Photodegradation Of Orange Ⅱ By Mesoporous TiO₂

Production of textile dyestuffs in China takes up more than half of that of the world. The printing and dyeing industry that were difficult to be degraded because of the high chroma, high toxicity, has a paramount potential environmental impair. Dyes can enter the water body which can be proved to be carcinogenic to living systems. There are many kinds of dyes. Decolouration of dye effluent does not occur when treated aerobically by municipal sewerage systems. Dye effluent treatment gained more and more attention.TiO2 nanoparticles are effective for the photocatalytic degradation of various organic pollutants in water, owning to its unique photocatalytic efficiency, low cost, nontoxicity and high stability. However, the use of TiO2 nanoparticles (P25) in slurry photoreactors may constitute a limitation because of filtration problems due to the small size of the particles that should be removed from the treated stream. So the mesoporous materials with tampered pore structures, high surface areas and high ability of charge separation have expected in the field of adsorption and catalysis. However, the mesoporous TiO2 was seldom used as a catalyst to degrade dyes.Mesoporous TiO2 was prepared and characterized through X-ray diffraction (XRD) technique, Scanning Electron Microscopy and Transmission Electron Microscopy. The pore structure and adsorption capacity of the mesoporous spherical TiO2 catalysts was tested by N2 adsorption-desorption experiments. Those results together prove the existence of mesoporous structures.Control experiment, different light intensity experiment, adsorption of different concentrations of OrangeⅡexperiment, photocatalytic degradation of different concentrations of OrangeⅡexperiment, photocatalytic degradation of OrangeⅡin defferent initial solution pH experiment, recycling experiment, photocatalytic degradation of OrangeⅡwith plus ions experiment were taken. TOC, COD, sulfate formation, luminescent bacteria acute toxicity were detected during the photodegradation in natural initial pH value. GC-MS, Fourier-transform infrared (FT-IR) were used to analysis intermediates. Free radical scavengers were usd to test the active speices during the photodegradation. Generated hydrogen peroxide was also tested and analyzed during the photodegrdation to understand free radicals which were took responsibility of the photodegradation.The results show that photodegradation in initial solution pH 6.38 was the optimal condition with the highest removal of Orange II. Ion chromatography results showed that sulfur gradually released from the Orange II molecules, which was consistent with results of FT-IR spectrum. With the results of GC-MS, we can see that the Orange II molecules photodegraded into small organic molecules. TOC, COD results showed that Orange II has been degraded and the toxicity was reduced after photocatalysis.Free radical scavengers were used to determine the active radical species in the photodegradation systems of OrangeⅡby mesoporous TiO2 and the titanium dioxide (P25).The results showed that the two systems shared the same free radical species, and photo-oxidation hole(h+) took the main responsibility of the photodegradation. The roles of O2-·superoxide free radicals and singlet oxygen 1O2 were obvious. However, the role of hydroxyl radical·OH was negelible.