E. V. Abkhalimov

The crucial role of self-assembly in nonlinear optical properties of polymeric composites based on crown-substituted ruthenium phthalocyaninate†

Ruthenium(II) tetra-15-crown-5-phthalocyaninate with axially coordinated molecules of pyrazine [(15C5)4Pc]Ru(pyz)2 (1) was synthesized from a carbonyl complex [(15C5)4Pc]Ru(CO)(MeOH) (2), and the structure of the solvate complex (1)·6CHCl3 was revealed using the single crystal X-ray diffraction method. Analysis of the crystal packing showed that the weak intermolecular interactions, such as CH⋯π, CH⋯N, CH⋯O and CH⋯Cl, played an essential role in the formation of stable assemblies and their organization within the crystals. The interplay between the intramolecular axial coordinated pyrazine contacts and the weak intermolecular interactions of solvate molecules with crown-ether fragments provided the basis for rationalizing the observed self-assembly of molecules in solutions of tetrachloroethane and polymeric composites with polyvinylcarbazole. The self-assembly was investigated using UV-Vis spectroscopy, dynamic light scattering measurements, atomic force microscopy and transmission electron microscopy techniques. The formation of nanoparticles of complex (1) from a tetrachloroethane solution after three cycles of heating to 70 °C/cooling to 5 °C and two days storage was proved. Thin films (7 μm) of polymeric composites with polyvinylcarbazole prepared from a solution containing nanoparticles exhibited a nonlinear optical response measured by the Z-scan technique with application of femtosecond (1030 nm) and nanosecond (1064 nm) pulse lasers. The measured third-order susceptibility (χ(3)) of the polyvinylcarbazole composite with 4 wt% of complex (1) was equal to 1.94 × 10−10 esu, while the same composite prepared without the previously described special treatment had zero susceptibility. This result proves the essential role of self-assembly in future development of nonlinear optical materials.

PtcoreAgshell nanoparticle-catalyzed reduction of methylviologene with hydrogen in aqueous solution

Bimetallic PtcoreAgshell nanoparticles demonstrate the ability to catalyze methylviologene reduction with hydrogen in water-alkali solutions, which is inherent in platinum nanoparticles. The onset of the reaction is preceded by an induction period whose duration increases with the thickness of a silver layer covering a platinum core. The reaction slows down with a rise in the thickness of the silver layer. The mechanism of catalysis is discussed.

Interaction of silver nanoparticles with ozone in aqueous solution

The interaction between ozone and silver nanoparticles stabilized with sodium polyphosphate is studied in aqueous solutions. The process of ozone decomposition is established to have a chain character. The oxidation of one silver atom initiates the decomposition of about three ozone molecules. The stability of colloidal silver decreases upon the oxidation, which leads to its partial aggregation.

Preparation of silver nanoparticles in aqueous solutions in the presence of carbonate ions as stabilizers

Silver nanoparticles are prepared by reducing Ag+ ions with sodium borohydride in aqueous solutions containing carbonate ions (5 × 10−5−1 × 10−2 mol l−1). It is established that carbonate ions represent an efficient stabilizer that provides nanoparticles with electrostatic protection via the formation of an electrical double layer. The maximum stability of a silver dispersion is observed at a carbonate ion concentration of 1 × 10−3 mol l−1. The average size of silver nanoparticles is 10.0 ± 2.5 nm. The formation kinetics of silver nanoparticles is described by an equation for a first-order reaction with a rate constant of 2.3 × 10−3 s−1 (±20%).

Preparation of PtcoreÅgshell Nanoparticles: Catalytic Reduction of Ag+ Ions by Hydrogen

It is shown that the saturation of an aqueous solution containing silver ions with hydrogen in the presence of 9.5-nm platinum nanoparticles leads to the reduction of silver and the formation of PtcoreAgshell bimetal nanoparticles. An increase in the concentration of silver ions gives rise to a number of elementary silver layers that cover the platinum core. It is established that the concentration of silver ions does not substantially affect the rate of the formation of a silver shell on the surface of platinum nanoparticles.

Catalytic properties of gold nanoparticles in H2—D2 exchange and ortho—para hydrogen conversion

Gold nanoparticles of 3.8, 4.6, and 19.4 nm size, unlike the bulk metal, can adsorb hydrogen and catalyze the deuterium—protium exchange in the 77—523 K range. It has been shown that as the particle size decreases, the specific catalytic activity increases. The exceptionally high catalytic activity of gold nanoparticles in the ortho—para hydrogen conversion with respect to the deuterium—hydrogen exchange may indicate that at low temperatures the nanoparticles exhibit magnetic properties.

Bimetallic Pd-M (M = Co, Ni, Zn, Ag) nanoparticles containing transition metals: Synthesis, characterization, and catalytic performance

The reductive thermolysis of Pd(OOCMe)4M(OH2) (M = NiII, CoII, ZnII) and Pd(OOCMe)4Ag2(HOOCMe)4 molecular complexes results in the generation of bimetallic Pd-based Pd-M (M = Co, Ni, Zn, Ag) nanoparticles. The composition and morphology of nanoparticles and the electron state of metal atoms were characterized using electron microscopy, elemental ICP analysis, X-ray diffraction, and XAFS (XANES/EXAFS) techniques. The catalytic performance of nanoparticles was studied using the example of reactions of catalytic hydrazine decomposition and U(VI) reduction to U(IV) by hydrazine and formic acid. The catalytic performance of Pd-Ni nanoparticles is superior to that of the standard supported Pd/SiO2 catalyst containing a similar amount of Pd atoms, while Pd-Co, Pd-Zn, and Pd-Ag nanoparticles do not catalyze the studied reactions.

The Effects of Hydrogen and pH on Plasmon Absorption of Gold Hydrosol. Electrochemical Reactions on Nanoelectrodes

A short-wavelength shift in the plasmon absorption band of 3-nm gold nanoparticles at their hydrosol saturation with hydrogen has been discovered and analyzed. It has been shown that dissociative adsorption of hydrogen occurs on a gold nanoparticle followed by the transfer of hydrogen in the form of a proton to a dispersion medium, with an electron remaining on the nanoparticle; i.e., a hydrogen nanoelectrode is realized. A linear increase in the magnitude of the experimentally observed shift in the plasmon resonance band with solution pH has been qualitatively explained.

Palladium nanoparticles in aqueous solution: Preparation, properties, and effect of their size on catalytic activity

A method has been developed for the preparation of palladium nanoparticles with different sizes of up to 7 nm via the reduction of Pd(II) ions with hydrogen in an aqueous solution on seed metal nanoparticles (2.5 nm). The effect of the size of nanoparticles on their catalytic activity in methyl viologen reduction with molecular hydrogen in an alkaline medium has been studied. It has been found that the specific catalytic activity of palladium nanoparticles is independent of their size.

One-Stage Synthesis of Gold Hydrosol with Nanoparticles of Desired Shape

The effect of borohydride concentration on the synthesis of gold nanoparticles in solutions of chloroauric acid, cetyltrimethylammonium bromide, and ascorbic acid in the absence of seeds has been studied systematically. Variations in the concentration of NaBH4 allow one to obtain particles of different sizes and shapes. A method has been developed for the one-stage synthesis of large pentagonal gold rods (the average length and thickness are 550 ± 135 and 71.2 ± 11.6 nm, respectively) with a high yield using borohydride in an ultra-low (≤5 × 10–8 mol/L) concentration. The resulting particles have been characterized using optical spectroscopy, scanning and transmission electron microscopy (including high-resolution technique), and electron diffraction.