Role of the concentration and nature of grafted groups in the adsorption of hydrocarbon vapors on silica modified by monofunctional polyfluoroalkylsilanes

The role of the grafting density of monofunctional polyfluoroalkylsilanes of the C _n F_{2n − 1}(CH₂) _m Si(CH₃)₂Cl general formula (where n = 3, 4, and 6; and m = 2 and 3) and their composition in intermolecular interactions of the molecules of saturated and aromatic hydrocarbons with a surface of chemically modified silica is studied by means of IR spectroscopy and adsorption-static and gas chromatography. It is shown that the higher the concentration and the shorter the length of the grafted chain, the greater (by a factor of 2 to 25) the drop in the adsorption values of hydrocarbons as a result of modifications, due to an increase in the degree of oleophobization of surface upon the formation of polyorganofluorine coatings. The high specificity of the surface with respect to benzene, which is due to the active participation of the polar fragment of a grafted chain in adsorption process, is related to the features of a relatively low-density sample with a concentration of grafted perfluorobutyl groups of 1.7 nm⁻². It is shown that the thermodestruction of polyfluoroalkyl silica remains virtually unobserved upon heating to 523 K in an argon flow.     

Interaction of benzene,L-histidine and L-proline with urea,N,N-dimethylpropyleneurea,and N,N-dimethylformamide in water

Russian Journal of General Chemistry - The paper focuses on the interaction of two heterocyclic amino acids and hydrophobic benzene with urea, dimethylformamide, and dimethylpropyleneurea in water...     

Catalytic properties of supported gold nanoparticles in organic syntheses

Gold nanoparticles exhibit unique properties due to their ability to form aggregates of atoms of diverse morphology shapes and sizes of which depend, to a considerable extent, on specific features of the nearest environment. The nature of gold nanoparticles varies in a wide range: from the particles with pronounced Lewis acidic properties to the negatively charged particles bearing a formal zero-valence charge. The most examples of new reactions catalyzed by gold nanoparticles include unsaturated compounds and strong nucleophiles (such as amines) as substrates. This short review provides a digest of the catalytic properties of gold nanoparticles. The main attention is paid to the possible role of certain forms of the metal in catalytic reactions. Of special interest are reactions in which effects of synergism of gold and other active species or second metals present in the catalyst are revealed or a size effect is established.     

Effect of adamantane-containing additives on the isomerization of n-heptane in the ionic liquid trimethylammonium hydrochloride-aluminum chloride

We study the effect of adamantane-containing additives on the process of isomerization of n-heptane in the ionic liquid trimethylammonium hydrochloride-aluminum chloride (1 : 2 mol). It is shown that introducing 1-cyanomethyl-3-cyanoadamantane (5.0 wt %) into the reaction mixture slows conversion and lowers the yield of iso-products by a factor of more than 1.5, while adding adamantylpolyimide (0.5–5.0 wt %) substantially accelerates the isomerization of n-heptane and increases the yield of iso-products. In addition, this reaction proceeds under mild conditions at 40°C in the absence of hydrogen and precious metals.     

synthesis and properties of β-brominated metal complexes of meso-triphenylcorrole

Spectral properties and chemical stability of Mn(III), Mn(IV), Fe(III), Fe(IV), and Cu(III) complexes of β-octabromotriphenylcorrole [(β-Br)₈(ms-Ph)₃Cor], synthesized from β-unsubstituted compounds by their reaction with molecular bromine, were studied. Cyclic voltammetry, electron microscopy, and X-ray spectral microanalysis were used to obtain electrochemical characteristics of metal corroles M(β-Br)₈(ms-Ph)₃Cor and gain insight into the surface texture of active catalysts on the basis of metal corroles. The electron-acceptor β-bromine substitution in the MCor macrocycle shifts the equilibrium in electron-donor solvents to lower oxidation states of the metals and also stabilizes manganese and destabilizes copper complexes in the protondonor medium HOAc-H₂SO₄. The electrocatalytic activity of the complexes in the reduction of molecular oxygen depends on the nature of the ligand and increases in the order Mn ≤ Cu ? Fe in the case of β-octabrominated macrocycles. The character of distribution of active centers on the surface of the catalysts was established for the first time.     

Evaluation of stability of silica-supported Fe–Pd and Fe–Pt nanoparticles in aerobic conditions using thermal analysis

The applications of zerovalent iron nanoparticles (nZVI) exploit their high reactivity which decreases due to oxidation in aerobic conditions during manufacture, application, and storage. In this study, we present the new procedure for estimation of the nZVI stability to oxidation in air. The procedure is suitable for characterization of the novel materials based on the supported nZVI. Nanoscale particles were synthesized inside porous silica supports by incipient wetness impregnation with the metal precursor solutions followed by thermal treatment. The TG–DTA studies revealed the decomposition temperature of the supported precursors, as well as the interaction of Fe and precious metal precursors, which resulted in the formation of alloy nanoparticles. Characterization of the samples by XRD confirmed the formation of the nanoparticles of the metallic Pd, Pt, and Fe phases supported on SiO₂ carriers, as well as the formation of solid solutions based on the structure of precious metals. The new procedure for estimation of the nZVI stability included (1) TPR with hydrogen up to 400–425 °C followed by isothermal reduction at these temperatures; (2) in situ reoxidation with oxygen at room temperature. The samples were reduced “as obtained” and after in situ reoxidation. The results of the TPR studies exhibited that introduction of both Pd and Pt protected the Fe nanoparticles from oxidation with oxygen and air at ambient conditions.     

Magnetochemistry of dimers with iron group ions

General theory of matrix interactions of dimers of iron group ions is considered. Equations for calculation of matrix elements of the exchange energy of dimers and equations for calculation of the magnetic moments of dimers of different d ⁿ configurations and different exchange parameters are reported. The energies of the spin states of dimers are calculated with inclusion of exchange interactions of the first J ₀ and second J ₂ orders, and energy state diagrams for dimers with different spins and exchange energies are reported. For heterospin dimers, equations for calculation of the magnetic moment ?? and magnetic susceptibility ?? are introduced, and for homospin dimers, analytical formulas of calculation are presented. The tables of magnetic moments are calculated and their diagrams as a function of J ₀ for homospin dimers with spins S = 5/2, 2, 3/2, 1, and 1/2 are given. The experimental data are interpreted for Co²⁺ dimers as an example: the experimental and theoretical dependences of ?? and ?? on temperature are considered.     

Acoustic study of martensitic-phase aging in copper-based shape memory alloys

An acoustic technique was applied to study aging of the β ₁ ^′ martensitic phase in a number of copper-based shape memory alloys (Cu-Zn-Al, Cu-Al-Ni, Cu-Al-Be) characterized by various degrees of martensitic-phase stabilization. The nonlinear anelasticity of the martensitic phase was studied in wide ranges of temperature (7–300 K) and vibrational strain amplitude (2 × 10^?7 ?2 × 10^?4) at vibrational-loading frequencies of ～100 kHz. It was shown that aging effects of the martensitic phase can have homogeneous and heterogeneous components. The homogeneous component is associated with a change in the degree of atomic order in the crystal volume. The basic heterogeneous mechanisms of martensitic-phase aging are associated with the formation of atmospheres of point defects and local changes (which are greater than those in the crystal volume) in the degree of atomic order in the vicinity of partial dislocations and the boundaries between martensite variants. It is concluded that various stabilization properties of the alloys at hand result not only from the different diffusion properties of quenching point defects but also from the different influence of these defects on the degree of atomic order and the different features of their interaction with partial dislocations and intervariant boundaries.     

Rapid crack growth in a thermoelastic solid under mixed-mode thermomechanical loading

A two-dimensional steady-sate analysis of semi-infinite brittlecrack growth at a constant subcritical rate in an unboundedfully-coupled thermoelastic solid under mixed-mode thermomechanicalloading is made. The loading consists of normal and shear tractionsand heat fluxes applied as point sources (line loads in theout-of-plane direction). A related problem is solved exactly in an integral transformspace, and robust asymptotic forms used to reduce the originalproblem to a set of integral equations. The equations are partiallycoupled and exhibit operators of both Cauchy and Abel types,yet can be solved analytically. The temperature change field at a distance from the moving crackedge is then constructed, and its dominant term is found tobe controlled by the imposed heat fluxes. The role of this termis, indeed, enhanced if the heat fluxes serve to render thecrack as a net heat source/sink for the solid, as opposed tobeing a transmitter of heat across its plane. More generally,the influence of the thermoelastic coupling on this field, aswell as other functions, is found to increase with crack speed.     

Physicochemical properties of the surfaces of silica species

The results from studying the physicochemical characteristics of the adsorption of n-alkanes, arenes, and acetonitrile on silicas of different origins, silica gels, and silochromes are presented. It is shown that increasing the concentration of silanol groups reduces the role of dispersion interactions accompanied by the intensification of specific interactions on silica gels, compared to silochromes. According to diffuse reflectance FTIR spectroscopy data, the acidity of silanol groups on silica gel is in this case less pronounced.