Au Core Research Articles

Modulating Pt Interaction in Au@Pt Nanoparticle/WO3 Photocatalysts for Enhanced Production of Peroxodisulphate

Production of peroxodisulphate (S2O82–) on powdered photocatalysts is a promising way to obtain high-value-added chemicals using solar energy; however, it is still suffering from low efficiency. In the present work, we fabricated bimetallic Au core and Pt shell nanoparticle-loaded WO3 (Au@Pt/WO3) photocatalyst for enhanced production of S2O82–, which is 1.7 times that of Pt nanoparticle-loaded WO3 (Pt/WO3), and was reported to be the best catalyst for S2O82– production. A further study demonstrated that the electronic interaction of Pt was successfully modulated by the core–shell nanoparticle architecture, and the core–shell nanoparticle structure between Au and Pt improved the formation of the surface chemical state of Pt to be metallic Pt, proposed as the active site for oxygen reduction. Besides, the core–shell nanoparticle structure also exposed a large amount of Pt on the surface of the substrate. As a result, Au@Pt/WO3 showed significantly enhanced photocatalytic activity of S2O82– with a quantum efficiency of 5.2% at 420 nm, whereas Pt–Au bimetallic alloy nanoparticle-loaded WO3 with a large amount of surface PtOx and exposed both Au and Pt on the surface showed very low activity. This work provides insights into the bimetallic Pt nanoparticle-loaded WO3 for enhanced photocatalytic activity.

Pt-Sn alloy shells with tunable composition and structure on Au nanoparticles for boosting ethanol oxidation.

Combining the core-shell structure with the optimization of surface composition and structure in the shell is a fantastic strategy to enhance the electrocatalytic performances. Here, we synthesized trimetallic Au@PtxSny core-shell nanoparticles (NPs) with tunable composition and structure of Pt-Sn alloyed shells. Impressively, the Au@PtSn core-shell NPs with hexagonal PtSn alloyed shells exhibited the highest mass activity and specific activity toward ethanol oxidation reaction (EOR) in alkaline electrolyte, which are 13.0 and 12.7 times higher than those of the commercial Pt/C. In addition, the Au@PtSn core-shell NPs displayed the best stability compared to commercial Pt/C, with only 44.8% loss vs. 86.8% loss in mass activity after 1,000 s due to the stronger anti-poisoning ability for reaction intermediates. The theory calculations reveal that the introduction of Au core and alloying Pt with Sn both endow Pt with an appropriate d-band center, and thus effectively boosting the EOR activity.

Kernels‐Different Au25Nanoclusters Enhanced Catalytic Performance via Modification of Ligand and Electronic Effects

Comprehensive SummaryUltrasmall atomically precise thiolate‐protected gold nanoclusters with surface open sites are crucial for practical applications in catalysis. However, there is a lack of systematic studies that unify the kernels‐isomerization, modification of peripheral ligands and electronic effects into one system, as well as their correlation to catalytic performances. In this work, three structurally related Au25nanoclusters with reported star Au25 kernels, Au25‐i‐FTP, Au25‐bi‐FTP, and Au25‐bi‐CHT have been synthesized through two different methods: one‐pot direct reduction and two‐step reduction by using AsPh3 as converter. Their structures and catalytic performance have been comparatively investigated. Au25‐i‐FTP has a classic Au13 core capped by six dimeric RS‐Au‐SR‐Au‐SRs, while Au25‐bi‐FTP and Au25‐bi‐CHT feature typical rod‐shaped biicosahedral geometric kernel. All of the three Au25 clusters were effective catalysts for oxidation of organosilanes, different from conclusions obtained in literature. Especially, the nanorod‐type Au25‐bi‐CHT clusters protected by flexible thiol ligands showed very good catalytic performance in this reaction, the conversion and selectivity were close to 100% within 5 min. The ligand rigidity and electron effects work together to modulate the catalytic properties. The findings inspire us to rethink kernel and ligand effects on catalytic property, and the principle demonstrated here will possibly be widely‐used in high active atom‐precise catalysts modification.

Highly strained gold (Au)-palladium (Pd) core-shell nanobipyramids with extraordinary high activity and durability towards ethanol electrooxidation

Direct ethanol fuel cells (DEFCs) have emerged as promising power sources for mobile electronics due to their eco-friendly advantages over analogous devices fed with hydrogen. However, the ethanol oxidation reaction (EOR), the anode reaction of DEFCs, suffers from slower oxidation kinetics compared to the existing H2-fuel cells. Herein, we report a strategy based on maximum strain in Au@Pd core-shell nanobipyramid (NBP) structure where strain induced electronic effect enhances surface adsorption of ethanol towards boosted EOR. The novelty of construction of the present core-shell nanoparticle (NP) lies not only in showing up maximum tensile strain due to the lattice mismatch between the core (Au) and shell (Pd) atoms but also in introducing an additional amount of strain manifested by the 5-fold twins and stacking faults type defects, caused by the presence of an optimally size selected bipyramid shape Au core. Finally, we have discovered that such highly strained Au@Pd core-shell NBPs with the thinnest possible Pd shell exhibit extraordinary high electrocatalytic effect up to highest level of mass activity of 15.26 A mgPd−1 in the EOR under alkaline conditions which is superior to that of any Pd-based catalysts reported so far and commercial Pd/C catalysts.

Electrochemiluminescence biosensor for determination of lead(II) ions using signal amplification by Au@SiO2 and tripropylamine-endonuclease assisted cycling process.

MXene@Au as the base and Au@SiO2 as signal amplification factor were used for constructing an ultrasensitive "on-off" electrochemiluminescence (ECL) biosensor for the detection of Pb2+ in water. The use of MXene@Au composite provided a good interface environment for the loading of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)32+) on the electrode. Based on resonance energy transfer, the Au (core) SiO2 (shell) (Au@SiO2) nanoparticles stimulate electron transport and promote tripropylamine (TPrA) oxidation. The luminescence effect of Au@SiO2 was five times that of AuNPs and SiO2 nanomaterials alone, and the ECL intensity was greatly improved. In addition, Pb2+ activated the aptamer to exert its endonuclease activity, which realized the signal cycle amplification in the process of Pb2+ detection. When Pb2+ was added, the ECL signal weakened, and the Pb2+ concentration was detected according to the decreased ECL intensity. Under optimized experimental conditions, this aptamer sensor for Pb2+ has a wide detection range (0.1 to 1 × 106ng L-1) and a low detection limit (0.059ng L-1). The relative standard deviation (RSD) of the sensor is 0.39-0.99%, and the recovery of spiked standard is between 90.00 and 125.70%. The sensor shows good selectivity and high sensitivity in actual water sample analysis. This signal amplification strategy possibly provides a new method for the detection of other heavy metal ions and small molecules.

Anisotropic deformation of colloidal particles under 4 MeV Cu ions irradiation

Anisotropic deformation of colloidal particles was investigated under ion irradiation with 4 MeV Cu ions. In this study, 0.5 μm-diameter colloidal silica particles, 0.5 μm-diameter Au-silica core–shell particles, and 15 nm-diameter Au colloids embedding in a planar Si/SiO2 matrix were irradiated with 4 MeV Cu ions at room temperature and normal incidence. In colloidal silica particles, ion beam irradiation causes dramatic anisotropic deformation; silica expands perpendicular to the beam and contracts parallel, whereas Au cores elongate. Au colloids in a planar SiO2 matrix were anisotropically transformed from spherical colloids to elongated nanorods by irradiating them with 4 MeV Cu ions. The degree of anisotropy varied with ion flux. Upon irradiating the embedded Au colloids, dark-field light scattering experiments revealed a distinct color shift to yellow, which indicates a shift in surface plasmon resonance. A surface plasmon resonance measurement reveals the plasmon resonance bands are split along the arrays of Au colloids. Our measurements have revealed resonance shifts that extend into the near-infrared spectrum by as much as 50 nm.

Exploring bimetallic Au–Ag core shell nanoparticles reduced using leaf extract of Ocimum tenuiflorum as a potential antibacterial and nanocatalytic agent

Biosynthesis of bimetallic Au–Ag core shell nanoparticle under ambient condition using Ocimum tenuiflorum (Krishna Tulsi) leaf extract is being reported for the first time. For the biosynthesized bimetallic core shell nanoparticles (OTAuAgNPs) visual and spectrophotometric analysis was performed. Development of a deep purple color suggested the creation of OTAuAgNPs. It was then validated by UV–Vis spectrophotometry within 4 h of incubation showing a surface plasmon resonance peak at 560 nm. FESEM-EDAX, FT-IR, particle analyzer and XRD were the analytical techniques employed to characterize the biosynthesized OTAuAgNPs. Using a known antibiotic as a control, OTAuAgNPs (10 mg/ml) had a substantial bacteriostatic effect against Gram + ve (Bacillus subtilis) and Gram −ve (E.coli, Pseudomonas aeruginosa) bacteria. The OTAuAgNPs (6.5 mg) showed good catalytic action for the adsorption of Coomassie brilliant blue R250 dye (CBB) (50 mg/L, 25 mL), confirmed by the reduction in absorbance maxima that is time dependent. A remarkable adsorption of CBB (94.79%) was attained within 120 min, and the results were best-suited PSO and Elovich models with adsorption kinetic constant of 5.96E−04 g/mg.min and 37.81 mg/g.min, respectively. Further the toxicity studies of brilliant blue R250 dye and metabolite of CBB (post nano-remediated dye solution) was carried out on Vigna radiata (green gram) germination and growth. OTAuAgNPs as nanocatalyst remediated water revealed that it was nontoxic. Thus an ecofriendly and cost-effective approach for bimetallic nanoparticle synthesis could be further explored for removal of CBB from wastewater effluents.

Tailoring Plasmonic Bimetallic Nanocatalysts Toward Sunlight‐Driven H2 Production

AbstractHybrid nanoparticles combining plasmonic and catalytic components have recently gained interest for their potential use in sunlight‐to‐chemical energy conversion. However, a deep understanding of the structure–performance that maximizes the use of the incoming energy remains elusive. Here, a suite of Au and Pd based nanostructures in core–shell and core‐satellites configurations are designed and their photocatalytic activity for Hydrogen (H2) generation under sunlight illumination is tested. Formic acid is employed as H2 source. Core‐satellite systems show a higher enhancement of the reaction upon illumination, compared to core–shell ones. Electromagnetic simulations reveal that a key difference between both configurations is the excitation of highly localized and asymmetric electric fields in the gap between both materials. In this scheme, the core Au particle acts as an antenna, efficiently capturing visible light via the excitation of localized plasmon resonances, while the surrounding Pd satellites transduce the locally‐enhanced electric field into catalytic activity. These findings advance the understanding of plasmon‐driven photocatalysis, and provide an important benchmark to guide the design of the next generation of plasmonic bimetallic nanostructures.

In situ monitoring of Suzuki-Miyaura cross-coupling reaction by using surface-enhanced Raman spectroscopy on a bifunctional Au-Pd nanocoronal film

Surface-enhanced Raman spectroscopy (SERS), a powerful surface vibrational spectroscopic technique, is ideally suited for in situ monitoring the chemical transformations occurred at surfaces and/or interfaces. For in situ SERS monitoring, a platform integrated both plasmonic and catalytic activity is a prerequisite. Here, we fabricate a bifunctional Au-Pd nanocoronal film for in situ SERS monitoring Suzuki-Miyaura cross-coupling reaction. This excellent bifunctional substrate leads to the coupling of high catalytic activity with a strong SERS effect at the center of two adjacent Au cores and shows fine reproducibility and stability of SERS signals. During investigating the Suzuki reaction with in situ SERS, we found two distinct catalytic kinetic processes resulted from two disparate catalytic sites on a Au-Pd nanocoronal. Comparing with conventional analytical techniques, this work provides a novel approach for studying Suzuki reactions at surfaces and/or interfaces with in situ SERS.

Geometric and electronic structure analyses on three Au42(SR)26 isomers

In this paper, we present the geometric and electronic structure analyses of three Au42(SR)26 isomers based on a combination of grand unified model (GUM), ring model, superatom network model, and density functional theory calculations. Structural decompositions, Au–Au and Au–S distances, Wiberg bond orders, density of states, composition of the frontier orbitals, and origin of the optical absorption spectra are presented and discussed in detail. The structural decomposition of the Au cores of the three isomers into eight tetrahedral Au4 elementary blocks based on GUM shows that the isomeric mechanism of the three isomers can be ascribed to core and complex isomerism. Inspection of Au–Au and Au–S distances reveals the key role of the aurophilic interactions in the stability of the three Au42(SR)26 isomers. Furthermore, by analyzing the composition of the frontier orbitals, the origin of the optical absorption spectra of the three isomers is attributed to the sp → sp transition. Overall, the geometric and electronic structure analyses of the three Au42(SR)26 isomers illustrate the inherent structure–property correlations among these isomers.

Star-Shaped Magnetic-Plasmonic Au@Fe3O4 Nano-Heterostructures for Photothermal Therapy.

Here, we synthesize a Au@Fe3O4 core@shell system with a highly uniform unprecedented star-like shell morphology with combined plasmonic and magnetic properties. An advanced electron microscopy characterization allows assessing the multifaceted nature of the Au core and its role in the growth of the peculiar epitaxial star-like shell with excellent crystallinity and homogeneity. Magnetometry and magneto-optical spectroscopy revealed a pure magnetite shell, with a superior saturation magnetization compared to similar Au@Fe3O4 heterostructures reported in the literature, which is ascribed to the star-like morphology, as well as to the large thickness of the shell. Of note, Au@Fe3O4 nanostar-loaded cancer cells displayed magneto-mechanical stress under a low frequency external alternating magnetic field (few tens of Hz). On the other hand, such a uniform, homogeneous, and thick magnetite shell enables the shift of the plasmonic resonance of the Au core to 640 nm, which is the largest red shift achievable in Au@Fe3O4 homogeneous core@shell systems, prompting application in photothermal therapy and optical imaging in the first biologically transparent window. Preliminary experiments performing irradiation of a stable water suspension of the nanostar and Au@Fe3O4-loaded cancer cell culture suspension at 658 nm confirmed their optical response and their suitability for photothermal therapy. The outstanding features of the prepared system can be thus potentially exploited as a multifunctional platform for magnetic-plasmonic applications.

Unveiling the presence of metallic Co in chemically fabricated Au@CoO core-shell nanoparticles by magnetic circular dichroism (MCD) spectroscopy

In this article, we focus on optical and magneto-optical properties of Au@CoO core-shell nanoparticles synthesized by a solution-phase seeded growth route under ambient atmosphere, in which the pyrolysis of Co(acac)2 in oleylamine is conducted in the presence of preformed Au nanoparticles. Optical absorption exhibits a broad peak that can be ascribed to localized surface plasmon resonance (LSPR) of the Au counterpart, but its position is red-shifted as compared to that of pure Au nanoparticles, meaning that the Au cores are coated by a dielectric material (=CoO) with high permittivity. Nanoscopic analysis based on X-ray photoelectron spectroscopy (XPS) only weakly implies the slight existence of zero-valent Co metal. In contrast, magnetic circular dichroism (MCD) shows a very intense characteristic response that is completely different from those of both Au and CoO counterparts but close to metallic Co, demonstrating that the MCD response is dominated by a very small amount of metallic Co within the core-shell nanostructures. Hence MCD analysis can be a very efficient way with a great potential for definitely identifying the presence of slight ferromagnetic components in non-magnetic nanostructures.

Ligand-Induced Cuboctahedral versus Icosahedral Core Isomerism within Eight-Electron Heterocyclic-Carbene-Protected Gold Nanoclusters

The controlled structural modification of ligand-protected gold clusters is evaluated by a proper variation of the size and shape of N-heterocyclic carbene (NHC) ligands. Density functional theory calculations show that the Au13 core of [Au13(NHC)8Br4]+ can be shaped into an icosahedron and/or a so far unexpected cuboctahedron depending on the sterical effect inferred by the NHC ligand side arms. As a result, the cluster properties can be modified, encouraging further exploration on controlled core isomerization in ligated gold cluster chemistry.

Theoretical insights on the influence of Au core in Au[formula omitted]@Pd[formula omitted] for improving HCOOH dissociation

The core–shell bimetallic catalysts have unique catalytic activity due to the synergistic effect of the different elements. In this study, HCOOH dissociation on Au3@Pd1 and Au2@Pd2 has been investigated by using the density functional method. The results indicated that compared with pure Pd, the adsorption of the intermediates on the core–shell structures is strengthened by the introduced Au core. Strain effect plays an important role for the adsorption strength, which is also confirmed by the d band center. Compared with Au3@Pd1, Au2@Pd2 has better catalytic activity in the dissociation of HCOOH to produce H2. The rate determining step is bi-HCOO → mono-HCOO, which is also supported by the turnover frequency calculations for H2 production. In addition, the calculated turnover frequency shows that the order of the rate of H2 production is Au2@Pd2 > Au3@Pd1 > Pd(111), in agreement with the order of the catalytic activity from the energy barrier at the rate determining step for the three catalysts. This work provides insights concerning the influence of Au core on the catalytic activity at the atomic level and offers practical guidelines for the design of highly efficient catalysts.

SERS and Indicator Paper Sensing of Hydrogen Peroxide Using Au@Ag Nanorods.

The detection of hydrogen peroxide and the control of its concentration are important tasks in the biological and chemical sciences. In this paper, we developed a simple and quantitative method for the non-enzymatic detection of H2O2 based on the selective etching of Au@Ag nanorods with embedded Raman active molecules. The transfer of electrons between silver atoms and hydrogen peroxide enhances the oxidation reaction, and the Ag shell around the Au nanorod gradually dissolves. This leads to a change in the color of the nanoparticle colloid, a shift in LSPR, and a decrease in the SERS response from molecules embedded between the Au core and Ag shell. In our study, we compared the sensitivity of these readouts for nanoparticles with different Ag shell morphology. We found that triangle core–shell nanoparticles exhibited the highest sensitivity, with a detection limit of 10−4 M, and the SERS detection range of 1 × 10−4 to 2 × 10−2 M. In addition, a colorimetric strategy was applied to fabricate a simple indicator paper sensor for fast detection of hydrogen peroxide in liquids. In this case, the concentration of hydrogen peroxide was qualitatively determined by the change in the color of the nanoparticles deposited on the nitrocellulose membrane.

A novel ZIF-8@ZIF-67/Au core–shell metal organic framework nanocomposite as a highly sensitive electrochemical sensor for nitrite determination

A novel electrochemical sensor has been introduced in the present work. The proposed sensor is a nanocomposite of imidazole zeolites and gold metal nanoparticles that was easily designed and synthesized (core-shell ZIF-8@ZIF-67/Au NPs). This sensor was used to determine nitrite using the differential pulse voltammetry (DPV) technique. Nanocomposites have been characterized using transmission electron microscopy (TEM), Fourier transform (FT-IR), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet spectroscopy, scattered X-ray spectroscopy Energy (EDX) and electrochemical element maps and electrochemical techniques. After the plotted the calibration diagram with the differential pulse voltammetry technique, the detection limit was 2 nM and the linear range was obtained 0.64×10−8-22.14×10−3 M for nitrite oxidation. Therefore the method is simple, sensitive, and specific, with a short analysis time, and the main advantages of this purpose sensor are the easy synthesis method, low limit of detection, and good selectivity, excellent stability, reproducibility, and good repeatability in nitrite determination. One of the successes of this sensor is in determining nitrite in water, sausage, and deli meat samples.

Scattering-type Scanning Near-Field Optical Microscopy of Polymer-Coated Gold Nanoparticles.

Scattering-type scanning near-field optical microscopy (s-SNOM) has emerged over the past years as a powerful characterization tool that can probe important properties of advanced materials and biological samples in a label-free manner, with spatial resolutions lying in the nanoscale realm. In this work, we explore such usefulness in relationship with an interesting class of materials: polymer-coated gold nanoparticles (NPs). As thoroughly discussed in recent works, the interplay between the Au core and the polymeric shell has been found to be important in many applications devoted to biomedicine. We investigate bare Au NPs next to polystyrenesulfonate (PSS) and poly(diallyldimethylammonium chloride) (PDDA) coated ones under 532 nm laser excitation, an wavelength matching the surface plasmon band of the custom-synthesized nanoparticles. We observe consistent s-SNOM phase signals in the case of bare and shallow-coated Au NPs, whereas for thicker shell instances, these signals fade. For all investigated samples, the s-SNOM amplitude signals were found to be very weak, which may be related to reduced scattering efficiency due to absorption of the incident beam. We consider these observations important, as they may facilitate studies and applications in nanomedicine and nanotechnology where the precise positioning of polymer-coated Au NPs with nanoscale resolution is needed besides their dielectric function and related intrinsic optical properties, which are also quantitatively available with s-SNOM.

The restructure of Au@Ag nanorods for cell imaging with dark-field microscope

The facile and noninjurious image of cells with high resolution and low toxicity is essential since imaging can offer rich and direct information and insights into metabolic activities, clinical diagnosis, drug delivery and cancer therapy. In this contribution, a smart imaging probe was employed as a contrast agent for dark-field cell imaging. Au core/Ag shell nanorods (Au@Ag NRs) that characterized by X-ray diffraction and X-ray photoelectron spectroscopy, formed Au@Ag@AgI NRs when exposed to iodine, which greatly enhanced the light scattering of nanorods. Herein, the silver shell acted as the response element for iodine as well as the protective agent for Au core. When conjugated with folate, the nanorods can be used to image human cervical cancer cells (HeLa cells) under a dark-field microscope. Nanorods were demonstrated with excellent tumor cellular uptake ability without obvious cytotoxicity, making them ideal candidates in biosensing and bioimaging applications.

Controlled Synthesis and Photoelectrochemical Performance Enhancement of Cu2−xSe Decorated Porous Au/Bi2Se3 Z-Scheme Plasmonic Photoelectrocatalyst

In this paper, uniform Cu2−xSe-modified Au/Bi2Se3 hybrid nanoparticles with porous shells have been prepared through a cation exchange method. Bi2Se3/Cu2−xSe Z-scheme heterojunction is introduced onto Au nanocube by replacing Bi3+ with Cu2+. Owing to the effective coupling between Au core and semiconductor shells, Au/Bi2Se3/Cu2−xSe hybrids present a broad and strong plasmon resonance absorption in the visible band. More intriguingly, the carrier lifetime of Au/Bi2Se3/Cu2−xSe hybrid photoelectrodes can be further tailored with corresponding Cu2−xSe content. Through parameter optimization, 0.1-Au/Bi2Se3/Cu2−xSe electrode exhibits the longest electron lifetime (86.03 ms) among all the parallel samples, and corresponding photoelectrochemical performance enhancement is also observed in the tests. Compared with that of pure Bi2Se3 (0.016% at 0.90 V vs. RHE) and Au/Bi2Se3 (0.02% at 0.90 V vs. RHE) nanoparticles, the maximum photoconversion efficiency of porous Au/Bi2Se3/Cu2−xSe hybrid photoanodes increased by 5.87 and 4.50 times under simulated sunlight illumination, attributing to the cooperation of Z-scheme heterojunction and plasmon resonance enhancement effects. All the results indicate that Au/Bi2Se3/Cu2−xSe porous hybrids combine eco-friendliness with excellent sunlight harvesting capability and effectively inhibiting the charge recombination, which provide a new idea for efficient solar-driven water splitting.

Potential application of Au core labeling for tracking Ag nanoparticles in the aquatic and biological system

The entering of silver nanoparticles (Ag NPs) in natural environments constantly increases due to their widespread production and application. While the environmental behavior, impacts, and fate of Ag NPs were critically assessed, the main challenge represents continuous tracking and quantification of Ag NPs in environmental and biological matrices. A group of labeled Ag NPs with gold cores (Au@Ag NPs) was developed for distinguishing between pristine Ag NPs and their other forms, and we comprehensively compared their physicochemical properties, environmental behavior, and biological effects with unlabeled Ag NPs. The electron transfer process from the Au core to the Ag shell gradually decreased with the increase of Ag shell thickness, then the inhibition of Ag+ release induced by the Au core was gradually alleviated, but the generation of superoxide radicals was intensified sharply. Then, the effect of the Au core on the dissolution capacity and free radicals' generation significantly altered the biological toxicity of Ag NPs, and the influence degree was related to the test organism's species. Nevertheless, the Au core retained the surface properties of Ag NPs, leading to the uptake of Au@Ag NPs, entirely consistent with the behavior of unlabeled Ag NPs. These findings confirmed that Au core labeling provides new opportunities for tracking Ag NPs in environmental and biological systems, and the exposure conditions and test organisms should be carefully assessed before employing the Au core labeling technology.