Coverage Of Au Nanoparticles Research Articles

Delicate control of a gold-copper oxide tandem structure enables the efficient production of high-value chemicals by electrochemical carbon dioxide reduction

The electrochemical carbon dioxide reduction reaction (CO2RR) has substantial potential for carbon capture and utilization (CCU), aiming to produce carbon-neutral fuels and valuable chemical feedstocks. Copper (Cu) is recognized as the primary metal catalyst capable of facilitating C-C coupling and producing multi-carbon compounds. The tandem catalyst approach, particularly the oxide-derived Cu (OD-Cu)-based tandem catalyst, has been reported to improve the selectivity for multicarbon compounds such as ethylene and ethanol. However, the impact of the loading structure of the CO-producing catalyst in the tandem catalyst on CO2RR performance has not been thoroughly investigated. In this study, we developed Au nanoparticles with different sizes and loading densities on Cu2O and investigated their CO2RR properties. Tandem catalysts featuring smaller Au nanoparticles exhibited increased activity in the electrochemical CO2RR, resulting in an anodic shift in the potential. Improved Faradaic efficiencies (FEs) and partial current densities (PCDs) of C2+ were also observed for tandem catalysts with smaller Au nanoparticles. Remarkably, the FE and PCD of n-propanol increased as the coverage of Au nanoparticles increased, in contrast to those of C2 products such as ethylene and ethanol. The effectiveness of the tandem effect depends on the increase in local CO concentration facilitated by the CO-generating catalyst on the confined OD-Cu surface. Our research presents a strategy for constructing a productive tandem structure for the CO2RR.

Ultrafast Detection of Low Acetone Concentration Displayed by Au-Loaded LaFeO3 Nanobelts owing to Synergetic Effects of Porous 1D Morphology and Catalytic Activity of Au Nanoparticles.

Herein, we report on one-dimensional porous Au-modified LaFeO3 nanobelts (NBs) with high surface area, which were synthesized through the electrospinning method. The incorporation and coverage of Au nanoparticles (NPs) on the surface of the LaFeO3 NBs was achieved by adjusting the HAuCl amount in the precursor solution. Successful incorporation of Au NPs was examined by X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The gas-sensing performance of both the pure and Au/LaFeO3 NB-based sensors was tested toward 2.5–40 ppm of acetone at working temperatures in the range from room temperature to 180 °C. The gas-sensing findings revealed that Au/LaFeO3 NB-based sensor with the Au concentration of 0.3 wt % displayed improved response of 125–40 ppm of acetone and rapid response and recovery times of 26 and 20 s, respectively, at an optimal working temperature of 100 °C. Furthermore, all sensors demonstrated an excellent response toward acetone and remarkable selectivity against NO2, NH3, CH4, and CO. Hence, the Au/LaFeO3-NB-based sensor is a promising candidate for sensitive, ultrafast, and selective acetone detections at low concentrations. The gas-sensing mechanism of the Au/LaFeO3 sensors is explained in consideration of the catalytic activity of the Au NPs, which served as direct adsorption sites for oxygen and acetone.

High-performance UV‐Vis-NIR photodetectors based on plasmonic effect in Au nanoparticles/ZnO nanofibers

In this study, UV‐Vis-NIR photodetectors based on decorated ZnO nanofibers (NFs) with optimized coverage of Au nanoparticles (NPs) fabricated via combined simple electrospinning and sputtering techniques are introduced. The effect of different coverages of Au NPs resulted from different Au nominal layer thicknesses on the morphology and optical properties of the ZnO fibers are investigated through various characterization methods. It is discovered that 4 nm Au nominal thickness provides the highest UV on/off ratio (~460), responsivity (~332 A/W), detectivity (~2.93×1011 Jones) as well as faster rise and decay times as compared to pure ZnO nanofibers. A broad spectral response from UV to NIR with high photoresponsivity and fast response time (<0.5 s) in the visible and NIR regions are achieved for the sample decorated with 8 nm Au nominal thickness. Response to visible and IR irradiations and initial fast response to UV are originated from localized surface plasmon resonance (LSPR) absorption of the Au NPs and effective separation and transport of photogenerated carriers, wherein slow response to UV is due to adsorption/desorption of oxygen species.

A Rational Design of the Sintering-Resistant Au-CeO₂ Nanoparticles Catalysts for CO Oxidation: The Influence of H₂ Pretreatments.

The redox pretreatment of samples is one of the crucial ways of altering the catalytic properties of the supported noble metal materials in many heterogeneous reactions. Here, H2-reducing pretreatment is reported to enhance the thermal stability of Au-CeO2 catalysts prepared by the deposition–precipitation method and calcination at 600 °C for CO oxidation. In order to understand the improved activity and thermal stability, a series of techniques were used to characterize the physico-chemical changes of the catalyst samples. H2 pretreatment may lead to: (i) a strong metal–support interaction (SMSI) between Au nanoparticles (NPs) and CeO2, evidenced by the particular coverage of Au NPs by CeO2, electronic interactions and CO adsorption changes. (ii) the production of surface bicarbonates which can accelerate CO oxidation. As a result, the H2 pretreatment makes the Au NPs more resistant to sintering at high temperature and enhances the CO oxidation activity. Furthermore, this reduction pretreatment strategy may provide a potential approach to enhance the thermal-stability of other supported noble metal catalysts.

(Invited) Magneto-Optical and Plasmonic Composite Particles Synthesized By Deposition of Au Nanoparticles on Bismuth-Substituted Yttrium-Iron Garnet Core

Although immunochromatograph using nanoparticles has some merits such as an ease of use and a quick response, it has some issues such as a poor sensitivity and a lack of quantitativity. To overcome the issues, we propose a new immunoassay method using a magneto-optical (MO) effect based on nanoparticle technologies. It is expected that the MO immunoassay leads to a higher sensitivity and a quantitative measurement. Nanoparticles with a high MO effect are required for this technique. Bismuth-substituted yttrium-iron garnet (Bi-YIG) is one of the candidates, which exhibits a large Faraday effect. To enhance the Faraday effect for highly sensitive MO immunoassay, surface plasmon resonance (SPR) effect is employed in the preset study. Au nanoparticles have an absorption peak based on the SPR effect in the wavelength range of 500-600 nm by optimizing their size and interparticle distance. Since Bi-YIG has a peak in its MO spectrum at around 550 nm, the SPR absorption will enhance the MO effect, obtaining a maximum Faraday rotation in the range.In the present study, we fabricated MO and plasmonic particles composed of a Bi-YIG particle as a core and Au nanoparticles deposited on the core. First, Bi-YIG particles of 300-600 nm in size as the core were synthesized by coprecipitation and heat-treatment for crystallization, followed by milling to optimize the size. Then, Au nanoparticles were deposited on the Bi-YIG particles by a polyol reduction method using formaldehyde as a reducing agent. Morphological properties such as size and interparticle distance of the Au nanoparticles manipulated by the concentrations of Au ion and formaldehyde for their deposition are important in the SPR effect, resulting in the enhancement of the magneto-optical effect. The specimens were characterized by transmission electron microscopy, X-ray diffraction (XRD), optical absorption spectroscopy, and magneto-optical evaluations in a transmission mode (Faraday rotation).The morphology of Au nanoparticles on Bi-YIG particles depended on the deposition conditions. The clear SPR absorption and the MO enhancement were obtained in the composites with a larger amount of Au nanoparticles deposited on Bi-YIG particles as shown in Fig. 1. The enhancement of the Faraday rotation was observed in the range of 500-700 nm (Fig. 1(a)), corresponding to the wavelength range where the clear SPR absorption was observed (Fig. 1(b)). The enhancement of the Faraday rotation reached 1.54 times in maximum at around 550 nm of wavelength. The dependence of optical and magneto-optical properties as a function of Au concentration was attributed to the morphology of the Au nanoparticles deposited on Bi-YIG particles. The coverage of Au nanoparticles on Bi-YIG strongly influenced the enhancement of the Faraday rotation based on the SPR effect. Although the quantity of the deposited Au nanoparticles confirmed by XRD was increased, the MO enhancement was not confirmed in the case that large Au nanoparticles were deposited and the coverage was low on the Bi-YIG surface. Figure 1

Extremely high efficient nanoreactor with Au@ZnO catalyst for photocatalysis

We fabricated a photocatalytic Au@ZnO@PC (polycarbonate) nanoreactor composed of monolayered Au nanoparticles chemisorbed on conformal ZnO nanochannel arrays within the PC membrane. A commercial PC membrane was used as the template for deposition of a ZnO shell into the pores by atomic layer deposition (ALD). Thioctic acid (TA) with sufficient steric stabilization was used as a molecular linker for functionalization of Au nanoparticles in a diameter of 10 nm. High coverage of Au nanoparticles anchored on the inner wall of ZnO nanochannels greatly improved the photocatalytic activity for degradation of Rhodamine B. The membrane nanoreactor achieved 63% degradation of Rhodamine B within only 26.88 ms of effective reaction time owing to its superior mass transfer efficiency based on Damköhler number analysis. Mass transfer limitation can be eliminated in the present study due to extremely large surface-to-volume ratio of the membrane nanoreactor.

Urchin-like LaVO4/Au composite microspheres for surface-enhanced Raman scattering detection

The availability of sensitive, reproducible and stable substrate is critically important for surface enhanced Raman scattering (SERS)-based application, but it still remains a challenge up to now. In this work, urchin-like LaVO4 microspheres prepared by a hydrothermal method were used as a template to fabricate SERS substrate by deposition of Au nanoparticle onto the surfaces of LaVO4 microspheres. The coverage of Au nanoparticles on the surfaces of LaVO4 microspheres can be easily controlled by varying the amount of Au precursor. SERS measurement showed that the coverage of Au nanoparticles on the surfaces of LaVO4 microspheres had a great effect on SERS activity. The SERS signals collected from 80 microspheres indicated that as-prepared SERS substrate exhibited a good reproducibility. Detection of melamine molecules with a low concentration (1.0×10−9M) was used as an example to show the possible application of such substrate. In addition, the effect of iron ion (Fe3+) on detection melamine from the mixture of melamine and benzoic acid was also investigated. It was found that the interference of benzoic acid in detecting melamine from the mixture can be removed by adding Fe3+.

Importance of ion bombardment during coverage of Au nanoparticles on their structural features and optical response

This work studies the changes in the optical response and morphological features of 6 ± 1 nm diameter Au nanoparticles (NPs) when covered by a layer of a-Al2O3 by pulsed laser deposition (PLD). The laser fluence used for ablating the Al2O3 target is varied in order to modify the kinetic energy (KE) of the species bombarding the NPs during their coverage. When the ion KE &amp;lt; 200 eV, the structural features and optical properties of the NPs are close to those of uncovered ones. Otherwise, a shift to the blue and a strong damping of the surface plasmon resonance is observed as fluence is increased. There are two processes responsible for these changes, both related to aluminum ions arriving to the substrate during the coverage process, i.e., sputtering of the metal and implantation of aluminum species in the metal. Both processes have been simulated using standard models for ion bombardment, the calculated effective implanted depths allow explaining the observed changes in the optical response, and the use of a size-dependent sputtering coefficient for the Au NPs predicts the experimental sputtering fractions. In spite of the work is based on PLD, the concepts investigated and conclusions can straightforwardly be extrapolated to other physical vapor deposition techniques or processes involving ion bombardment of metal NPs by ions having KE &amp;gt; 200 eV.

Optical Properties of ZnO Nanowires Decorated with Au Nanoparticles

One of the key technologies in future optoelectronics is control of excitons in oxide materials by the coupling with plasmons on noble metal surfaces. Optical properties of ZnO nanowires decorated with Au nanoparticles were studied to understand fundamental mechanism of the coupling and to develop optoelectronic devices with new functionalities. Light intensity at the main peak position in the photoluminescence (PL) spectra of ZnO nanowires was enhanced with the coverage of Au nanoparticles. Lifetime of excitons excited optically decreased by the decoration of Au nanoparticles. Understanding of the coupling between excitons and plasmons leads to optical control of excitons and will pave the way for new type of optoelectronic devices.

Enhanced acetone sensing characteristics by decorating Au nanoparticles on ZnO flower-like structures

A well-organized hierarchical structure of ZnO was developed by chemical bath deposition and used as templates for making gold-coated ZnO (Au/ZnO) hybrid nanostructures. The coverage of Au nanoparticles (Au NPs) on ZnO was controlled by changing the amount of the Au precursor. The Au/ZnO hybrids were applied as gas sensing materials to detect acetone. The improved sensor response, selectivity and short response, and recovery time to acetone vapor due to Au NPs on ZnO nanostructures has been observed and explained by considering the formation of Au/ZnO heterostructures, which are favorable for the diffusion of gas molecules. In addition, the dependence of Au amount on gas sensor properties was systematically investigated. ZnO decorated by 6 wt% Au NPs displayed a 9.05-fold enhancement in gas response to 100 ppm of acetone at 280 °C compared to pristine ZnO.

Synthesis and characterization of ZnO/4-mercaptobenzoic acid/Au composite particles

ZnO/4-mercaptobenzoic acid (4-MBA)/Au composite particles have been prepared by interconnecting the flower-like ZnO particles and Au nanoparticles with functional molecules 4-MBA. SEM measurements have shown that the obtained composite particles have very homogeneous shape and size. The surface coverage of Au nanoparticles on ZnO/4-MBA particles can be tuned by changing the molar ratio of ZnO/4-MBA to Au. The Raman spectra of ZnO/4-MBA and ZnO/4-MBA/Au particles indicate the presence of the interaction between ZnO, Au particles and 4-MBA molecules.

ZnS–Au planet-like structure: a facile fabrication and improved optical performance induced by surface plasmon resonance

Semiconductor-metal planet-like structure composed of ZnS crystals and Au nanoparticles (NPs) were successfully synthesized using a simple method. The external surface of ZnS was pre-modified with sodium dodecyl sulfate (SDS). With the assistance of this anionic surfactant, Au NPs could be deposited onto the surface of ZnS crystals via electrostatic adsorption. The samples were structurally characterized by X-ray diffraction, Fourier transform infrared, and transmission electron microscope. It was shown that all samples were made up of face-centered cubic Au and wurtzite ZnS. In this structure, the surface coverage of Au NPs could be readily adjusted by varying the Au/ZnS ratio during the synthesis. Photoluminescence results showed that the defect emission intensity of the ZnS–Au planet-like structure improved by 20 % at the Au/ZnS molar ratio of 1:588, with the Au NPs measuring 12 nm in diameter. This enhancement can be primarily ascribed to localized surface plasmon resonance on the surface of the Au NPs.

High-conductivity graphene nanocomposite via facile, covalent linkage of gold nanoparticles to graphene oxide

Graphene and its derivative, graphene oxide (GO) have been substantively used as the main framework for dispersing or building nanoarchitectures because of their excellent properties in electronics and catalysis. The requirement to obtain superior graphene-metal hybrid nanomaterials has led us to explore a facile way to design 4-aminobenzenethiol/1-hexanethiolate-protected gold nanoparticles (aAuNPs)-functionalized graphene oxide composite (aAuNPs-GO) in solution. We demonstrate that when aAuNPs with amino groups are exposed to GO, well-dispersed coverage of Au nanoparticles are mainly observed on the edge of GO sheet. In contrast, when 1-hexanethiolate-protected gold nanoparticles (hAuNPs) without amino groups are exposed to GO, hAuNPs simply aggregate on the surface of GO. This indicates that amino groups located on the surface of Au nanoparticles are an essential prerequisite for attachment of nearly monodispersed aAuNPs. The strategy described here for the fabrication of aAuNPs-GO provides a straightforward approach to develop graphene-based nanocomposites with undamaged sheets structure and good solubility and also improve the conductivity of GO sheets evidently.

ZnO/Au Composite Nanoarrays As Substrates for Surface-Enhanced Raman Scattering Detection

Well-aligned ZnO nanoneedle and nanorod arrays were grown on an aluminum-doped zinc oxide (AZO) buffer layer by chemical vapor deposition and used as templates for making gold-coated ZnO (ZnO/Au) composite nanoarrays. The coverage of Au nanoparticles on ZnO nanoneedle and nanorod was controlled by varying the concentration of Au precursor. High coverage led to the formation of ZnO/Au nanoneedle bundles. The ZnO/Au composite nanoarrays were applied as substrates in surface-enhanced Raman scattering (SERS) measurement. The SERS enhancement factor is mainly controlled by gold coverage and morphologies of the ZnO/Au nanoarrays. Their application in rapid detection of melamine in egg white is demonstrated. This SERS-based melamine detection is advantageous in that sample pretreatment is not needed. It showed the potential of the ZnO/Au nanoarrays as a convenient and robust SERS-active substrate for food safety monitoring.

A facile method of achieving low surface coverage of Au nanoparticles on an indium tin oxide electrode and its application to protein detection

Low surface coverage of Au nanoparticles on an indium tin oxide electrode for sensitive electrochemical detection was achieved using electrostatic adsorption of AuCl(4)(-) followed by reduction.

Electrosynthesized poly(1,6-hexanedithiol) as a new immobilization matrix for Au-nanoparticles-enhanced piezoelectric immunosensing

Electrosynthesized poly(1,6-hexanedithiol) (PHDT) was proposed as a new immobilization matrix for Au-nanoparticles-enhanced piezoelectric immunosensing, with human immunoglobulin G (hIgG)/anti-hIgG as an example. In ethanol containing 0.10 M LiClO4, the electropolymerization of 1,6-hexanedithiol (HDT) occurred through the oxidation of the –SH groups of HDT and then –S–S– linking at potentials positive of ∼0.7 V vs. SCE, as characterized by the electrochemical quartz crystal microbalance (EQCM). PHDT was prepared potentiostatically at 1.25 V vs. SCE, and Au nanoparticles (AuNPs) were then immobilized on the prepared PHDT films by dip-dry coating. The immobilization amount of AuNPs was investigated vs. the volume of dipped AuNPs solution, and a theoretical discussion is given on the coverage of AuNPs on the PHDT film. Under the optimized experimental conditions, the adsorption amount of anti-hIgG was the greatest on the AuNPs/PHDT/Au electrode, as compared with those at the bare Au and PHDT/Au electrodes. The molar combination ratio of anti-hIgG to hIgG was estimated to be 1:0.493 on the AuNPs/PHDT/Au electrode in a subsequent immunoreaction. Compared with the common immobilization protocol with HDT, namely, AuNPs immobilized directly on an HDT self-assembly (HDT-SA) at an Au electrode (AuNPs/HDT-SA/Au), the AuNPs/PHDT/Au electrode shows better stability and can be constructed more time-effectively, though the adsorption amount of anti-hIgG was comparable with each other. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized for characterizations of and comparison among various surfaces. The electrosynthesized PHDT presented here as a new bio-immobilization matrix is highly recommended for wider applications in biosensing.

Enhanced Charge Transport and Incorporation of Redox Mediators in Layer-by-Layer Films Containing PAMAM-Encapsulated Gold Nanoparticles

In this work, we exploit the molecular engineering capability of the layer-by-layer (LbL) method to immobilize layers of gold nanoparticles on indium tin oxide (ITO) substrates, which exhibit enhanced charge transfer and may incorporate mediating redox substances. Polyamidoamine (PAMAM generation 4) dendrimers were used as template/stabilizers for Au nanoparticle growth, with PAMAM-Au nanoparticles serving as cationic polyelectrolytes to produce LbL films with poly(vinylsulfonic acid) (PVS). The cyclic voltammetry (CV) of ITO-PVS/PAMAM-Au electrodes in sulfuric acid presented a redox pair attributed to Au surface oxide formation. The maximum kinetics adsorption is first-order, 95% of the current being achieved after only 5 min of adsorption. Electron hopping can be considered as the charge transport mechanism between the PVS/PAMAM-Au layers within the LbL films. This charge transport was faster than that for nonmodified electrodes, shown by employing hexacyanoferrate(III) as the surface reaction marker. Because the enhanced charge transport may be exploited in biosensors requiring redox mediators, we demonstrate the formation of Prussian blue (PB) around the Au nanoparticles as a proof of principle. PAMAM-Au@PB could be easily prepared by electrodeposition, following the ITO-PVS/ PAMAM-Au LbL film preparation procedure. Furthermore, the coverage of Au nanoparticles by PB may be controlled by monitoring the oxidation current.

Synthesis of Au nanotubes with SiOx nanowires as sacrificial templates

Gold nanotubes with SiOx nanowires as sacrificial templates have been synthesized. SiOx nanowires were functionalized by 3-aminopropyl trimethoxysilane that generates a charged surface. The attachment of negatively charged Au nanoparticles was followed. The coverage of Au nanoparticles was initially less than 30%. Further coverage was achieved by the reduction of gold hydroxide to grow the continuous nanoshell on Au nanoparticles, which serve as nucleation sites. The final coverage of Au nanoshells on SiOx nanowires depends strongly on the relative amount of SiOx nanowires in gold hydroxide solution. Both transmission electron microscope and scanning electron microscope images revealed the formation of Au nanotubes with the removal of SiOx nanowires by etching in a dilute HF solution.

PH-Dependent Adsorption of Gold Nanoparticles on p-Aminothiophenol-Modified Gold Substrates

Colloidal Au nanoparticles were assembled on a gold substrate via a p-aminothiophenol coupling layer. The surface coverage of Au nanoparticles was found to be closely related to the pH value of gol...