| Chemically modified electrodes (CMEs) have been used in a wide range of applications: chemical analysis and electrochemical catalysis. To accomplish these purposes, an electrode can be modified by four different techniques (1) Incorporation of modifying particles (including molecules, ions, enzymes, clusters, etc) into the electrode body (e.g., into graphite). (2) Direct attachment of modifying particles. (3) Application of films from modifying particles (e.g., conductive polymers). (4) In corporation of modifying particles into the supporting matrix.The transition metal compounds have particular attention for their applications in many fields of science owing to their chemical, structural and the number of electron transfer versatility. These compounds offer the most complete range of interesting properties required at an electrochemical interface,including reversible multivalence redox, change selectivity, physical and chemical stability, high ion exchange capacity and their catalytic capability in a micro-structured environment. So the use of these materials as the modifying agents represents another useful and promising approach.Vanadium tri (isopropoxide) oxide (VO(OC3H7)3), molybdenum bronzes (LixMoOy) and 12-molybdophosphoric acid (PM012) were used as modifier to modify glassy carbon or gold electrodes, respectively, and electrochemical behaviors of all the species presented in above modified electrode are studied in this paper. To our knowledge, several groups studied the voltammetric response of transition metal compounds modified electrodes. But up to now, the chemical modified electrodes containing the transition metal compounds for electrocatalysis and analytical application are unusually reported in China and aboard. The research of the paper is developed based on the above topic. The results illustrate that our work provides some reference for the studying and application of the transition metal compounds modified electrode. The research in this paper area follows.First, the electrode was prepared by casting a mixture of vanadium tri (isopropoxide) oxide (VO(OC3H7)3) and Poly (propylene carbonate) (PPC) onto the surface of a glassy carbon electrode. The morphology of this novel polymer film containing VO(OC3H7)3 is characterized by TME. The result suggest that the distribution of the VO(OC3H7)3 in the film is very homogeneous. The structure of VO(OC3H7)3 in the film have been characterized by FTIR spectrophotometry, which shows a weak interaction between the VO(OC3H7)3 and PPC. The electrochemical behavior of VO(OC3H7)3 doped PPC filmmodified electrode is studied by cyclic voltammetry in detail. The results show that: (1) The film electrode obtained is very stable owing to weak interaction between the VO(OC3H7)3 and PPC; (2) VO(OC3H7)3 in the modified film could catalyze oxidation of ascorbic acid in pH 8.06 B-R buffer solution. (3) By determining the steady-state current of ascorbic acid with constant potential amperometry, optimal conditions are obtained and the mechanism of catalyticoxidization is inferred. 4×10-8 mol L-1 - 1×10-4 mol L-1 of the linear range, 1.5×10-8 of the detection limit and 95.5-103.8% of recovery for ascorbic acid are obtained in the optimal conditions. The proposed method is simplicity, rapidity, sensitivity, and high selectivity, and offer great practical interest for the periodic control of ascorbic acid in fruits and vegetables. This work is advantageous to facilitate the biosensor development based on the transition metal compoundsSecond, the electrochemical behavior of the vanadium tri (isopropoxide) oxide (VO(OC3H7)3) and Poly (propylene carbonate) (PPC) modified electrode is studied. The results illustrate that the diffusing controls the redox process of VO(OC3H7)3. The electrochemical reaction process can be represented. Moreover, the film electrode obtained shows to exhibit a high electrocatalytic response for the oxidation of iodide. Based on this, Flow injection amperometry was proposed for the determination of iodide. Flow injection amperometry (FIA) exhibited a good linear relationship with the concentration of iodide in therange of 5×10-7mol L-1 and 1×10-3mol L-1, and the detection limit was 1× 10-7mol L-1. The method has been successfully applied to the determination ofiodide in dry edible seaweed. The concentrations of iodide measured by this method are in good agreement with those obtained by spectrophotometric method.Third, Molybdenum bronzes (LixMoOy) were synthesized by electrochemical method. A novel amorphous mixed-valent molybdenum oxide film was grown on a glassy carbon by the electrodepositing method. Its electrochemical behaviors were studied by cyclic voltammetry and amperometry. This film electrode exhibits a high catalytic activity for iodate. By determining the steady-state current of iodate with constant potential amperometry, optimal conditions are obtained and the mechanism of catalytic reduction is inferred. It exhibited a high stability and electrocatalytic activity for the reduction of iodate. Amperometry revealed a good linear relationshipbetween peak current with the concentration of iodate in the range of 1×10-6 and 2 × 10-4 mol L-1 with a correlation coefficient of 0.9997 and the detection limit of 5 × 10-7 mol L-1. The diffusion coefficient of 4.45 × 10-7cm2 s-1 for iodate was calculated. As a result, it is much promising for themodified films to be used as an electrochemical sensor for detecting the reduction of iodate.Forth, We first describe one example of electrode modification by a polypropylene carbonate (PPC) film doped with LixMoOy, which has electrochemical activity. The structure of LixMoOy in the gel films have been characterized by FTIR spectrophotometry, which shows that the structure ofin the gel films is not affected by the gelation processes and no major structural or conformational changes have taken place in it. The electrochemical behavior of LixMoOy doped gel film electrode is studied in pH 2.33 phosphate buffer solution by cyclic voltammetry in detail. The film modified electrode obtained is very stable and shows to exhibit a high electrocatalytic response for the reduction of iodate. Furthermore, this kind of electrode has been used in flow injection amperometric systems for the determination of iodate. This new modified electrode has advantages such as simple fabrication, fast response, independence of electrode size and topology, good mechanical and chemical stability, and so on.Fifth, Polypropylene carbonate gel film doped with 12-molybdophosphoric acid (PMo12) can be modified on the surface of the glass carbon electrode, which retains its electrochemical activity. The electrochemical behavior of PMo12 doped gel film electrode is studied in pH 2.3 phosphate buffer solution by cyclic voltammetry in detail. The PMo12 embedded in the gel film exhibits three reversible redox peaks, the shape of which is very similar to that of PMo12 in an acidic aqueous solution. All waves (both the peak potential and the peak current) are pH dependent: along with increasing pH, the redox peak potentials shift negatively and the peak currents are also decreased. This behavior of PMo12 in the gel film is concerned with the protonation and the charge compensation processes. The film electrode obtained is very stable and exhibits a high electrocatalytic response for the reduction of iodate and H2O2. It can act as amperometric detector for iodate and H2O2. The method gives a linear range from 5×10-6 to 6 ×10-3M and a...
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