Mechanism Of Catalytic Degradation Of Organic Pollutants By Keggin-type Heteropoly Compound

The history of heteropoly acid has been more than one hundred years, it is an important research field of inorganic chemistry. Heteropoly compounds were also known as the polyoxometalates(POMs), formed by condensation of the acid containing oxygen, including heteropoly acid and salts, which have the potential application in catalytic and analytical chemistry, and materials science. The most classical Keggin-type H3PW12O40 are a kind of catalyst with new and efficient catalysts that have clear possess of unique properties, acidity,redox, and the pseudo-liquid phase characteristic. Their distinctive and redox properties can be controlled by changing acidity element composition modified on molecular level or atom level or controlled by the hetero atom or the framework transition-metal atoms. They have been synthesized based on Keggin-type H3PW12O40, which has aroused the enthusiasm of researchers because of their high catalytic and selectivity, moderate reaction conditions, their easy synthesis,non-corrosion low cost and good thermal stability.In this paper, the classical Keggin-type H3PW12O40 was synthesized and modified. The Keggin-type heteropoly compound(NH4)3[PW12O40] and a series of transition metal substituted heteropoly compounds(NH4)5[{PW11O39}MII(H2O)](M = Mn, Fe, Co, Ni, Cu, Zn) were synthesized by choosing NH4+ as appropriate counter ion. The structure of the heteropoly compounds were characterized by Fourier infrared spectroscopy and UV-vis absorption spectra,and the catalytic performance of a series of complex catalysts were investigated and compared by the catalytic oxidation reaction of organic pollutants from Jilin Petrochemical Company.From an experimental and theoretical study, it is suggested that the methyl group and the flexibility of dye molecule play the important role in adsorbing on the surface of POM catalyst.The photodegradation study shows that introduction of transition metal ion leads to an increase in the degradation of malachite green in the following order: Mn < Fe < Co < [PW12O40]3– < Ni <Cu < Zn. Electronic structure analysis shows that a moderate decrease of oxidizing ability of POM catalyst may improve the photocatalytic activity in the degradation of dye under visible–light irradiation. The mechanism of interfacial electron transfer between dye adsorbate and POM catalyst have been studied by using spectroscopic and computational methods, a large rate constant of the electron transfer reaction was observed for the Keggin–type POM,[PW12O40]3–. The large electronic coupling element and low reorganization energy of[PW12O40]3– account for this high efficiency of electron transfer process. Homogeneous catalytic degradation of decabromodiphenyl ethers(BDE209) in 12-phosphotungstic acid(H3PW12O40),the high-performance liquid phase chromatography and the ion chromatography were used to examined the homogeneous catalytic degradation kinetics of BDE209, it was showed that almost the whole of the added BDE209 was removed after 14 h. When BDE209 was completely transformed, extending the aeration time of O2 were used to treated the toxic intermediate products generated during the process of debromination of BDE209. And the possible mechanism for the oxidation of BDE209 in H3PW12O40 has been proposed in this study.