Periodate activated by different crystalline phases MnO2 for profound oxidation tetracycline hydrochloride: Oxygen vacancy-dominated active pivots and mechanism

Four different crystalline phases of MnO2 (α-, β-, γ-, -and δ-) catalysts were prepared to effectively activate periodate (PI, IO4-) for tetracycline hydrochloride (TC) degradation. The as-synthesized δ-MnO2 showed superior activity for PI catalytic activation than that of α-, β- and γ-MnO2, which could attain 100 % decomposition efficiency for 0.4 g∙L-1 of TC within 15 min. By characterization analysis including XPS, H2 - TPR, O2 - TPD, and EPR to investigate the surface properties of MnO2, the crucial role of oxygen vacancy (Ov) in PI activation was testified. It was demonstrated that the content of Mn(II) + Mn(III) (R2 = 0.856), adsorbed oxygen (Oads) (R2 = 0.904) played an important role in the emerge-annihilate cycling of Ov on the MnO2 surface. The formation of Ov was caused by sharp Jahn-Teller distortion of high content Mn(II) + Mn(III) and Oads overflow. The existence of Ov accelerated the electron transfer to improve the PI activation. The primary contribution of singlet oxygen (1O2) was proved by the radical scavenging and ESR tests, followed by iodate radical (IO3∙) for TC degradation. This study provided insight into the mechanism of PI activation on the MnO2 surface.