Fabrication Of Ordered Micron Or Submicron Cavity Arrays And Their Electrochemical Properties

In this paper, two-dimensional ordered micro/nano-scale non-metallic (SiO2)spherical cavity array have been fabricated through electrochemical and electrolessdeposition method using close-packed monodisperse polystyrene (PS) spheres astemplates. The morphology of the as-prepared cavity array can be modulated bychanging the size of microspheres and the deposition conditions. On this basis, thenovel glucose and H2O2electrochemical sensors have been constructed. Next, we havedeveloped a new and simple approach for preparing a highly ordered Au (111)nanoparticle (NP) array in SiO2cavities on indium-doped tin oxide (ITO) electrodes.The ordered (111) facet enriched gold metal exhibited excellent electrocatalytic activityto the electrooxidation of alcohol (e.g., methanol, ethanol and glycerol), then we havedeveloped the Au(111)/SiO2cavity/ITO electrode as a promising candidate for futureglycerol sensors.Major innovative research results are as follows:1. A close-packed two-dimensional ordered PS template are first constructed onthe interface of water and gas via self-assembly method, the ordered PS template can beeasily transferred to the surface of ITO glass slide, which are used as working electrodefor the electrodeposition. The highly ordered cavities structures provide the uniquemicroenvironment for chemical or electrochemical reactions that occur inside thecavities. The highly ordered cavities acted as the microelectrode arrays have uniqueelectrochemical properties such as high current density, edge effect, confinement effectand steady-state diffusion currents. The surface of the SiO2cavities could befunctionalized easily with various molecules via silanation to provide specific microenvironments inside the cavities.2. We have developed a novel amperometric detection of glucose using an Au(111)-like/SiO2ITO electrode. First, we fabricated an array structure of SiO2cavities onthe ITO electrodes via the ordered PS templates. Secondly, the nucleation stage of goldNPs was generated by a high overpotential and a short time of potentiostatic transient.Due to the fact thatAuCl4ions will be preferentially reduced and deposited on thepreviously formed Au seeds in a subsequent cyclic voltammertrical process, we achievethe raspberry-like Au NPs which are enriched in Au (111) facet orientation. The highcontrollability with the density and the size of raspberry-like Au NPs on the ITOelectrode are realized. The as-prepared electrode provided excellent electrochemicalperformance for glucose oxidation reaction with a linear response range from50μM to1.5mM (R=0.9995), and a low detection limit of12μM (signal to noise ratio of3), butalso good selectivity of the interferences of AA, UA and good antidrug of highconcentration of Cl-. The raspberry-like Au (111)-like/SiO2ITO electrode with highsensitivity, good stability and reproducibility made it promising for the development ofenzyme-free sensors.3. We have developed a novel amperometric detection of H2O2using the Prussianblue@Au/SiO2/ITO electrode. First, we fabricated an array structure of SiO2cavities onthe ITO electrodes via the ordered PS templates. Secondly, Au NPs wereelectrodeposited at the bottom of the SiO2cavities, to increase the conductivity and tocatalyze the chemical deposition of Prussian blue (PB). The SiO2cavity provided afavorable microenvironment for PB@Au nanocomposite to catalyze the reduction ofH2O2. Electrochemical measurements showed that the PB@Au/SiO2/ITO electrodeexhibited good electrocatalytic behavior for the detection of H2O2with a wide linearrange from80μM to8mM, a low detection limit down to0.3μM (S/N=3).4. In the present work, we report a new and simple approach for preparing a highlyordered Au (111) nanoparticle (NP) array in SiO2cavities on indium-doped tin oxide(ITO) electrodes. We fabricated a SiO2cavitiy array on the surface of an ITO electrode using highly ordered self-assembly of polystyrene spheres as a template. Gold NPs wereelectrodeposited at the bottom of the SiO2cavities, and single gold NPs dominated with(111) facets were generated in each cavity by annealing the electrode at a hightemperature. Such (111) facets were the predominate trait of the single gold particlewhich exhibited considerable electrocatalytic activity toward oxidation of methanol,ethanol, and glycerol. This has been attributed to the formation of incipient hydrousoxides at unusually low potential on the specific (111) facet of the gold particles.Moreover, each cavity of the SiO2possibly behaves as an independent electrochemicalcell in which the methanol molecules are trapped; this produces an environmentadvantageous to catalyzing electrooxidation. The oxidation of methanol on theelectrodes is a mixed control mechanism (both by diffusion and electrode kinetics). Thisstrategy both provided an approach to study electrochemical reactions on a singleparticle in a microenvironment and may supply a way to construct alcohols sensors.5. We report a direct electrochemical glycerol detection method using thermallyannealed, facet-specific, single gold particles, Au (111), located in the cavities of ahighly ordered SiO2cavity array on an indium-doped tin oxide (ITO) electrode. Wefabricated an interconnected array structure comprised of SiO2cavities onto ITOelectrodes via monolayer colloidal crustal (MCC) templates. Au NPs wereelectrodeposited at the bottom of the SiO2cavities in direct contact with the ITOelectrodes (Au (poly)/SiO2cavity/ITO electrode). Upon annealing the electrodes at700°C, single gold particles were formed, dominated by the (111) facet (Au(111)/SiO2cavity/ITO electrode). The Au (111)/SiO2cavity/ITO electrode exhibitedsatisfactory electrocatalytic activity to the oxidation of glycerol. More importantly, eachcavity of the SiO2possibly behaves as an independent electrochemical cell in which theglycerol molecules are trapped; this produces a microenvironment advantageous tocatalyze electrooxidation. Moreover, Au (111)/SiO2cavity/ITO electrode design gave awide linear range from0.01mM to0.8mM, and a low detection limit of1.49M. As aglycerol sensor, the electrode displayed good reproducibility and long-term stability.The electrode was applied to directly determine the free glycerol in the biodiesel samples. This strategy might provide an approach to study electrochemical reactions onsingle particles in a microenvironment and offers a method for constructing alcoholssensors.