Size-controlled Au Nanoparticles Research Articles

Design of size-controlled Au nanoparticles loaded on the surface of ZnO for ethanol detection

Schematic diagram of the reaction mechanism of the sensor in air and ethanol.

Photo-induced generation of size controlled Au nanoparticles on pure siliceous ordered mesoporous silica for catalytic applications

Abstract A versatile in situ photochemical reduction approach was used to generate a composite of gold nanoparticles and pure siliceous SBA-15 silica support with regular mesopores. The mesoporous silica support was first synthesized and, after calcination, was suspended in a solution of gold bromide (EtOH or H2O) containing a free radical generator activated by UV irradiation and used for the photochemical reduction of gold precursor. The influence of gold precursor concentration, light intensity and nature of the solvents on the formation and properties of gold nanoparticles (size, dispersion, stability) on the mesoporous SBA-15 support have been studied with the aim of optimizing the dispersion of the gold nanoparticles in the mesoporous network and their chemical stability. The catalytic activity of the resulting AuNPs@SBA-15 nanocomposite was successfully evaluated for the oxidation of benzyl alcohol reaction in liquid-phase.

Plasmon-enhanced ZnO nanorod/Au NPs/Cu2O structure solar cells: Effects and limitations

Cu-based compounds can be a good candidate for a low cost solar cell material. In particular, Cu x O (x : 1–2) has a good visible light absorbing bandgap at 1–2 eV. As for using nanostructures in solar cell applications, metal nanoparticle-induced localized plasmon resonance is a promising way to increase light absorbance, which can help improve the efficiency of solar cells. We fabricated ZnO nanorod/Au nanoparticles/Cu2O nanostructures to study their solar cell performance. ZnO nanorods and Cu2O layer were synthesized by the electrodeposition method. Size-controlled Au nanoparticles were deposited using E-beam evaporator for localized surface plasmon resonance (LSPR) effect. By inserting Au plasmon nanoparticles and annealing Au NPs in solar cells, we could tune the maximum incident photon-to-current efficiency wavelength. However, the potential well formed by Au NP at the ZnO/Cu2O junction leads to charge-trapping, based on the constructed electronic band analysis. LSPR-induced hot carrier generation is proposed to promote carrier transport further in the presence of Au NPs.

One-step synthesis of Au/porous ZrO2 SERS-active nanocomposite: Fabrication and tunable optical properties

One-step synthesis of gold (Au) nanoparticles (NPs) and Au/porous ZrO2 nanocomposites (Au/PZrO2 NCPs) have been developed using an ultra-low water content process. The reduction of HAuCl4 was accomplished in a sodium citrate sol (SCS) which had been prepared in anhydrous ethanol, instead of in water or in ethanol/water mixture. Then, highly uniform, well-distributed and size-controllable Au NPs and Au-based NCPs (Au/PZrO2) have been obtained using this SCS. The new method provides a simple and effective physical step that can control the Au particle size freely within a broad range from 5 to even 160 nm. The SCS can also greatly improve the dispersity of Au NPs situated on the ZrO2 substrate, which makes the hybrids (Au/PZrO2) achieving a very good stability and high sensitivity to organic molecule of 4-mercaptobenzoic acid (4-MBA). Furthermore, the new method requires no additional protectants or stabilizers and is capable to fabricate Au NPs with simultaneously good dispersity and small size even below 5 nm, which provides a promising avenue for preparing high quality of Au NPs and Au-based NCPs.

Easy Preparation of Electrode Surfaces with Dispersed Size-Controlled Au Nanoparticles by Electrodeposited PPI-Dendrimers as Templates

The main target of this work is the preparation of nanostructurated surfaces with size-controlled gold nanoparticles to obtain effective electrocatalytic surfaces. In this paper, we show that dispersed Au nanoparticles (AuNPs) having diameters of less than 3 nm can be synthesized in situ with aminoferrocenyl- and amidoferrocenyl-poly(propyleneimine) (PPI) dendrimers previously electrodeposited onto electrode surfaces. Dendrimers of first, third and fifth generation have been studied and good dispersed non aggregated nanoparticles were obtained in all the cases. In a similar way than in homogeneous media, inter-dendrimer Au nanoparticles have been obtained when first or third generation dendrimer modified electrodes were used, while smaller nanoparticles were obtained with fifth generation dendrimer, indicating that intra-dendrimer Au nanoparticles have been synthesized. The AuNPs were obtained from a HAuCl4 solution after chemical reduction with NaBH4. The formation of AuNPs was followed by UV-Vis spectroscopy; electrochemistry and ultra-high resolution scan electron microscopy (HRSEM). The obtained electrodes have been successfully used for the tetraelectronic oxygen reduction reaction (ORR) with a low onset potential (0.00 V vs. SCE), high kinetic current densities and also high heterogeneous electron transfer rate constants.

TiO2 Nanotubes Arrays Loaded with Ligand-Free Au Nanoparticles: Enhancement in Photocatalytic Activity.

A new protocol to synthesize size-controlled Au nanoparticles (NPs) loaded onto vertically aligned anatase TiO2 nanotubes arrays (TNTAs) prepared by electrochemical anodization is reported. Ligand-free Au NPs (<10 nm) were deposited onto anatase TNTAs supports, finely tuning the Au loading by controlling the immersion time of the support into metal vapor synthesis (MVS)-derived Au-acetone solutions. The Au/TNTAs composites were characterized by electron microscopies (SEM, (S)TEM), X-ray diffraction, X-ray photoelectron spectroscopy, and UV-vis spectroscopy. Their photocatalytic efficiency was evaluated in toluene degradation in air under ambient conditions without thermal or chemical postsynthetic treatments. The role of Au loadings was pointed out, obtaining a three times enhancement of the pristine anatase TNTAs activity with the best sample containing 3.3 μg Au cm-2.

Temperature-independent formation of Au nanoparticles in ionic liquids by arc plasma deposition

An effective preparation method of Au nanoparticles (NPs) is presented, wherein an arc plasma deposition technique is combined with ionic liquids (ILs) used as capture media. This method requires no chemical reaction. By selecting ILs, size-controlled Au NPs are produced easily and on a massive scale.

CO Adsorption on Au Nanoparticles Grown on Hexagonal Boron Nitride/Rh(111)

CO adsorption on size-controlled Au nanoparticles grown on an h-BN/Rh(111) nanomesh surface has been examined to probe their potential catalytic properties. A combination of high-resolution electron energy loss spectroscopy (HREELS), temperature-programmed desorption (TPD), and density functional theory (DFT) calculations demonstrate that the CO adsorption strength depends heavily on the Au deposition coverage and particle morphology. Particles resulting from low Au coverages deposited at the liquid nitrogen temperature exhibit significantly enhanced CO binding relative to bulk crystalline Au. The resulting CO TPD spectra, and the significantly red-shifted C–O stretching frequency and negative charging of the Au nanoparticles as evidenced by HREELS and DFT, all correspond to those reported for catalytically active Au nanoparticles grown on reactive metal oxides, even though the h-BN/Rh(111) surface is free of carbon, oxygen, or defects. DFT modeling further suggests that the enhanced CO adsorption occurs ...

Monitoring of glucose in fermentation processes by using Au/TiO2 composites as novel modified electrodes

This paper demonstrates an effective method of monitoring glucose in fermentation processes based on the development of enzyme-free glucose electrochemical sensors. The sensing electrodes were manufactured by preparing size-controlled Au nanoparticles (NPs), in the form of colloidal solutions, which were dispersed on TiO2 substrates, and then deposited on commercial carbon screen printed electrodes. The as-synthesized samples were fully characterized by transmission electron microscopy, X-ray diffraction, atomic absorption spectroscopy, and UV–visible diffuse reflectance spectroscopy to obtain information about their morphological, structural, and electronic properties. Particularly, the ability to control the size of Au NPs in the colloidal solution by using different reducing agents and stabilizers is presented here. The Au/TiO2-based modified sensors were assembled and tested for glucose monitoring in an alkaline solution. Results of cyclic voltammetry showed the high electrocatalytic activity of these sensors toward glucose oxidation, whereas no response was detected toward ethanol. This suggests the possibility of using this type of sensor for glucose monitoring in the fermentation processes without ethanol interference. The efficient sensing properties of Au NP-embedded TiO2 composites may be ascribed to the higher electrocatalytic activity of smaller Au NPs stabilized on TiO2.

Controlled deposition of Au on (BiO)2CO3microspheres: the size and content of Au nanoparticles matter

Novel 3D Au/(BiO)2CO3 (Au/BOC) heterostructures with size-controlled Au nanoparticles (NPs) (2-10 nm) were first synthesized and used in photocatalytic removal of ppb-level NO for air cleaning. The photocatalytic performance of Au/BOC heterostructures was enhanced by fine-tuning the content of Au and the size of Au NPs. A new photocatalysis mechanism of surface scattering and reflecting (SSR) coupled with surface plasmon resonance (SPR) was proposed to understand the enhanced photocatalytic activity.

Size-dependent catalytic properties of Au nanoparticles supported on hierarchical nickel silicate nanostructures

The precise control of nanostructures, assembly processing, and the size of each component is important for the construction of integrated functional nanocomposites. In this paper, we describe a simple two-step method for the synthesis of novel flower-like nanocomposites (AuNPs/NiSiO) composed of well-dispersed and size-controlled Au nanoparticles (AuNPs) immobilized on hierarchically structured layered nickel silicate (NiSiO). The as-prepared AuNPs/NiSiO nanocomposites exhibited excellent catalytic activity in the reduction of 4-nitrophenol (4-NP). The experimental results proved that the size of AuNPs played an important role in enhancing the catalytic activity. In particular, there was no visible decrease in the catalytic activity of the reused catalysts even after being recycled five times. Therefore, the hierarchically nanostructured material can be a promising candidate as the catalytic support.

Effects of Au nanoparticles on photoluminescence emission from Si-vacancy in diamond

We studied the coupling of diamond Si color centers with size-controlled Au nanoparticles obtained by chemical routes. The diamond samples, synthesized by Chemical Vapor Deposition, were polycrystalline films or isolated grains. The plasmonic responses of the Au nanoparticles were found to couple with the Ar+ laser frequency or with the frequency of the Si-defects photoluminescence (PL). When the PL of Si optical centers is resonant with the maximum of the Au extinction spectrum, a threshold behavior and a decrease of the PL band FWHM with increasing laser energy is detected, suggesting the transition from spontaneous to stimulated emission.

Size-controllable synthesis of catalyst of gold nanoparticles with capping agents of natural chitosan

In this study, size-controllable gold nanoparticles (NPs) are synthesized by using sonoelectrochemical methods in the presence of natural chitosan (Ch). First, positively charged Au-containing complexes were prepared in 0.1N NaCl by using oxidation–reduction cycle (ORC) treatment to Au substrate. Then size-controllable Au NPs, ranging from 10 to 80nm in diameter, were synthesized by varying the addition quantities of Ch from 1 to 2g/L, respectively, in solutions under using sonoelectrochemical reduction. Experimental results indicate that the optimal molar ratio of used Ch to synthesized Au NPs is ca. 3 for obtaining the smallest Au NPs. Moreover, the catalytic activity of the size-controllable Au NPs on the decomposition of acetaldehyde in solution was examined. Au NPs with 10nm in diameter demonstrate significantly catalytic activity. However, bigger Au NPs with 80nm in diameter are almost inert for the decomposition of acetaldehyde.

Uniform charging energy of single-electron transistors by using size-controlled Au nanoparticles

Single-electron transistors have the potential to become next-generation nanodevices and sensors owing to their small size, low power consumption, and high charge sensitivity, where the charging energy of the devices is the most important parameter determining the operational temperature. Here, we have demonstrated that the charging energy of single-electron transistors can be controlled (48 ± 4 meV) by adopting electroless gold plating to make separation-defined nanogap electrodes and employing size-controlled chemically synthesized Au nanoparticles (5.2 ± 0.5 nm) as a Coulomb island. At this charging energy, the devices can be operated up to 160 K with on/off current ratio of 60%.

Nanocarbon Materials Growth Dependent on Au Nanoparticle Catalyst Size

We have investigated growth of nanocarbon materials from Au nanoparticle catalysts. Site- and size-controlled Au nanoparticles are formed using atomic steps of a Si surface as templates. Au nanoparticles act as catalysts for chemical-vapor-deposition growth of single-walled carbon nanotubes or carbon nanowires (CNW), depending on the particle size. CNW growth is consistent with the well-known VLS (Vapor-Liquid-Solid) mechanism for semiconductor nanowires, demonstrating that nanocarbon materials grow from liquid Au-C eutectic alloy nanoparticles.

Size-controllable synthesis of surface-enhanced Raman scattering-active gold nanoparticles coated on TiO2

As shown in the literature, gold nanoparticles (NPs) were popularly used in the fields of catalyst and surface-enhanced Raman scattering (SERS). In this work, size-controllable Au NPs coated on TiO(2) are synthesized by adjusting the pH of solutions based on sonoelectrochemical methods. The size-controlled Au NPs on TiO(2), ranging from 2 to 80 nm in diameter, can be obtained by varying the pH of solutions from 3 to 7 and placing the sample for 3 h before sonoelectrochemical reductions. The optimal particle sizes of Au NPs on TiO(2) to obtain the strongest SERS effects under an irradiation of 785 nm for probe molecules of adsorbed Rhodamine 6G (R6G) and deposited polypyrrole (PPy) are all ca. 60 nm.

Self-Assembly Proton Exchange Membranes for Direct Methanol Fuel Cell with Size-Controlled Au Nanoparticles

Charged Au nanoparticles with various diameters, from 2.7 nm to 10.3 nm, were synthesized by using various reducing agents. Then charged Au nanoparticles were self-assembled onto the NafionTM membrane surface as methanol barriers. It was found that the proton exchange membrane self-assembled with 3.9 nm Au particles had the lowest methanol crossover. The proton conductivity decreased with the increase of the particles size until the particles size was more than 6.2 nm and they had little influence on the membrane conductivity. All the self-assembled membranes have higher open circuit voltage (OCV) and performance than original Nafion212TM membrane. And the membranes self-assembled with 3.9 nm poly (diallymethylammonium chloride) (PDDA) modified Au (PDDA-Au) particles had the highest performance due to the reciprocal of the methanol permeation current density and membrane area resistance.

Photochemical fabrication of size-controllable gold nanoparticles on chitosan and their application on catalytic decomposition of acetaldehyde

In this work, we report a new pathway to prepare size-controllable gold nanoparticles (NPs) on chitosan (Ch) in aqueous solutions for improving catalytic decomposition of acetaldehyde by pure gold NPs at room temperature. First, Au substrates were cycled in deoxygenated aqueous solutions containing 0.1N NaCl and 1 g/L Ch from −0.28 to +1.22 V vs Ag/AgCl at 500 mV/s for 200 scans. Then the solutions were irradiated with UV lights of different wavelengths to prepare size-controllable Au NPs on Ch. Experimental results indicate that the particle sizes of prepared NPs are increased when UV lights with longer wavelengths were employed. The particle sizes of resulted Au NPs can be controlled from 10 to 50 nm. Moreover, the decomposition of acetaldehydes in wines can be significantly enhanced by ca. 190% of magnitude due to the contribution of the adsorption of Au NPs on Ch.

Synthesis of efficient and reusable catalyst of size-controlled Au nanoparticles within a porous, chelating and intelligent hydrogel for aerobic alcohol oxidation

Synthesis of size-controlled Au nanoparticles for aerobic alcohol oxidation within a porous, chelating and intelligent hydrogel of poly( N-isopropylacrylamide)- co-poly[2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxypropyl ester] (PNIPAM- co-PMACHE) is studied. The PNIPAM- co-PMACHE hydrogel is demonstrated to be a suitable scaffold, within which Au nanoparticles with size ranging from 2.6 to 6.3 nm are synthesized by reducing the Au precursor of HAuCl 4 with different reducing agents. The synthesized composite of the hydrogel and the encapsulated Au nanoparticles is thermoresponsive, which can reversibly deswell/swell at the volume-phase-transition temperature (VPTT) at 27 °C. The encapsulated Au nanoparticles keep stable during the reversible deswelling/swelling of the thermoresponsive hydrogel/Au composite. The catalysis of the thermoresponsive composite is tested employing aerobic alcohol oxidation as model reaction and it is found that the catalytic activity of the thermoresponsive composite is strongly dependent on the size of the encapsulated Au nanoparticles. Besides, it is found that the thermoresponsive composite is catalytically efficient for aerobic alcohol oxidation partly since the reactant of alcohol is highly concentrated within the hydrogel matrix through the reversible deswelling and partly since the reactant of alcohol can be activated through the strong hydrogen bonding between the alcohol molecules and the poly( N-isopropylacrylamide) segment. And furthermore, the reversible deswelling/swelling of the thermoresponsive composite provides great convenience for catalyst recycling.

Organosulfur-Functionalized Au, Pd, and Au−Pd Nanoparticles on 1D Silicon Nanowire Substrates: Preparation and XAFS Studies

A hybrid preparative method was developed to prepare organosulfur-functionalized Au nanoparticles (NPs) on silicon nanowires (SiNWs) by reacting HAuCl(4) with SiNW in the presence of thiol. A number of organosulfur molecules-dodecanethiol, hexanethiol, 1,6-hexanedithiol, and tiopronin-were used to functionalize the Au surface. Size-selected NPs ranging from 1.6 to 7.5 nm were obtained by varying the S/Au ratio and the concentration of HAuCl(4). This method was further extended to the preparation Pd and Pd-Au bimetallic NPs on SiNWs. The morphology of the metal nanostructures was examined by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The local structure and bonding of the SiNW-supported metal nanostructures were studied using X-ray absorption fine structures (XAFS) [including both X-ray near-edge structures (XANES) and extended X-ray absorption fine structures (EXAFS)] at the Au L(3)-, Pd K-, S K-, and Si K-edges. It was also found that the annealing of the thiol-capped Au NPs up to 500 degrees C transforms the surface of the thiol-capped NPs to gold sulfide, as identified using Au L(3)- and S K-edge XANES. We also illustrate that this preparative approach can be used to form size-controllable Au NPs on carbon nanotubes.