Thiol-capped gold nanoparticles on graphite: Spontaneous adsorption and electrochemically induced release (original) (raw)
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Physical Chemistry …, 2010
In the present work new findings on the structure of the S-Au interface are presented. Theoretical calculations using a new semiempirical potential, based on density functional theory and a bond-order Morse potential, are employed to simulate the adsorption process in a more realistic way. The simulation results reveal the formation of gold adatoms on the nanoparticle surface and high surface disorder due to the strong S-Au bond. Experimental data were acquired by aberration (Cs) corrected scanning transmission electron microscopy (STEM) using a high angle annular dark field detector (HAADF) that showed a great similarity with the theory predicted. w Electronic supplementary information (ESI) available: S1: particle size distribution, average size and standard deviation were based on the measurement of 303 nanoparticles. Random gold atom aggregates were not considered for statistics. S2: energy-dispersive X-ray (EDX) analysis of the thiol-capped Au nanoparticles. See
The Journal of Physical Chemistry C, 2014
Small gold nanoparticles capped with 4trimethylsilylethynyl-1-acetylthiobenzene (SEB) were prepared with spherical shape and different mean sizes (5−8 nm). The functionalized gold nanoparticles (AuNPs-SEB) were deposited onto TiO 2 substrates, and the interaction at the molecule−gold interface, the molecular layer thickness, and the ligand organization on the surface of Au nanospheres were investigated by means of synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS) and angular dependent near edge X-ray absorption spectroscopy (NEXAFS) at the C K-edge. In order to obtain better insight into the molecular shell features, the same measurements were also carried out on a self-assembling monolayer (SAM) of SEB anchored on a "flat" gold surface (Au/Si(111) wafer). The comparison between angular dependent NEXAFS spectra collected on the self-assembling monolayer and AuNPs-SEB allowed for successfully probing the molecular arrangement of SEB molecules on the gold nanospheres surface. Furthermore, DFT calculations on the free SEB molecule as well as bonded to a small cluster of gold atoms were developed. The comparison with experimental results allowed better understanding of the spectroscopic signatures in the experimental absorption spectra and rationalization of the molecular organization in the SAM, NPs having a thin molecular shell, and NPs covered by a thick layer of ligands. Figure 4. Angular dependent NEXAFS C K-edge spectra collected with normal (black line) and grazing (red line) incidence of the beam on the sample surface for (a) SAM, (b) NP , and (c) NP(2). The blue lines are obtained by subtracting the normal from the grazing signal, and evidence the observed angular (dichroic) effects. To evidence the polarization dependence of the main π* feature, the aromatic ring π* region is zoomed and reported in (d) SAM, (e) NP , and (f) NP(2).
X-Ray Optics of Gold Nanoparticles
Gold nanoparticles have been investigated as contrast agents for traditional x-ray medical procedures, utilizing the strong absorption characteristics of the nanoparticles to enhance the contrast of the detected x-ray image. Here we use the Kramers-Kronig relation for complex atomic scattering factors to find the real and imaginary parts of the index of refraction for the medium composed of single-element materials or compounds in the x-ray range of the spectrum. These complex index of refraction values are then plugged into a Lorenz-Mie theory to calculate the absorption efficiency of various size gold nanoparticles for photon energies in the 1-100 keV range. Since the output from most medical diagnostic x-ray devices follows a wide and filtered spectrum of photon energies, we introduce and compute the effective intensityabsorption-efficiency values for gold nanoparticles of radii varying from 5 to 50 nm, where we use the TASMIP model to integrate over all spectral energies generated by typical tungsten anode x-ray tubes with kilovolt potentials ranging from 50 to 150 kVp.
Gold Nanoparticles with Different Capping Systems: An Electronic and Structural XAS Analysis
The Journal of Physical Chemistry B, 2005
Gold nanoparticles (NPs) have been prepared with three different capping systems: a tetralkylammonium salt, an alkanethiol, and a thiol-derivatized neoglycoconjugate. Also gold NPs supported on a porous TiO 2 substrate have been investigated. X-ray absorption spectroscopy (XAS) has been used to determine the electronic behavior of the different capped/supported systems regarding the electron/hole density of d states. Surface and size effects, as well as the role of the microstructure, have been also studied through an exhaustive analysis of the EXAFS (extended X-ray absorption fine structure) data. Very small gold NPs functionalized with thiol-derivatized molecules show an increase in d-hole density at the gold site due to Au-S charge transfer. This effect is overcoming size effects (which lead to a slightly increase of the d-electron density) for high S:Au atomic ratios and core-shell microstructures where an atomically abrupt Au-S interface likely does not exist. It has been also shown that thiol functionalization of very small gold NPs is introducing a strong distortion as compared to fcc order. To the contrary, electron transfer from reduced support oxides to gold NPs can produce a higher increase in d-electron density at the gold site, as compared to naked gold clusters.
Evaluation of the X-Ray Absorption by Gold Nanoparticles Solutions
ISRN Nanotechnology, 2013
The increase in the X-ray absorption due to gold nanoparticles was investigated by using aqueous solutions containing gold (Au) nanoparticles. A sample with 15 nm in size nanoparticles and 0.5 mg/mL gold concentration and a distilled water sample were used. Transmitted X-ray beams through the samples were registered with a CdTe detector and with an ionization chamber. Results show an enhancement in the X-ray absorption in the range 20%–6% for beams generated from 20 kV to 120 kV tube voltages, respectively. Results show that the use of gold nanoparticles, even at low concentrations, should result in a significant contrast enhancement for low-energy X-ray beams.
Determination of Size and Concentration of Gold Nanoparticles from UV-Vis Spectra
The dependence of the optical properties of spherical gold nanoparticles on particle size and wavelength were analyzed theoretically using multipole scattering theory, where the complex refractive index of gold was corrected for the effect of a reduced mean free path of the conduction electrons in small particles. To compare these theoretical results to experimental data, gold nanoparticles in the size range of 5 to 100 nm were synthesized and characterized with TEM and UV-vis. Excellent agreement was found between theory and experiment. It is shown that the data produced here can be used to determine both size and concentration of gold nanoparticles directly from UV-vis spectra. Equations for this purpose are derived, and the precision of various methods is discussed. The major aim of this work is to provide a simple and fast method to determine size and concentration of nanoparticles.
Controlled X-Ray Induced Gold Nanoparticles Deposition
This paper outlines new approaches for utilizing X-rays for gold nanoparticles deposition by performing Surface Photochemistry Induced by Xray Irradiation (SPIXI). High-energy synchrotron radiation was used to induce the deposition of gold nanoparticles from a gold-salt solution onto different surfaces. By controlling the deposition parameters (dose, solution, surfactants, and stabilizer polymer concentrations), the distribution and average size of the nanoparticles can be influenced. The distribution of the deposited particle heights and diameters at low doses suggests there is a mechanism of growth of the particles after nucleation on the surface.
ELSEVIER, 2021
This paper reports the effects of low energy X-ray irradiation doses on the structures, morphologies and absorbance of some colloidal gold nanoparticles (AuNPs) produced in distilled water via the one-step pulse laser ablation in liquid (PLAL) method. An Nd:YAG pulse laser (wavelength of 1064 nm and fluence ranges of 0.076–7.692 J/cm2) was used to ablate the gold plate surface (acted as a target) immersed in distilled water (10 mL). The laser pulse duration was adjusted to 2.5 min (1000 pulses), 5 min (2000 pulses). Simultaneously, the colloidal suspension was irradiated with low energy X-ray. The obtained samples were characterized thoroughly using different analytical instruments. High quality, pure, surfactant-free AuNPs with well-defined morphology and broad size distribution were achieved. The recorded values of the Zeta potential of the as-synthesized AuNPs were increased from -33.1 to -41.2 mV which was mainly due to the low energy X-ray dose-mediated photo- and Auger-electrons generation plus the fragmentation of the bigger NPs into highly stable tinier species inside the colloidal suspension. The observed blue-shift in the absorbance peaks of the NPs centered at 523, 529, and 526 nm irradiated with the corresponding fluences of 0.076, 3.846, and 7.692 J/cm2 was ascribed to the quantum size effects. It is established that the synergy between laser ablation and low energy X-ray does may be effective to prepare the contaminants-free AuNPs in the liquid suspension in a simple rapid and cost-effective way.
Journal of Nanoscience and Nanotechnology, 2009
X-ray magnetic circular dichroism (XMCD) and Small Angle Neutron Scattering (SANS) measurements were performed on thiol capped Au nanoparticles (NPs) embedded into polyethylene. An XMCD signal of 0.8 · 10 −4 was found at the Au L 3 edge of thiol capped Au NPs embedded in a polyethylene matrix for which Superconducting Quantum Interference Device (SQUID) magnetometry yielded a saturation magnetization, M S , of 0.06 emu/g Au . SANS measurements showed that the 3.2 nm average-diameter nanoparticles are 28% polydispersed, but no detectable SANS magnetic signal was found with the resolution and sensitivity accessible with the neutron experiment. A comparison with previous experiments carried out on Au NPs and multilayers, yield to different values between XMCD signals and magnetization measured by SQUID magnetometer. We discuss the origin of those differences.
Synthesis of a colloid solution of silica-coated gold nanoparticles for X-ray imaging applications
Journal of Nanoparticle Research, 2014
This work proposes a method for fabricating silica-coated gold (Au) nanoparticles, surface modified with poly(ethylene glycol) (PEG) (Au/SiO 2 / PEG), with a particle size of 54.8 nm. X-ray imaging of a mouse is performed with the colloid solution. A colloid solution of 17.9 nm Au nanoparticles was prepared by reducing Au ions (III) with sodium citrate in water at 80°C. The method used for silica-coating the Au nanoparticles was composed of surface-modification of the Au nanoparticles with (3-aminopropyl)-trimethoxysilane (APMS) and a sol-gel process. The sol-gel process was performed in the presence of the surface-modified Au nanoparticles using tetraethylorthosilicate, APMS, water, and sodium hydroxide, in which the formation of silica shells and the introduction of amino groups to the silica-coated particles took place simultaneously (Au/SiO 2 -NH 2 ). Surface modification of the Au/SiO 2 -NH 2 particles with PEG, or PEGylation of the particle surface, was performed by adding PEG with a functional group that reacted with an amino group in the Au/SiO 2 -NH 2 particle colloid solution. A computed tomography (CT) value of the aqueous colloid solution of Au/SiO 2 / PEG particles with an actual Au concentration of 0.112 M was as high as 922 ± 12 Hounsfield units, which was higher than that of a commercial X-ray contrast agent with the same iodine concentration. Injecting the aqueous colloid solution of Au/SiO 2 / PEG particles into a mouse increased the light contrast of tissues. A CT value of the heart rose immediately after the injection, and this rise was confirmed for up to 6 h.