Preparation And Functionalization Of Polyoxometalate-based Microtubes

In this thesis, the classical Keggin-type polyoxometalate （POM） with potentialapplications in industrial catalysis is selected as a substrate, four kinds of POMmicrotubes have been synthesized through a simple free-template aqueous synthesismethod, i.e., Zn²⁺and Cd²⁺cation-tuned Keggin-type POM microtubes, bioactivemolecule-doped Keggin-type POM microtubes, Mo/V-substituted Keggin-type POMmicrotubes, and Keggin-type heteropoly blue microtubes. Synthesis conditions,growth mechanism, chemical and physical properties of the POM microtubes arediscussed.1. Transition metal cations with abundant physical and chemical properties canbe introduced into the POM microtubes through replacing part of K+or Na+ions inthe microtubes, so that the POM microtubes are endowed with the properties oftransition metals. Based on this principle, Zn²⁺and Cd²⁺cation-tuned POM (Zn-SiW₁₂and Cd-SiW₁₂) microtubes are prepared. Fluorescence emission spectra of theobtained microtubes dealt with an ethanol solution of8-hydroxyquinoline （Q） aremeasured, which display fluorescence of ZnO2and CdQ₂.2. During the study on mechanism for the formation of the POM microtubes, wefound that some organic components can be doped into the POM microtubes undersuitable conditions. Thus, the POM microtubes may possess the properties of thedopant. We have doped ascorbic acid （AA） and L-cysteine （Lcys） into POMmicrotubes during the growth process of the microtubes. The content of the dopantscan be controlled to some extent. The obtained AA-SiW₁₂and Lcys-SiW₁₂microtubesshow sensitivity to ammonia gas.3. The W atom in the Keggin-type tungstosilicate can be substituted by Mo, Vand the other transition metals, and the substituted POM will have differentelectrochemical and electrocatalytic properties from the full-W series. Themono-vacant Keggin-type tungstosilicate is unstable in an acidic medium, and readilyforms Mo and V-substituted POMs in the presence of Mo and V. According to thisreactivity, we have prepared the Mo and V-substituted POM (SiW₁₁Mo and SiW₁₁V)microtubes and investigated their redox properties.4. The POM in oxidation state can accept electrons and form heteropoly blue（HPB）. Accordingly, the SiW₁₂-HPB and SiMoVW₁₁microtubes are prepared. The obtained microtubes can be used as electron donor to in situ reduce the noble metalcations with matchable redox potential to metal nanoparticles （NPs）, thus NPs aredeposited on the microtubes. The size of the obtained NPs is consistent, and the NPsare evenly spreaded. The NP-immobilized microtubes can be used as excellentcatalysts for some organic reactions, such as the epoxidation of alkene and theoxidation of alcohol.The as-prepared POM tubular materials display potential applicationsin photoelectrical materials, catalysts, molecular absorbers, microreactors, biologicaland chemical sensors, due to combination of the perfect physicochemical properties ofPOMs and the mesoscopic hollow structure of microtubes.