Activation Of Peroxymonosulfate By Fe₂（MoO₄）₃ To Degrade Of Organic Pollutants

The increasing range of pollutants in water and their potential harmful effects on the environment have become a common problem.Therefore,how to remove the organic pollutants in rainwater runoff pollution has become the focus of urban water environment remediation.Now we need a more effective,environmentally friendly and low-cost method to degrade and remove emerging pollutants.At present,persulfate dominated advanced oxidation technology as a new technology has come into our sight,because of its simple design,low cost and effective removal of pollutants.However,the selection of suitable catalyst is the main determinant of catalytic efficiency.Among them,iron-based catalyst is the most widely used and the lowest cost PMS catalyst,but the traditional iron-based catalyst has many problems,such as large amount of iron leaching,complex synthesis process,low degradation efficiency and so on.In view of the above problems,this study intends to synthesize stable,efficient and economic Fe₂（MoO₄）₃ catalyst to activate peroxydisulfate（PMS）to degrade organic pollutants in water by environmental friendly and simple biological template method.The main research contents and conclusions are as follows:（1）A series of Fe/Mo based oxide（Fe₂（MoO₄）₃）mesoporous composites with different Fe/Mo molar ratios were synthesized and characterized.The main methods and results are as follows:using coffee grounds as bio-templates,the coffee grounds were impregnated with metal solutions with different Fe/Mo molar ratios,and then calcined at 400℃to remove the templates.The preparation process was simple,environmentally friendly,economical and nontoxic.The results showed that the ratio of Fe to Mo is 8:1,6:1,4:1,and the catalyst is Fe₂（MoO₄）₃.When the dosage of Mo increases to 2:1,the catalyst is the mixture of Fe₂（MoO₄）₃ and MoO₃.When there was only iron,the material was amorphous iron oxide,while when there was only Mo,the material was MoO₃.The amorphous iron oxide obtained before Mo doping had smooth surface and irregular structure.After doping with phosphomolybdic acid,many pores and square plate-like scales were formed on the surface of Fe₂（MoO₄）₃-4.The specific surface areas of amorphous iron oxide and Fe₂（MoO₄）₃ catalysts were 46.87 m²/g and27.87 m²/g,respectively,and the average pore sizes were 4.63 nm and 35.55 nm,respectively,indicating that the surface of the catalysts was changed from microporous to mesoporous.According to XPS analysis,Fe₂（MoO₄）₃ was mainly composed of Fe（Ⅲ）and Mo with five valence and six valence.The internal oxygen is mainly in the form of lattice oxygen（O_α）,chemically adsorbed oxygen on the surface,weakly bonded oxygen（O_β）and adsorbed water（O_γ）.（2）In this paper,the effects of Fe₂（MoO₄）₃ with different ratios on the degradation of RhB by PMS were compared,and the influencing factors of the catalytic effect were explored.The results showed that the order of catalytic performance is 4:1>2:1>6:1>8:1,and the effect of amorphous iron oxide before adding Mo is worse than those of these proportions.It can be seen that the combined action of Mo and Fe improves the catalytic performance of the catalyst,and Mo in Fe₂（MoO₄）₃ may have a potential role in improving Fe³⁺/Fe²⁺cycle.Through the analysis of the environmental factors affecting the degradation performance of Fe₂（MoO₄）₃/PMS activation system,it was found that the degradation removal rate increased with the increase of PMS concentration;the degradation removal rate increased with the increase of catalyst dosage;the degradation effect increased with the increase of solution temperature from15℃to 25℃;p H had little effect on the degradation removal rate,and the p H had excellent effect in the range of 3-11,and the optimal p H value was 3.In the interference experiment,Cl^-and NO₃^-had no inhibitory effect at low concentration.The inhibition of H₂PO₄^2-and HA was obvious.Fe₂（MoO₄）₃/PMS activation system had very good catalytic degradation performance for organic pollutants such as dyes（Mo,MB）and antibiotics（PEF,CIP）,and the catalytic degradation was fast and efficient.For natural water,the degradation effect of Fe₂（MoO₄）₃/PMS activation system was inhibited.The results showed that the degradation rate of RhB remained at 80%and the iron leakage rate was 0.048 mg/L after 5 times reuse of Fe₂（MoO₄）₃.Fe₂（MoO₄）₃had good reusability and structural stability.（3）In order to further explored the degradation mechanism of the activated system,the active oxidation species in Fe₂（MoO₄）₃/PMS activation system were mainly·OH,SO₄^·-and ¹O₂ by quenching and EPR experiments.Through the analysis of intermediate products by LC-MS,RhB was degraded in Fe₂（MoO₄）₃-4/PMS system through four steps:n deethylation,chromophore cracking,ring opening and mineralization.The degradation mechanism in Fe₂（MoO₄）₃/PMS system:on the one hand,Mo element in the catalyst can promote the conversion of Fe（Ⅲ）to Fe（Ⅱ）as a cocatalyst.On the other hand,in Fe₂（MoO₄）₃/PMS system,Mo（VI）peroxides and lattice oxygen（O_α）can produce singlet oxygen,which can degrade RhB.In this paper,the catalytic performance,influencing factors,stability,universality and degradation pathway of Fe₂（MoO₄）₃/PMS activation system were analyzed.Meanwhile,the degradation mechanism of Fe₂（MoO₄）₃/PMS activation system was revealed from two ways of free radical and non free radical,which provided more theoretical support for the practical application of activation system.