared by precipitation method, Ag-BiVO4-TiO2 and Ag-Bi2WO6-TiO2 were prepared by ultrasonic method.The optimal experimental conditions were determined through different combinations of ultrasonic frequencies, ozone flux and two dye wastewater. The effects of degradation of methylene blue and methyl orange with single, double or synergism between the three advanced oxidation were investigated. Meanwhile, reaction mechanisms of degradation of methylene blue and methyl orange with photocatalysis, ultrasound and/or ozone were studied, too.The conclusions of the experiment were as follows:Three photocatalysts were successfully synthesized.The best experimental conditions:ultrasonic frequency was 28kHz; ozone flow rate was 60mL/min.When the reaction time was 120min, the degradation rates of methylene blue were 80.9% and 82.3% respectively, and the degradation rates of methyl orange were 84.4% and 85.8% respectively to synergism of ultrasound, ozone and visible light photocatalysis with Ag-BiVO4-TiO2 and Ag-Bi2WO6-TiO2. Moreover, the degradation rates of methylene blue were 94.0%,91.0% and 92.9% respectively, and the degradation rates of methyl orange were 94.5%,92.0% and 93.6% respectively to synergism of ultrasound, ozone and UV photocatalysis with Ag-TiO2, Ag-BiVO4-TiO2 and Ag-Bi2WO6-TiO2. The effect of degradation of methylene blue and methyl orange was remarkable. There had synergism between ultrasound, ozone and photocatalysis.The mechanism of synergism had five aspects:cleaning the catalyst surface rapidly and efficiently; reducing the diameter of photocatalysts particle to disperse catalyst particles more scatteredly; accelerating mass transfer rate from organic matter to the surface of the powder catalyst; promoting the mass transfer rate of ozone in the solution to improve the diffusion; generating hydrogen peroxide (H2O2) so as to produce more strong oxidative free radicals.