Sol-gel Electrodeposition Technology And Its Application In Surface Functionalization Of Materials

Silane sol-gel materials have been widely used in corrosion protection of metal, optical and photocatalytic materials, electroanalysis and biosensors, etc. Due to the limited by the dynamics for the formation of silane films, the dip-coated and spin-coated films are very thin and poor in regulating. The novel electrodeposition method, which is based on the facilitation of silane sol-gel film by cathodic generated OH-ions, effectively solved this problem. Nowadays, the research on electrodeposited silane sol-gel films are mainly focused on electroanalysis and biosensors. In this thesis, some fundamental issues in the electrodeposition of silane sol-gel films were investigated. Based on this, gradient sol-gel films were fabricated. One-step preparation of zinc doped silane films and silane incorporated electrophoretic coating were proposed for the corrosion protection of metals. Porous functional film materials based on electrodeposited SiO2as template were proposed. And superhydrophobic sol-gel films have been fabricated via two-step or one-step, which expanded the application of electrodeposited silane sol-gel films. The main contents are listed as follows:(1) Some fundamental issues in the electrodeposition of silane sol-gel films wereinvestigated. EQCM was used for in-situ monitoring the deposition process of silane sol-gel film. We divided the formation of silane sol-gel film into three stages:the introduction of film formation stage, low growing rate stage and faster gelification stage. The period of the introduction of film formation stage is dependent on the applied potentials. Theoretic calculation results show that the sol-gel films can be generated when the pH near the electrode surface reached to～9.8, and the porosity of the film increases with the deposition potential shift negatively. N2absorption and desorption test indicates that the more negative potential applied, the smaller of the specific surface area of the films. While fluorescent dye adsorption test results show that more dye would be loaded on the films prepared at more negative potentials. Based on the results, gradient silane sol-gel films were fabricated.(2) Silane electrodeposition for the corrosion protection of metals. Firstly, based on the doped zinc ions in the precursor would be reduced to zinc under cathodic potential, and the generated OH-ions due to the reduction of H2O, O2and/or NO3-could facilitate the formation of silane films, zinc-doped silane films were fabricated via one-step electrodeposition. EIS, open circuit potential, wet heat test and iron ions dissolving test show that the corrosion protection property would be enhanced due to the doped zinc. XPS further indicates the existence of metallic zinc in the hybrid films. Secondly, based on both cationic epoxy resin and silane film could be formed under cathodic potential, silane incorporated electrophoretic coating were fabricated via one-step for the corrosion protection of galvanized steel. EIS test results show that the incorporation of tiny amount silane (0.3wt.%BTSE or0.5wt.%MTMS) could significantly enhance the corrosion protection property, reduce water uptake, improve hydrophobicity and mechanical property of the coating. FITR further indicates the silane-enriched layer preferentially formed on the metal/coating interface could improve the adhesion between the coating and substrate.(3) Electrodeposition of SiO2template technology and its application in the preparation of nano-porous materials. Firstly, the preparation of electrocatalytic activity enhanced porous films based on electrodeposited SiO2as templates. At first, one-step electrodeposition of SiO2/Ni or SiO2/Co3O4hybrid films, then porous Ni or Co3O4films could be formed by consecutive CV scans in KOH solution. SEM and TEM indicate the the porosity of the obtained Ni or Co3O4films are improved. FTIR and EDX show that the silica component could be removed completely by repeated CV scans in KOH solution. Electrochemical test (CV and LSV) demonstrate that the electrocatalytic activity and specific capacity of these porous Ni or Co3O4films are obviously improved.(4) Electrodeposition of superhydrophobic sol-gel films and the study of its performance. Firstly, the fabrication of superhydrophobic sol-gel films based on the highly porous E-SiO2film and environmental friendly hydrophobic alkoxysilane via two-step. SEM images and profiler tests show the thickness, roughness and hydrophobicity of the sol-gel films could be regulated easily by altering the electrolysis time and applied potential. What’s more, the influence of substrate and surfactant on the superhydrophobic films are also investigated. Secondly, one-step fabrication of superhydrophobic organic silane films and inorganic and organic hybrid silane films. It is found that the thermal stability, chemical stability and mechanical strength of the superhydrophobic films can be significantly improved due to the introduction of inorganic SiO2component.