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The Application of the Electrochemical Impedance Spectroscopy in the Study on the Structures and the Properties of Composites

Author: WangZuo
Tutor: XieChangSheng
School: Huazhong University of Science and Technology
Course: Materials Science
Keywords: Electrochemical impedance spectroscopy Interface property Cu/LDPE composites Release property ZnO/WO3 nanocomposites Photoelectrocatalytic efficiency Energy band structures
CLC: TB33
Type: PhD thesis
Year: 2011
Downloads: 247
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Abstract

The electrochemical impedance spectroscopy is a quasi-steady-state method. It can give more dynamic informations and interface structure informations that other conventional electrochemical methods can not give. Therefore, it is widely used in the materials researches.The composites are the materials that composed of more than two components with a certin amount which are selected. The composites are the artificial compounds with multiphases, three-dimensional integration, clear interface between each phase, and the special properties. The relationship between the structures and properties of composites is close.Cu/LDPE composites and ZnO/WO3 nanocomposites both belong to the composites. Cu/LDPE composites are metal/polymer composites. It is a novel Cu-IUD material that can overcome the shortcomings of traditional Cu-IUDs. ZnO/WO3 nanocomposites belong to the nano functional composites.They are widely used as photocatalytic materials.In order to investigate the relationship between the interface property and the Cu2+ release property of Cu/LDPE composite, the electrochemical impedance spectroscopy was used to obtain the interface property. The microstructure characteristics and the equivalent circuit of pure LDPE and Cu/LDPE composites that immersed in the solutions for different periods were presented.The electrochemical impedance spectroscopy and Cu2+release results showed that with the increasing of the content of copper particles in the composites the interface between polyethylene and the solution increased. That resulted in the interface resistance {Rint) increasing and the interface capacitance (Cint) decreasing. The release rate of cupric ions increased with the increasing of the interface. The interface between polyethylene and the solution in the microcomposites was more than that in the nanocomposites with the same copper content. The interface resistance in the microcomposites was larger and the interface capacitance in the microcomposites was smaller than that in the nanocompsoites. When the concentration of copper particles in the composite was high, the release rate of cupric ions in the microcomposite was larger than that in the nanocomposite.When the nanocomposite with 25 wt.% copper nanoparticles immsered in Solution A (pure water), Solution B (containing normal salts with CI-), Solution C(containing B and NaHCO3), Solution D (containing C and NaH2PO4), and Solution E (containing D and glucose), the change of the interface resistance (Rint) and the interface capacitance (Cint) between LDPE and the solution in the solutions were that Rint(A)[Rint(B)、Rint(C)、Rint(D)]<Rint(E) and Cint(A)[Cint(B)、Cint(C). Cint(D)]>Cint(E). The order of the diffusion impedance in the solutions was that Zw(B)<Zw(E)<Zw(D)<Zw(C)<Zw(A). The order of the release rate of cupric ions in these five solutions was r(A)< r(C)< r(D)< r(B)< r(E).When the nanocomposite with 25 wt.% copper nanoparticles immersed in the simulated uterine solutions with 0.5 g/L,1 g/L,2 g/L,4 g/L,6 g/L and 8 g/L, respectively, the diffusion impedance first reduced with the increasing of the concentration of protein until the concentration of protein reached 2 g/L. Then the diffusion impedance increased with the increasing of the concentration of protein. Along with the increasing of the concentration of protein, the protein that covering the copper particles increased. When the concentration of protein was low, the protein accelerated the Cu2+release rate. When the protein concentration increased, the rate of coverage of protein increased that preventing the release of cupric ions.Based on the fitting results of the electrochemical impedance spectroscopy of the nanocomposite with 25 wt.% copper nanoparticles that immersed in the solution for different days, the diffusion impedance decreased with the increasing time until the diffusion impedance reached a platform. The release rates of cupric ions was very large in the early period, then the release rates of cupric ions became small and the change of the release rates of cupric ions was steady.In order to investigate the relationship between the interface property and the photocatalytic property of ZnO/WO3 nanocomposite, the photoelectrocatalytic efficiency and the electrochemical impedance spectroscopy of ZnO/WO3 nanocomposite were obtained. The results showed that the composites with 40-50 wt.% WO3 had the higher photoelectrocatalytic efficiency. With the results of XRD and HR-TEM, it was found that ZnWO4 phase was formed in the composites.The existence of ZnWO4 introduced a type of ZnO/ZnWO4/WO3 double heteroj unctions into the composites, which gave the contribution to the photocatalytic property and the response to the light.The equivalent circuit of pure ZnO, ZnO/WO3 nanocomposite and pure WO3 were presented. The results of the electrochemical impedance spectroscopy showed that the interface resistance (Rint) and the interface capacitance (Cint) were related to the amount of the grains and the heteroj unctions in the composites.The energy band structures of ZnO/WO3 composites were obtained using the electrochemical impedance spectroscopy and UV-vis diffuse reflection absorption spectroscopy. When the amount of WO3 was 50 wt.%, the valence band was the most positive.That resulted in the more holes and hydroxyl radical with strong oxidation ability producing. Therefore, the methyl organge could degrade effectively.

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