Catalytic role of gold nanoparticle in GaAs nanowire growth: a density functional theory study

The energetics of Ga, As, and GaAs species on the Au(111) surface (employed as a model for Au nanoparticles) is investigated by means of density functional calculations. Apart from formation of the compound Au(7)Ga(2), Ga is found to form a surface alloy with gold with comparable ΔH ~ -0.5 eV for both processes. Dissociative adsorption of As(2) is found to be exothermic by more than 2 eV on both clean Au(111) and AuGa surface alloys. The As-Ga species formed by reaction of As with the surface alloy is sufficiently stable to cover the surface of an Au particle in vacuo in contact with a GaAs substrate. The results of the calculations are interpreted in the context of Au-catalyzed growth of GaAs nanowires. We argue that arsenic is supplied to the growth zone of the nanowire mainly by impingement of molecules on the gold particle and identify a regime of temperatures and As(2) partial pressures suitable for Au-catalyzed nanowire growth in molecular beam epitaxy.     

The synthesis of nickel nanoparticles by hydrazine reduction

A pure metallic nickel nanoparticle, spherical in shape, has been successfully synthesized by the chemical reduction of nickel chloride with hydrazine at room temperature without any protective agent and inert gas protection. The effect of nickel salt concentration and the molar ratio of hydrazine to Ni²⁺ on the properties of the resultant products were investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Also, the reaction mechanism is discussed in this paper. This synthetic method is proven to be simple and very facile. In addition, it is very interesting to note that the obtained nickel nanoparticle can be isolated in the solid state and stabilized for several months in the atmosphere.     

Controlled synthesis of gold nanoparticles by fluorescent light irradiation

A novel photochemical synthesis of size-controlled gold nanoparticles was reliably accomplished via both a direct reduction and a seeded-growth method at room temperature under the irradiation of fluorescent light. These methods utilized the intensity of fluorescent light that closely resembles daily sunlight (～100 mW cm(-2)). This effectively allowed for the formation of gold nanoparticles with tunable sizes simply by controlling the concentration of trisodium citrate and gold chloride. The broad band fluorescent light was found to be an efficient source for inducing the formation of gold nanoparticles at ambient conditions. The size distribution and absorption property of the resulting nanoparticles were thoroughly characterized by scanning/transmission electron microscopy, dynamic light scattering, UV-visible spectroscopy and powder x-ray diffraction. This photochemical synthesis demonstrates, for the first time, the reliable preparation of gold nanoparticles at room temperature upon irradiation with fluorescent light.     

Phospholipid-assisted synthesis of size-controlled gold nanoparticles

Morphology and size control of gold nanoparticles (AuNPs) by phospholipids (PLs) has been reported. It was found that gold entities could form nanostructures with different sizes controlled by PLs in an aqueous solution. During the preparation of 1.5 nm gold seeds, AuNPs were obtained from the reduction of gold complex by sodium borohydride and capped by citrate for stabilization. With the different ratios between seed solution and growth solution, which was composed by gold complex and PLs, gold seeds grew into larger nanoparticles step by step until enough large size up to 30 nm. The main discovery of this work is that common biomolecules, such as PLs can be used to control nanoparticle size. This conclusion has been confirmed by transmission electron micrographs, particle size analysis, and UV-vis spectra.     

Photochemical synthesis of colloidal gold nanoparticles

Monodisperse gold nanoparticles protected by small organic molecules or by macromolecules with different sizes and shapes are widely used as a precursor material in various applications of gold nanotechnology. However, their preparation is still a formidable task. In this paper the use of photochemically assisted syntheses of monodisperse gold nanoparticles is summarized and some preparations by the authors’ group are introduced. These include spherical and rod-like particles, bimetallic composite nanoparticles, and syntheses using complex intramolecular photoreduction to generate the reducing agent.     

Sonochemical synthesis of gold nanoparticles on chitosan

Au nanoparticles deposited on chitosan were readily prepared from aqueous solution of NaAuCl₄ containing chitosan powder by the reaction with sonochemically formed reducing species. The average size of the formed Au particles was measured to be 22 nm with a relatively narrow size distribution, although there was no specific stabilizer for Au nanoparticles.     

Facile synthesis of chondroitin sulfate-stabilized gold nanoparticles

A facile and simple method for the synthesis of biocompatible gold nanoparticles (AuNPs) at room temperature has been developed by using sodium borohydride as the reducing agent and employing an inexpensive water-soluble chondroitin sulfate (CS) biopolymer as the stabilizing agent. The as-prepared AuNPs were characterized with ultraviolet–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM). Additionally, the stability of AuNPs in aqueous solution was investigated as a function of the electrolyte sodium chloride concentration. The experimental results showed that even high sodium chloride concentration (1 M) also did not destabilize the colloidal gold solution. So it could be speculated that the high stability of AuNPs should be attributed to the electrostatic repulsion and steric hindrance between the AuNPs stabilized by CS molecules, which wrapped around the surface of as-prepared AuNPs and prevented their agglomeration, and simultaneously improve biocompatibility of AuNPs as well.     

Synthesis of gold nanowire networks and nanoparticles by tyrosine reduction of chloroaurate

A simple and facile synthesis of gold nanowire networks and sol particles at room temperature is presented using L-tyrosine (Tyr) as both the reducing and capping agent. The synthesis conditions with varying the gold precursor concentration ([HAuCl4], 0.1-2.5 mM) and concentration ratio of tyrosine to gold precursor R ([Tyr]/[HAuCl4], 0.05-10) were identified for the preparation of network-like nanowires and sol nanoparticles. Gold sol particles with sizes between 10 and 18 nm were mostly obtained at R > or = 0.2. Network-like gold nanowires with average diameters as thin as 8 nm can be reproducibly synthesized at R < or = 0.1. The experimental data revealed that the phenolic and carboxyl group of Tyr were oxidized to form quinone and alcohol, respectively. The growth process was examined to elucidate the influence of the synthesis conditions on different morphologies, showing marked difference in isotropic and anisotropic growth of gold nanostructures at different synthesis conditions. The study showed that tyrosine possesses excellent reducing capability with short nucleation period and long growth period as compared with other amino acids.     

Biostabilised icosahedral gold nanoparticles: synthesis,cyclic voltammetric studies and catalytic activity towards 4-nitrophenol reduction

A green and cost-effective biosynthetic approach for the preparation of icosahedral gold nanoparticles (AuNPs) using an aqueous leaf extract of Polygonum minus as reducing and stabilising factor is described. The reduction of Au³⁺ ions to elemental Au rapidly occurred and is completed within 20 minutes at room temperature. The size of the nanoparticles is highly sensitive to the AuCl₄^?/leaf extract concentration ratio and pH. Transmission electron microscopy and X-ray diffraction data indicated that the nanoparticles were in a crystalline shape (face-centred cubic), mostly icosahedral and nearly monodispersed with an average size of 23 nm. Cyclic voltammetric studies suggested that flavonoids, such as quercetin and myricetin present in the leaf extract had a tendency to donate electrons to Au³⁺ ions and the formation of elemental Au was possible due to the transfer of electrons from these flavonoids to Au³⁺ ions. Infrared absorption of the AuNPs and the leaf extract revealed that the oxidised (quinone) form of quercetin and myricetin were presumably the main stabilising agents in the formation of stable nanoparticles. The present biosynthesis of AuNPs was simple, rapid, cost-effective and environmentally friendly. The newly prepared biostabilised icosahedral AuNPs show good catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP).     

A study on adsorption of acetonitrile on gold nanorods by non-resonant Raman measurements and density functional theory calculations

Adsorption of acetonitrile (Ac) molecules on gold (Au) nanorods has been investigated by Raman spectroscopic measurements and density functional theory (DFT) calculations. DFT calculations provide a valuable insight into the underlying structure of the metal-molecule complex. From the best agreement between the observed and the calculated Raman frequencies and also from other spectroscopic observations, we propose that Ac molecules interact with Au nanorods and form an [Ac+2Au](0)-like complex on the surface of nanostructures. The environmental effect has also been taken into consideration to explain the Raman activity of the complex.     

Chitosan-mediated synthesis of gold nanoparticles by UV photoactivation and their characterization

Recent researches have largely been focused on chitosan, which is deacetylated chitin, the most abundant natural polysaccharide after cellulose. In this paper, we report the fabrication of gold nanoparticles (GNPs) by UV photoactivation in the presence of biopolymeric chitosan and the tracing of the gold salt solution aging. Detailed UV-visible spectroscopy study witnessed the evolution of the surface plasmon resonance (SPR) adsorption during the GNP growth. The effect of chitosan in aqueous solution for the GNP preparation was investigated in detail. The results indicated the size and distribution of GNPs could be controlled over by altering the concentration of chitosan, and the GNP growth during aging was a chitosan-mediated autocatalytic process. Fourier transform infrared spectroscopy (FTIR) showed the hydroxyl in molecular chitosan was oxidized to carbonyl groups in the fabrication of GNPs after aging and nitrogen atoms are the main sites for the complexation of chitosan with Au atoms. Our synthesis method in the present way can be used to form self-assemble monolayers of GNPs and fabricate biosensors based on surface plasmon resonance effect.     

Size-controlled synthesis of monodispersed gold nanoparticles stabilized by polyelectrolyte-functionalized ionic liquid

The size-controlled synthesis of monodispersed gold nanoparticles (AuNPs) stabilized by polyelectrolyte-functionalized ionic liquid (PFIL) is described. The resulting AuNPs' size, with a narrow distribution, can be tuned by the concentration of HAuCl(4). Such PFIL-stabilized AuNPs (PFIL-AuNPs) showed a high stability in water at room temperature for at least one month; they were also quite stable in solutions of pH?7-13 and high concentration of NaCl. In addition, the PFIL-AuNPs exhibited obvious electrocatalytical activity toward β-nicotinamide adenine dinucleotide (NADH for short, a cofactor in enzymatic reactions of NAD(+)/NADH(-)-dependent dehydrogenases) oxidation, suggesting a potential application for bioelectroanalysis.     

Efficient one pot synthesis of chitosan-induced gold nanoparticles by microwave irradiation

An efficient and rapid method for the preparation of gold nanoparticles (AuNPs) within a few minutes has been developed by direct microwave irradiation of HAuCl₄ and chitosan mixed solution in one pot. Herein, chitosan molecules acted as both the reducing and stabilizing agent for the preparation of AuNPs. The obtained AuNPs have different shapes, such as the spherical nanoparticles, triangular nanoplates and nanorods, which were characterized by ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FTIR). Additionally, the results showed that microwave power could affect the required time for preparing the AuNPs arising from the distinction of heating rate, and long irradiation time was favorable for complete reduction of HAuCl₄ when a low microwave power was applied.     

Biological synthesis of gold and silver nanoparticles mediated by the bacteria Bacillus subtilis

Biological synthesis of gold and silver nanoparticles was carried out using the bacteria Bacillus subtilis. The reduction processes of chloroaurate and silver ions by B. subtilis were found to be different. Gold nanoparticles were synthesized both intra- and extracellularly, while silver nanoparticles were exclusively formed extracellularly. The gold nanoparticles were formed after 1 day of addition of chloroaurate ions, while the silver nanoparticles were formed after 7 days. The nanoparticles were characterized by X-ray diffraction, UV-vis spectra and transmission electron spectroscopy. X-ray diffraction revealed the formation of face-centered cubic (fcc) crystalline gold nanoparticles in the supernatant, broth solution and bacterial pellet. Silver nanoparticles also exhibited diffraction peaks corresponding to fcc metallic silver. UV-vis spectra showed surface plasmon vibrations for gold and silver nanoparticles centered at 530 and 456 nm, respectively. TEM micrographs depicted the formation of gold nanoparticles intra- and extracellularly, which had an average size of 7.6 +/- 1.8 and 7.3 +/- 2.3 nm, respectively, while silver nanoparticles were exclusively formed extracellularly, with an average size of 6.1 +/- 1.6 nm. The bacterial proteins were analyzed by sodium dodecyl sulfonate-polyacrylamide electrophoresis (SDS-PAGE) before and after the addition of metal ion solutions. We believe that proteins of a molecular weight between 25 and 66 kDa could be responsible for chloroaurate ions reduction, while the formation of silver nanoparticles can be attributed to proteins of a molecular weight between 66 and 116 kDa. We also believe that the nanoparticles were stabilized by the surface-active molecules i.e., surfactin or other biomolecules released into the solution by B. subtilis.     

Continuous synthesis of gold nanoparticles in a microreactor

A continuous flow microreactor was used for the synthesis of gold nanoparticles (5 to 50 nm) directly from a gold salt (HAuCl(4)) and a reducing agent (ascorbic acid). Experimental parameters were optimized to obtain narrow size distributions, which were at average two times narrower than those obtained in a conventional synthesis. Additionally, two approaches, i.e., elevation of pH during reaction and hydrophobization of internal reactor surfaces were tested to suppress reactor fouling.     

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.     

Peptide-assisted synthesis of gold nanoparticles and their self-assembly

A novel gold nanoparticle-tripeptide (GNP-tripeptide) conjugate was prepared by peptide in-situ redox technique at ambient temperatureusing a newly designed tripeptide. This new tripeptide was nso designed that it has a C-terminus tyrosine residue, which reduced Au+3 to Au, and the terminally located free amino group was bound to the gold nanoparticle (GNP) surface resulting in highly stable Au colloids. The average diameter of the tripeptide-stabilized GNP is 8.7 +/- 2.3 nm. Tripeptide bound gold nanoparticles formed three-dimensional assemblies in the presence of an excess of similar or disimilar tripeptides. The aggregation of GNPs results in a red shift in the surface plasmon resonance from lambda max = 527 to 556 nm. The effect of the solvent, concentration, and nature of the tripeptides on the assembly process were investigated by TEM and UV-visible spectroscopy.     

RETRACTED ARTICLE: Determination of dopant of ceria system by density functional theory

Oxides with the cubic fluorite structure, e.g., ceria (CeO₂), are known to be good solid electrolytes when they are doped with cations of lower valence than the host cations. The high ionic conductivity of doped ceria makes it an attractive electrolyte for solid oxide fuel cells, whose prospects as an environmentally friendly power source are very promising. In these electrolytes, the current is carried by oxygen ions that are transported by oxygen vacancies, present to compensate for the lower charge of the dopant cations. Ionic conductivity in ceria is closely related to oxygen-vacancy formation and migration properties. A clear physical picture of the connection between the choice of a dopant and the improvement of ionic conductivity in ceria is still lacking. Here we present quantum-mechanical first-principles study of the influence of different trivalent impurities on these properties. Our results reveal a remarkable correspondence between vacancy properties at the atomic level and the macroscopic ionic conductivity. The key parameters comprise migration barriers for bulk diffusion and vacancy–dopant interactions, represented by association (binding) energies of vacancy–dopant clusters. The interactions can be divided into repulsive elastic and attractive electronic parts. In the optimal electrolyte, these parts should balance. This finding offers a simple and clear way to narrow the search for superior dopants and combinations of dopants. The ideal dopant should have an effective atomic number between 61 (Pm) and 62 (Sm), and we elaborate that combinations of Nd/Sm and Pr/Gd show enhanced ionic conductivity, as compared with that for each element separately. An erratum to this article can be found at