The Preparation, Characterization Of Modified Titanium Dioxide And Its Application Of Photocatalytic Degradation Of Dyes Wastewater

A systematic study of the preparation, token and photocatalytic activity of quantum-sized titanium dioxide and modified titanium dioxide is presented. The photocatalytic oxidation reaction process of dye molecular and the inorganic species from the photocatalytic oxidation of organic compounds is investigated and tested. The photocatalytic degradation kinetics is also investigated. And the photocatalytic process is applied to treat dye wastewater.Titanium dioxide is modified by means of metal oxide depositing, metal ion doping, and precious metal depositing. The crystal structure, particle size, surface area, band-gap energy and optical absorption properties of modified titanium dioxide have been investigated and compared with pure titanium dioxide by means of XRD, BET, TEM, LRS, DRS, XPS. The results are showed as follows: (1) The photo-activity of titanium dioxide increases drastically with the decreasingof the crystallite size, indicating that quantum size effect play a very importantrole in improving the photo-activity of titanium dioxide. (2) Metal oxide deposition or ions doping inhibits phase transformation to rutile, andmake the quantum size of modified titanium dioxides decrease;on the contrary,the size of particle of titanium dioxides deposited precious metal significantlyincreases. (3) Gold ion, WO₃, or Sb₂O₃ deposition in titanium dioxide all enhances the propertyof UV-visible light absorption. (4) Binding energy of Ti2p increases owing to WO₃, or Sb₂O₃ deposition, anddecreases owing to doping gold ion. The band-gap potential energy of Au37Ti02 is only 2.43eV, corresponding to absorption threshold at 501nm;which show red-shifted absorption spectra.Photocatalytic degradation of methylene blue and methyl orange in modified semiconductor nanopowder suspension irradiated by high-pressure mercury lamp is comparatively investigated. As a result, the addition of WO3, ZrO2, Sb2O3, gold ion or gold in titanium dioxides all greatly enhances its photocatalytic behavior of degradation of methylene blue, while their optimum molar fraction is respectively 2%, 5%, 2%, 0.5%, 0.5%. And the addition of Y2O3, gold ion or Pt in titanium dioxide enhances its photocatalytic behavior of degradation of methyl orange, while their optimum molar fraction is respectively 5%, 0.5%, 0.96%. Photocatalytic behavior of degradation of methylene blue solution of Au3+ /WO3/TiO2 is less than that of Au3+/Ti02, implying that the simultaneous addition of gold ion and WO3 in titanium dioxide do not work in coordination with enhancement its photocatalytic behavior. Addition of gold ion in titanium dioxides greatly enhanced its photocatalytic behavior of degradation of methyl orange, however greatly slow down the degradation of methyl orange, implying that the mechanism of metal ions doping be absolutely different with that of precious metals deposition. A comparative study of photocatalytic degradation methylene blue and methyl orange suggests that Pt/TiO2 have a higher photocatalytic activities of the oxidation of methyl orange and lower photocatalytic activities of the oxidation of methylene blue owing to stronger surface acidity and more positive charges on the surface of Pt/TiO2.The photocatalytic decolorization process and degradation products of methylene blue, rhodamine B, methyl orange, and cresol red, malachite green are investigated by means of UV-Vis absorption spectra, ion chromatography and Langmuir-Hinshelwood kinetics equation in TiO2 suspension irradiated by high pressure mercury lamp. The results are showed as follows: photocatalytic degradation of organic compounds is greatly effected by pH value. After illuminated for 30 minutes, a part of organic compound is completely mineralized and Cl\ NH/, NO3\ SO42' from the photocatalytic oxidation of organic compounds are identified. The addition of H2O2 promotes more organic molecular to be completely mineralized. The purification rate of COD in 5 kinds of solution ranges from 71.7% to 88.7%.The photocatalytic degradation of methylene blue in solar irradiating with TiO2 suspension is investigated in the shallow pond solar photocatalysis reactor. The kinetic relationship between the first-order reaction rate constant k and average radiant intensity I, and the aperture to volume ratio A/V is expressed in a new kinetics equation built in this works. At meantime, another new equation is built to calculate apparent quantum yield, which is 0.1683%-0.3016% in this works. The apparent quantum yield increases with the increasing of A/V and initial concentration, and with the decreasing of I.A new reactor system is designed to combine flocculent process with photocatalytic reactor and applied to treat dye wastewater from a dye mill. The removal rate of COD and BOD5 is up to 90.1% and 93.7% respectively. The system can treat dye wastewater with a higher organic concentration.