Fabrication And Electrocatalytic Properties Of Polyoxometalates Modified Electrode

The purpose of chemically modified electrodes is to carry out the moleculardesign on the electrode surface. Some molecule, ion and polymer with excellentproperties are immobilized on electrode surface and the electrode with speciallychemical and physical properties is obtained. And it has been intensively used inelectroanalysis due to their high sensitivity and excellent selectivity. Therefore, a newtype of chemically modified electrode built with different materials and differentmethods should provide a new idear for its development and application in biosensors,catalysis and other areas.Polyoxometalates （POMs） have become attractive candidates for chemicallymodified electrodes due to their reversible redox activities and excellentelectrocatalytic properties. Thus, it has great significance that the design anddevelopment of modified electrode based on POMs, extending the application ofPOMs modified electrode in electrocatalysis and photoelectrocatalysis.This thesis focuses on the POMs, carbon nanotubes （CNTs） and polymerscomposite-based chemically modified electrodes prepared throughelectropolymerization technology, and their applications in the electrocatalyticdetection of some inorganic substances and small biomolecule with electrochemicalactivity. This thesis carried out some researches as follows:1. A facile strategy to fabricate phosphomomolybdic acid (PMo₁₂), polyanilineand CNTs modified glassy carbon electrode （GCE） was developed for the first time.In this work, multi-walled carbon nanotubes were reflowed in acid solution to make itto be functionalized with hydroxyl and carboxyl groups. Then PMo₁₂-MWCNT-PAnmodified electrode was prepared by electropolymerization method. Theelectrochemical and electrocatalytic activities for the modified electrode wereinvestigated. The results suggest that the presence of CNTs in the composite film notonly enhances the conductivity of the film but also increases the surface area of theelectrode and the surface coverage of PMo₁₂. The developed composite electrodegreatly enhanced greatly the sensitivity and stability of PMo₁₂-MWCNT-PAnmodified electrode. 2. A novel composite film modified GCE based on the POMs-CNT-PAn wasfabricated due to the good electrocatalytic ability of POMs and excellentelectrochemical properties of CNT. In this work, poly（sodium-p-styrenesulfonate）（PSS） was used as a dispersant to form a stable PSS-SWCNT composite, which wasthen used to prepared a SiW₁₂-SWCNT-PAn modified electrode byelectropolymerization method. The electrochemical behavior of the composite filmmodified electrode was characterized by cyclic voltammetry in detail. The preparationprocess of the modified electrode is simple and convenient. The resulting film hashigh stability and good electrocatalytic activity for ascorbic acid （AA）.3. A polyoxometalate (PW₁₂) and MWCNT doped polypyrrole （PPy） modifiedelectrode was prepared by electrochemical polymerization in aqueous0.5mol·L^-1H2SO4solution. During the polymerization of PPy, PW₁₂acted as both catalyst anddopant, CNT suggested that they had the ability to promote electron transfer reaction.The electrochemical behavior of nitrite （NO₂^-） at the PW₁₂-MWCNT-PPy modifiedelectrode was investigated including pH effect, scan rate and so on. It showed acatalytic effect toward nitrite. The developed method could be applied to thedetermination of NO₂^-in pickled foods samples.4. A polyaniline doped POMs modified electrode was prepared and itselectrochemical and electrocatalytic properties were studied. Because polyanilinedoped POMs are difficult to dissolve, polyaniline doped POMs were mixed directlywith paraffin oil and used for the preparation of carbon paste electrode. Theelectrochemical behaviors of the modified electrode were studied in details, includingpH, stability and so on. Experimental results showed that the modified electrode notonly maintains the electrochemical activity and electrocatalytic properties of PW₁₂,but also exhibited good reproducibility and stability. In pH2.0Na₂SO₄-H₂SO₄buffersolution, the cathodic peak of PW₁₂showed good catalytic effect on the reduction ofbromate using cyclic voltammetry.