I. A. Druzhinina

Kinetics of dissolution of silver nanoparticles inside triton N-42 reversed micelles

Our spectrophotometric study of the kinetics of dissolution of silver nanoparticles by nitric acid inside inverted micelles of Triton N-42 (a nonionic surfactant) verified the universal character of the mechanism for this type of process, which includes the interaction of surface metal atoms with an oxidizer in two routes: either with (autocatalysis) or without newly formed ionic species of the oxidized metal. Effective rate constants for both routes are independent of the value of solubilization capacity (Vs/Vo is the ratio of the volume of the dispersed aqueous phase to the volume of the micellar solution); the solubilization capacity is useful to control the micelle and particle sizes: k1 = 0.018±0.003, 0.010±0.003, and 0.012±0.003 s−1 and k2 = 2.5±0.8, 1.5±1.1, and 1.4±0.4 L/(mol s) for 100 Vs/Vo = 1, 2, and 3%, respectively.

JUSTIFICATION OF THE CHOICE OF AN EXTRACTION SYSTEM ON THE BASIS OF PETROLEUM SULFIDES FOR EXTRACTING FRAGMENT PALLADIUM

The article summarizes experiments performed on the extraction of palladium from spent nuclear fuels. Palladium extraction from high-level nitric acid solutions was performed using diesel fuels and petroleum sulfides. Petroleum sulfide extraction systems with aromatic solvents provided the highest selectivity for palladium. Experimental results for refinement of palladium after extraction are also summarized. 14 refs., 4 tabs.

Kinetics of oxidative dissolution of gold nanoparticles in triton N-42 reversed micelles

The dissolution of gold nanoparticles as a result of a reaction with dispersed aqueous solution of Cl− and H2O2 solubilized in Triton N-42 reversed micelles (an oxyethylated surfactant) in n-decane was studied photocolorimetrically. An adequate description of the process kinetics is provided by the following autocatalytic scheme (in a Cl− + H2O2 excess): Au0 → Au+, Au0 + Aun+ → 2Au3+, n = 1 and 3. The reactions involve the formation and redox decomposition of intermediate complexes with the oxidizer on the surfaces of metallic particles. Dimensional factors associated with gold particles (the surface and reactivity of gold particles change during the process) and micelles (as nanoreactors) affect the process kinetics. The first effect is taken into account when data processing is performed in terms of the current number and effective charge density of surface gold atoms; therefore, it does not affect the observed rate constants kd1 and kd2. The second effect makes kd1 and kd2 dependent on the micelle size through changing the quality of the aqueous medium and the reactivity of the reaction components, mainly the activity of water and its hydration and adsorption abilities.

Behavior of precious metals in extraction recovery and refining of fission product palladium

ConclusionThe experimentally determined total purification factors for palladium relative to silver (first cycle 102, second cycle >103) and rhodium and ruthenium (first cycle >104, second cycle >10) are greater than 105. In connection with the insufficient sensitivity of the atomic absorption method for monitoring and the relatively high value from the control run, we could not determine the true values of the purification factors in some operations of the second extraction cycle and for precipitation of palladosammine. The noted chemical aspects of the behavior of precious metals in extraction systems with petroleum sulfides lead to an estimate of the purification factors for palladium at the 108 level. In particular, the total purification factors increase by 10–100 times when the extraction is carried out in both cycles with W:O=10:1 (F=(W:O)/Dj, where j is the component to be separated [10]). Larger-scale laboratory testing of the proposed flow diagram for recovery and refining of palladium using Ag, Pd, Ru, Rh, and Sb will allow us to experimentally confirm that such estimates are realistic.

Formal kinetics of growth of nanosized silver particles upon silver nitrate reduction with sodium citrate in a reverse micellar solution of AOT

The growth kinetics of silver nanoparticles upon silver(I) reduction with sodium citrate in an aqueous solution solubilized to a reverse micellar solution of sodium bis(2-ethylhexyl) sulfosuccinate in decane is studied spectrophotometrically under constant conditions of irradiation of the reaction mixture with visible light. The formal kinetics of the process corresponds to an autocatalytic mechanism. The effective rate constants of growth of silver nanoparticles, unlike those of gold nanoparticles, are independent of the size of the inner micellar cavity when its radius changes from 2 to 6 nm. This is most likely due to a great effect of the photochemical factor or Ag+ localization in the inner surface layer of the micelles on the rate constants.

Preparation and properties of gold nanoparticles stabilized by abietic acid

Hydrophobic gold nanoparticles were prepared via the reduction of HAuCl4 by sodium borohydride in the presence of abietic acid (AA) in nonaqueous polar media based on dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, and isopropanol. The particles prepared in DMF had spherical gold cores, with a narrow size distribution and the average diameter dAu = 7.1 ± 1.0 nm, and a protective shell formed of abietic acid anions and sodium cations. A violet nanoparticle sediment separated by centrifugation was stored under DMF and could be used for preparing colloidal dispersions of nanoparticles in polar solvents. Ethanol dispersions of nanoparticles were most resistant to sedimentation. The nanoparticles were shown to be useful for sensing nonaqueous polar media.

Synthesis of gold nanoparticles stabilized with di-(2-ethylhexyl)dithiophosphoric acid and tris(2-aminoethyl)amine

Methods for preparing gold nanoparticles (NPs) surface-stabilized with di-(2-ethylhexyl)dithiophosphoric acid (DTPA) and tris(2-aminoethyl)amine (TAEA), which endow the nanoparticles with hydrophobic and hydrophilic properties, are described. In the case of DTPA, Au-NPs are first synthesized with surfactant shells by means of reducing [AuCl4]− with hydrazine in inverted micelles of oxyethylated Triton N-42 in a low-polarity medium of decane; then, the micelles are destroyed by polar chloroform in the presence of DTPA, which has a great affinity to gold due to its sulfur donor atoms and substitutes for the surfactant on the surface of the nanoparticles. In preparing hydrophilic nanoparticles, [AuCl4]− is reduced with solid NaBH4 directly in a nonaqueous solution of TAEA based on an ethanol and 2-propanol (3: 10) mixture. The nanoparticles are characterized by elemental analysis (for Au, C, H, N, and Na), X-ray powder diffraction, electronic absorption spectra, IR spectra, photon-correlation spectra, and transmission electron microscopy (TEM).

Microemulstion synthesis of powders of water-soluble energy-saturated salts

The feasibility of preparing energy-saturated salts (NH4NO3, KNO3, and NaBH4) in powders with various particle sizes in microemulsion systems based on oxyethylated surfactant Tergitol NP-4 has been demonstrated. Powders were isolated by destroying microemulsions with acetone. The regions of micellar synthesis have been determined depending on the solubilization capacities and concentrations of the reagents and salts at a fixed Tergitol NP-4 concentration (0.25 mol/L). The morphologies and particle sizes of the thus-prepared salt powders were characterized by scanning electron microscopy (SEM), X-ray powder diffraction, differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermogravimetry; the hydrodynamic radii of microemulsions were characterized by photon-correlation spectroscopy.

Rhodium and palladium joint extraction by dihexyl sulfide and alkylanilinium nitrate mixtures from nitrate solutions

We studied nonequilibrium distribution of inert rhodium(III) in extraction by dihexyl sulfide (DHS)and alkylanilinium nitrate mixtures from joint nitrate solutions of triaquatrinitrorhodium (0.1–4 g/L Rh) and palladium (0–2 g/L Pd). We discovered the effect of increasing rhodium recovery in the presence of palladium. This effect has a kinetic nature and arises from the fact that bis(alkyl sulfide) palladium(II) species catalyze the reaction between dihexyl sulfide and a rhodium intermediate based on alkylanilinium nitrate micelles. Depending on initial rhodium and palladium concentrations, the extraction system provides effective distribution factors for rhodium in the range DRh* = 8−300 and rhodium recoveries of 43–97% with ∼100% palladium recovery; single 5-min phase contact at 35°C ensures the 10-fold concentration of both metals in the extract. Our results are useful for developing processes for recovering fission rhodium from spent nuclear fuel.

Dissolution kinetics of silver metal nanoparticles in their reaction with nitric acid in an reverse micelle solution of AOT

The dissolution of silver nanoparticles in their reaction with aqueous HNO3 solubilized to an reverse micelle solution of sodium bis(2-ethylhexyl)sulfosuccinate in decane is studied spectrophotometrically. A physicochemical model is advanced for quantifying the process kinetics on th basis of the following autocatalytic scheme: Ag0 + H+ + NO3− → Ag+ + products (k1), and Ag0 + Ag+ + NO3− → 2Ag+ + products (k2). The effective rate constant k2 decreases with decreasing solubilization capacity VS/VO (where VS is the volume of the solubilized dispersed aqueous phase and VO is the volume of the micelle solution); the solubilization capacity determines the size of the micelle cavities in which the reaction between Ag0 and HNO3 occurs: k2 = 74 (VS/VO) · 100% ≈ 3.8%), 41 (2.9), and 35 (2.0) L/(mol s). The effective constant k1 is determined with a high uncertainty; the effect of VS/VO on k1 has the opposite tendency.