【文章內(nèi)容簡(jiǎn)介】 he posite system could be used for effective organic wastes mineralization or as a feasible detoxification and color removal pretreatment stage for biological post treatment. Author Keywords: Titanium dioxide。 Rhodamine 6G。 Hydroxyl radical。 Electrolysis。 Wastewater Article Outline 1. Introduction 2. Experimental . Chemical reagents . Apparatus . Photoreactivity . Characterization techniques 3. Results and discussion . Hydroxyl radical generation in electrochemically assisted TiO2 photocatalytic system . Comparison of rhodamine 6G degradation in different bination patterns . Photocatalytic characteristics of rhodamine 6G degradation 13 . Wastewater treatment 4. Conclusion Acknowledgements References 1. Introduction Textile dye wastewater (TDW) is well known to contain strong color, high chemical oxygen demand (COD) and low biodegradability ([Miguel et al., 2020]). Biological oxidation and coagulation by aluminum or iron salts could not treat it adequately. Ozone and hypochlorite oxidation are efficient decolorization methods, but they are not desirable because of the high cost for equipment and operating, and the secondary pollution arising from the residual chlorine ( [Alfano et al., 2020]。 [Hoffmann et al., 1995]。 [Linsebigler et al., 1995]). Over the past several decades, studies have revealed that nanosized TiO2 particles can photocatalytically oxidize many organic wastes into inorganic substances (such as CO2, H2O, etc.) under moderate conditions, without any serious secondary pollution ([Hagfeldt and Gratzel, 1995]。 [Serpone and Pelizzetti, 1989]). However, not only the photo efficiency or activity but also the photo response of TiO2 is not suitable for direct application in environmental optimization ([Kawai and Sakata, 1980]). One of the main factors responsible for these disadvantages is the high rebination of photogenerated electron/hole pairs ( [Li and Li, 2020]). In order to enhance the photocatalytic process, much meaningful work has been carried out. Electro assisted photocatalytic process ( [Hidaka et al., 1999 and Hidaka et al., 1995]), which applied a positive voltage on the TiO2 layer electrode, and modifications on TiO2 by means of noble metal deposition ([Hiramoto et al., 1990]。 [Viswanathan et al., 1990]), metal ions or oxides doping ( [Paola et al., 2020]。 [Yamashita et al., 2020]) and etc. have already been proved promising methods. Addition of oxidants (usually bromate or hypochlorite) is also a theoretically, even more efficient way 。 however, the method is inhibited from practical application for its disadvantages such as higher cost for reagents, and possible secondary pollution from the residual oxidants. In this paper, we attempt to introduce H2O2 into TiO2 photocatalytic cell through an environmentally desirable way to improve the photocatalytic process. Fortunately, electrochemistry offers such a method, which was characterized by the following three potential benefits. (1) H2O2, one product of the electrochemical process, traps photogenerated electrons at a faster rate than O2 for its higher oxidative potential, leading 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。C water in the interlayer of the reactor. The electrolysis unit consisted of a carbon electrode (cathode), a cylindrical Pt (anode) and a saturated calomel electrode (SCE, reference electrode). An 11 W specially prepared UV lamp with an energy peak at λ= nm, free of ozone, was located in the centre of the reactor, providing radiation to excite TiO2. In addition, an air pump was used to aerate the solution to pensate the consumed O2 and a magic stirrer to ensure uniform distribution of the TiO2 particles in suspension. 15 Fig. 1. Setup of the experiment. (a) 11W UV lamp, (b) air pipe, through which a air pump connected (c) SCE, (d) carbon electrode, (e) Pt electrode, (f) magic stirrer, CB and VB represent conduction and valence band, respectively. . Photoreactivity Fifty milligrams of TiO2 was suspended in 50 ml of wastewater and sonicated for 30 min. The resulting suspension was saturated with air for 15 min before the reaction started and kept aerated throughout the experiments. Then a potential of ? V (vs. SCE) was applied on the carbon electrode. Simultaneously the UV lamp was switched on to illuminate the suspension for h. Samples were withdrawn at regular intervals, centrifuged for 6 min at the speed of 11,000 rpm and finally analyzed. . Characterization techni