Synthesis And Properties Of Hybrids Based On Keggin-type Heteropoly Acids By Low-heating Solid-state Chemical Reaction

Inorganic-organic hybrid polyoxometalates possess some active physical and chemical properties, such as mechanical, optical, electrical and magnetic properties, etc. Preparation method about it is important. In addition, how to study its properties under solid state condition is another challenge. Solid-state chemical reaction at room temperature, which has the advantage of high efficiency, low energy consumption, convenient operation, and lack of pollution, has been operated to synthesize functional materials. In this paper, this method was applied to synthesize heteropoly compounds. A series of quaternary phosphonium heteropoly acid compounds and thiourea-heteropoly acid compounds were synthesized from Keggin-type heteroploy acids. And the electrochemical behavior and electrocatalytic activity of compounds were investigated under solid state condition by means of I/PVA/GC electrode and carbon paste electrode. The experimental content of this paper is divided into three chapters.In the second chapter, using methyl triphenyl phosphonium iodide (MePh3PI) and three Keggin-type heteropoly acids, we have synthesized polyhedron hybrids by solid-state chemical reaction at room temperature. The relation between the morphology and the content of crystal water in heteropoly acids was investigated. The morphology of polyoxometalate-based quaternary phosphonium salt hybrids had a strong dependence on the content of crystal water in heteropoly acids. The hypothesis of'semi-solid nonlocalized waters'in solid-state chemical reaction at room-temperature about polyoxometalate was suggested to explain the possible formation mechanism of polyhedrons. The composition of products was determined by means of elemental analysis, IR, TG-DSC and XRD. The morphology of products was observed by SEM. Results of fluorescence spectra of products shown that the polyanions could efficiently quench the fluorescence of MePh3PI. Antibacterial experimental results reveal that the samples have good antibacterial activities against E.Coli and S.Aureus.In the third chapter, the plate-shaped heteropoly compounds were synthesized from Keggin-type silicotungstic acid, thiourea and zinc acetate dihydrate by low-heating solid-state chemical reaction. The composition of products was determined by means of elemental analysis, IR, TG-DSC and XRD. The morphology of products was observed by SEM. By means of I/PVA/GC electrode and carbon paste electrode (CPE), the electrochemical behavior and electrocatalytic activity of compounds under solid state condition were investigated with a CHI660b electrochemical workstation using a typical three-electrode cell. Results indicate that the redox properties of compounds are similar to those of corresponding Keggin-type polyanion. The three peaks of sample were found. But the peak potential values of product were shifted slightly from those of pure heteropoly anions due to the change of electric circumstance around polyanion. The excellent electrochemical properties of I/PVA/GC film electrode were obtained in the acidic solution. The pH of the supporting electrolyte has an effect on the electrochemical behavior of the I/PVA/GC electrode in H2SO4 aqueous solution. The peak potentials for all three redox couples shift negatively with increase in pH. Reduction of compound I in I/PVA/GC electrode is accompanied by the evolution of protons from solution to the electroactive section of the electrode to maintain charge neutrality. Compound retains electrocatalytic activities of Keggin-type silicotungstic anion toward the reduction of nitrite and hydrogen peroxide. The deep reduced POMs have higher electrocatalytic activity than lower reduced POMs. I/PVA/GC electrode possessed the better excellent electrochemical properties than CPE electrode.In the forth chapter, Keggin-type molybdophosphoric acid compounds were synthesized, from thiourea and/or Co2+, Ni2+, Cu2+, Zn2+ by low-heating solid-state chemical reaction. The composition of products was determined by means of elemental analysis, IR, TG-DSC and XRD. Due to determinate the stability of solid state products in PVA, the morphology under solid state condition and in PVA thin film of products were compared by SEM. Results presented that the state of heteropoly compounds was held in PVA thin film. Compounds displayed excellent electrochemical properties. The stability of thin film electrode was good in acidic solution. Reduction of compound I in I/PVA/GC electrode is accompanied by the evolution of protons from solution to the electroactive section of the electrode. The metal ions improved the circular reversibility of hybrids, advancing the current and raising the catalytic efficiency of heteropoly compounds.