V.N. Zakharov

Surface tension of silver in different media

Abstract By means of electron microscopy, the stability of silver particles in redox buffers has been studied and values of the surface tension of silver in aqueous solution of buffers and a gelatin medium have been determined to be 0.72 J m −2 and 0.68 J m −2 , respectively. Using calculations of the binding energy per atom in vacuum, an effective value of 0.86 J m −2 for the surface tension for silver clusters was determined.

Double stabilization of nanocrystalline silicon: a bonus from solvent

Double stabilization of the silicon nanocrystals was observed for the first time by 29Si and 13C MAS NMR spectroscopy. The role of solvent, 1,2-dimethoxyethane (glyme), in formation and stabilization of silicon nanocrystals as well as mechanism of modification of the surface of silicon nanocrystals by nitrogen-heterocyclic carbene (NHC) was studied in this research. It was shown that silicon nanocrystals were stabilized by the products of cleavage of the C–O bonds in ethers and similar compounds. The fact of stabilization of silicon nanoparticles with NHC ligands in glyme was experimentally detected. It was demonstrated that MAS NMR spectroscopy is rather informative for study of the surface of silicon nanoparticles but it needs very pure samples.Graphical Abstract

Stabilization of silicon nanoparticles by carbenes

Sodium reduction of a mixture of tetrabromosilane with imidazole ionic liquids in organic solvents gives dispersions of silicon nanoparticles stabilized by carbene ligands. It was shown that the size of silicon nanoclusters depends on the size of substituents at nitrogen atoms of 1,3-dialkylimidazol-2-ylidenes.

An INDO/S study of the second ππ* transition in the spectra of 1,4-diaminoanthraquinones responsible for their green hue

Abstract The INDO/S approach is used to study the structure/spectra relationship for some N,N′-disubstituted 1,4-diaminoanthraquinones. The calculated intensity and position of the short-wavelength absorption band depend on the molecular conformation, in agreement with the experimental data. The reflection spectra of crystalline 1,4-bisanilinoanthraquinone and 1,4-bis(mesitylamino)anthraquinone are reported and the crystal structure of the latter compound has been determined.

Free-Standing 2D Silicon Nanocrystals Stabilized with Perfluorophenyl Ligands: Experiment and Ab Initio Research

Silicon (Si) is currently the basis of most of nanodevice technology, therefore ultrathin materials based on Si have the great advantage of easy integration into existing circuitry. First flat silicon nanoparticles have been obtained with perfluorophenyl (PFPh) ligand coating. The size of these particles varied from 15 to 50 nm. Their thickness evaluated with the atomic force microscopy was about 3.3 nm. Based on ab initio DFT calculations we investigate the geometries and electronic structures of free-standing PFPh-stabilized 2D silicon in order to see if such systems have promising electronic and optical properties. We also examined the effect of doping PFPh-stabilized 2D silicon by the Mn atoms.

Stabilization of Nanocrystalline 2D Structures of Silicon with Perfluorophenyl Ligands

Use of perfluorophenyl ligands for stabilization of silicon nanocrystals gives rise to 2D structures with an area up to 50 × 15 nm2 and a thickness of about 3 nm. Their formation can be explained by specific interactions of perfluorophenyl ligands.

Synthesis and properties of nanosilicon stabilized by butyl and perfluorobutyl ligands

Nanocrystalline silicon stabilized by butyl and perfluorobutyl ligands that form improper surface states of silicon nanocrystals were synthesized. The presence of perfluorobutyl ligands on the surface of silicon nanocrystals was proved by IR spectroscopy. Nanocrystals with perfluorobutyl ligands form aggregates, which decreases the efficiency of photoluminescence. The nanocrystals with butyl ligands have smaller size but their photoluminescence can be clearly recorded.

Heterogeneous catalysis in ionic liquids: The heck reaction of bromobenzene with styrene over palladium supported on mesoporous carbon

Tributylhexylammonium bistriflamide [(C4H9)(C6H13)N][(CF3SO2)2N], an ionic liquid, was used as a solvent for the Heck reaction of bromobenzene with styrene in the presence of Pd deposited onto a mesoporous carbon support. It was found that dibutylamine used as a basic reagent to scavenge hydrogen bromide results in higher conversions of the reactants and higher yields of stilbene than sodium acetate. It was shown that the IL is fully recoverable after use in the catalytic reaction.

The heterogeneous catalytic heck reaction in an ionic liquid

The C-C cross coupling reaction between bromobenzene and styrene in the presence of Pd deposited on mesoporous acetylene soot (Pd/C) occurred in a tetraalkylammonium ionic liquid (IL) as a truly heterogeneous catalytic process. The active palladium form was not transferred into the reaction solution. Deposited palladium activation was observed when the Pd/C catalyst was preliminarily heated in the IL in the presence of dibutylamine as a base.

Synthesis and properties of nanosilicon prepared by homogeneous and heterogeneous reduction of tetraethyl orthosilicate

Nanocrystalline silicon was synthesized by reduction of tetraethyl orthosilicate both in homogeneous and heterogeneous processes with surface stabilization by nitrogen heterocyclic carbene (NHC) ligands. The presence of NHC ligands on the surface of silicon nanocrystals was demonstrated by IR spectroscopy. According to transmission electron microscopy data, the size of silicon nanocrystals is in the range of 2.2–8.4 nm. Photoluminescence of the samples is clearly recorded in the blue spectral region.