SiO2 Cavity Research Articles

Electrocatalytic oxidation of alcohols on single gold particles in highly ordered SiO2 cavities

In the present work, we report a new and simple approach for preparing a highly ordered Au (111) nanoparticle (NP) array in SiO2 cavities on indium-doped tin oxide (ITO) electrodes. We fabricated a SiO2 cavity array on the surface of an ITO electrode using highly ordered self-assembly of polystyrene spheres as a template. Gold NPs were electrodeposited at the bottom of the SiO2 cavities, and single gold NPs dominated with (111) facets were generated in each cavity by annealing the electrode at a high temperature. Such (111) facets were the predominate trait of the single gold particle which exhibited considerable electrocatalytic activity toward oxidation of methanol, ethanol, and glycerol. This has been attributed to the formation of incipient hydrous oxides at unusually low potential on the specific (111) facet of the gold particles. Moreover, each cavity of the SiO2 possibly behaves as an independent electrochemical cell in which the methanol molecules are trapped; this produces an environment advantageous to catalyzing electrooxidation. The oxidation of methanol on the electrodes is a mixed control mechanism (both by diffusion and electrode kinetics). This strategy both provided an approach to study electrochemical reactions on a single particle in a microenvironment and may supply a way to construct alcohols sensors.

Hydrogen peroxide biosensor based on microperoxidase-11 immobilized in a silica cavity array electrode

Hydrogen peroxide biosensor based on the silica cavity array modified indium-doped tin oxide (ITO) electrode was constructed. An array of silica microcavities was fabricated by electrodeposition using the assembled polystyrene particles as template. Due to the resistance gradient of the silica cavity structure, the silica cavity exhibits a confinement effect on the electrochemical reactions, making the electrode function as an array of “soft” microelectrodes. The covalently immobilized microperoxidase-11(MP-11) inside these SiO2 cavities can keep its physiological activities, the electron transfer between the MP-11 and electrode was investigated through electrochemical method. The cyclic voltammetric curve shows a quasi-reversible electrochemical redox behavior with a pair of well-defined redox peaks, the cathodic and anodic peaks are located at −0.26 and −0.15V. Furthermore, the modified electrode exhibits high electrocatalytic activity toward the reduction of hydrogen peroxide and also shows good analytical performance for the amperometric detection of H2O2 with a linear range from 2×10−6 to 6×10−4M. The good reproducibility and long-term stability of this novel electrode not only offer an opportunity for the detection of H2O2 in low concentration, but also provide a platform to construct various biosensors based on many other enzymes.

Fabrication and electrocatalytic activity of single gold particles in highly ordered SiO2 cavities

An array structure of SiO2 cavities was fabricated on the surface of an indium-doped tin oxide (ITO) electrode by using highly ordered self-assembly of polystyrene spheres as a template. The SiO2 cavities exhibited a confinement effect on the electrochemical deposition of gold nanoparticles, which are formed only at the bottom of the SiO2 cavities. A single particle dominated with the [111] facets was generated in the cavity by annealing the gold nanoparticles at high temperature. The single gold particles showed excellent electrocatalytic activity for the oxidation of glucose. This strategy might provide an approach to study electrochemical reactions on a single particle in a microenvironment.

The Correlation between Play-of-Color Effect and SiO<sub>2</sub> Cavities Size of Australian Blue Opal

Its play-of-color effect of Australian opal makes it unique and much more precious than any other gemstones in the world. More than 50 Australian opals were chosen to conduct the experiments, including boulder and black opals with blue-green to blue-purple color. Spectropotometer Color i5 was used to analyze the color of opal samples with CIE L*a*b* uniform color space. Dominant wavelength was put into comparison with hue angle. SEM and AFM were the main means to analyze the internal structure of opal samples, and the diameter and size of cavities of SiO2 were measured and discussed. It is revealed that the hue angle of blue-purple opal is 302.15° with 449nm as its dominant wavelength, and so the size of SiO2 cavities in the sample is about 155.32nm; the hue angle of blue opals is between (256°, 286°) with the dominant wavelength between (471nm, 485nm), and so their size of SiO2 cavities is between (154.35nm, 182.54nm); the hue angle of blue-green opal is between (183°, 213°) with the dominant wavelength between (489nm, 500nm) and so their size of SiO2 cavities is between (172.95nm, 193.66nm). Besides, the diameter and size of SiO2 cavities were analyzed against the dominant wavelength, hue angle, lightness, and saturation to reveal their correlation. It is indicated that the diameter and size of SiO2 cavities are in positive correlation with the dominant wavelength, but negative correlation with the hue angle. As the diameter and size of SiO2 cavities grow, the dominant wavelength increases but the hue angle decreases. Also they are in positive correlation with lightness but their correlation with saturation was not discovered.

Whispering gallery modes at 800 nm and 1550 nm in concentric Si-nc/Er:SiO2 microdisks

We examined a concentric Si nanocrystal (Si-nc) and Er doped SiO2 (Er:SiO2) microdisk structure supporting high-Q whispering gallery modes (WGMs) at both visible and telecom wavelengths. This structure provides a means to utilize Si-nc luminescence as an optical pump for an Er:SiO2 cavity without subjecting a telecom-wavelength, Er:SiO2-based mode to loss mechanisms associated with the Si-nc material. After fabricating a concentric microdisk consisting of an inner Si-nc disk and an outer Er:SiO2 ring, we characterize visible wavelength WGMs excited by the Si-nc photoluminescence and observed spectrometer limited quality factors as high as 103. Telecom wavelength photoluminescence from the Er:SiO2 ring was measured to have a quality factor as high as 104 in the erbium luminescence region using a passive pulled fiber setup.