Double layer micellar stabilization of gold nanocrystals by greener ionic liquid 1-butyl-3-methylimidazolium lauryl sulfate

We report the first synthesis of anisotropic gold nanocrystals (AuNC) prepared by a seeding approach using the greener ionic liquid, 1-butyl-3-methylimidazolium lauryl sulfate, [BMIM] [C₁₂H₂₅OSO₃]. Crystal growth was successfully achieved by successive addition of growth solution containing HAuCl₄ and ascorbic acid to 2.5-nm Au seeds. These nanocrystals were stabilized by the ionic liquid via a two layer micellar formation. SEM and TEM results showed Au nanocrystals with particle sizes ranging from 20 to 50 nm. Selected-area electron diffraction (SAED) and PXRD pattern gave indices that correspond to Au nanocrystals. Direct addition of ionic liquid to Au seeds in 3:1 volume ratio afforded the formation of Au nanoparticles. TEM image and UV-vis data revealed the formation of 20-50 nm Au nanocrystals. These results show that the greener ionic liquid, [BMIM] [C₁₂H₂₅OSO₃], is a suitable reaction medium for the direct synthesis of larger Au nanoparticles from Au seeds.     

Synthesis of nearly monodispersive gold nanoparticles by a sodium diphenylamine sulfonate reduction process

Au nanoparticles have been prepared by the reaction of HAuCl₄ and sodium diphenylamine sulfonate in the presence/absence of poly(vinylpyrrolidone)(PVP) at room temperature. The nanoparticles were characterized by Transmission electron microscopy (TEM), UV-Vis absorption spectrum. The research showed that the molar ratio of PVP/ HAuCl₄ has effect on the size and the morphology of Au nanoparticles.     

Au+-cetyltrimethylammonium bromide solution: A novel precursor for seed-mediated growth of gold nanoparticles in aqueous solution

The appropriate choice of chemical composition of a metallic precursor, which produces the basic structure units in the growth process of nanocrystals, is a high priority in the synthesis of metal-especially Au-nanoparticles. In the present work, Au seeds (prepared by the reduction of Au³⁺ solution with NaBH4 in the presence of cetyltrimethylammonium bromide (CTAB)) have been used to initiate the growth of Au nanoparticles from two different Au precursors. When an aqueous Au⁺ solution prepared in the presence of CTAB micelles was treated with ascorbic acid in the presence of the gold seeds, a high yield (up to 92%) of gold nanoparticles was obtained. By varying the volume of the seed solution with a fixed amount of Au⁺, we can effectively control the morphological transformation of the resulting Au nanoparticles from cubes to octahedra. When an aqueous Au³⁺ solution was prepared in the presence of CTAB micelles and treated with ascorbic acid in the presence of the gold seeds, smaller yields of Au nanoparticles were obtained. A preliminary growth mechanism has been proposed based on the changes induced by varying the amount of ascorbic acid and the ratio of the concentration of Au⁺ to the number of seeds.      

Synthesis of nanocomposite gold-semiconductor materials by seed-growth method

Gold-semiconductor nanocomposite hybrid materials were synthesized by applying the seed-growth approach. Citrate stabilized gold nanoparticles were prepared by the reduction of HAuCl₄ with borohydride and used as seeds. The structural and morphological features of semiconductor materials i.e. CdS, CuS, NiS, and PbS in the presence of Au NP were examined with the help of UV-Visible spectroscopy, phase contrast microscopy, transmission electron microscopy (TEM) and X-ray diffraction measurements. The experimental results revealed that a network of semiconductor-Au NP nanocomposite material is formed in each case.     

Size effect of Au seeds on structure of Au–Pt bimetallic nanoparticles

Au–Pt bimetallic nanoparticles (NPs) were synthesized by a seeded growth method. Au NPs with different sizes were obtained by reducing HAuCl₄ with butyllithium, and AuPt bimetallic NPs were synthesized by reducing H₂PtCl₆ with oleylamine using the pre-synthesized Au NPs as seeds. The size of Au seeds was found to be a key factor on the structure of Au–Pt bimetallic NPs. Using big Au NP seeds (8 nm or 12 nm) resulted in the formation of Au–Pt dendritic structures. While relatively small Au NPs (3 nm) were used as seeds, the fast atomic diffusion inside relatively small bimetallic NPs will result in an Au–Pt alloy formation.     

One-step preparation of gold nanoparticles with different size distribution

Gold nanoparticles with different size distributions have been prepared through a one-step route, carried out by mixing 3-thiophenemalonic acid and HAuCl₄ aqueous solutions without the additional step of introducing other reducing agents and protective agents. The growth of such gold nanoparticles follows the Ostwald ripening growth mechanism.     

Localized surface plasmon resonance sensing properties of photocatalytically prepared Au/TiO2 films

Photocatalytic deposition of Au nanoparticles from a mixed aqueous solution of HAuCl₄ and ethylene glycol onto TiO₂ films (Au/TiO₂ films) was carried out by using ultraviolet light irradiation at room temperature. In the optical absorption spectra of the Au/TiO₂ film, the localized surface plasmon resonance (LSPR) peak of Au nanoparticles was observed at 534.5 nm. When the film was immersed in various kinds of solutions, such as alcohols, NaCl and d-glucose aqueous solutions, a linear relation was clearly observed between the LSPR peak wavelength and the refractive index of the solutions, in the range of 1.0003–1.4181.     

The morphology and size of nanostructured Au in Au/SBA-15 affected by preparation conditions

Template-free mesoporous silica SBA-15 was reacted with TPTAC to generate positively charged functional groups PTA⁺ on the pore surface. Through ion exchange, a uniform distribution of anionic metal complexes on the intrachannel surface of host silica was achieved. In this study, ethanol and water were used as solvent for HAuCl₄ precursor solutions impregnated on SBA-15 mesoporous silica. The solvent used can affect the size and location of the resulting nanoparticles. Large Au nanoparticles (15–43 nm) were found on the as-prepared Au/SBA-15 as observed by PXRD, XAS, UV–vis and TEM. This may have originated through Si–OH reduction of chloroaurate complexes generated in the aqueous solution of HAuCl₄, and such particles were not present when ethanolic solution was used. After NaBH₄ and H₂ reduction, the average size of Au nanoparticles, which was incorporated into the channels of SBA-15, was found to be limited to ≤  7 nm.     

Structural verification and optical characterization of SiO2–Au–Cu2O nanoparticles

In this paper, SiO₂–Au–Cu₂O core/shell/shell nanoparticles were synthesized by reducing gold chloride on 3-amino-propyl-triethoxysilane molecules attached silica nanoparticle cores for several stages. Cu₂O nanoparticles were synthesized readily with the size of 4–5 nm using a simple route of sol–gel method Then, they were clung to the surface of Au seeds. The morphology of the resultant particles was studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Transmission electron microscopy images demonstrate growth of monodispersed gold seeds and Cu₂O nanoparticles in narrow size up to 10 nm and 5 nm, respectively. The presence of gold and Cu₂O coating was confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and UV–Vis spectroscopy. Absorption spectroscopy shows considerably 40 nm blue shift in absorption edge for SiO₂–Au–Cu₂O nanostructure rather than SiO₂–Au core/shell nanoparticles.     

Formation of gold nanoparticles via a thiol functionalized polyoxometalate

A useful method for the synthesis of Au nanoparticles is presented. The synthesis of Au nanoparticles with various morphologies was carried out at room temperature using gamma radiolysis and NaBH₄ reduction of HAuCl₄ in N,N′-dimethylformamide:water solutions containing polyoxometalate (POM). The results demonstrated that by controlling the rate of reduction and ratio of DMF and water, metal particle size and shape can be further tailored. It is shown that gold nanoparticles with controllable size can be synthesized. In principle, the general finding of this work can be extended to other transition/noble metal nanoparticles.     

Au/Fe3O4磁性纳米粒子的合成及表征

报道了一种合成具有巯基官能团修饰的Au/Fe_3O_4磁性纳米粒子的新方法。采用共沉淀法制备Fe_3O_4磁性纳米颗粒,并在此基础上用聚(烯丙胺)溶液还原HAuCl4,制得Au/Fe_3O_4磁性核壳纳米颗粒,再用3-巯基-1-丙磺酸钠修饰Au/Fe_3O_4磁性纳米粒子,最后得到具有巯基官能团稳定的Au/Fe_3O_4磁性纳米粒子。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线能谱仪(EDS)、X射线衍射仪(XRD)、X射线光电子能谱(XPS)、振动样品磁强计(VSM)分别对产物的微观结构及磁性特征进行表征。     

Synthesis, morphology and optical properties of multi-pods Au/FeO(OH) and Au/Fe2O3 nanostructures

Multi-pods Au/FeOOH nanostructures were synthesized by a hydrothermal treatment of an aqueous solution of mixed micellar formed by gold nanoparticles, hexadecyltrimethyl ammonium bromide (CTAB), and (NH₄)₃[FeF₆] at 160 °C for 48 h and sequential calcined at 290 °C for 1.5 h, resulting in the formation of multi-pods Au/Fe₂O₃ nanostructures. The as-obtained products were characterized by powder X-ray diffraction, transmission electron microscopy, selected area electron diffraction, field emission scanning electron microscopy, and UV-vis spectroscopy. Surface plasmon resonance band of gold nanoparticles was observed in the multi-pods Au/FeOOH nanostructures. However, a similar behavior was not seen with multi-pods Au/Fe₂O₃ nanostructures. The critical role of F⁻ ions and CTAB molecules in the formation of FeO(OH) multipods and the probable mechanism of the formation of multi-pods Au/FeOOH and Au/Fe₂O₃ nanostructures were discussed.     

Synthesis of silica/Au core-shell nanostructures by galvanic replacement of silica/Ag in aqueous and alkaline medium

We present here a facile one-step method for the synthesis of silica/Au core-shell nanostructures by exploiting the potential difference of AuCl₄^? and Ag in aqueous as well as alkaline media. Initially, silica/Ag core-shell nanostructures were synthesised by coating Ag nanoparticles on silica core (size ～150 nm) in a two-step process (seeding and growth) and were characterised for their morphological, structural and optical behaviours. A complete coverage of silica core with Ag nanoparticles was seen from scanning electron microscope and transmission electron microscope images. The presence of resonance peaks in the optical spectrum manifests the nature of the shell (thin shell ～413 and 650 nm, thick shell ～434 nm). Galvanic replacement of silica/Ag core-shell nanostructures in chloroauric acid solution (HAuCl₄) was studied in both the aqueous and alkaline medium, where an aqueous environment results into fast and effective replacement as compared to an alkaline medium, which has been confirmed from optical absorption studies. The optical studies showed that in an alkaline environment, on galvanic replacement of Ag with Au, the individual absorption peak of Ag (～414 nm) and Au (～520 nm) disappeared, whereas new absorption wavelengths in higher region (600–800 nm) of electromagnetic spectrum were observed. A detailed mechanism is proposed for the same to explain this behaviour. A range of novel new plasmonic core-shell nanomaterials can be synthesised as an intermediate of this facile one-step reaction.     

Controllable synthesis of gold nanowires

In this work, we demonstrate a new and simple method for preparing Au nanowires by ethanol reduction of hydrogen tetrachloroaurate (HAuCl₄) without additional capping agents by a thermal process. The resulting products were investigated by UV-vis spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results indicated that the size and shape of the Au nanocrystals could be controlled by systematic variation of the experimental parameters including the concentration of HAuCl₄ in the reaction solution, heating temperature and reaction time. We suggest that this method introduced in our work may be more practical for the large-scale synthesis of shape-controlled metal nanomaterials.     

In situ synthesis of gold–polyaniline composite in nanopores of polycarbonate membrane

In situ one-step chemical synthesis route for the preparation of a gold–polyaniline composite in nanopores of polycarbonate (PC) membrane is reported. PC membrane, which was placed in a specially designed two-compartment cell, separated the aqueous solution of aniline from HAuCl₄ solution. Concentration gradient across the membrane caused movement of AuCl₄ ⁻ and anilinium ions in the pores of polycarbonate membrane. Nanopores in PC membrane acted as reaction vessels where aniline and HAuCl₄ were allowed to mix together, and the redox reaction between aniline and HAuCl₄ led to the formation of gold–polyaniline composite. The gold–polyaniline composite in PC membrane was characterised by EDXRF, XRD, UV–Vis spectroscopy, FTIR and TEM. Peak broadening in XRD suggests that Au particles formed in the membrane are nanocrystallites and average crystallite size is (24 ± 4) nm. TEM studies show that gold nanoparticles are randomly dispersed in polyaniline clusters formed in the nanopores of PC membrane. Characterisation results show that the surfaces of the PC membrane exposed to HAuCl₄ and aniline have significantly higher concentrations of Au nanoparticles and polyaniline, respectively.     

Silver, gold and bimetallic nanoparticles production using single-cell protein (Spirulina platensis) Geitler

Interaction of single-cell protein of Spirulina platensis with aqueous AgNO₃ and HAuCl₄ was investigated for the synthesis of Ag, Au and Au core—Ag shell nanoparticles. Biological reduction and extracellular synthesis of nanoparticles were achieved in 120 h at 37 °C at pH 5.6. The nanometallic dispersions were characterized by surface plasmon absorbance measuring at 424 and 530 nm for Ag and Au nanoparticles, respectively. For bimetallic nanoparticles, absorption peak was observed at 509, 486 and 464 nm at 75:25, 50:50 and 25:75 (Au:Ag) mol concentrations, respectively. High-resolution transmission electron microscopy showed formation of nanoparticles in the range of 7–16 (silver), 6–10 (gold) and 17–25 nm (bimetallic 50:50 ratio). XRD analysis of the silver and gold nanoparticles confirmed the formation of metallic silver and gold. Fourier transform infrared spectroscopic measurements revealed the fact that the protein is the possible biomolecule responsible for the reduction and capping of the biosynthesized nanoparticles.     

Fabrication of dumbbell-like CdTe/Au nanohybrids

Dumbbell-like CdTe/Au nanohybrids were synthesized by assembly of CdTe quantum dots with the assistance of AuCl₄⁻ in aqueous solution. The products were characterized by TEM and SEM techniques. The images reveal that dumbbell-like nanostructures with uniform size were well formed. The dumbbell-like nanostructures were further characterized by HRTEM and EDX spectrum. The results indicate that the as-prepared dumbbell-like nanostructures were composed of CdTe quantum dots and Au nanoparticles. The effect of HAuCl₄ concentration on the morphology of the products was also investigated, which shows that the morphology of the products evolved from sheaf-like nanostructures to rod-like nanostructures and finally dumbbell-like nanostructures as the HAuCl₄ concentration increased. Based on the above results, a possible mechanism for the formation of dumbbell-like CdTe/Au nanohybrids is proposed.     

Bimetallic Pt–Au thin film electrocatalysts with hierarchical structures for the oxidation of formic acid

A series of bimetallic Pt–Au thin films with different Pt/Au ratios were fabricated on glassy carbon (GC) substrates through galvanic replacement reactions between hierarchical Co thin films prepared by cyclic voltammetric deposition and mixed solutions of HAuCl₄ and H₂PtCl₆. The morphologies of the as-prepared Pt–Au thin films resemble those of the sacrificial Co templates, and the Pt/Au ratios in the films are dependent on the HAuCl₄/H₂PtCl₆ molar ratios in the mixed solutions. Because of good stability and excellent synergistic effect of Au and Pt, the bimetallic films with novel structures display unexpected high catalytic activity for the oxidation of formic acid. The as-prepared hierarchical Pt–Au micro/nanostructures are expected to find applications as catalysts in direct formic acid fuel cells (DFAFCs).     

A facile synthesis of monodisperse Au nanoparticles and their catalysis of CO oxidation

Monodisperse Au nanoparticles (NPs) have been synthesized at room temperature via a burst nucleation of Au upon injection of the reducing agent t-butylamine-borane complex into a 1, 2, 3, 4-tetrahydronaphthalene solution of HAuCl₄·3H₂O in the presence of oleylamine. The as-synthesized Au NPs show size-dependent surface plasmonic properties between 520 and 530 nm. They adopt an icosahedral shape and are polycrystalline with multiple-twinned structures. When deposited on a graphitized porous carbon support, the NPs are highly active for CO oxidation, showing 100% CO conversion at −45 °C. This article is published with open access at Springerlink.com     

Microwave-assisted synthesis of palladium nanocubes and nanobars

Microwave was employed in the shape-controlled synthesis of palladium nanoparticles. Palladium nanocubes and nanobars with a mean size of about 23.8 nm were readily synthesized with H₂PdCl₄ as a precursor, tetraethylene glycol (TEG) as both a solvent and a reducing agent in the presence of PVP and CTAB in 80 s under microwave irradiation. The structures of the as-prepared palladium nanoparticles were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and ultraviolet-visible (UV-vis) absorption spectroscopy. The formation of PdBr₄²⁻due to the coordination replacement of the ligand Cl⁻ ions in PdCl₄²⁻ ions by Br⁻ ions in the presence of bromide was responsible for the synthesis of Pd nanocubes and nanobars. In addition, a milder reducing power, a higher viscosity and a stronger affinity of TEG were beneficial to the larger sizes of Pd nanocubes and nanobars.