The oxidation of toluene sorbed on activated carbon in the presence of H_2O_2 and manganese oxide

摘要

We investigated the oxidation of toluene sorbed on activated carbon (AC) in the presence of hydrogen peroxide (H_2O_2) and pyrolusite (MnO_2). Sorbed toluene was prepared by reacting a toluene-saturated solution and AC. The amounts of sorbed toluene (mg of toluene/g of AC) decreased as the amounts of AC were increased. The reaction was conducted in a gas-purging (GP) reactor and the gas flow at the outlet of a GP reactor was carefully maintained. As a result, the percentage of toluene captured by ORBO tube was 28% in the control system with pure water. When H_2O_2 was catalyzed by AC (i.e. this forms a hydroxyl radical by electron transfer), approximately 17% of the desorbed toluene was oxidized and 68% of toluene remained on AC which was similar to the control system. However, when pyrolusite (650 mg/L) was added together with H_2O_2 (10, 000 mg/L), only 5% of toluene was captured by the ORBO tube and 55% of toluene remained on AC, which indicated that both desorbed and sorbed toluene was oxidized. Moreover, toluene oxidation increased when concentrations of pyrolusite and H_2O_2 were increased. It was suggested that superoxide anion, which is generated by the reaction of H_2O_2 and pyrolusite, might stimulate toluene desorption and then toluene in the aqueous phase could be oxidized by hydroxyl radical.