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.     

Preparation of Au-TiO2 Hybrid Nano Particles in Silicate Film Made by Sol-Gel Method

TiO₂ nano particles with photo catalytic property were mixed with silica alkoxides solution with HAuCl₄/4H₂O. STS02 (purchased from Ishihara Sangyo Kaisha, Ltd.) was used as TiO₂ nano particles. The average size of TiO₂ nano particles was 7 nm in diameter. The gel film coated on glass substrate was heated and then HAuCl₄/4H₂O was thermally reduced at 390 degree. The coated silica gel film doped with HAuCl₄/4H₂O and TiO₂ nano particles was turned into light blue from colorless gel film after heat treatment. The optical absorption spectrum showed the absorption peak of the film heated at 390 degree shifted to at about 650 nm compare to SiO₂ film doped with Au nano particles without TiO₂ nano particles that had absorption peak at 542 nm. On the other hand, the film formed from coating solution incorporated TiAA (titanium tetraisopropoxide chelated by acetyl acetone) as TiO₂ source instead of TiO₂ nano particles had absorption peak at 550 nm. That means there was no effect on formation of Au nano particles when TiAA was incorporated. The average size of the particles was found to be about 23 nm in diameter by TEM observation. Furthermore EDX (Energy Dispersive X-ray Fluorescence Spectrometer) analysis of nano particles in the film indicated that Au-TiO₂ nano hybrid particles were formed. Simulation results also supported that the size in diameter of Au nano particles had little influence on the absorption coefficient of the silica film doped with Au nano particles.     

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.     

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene

Photochemical synthesis of gold nanoparticles in aqueous dispersions of carboxylated polystyrene with microsphere sizes of 100, 300, 500, and 1410 nm under the action of monochromatic light with an excitation wavelength of 254 nm was studied. Preliminary irradiation of the polymer dispersion induces formation of gold particles under dark conditions. Dependences of gold nanoparticles formation on the duration of preliminary polymer irradiation and concentration of introduced HAuCl₄ aqueous solution were determined. A mechanism of the polystyrene-assisted formation of gold nanoparticles was proposed. The size and structure of gold nanoparticles were determined.     

Piece by Piece—Electrochemical Synthesis of Individual Nanoparticles and their Performance in ORR Electrocatalysis

The impact of individual HAuCl₄ nanoreactors is measured electrochemically, which provides operando insights and precise control over the modification of electrodes with functional nanoparticles of well‐defined size. Uniformly sized micelles are loaded with a dissolved metal salt. These solution‐phase precursor entities are then reduced electrochemically—one by one—to form nanoparticles (NPs). The charge transferred during the reduction of each micelle is measured individually and allows operando sizing of each of the formed nanoparticles. Thus, particles of known number and sizes can be deposited homogenously even on nonplanar electrodes. This is demonstrated for the decoration of cylindrical carbon fibre electrodes with 25±7 nm sized Au particles from HAuCl₄‐filled micelles. These Au NP‐decorated electrodes show great catalyst performance for ORR (oxygen reduction reaction) already at low catalyst loadings. Hence, collisions of individual precursor‐filled nanocontainers are presented as a new route to nanoparticle‐modified electrodes with high catalyst utilization.     

Preparation of reversibly photo-cross-linked nanogels from pH-responsive block copolymers and use as nanoreactors for the synthesis of gold nanoparticles

Reversibly photo-cross-linkable pH-responsive block copolymer poly(ethylene oxide)-b-poly((2-(diethylamino)ethyl methacrylate-co-4-methyl-[7-(methacryloyl)oxyethyloxy] coumarin)) (PEO-b-P(DEA-co-CMA)) was synthesized via atom transfer radical polymerization (ATRP). Block copolymer nanogels could be easily prepared by first photo-cross-linking of the micelles at pH > 7 and then adjusting the solution to pH < 7. The photo-cross-linking was proved to be reversibly controlled under alternative irradiation of UV light at 365 nm and 254 nm. As a result, the cross-linking degrees and sizes of the nanogels can be easily controlled by alternatively UV light irradiation. Finally, the nanogels can serve as nanoreactors for the synthesis of gold nanoparticles. The protonated DEA units were first coordinated with HAuCl₄, and then the electrostatically bounded AuCl⁴⁻ anions were reduced to gold nanoparticles by NaBH₄. The nanogel-supported gold nanoparticles were used in chemical catalysis. The pH-responsive photo-cross-linked nanogels have been characterized using dynamic light scattering, transmission electron microscopy, UV-vis spectra and ¹H NMR spectroscopy measurements, respectively.     

Mineralization of gold in block copolymer micelles

Ultrasmall gold particles have been prepared inside the micelles of polystyrene-block-poly(ethylene oxide) and polystyrene-block-poly(2-vinylpyridine) in toluene. Starting point was the formation of a thermodynamically stable dispersion of HAuCl₄ or LiAuCl₄ in the inverse micelles of the block copolymer which were treated with hydrazine or pyrrole. Analysis of the effect of the reduction agent on the stability of the micelles yielded a simple model for the transformation process involving coagulation of the swelling micelles. Kinetic control of the different steps, i.e., reduction, mineralization, coagulation, film formation, allowed to prepare thin films in which highly uniform gold particles were arranged in yet unknown order. When pyrrole was employed for the reduction, the gold monocrystals got embedded in a shell of polypyrrole.     

Synthesis of star‐shaped poly(n‐butyl acrylate) oligomers with coumarin end groups and their networks for a UV‐tunable viscoelastic material

Solvent‐free isothermal tuning of viscoelasticity of polymer materials is important for an emerging photochemical molding technology and photoreversible adhesives. In this study we designed a four‐armed star‐shaped poly(butyl acrylate, BA) oligomer having four coumarin end groups. The irradiation of UV at the wavelength of 365 nm (UV₃₆₅) to the viscous poly(BA) oligomer under a solvent‐free condition produced a solid network material along with the progress of dimerization reaction with coumarin end groups. The subsequent irradiation of UV at the wavelength of 254 nm (UV₂₅₄) caused dimer dissociation reaction to attain change in the mixing degree of star and network architectures in the material. Moreover, viscoelasticity of the network material was tunable by repetitive UV₃₆₅ and UV₂₅₄ irradiations. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 9–15     

Factors affecting photoisomerization of 4-styrylpyridine

Photoisomerization of 4-styrylpyridine at different irradiation wavelengths (λ 365 and 254 nm) and in different solvents was studied by UV and ¹H NMR spectroscopy. A procedure for recording the UV spectra of 4-styrylpyridine dissolved in liquid crystalline films freely suspended within a frame. The results of quantum-chemical calculations of the geometry and UV spectra of 4-styrylpyridine isomers are presented.     

免疫纳米金催化氯金酸与羟胺反应-共振散射光谱检测痕量青霉素G

小粒径的金和免疫金纳米粒子对氯金酸-盐酸羟胺这一反应具有较强的催化作用,其产物在580 nm处有一共振散射峰。以半抗原青霉素G为模型,用粒径为9 nm的金纳米微粒标记羊抗兔青霉素噻唑蛋白抗体制备了青霉素G的免疫纳米金共振散射光谱探针。在pH5.4的柠檬酸-磷酸氢二钠缓冲溶液中,青霉素G与金标兔抗青霉素发生特异性结合生成胶体金免疫复合物,离心分离。取适量金标羊抗兔青霉素的上层清液做催化剂,在pH3.36盐酸-柠檬酸钠缓冲溶液－40μg/mL氯金酸－21.6μg/mL的盐酸羟胺条件下,进行催化反应后金纳米粒径增大,在580nm共振散射强度处增强。随着青霉素G浓度c增大,上层清液中免疫金纳米微粒数量降低,I580nm值降低。其降低值△I580nm与c在0.15-225 ng/mL范围内成线性关系,其回归方程为△I580nm=0.28c+5.16,检出限为0. 05 ng/mL。该法用于牛奶中青霉素G的检测,结果较好。     

Synthesis, characterization and preliminary toxicity assays of NIR-active Au-silicate nanoparticles through a sol-gel processing

Monodisperse Au-silicate nanoparticles (10.7±1.6 nm in diameter) were prepared by reduction of aqueous solution containing 2 mM HAuCl₄ with sodium citrate (1 wt.%) in a hydrosol, in which small clusters of silicate formed by hydrolysis and polymerization of 3-aminopropyltrimethoxysilane (APTMS). APTMS covalently linked to reduced gold particles through its -NH₂ end-group. UV-vis spectra of the obtained Au-silicate nanoparticles showed a peak at ∼690 nm due to the interface effects between the Au and the silicate matrix. The Au-silicate nanoparticles exhibited near-IR (NIR) sensitivity. Cytotoxicity and limited hemocompatibility in vitro for the prepared Au-silicate nanoparticles were also investigated. It was shown that at lower concentration (<1 μg/ml), the Au-silicate nanoparticles were biocompatible without causing any cytotoxicity and hemolysis.     

Selective detection and recovery of gold at tannin-immobilized non-conducting electrode

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl₄, and the electrochemical reduction of HAuCl₄ to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl₄ along with FeCl₃ and/or CuCl₂, the NCPF remained selective toward the electrochemical reduction of HAuCl₄ into the metallic state. The chemical reduction of HAuCl₄ into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29 ± 1.45 mg g⁻¹ at 60 °C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.     

Introducing lanthanide metal–organic framework and perovskite onto pulp fibers for fluorescent anti-counterfeiting and encryption

The research of anti-counterfeiting and encryption has always been a subject of universal concern all over the world. Herein, lanthanide metal–organic framework (Eu-MOF) and CH₃NH₃PbBr₃ (MAPbBr₃) perovskite were introduced onto pulp fibers (PFs) to prepare fluorescent anti-counterfeiting and encryption papers. Eu-MOF@PFs paper emitted red fluorescence at 254 nm UV excitation. The optimum preparation conditions of Eu-MOF@PFs were 2.5 mmol of Eu(NO₃)₃, 4 h of reaction time and room temperature. When MABr ink was written on Pb/Eu-MOF@PFs paper, the green fluorescent handwriting and red fluorescent paper were observed under 365 nm and 254 nm UV excitation, respectively. The appropriate addition amount of lead nitrate was 0.6 mmol. Pb/Eu-MOF@PFs paper was immersed in MABr solution to prepare MAPbBr₃@Pb/Eu-MOF@PFs paper. Under 254 nm and 365 nm UV irradiations, MAPbBr₃@Pb/Eu-MOF@PFs paper emitted red-green double fluorescence and the quantum yields of which were 3.11% and 2.48%, respectively. The crystal structure of MAPbBr₃ was easily destroyed by polar solution, which realized on/off switching of the luminescence signal for multistage information encryption. The above paper-based fluorescence materials were potential for advanced anti-counterfeiting and encryption applications.

     

Ultraviolet Protection Characteristics of Silicone/Titanium Dioxide Composite Sheets

Silicone/titanium dioxide (TiO₂) composite sheets were prepared from TiO₂ particles and silicone elastomer by a compression-molding process at 140 °C. The particles were produced through sol-gel method, and emulsion technique consecutively. The prepared composite sheets with thickness of 0.8 mm had ultraviolet radiation protection property such that the transmission of ultraviolet (UV) B ray through the sheets was less than 1%. The UVA ray transmitted the sheets in the range of 0.02–4% at 320 nm and 2–43% at 400 nm, depending on the amount of TiO₂ emulsion presented in the silicone elastomer. The composite sheets still remained transparent since the transmission of the visible light through the sheets was up to 60%. On the other hand, the transmissions of UVB ray, UVA ray, and visible light through the pure silicone elastomer sheets were in the range of 47–58%, 58–71%, and 71–88%, respectively. Comparable with silicone elastomer sheets, the addition of TiO₂ emulsion resulted in the composite sheets with higher strain and lower modulus; however, these differences in tensile properties were up to the amount of the emulsion in the silicone elastomer.     

Regioselective Bridging Calix[6]arenes: Synthesis and X-ray Structure of Trisbridged Calix[6]arene

The preparation and characterization of gold nanoparticles (～6 nm in diameter) modified with mono-6-thio-β-cyclodextrin (II) is described. The resulting monolayer-protected gold nanoparticles are water-soluble and more stable. The concentration of II plays a crucial role for the distribution of the modified nanoparticles. When the ratio of concentration of II to HAuCl₄,[II]/[HAuCl₄] ≥ 0.93, a stable gold nanoparticle with uniform distribution and diameter of 6.0 ± 0.9 nm will be obtained. The recognition of modified gold nanoparticles to organic guest molecule is researched. The modified gold nanoparticles can make the electrochemical reduction current of nitrobenzene decrease and can be self-assembled in three-dimensional to form spherical clusters with ligand of methylene green.     

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.     

Reversible SC‐SC Transformation involving [4+4] Cycloaddition of Anthracene: A Single‐Ion to Single‐Molecule Magnet and Yellow‐Green to Blue‐White Emission

In search of magneto‐optic materials, the mononuclear compounds Ln^III(depma)(NO₃)₃(hmpa)₂ (Ln=Dy, Gd) were synthesized. The anthracene moieties undergo [4+4] dimerization when irradiated at 365 nm without loss of crystallinity. The Dy compound switches from a single‐ion to a single‐molecule magnet with doubling of the spin reversal barrier energy and from yellow‐green to blue‐white emission. The dimerization is reversed by heating at 100 °C or partially on light irradiating at 254 nm. The results suggest that lanthanide phosphonates with anthracene are promising smart materials displaying synergistic magneto‐optic property.     

Polymer-Protected Bimetallic Clusters. Preparation and Application to Catalysis

Colloidal dispersions of polymer-protected Pd/Pt and Pd/Au bimetallic clusters were prepared by reduction of an alcoholic solution of PdCl₂ and H₂PtCl₆ or HAuCl₄ in the presence of poly(N-vinyl-2-pyrrolidone). The reduction can be carried out by refluxing in alcohol or by irradiation with visible light. The dispersions of the bimetallic clusters obtained are stable for months at room temperature and have from dark brown to brownish red color. Transmission electron micrographs show that the bimetallic clusters are composed of well-dispersed ultrafine particles of uniform size, about 1.5 nm for Pd-Pd and 3.4 nm for Pd-Au in diameter. The catalytic activity of the bimetallic clusters depends on the metal composition. In the case of the partial hydrogenation of 1, 3-cyclooctadiene, the activity went through a maximum when the alloy composition reached about 80% Pd and 20% Pt, or 60% Pd and 40% Au.     

Evolution of water vapor from indium-tin-oxide transparent conducting films fabricated by dip coating process

Tin-doped indium oxide In₂O₃ (indium-tin-oxide) transparent conducting films were fabricated on silicon substrates by a dip coating process. The thermal analysis of the ITO films was executed by temperature-programmed desorption (TPD) or thermal desorption spectroscopy (TDS) in high vacuum. Gas evolution from the ITO film mainly consisted of water vapor. The total amount of evolved water vapor increased on increasing the film thickness from approx. 25 to 250 nm and decreased by increasing the preparation temperature from 365 to 600°C and by annealing at the same temperature for extra 10 h. The evolution occurred via two steps; the peak temperatures for 250 nm thick films were approx. 100-120 and 205-215°C. The 25 nm thick films evolved water vapor at much higher temperatures; a shoulder at approx. 150-165°C and a peak at approx. 242°C were observed. The evolution temperatures increased by increasing the preparation and the annealing temperatures except in case of the second peak of the 25 nm thick films. The evolution of water vapor at high temperature was tentatively attributed to thermal decomposition of indium hydroxide, In(OH)₃, formed on the surface of the nm-sized ITO particles. This revised version was published online in August 2006 with corrections to the Cover Date.