G. B. Sergeev

Destruction of organohalides in water using metal particles: carbon tetrachloride/water reactions with magnesium, tin, and zinc.

As a possible method for degrading chlorocarbons in contaminated water supplies, the reactions of metallic magnesium, tin, and zinc with CCl4/H2O mixtures have been studied. In the case of Mg, oxidation by water overwhelmed the Mg-CCl4 reaction. However, Sn and Zn were successfully used to degrade CCl4. Sn and Zn behave quite differently with the final carbon-containing product, with Zn being CH4 but with Sn being CO2. This is rationalized by the competing reactions of a possible intermediate Cl3CMCl, which can be protonated by H2O to give CHCl2 or eliminate CCl2 (which subsequently reacts with water to form CO2 and HCl). Metal surface areas are also important, and the most active metal samples were prepared by a metal vapor-solvent codeposition method (SMAD cryo-particles). However, conventional Zn dust and Sn granules were also effective, only with lower reaction rates.

Reactions of atomic magnesium in the basic state with organic chlorine derivatives at low temperatures

Abstract Low-temperature solid-phase reactions of atomic magnesium in the basic state with a number of aliphatic monochlorine derivatives, chlorobenzene, carbon tetrachloride and 1,2-dichloroethane, have been investigated. The nature of the intermediate particles is discussed, the effect of the phase state of a frozen hydrocarbon on its reactivity examined, and the mechanisms of reactions with the participation of radicals and ion radicals proposed.

Sensor activity of thin polymer films containing lead nanoparticles

Thin poly(p-xylylene) films containing lead nanoparticles were prepared by vacuum deposition technique. The vapors of p-xylylene monomer and lead were condensed onto the surfaces cooled down to 80 K. Films thus obtained were characterized by electric conductivity measurements during film samples formation. Such metallopolymer films exhibit sensor activity in the presence of ammonia in the atmospheric air. The influence of air humidity and the co-operative effect of ammonia together with water vapors on film resistance were studied.

Encapsulation of small metal particles in solid organic matrices

Abstract The methods of synthesis of macroscopic amounts of size-selected clusters with desired properties, and most importantly, the possibility of their controlled assembly into new materials with novel properties are currently of great interest. The interaction of metal atoms and small clusters with solid organic matrices may lead to the stabilization of reactive particles up to room temperatures. Thus obtained nanoscale heterogeneous materials offer an area of intriguing technological promise. In this review, we discuss recent developments in the encapsulation of small metallic particles in different organic solid matrices: organic monomeric compounds, polymers and carbon derivatives.

Low temperature surface chemistry and nanostructures

Abstract The new scientific field of low temperature surface chemistry, which combines the low temperature chemistry (cryochemistry) and surface chemistry approaches, is reviewed in this paper. One of the most exciting achievements in this field of science is the development of methods to create highly ordered hybrid nanosized structures on different organic and inorganic surfaces and to encapsulate nanosized metal particles in organic and polymer matrices. We consider physical and chemical behaviour for the systems obtained by co-condensation of the components vapours on the surfaces cooled down to 4–10 and 70–100 K. In particular the size effect of both types, the number of atoms in the reactive species structure and the thickness of growing co-condensate film, on the chemical activity of the system is analysed in detail. The effect of the internal mechanical stresses on the growing interfacial co-condensate film formation and on the generation of fast (explosive) spontaneous reactions at low temperatures is discussed. The examples of unusual chemical interactions of metal atoms, clusters and nanosized particles, obtained in co-condensate films on the cooled surfaces under different conditions, are presented. The examples of highly ordered surface and volume hybrid nanostructures formation are analysed.

Spectroscopic investigation of molecular association in thin films of mesogenic cyanophenyl derivatives

Abstract Molecular association of liquid-crystalline 4,4−pentylcyanobiphenyl (5CB), 1-p-cyanophenyl-4-pentyl-cyclohexane (5CH) 2-p-cyano-phenyl-5-pentylpyridine (5Py) was studied in thin films, solutions and inert matrices at 77–330 K by low-temperature reflection IR spectroscopy. The thermodynamic parameters have been obtained for cyanophenyl molecule dimerization in the nematic mesophase. The factors affecting the dimer stability were considered.

Nanosize metal particles in poly(p-xylylene) films obtained by low-temperature codeposition

A method of preparing polymer materials containing nanometre-scale metal particles has been developed, involving low-temperature techniques. In particular the codeposition of several metal vapours (Mg, Zn, Cd, Pb, Ag) with pxylylene on surfaces cooled by liquid nitrogen results in the formation of poly(p-xylylene) films containing metal particles that are typically 3–8 nm in diameter.

Preliminary study of the interaction of metal nanoparticle-containing poly-p-xylylene films with ammonia

The interaction of metal particles encapsulated in poly-p-xylylene films and the gas phase NH 3 molecules has been studied. It has been found that in the presence of NH 3 the resistivity of the lead-containing samples could be reversibly changed by a factor of 6–8 within a few seconds. As a result, it is suggested that these materials could be used as sensors for ammonia detection in the gas phase. The response and recovery times, temperature dependence, and long-term stability of these sensors have been examined.

Mechanism of the solid-phase reaction of magnesium with organic halides

Abstract Low-temperature solid-phase reactions of magnesium with monosubstituted benzene halides and primary alkane halides have been investigated. On the basis of EPR and chromatographic data on the reactions products it was found that the carbon—halogen bond energy substantially influences the mechanism of formation of Grignard reagents.

Thermal behavior of silver-containing mesogenic cyanobiphenyl films

Abstract Formation of nanostructures in metal-mesogenic co-condensate films have been studied during low temperature codeposition of metal and organic component vapors—long chain alkyl(alkoxy)cyanobiphenyls (CB): C n H 2 n +1 →C n H 2 n +1, where n =5 (5CB), 8 (8CB), and C n H 2 n +1 OC 6 H 5 C 6 H 5 CN, n =8 (8OCB). The existence of low temperature Ag–CB complexes was shown by IR, UV-visible and ESR techniques. Thermal degradation of the complexes by annealing of the samples up to 300 K led to the formation of nanosize (15–30 nm) silver particles incorporated in anisotropic CB-structure and their further aggregation in mesogenic matrices.