Activation Of Peroxymonosulfate By Manganese Dioxide For Degradation Of Dye Wastewater

Dye wastewater is a kind of the typical refractory industry wastewater with high COD, high chromaticity, high toxicity and poor biodegradability. The traditional wastewater treatment technologies, such as adsorption, flocculation precipitation and biodegradation method, are difficult to adapt to the wastewater treatment of various dyes. Recently, an advanced oxidation technology based on sulfate radicals （SO₄） as the main active species has attracted more and more attention. This technology has several advantages:（1） the solid oxidant is more stable than H₂O₂ and O₃; （2） pH has little effect on the activation of oxidant for generating SO₄^-·; （3） SO₄^-· has a long half-life time, which can greatly improve the efficiency of the degradation of organic pollutants..MnO₂ is a kind of common transition metal oxides. The excellent physical and chemical properties of MnO₂ might be ascibed to the diversity of its crystal structure. MnO₂ are widely used as molecular sieve, oxidant, catalyst, battery materials and sensor materials. For its rich sources, low price and green pollution-free, MnO₂ has a broad prospect in the activation of PMS for the degradation of dye. In this paper, the main work includes the following several parts:（1） MnO₂ was prepared by a simple hydrothermal method and characterized by X-ray diffraction （XRD）, Scanning electron microscope （SEM） and Transmission electron microscope （TEM） and N2 adsorption. Results show that the XRD peaks of synthesized sample matches with the standard peaks very well （JCPDS No.01-072-1982） and the MnO₂ sample presents a nanowire morphology with the width of 50-100 nm. The specific surface area of the sample is about 228.7 m2/g.（2） The degradation of triphenylmethane dyes through MnO₂/PMS system was investigated. In the experiments, Malachite Green was used as the representative pollutant. The results show that the first-order kinetic model can well describe the degradation kinetic of malachite green with the combination of MnO₂ and PMS. With increasing of PMS concentration, MnO₂ dose and reaction temperature, the degradation efficiency of Malachite Green was improved. According to Arrhenius equation, the activation energies of MnO₂ for degradation of malachite green is 47.3 kJ/mol. Reusability experiments show that MnO₂ has stable catalytic activity and can be reused. UV/Vis and GC-MS technique was used to analyze the mechanism of the degradation of Malachite Green.（3） The degradation of xanthene dye through MnO₂/PMS system was investigated. In the experiments, Rhodamine B was used as the representative pollutant. The results show that Rhodamine B degradation curves were fitted well to the first order reaction kinetics. PMS concentration and MnO₂ dose present a linear relationship with Rhodamine B degradation reaction rate constant. In addition, MnO₂/PMS system also showed good performance in the mineralization of Rhodamine B. Finally, UV/Vis and GC-MS technique was used to analyze the mechanism of the degradation of Rhodamine B.（4） Quenching tests of radicals by using ethanol and tert-butyl alcohol were applied to differentiate the contribution of major reactive species for the degradation of RhB in the MnO₂/PMS system. The mechanism of PMS activation on MnO₂ for organic dyes degradation was suggested.