Efficient oxidation of phenol by persulfate using manganite as a catalyst

• γ-MnOOH was an efficient catalyst for persulfate activation in phenol oxidation.
• Phenol can be effectively oxidized in the full pH range.
• Mechanisms involved in phenol oxidation were pH-dependent in PS-γ-MnOOH system.

In this study, three trivalent Mn (oxyhydr)oxides, bixbyite (α-Mn2O3), hausmannite (Mn3O4) and manganite (γ-MnOOH) were synthesized and used as persulfate (PS) activators in phenol oxidation. Of these three Mn (oxyhydr)oxides, only γ-MnOOH shows a good catalytic activity in PS activation with more than 80% phenol oxidized within 360 min in the full pH range. With increasing concentrations of PS and γ-MnOOH, phenol removal efficiency increased. TOC results also suggest that phenol oxidation at pH 11 is more complete than those at pH 7 and 3. We further confirm that mechanism involved in phenol oxidation is pH dependent in γ-MnOOH/PS system. Although SO4− and OH were both found under acidic and alkaline conditions, they did not contribute equally under different pHs. At pH 11, SO4− and OH generated from PS activation efficiently oxidize phenol. At pH 3, the strong oxidation activity of γ-MnOOH and an oxidative intermediate formed between S2O82− and γ-MnOOH primarily contribute to phenol oxidation. At pH 7, an oxidative intermediate formed between γ-MnOOH and S2O82− is the predominant oxidative species in phenol oxidation.

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