Synthesis And Properties Of Two Inorganic-organic Hybrids Based On Keggin-type Heteropolyacids

The synthesis and properties of new structure polyacid compounds have always been an important research content of polyacid chemistry.In this paper,two cases of inorganic-organic hybrids material based on Keggin-type heteropolyacids were synthesized,and their composition and structure were characterized by single crystal X-ray diffraction,infrared spectroscopy（IR）,thermogravimetric curve,powder X-ray diffraction（XRD）,inductively coupled plasma spectrometer（ICP）etc.,and the pairing of synthetic compounds was explored.The photocatalytic activity of organic dyes.The main innovations are as follows:1.Two inorganic-organic hybrids material based on Keggin-type heteropolyacids were synthesized by hydrothermal method.The chemical formulas are{[Cu₂（4,4’-bipy）₄（H₂O）₄](SiMo₁₂O₄₀)·18H₂O}_n（1）,{[Cu₂（4,4’-bipy）₄（H₂O）₄](PMo₆W₆O₄₀)·18H₂O}_n（2）（bipy=bipyridine）.The structural analysis shows that the two compounds are isomorphic,and Cu²⁺is six-coordinated to combine with the N atoms on the four 4,4’-bipy and the O atoms on the two water molecules to form[Cu（4,4’-bipy）₂（H₂O）₂]_n²ⁿ⁺two-dimensional layer structure.Heteropolyanions are arranged in the interlayers by electrostatic interaction with complex cations[Cu（4,4’-bipy）₂（H₂O）2]_n²ⁿ⁺.The properties of the compound were characterized by infrared,powder X-ray diffraction,solid ultraviolet-visible diffuse reflectance spectroscopy,etc.2.The photocatalytic degradation of methylene blue catalytic performance of the synthesized compound was studied,and it was found that the catalytic activity of compound 2 was significantly better than that of compound 1 at room temperature.The investigation results show that the reason for the difference in photocatalytic performance is the different types of polyacid anions:SiMo₁₂O₄₀^4-anion has a strong binding ability to photogenerated electrons,and it is difficult for photogenerated electrons to combine with H₂O₂,which hinders the progress of photocatalytic reaction.The binding capacity of PMo₆W₆O₄₀^3-anion to photogenerated electrons is weaker than that of SiMo₁₂O₄₀^4-anion,so the photocatalytic activity is different in the process of photocatalytic degradation of methylene blue（MB）.The photocatalytic reaction mechanism was studied using isopropanol（IPA）,triethanolamine（TEOA）and 2,2,6,6-tetramethylpiperidine oxide（TEMPO）as free radical scavengers,indicating that the catalytic process is First,a catalyst absorb light to excite electrons from the valence band（VB）of the catalyst to the conduction band（CB）,leaving holes（h⁺）in the valence band,and the photogenerated electrons（e^-）quickly migrate to the surface of the catalyst and combine with hydrogen peroxide（H₂O₂）to form·OH,formed·OH can deprive water molecules of hydrogen to generate water and new·OH radicals,to achieve·OH regeneration,so that the photocatalytic reaction can continue.