Sonochemical intercalation of preformed gold nanoparticles into multilayered clays

Multilayered Na (+)-montmorillonite clays intercalated with Au nanoparticles were synthesized by direct ultrasonic impregnation of preformed gold colloid into the clay matrix. The sonicated composite product then consists of Au nanoparticles homogeneously dispersed in the clay. The resulting clay/nano-Au composite was calcined at 800 degrees C and characterized by BET surface area analysis, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared measurements. Nearly spherical-shaped gold nanoparticles, with a size of 6 +/- 0.5 nm, are located in the pores of clay calcined at 800 degrees C. Their nanocomposites are thermally stable as was shown by thermogravimetric analysis. No aggregation of the gold nanoparticles was observed during calcination. The proposed ultrasonic intercalation approach is an universal one and can be employed for synthesis of catalytically active metal-clay nanocomposites stable at high temperatures with high dispersability of the metal nanoparticles in the clay matrix.     

Resonance light scattering spectroscopy study of interaction between gold colloid and thiamazole and its analytical application

In this paper, we used resonance light scattering (RLS) spectroscopy to study the interaction between thiol-containing pharmaceutical-thiamazole and gold colloid. At pH 5.2, the resonance light scattering spectrum of gold nanoparticles has a maximum peak at 555 nm and the RLS intensity is enhanced by trace amount of thiamazole due to the interaction between thiamazole and gold colloid. The binding of colloidal gold to thiamazole results in ligand-induced aggregation of colloidal gold, which was characterized by RLS spectrum, ultraviolet-visible (UV-Vis) spectrum, and transmission electron microscopy (TEM). Based upon the study, we proposed a highly sensitive, gold colloid-based assay using RLS spectrum to detect pharmaceuticals for the first time. The mechanism of binding interaction between Au colloid and thiamazole was also discussed.     

Preparation of Gold Nanoparticles Using 2-Ethoxyethanol, 2-Methoxyethanol and 1,3-Butyleneglycol Supported in Chitosan

The aim of this work was to prepare and characterize several properties of Au nanoparticles colloids prepared by the “chemical liquid deposition” method, which involves the co-deposition of metallic Au with organic vapors (2-ethoxyethanol, 2-methoxyethanol and 1,3-butylenglycol at 77 K). AuNPs supported on chitosan were performed by solvated metal atom dispersed method. Then, colloids were characterized by transmission electron microscopy (TEM), electron diffraction (ED), UV–Vis spectroscopy, electrophoretic mobility, physical stability, medium–far infrared spectroscopy and thermogravimetric analysis. These studies had demonstrate that Au nanoparticles solvated with 1,3-butylenglycol and 2-ethoxyethanol, shows higher stability, due to their high dielectric constant and a better NPs solvation. TEM analysis showed a size distribution between 4.61 and 48.8 nm. From ED, a face-centered cubic structure was found. UV–Vis analysis showed lower stability of nanoparticles solvated with 2-methoxyethanol. FTIR spectra showed that the solvent was incorporated and surround the Au NPs. The thermograms shows that thermal decomposition of AuNPs–chitosan decreases with the metal presence. Bioassays of acute toxicity on fishes with AuNPs–chitosan with 1,3-butylenglycol were carried out due to the lower toxicity. The bioassay showed that 0.94 mL/L produce mortality of 50 % (LD 50) of fishes exposed 96 h calculated with a confidence interval of 0.810–1.148 mL/L.     

Aerosol assisted chemical vapor deposition using nanoparticle precursors: a route to nanocomposite thin films

Gold nanoparticle and gold/semiconductor nanocomposite thin films have been deposited using aerosol assisted chemical vapor deposition (CVD). A preformed gold colloid in toluene was used as a precursor to deposit gold films onto silica glass. These nanoparticle films showed the characteristic plasmon absorption of Au nanoparticles at 537 nm, and scanning electron microscopic (SEM) imaging confirmed the presence of individual gold particles. Nanocomposite films were deposited from the colloid concurrently with conventional CVD precursors. A film of gold particles in a host tungsten oxide matrix resulted from co-deposition with [W(OPh)(6)], while gold particles in a host titania matrix resulted from co-deposition with [Ti(O(i)Pr)(4)]. The density of Au nanoparticles within the film could be varied by changing the Au colloid concentration in the original precursor solution. Titania/gold composite films were intensely colored and showed dichromism: blue in transmitted light and red in reflected light. They showed metal-like reflection spectra and plasmon absorption. X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis confirmed the presence of metallic gold, and SEM imaging showed individual Au nanoparticles embedded in the films. X-ray diffraction detected crystalline gold in the composite films. This CVD technique can be readily extended to produce other nanocomposite films by varying the colloids and precursors used, and it offers a rapid, convenient route to nanoparticle and nanocomposite thin films.     

Synthesis, characterization and SERS activity of Au-Ag nanorods

The formation mechanism and morphology of Au-Ag bimetallic colloidal nanoparticles depend on the composition. Ag coated Au colloidal nanoparticles have been prepared by deposition of Ag through chemical reduction on performed Au colloid. The composition of the Au(100-x)-Ag(x) particles was varied from x=0 to 50. The obtained colloids were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The Au(80)-Ag(20) colloid consists of alloy nanorods with dimension of 25nmx100nm. The activity of these nanorods in surface enhanced Raman spectroscopy (SERS) was checked by using sodium salicylate as an adsorbate probe. Intense SERS bands are observed indicating its usefulness as a SERS substrate in near infrared (NIR) laser excitation.     

Synthesis,characterization and properties of magnetic colloids supported on chitosan

This work proposes the synthesis, characterization and investigation of the stabilization capabilities of chitosan doped with magnetic nanoparticles. Nanoparticles of Fe, Co, Co(II,III) oxide, Ni and Ni/Ag mixture in 2-propanol were synthesized by chemical liquid deposition and the incorporation on the polymeric matrix was performed by solvated metal atom dispersion. Colloids and nanoparticles supported on chitosan were characterized by ultraviolet, Fourier-transform infrared, thermogravimetric analysis, electron diffraction X-ray and magnetic behaviour; transmission and field electronic scanning electron microscopy. The particle size distribution of colloids ranges from 6 to 50 nm with low particle stability due to flocculation after 120 days. The nanoparticles supported on chitosan had a particle size distribution of approximately between 10 and 80 nm, with low particle distribution; however, these particles do not flocculate because the matrix increases the stabilization of nanoparticles. All compounds present superparamagnetic behaviour at low temperature.     

Biopolymeric delivery system for controlled release of polyphenolic antioxidants

A chitosan based delivery system has been developed for the controlled release of polyphenolic antioxidants such as catechin. Placebo and catechin entrapped particulate delivery systems were prepared using the sodium tripolyphosphate ionic crosslinking technique. The particles have been characterised by transmission electron microscopy, particle size and charge distribution analysis, Fourier Transform infrared spectroscopy, differential scanning calorimetry and entrapment efficiency studies. These studies gave an understanding of the physico-chemical interactions that influence the biopolymer during particle formation and entrapment of catechin. The in vitro release of catechin was carried out in enzyme-free simulated gastric and intestinal fluids. Although nanoparticles could be formed by the crosslinking technique used, there was aggregation behaviour observed after retrieval and freeze-drying of the particles as shown by transmission electron microscopy. Both the placebo and catechin-loaded particles had mean particle size range of about 4.27-6.29 μm after freeze-drying and were charged. Fourier Transform infrared spectroscopy, differential scanning calorimetry studies indicated minor structural interactions between catechin and chitosan matrix. Entrapment efficiency of the particles ranged between 27% and 40%. In vitro release studies indicated that the release of catechin in simulated gastric and intestinal fluids was between 15% and 40%, depending on the structural interactions between catechin and the chitosan matrix.     

Kinetics of gold nanoparticle aggregation: experiments and modeling

We investigate the aggregation kinetics of gold nanoparticles using both experimental techniques (i.e., quasi-elastic light scattering, UV-visible spectroscopy, and transmission electron microscopy) and mathematical modeling (i.e., constant-number Monte Carlo). Aggregation of gold nanoparticles is induced by replacing the surface citrate groups with benzyl mercaptan. We show that the experimental results can be well described by the model in which interparticle interactions are described by the classical DLVO theory. We find that final gold nanoparticle aggregates have a fractal structure with a mass fractal dimension of 2.1-2.2. Aggregation of approximately 11 initial gold nanoparticles appears to be responsible for the initial color change of suspension. This kinetic study can be used to predict the time required for the initial color change of a gold nanoparticle suspension and should provide insights into the design and optimization of colorimetric sensors that utilize aggregation of gold nanoparticles.     

The Enhanced Catalytic Performance and Stability of Ordered Mesoporous Carbon Supported Nano‐Gold with High Structural Integrity for Glycerol Oxidation

Ordered mesoporous carbon (OMC) supported gold nanoparticles of size 3–4 nm having uniform dispersion were synthesized by sol‐immobilization method. OMCs such as CMK‐3 and NCCR‐56 with high surface area and uniform pore size were obtained, respectively, using ordered mesoporous silicas such as SBA‐15 and IITM‐56 as hard templates, respectively. The resulting OMC supported monodispersed nano‐gold, i. e., Au/CMK‐3 and Au/NCCR‐56, exhibited excellent performance as mild‐oxidizing catalysts for oxidation of glycerol with high hydrothermal stability. Further, unlike activated carbon supported nano‐gold catalysts (Au/AC), the OMC supported nano‐gold catalysts, i. e., Au/CMK‐3 and Au/NCCR‐56, show no aggregation of active species even after recycling. Thus, in the case of Au/CMK‐3 and Au/NCCR‐56, both the fresh and regenerated catalysts showed excellent performane for the chosen reaction owing to an enhanced textural integrity of the catalysts and that with remarkable selectivity towards glyceric acid. The significance of the OMC supports in maintaining the dispersion of gold nanoparticles is explicit from this study, and that the activity of Au/AC catalyst is considerably decreased (～50 %) upon recycling as a result of agglomeration of the active gold nanoparticles over the disordered amorphous carbon matrix.     

Pt负载复合氧化物催化剂的CO催化发光性能

采用非晶态络合物法制备了La0.9Cu0.1MnO3和LaCoO3钙钛矿催化剂, 并利用固定化溶胶工艺合成了Pt纳米粒子负载的Pt/La0.9Cu0.1MnO3和Pt/LaCoO3复合催化剂. 通过透射电镜(TEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)等手段对催化剂的微观结构、形貌及Pt的价态进行了研究; 考察了催化剂的CO催化氧化发光性能. 结果表明, 若La0.9Cu0.1MnO3催化剂表面上负载的Pt纳米颗粒形成团聚, 则在其CO催化氧化发光谱中出现发光峰分裂的现象, 而在Pt纳米颗粒分散较好的Pt/LaCoO3体系中却没有出现这一情况. 因此可以利用CO催化发光谱来初步判断贵金属纳米颗粒在载体表面的分散状态.     

Monolayer-protected gold nanoparticles by the self-assembly of micellar poly(ethylene oxide)-b-poly(epsilon-caprolactone) block copolymer

A study is presented of the preparation of gold nanoparticles incorporated into biodegradable micelles. Poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL) copolymer was synthesized by ring-opening polymerization, and the hydroxyl end group of the PCL block was modified with thioctic acid using dicyclohexyl carbodiimide as the coupling reagent. The PEO-b-PCL-thioctate ester (TE) thus obtained was used in a later step to form monolayer protected gold nanoparticles via the thioctate spacer. Gold nanoparticles stabilized with the PEO-b-PCL block (named Au/Block (x/y), where x/y is the mole feed ratio between HAuCl4 and PEO-b-PCL-TE) were prepared and analyzed. Au/Block (1/1), Au/Block (2/1), and Au/Block (3/1) nanoparticles were found to form stable dispersions in the organic solvents commonly used to dissolve the unlabeled block copolymer. The average diameter of the nanoparticles was determined by transmission electron microscopy (TEM) and found to be 6+/-2 nm. Au/Block (4/1) nanoparticle dispersions in organic solvents, on the other hand, were not stable and produced large gold clusters (50-100 nm). Cluster formation was attributed to the low grafting density of the block copolymer, which facilitates agglomeration. For Au/Block (12/1), along the same trend, only an insoluble product was isolated. Micelles in water were prepared by the slow addition of the dilute Au/Block solution in dimethylformamide into a large excess of water with vigorous stirring. Au/Block (1/1) and Au/Block (2/1) formed nanosized structures of 5-7 nm. TEM images of stained Au/Block (1/1) micelles, made in water, clearly showed the formation of core-shell structures. Au/Block (3/1) micelles, on the other hand, were not stable and large agglomerates a few microns in size were observed. The study focuses on the synthesis, characterization, and aggregation behavior of gold-loaded PEO-b-PCL block copolymer micelles, a potential system for drug delivery in conjunction with tissue and subcellular localization studies.     

Synthesis and aggregation study of tin nanoparticles and colloids obtained by chemical liquid deposition

Tin colloids (Sn-Colls) and nanoparticles were synthesized by a chemical liquid deposition method (CLD). Sn⁰ was evaporated and codeposited with acetone, 2-propanol, and tetrahydrofurane vapors at 77 K to obtain colloidal dispersions. Sn-Coll were characterized by UV spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy, selected area electron diffraction, thermal analysis, infrared spectroscopy [Fourier transform infrared (FTIR)], and light scattering. TEM micrographs of tin nanoparticles (Sn-Nps) revealed a particle size distribution between 2 and 4 nm for the three solvents used in the synthesis. UV studies showed strong absorption bands in the UV region, suggesting that the Sn-Nps obtained by CLD exhibit quantum confinement and typical bands of plasmons corresponded to aggregated particles. Electrophoresis measurement indicated a significant tendency of particle aggregation along time, which was verified by light scattering studies. The diffraction patterns revealed phases corresponding to metallic tin and FTIR studies showed the interaction Sn-solvent in the metal surface by Sn-O bonds, indicating a solvatation of metallic clusters. Thermal analysis revealed a good thermal stability of Sn-Nps. The mechanism of tin nanoparticles formation was also examined.     

Kinetic evaluation of highly active supported gold catalysts prepared from monolayer-protected clusters: an experimental Michaelis-Menten approach for determining the oxygen binding constant during CO oxidation catalysis

Thiol monolayer-protected Au clusters (MPCs) were prepared using dendrimer templates, deposited onto a high-surface-area titania, and then the thiol stabilizers were removed under H2/N2. The resulting Au catalysts were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared spectroscopy of adsorbed CO. The Au catalysts prepared via this route displayed minimal particle agglomeration during the deposition and activation steps. Structural data obtained from the physical characterization of the Au catalysts were comparable to features exhibited from a traditionally prepared standard Au catalyst obtained from the World Gold Council (WGC). A differential kinetic study of CO oxidation catalysis by the MPC-prepared Au and the standard WGC catalyst showed that these two catalyst systems have essentially the same reaction order and Arrhenius apparent activation energies (28 kJ/mol). However, the MPC-prepared Au catalyst shows 50% greater activity for CO oxidation. Using a Michaelis-Menten approach, the oxygen binding constants for the two catalyst systems were determined and found to be essentially the same within experimental error. To our knowledge, this kinetic evaluation is the first experimental determination of oxygen binding by supported Au nanoparticle catalysts under working conditions. The values for the oxygen binding equilibrium constant obtained from the Michaelis-Menten treatment (ca. 29-39) are consistent with ultra-high-vacuum measurements on model catalyst systems and support density functional theory calculations for oxygen binding at corner or edge atoms on Au nanoparticles and clusters.     

Novel Green Synthesis and Characterization of the Antioxidant Activity of Silver Nanoparticles Prepared from Nepeta leucophylla Root Extract

Bioinspired silver nanoparticles were synthesized using nontoxic, eco-friendly, and novel root extract of Nepeta leucophylla. The reduction of silver nitrate salt into nanoparticles is performed using the root extract, which is rich in polyphenolic and flavonoid contents. The reduction of silver salt by this extract is occurred at several temperatures and the reaction mixture turns brown and displayed representative absorbance spectra of silver nanoparticles. The influence of numerous synthesis parameters such as the concentration of root extract, time, temperature, and reaction pH on the synthesis of silver nanoparticles was also examined. Furthermore, the synthesized silver nanoparticles were characterized by ultraviolet–visible spectroscopy, Fourier transformed infrared spectroscopy, X-ray diffraction, and transmission electron and field emission scanning electron microscopy. The formation of silver nanoparticles was enhanced with time, temperature, and at basic pH. The surface plasmon resonance band characteristics of silver nanoparticles were detected at 410?nm in the ultraviolet–visible absorbance spectra. The infrared spectroscopy results show that the extract contains phenol which is responsible for reduction and proteins may be capping the silver nanoparticles which prevent agglomeration. Transmission electron microscopy revealed that silver nanoparticles were spherical and the sizes matched well with X-ray diffraction and theoretical calculations by Mie theory. Furthermore, the antioxidant potential of the synthesized silver nanoparticles was assessed using 2,2-diphenyl-1-picrylhydrazyl assay and showed considerable antioxidant potential.     

壳聚糖修饰炭黑负载Pt-Au催化剂对甲醇氧化的电催化性能

以炭黑及自制的壳聚糖-炭黑(CHI-C)复合材料为载体,采用溶胶负载法制备了Pt_m＾Au/C及Pt_m＾Au/CHI-C催化剂(＾ 代表Au、Pt为分步负载,m代表Pt/Au原子比),通过紫外-可见吸收光谱、X射线衍射、透射电镜及X射线光电子能谱对催化剂进行了表征。利用循环伏安法和计时电流法分别测定了Pt-Au催化剂对甲醇电催化氧化反应的活性和稳定性,考查了Pt/Au原子比及CHI改性对电催化活性和稳定性的影响。结果表明,Pt_1.0＾Au/C具有最高的催化活性,炭黑中加入少量CHI能提高Pt_1.0＾Au/C催化剂的稳定性。     

Restructuring-induced activity of SiO(2)-supported large au nanoparticles in low-temperature CO oxidation

Large Au nanoparticles with an average size of approximately 10 nm supported on inert SiO(2) become active in low-temperature CO oxidation after the addition of NaNO(3). The catalyst structures have been characterized in detail by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray absorption spectroscopy. The NaNO(3) additive in Au/SiO(2) catalysts does not lead to the formation of fine Au nanoparticles, which are generally considered to be inevitable in low-temperature CO oxidation catalyzed by gold, nor does it alter the electronic structure of Au. The NaNO(3)-induced restructuring of large Au nanoparticles was proposed to create low-coordinated Au sites on the surface capable of catalyzing low-temperature CO oxidation. These results experimentally prove that the activity of supported Au nanoparticles in low-temperature CO oxidation could solely arise from their geometric structure, which greatly deepens the fundamental understandings of Au nanocatalysis.     

Negative Charging of Au Nanoparticles during Methanol Synthesis from CO2/H2 on a Au/ZnO Catalyst: Insights from Operando IR and Near‐Ambient‐Pressure XPS and XAS Measurements

The electronic and structural properties of Au/ZnO under industrial and idealized methanol synthesis conditions have been investigated. This was achieved by kinetic measurements in combination with time‐resolved operando infrared (DRIFTS) as well as in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS) and X‐ray absorption near‐edge spectroscopy (XANES) measurements at the O K‐edge together with high‐resolution electron microscopy. The adsorption of CO during the reaction revealed the presence of negatively charged Au nanoparticles/Au sites during the initial phase of the reaction. Near‐ambient‐pressure XPS and XANES demonstrate the build‐up of O vacancies during the reaction, which goes along with a substantial increase in the rate of methanol formation. The results are discussed in comparison with previous findings for Cu/ZnO and Au/ZnO catalysts.     

Aggregation of photolytic gold nanoparticles at the surface of chitosan films

Formation and aggregation of photolytic gold nanoparticles at the surface of chitosan (CTO) films have been investigated. When thin films of chloroauric acid salt of CTO were irradiated with UV light in wet air at room temperature for 10 min, gold nanoparticles of approximately 10 nm size are formed at the film surface. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize gold nanoparticles at the film surface. The shift of Au(4f) peak to the higher energy side and broadening of full width at half-maximum in the XPS spectrum are the direct evidence of the existence of gold atoms and small clusters in the early stage of photolysis. According to FE-SEM observation, growth in the particle diameter and aggregation of nanoparticles were observed after prolonged irradiation, and, finally, the film surface was densely covered with gold particles of 20-100-nm size. Gold atoms and clusters could move in the film and precipitate to the irradiated surface. Chemical composition analysis further suggests that gold particles at the surface are covered with an ultrathin CTO layer, which is partly oxidized by oxygen and chlorinated by chlorine during photochemical reactions.     

Nanoelectrocatalyst Based on High‐Density Au/Pt Hybrid Nanoparticles Supported on a Silica Nanosphere

A high‐efficiency nanoelectrocatalyst based on high‐density Au/Pt hybrid nanoparticles supported on a silica nanosphere (Au‐Pt/SiO₂) has been prepared by a facile wet chemical method. Scanning electron microscopy, transmission electron microscopy, energy‐dispersive X‐ray spectroscopy, and X‐ray photoelectron spectroscopy are employed to characterize the obtained Au‐Pt/SiO₂. It was found that each hybrid nanosphere is composed of high‐density small Au/Pt hybrid nanoparticles with rough surfaces. These small Au/Pt hybrid nanoparticles interconnect and form a porous nanostructure, which provides highly accessible activity sites, as required for high electrocatalytic activity. We suggest that the particular morphology of the Au‐Pt/SiO₂ may be the reason for the high catalytic activity. Thus, this hybrid nanomaterial may find a potential application in fuel cells.