Engineering of electrochemically and optically active silica nanocomposites.

摘要

Sol-gel based silica materials have received tremendous attention because of their solution process and nanoporous structures in nature that are suitable to encapsulate small molecules, nanoparticles, biomolecules, and even living organisms, making them ideal materials for optical and electrochemical applications such as sensing, fuel cells, and biofuel cells. However, the poor electron conductivity of the silica matrix has to be overcome by supplementing electrochemically active species. Examples are carbon nanoparticles and metallic nanoparticles. Metallic nanoparticles and aminosilane have been identified to be the focus of this doctorate study and the objective of the research is to synthesize nanocomposite materials through reduction and sol-gel reactions. Here aminosilane, bis[3-(trimethoxysilyl)propyl]ethylenediamine (enTMOS, i.e., an aminosilica precursor), known for its metal-binding capability was found to enable spontaneous reduction reaction of silver ions even though the redox potential of the amino group is lower than that of the silver.In order to investigate the electrochemical property of both aminosilica and the nanocomposite, as well as to deposit the nanocomposite film onto the substrates, a rapid prototyping method for a poly(dimethylsiloxane) (PDMS) electrochemical device with miniaturized electrodes and liquid cell was developed. Cyclic voltammetry studies showed that electrochemical properties of the aminosilica matrix is dependent on the water amount and found that the synthesis of silver nanoparticles can be controlled by water concentration. These colloids were later found capable of self-assembling on hydrophobic surfaces such as silicon wafer, polystyrene, polypropylene, PDMS, and glass substrates, making it possible to pattern the nanocomosite layer through soft-lithography and micro-contact printing. In addition, the thickness of the self-assembled layer is the function of time, allowing films of 200 nm thick to be produced. Electrochemical studies of the nanocomposite film also showed that the embedded silver nanoparticles that produced by spontaneous reduction reaction exhibit fast redox chemical reactions with their performance similar to the solution-synthesized silver nanoparticles. The electron transfer rate and electron hopping diffusion between silver nanoparticles were also investigated using the self-built opto-electrochemical cells and showed that the embedded nanoparticles do not significantly hinder the diffusion of redox chemicals.Finally, the successful fabrication of silver nanocomposite on the hydrophobic surface through self-assembled process were applied to gold nanocomposites. Spacing of gold nanoparticles within a monolayer of the film has been successfully controlled through sol-gel reaction to exhibit various plasmonic effects. Such films that have been able to self-assemble onto the surface of polystyrene beads as core-shell structures may have applications in sensing, catalysts, optical devices, and bio-labeling.