HYDROSOL

Abstract: Aqueous reduction of hydrogen tetrachloroaurate(III) with alkaline tetrakis(hydroxymethyl)phosphonium chloride yields gold in an ultrafinely divided form as a stable colloidal hydrosol, with mean metal-cluster diameter between 1 and 2 nm, without the need for large organic stabilizing molecules. The ultraviolet-visible extinction spectrum is very similar to those of other gold colloids of similar dimensions and includes a weak plasmon feature. Dispersions with characteristics of yet finer clusters are prepared using lower initial concentrations of Au3+ ions. Boiling the sols in the presence of appropriate colloidal stabilizers (ionic and/or polymeric) is a route to coarser (3-10 nm particle diameter) gold hydrosols. © 1993 American Chemical Society.

Abstract: Synthesis of silver nanoparticles using α-NADPH-dependent nitrate reductase and phytochelatin in vitro has been demonstrated for the first time. The silver ions were reduced in the presence of nitrate reductase, leading to the formation of a stable silver hydrosol 10–25 nm diam. and stabilized by the capping peptide. The nanoparticles were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-Vis absorption. These studies will help in designing a rational enzymatic strategy for the synthesis of nanomaterials of different chemical composition, shapes and sizes as well as their separation.

Abstract: Nanosized hydrophobic, oleate stabilized silver organosols in various organic solvents are obtained using a solvent exchange method. The silver particles are initially prepared as a hydrosol in the presence of sodium oleate (surfactant). Then a transfer of the colloid to an organic phase is induced by a low concentration of several agents such as orthophosphoric acid, with a transfer efficiency of 50−70%. The hydrophobic colloid is stable and the particles retain their integrity even after the solvent is evaporated and the dried deposit is resuspended in a variety of other solvents. We present the preparation method in detail and characterize the hydrosol and organosol particles by electron microscopy, electrophoresis, and UV−visible extinction spectroscopy. On the basis of IR spectroscopy we discuss the conformation of the surfactant adsorbed on the silver cores and the changes in it as the particles transfer into the organic environment.

Abstract: The optical properties of silver colloidal particles derivatized using an aromatic bifunctional molecule, 4-carboxythiophenol, are presented in this communication. The capping molecule forms a thiolate bond with the silver colloidal particle yielding a carboxylic acid terminal functionality which may then be charged to varying degrees by controlling the silver hydrosol pH. A progressive red shift together with a damping and broadening of the surface plasmon feature (λmax) of the silver particles is observed as the pH is reduced from 10 to 3. Ag colloidal particles with high surface coverage of the bifunctional molecule showed negligible flocculation with time at high solution pH indicating good stabilization due to coulombic repulsive interactions. At low pH, considerable flocculation was observed even for high surface coverage due to lack of coulombic stabilization. A tentative explanation is put forward to explain changes in the optical properties of the colloidal particles due to variation in the pH dependent surface charge of the particles.

Abstract: Reduction of gold(III) ions by tetrakis(hydroxymethyl)phosphonium chloride gives a hydrosol of gold clusters with mean diameter 1.5 nm (average nuclearity about Au170) and smaller.