【正文】 to the direct production of hydroxyl radicals (√OH) and higher utilization ratio of photogenerated holes for redox reactions, so the photocatalytic process is greatly promoted. (2) The method requires no more reagents added, so the cost of the setup and operation does not rise apparently. (3) If residual H2O2 left in the solution, it would depose by itself to H2O and O2, without secondary pollution. 14 2. Experimental . Chemical reagents P25 TiO2 (30 nm primary crystal size) was purchased from Degussa, which contains predominantly anatase (79% anatase and 21% rutile as determined from Xray diffraction). Degradation of 125 mmol/l Rhodamine 6G (chemical grade, dissolved in mol/l phosphate buffer solution with a pH of ) solution was used to evaluate the catalytic ability of the electrochemically assisted TiO2 photocatalytic system. TDW (COD=3320 mg/l and biochemical oxygen demand, BOD5=1540 mg/l) used in the experiments was adopted from a reactive azo dyeing process. . Apparatus All experiments were carried out in the experimental setup (Fig. 1), which consisted of a thermostatic reactor, a threeelectrode potentiostatic unit and an ultraviolet (UV) lamp. The reactor was served by a cylindrical Pyrex glass vessel of 100 ml, which contained the suspension, . wastewater with % (w/w) TiO2 added. The temperature of the suspension was kept constant by circulation of 40 176。 its high value indicated that the wastewater is not much amenable for biological treatment. As an advanced oxidation process, photocatalysis with TiO2 can be an efficient method to mineralize the organic pounds in the wastewater. Assisted by threeelectrode potentiostatic unit, P25 TiO2 particles were applied into wastewater treatment. Fig. 5 showed that COD and BOD5 of TDW were reduced by and %, respectively, after continuous treatment for h. At the same time, COD/BOD5 ratio was reduced from to , indicating that the biodegradability of the wastewater is greatly improved. Fig. 5. COD and BOD5 reduction during the electrochemically assisted TiO2 photocatalytic processes. 4. Conclusion 21 In this article, H2O2 was introduced into TiO2 photocatalytic cell by a threeelectrode potentiostatic unit, an environmentally desirable way, and the posite system showed rather high photocatalytic activity towards organic wastes mineralization. The promotion was attributed to the following two reasons. (1) H2O2 traps electrons faster than O2, and more holes are reserved to react with the adsorbed H2O and surface hydroxide group, leading to the production of more √OH. (2) The reaction between H2O2 and electrons consume the photogenerated electrons, and generate √OH simultaneously. So the quantum yields of OH and the whole availability of the electron/hole pairs is greatly enhanced. The posite system was applied into continuous sample treatment for h, and satisfying results were achieved. The maximum absorption of R6G was decreased by more than 90%。 [Linsebigler et al., 1995]). 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