Magnetic polymer microsphere stabilized gold nanocolloids as a facilely recoverable catalyst

Magnetically responsive hierarchical magnetite/silica/poly(ethyleneglycol dimethacrylate-co-4-vinylpyridine) (Fe₃O₄/SiO₂/P(EGDMA-co-VPy)) tri-layer microspheres were used as stabilizers for gold metallic nanocolloids as a facilely recoverable catalyst with the reduction of 4-nitrophenol to 4-aminophenol as a model reaction. The magnetic microsphere stabilized gold metallic nanocolloids were prepared by in situ reduction of gold chloride trihydrate with borohydride as reductant via the stabilization effect of the pyridyl groups to gold nanoparticles on the surface of the outer shell-layer of the inorganic/polymer tri-layer microspheres.     

Catalytic properties of carboxylic acid functionalized-polymer microsphere-stabilized gold metallic colloids

Polymer-microsphere-stabilized gold metallic colloids have been prepared by a novel strategy of simple and convenient reduction of the metallic salt through the stabilization of the active carboxylic acid group on the gel and surface layer of the microsphere. The nature of the interaction between the carboxylic acid and Au nanoparticles was studied in detail by XPS. Preliminary results indicate that polymer-microsphere-stabilized gold colloids are active catalysts for the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride as reductant. The catalytic properties of the stabilized catalyst for recycling were also investigated.     

One-step synthesis of gold nanoparticles using azacryptand and their applications in SERS and catalysis

A new aqueous-phase method for the preparation of stable gold nanoparticles by using 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane (azacryptand) as both reductant and stabilizer is reported. Reduction of HAuCl(4) with azacryptand at room temperature yields nano-sized particles within a short time. The obtained gold nanoparticles have been characterized by UV-vis spectroscopy, transmission electron microscopy, and X-ray diffraction. Comparison of FT-IR spectra of azacryptand before and after reaction revealed that azacryptand molecules reduce gold ions as the amino moieties in the molecules are oxidized to imino groups. The prepared gold nanoparticles show efficient surface-enhanced Raman scattering properties and can effectively catalyze reduction of 4-nitrophenol by sodium borohydride in aqueous solution.     

Voltage effects on the nanoelectrospray characteristics in fully voltage-controlled atomisation of gold nanocolloids

The voltage effects on fully voltage-controlled nanoelectrospraying of aqueous gold nanocolloids were investigated. In the nanoelectrospray using 30 μm nozzle, with an increasing of voltage two stable spray regimes of pulsating and cone-jet mode were clearly observed by a combination of current measurement and fast imaging technology. In this nanoelectrospray uniquely determined by the electrical field voltage the current-voltage characteristics were analysed and evaluated based on an equivalent circuit method. At high field in cone-jet regime all the equivalent resistances derived by fitting appear close to a value of 0.53 ± 0.03 GΩ, showing independence to the conductivity of the nanocolloids. In low field pulsating regime a high pulsation frequency up to 100 kHz with relatively stable current pulse was exhibited in all the gold nanocolloids. A linear relationship between the DC components in the pulsating current and the voltage was found and the DC equivalent resistance obtained from the fitting varies between 0.90 and 1.47 GΩ. A strong correlation between the pulsating properties and the conductivity of the colloids was identified.     

Synthesis of tetraoctylammonium-protected gold nanoparticles with improved stability

This paper shows that an introduction of thiosulfate anions in place of bromide anions greatly improves both chemical and thermal stability of tetraoctylammonium-protected gold nanoparticles. Tetraoctylammonium thiosulfate [(Oct)4N+-O3SS]-protected gold nanoparticles are synthesized by the reduction of (Oct)4N+-AuCl4 to Au(I)-SSO3-, followed by the addition of sodium borohydride. The presence of thiosulfate anions instead of bromide anions on the surface of gold nanoparticles results in a significant dampening of the surface plasmon band of gold at 526 nm due to the strong interaction between thiosulfate and the gold nanoparticle surface. Cyanide decomposition and heating treatment studies suggest that (Oct)4N+-O3SS-protected nanoparticles have much higher overall stability compared to (Oct)4N+-Br-protected gold nanoparticles.     

Self-assembled gold nanoparticles on functionalized gold (111) studied by scanning tunneling microscopy

Nanogold colloidal solutions are prepared by the reduction of HAuClO4 with sodium citrate and sodium borohydride.4-Aminothiophenol (ATP) self-assembled monolayers (SAMs) are formed on gold(111) surface,on which gold nanopartides are immobilized and a sub-monolayer of the particles appears.This sub-monolayer of gold nanopartides is characterized with scanning tunneling microscopy (STM),and a dual energy barrier tunneling model is proposed to explain the imageability of the gold nanopartides by STM.This model can also be used to construct multiple energy barrier structure on solid/ liquid interface and to evaluate the electron transport ability of some organic monolayers with the aid of electrochemical method.     

Triphasic nanocolloids

Triphasic nanocolloids, that is, nanocolloids with three distinct compartments, were successfully produced by use of electrified co-jetting. Simultaneous manipulation of the three parallel liquid with laminar flows yielded a liquid droplet with three interfaces between the jetting liquids. Under a high electric potential, a single liquid jet was produced from the triple point of the droplet. Separation between the phases was maintained throughout the jetting process and resulted in triphasic nanocolloids. Poly(ethylene oxide), poly(acrylic acid), and poly(acrylamide-co-acrylic acid) solutions were used and verified to be compatible with the process. Fluorescent-labeled biomolecules were selectively incorporated in each phase of the nanocolloids, and confocal laser scanning microscopy was employed for the characterization. Scanning electron microscopy results verified that the sizes of the colloids are in the range of nanocolloids. This simple and versatile technique to fabricate multicompartment nanocolloids is expected to have great impact on drug delivery, molecular imaging, and smart displays.     

以硼氢化钠为还原剂化学镀镍的电化学研究

采用线性电位扫描伏安法研究了以硼氢化钠为还原剂的化学镀镍体系, 考查了镀液组成及工艺条件对化学镀镍硼阴、阳极过程的影响, 结果表明: 乙酸镍和硼氢化钠含量的提高分别促进了Ni²⁺的还原反应和BH₄^-的氧化反应; 乙二胺、氢氧化钠以及添加剂硫脲、糖精钠对阴、阳极反应均有不同程度的抑制作用, 同时添加剂中的硫元素加速了镍的氧化; 升高温度有利于阴、阳极反应的进行.     

Preparation and characterization of noble metal nanocolloids by silk fibroin in situ reduction

Silk fibroin (SF) is a natural protein from silkworm. It represents Chinas resplendent civili-zation as dress materials in the past 5000 a. To this day, the silk output in China is about 90000 tons per year, which is about 70% of the world overall output. In the past decade, it has been found that silk fibroin has special properties for being used as healthy foods, cosmetics, enzyme immobilizing materials, cell culture medium, biosensor, artificial skin, artificial muscle, perme-able membran…     

Size-selective synthesis and stabilization of gold organosol in C(n)TAC: enhanced molecular fluorescence from gold-bound fluorophores

Gold nanoparticles of variable sizes have been synthesized in toluene employing two-phase (water-toluene) extraction of AuCl4- followed by its reduction with sodium borohydride in the presence of a series of cationic surfactants of a homologous series having the general formula C(n)TAC. The solubility features of the gold particles in the organic solvent have been accounted qualitatively by calculating the van der Waals interaction potential between the particles. The effect of thermal energy and medium dielectric constant on the stability of metal particles has been studied by measuring the surface plasmon resonance. The stabilization of surfactant-mediated gold particles as hydrosol or organosol has been elucidated by considering the double-layer interaction as a function of the dielectric constant of the solvent medium. The influence of the counterion of the phase transfer reagent and stabilizing ligand on the photochemical stability of the gold colloids has been investigated. The fluorescence probe 1-methylaminopyrene (MAP) was considered for the surface functionalization of the gold particles, and it has been found that there is an enhancement of molecular fluorescence from the gold-probe assembly.     

Water-stable biphasic nanocolloids with potential use as anisotropic imaging probes

Electrified co-jetting of two aqueous polymer solutions followed by a thermal cross-linking step was used to create water-stable biphasic nanocolloids. For this purpose, aqueous solution mixtures of poly(acrylamide-co-acrylic acid) and poly(acrylic acid) were employed as jetting solutions. When the biphasic nanocolloids created by side-by-side electrified co-jetting were thermally treated, a cross-linking reaction occurred between amide groups and carboxylic groups to form stable imide groups. Infrared spectroscopy was employed to monitor the reaction. The quality and the integrity of the resulting biphasic nanocolloids were confirmed by confocal laser scanning microscopy, flow cytometry analysis, and dynamic light scattering. Selective encapsulation of two biomolecules in each phase of the biphasic colloids was maintained even after thermal reaction and suspension in aqueous environment. Well-dispersed spherical colloids with stable dye loadings in each hemisphere were kept intact without aggregation or dissolution for several weeks. Finally, biphasic nanocolloids were selectively surface-modified with a biotin-dextran resulting in water-stable particles to ensure binding of proteins only to a single hemisphere.     

Controlled growth and catalytic activity of gold monolayer protected clusters in presence of borohydride salts

In the presence of large excesses of borohydride salts, gold monolayer protected-clusters can be grown to larger sizes simply by controlling the amount of reducing agent added to smaller clusters. In addition, gold monolayer clusters can be used as catalysts for reduction reactions by sodium borohydride; results suggest such catalysts have sterically constrained active sites.     

Spectrophotometric analysis of stability of gold nanoparticles during catalytic reduction of 4-nitrophenol

Spectrophotometric monitoring of 4-nitrophenol (4-NP) reduction by sodium borohydride (NaBH₄) using gold nanoparticles (GNPs) as a catalyst has been extensively studied, but the stability of GNPs in terms of change in the surface plasmon resonance (SPR) at different temperatures has not been explored. In the present investigation, our aim was to evaluate the SPR stability of GNPs as a catalyst during the reduction of 4-NP at different elevated temperatures (i.e. 30–60 °C) and sodium borohydride concentrations. Sensitivity of this degradation process toward concentration of GNPs at a range of temperatures is also evaluated. The spectrophotometric results reveal that up to 45 °C, 12 ± 1.5 nm catalyst has a consistent optical density (OD) during the entire 4-NP reduction process, which is related to the surface integrity of catalyst atoms. As the temperature approached 50 °C, the OD gradually decreased and showed a blue shift as the reaction proceeded, which could be related to a decrease in particle size or surface dissolution of gold atoms. The present study may find application in the design of catalysts for the reduction of organic pollutants in industrial wastewater at a range of temperatures.     

Green preparation of hollow mesoporous silica nanosphere inside-loaded gold nanoparticles and the catalytic activity

In this work, an active nano-catalyst with gold nanoparticles loaded in hollow mesoporous silica nanospheres (HMSNs/Au) was prepared by a one-pot sol-gel method, in which gold ions were loaded in hollow mesoporous silica spheres followed by sodium alginate reduction. The characterization of the HMSNs/Au were determined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption–desorption isotherms (BET). The high catalytic activity of HMSNs/Au, denoted as apparent turn-over frequency (TOF), was detected by UV-Vis spectrophotometer for the catalytic reduction of 4-nitrophenol (74.5 h^?1) and 2-nitrophenol (108.7 h^?1) in the presence of sodium borohydride solution due to the small gold nanoparticles size and overall exposure of active sites. It is expected that this ecofriendly approach to prepare inorganic composited nanoparticles as high active catalysts based on hollow mesoporous materials was a promising platform for loading noble metal nanoparticles.     

Graphene oxide nanocolloids

Graphene oxide (GO) nanocolloids-sheets with lateral dimension smaller than 100 nm-were synthesized by chemical exfoliation of graphite nanofibers, in which the graphene planes are coin-stacked along the length of the nanofibers. Since the upper size limit is predetermined by the diameter of the nanofiber precursor, the size distribution of the GO nanosheets is much more uniform than that of common GO synthesized from graphite powders. The size can be further tuned by the oxidation time. Compared to the micrometer-sized, regular GO sheets, nano GO has very similar spectroscopic characteristics and chemical properties but very different solution properties, such as surface activity and colloidal stability. Due to higher charge density originating from their higher edge-to-area ratios, aqueous GO nanocolloids are significantly more stable. Dispersions of GO nanocolloids can sustain high-speed centrifugation and remain stable even after chemical reduction, which would result in aggregates for regular GO. Therefore, nano GO can act as a better dispersing agent for insoluble materials (e.g., carbon nanotubes) in water, creating a more stable colloidal dispersion.     

Spectroscopic identification of S-Au interaction in cysteine capped gold nanoparticles

This study deals with the synthesis of cysteine capped gold nanoparticles with an average size of 12 nm by borohydride reduction and spectroscopic identification of SAu interaction. We have studied the interaction of thiol with gold nanoparticles in aqueous medium by employing UV-vis, Raman, NMR, and FT-IR spectroscopy. The shifting of gold plasmon resonance in the UV-vis spectra shows the stabilization of gold nanoparticles by cysteine. The disappearance of S-H stretching in both the IR and Raman spectra and the shifting of the NMR signals of the protons in close proximity to the metal center supported the existence of the S-Au interaction in cysteine capped gold nanoparticles. The TEM images shows cysteine capped gold nanoparticles as distinct and spherical entities as compared to free colloidal gold nanoparticles.     

Tiopronin gold nanoparticle precursor forms aurophilic ring tetramer

In the two step synthesis of thiolate-monolayer protected clusters (MPCs), the first step of the reaction is a mild reduction of gold(III) by thiols that generates gold(I) thiolate complexes as intermediates. Using tiopronin (Tio) as the thiol reductant, the characterization of the intermediate Au(4)Tio(4) complex was accomplished with various analytical and structural techniques. Nuclear magnetic resonance (NMR), elemental analysis, thermogravimetric analysis (TGA), and matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) were all consistent with a cyclic gold(I)-thiol tetramer structure, and final structural analysis was gathered through the use of powder diffraction and pair distribution functions (PDF). Crystallographic data has proved challenging for almost all previous gold(I)-thiolate complexes. Herein, a novel characterization technique when combined with standard analytical assessment to elucidate structure without crystallographic data proved invaluable to the study of these complexes. This in conjunction with other analytical techniques, in particular mass spectrometry, can elucidate a structure when crystallographic data is unavailable. In addition, luminescent properties provided evidence of aurophilicity within the molecule. The concept of aurophilicity has been introduced to describe a select group of gold-thiolate structures, which possess unique characteristics, mainly red photoluminescence and a distinct Au-Au intramolecular distance indicating a weak metal-metal bond as also evidenced by the structural model of the tetramer. Significant features of both the tetrameric and the aurophilic properties of the intermediate gold(I) tiopronin complex are retained after borohydride reduction to form the MPC, including gold(I) tiopronin partial rings as capping motifs, or "staples", and weak red photoluminescence that extends into the Near Infrared region.     

Synthesis and spectroscopic characterization of gold nanoparticles

Photoluminescent nanoparticles of gold with size 3, 4, 6, and 9nm are prepared by borohydride/citrate reduction in presence of polyethylene glycol (PEG)/tannic acid. The prepared nanomaterials are characterized by UV-vis spectroscopy and dynamic light scattering (DLS) technique. Intense photoluminescence (PL) is observed in nanoparticles prepared by fast reduction with borohydride in presence of PEG. A red shift of PL emission from 408 to 456nm is observed for the change of size from 4 to 6nm. Increase in PL intensity is observed for all the nanoparticles on the addition of KCl. Citrate reduced gold colloid which consists of large particles of size approximately 35nm with anisotropic shapes showing two plasmon peaks is also prepared. The anisotropy is confirmed by TEM measurement. SERS activity of this colloid is tested using glutamic acid as an adsorbate probe. Assignment of the observed bands is given.     

Preparation and characterization of noble metal nanocolloids by silk fibroin <Emphasis Type="Italic">in situ</Emphasis> reduction

Noble metal nanocolloids are prepared from their precursors by in situ reduction of a silk fibroin solution at room temperature without any reducing agent. The mechanism, the effects of pH and the molar ratio of the reactants on the reduction reaction are studied by UV-Vis spectroscopy. The structure of the colloids is characterized by FT-IR, TEM and AFM. According to the TEM images, the gold-silk fibroin colloid is a nanostructured bioconjugate with novel core-shell, while the silver-silk fibroin colloid tends to be congregated as clusters having more than ten nanoparticles of silver-silk fibroin. The gold colloid is highly dispersed and stable while the silver colloid is less dispersed and stable than the gold colloid.     

Preparation of magnetic microspheres with thiol-containing polymer brushes and immobilization of gold nanoparticles in the brush layer

Narrow-disperse magnetic microspheres were prepared by alkaline coprecipitation of Fe²⁺ and Fe³⁺ ions within poly(acrylic acid–divinylbenzene) microspheres that were prepared by distillation–precipitation copolymerization. Magnetic microspheres with polymer brushes that contain epoxy groups were prepared by graft copolymerization of glycidyl methacrylate and glycerol monomethacrylate via atom transfer radical polymerization (ATRP) from the magnetic microsphere surfaces. Subsequently, magnetic microspheres with thiol-containing polymer brushes were prepared by treating the epoxy group-containing magnetic microspheres with sodium hydrosulfide. Gold nanoparticles were immobilized in the brush layer of the thiol-containing magnetic microspheres through Au–S coordination. The catalytic activity of the gold nanoparticle-immobilized magnetic microspheres was investigated using the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride as a model reaction. The catalyst could be reused for over 10 cycles without noticeable loss of catalytic activity.