Co nanoparticles with three different crystal structures were synthesized in a microfluidic reactor through manipulation of reaction times, flow rates, and quenching procedures. Cobalt nanoparticles ...of face-centered cubic (β) phase were obtained from a high flow rate of the reactants followed by in situ quenching of the reaction. hcp and ε-cobalt nanoparticles were obtained at a low flow rate of the reactants followed by in situ quenching and delayed quenching, respectively. The crystal structures were characterized using Co K-edge X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction (XRD), and selected area electron diffraction (SAED). In situ XANES measurements on Co nanoparticles coming out of the outlet of the microfluidic reactor at different flow rates seem to indicate that the difference in flow rate influences the nucleation process in a critical way and that particle growth occurs mainly outside the reactor. The magnetic properties of the cobalt nanoparticles, measured using a SQUID magnetometer system, showed significant differences among the samples and are consistent with the three different crystal structures.
The mechanistic aspects of the formation of sulfobetaine-stabilized copper nanoparticles were investigated by using in situ XANES (X-ray absorption near edge structure), UV−vis spectroscopy, and ...reaction calorimetry. The tetracoordinated sulfobetaine−Cu(II) complex was reduced to a stable sulfobetaine−Cu(I) complex prior to the formation of sulfobetaine-stabilized copper nanoparticles. The stability of the Cu(I) complex was found to be sensitive to the concentration of the sulfobetaine stabilizer and the addition rate of the reducing agent. It appears to exist primarily as a linear complex. A tetracoordinated Cu(I) complex as an intermediate has also been postulated. Based on the understanding from these investigations, a microfluidic process for copper nanoparticle synthesis was designed by using sulfobetaine−Cu(I) complex as the starting material. When compared with the copper nanoparticles synthesized by a conventional batch process, the microfluidic reactor process provided particles with a smaller size and narrower size distribution. The copper nanoparticles from the microreactor process could also be more easily purified and the particles were relatively stable in air. Both XRD and SAED indicated that the Cu nanoparticles synthesized have fcc structure.
Copper shells were fabricated by a displacement method around Co nanoparticles (3.2 - 0.6 nm) at room temperature in a copper-citrate aqueous electrolyte. The nanoparticles were synthesized by a wet ...chemical approach using the surfactant sulfobetaine, dodecyldimethyl (3-sulfopropyl) ammonium hydroxide (98%) in tetrahydrofuran. X-ray absorption near-edge structure analysis confirmed that cobalt oxide was not present in the nanoparticles upon exposure to air, consistent with a shell formation. Additionally, the presence of the shell resulted in an increase of the blocking temperature of the core-shell nanoparticles, stabilizing the ferromagnetic behavior up to 135 K.
A 23-amino-acid synthetic lytic peptide (Hecate) was covalently linked to magnetite nanoparticles and the lytic peptide-bound nanoparticles were characterized by X-ray absorption near-edge structure ...spectroscopy, transmission electron microscopy, and electron diffraction. Investigation of magnetic properties with a superconducting quantum interference device (SQUID) magnetometer has shown a reduction in the saturation magnetization (Ms) of magnetite nanoparticles after binding with lytic peptide. An in vitro cell culture assay with breast cancer cell lines MDA-MB-435S revealed that the lytic peptide-bound magnetite nanoparticles were therapeutically active.
We report results from our use of X-ray absorption spectroscopy to obtain chemical and structural features of dielectric multilayer (SiO
2/Ta
2O
5) mirror coatings. For the ion beam sputtered ...multilayers studied here, we obtained Ti/Ta atom ratios in the range of 0.07–1.01. Relatively minor amounts Fe and Cr appear in the spectra at a constant atom ratio, Cr/Fe, of 0.41±8.31%. All the samples show maxima in the radial distribution functions between 1 and 2
Å, assigned to Ta–O bonds.
Self-assembled monolayers of
n-alkanethiols, CH
3–(CH
2)
x
–SH, on Au, Ag, and Cu have been studied with GIXAFS at the sulfur K-edge. For both pentanethiol and decanethiol monolayers on Ag and Cu, ...the three-fold hollow site is found to be the most probable sulfur binding site. However, observations for octadecanethiol indicate that the three-fold hollow site is not the exclusive binding site. In addition, the possible existence of disulfide bonds on the metal surface (adsorbed dialkyldisulfides) is not supported by the data. Preliminary results from monolayers on Au are also reported.
We report on the sulfur K-edge X-ray absorption near-edge structure (XANES) spectra of self-assembled monolayers for a series of n-alkanethiols adsorbed on Ag(111). We investigate the effects of ...chain length and incidence angle on the XANES spectra of n-alkanethiols CH3−(CH2) x - 1−SH, x = 6, 12, 14, 16, 18, and 22; hereafter referred to as C x . Other than that of the C18 sample, the XANES spectra were similar to one another. The C18 spectrum displayed an above-threshold feature that was absent in all of the other spectra, and the shape of the principal subthreshold peak is different than that for all of the other compounds. Moreover, the intensities of these features exhibit an atypical angular dependence, as well. These data are consistent with recent EXAFS studies of thiol adsorption on silver, and suggest that the local environment of the sulfur adatom is different for the octadecanethiol adsorbate.
A detailed X-ray Absorption Spectroscopic examination of S-Au interaction in gold nanoparticle bound to Polystyrene-Divinyl Benzene (PS-DVB) micro beads was carried out. Gold nanoparticles were bound ...to the surface of the commercially available PS-DVB beads using a simple one step procedure. Influence of polystyrene backbone on the electronic structure of the gold nanoparticles was observed through X-ray Absorption Near Edge Structure (XANES) spectra of Au at L III edge. An additional structure in the white line of the S K-edge XANES spectrum confirmed the presence of S-Au bonding. Transmission Electron Microscopy (TEM) studies coupled with Selected Area Electron Diffraction Pattern and X-ray Diffraction studies revealed the morphology of the Au nanoparticles bound to the micro beads.PUBLICATION ABSTRACT
