De-colorization Of Dye Wastewater Using Complex Rotating Disk Thin-film Pc Reactor

As a new wastewater treatment technology, a lot of work has been done relating to enlarge TiO2 thin film electrode areas, select suitable electrode substrate, and material modification of electrode substrate. However, the work for designing high efficiency PC reactor is not enough, leading to the lag of its application to water treatment. The photo-anode employed in photoelectrocatalytic (PEC) reactors in laboratory is always immerged completely into solution, and the irradiation light has to penetrate a very thick fluid layer to reach the catalyst surface, which results in low efficiency of irradiation light utilization. In order to solve the above problem, we firstly developed a new type of reactor: rotating disk thin-film PEC reactor (RPEC). The bottom half of the electrode (rotating disk) of RPEC is immerged in the solution, and the other half left in the air. Micron thick film is formed on the surface of the half electrode in the air through rotating, which greatly reduces the the light loss before it reaches the catalyst surface. Therefore, the efficiency of mass transfer of solution is strengthened. On the basis of RPEC, we further developed dual rotating disks thin-film photocatalytic reactor (DRPC), whose anode and cathode rotate at the same time and no external electric field is needed. Photogerenated electrons can be driven from TiO2 to Ti substrate by Schottky Barrier between metal Ti and N-type semiconductor (TiO2) instead of by bias potential, and then to Cu surface, where those photogerenated electrons can participate in dye oxidation. As a result, treatment efficiency is improved and energy cost decreased. However, there still exist some problems, such as the high cost of titanium substrate and complexity of electrode structure. In order to solve the problem of DRPC, this paper designed an improved reactor: complex rotating disk thin-film photocatalytic reactor (CRPC).It takes metal disk as the substrate, one side of which coated TiO2 film as light anode, the other side of copper cathode. Therefore, the dual disk of DRPC is transformed into a complex one, and the electrode structure is simplified. Moreover, CRPC can take stainless steel as the substrate, thus reduces the cost and improves substrate conductivity. Besides, the corrosion of the stainless steel substrate can be prevented from acidic solution, for the substrate is well coated with TiO2 and Cu film. The detailed work is described below:1. The TiO2 anode is prepared by titanium and stainless steel substrate respectively, and the copper cathode is made by EDTA method and tartaric acid method. Regarding dye solution as the target pollutant, the decolorization efficiency of dye solution is used to evaluate the photoelectrocatalytic capability of CRPC. Results show that: CRPC-Steel has better photoelectrocatalytic capability than CRPC-Ti, for the decolorization efficiencies of CRPC-Steel to 7 kinds of dye solutions rang from 35.0% to 95.5%, and CRPC-Ti from 23.5% to 92.5%; The copper layer made by EDTA method is more uniform and adhesive than by tartaric acid method, and the photoelectrocatalytic capability of it is better as well.2. The influence of reaction condition to the photoelectrocatalytic capability of CRPC-Steel was studied. The best experimental conditions are: initial concentration of RBR 20mgL-1, pH 2.5, Na2SO4 2.0g L - 1, rotating speed 60rpm. The photoelectrocatalytic capability of CRPC-Steel to easily decolorizated dyes is similar with that of DRPC-Ti, while its photoelectrocatalytic capability to hardly decolorizated dyes is better than DRPC-Ti. As the stainless steel substrate of CRPC-Steel is well coated with TiO2 and Cu film, the corrosion of stainless steel can be prevented from acidic solution.3. Exponential function was employed to establish the kinetics model of CRPC-Steel: Ct=C0exp( -3.8781C0-0.47074 pH-2.1958CE0.08055 t) The model can describe the pseudo first order of RBR solution well degraded by CRPC-Steel.4. The decolorization mechanism of CRPC-Steel was preliminary studied. The results demonstrate that in the process of decolorization, the chromophore"-N=N-"of RBR is destroyed, and Benzene group and naphthalene ring structure are changed as well. Photo-degradation and adsorption process contribute little in the reaction process, while photocatalysis contributes 22.5% to decolorization efficiency and bipolar oxidation process plays the greatest part. Basically, no Cu-Fe primary cell reaction exists, but the copper cathode takes reaction with DO in the thin-film, and the generated Cu ions have little change to the color of RBR solution.