Degradation And Treatment Of Chlorophenols By Electrochemical Technologies

Chlorophenols (CPs), having high toxicity, biorefractory, bioaccumulation and carcinogenic potential, are widely found in the environment and are significant contaminants at many sites selected for cleanup on the USEPA top priority toxic pollutants list. There is need to treat such contaminants in concerning of environmental protection. In present work, various electrochemical methods such as electrocatalytic activation of dioxygen, photo-assisted electrocatalysis, and electrochemical dechlorination by activated carbon loaded palladium, were developed to treat and remediate water and soil contaminated by chlorophenols.Calculation of molecular structure and properties of the whole chlorophenols series by applying Gaussian'98 software were carried out to arrange and assist experiments design based on their stabilities and pKa values. Electrochemical degradation behaviors of chlorophenols were systematically investigated by employing analytical techniques of UV-VIS, Raman spectroscopy and HPLC. For electrochemical degradation of 4-CP, the C-Cl bond was broken and chlorine ion was taken away from the benzene ring as a result of electrophilic addition reaction of hydroxyl radical. The combination technologies of reduction dechlorination and oxidation degradation were proposed.Electrocatalytic activation of dioxygen for chlorophenol degradation was studied. At ambient temperature and atmosphere pressure, dioxygen can be activated to generate stronger oxidants such as HO and HO2 under the electrocatalysis. The process of activated dioxygen with electrocatalysis can significantly improve the degradation of chlorophenol and its intermediate. The promoting factor for 4-CP degradation was 110%. Operational parameters can affect the activation of dioxygen in electrochemical process such as current density, sparged dioxygen rate, pH, and temperature. By applying the technique, acid/alkali and enriched wastewater can be treated without necessary pretreatment with efficiency over 95% for a 240 min treatment of a 50 mg L^-1 concentration. It was found that removal rate of chlorophenol could be 80% for high concentration of 2000 mg L^-1, 40 times as normal, and highly descended for its intermediate of benzoquinone. The preliminary systematic design and economic validity of the technology were analyzed.Photo-assited electrocatalysis technology was developed. Synergetic effects of the combined process were obvious and the promoting factor was 108%. Given the same operating conditions and reaction time, the removal rate of 4-CP followed the sequence: photo-assited electrocatalysis activation of dioxygen > photo-assited electrocatalysis > electrocatalysis activation of dioxygen > electrocatalysis. Photo -assited electrocatalysis technology had good efficiency on the lower concentration chlorophenol wastewater (less than 1000 mg L^-1). The combination of photocatalysis and electrocatalysis could enhance the...