Electrochemical Behaviors And Deactivation Of Ti/IrO₂ Electrodes In 4-chlorophenol Aqueous Solutions

With the fast development of petrochemistry and medicine, waste waters of organic are produced every day. Chlorinated phenols (CPs) are labeled as "Priority Pollutants", due to their slow degradation, bioaccumulation and extreme toxicity. In recent years, as the increasing interests in environment and energy issues, electrochemical oxidation are used as the effective method for the removal of organics from waste waters. However, most of researches show that passivation of oxide electrods caused by the organic film could be happened, even at the boron dopped diamond electrodes. There is rarely research on the electrochemical oxidation of organics or the influence of the organic film on the electrodes still. According to limitation of the study presently, we take Ti/IrO₂ as the model to reseach the electrochemical oxidation of 4-CP and the deactivation of electrodes. What is more, changing the preparetion technics, we modify the anodes to improve their electrocatalytic activities and durability.Firstly, we investigated the oxidation behavior including the soluble oxidation in lower potential and polymerization process in higher potential of 4-CP on the surface of the traditional DSA. At the same time, an electrochemical method was set up to analyze the durability and property of anodes. And the influence of calcinations temperatures on the electrocatalytic activities of Ti/IrO₂ electrodes in acidic and 4-CP aqueous solutions was studied. The results indicate that the electro-activity of Ti/IrO₂ electrodes generally decreases as the sintering temperature increases. And the presents of 4-CP increase the electrocatalytic activities.Secondly, the influence of the heating procedure on electrocatalytic properties of Ti/IrO₂ electrodes in aqueous solution is investigated. Thermal decomposition at single 500℃for each layer is adopted as the standard procedure. As a whole, the electrodes made using the programming heating own higher activity than other. However, the presence of 4-CP in aqueous dramatically increases the electrochemical properties of electrodes prepared by each heating procedures. Programming heating is also found to be the ones with highest activities and seemed to be the least influenced by 4-CP.Thirdly, we investigated the influence of silica on the property of Ti/IrO₂ prepared at 500℃. The SEM and XRD results show that the addition of silica increases the active area of electrodes and minishes the crystal size of IrO₂. And as a result, the anode with 50%mol silica has the best effective to oxide 4-CP. When the percent of silica is over 66%, the property and durability of anodes degraded instead.Finally, we investigate the long-term stability and deactivation characteristics of all types DSA in blank, methanol and 4-CP aqueous solutions. Accelerated lifetime tests are used to identify the long-term stability of electrodes in Na₂SO₄ aqueous solution, CH3OH aqueous solution and 4-CP aqueous solution respectively. It is found that the stability of electrodes increased as sintering temperature increasing firstly and then decreased after went highest value. But in organic solutions, because of presence of Ir, the decline extent of anodes service life prepared at high temperature is smaller than that of anodes prepared at lower calcinations temperatures. The electrodes prepared with heating procedure also have a high durability. The direct reason of this result is the adequately decomposition of H₂IrCl₆ and the protection of Ti in the preparation of anodes with heating procedure. At last, we also find the composition of anodes plays an important part in the testing of service life of anodes modified by adding silica. Due to the interaction of silica and iridium, anodes with 50%mol silica have a longest life in organic solution.