Study On Catalytic Mechanism Of γ - MnOOH And CuO Catalyzed By Persulfate Oxygen To Phenol

Recently, advanced oxidation progresses （AOPs） based on sulfate radicals attract more attention in the treatment of organic wastewaters from industries. In this study, various transitional metal oxides were used for the activation of persulfate （PS）, and their catalytic efficiencies and mechanisms in the oxidation of phenol were investigated.Three Mn （oxyhydr）oxides including bixbyite （a-Mn₂O₃）, hausmannite （Mn₃O₄） and manganite （y-MnOOH） were used as persulfate （PS） activators in phenol oxidation. Only y-MnOOH shows a good activity in the oxidation of phenol, and more than 80% could be removed within 360 min in the full pH range, with rate constants in phenol oxidation follow the order of pH 11.0 (2.57×10^-1min ^-1)> pH 7.0 (7.0× 10-3 min ^-1)> pH 3.0 (4.7×10^-1min^-1). Mechanism involved in phenol oxidation is dependent on pH conditions. At pH 3.0, the strong oxidation capacity of y-MnOOH and the oxidative intermediate=Mn（Ⅲ）-"3OSOOSO3- formed between S2O82- and y-MnOOH primarily contribute to phenol oxidation. At pH 11.0, SO₄- and·OH generated during PS activation can efficiently oxidize phenol. At pH 7.0, an oxidative intermediate,≡Mn（Ⅲ）--3OSOOSO3- formed between γ-MnOOH and S2O82- is the predominant oxidative species in phenol oxidation.CuO has been successively used for catalytic oxidation of organic contaminants by PS under acidic and neutral conditions. Nevertheless, it has not been used as catalyst under alkaline condition. Our study shows that phenol could be degraded within 180 min at pH 11.0. We also confirm that=Cu（II） or=Cu（I）, generated from the reduction of=Cu（II） by phenol, can be effectively oxidized to Cu（III） by PS, or activate PS to generate SO₄^- radicals. Although both SO₄^- and the oxidative Cu（III） were found to coexist in the system, Cu（III） but not SO₄^- plays the predominant role in the oxidation of phenol. In addition, after CuO was used for three cycles, phenol removal percentage can still reach 90%, indicating the good reusability of this catalyst.This study provides instructive guidances for the investigation of novel transitional metal oxides in PS activation, and it also enriches our understandings on the catalytic mechanisms of PS involved in different transitional metal oxides.