Magnetite nanoparticles of nearly uniform size have been prepared by precipitating ferrous ions in the presence of two different polyelectrolytes, viz., poly(acrylic acid) and the sodium salt of carboxymethyl cellulose at high pH (∼13). The size of the magnetite nanoparticles can be controlled easily by varying the concentration of the polyelectrolyte in the medium. Transmission electron microscopy study indicates that the average particle size varies from 5 to 15 nm, depending on the concentration and the nature of the polyelectrolyte. X-ray diffraction study shows the presence of only magnetite phase. FTIR spectroscopy and thermogravimetric analysis confirmed the presence of polyelectrolyte on the magnetite surface. The magnetization and Mössbauer studies were performed on two samples with mean diameters 7.0 and 14.7 nm. Magnetization measurements suggest that both of these particles are of single magnetic domain. The measurements also estimate the superparamagnetic blocking temperature, T B = 145 K for smaller particles, while T B > 300 K for the larger particles. Mössbauer spectra at 300 K show only a quadrupole doublet for the smaller particles and mostly a magnetically separated sextet for the larger ones, indicating also the marked size dependence of moment dynamics.
A simple and easier chemical method for preparing spongy gold nanocrystals has been developed on the basis of a modified-citrate reduction technique of the corresponding gold salt at 25 degrees C in the absence of template. These nanocrystals possessed autocatalytic behavior and exhibited pronounced catalytic activity in the borohydride reduction of 4-nitrophenol due to their unique spongy morphology.
Carboxylated peptide-functionalized gold nanoparticles (peptide-GNPs) were self-assembled into networks of one-dimensional (1D) chains in the presence of mercury ion (Hg 2+ ) at room temperature without use of any template. Transmission electron microscopy (TEM) confirmed the formation of a 1D array of gold nanoparticle (GNP) chains and revealed that the length of the chain can be tuned by varying the Hg 2+ ion concentration in the medium. Dynamic light scattering (DLS) measurements showed that the assembly of peptide-GNPs actually occurred in the medium and not during TEM specimen preparation. The assembly of peptide-GNPs resulted in a change of color of the suspension from red to purple to blue. This color change is due to the development of a new surface plasmon resonance (SPR) band at 670 nm. A mechanistic pathway is suggested for this 1D assembly on the basis of some control experiments, and we believe that the main driving force for the 1D array of GNPs is dipole-dipole interactions. The change of color and the absorption spectrum of the peptide-GNP suspension due to this assembly enabled us to sense the Hg 2+ ion up to parts per million levels in water by the naked eye, as well as by UV-vis spectroscopy.
A series of newly designed ascorbic acid based room temperature ionic liquids were successfully used to prepare quasi-spherical and anisotropic gold nanostructures in an aqueous medium at ambient temperature. The synthesis of these room temperature ionic liquids involves, first, the preparation of a 1-alkyl (such as methyl, ethyl, butyl, hexyl, octyl, and decyl) derivative of 3-methylimidazolium hydroxide followed by the neutralization of the derivatised product with ascorbic acid. These ionic liquids show significantly better thermal stability and their glass transition temperature (Tg) decreases with increasing alkyl chain length. The ascorbate counter anion of these ionic liquids acts as a reducing agent for HAuCl4 to produce metallic gold and the alkylated imidazolium counter cation acts as a capping/shape-directing agent. It has been found that the nature of the ionic liquids and the mole ratio of ionic liquid to HAuCl4 has a significant effect on the morphology of the formed gold nanostructures. If an equimolar mixture of ionic liquid and HAuCl4 is used, predominantly anisotropic gold nanostructures are formed and by varying the alkyl chain length attached to imidazolium cation of the ionic liquids, various particle morphologies can formed, such as quasispherical, raspberry-like, flakes or dendritic. A probable formation mechanism for such anisotropic gold nanostructures has been proposed, which is based on the results of some control experiments.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.