Study On The Photoelectrochemical Degradation Of Simulative Dye Wastewater

Photoelectrochemical oxidation process using semiconductor anodes such as TiO₂/Ti is widely used for wastewater treatment, and synergic effect has been found significantly important in these progresses. Generally, the effect of photoelectrochemical degradation in chloride medium is better than that in other electrolyte, and it is considered that the dye degradation is caused both by the active holes which are formed through UV irradiation and by the chlorine species (such as: Cl., Cl₂.) which are formed through the electrolysis of Cl^-. But the mechanism of the synergic effect and the role of NaCl in photoelectrochemical process are still not quite clear.In order to study the mechanism of photoelectrochemical degradation in chloride medium, two parts of work is carried out in the self-designed photoelectrochemical reactor:Part one: In the present work, photochemical, electrochemical and photoelectrochemical degradation of Reactive Brilliant Red X-3B are studied using TiO₂/Ti, Sn_xSb_1-xO₂/Ti and Pd_xRu_1-xO₂/Ti as anodes respectively. 400 ml 4.2×10^-5 mol/L Reactive Brilliant Red X-3B is used, and 1.7×10^-2 mol/L NaCl is chosen as supporting electrolyte. The results show that the photoelectrochemical discoloration efficiency over the three anodes could afford for more than 97% within 60 min. The synergic effect of photoelectrochemical process is observed over all the three anodes, that is, over both semiconductor anodes and conductor anodes. When Pd_xRu_1-xO₂/Ti(with the strongest ablility of chlorine evolution in the former three anodes) is used as photoanode, the effect of dye discoloration is better than the effect using semiconductor anode. It is tentatively inferred that chloride species may be the main oxidants in the photoelectrochemical discoloration of dyestuffs.Part two: The anode PdxRui.xO2/Ti with strong ability of chlorine evolution is used as the main anode in the further research of active species in photoelectrochemical degradation. Reactive Red 3BS with more complicated composition than Reactive Brilliant Red X-3B is used as the substrate. In additon, a controlled experiment is performed using NaCIO as a direct oxidant. A sudden increase of discoloration efficiency caused by photo irradiation is found in the system with NaCIO, just as in EP process with PdxRui.xO2/Ti anode. And active chlorine is found in the solution of electrochemical process by "iodine amount method". These facts suggest that in EP process, H0C1 and CIO' from the hydrolyzation of CI2 generated by electrolysis is immediately photolyzed to HO-, CT and C1-, which can decolorize the solution very quickly. This may be the origin of the synergic effect in photoelectrochemical process. Effects of current density, concentration of electrolyte and pH value are investigated. It is found that in a certain limit, the photoelectrochemical discoloration efficiency of dye increases with the increase of current density and concentration of electrolyte. But for pH value, the best efficiency occurs in the range of 2 to 3.