Research Of Shape-controlled α-MnO₂ In Activation Of Peroxymonosulfate For Degradation Of Phenol In Water

In recent years, in the field of advanced oxidation technologies, advanced oxidation technology that based on the sulfate radical got more extensive attentions, at present in the various ways to activation persulfate, transition metal oxides used as heterogeneous catalytic have the characteristics of efficient and security gradually cause for concern.This paper respectively using two methods to prepare alpha crystal type manganese dioxide(α-MnO2)catalyst, use PMS(Peroxymonosulphate) as oxidant and phenol as the target pollutant, examines the heterogeneous α-MnO2 / PMS system effect on the degradation of phenol in water, finally considered the change of preparation conditions of the catalyst and the initial reaction conditions for phenol degradation effect, and discusses the two methods of preparation of α-MnO2 catalytic performance difference.Prepared by precipitation calcination method of α-MnO2 catalysts, and then characterized the catalyst by X-ray diffraction and scanning electron microscope. Preliminary study of the catalytic effect for PMS, the experimental results show that 60 min phenol degradated 87.03%, the TOC(Total Organic Carbon) removal rate was 74.52%, shows its good catalytic activity. Precipitation calcination method by studying the influence of preparation conditions on the catalytic activity of α-MnO2, determine the best preparation conditions for the α-MnO2 is that calcination temperature is 300℃ and the time for calcination is 2 h; Reaction conditions for room temperature pH = 7, phenol concentration 50 mg/L, the PMS concentration of 1 mmol/L, α-MnO2 1.5 g/L, phenol can be completely degraded in 60 min. Effect of catalyst reused four times, drop less than 5%, show its stable performance.By potassium permanganate hydrothermal prepared the α-Mn O2, and then characterized the catalyst by X-ray diffraction and scanning electron microscope. Preliminary study of the catalytic effect for PMS, the experimental results show that the 10 min when the phenol degradation rate is 100%, 60 min TOC removal 93.12%, shows that this catalyst has very good catalytic ability. By studying hydrothermal method the influence of preparation conditions on the catalytic activity of α-MnO2, determined the best preparation conditions for hydrothermal temperature is 160℃, hydrothermal time of 6 h. Reaction conditions for room temperature pH = 7, phenol concentration 50 mg/L, the PMS concentration is 0.65 mmol/L, the α-Mn O2 0.25 g/L, phenol can be completely degraded in 60 min. Preliminary determine SO4·- and OH· exist in the reaction system. Effect of catalyst reused four times, drop less than 7%, show its stable performance.Through the determination of the specific surface area, found that the special preparation will make α-MnO2 crystal has a higher specific surface area, this is the apparent reasons for the difference between its catalytic activity. Characterize by XPS, speculated that the catalytic reaction mechanism is: the catalysts in the catalytic reaction occurs ≡ Mn(Ⅳ) and ≡ Mn(Ⅲ) switch and produce sulfate radical, and the ≡ Mn(Ⅲ) content of hydrothermal method α-MnO2 is higher than α-MnO2 that prepared by calcination method, that is from the deep level to explain the mechanism of the catalytic activity of α-MnO2 hydrothermal method is higher than that of precipitation of α-MnO2.