Magnéli phases Ti_nO_2n−1 as novel ozonation catalysts for effective mineralization of phenol

Magnéli phases Ti_nO_2n−1 have been demonstrated as promising environmentally friendly materials in advanced oxidation processes. In this study, Magnéli phases Ti_nO_2n−1 have been used as catalysts for the ozonation of phenol in aqueous solution for the first time. The materials exhibited excellent catalytic ozonation activities both in phenol degradation and mineralization. When Ti₄O₇ was added, the reaction rate was six-fold higher than that of with ozone alone, while the total organic carbon removal rate was substantially elevated from around 19.2% to 92%. By virtue of the good chemical stability of the materials, a low metal leaching of less than 0.15 mg·L^{− 1} could effectively avoid the secondary pollution by metal ions. Radical quenching tests revealed [rad]O₂ ⁻ and ¹O₂ to be active oxygen species for phenol degradation at pH 5. As semiconductor catalysts, Ti_nO_2n−1 materials show electronic transfer capability. Ozone adsorbed at B-acid sites of the catalyst surface can capture an electron from the conversion of Ti(III) to Ti(IV), and is thereby broken into the active oxygen species. It was interesting to observe that Ti_nO_2n−1 exhibit better catalytic activity for phenol degradation and mineralization with lower n value. The difference in electrical conductivity can be considered as a major factor for the catalytic performances. More highly conductive catalysts show a faster electron-transfer rate and better catalytic activity. Thus, significant evidences have been obtained for a single-electron-transfer mechanism of catalytic ozonation with Magnéli phases Ti_nO_2n−1.