Efficient oxidation of phenol by persulfate using manganite as a catalyst

In this study, three trivalent Mn (oxyhydr)oxides, bixbyite (α-Mn 2 O 3 ), hausmannite (Mn 3 O 4 ) 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 SO 4 − and OH were both found under acidic and alkaline conditions, they did not contribute equally under different pHs. At pH 11, SO 4 − 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 S 2 O 8 2− and γ-MnOOH primarily contribute to phenol oxidation. At pH 7, an oxidative intermediate formed between γ-MnOOH and S 2 O 8 2− is the predominant oxidative species in phenol oxidation.