Photoelectrocatalytic Degradation Of Environmental Pollutants By TiO 2 Electrode

Along with the further steadily development of dyestuff industry in China, dyeing industryhas gradually become a large part in the discharge of industrial wastewater. In general, followingare the characteristics that are always found in dyeing wastewater: pollutant concentration,different types, high salt content, poisonous components, higher chrominance and so on. So thetreatment of dyeing wastewater has become more and more difficult in the industrial wastewatertreatment. Alizarin red is a kind of anthraquinone structure, and it is the typical representative ofdyes that are difficult to degradate. Therefore, the study takes Alizarin Red as the modelpollutant in order to research in a basic science of photoelectrocatalytic degradation of thedyeing wastewater. During the process of researching photoelectrocatalytic degradation of thedyeing wastewater, the choice of electrode materials and the preparation methods are the mainfactors that can affect the electrode structure. Meanwhile, they also deeply affect the photovoltaiccatalytic founcion and stability of electrode. Therefore, the choice of electrode materials and thepreparation methods has become the main problems in the photoelectrocatalytic degradation ofdyeing wastewater. The study chooses Ti as substrate and uses anodic oxidation to preparateTiO₂nanotubes. At the same time, the study takes Alizarin Red as the target pollutant in orderthat can investigate the degradation effect of the preparation electrode, optimize the preparationconditions and change the electrolyte conditions, which aims to improve the degradationefficiency of organic pollutants. Meanwhile, the study also discusses the relationship among theelectrode preparation methods, electrode structure, photoelectric catalytic properties and thedegradation mechanism of Alizarin Red in order to provide the basic theory and experiment ofphotoelectrocatalytic degradation of the dyeing wastewater.The study firstly uses the method of constant voltage anodic oxidation to preparate TiO₂nanotubes electrodes, and then optimizes the conditions of electrode preparation: thecomposition of electrolyte, time and temperature of anode oxidation. After that the study takesAlizarin Red as the target pollutant to analyze and compare the photoelectric catalyticperformance of the preparating electrodes by using light polarization curve method and constantpotential chronoamperometry and so on. It showes that: at room temperature ?about25??, theusage of the electrolyte which contains0.15M containing NH₄F,0.5M H₃PO₄and water:ethylene glycol=3:7, the study set constant voltage as20V and preparate electrode throughanodic oxide for1h, then set the rate of temperature to5?/min from room temperature to500?, constant temperature for3hours and the natural cool to room temperature in muffle furnaceto obtain the crystal neatly TiO₂nanotube electrode. Under that condition, the preparation of theelectrode is showed good stability and combined with the base much better, which is also homogeneous and dense.The color of electrodes are generally deep grey or dark gray with blue.After determining the conditions of electrode preparation, the study uses the optimumconditions of the electrode and takes Alizarin Red as the target pollutant to conduct photoelectriccatalytic degradation. By using cyclic voltammetry, constant potential chronoamperometry andAC impedance method, the study optimizates degradation conditions including initialconcentration, the concentration of Na₂SO₄, illumination time, pH value, the applied voltage andtemperature. The three electrochemical test methods are all showed like that: in0.01mM alizarinred+0.03M Na₂SO₄solution, at natural pH value ?approximately8? or a weak base and roomtemperature ?approximately30?? or slightly higher, the degradation efficiency of alizarin red ishighest. Under0.8V constant potential degradation, the degradation efficiency of alizarin red isincreased after1h, then3.5h degradated completely. Finally, the study uses the optimizationconditions of the electrode and the degradation conditions and takes Alizarin Red as targetpollutant by conducting constant potential chronoamperometry with direct photolysis,electrocatalysis, photocatalysis and photoelectrocatalytic degradation. And then the studycompares the degradation effects and makes a conclusion: since there are synergistic effectsbetween photocatalytic and electrochemical degradation, the photoelectrocatalysis produces thebest effect.