Oxidative coupling and dechlorination of aromatic compounds on modified activated carbon

Dechlorination by oxidative coupling during the adsorption of mono-chlorophenols (mono-CPs) onto activated carbon (AC) was investigated, and the effects of various parameters such as amount of dissolved oxygen, surface structure and temperature of solution on dechlorination amount were examined. Under anoxic conditions, the amounts of adsorption and dechlorination for mono-CPs decreased compared to conditions where oxygen is present. This result indicated that the oxidative coupling would depend on dissolved oxygen. It is known that dissolved oxygen was transformed into reactive oxygen species on the AC surface. Therefore, we propose that reactive oxygen species originating from dissolved oxygen react with chlorophenol, causing dechlorination and the oxidative coupling by radical reaction. The introduction of pyrrole- and/or pyridine-like structures in the carbon by NH3 gas treatment at temperatures above 700 °C promoted the reduction of dissolved oxygen, which caused the increase in the amount of dechlorination. On the other hand, HNO3 oxidation of AC noticeably decreased the amount of dechlorination, indicating that the acidic functional groups possessing an electron-withdrawing ability inhibited the reduction of dissolved oxygen on the AC surface. It was also found that the amount of dechlorination and its rate were influenced by the temperature of the solution.