S. V. Saikova

Conditions for the Formation of Copper Nanoparticles by Reduction of Copper(II) Ions with Hydrazine Hydrate Solutions

Optimal conditions were found for the preparation of copper nanoparticles in aqueous solution via reduction of copper(II) ions with hydrazine hydrate. The effects of ligand environment of copper(II) in the initial solution (hydrate, ammonia, citrate, and glycine complexes), concentration, pH, surfactants, temperature, and mode of heating were examined. The obtained colloidal systems were studied by optical spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, and atomic force microscopy. The examined colloids were found to contain generally spherical copper nanoparticles with a diameter of about 10 nm, which were coated with a copper(I) or copper(II) oxide and hydroxide film.

Preparation and characterization of colloidal copper xanthate nanoparticles

Despite the important role of metal xanthates in a number of industrial processes and emerging applications, no attempts have been made to prepare the metal xanthate nanoparticles and to study colloidal solutions of insoluble heavy metal xanthates. Here, we examined the formation of colloidal copper xanthate particles during the reactions of aqueous solutions of cupric sulfate and various potassium xanthates, which occur in flotation and water treatment slurries and can be used to manufacture nanoparticles for materials science (e.g., as precursors for copper sulfide nanoparticles and biomedicine). The products were characterized using UV-vis absorption, dynamic light scattering, zeta potential measurements, transmission electron microscopy (TEM), electron diffraction, Fourier transform infrared spectroscopy, thermogravimetry, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy (XANES). Colloidal copper xanthates with compositions of ROCSSCu (R = ethyl, isopropyl, butyl, isobutyl, and amyl groups), disordered structures and average diameters of 20–80 nm easily formed and aggregated and were stable for at least several hours, especially if excessive xanthate was used. The hydrodynamic diameters of the nanoparticles were smaller at lower temperatures. Dixanthogens, which were produced in the reactions along with ROCSSCu, seemed to promote nanoparticle aggregation and precipitated with the copper xanthate, affecting their thermal decomposition. The TEM micrographs and S K- and Cu K-edge XANES spectra revealed core/shell particle morphologies, likely with Cu(I) bonded to four S atoms in the core and reduced copper coordination in the shell.

Anion Exchange Synthesis of Spinel-Type Cobalt-Containing Pigments

A method is proposed for synthesizing ultramarine blue pigment by co-precipitation of cobalt and aluminum from nitrate solutions by the anion exchanger AV-17-8 in the OH form followed by roasting a precursor at 750°C for 4 h. The product obtained was studied by thermographic and x-ray radiographic analyses as well as by spectrophotometry (IR and diffuse reflection). Electron microscopy shows the pigment particles to be 50 – 80 nm in size.

Ion-exchange synthesis of α-modification of nickel hydroxide

An anion-exchange method for synthesizing nickel hydroxide using industrial strongly basic AV-17-8 anionite has been proposed. The influence of conditions (concentration and nature of starting salt, amount of the anionite, process duration, etc.) on the precipitate yield has been established. The product has been investigated by scanning electron microscopy, IR and Raman spectroscopy, X-ray phase analysis, and thermal and chemical analyses. It has been established that the product is a disordered layered modification of nickel hydroxide α-Ni(OH)2, which contains anions and water molecules in the interlayer spacing. Nickel hydroxide particles are needle crystals (40–80 nm) that form agglomerates 0.3–0.5 μm in size.

Anion-Exchange Synthesis of Nickel-Containing Spinel-Type Pigments

It is proposed that light-blue pigment be synthesized by co-precipitation of nickel and aluminum from nitrate solutions by the anionite AB-17-8 in OH form followed by calcination of a precursor at temperature 750°C. The product obtained is investigated by means of thermographic and x-ray diffraction analyses as well as spectrophotometry (IR and diffuse reflection). Electron microscopy shows the pigment particles to be 0.3 μm in size.

Synthesis of anisotropic silver nanoparticles and investigation of their sensory properties

A simple procedure has been proposed for synthesis of planar triangular silver nanoparticles. Optimal conditions have been determined for particles to form, and the particles have been characterized by physicochemical methods. The halide-ion-sensory properties of sols of anisotropic silver nanoparticles prepared in different ways have been studied; sensitivity to halide ions is based on the changes in positions and intensities of longitudinal surface plasmon resonance (SPR) peaks in the range 500–800 nm in the optical absorption spectra of solutions.

A comparative study of the structure of copper and lead xanthates

XPS, PbL3 and CuK EXAFS, solid state NMR, and EPR techniques are used to study insoluble products formed in the interaction of aqueous solutions of lead(II) nitrate and copper (II) sulfate with potassium nbutylxanthate (KX). The XPS spectra of lead xanthates with the composition PbX2 are similar to those of KX, and interatomic distances of 0.279 nm suggest a nearly ionic character of Pb–S bonds. In copper xanthate precipitating together with dixanthogen (approximately 15 wt.%), the Cu(I)–S bond length is smaller (0.229 nm), and copper coordination number of 2.9 in a composite with dixanthogen increases to 3.3 after its removal by washing with acetone. The XPS spectra indicate the covalent character of the bond and non-equivalence of xanthate radicals. Solid state 1H and 13C NMR spectra as well as the actual absence of metal lines under the measurement conditions demonstrate strong disordering of the structure of xanthates, which is stronger for PbX2 and weakest in CuX after the removal of dixanthogen. EPR reveals sulfur-containing radicals and Cu2+ in CuX, however, their amounts are insignificant and decrease after the washing with acetone. The results of the work are significant for the understanding of the reactivity of xanthates, in particular, under the conditions of flotation of base metal ores.

Characteristics of copper sulfide nanoparticles obtained in the copper sulfate–sodium thiosulfate system

Stable hydrosols of copper sulfide nanoparticles are synthesized by heating aqueous solutions with different ratios of sodium thiosulfate and copper sulfate in the presence of polyvinylpyrrolidone and studied by a number of physicochemical methods in situ (optical spectroscopy, dynamic light scattering) and ex situ (transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy). The main product is CuS covellite nanoparticles with some impurities of other phases (Cu2S, Cu1,8S, Cu7S4). With an increase in the initial molar ratio S2O 2−3 / Cu from 0.2 to 5 the nanoparticle size increases from 1-5 nm to 30-50 nm and then decreases to 4 nm at a ratio of 10. A substantial increase in the intensity of plasmon absorption within 800-1500 nm is observed during the formation of planar nanoparticles with a lateral size of about 30 nm at S2O 2−3:Cu = 5. A band gap obtained from both direct and indirect optical absorption spectra of sulfides (2.6 eV and 1.7 eV respectively) remains constant for all particles.

Reactive ion exchange processes of nonferrous metal leaching and dispersion material synthesis

Two combining reactive ion exchange processes with the application of cation exchange resins have been considered: the cation resin exchange leaching of metal ions from mineral and technogenic raw materials using cation exchange resin in the form of hydrogen and the anion resin exchange precipitation of metal ions in the insoluble compound form with the application of anion exchange resin in hydroxide and salt forms. The applications of methods are illustrated by examples for selective leaching of metals from its oxides, hydroxides, and silicates, as well as by the synthesis of hydroxides, carbonates, oxalates of nickel, cobalt, and other metals.

Anion-Exchange Synthesis of Yttrium-Aluminum Garnet Powders

A new method is proposed for synthesizing yttrium-aluminum garnet Y3Al5O12 powder. The method consists in anion exchange coprecipitation of yttrium and aluminum from chloride solutions by the anionite Purolite A-300 in the OH-form and calcination at 900 °C of the precursor formed. The product was investigated by means of XPA, DSC, IR-spectroscopy, and electron microscopy. The Y3Al5O12 particle size was 300 nm.