Metal Oxide Thin Films Containing Au Nano-Particles Prepared with Gas Diffusion Method

Au particles dispersed thin metal oxide films were prepared from precursor films containing HAuCl₄ with H₂S gas diffusion method. HAuCl₄ was uniformly dissolved in the films as promoted by hydroxypropyl cellulose (HPC). The mechanism of the Au particle formation was studied. It was found that HAuCl₄ was converted directly to Au metal particles upon contacting with H₂S gas. Au particles generated by this method were characterized with small particle size, sharp size distribution and high volume fraction in the films. The surface plasma resonance absorption of Au particles shifted to longer wavelength when TiO₂ component was introduced in the matrix.     

Synthesis and Properties of ZrO2 Films Dispersed With Au Nanoparticles

Au nanoparticles dispersed ZrO₂ thin films were prepared from two precursors HAuCl₄·4H₂O and ZrOCl₂·8H₂O in air. The structural properties and size of Au particle in ZrO₂ film were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface analysis with atomic force microscopy (AFM) showed the effect of monoethanolamine on preventing the migration of Au particles to the surface. The absorption peak of Au particles by the surface plasma resonance was observed and the red shift of absorption peak was discussed.     

Control of optical properties of gel-derived oxide coating films containing fine metal particles

Control of the optical properties of gel-derived oxide films containing fine metal particles is described. The duration of the aging of Si(OC₂H₅)₄-derived sols and the amount of water for hydrolyzing Si(OC₂H₅)₄ were found to greatly affect the size and the shape of Au particles formed in the silica matrix, and accordingly the optical absorption of the Au/SiO₂ composite films. Employing dielectric media with high refractive indices like TiO₂ was shown to shift the absorption peak of Au particles to longer wavelengths. Pd/TiO₂ and Pt/TiO₂ composite films showed absorption in the visible region.     

Control of Optical Properties of Thin Films Doped with Au Fine Particles by the Sol-Gel Method

We have developed tinted glasses with thin films doped with Au particles by the sol-gel method for automotive windows. Pink-colored glasses are mass-produced. The observed color is from absorption due to surface plasma resonance of Au particles. The squeeze-out of fine Au particles out of gel films was restrained by an organic additive. The index of the matrix was adjusted by the mixing ratio of TiO₂ (refractive index n = 2.20) to SiO₂ (n = 1.46). The absorption of Au particles is more intense with the higher index of the matrix, and its peak varies from 530 nm for n = 1.46 to 630 nm for n = 2.20, which yields a transmission color from pink to blue. The combination of the color of the glass substrate and the absorption by the Au particles in the thin films with various indices yields a variety of tinted glasses such as pink, orange, blue, blue-green and gray.     

Preparation of Gold Microcrystal-Doped TiO2, ZrO2 and Al2O3 Films Through Sol-Gel Process

Au-microcrystal-doped TiO₂, ZrO₂ and Al₂O₃ films were made by sol-gel dip-coating method using titanium, zirconium and aluminum alkoxides with HAuCl₄ · 4H₂O. The influence of the oxide matrix composition on the maximum amount of the Au microcrystals that can be incorporated in the oxide film was examined. Some amount of Au microcrystals were exhausted to the surface of Au microcrystal-doped oxide films when an excess amount of HAuCl₄ · 4H₂O was dissolved in the coating solution. The maximum amount of Au that can be incorporated in the oxide film was found to increase with the increase of the pH point at zero charge (PZC) of the matrix oxide. This should be due to the fact that AuCl ₄ ^- ions are charged negative and also Au microcrystals tend to charge negative, so that the oxide gel with high PZC, which has a tendency to charge positive, may fix the ions and/or microcrystals to its interior. A maximum amount of Au microcrystals as high as 12.6 vol% was attained in an Au:Al₂O₃ film.     

Synthesis of Core-Shell (Pd-Au) Bimetallic Nanoparticles in Microemulsions

Palladium-gold core-shell nanoparticles were synthesized in the aqueous domains of water in oil microemulsions by the sequential reduction of H₂PdCl₄ and HAuCl₄. The nanoparticles were characterized by ultraviolet-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM). The UV-vis spectra confirm the presence of palladium nanoparticles after reducing H₂PdCl₄. These particles have been used as seeds for the core-shell particles. UV-vis spectra show that, after reducing HAuCl₄, the surface plasmon absorption of the nanoparticles is dominated by gold, revealing the encapsulation of the palladium seeds. These results agree with crystallographic analysis performed with high-resolution TEM pictures, as well as with selected area electron diffraction. The TEM pictures show the core-shell nanoparticles with an average diameter of 9.1 nm, as compared with 5 nm for the palladium seeds, in good agreement with the used Pd:Au molar ratio.     

Direct growth of comet-like superstructures of Au-ZnO submicron rod arrays by solvothermal soft chemistry process

The synthesis, characterization and proposed growth process of a new kind of comet-like Au-ZnO superstructures are described here. This Au-ZnO superstructure was directly created by a simple and mild solvothermal reaction, dissolving the reactants of zinc acetate dihydrate and hydrogen tetrachloroaurate tetrahydrate (HAuCl₄·4H₂O) in ethylenediamine and taking advantage of the lattice matching growth between definitized ZnO plane and Au plane and the natural growth habit of the ZnO rods along [001] direction in solutions. For a typical comet-like Au-ZnO superstructure, its comet head consists of one hemispherical end of a central thick ZnO rod and an outer Au-ZnO thin layer, and its comet tail consists of radially standing ZnO submicron rod arrays growing on the Au-ZnO thin layer. These ZnO rods have diameters in range of 0.2-0.5 μm, an average aspect ratio of about 10, and lengths of up to about 4 μm. The morphology, size and structure of the ZnO superstructures are dependent on the concentration of reactants and the reaction time. The HAuCl₄·4H₂O plays a key role for the solvothermal growth of the comet-like superstructure, and only are ZnO fibers obtained in absence of the HAuCl₄·4H₂O. The UV-vis absorption spectrum shows two absorptions at 365-390 nm and 480-600 nm, respectively attributing to the characteristic of the ZnO wide-band semiconductor material and the surface plasmon resonance of the Au particles.     

硼铈共掺杂纳米TiO2光催化降解三氯杀螨醇和菊酯类农药

采用溶胶-凝胶法在钛酸丁酯水解过程引入硼酸、硝酸铈,制备具有光催化活性的硼铈共掺杂纳米二氧化钛（TiO2）,经XRD、TEM、FT-IR、UV-Vis-DRS表征晶体结构,在日光灯照射下,光催化降解三氯杀螨醇、高氟氯氰菊酯、氟戊菊酯农药。结果表明：硼铈共掺杂的TiO2只有锐钛矿型,而纯的或掺铈的TiO2有含有锐钛矿型、金红石相和少量板钛矿型,UV-Vis-DRS测定结果表明硼铈共掺杂的TiO2禁带宽度变小,硼铈共掺杂的TiO2在可见光区吸光度高于掺杂铈和不掺杂的TiO2,在420nm~850nm有强的吸收;在同样光照下对三氯杀螨醇、高氟氯氰菊酯、氟戊菊酯的降解试验证明硼铈共掺杂纳米TiO2的光催化活性高于不掺杂或只掺杂铈的TiO2。     

An H2O2 Biosensor Based on Immobilization of Horseradish Peroxidase Labeled Nano‐Au in Silica Sol‐Gel/Alginate Composite Film

Abstract

A novel approach to assemble an H₂O₂ amperometric biosensor was introduced. The biosensor was constructed by entrapping horseradish peroxidase (HRP) labeled nano‐scaled particulate gold (nano‐Au) (HRP‐nano‐Au electrostatic composite) in a new silica sol‐gel/alginate hybrid film using glassy carbon electrode as based electrode. This suggested strategy fully merged the merits of sol‐gel derived inorganic‐organic composite film and the nano‐Au intermediator. The silica sol‐gel/alginate hybrid material can improve the properties of conventional sol‐gel material and effectively prevent cracking of film. The entrapment of HRP in the form of HRP‐nano‐Au can not only factually prevent the leaking of enzyme out of the film but also provide a favorable microenvironment for HRP. With hydroquinone as an electron mediator, the proposed HRP electrode exhibited good catalytic activity for the reduction of H₂O₂. The parameters affecting both the qualities of sol‐gel/alginate hybrid film and the biosensor response were optimized. The biosensor exhibited high sensitivity of 0.40 Al mol^?1 cm^?2 for H₂O₂ over a wide linear range of concentration from 1.22×10^?5 to 1.46×10^?3 mol L^?1, rapid response of <5 s and a detection limit of 0.61×10^?6 mol L^?1. The enzyme electrode has remarkable stability and retained 86% of its initial activity after 45 days of storage in 0.1 mol L^?1 Tris‐HCl buffer solutions at pH 7.     

Fabrication and characterization of TiO2 photocatalytic thin film prepared from peroxo titanic acid sol

A novel sol–gel technique using the PTA (peroxo titanic acid) sol as precursor for the fabrication of TiO₂ photocatalytic thin film is introduced in this paper. The peroxo titanic acid sol was synthesized from titanyl sulfate (TiOSO₄), ammonia and peroxide solution (H₂O₂). The transparent and porous TiO₂ thin film was prepared via a sol–gel technique using PTA sol and polyethylene glycol (PEG) as precursor and template, respectively. The TiO₂ thin film samples were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectrophotometry (UV–vis), X-ray photoelectron spectrum (XPS) and thermogravimetry and differential thermal analysis (TG-DTA) technique. The PTA sol displayed amorphous TiO₂ below 100 °C. The anatase phase formed at 200 °C to 700 °C. The crystallinity of anatase phase was improved with increasing temperature. The anatase crystals on the surface of TiO₂ film were strip-like, the size being about 100 nm in length and 40 nm in diameter. Addition of PEG to the PTA sol developed porous structures in the film and changed the size and shape of the particles. The surface of the film contained Ti, O and C elements and Na element that diffused into the film from the glass substrate. The photocatalytic performance of TiO₂ film was tested for the degradation of 10 mg/L methyl orange. The degradation of methyl orange solution reached 98.9% after irradiated for 180 min under UV light. The porous TiO₂ thin film exhibited high photocatalytic activity towards degrading methyl orange.     

Preparation and nonlinear optical properties of Au nanoparticles doped TiO2 thin films

Nano-sized noble metal nanoparticles doped dielectric composite films with large third-order nonlinear susceptibility due to the confinement and the enhancement of local field were considered to be applied for optical information processing devices, such as optical switch or all optical logical gates. In this paper, sol–gel titania thin films doped with gold nanoparticles (AuNPs, ~10 nm in average size) were prepared. AuNPs were firstly synthesized from HAuCl₄ in aqueous solution at ~60 °C, using trisodium citrate as the reducing agent, polyvinylpyrrolidone as the stable agent; then the particle size and optical absorption spectra of the AuNPs in aqueous solutions were characterized by transmitting electron microscopy and UV–Vis–NIR spectrometry. Sol–gel 2AuNPs–100TiO₂ (in %mol) thin films (5 layers, ~1 μm in thickness) were deposited on silica glass slides by multilayer dip-coating. After heat-treated at 300–1,000 °C in air, the AuNPs–TiO₂ thin films were investigated by X-ray diffraction, scanning electron microscopy and atomic force microscopy. The nonlinear optical properties of the AuNPs–TiO₂ thin films were measured with the Z-scan technique, using a femtosecond laser (200 fs) at the wavelength of 800 nm. The third-order nonlinear refractive index and nonlinear absorption coefficient of 2AuNPs–100TiO₂ films were at the order of 10^?12 cm²/W, and the order of 10^?6 cm/W, respectively, and the third-order optical nonlinear susceptibility χ⁽³⁾ was ~6.88 × 10^?10 esu.     

Optical fiber evanescent wave absorption spectrometry of nanocrystalline tin oxide thin films for selective hydrogen sensing in high temperature gas samples

SnO₂ nanocrystalline material was prepared with a sol-gel process and thin films of the nanocrystalline SnO₂ were coated on the surface of bent optical fiber cores for gas sensing. The UV/vis absorption spectrometry of the porous SnO₂ coating on the surface of the bent optical fiber core exposed to reducing gases was investigated with a fiber optical spectrometric method. The SnO₂ film causes optical absorption signal in UV region with peak absorption wavelength at around 320 nm when contacting H₂-N₂ samples at high temperatures. This SnO₂ thin film does not respond to other reducing gases, such as CO, CH₄ and other hydrocarbons, at high temperatures within the tested temperature range from 300 °C to 800 °C. The response of the sensing probe is fast (within seconds). Replenishing of the oxygen in tin oxide was demonstrated by switching the gas flow from H₂-N₂ mixture to pure nitrogen and compressed air. It takes about 20 min for the absorption signal to decrease to the baseline after the gas sample was switched to pure nitrogen, while the absorption signal decreased quickly (in 5 min) to the baseline after switching to compressed air. The adhesion of tin oxide thin films is found to be improved by pre-coating a thin layer of silica gel on the optical fiber. Adhesion increases due to increase interaction of optical fiber surface and the coated silica gel and tin oxide film. Optical absorption spectra of SnO₂ coating doped with 5 wt% MoO₃ were observed to change and red-shifted from 320 nm to 600 nm. SnO₂ thin film promoted with 1 wt% Pt was found to be sensitive to CH₄ containing gas.     

Transformation of Ag Hexagonal Shape into Ag@Au Core-Shell Nanostructure in a Polymer-Mediated Polyol Process

In this article, we report the galvanic replacement reaction between an Ag template and HAuCl₄ · 4H₂O in aqueous solution transforms 33.3 nm hexagonal shape Ag to Ag@Au core-shell nanostructure in the presence of the surface-regulating polymer poly (vinyl pyrrolidone) (PVP). By controlling the molar ratio of Ag to HAuCl₄ · 4H₂O, the extinction peak of resultant can be continuously tuned from the blue to the near infrared sections for both absorption and scatting. The results of UV-vis, XRD, TEM, and SEM show the different characters on the Ag and Ag@Au core-shell nanostructure which suggest that the transformation of Ag into Ag@Au by controlling their dimensions as well as the thickness and porosity of their walls.     

Highly transparent UV absorption TiO<Subscript>2</Subscript>-SiO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> films without oxidation catalytic activity prepared by a room temperature sol–gel route

TiO₂-SiO₂-Fe₂O₃ films as new UV absorption material were prepared through an epoxide derived sol–gel route. The films were formed at room temperature by doping of a little amount of γ-Fe₂O₃ nanoparticles in TiO₂-SiO₂. The obtained films show advantages such as high stability, efficient absorption in the UV region, high transparency in the visible range, and low oxidation catalytic activity to organic materials. It was found that 2.3 nm γ-Fe₂O₃ nanoparticles doped films exhibit stronger UV absorption than the films doped with 5.1 nm particles because of the increased grain strain of the nanoparticles with smaller size. These advantages of the films guarantee the broad application of this inorganic UV absorption film in the protection of heat sensitive organic materials such as artworks.     

Silane grafting of TiO2 nanoparticles: dispersibility and photoactivity in aqueous solutions

Titania nano‐sized particles were treated by various amounts of tetraethyl orthosilicate precursor. The extent of grafting was characterized using Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐Vis) spectroscopy techniques, thermal gravimetric analysis, X‐ray fluorescence and zeta potential measurements. Sedimentation behaviour of titanium dioxide (TiO₂) nanoparticles in aqueous solutions was evaluated visually and using a separation analyser. Photocatalytic activity of nanoparticles was studied by photo‐activated degradation reaction of Rhodamine B dyestuff in aqueous solutions. The results showed that grafted particles had acquired enhanced dispersion stability and lower photocatalytic activity in aqueous solutions. Untreated TiO₂ dispersions settled rapidly and sedimentation completed within 24 h through the coagulation mechanism, whereas that of the silica‐treated nanoparticles, depending on the silica content, showed different degrees of stability by flocculation mechanism. Photodebleaching of Rhodamine B in the presence of treated nanoparticles is evident by weaker intensity of UV absorption peak of 554 nm due to lowering concentration of Rhodamine B accompanied with the blue shift in UV absorption peaks. However, untreated TiO₂ nanoparticles showed only weaker intensity of UV absorption peak. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of chitosan-stabilized Au nanoparticles with controllable sizes

Au nanoparticles stabilized by chitosan have been prepared under the combined action of ultraviolet radiation and thermal exposure of its solutions doped with HAuCl₄. With the use of absorption spectrophotometry and small-angle X-ray scattering, it has been shown that the use of chitosan of different molecular masses allows one to control both the sizes of Au particles and their aggregative stability in nanodispersions.     

Light conversion efficiency of flower like structure TiO<Subscript>2</Subscript> thin film solar cells

Flower like structure TiO₂ thin films have been grown onto ITO coated glass substrates by sol–gel method. TiO₂ nano flowers have been sensitized using CdS quantum dots prepared using simple precursors by chemical method. The assembly of CdS quantum dots with TiO₂ nano flower has been used as photo-electrode in quantum dot sensitized solar cells. The surface morphology has been studied using scanning electron microscope; it shows that the film exhibits flower like structure. The absorption spectra reveals that the absorption edge of CdS quantum dot sensitized TiO₂ nano flower shifts towards longer wavelength side when compared to the absorption edge of TiO₂ nano flower. The efficiency of the fabricated CdS quantum dot sensitized TiO₂ nano flower based solar cell is 0.66%.     

掺杂纳米金粒子的火焰氧化TiO2膜的光电化学性质的研究

A nano-Au modified TiO2 electrode was prepared via the oxidation of Ti sheet in flame and subsequent modification with gold nanoparticles. The results of SEM and TEM measurements show that the Au nanoparticles are well dispersed on TiO2 surface. A near 2-fold enhancement in photocurrent was achieved upon the modification with Au nanoparticles. From the results of photocurrent and electrochemical impedance experiments it was found that the flatband potential of nano-Au/TiO2 electrode negatively shifted about 100 mV in 0.5 mol/L Na2SO4 solutions compared with that of bare TiO2 electrode. The improvement of photoelectrochemical performance was explained by the inhibition for charge recombination of photo-induced electrons and holes, and the promotion for interracial charge-transfer kinetics at nano-Au/TiO2 composite film. Such nanometal-semiconductor composite films have the potential application in improving the performance of photoelectrochemical solar cells.     

Preparation and application of poly(alkoxytitanate) as a TiO2 precursor with high storage stability

Titanium dioxide is a basic material of our daily life. Because of its favourable properties, such as harmlessness, chemical stability, photocatalytic activity, or whiteness it is increasingly applied in both micro and nano particles and thin films and coating. One of the available procedures for film forming is the sol–gel technology, an inexpensive low temperature process with wide possibilities to vary film properties by changing the composition of the precursor solution or other parameters. In the paper a new precursor polymer for TiO₂ film-preparation with high storage and processing stabilities is introduced and applied in thin film forming. The new precursor poly(alkoxytitanate) is prepared by a one step, water-free sol–gel method. A smooth TiO₂ film can be prepared using this precursor by spin-coating followed by H₂-plasma curing. Comparing to a common precursor such as Ti(O–iPr)₄, this precursor has a good solubility in different solvents and a much higher storage stability. The easy to modify precursor end groups enable the tailoring of properties regarding to hydrolysis to both TiO₂ particles and films.     

Size‐Dependence of the Activity of Gold Nanoparticle‐Loaded Titanium(IV) Oxide Plasmonic Photocatalyst for Water Oxidation

Mesoporous TiO₂ nanocrystalline film was formed on fluorine‐doped tin oxide electrode (TiO₂/FTO) and gold nanoparticles (NPs) of different sizes were loaded onto the surface with the loading amount kept constant (Au/TiO₂/FTO). Visible‐light irradiation (λ>430 nm) of the Au/TiO₂/FTO photoanode in a photoelectrochemical cell with the structure of photoanode|0.1 m NaClO4 aqueous solution|Ag/AgCl (reference electrode)|glassy carbon (cathode) leads to the oxidation of water to oxygen (O₂). We show that the visible‐light activity of the Au/TiO₂/FTO anode increases with a decrease in Au particle size (d) at 2.9≤d≤11.9 nm due to the enhancement of the charge separation and increasing photoelectrocatalytic activity.