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The study addresses layer-by-layer formation processes and properties of gold nanoparticle films deposited from reverse micellar solutions of Brij 30 surfactant on rigid glass and flexible polymer (PET) substrates. The films are of interest for transparent electronics and optical sensorics. The spectrophotometric studies of film formation revealed linear relationships between the extinction of growing film at definite wavelengths and the number of nanoparticle deposition cycles, and their parameters were determined. The effects of concentrations of gold and 1,2-ethanedithiol as an interlayer linker in the initial solutions on the film growth were elucidated. Data on the composition, morphology, optical spectra, and surface resistance of gold nanoparticle films, and changes of these characteristics during heat treatment in air and in boiling ethanol were gained using X-ray diffractometry, scanning electron and atomic force microscopy, UV-Vis spectroscopy, and electrical resistance measurements.

We studied the usefulness of dispersions of gold nanoparticles (Au-NPs) stabilized by abietic acid for manufacturing films on glass and silicon substrates and composites with nanosized and powder materials exemplified by SiO2 and TiO2 NPs, expanded graphite (EG), carbon nanotubes (CNTs), a porous carbon material (PCM), PCM containing 6% nitrogen, and CeO2 powder.

Gold nanoparticles (NPs) with the average core diameter d Au = 6.8 ± 1.6 nm have been synthesized in reverse micelles of the oxyethylated surfactant Brij 30. It has been shown that thin NP films can be produced directly from a micellar solution with the use of glass substrates functionalized with aminosilane. Synthesis of NPs and film formation have been studied by UV-Vis spectroscopy, photon correlation spectroscopy, X-ray diffraction, TEM, SEM, and AFM.

Comparison of extraction properties of macrocyclic calix[4,6]arenethiaethers (CATE) with their acyclic analogs R2S (R = C6H13, C8H17) for the recovery of [Rh(NO2)3(H2O)3]0 rhodium form from nitric acid solutions was carried out. Rhodium recovery with CATE (0.05 M) in the absence of accelerating additives under optimal conditions exceeds 90% at 5–10-fold preconcentration and is only 1–3% for R2S (1 M). Extraction kinetics was studied and hypothesis on the mechanism of multiple acceleration of rhodium recovery was proposed for CATE extraction, the mechanism includes the formation of intermediate product of colloidal- chemical nature on account of the surface activity of the macrocycle and its reaction with rhodium accompanied by rhodium chelation to the sulfur atoms of neighboring fragments of the macrocycle. The obtained results are of interest for the development of methods for the isolation of fission rhodium from nitrate–nitrite nitric acid solutions.

A method is advanced for preparing gold nanoparticles (NPs) at 50°C in aqueous acrylamide (AAm), which has the dual function of a reducing agent for HAuCl4 and a protective ligand for NPs. Nanoparticles have gold cores with the average size d Au = 20.9 ± 3.6 nm. The growth kinetics of NPs has been studied. Films of NPs have been produced on glass, silica, silicon, and polyethylene terephthalate (PET) substrates. The NPs and films have been characterized by UV-Vis and IR spectroscopy, X-ray powder diffraction, transmission and scanning electron microscopy, and atomic-force microscopy.

Hydrophilic gold nanoparticles stabilized with isonicotinic acid (INA) were prepared by reduction of HAuCl4 with sodium borohydride in the presence of INA in water, dimethylformamide, and dimethyl sulfoxide. The main condition for the preparation of good quality particles is to maintain reagent concentration ratio HAuCl4 : INA : NaBH4 = 1 : 2 : (5–10) at cAu ≤ 0.5 mM. Reaction products in water are mainly spherical primary particles with gold nuclei of 2–7 nm in diameter, those in dimethylformamide are secondary coalescent particles with nuclei of spheroid or slightly faceted shape 2–12 nm in diameter and larger elongated agglomerates from 15 to 100 nm long. Framework structures composed of chaotically agglomerated particles were obtained at HAuCl4 : INA ratio larger than 1 : 2. By the example of precipitate of particles prepared in dimethylformamide and on the basis of data of chemical and thermal analysis, XPD, and IR spectroscopy, it was shown that the product contains gold, INA anion, acetone, water, sodium cations, and oxygen boron compounds. The particles obtained as precipitate or concentrate are well redispersible in water and polar solvents. The particles in colloid dispersions are in aggregated state and suffer gradual coagulation and sedimentation, which are not irreversible, and dispersed state can be restored by ultrasound treatment. The particles stabilized by INA may be of interest as initial product for preparation of nanomaterials for biomedical purposes.

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.

A comparison was made for extraction systems based on the mixtures of calix[n]arenes phosphorylated at the upper and lower rims (PCA, n = 4 and 6) with dioctyl sulfide (DOS) for recovery of rhodium in the form of [Rh(H2O)3(NO2)3]0 from acid nitrate-nitrite media. Because of inertness of rhodium compounds, the main attention was devoted to extraction kinetics. The kinetic efficiency of DOS + PCA systems was found to be much higher than that for DOS alone, whereas the components of the mixtures do not extract rhodium. Alkyl(ethyl)calixphosphine oxides are the most promising, they behave as accelerating additives in extractant mixtures. Extraction kinetics of [Rh(H2O)3(NO2)3]0 species was studied and extraction systems were selected to develop method for the recovery of fission rhodium.

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).

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.

The effect of additions of hydrophobic dioctyl sulfide (L) on the kinetics of dissolution of gold nanoparticles in the interaction with a dispersed aqueous hydrochloric solution of H2O2 in Triton N-42 reverse micelles (decane was the dispersion medium) was studied spectrophotometrically. The process consists of a two-stage oxidation Au0 → AuCl2− → AuCl4− at the surface of gold particles; the first stage occurs in two ways: a spontaneous reaction and an autocatalytic reaction involving AuCl4− ions. With small additions of L (cL < cAu), only spontaneous oxidation of Au(0) to Au(I) takes place because Au(I) is completely bound in an inert complex AuLCl. When unbound L is exhausted, the newly formed AuLCl is accumulated in micellar shells, changes the properties of the medium inside the micelles, and affects the rate constant of the autocatalytic reaction, which increases with increasing cL. At high concentrations of L, the coagulation of particles occurs instead of their dissolution, because of the deterioration of the protective properties of micellar shells as a result of the ingression and accumulation of dioctyl sulfide molecules on account of selective adsorption on gold particles. The rate constants of all stages of dissolution and coagulation are determined.

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.

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.

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.

Extraction preconcentration of gold(III) by mixed Triton N-42 plus dioctyl sulfide (DOS) micelles from acid sulfate-chloride solutions was studied. The distribution ratio increases from 200 to 1200 as the DOS concentration rises from 0 to 0.25 mol/L (positive synergetic effect). Analysis of extraction equilibria shows that mixed micelles are key contributors into gold(III) extraction compared to Triton N-42 micelles and DOS molecular species in n-decane. Introduction of DOS at the synthesis stage increases the rate constants for gold reduction by hydrazine and enhances the coagulation of nascent nanoparticle

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+ + NO 3 − → Ag+ + products (k 1), and Ag0 + Ag+ + NO 3 − → 2Ag+ + products (k 2). The effective rate constant k 2 decreases with decreasing solubilization capacity V S/V O (where V S is the volume of the solubilized dispersed aqueous phase and V O 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: k 2 = 74 (V S/V O) · 100% ≈ 3.8%), 41 (2.9), and 35 (2.0) L/(mol s). The effective constant k 1 is determined with a high uncertainty; the effect of V S/V O on k 1 has the opposite tendency.

The manifold enhancement of the rhodium extraction efficiency from nitric acid solutions of triaquatrinitrorhodium is discovered with the use of two-component mixed extractants based on alkylaniline (AA), dihexyl sulfide (DHS), dihexyl sulfoxide (DHSO), tributyl phosphate (TBP), and oxime ACORGA P5100. A mixture of unimolar solutions of alkylanilinium nitrate and DHS is found to be the most efficient extractant: at 35°C, this mixture quantitatively extracts rhodium within 5 min from aqueous solutions containing 0.06 to 3 mol/L HNO3. The extraction kinetics are studied. The following two-stage extraction mechanism is substantiated: the equilibrium of formation of a colloidal-chemical intermediate involving [Rh(H2O)3(NO2)3], HNO3, and (BHNO3)p (an associated form of the alkylanilinium salt) and the reaction of the intermediate with DHS (the rate-controlling stage).

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.