Correlating structural dynamics and catalytic activity of AgAu nanoparticles with ultrafast spectroscopy and all-atom molecular dynamics simulations (original) (raw)
Related papers
Correlating Catalytic Activity of Ag–Au Nanoparticles with 3D Compositional Variations
Nano Letters, 2014
Significant elemental segregation is shown to exist within individual hollow silver−gold (Ag−Au) bimetallic nanoparticles obtained from the galvanic reaction between Ag particles and AuCl 4 −. Three-dimensional compositional mapping using energy dispersive Xray (EDX) tomography within the scanning transmission electron microscope (STEM) reveals that nanoparticle surface segregation inverts from Au-rich to Ag-rich as Au content increases. Maximum Au surface coverage was observed for nanoparticles with approximately 25 atom % Au, which correlates to the optimal catalytic performance in a three-component coupling reaction among cyclohexane carboxyaldehyde, piperidine, and phenylacetylene.
Quantitative Analysis of Catalysis and SERS Performance in Hollow and Star-Shaped Au Nanostructures
The Journal of Physical Chemistry C, 2019
Surface roughness of the metal nanoparticles is well-known to play an important role in the quantitative analysis and performance of their SERS performances but their analogous role in catalysis is not given the due credit yet. In the present work, we systematically investigated this by utilizing two significantly relevant gold (Au) nanostructures-the hollow and the star shapedin a comprehensive manner. For catalysis, the universal model reaction, the reduction of pnitroaniline (p-NA) to PDA using NaBH 4 , was engaged and SERS measurements were performed by employing methylene blue as the standard analyte molecule. At the outset, the predominantly fascinating role of the nanoparticle surface area in conjunction with surface roughness in catalysis was carefully evaluated for our robustly synthesized Au hollow nanoparticles (NPs), possessing an inherent thin inner core layer of Ag, and star shaped Au NPs
Structures and optical properties of 4–5 nm bimetallic AgAu nanoparticles
Faraday Discussions, 2008
Three types of bimetallic AgAu nanoparticles, with mean size of 4-5 nm, Ag core Au shell , Au core Ag shell and alloyed AgAu, have been synthesized using an inverse micelle method. To image these small size nanoparticles, quantitative high angle annular dark field imaging using scanning transmission electron microscopy was successfully applied. Our results show that good control of nanoparticle size dispersion and composition modulation was achieved. Optical properties of the nanoparticles are correlated with direct internal structure analysis. The structural stability is discussed, based on thermodynamic considerations.
2020
The understanding of relaxation dynamics of metallic nanoshells is important for a range of nanotechnological applications. In this work, we present a combined experimental-theoretical study of the relaxation dynamics of AgAu nanoshells. This was investigated using ultrafast pump-probe experiments resonant with the surface plasmon of the nanoshells, as well as via atomistic molecular dynamics simulations of relaxation and temperature-jump (DT-jump) processes. Both techniques were then discussed and complemented using a non-equilibrium statistical mechanical model. Data collected at low energies were consistent with our previously reported work and allowed the characterization of intrinsic electron-phonon coupling times (EPCT) and of the overall relaxation dynamics in terms of a two-temperature model. Data at intermediate and higher energies, in turn, showed a nonlinear dependence of EPCT as a function of the pump power, faster relaxation being observed at higher pump energies. In th...
2024
In this investigation, we employed simulations and computational methodologies to examine pure silver and gold nanoparticles (NPs), alongside their core−shell configurations. Our research delved into, assessing the effects and adsorption tendencies of methanethiol molecules on diverse sites within these NPs. In our calculations, the effects of the inclusion of dispersion forces are analyzed. Structural analysis unveiled contractions in larger NPs and notable variations in adsorption energies across silver and gold surfaces. Furthermore, our study scrutinized not only the growth process but also the adsorption behavior of a model molecule within core−shell structures. We found that the arrangement of metal layers within these structures significantly impacted the adsorption energies of methanethiol, closely resembling the behavior observed in the smaller pure gold NPs. Notably, even a single shell layer led to discernible changes in the electronic structure. Overall, our investigation underscored the profound influence of the NP size, composition, and arrangement on adsorption energies. Interestingly, introducing methanethiol molecules to larger-scale NPs exhibited minimal impact on the electronic structure despite the evident changes in adsorption behaviors.
The Journal of Physical Chemistry B, 2005
The formation of Ag nanoparticles by electrochemical techniques has been investigated through a timeresolved UV-vis spectroscopy study. The formation of Ag 4 2+ clusters is suggested as the main precursors to the particle formation. The mechanism also considers the electrodeposition which occurs as a parallel process in the electrochemical particle formation. Experiments at different current densities show that the electrodeposition is more important at low current densities. From the fittings of the change of the plasmon (λ ≈ 430 nm) and the cluster (λ) 250 nm) bands to the proposed mechanism, the kinetic constants of the formation and disappearance of the Ag 4 2+ cluster are derived. The kinetic fittings also allowed an estimation of the Ag 4 2+ cluster extinction coefficient (250) 1.0 × 10 4 M-1 cm-1). It is observed that the plasmon bandwidth (fwhm) follows the theoretical predicted 1/R law only for particles with sizes d J 3 nm, but the law is broken for the smallest particles (d < 2.5 nm). The break is associated with the existence of singleelectron (SE) transitions which are activated by the plasmon decay for the smallest nanoparticles. From the broken 1/R law, a limit relaxation time of about 4 fs is derived for the plasmon deactivation. Below this limit, the plasmon seems to decay mainly through a nonradiative channel with the formation of electron-hole (e-h) pairs. By comparison of the 1/R broken law with other literature results, it is concluded that large interactions of the Ag nanoparticles with the used capping molecule (tetrabutylammonium acetate) facilitate the e-h plasmon deactivation.
Journal of the Brazilian Chemical Society, 2016
We herein report the preparation of AgAu nanotubes displaying controlled surface morphologies and optical properties by varying the reaction temperature during the galvanic reaction between Ag nanowires and AuCl 4-(aq). As the AgAu nanotubes presented similar sizes and compositions, they enabled us to isolate the influence of surface morphology and optical properties over their catalytic and plasmonic photocatalytic activities towards methylene blue oxidation. At 25 °C, AgAu nanotubes (AgAu 25) presented branched walls and surface plasmon resonance (SPR) band with low intensities in the visible were obtained. However, at 100 °C, the AgAu nanotubes (AgAu 100) presented smooth surfaces and SPR bands that closely matched the emission spectra of a commercial halogen-tungsten lamp. The AgAu 25 nanotubes displayed better catalytic performances in classical heterogeneous catalysis as a result of its branched walls that lead to increased surface areas relative to the smooth nanotubes. Conversely, AgAu 100 nanotubes showed better activities in plasmonic photocatalysis due to its broader and more intense SPR bands. Thus, our results demonstrate the potential of the control over morphological and optical features towards the optimization of distinct catalytic phenomena.
Noble and Precious Metals - Properties, Nanoscale Effects and Applications, 2018
In this chapter, experimental and theoretical studies on surface segregation in Ag-Au systems, including our own thermodynamic studies and molecular dynamics simulations of surface restructuring, on the basis of density functional theory are reviewed. The restructuring processes are triggered by adsorbed atomic O, which is supplied and consumed during catalysis. Experimental evidence points to the essential role of Ag impurities in nanoporous gold for activating O 2. At the same time, increasing Ag concentration may be detrimental for the selectivity of partial oxidation. Understanding the role of silver requires a knowledge on its chemical state and distribution in the material. Recent studies using electron microscopy and photoelectron spectroscopy shed new light on this issue revealing a non-uniform distribution of residual Ag and coexistence of different chemical forms of Ag. We conclude by presenting an outlook on electromechanical coupling at Ag-Au surfaces, which shows a way to systematically tune the catalytic activity of bimetallic surfaces.
This study demonstrates the influence of electrokinetic parameters; surface charge and zeta potential on the optical absorption band and co-catalytic activity of Au nanospheres (AuNS) dispersed in polar solvents, i.e., methanol, propanol, dimethylformamide, and dimethyl-sulphoxide. The narrow intense surface plasmon (SP) absorption band of AuNS (520 nm) becomes broadened and a SP band at >970 nm is appeared, whose absorption intensity varies from 0.05 to 0.13 a.u. with the extent of aggregation in solvents of varying dipole moment from 1.66 D to 3.96 D while no such alteration in SP band occurs for AuNS dispersion in non-polar CCl 4 as confirmed by DLS and TEM analysis. It found that the zeta potential (+50.32 mV) and conductance (1673 S) of AuNS in water has been decreased to +24.06 mV and 1480 S in methanol, respectively. The effective electronic charge ca. +4306 equiv./l present over AuNS surface in water suspension is highly reduced to +512 equiv./l in photoreaction (TiO 2 + salicylic acid + AuNS) mixture and the zeta potential (+50.32 mV) and conductance (1673 S) of AuNS in water has been decreased to +24.06 mV and 1480 S in methanol, respectively. The co-catalytic activity of aggregated AuNS (formed in polar solvents) varied in a diverse extent depending on its degree of agglomeration, where the non-aggregated aqueous AuNS + TiO 2 mixture displayed higher degradation efficiency (r = 9.990 × 10 −3 mM/min) of salicylic acid than that (r = 9.172 × 10 −3 mM/min) of aggregated AuNS in MeOH + TiO 2 mixture under UV light irradiation.
Chemical Physics Letters, 2012
ABSTRACT This Letter reports on the synthesis of Ag–Au nanoparticles (NPs) with controlled structures and compositions via a galvanic replacement reaction between Ag NPs and AuCl4-(aq) followed by the investigation of their optical and catalytic properties. Our results showed the formation of porous walls, hollow interiors and increased Au content in the Ag–Au NPs as the volume of AuCl4-(aq) employed in the reaction was increased. These variations led to a red shift and broadening of the SPR peaks and an increase of up to 10.9-folds in the catalytic activity towards the reduction of 4-nitrophenol relative to Ag NPs.