Carbon nanotube with silica

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

Surface-assisted laser desorption/ionization (SALDI). SALDI is a matrix-free approach for the analysis of low-mass molecules. In this innovative approach, the sample solution is placed directly onto a solid surface prepared by depositing an active material, such as powdered graphite, active carbon, carbon nanotubes, or silica sol-gel, onto a suitable substrate (e.g., A1 foil or Cu tape) and bombarded with a laser beam [47,48,60]. 

Besides the typical syntheses of polymer brushes from flat, low-area substrates, STIMP can be conducted from cellulose membranes, carbon nanotubes, and silica or polymeric beads, which has allowed Sl-lMP to be used for synthesis of molecularly imprinted polymers (MIPs) from a variety of supports [76-80]. The use of SI-IMP to fabricate MIPs is particularly advantageous over more common fabrication of MIPs by surface-initiated polymerization from surface-bound conventional initiators because the dithiocarbamyl radicals generated from surface-bound iniferters do not cause polymerization in solution, resulting in improved separation capacity [76-80]. In this section a few examples of fabrication of MIPs synthesized by STIMP from a variety of supports for molecular recognition or separation applications are briefly summarized with a focus on particular advantages enabled by the STIMP method. 

The consequence of UV irradiation is the progressive decrease in the polyethylene viscosity [58]. This essential element must be correlated with the modification of diffusion property of polymer, by which the degradation is significantly accelerated. The type of nanofiller (multi-waUed carbon nanotubes, fumed silica, neat Cloisite and modified Cloisite) influences differently the behavior of pristine HDPE [59]. The increase order of tensile strength measured at Yield point places the contribution of studied nanoparticle phases for the first 100 h of UV exposure describes promotion of a crosslinking process involving the radicals formed by photolysis. 

The aluminum is incorporated in a tetrahedral way into the mesoporous structure, given place to Bronsted acidic sites which are corroborated by FTIR using pyridine as probe molecule. The presence of aluminum reduces the quantity of amorphous carbon produced in the synthesis of carbon nanotubes which does not happen for mesoporous silica impregnated only with iron. It was observed a decrease in thermal stability of MWCNTs due to the presence of more metal particles which help to their earlier oxidation process. 

Nanoporous materials like zeolites and related materials, mesoporous molecular sieves, clays, pillared clays, the majority of silica, alumina, active carbons, titanium dioxides, magnesium oxides, carbon nanotubes and metal-organic frameworks are the most widely studied and applied adsorbents. In the case of crystalline and ordered nanoporous materials such as zeolites and related materials, and mesoporous molecular sieves, their categorization as nanoporous materials are not debated. However, in the case of amorphous porous materials, they possess bigger pores together with pores sized less than 100 nm. Nevertheless, in the majority of cases, the nanoporous component is the most important part of the porosity. 

Many materials exist that have dimensions in the range of 1 rnn to several micrometers. Recall that colloidal particles (e.g., latex particles from emulsion polymerization, colloidal silica or alumina, etc.) fall in the range from about 10 nm to 1000 nm (1 jxm). A few examples of nanoparticles that are designed with more specific structures or geometries include carbon nanotubes, metal clusters, nanoscale magnetic crystals, and semiconducting ... 

Carbon nanotubes (CNTs) currently attract intense interest because of their unique properties which make them suitable for many industrial applications.28 Carbon nanotubes exhibit some of the properties implied in asbestos toxicity. Carbon nanotubes share with asbestos the fibrous habit - long fibers with a diameter of a few nanometers -and a very high biopersistence. On this basis they are suspected to be hazardous and indeed the first studies in vivo14,29,30 have shown an inflammatory response followed by some evolution towards fibrosis. When inhaled, CNTs may thus constitute a possible hazard to human health. The inflammatory and fibrotic responses elicited by CNTs is similar to that caused by other toxic particles which might be the result of oxidative stress caused by particle- and/or cell-derived free radicals. There is no direct experimental evidence of a capacity of carbon nanotubes to generate free radicals similar to silica asbestos and nano sized iron oxide particles. 

There are several reports on the preparation of SiC nanowires in the literature but fewer on the preparation of SisKi nanowires.38-39 The methods employed for the synthesis of SiC nanowires have been varied. Since both SiC and Si3N, are products of the carbothermal reduction of SI02, it should be possible to establish conditions wherein one set of specific conditions favor one over the other. We have been able to prepare SijN nanowires,40 by reacting multiwalled carbon nanotubes produced by ferrocene pyrolysis with ammonia and silica gel at 1360... 

Co-MCM-41 catalyst in H2 at temperatures up to 993 K. It is this intermediate species that preserves the tetrahedral environment in the silica framework and provides the resistance to complete reduction to the metal in the presence of H2. The Co(II) species is resistant to reduction in pure CO the intermediate Co(I) species is more reactive in CO, likely forming cobalt carbonyl-like compounds with high mobility in the MCM-41. These mobile species are the precursors of the metal clusters that grow the carbon nanotubes. Controlling the rates of each step of this two-step reduction process is a key to controlling the sizes of the cobalt metal clusters formed in the cobalt MCM-41 catalysts. 

This paper represents an overview of investigations carried out in carbon nanotube / elastomeric composites with an emphasis on the factors that control their properties. Carbon nanotubes have clearly demonstrated their capability as electrical conductive fillers in nanocomposites and this property has already been commercially exploited in the fabrication of electronic devices. The filler network provides electrical conduction pathways above the percolation threshold. The percolation threshold is reduced when a good dispersion is achieved. Significant increases in stiffness are observed. The enhancement of mechanical properties is much more significant than that imparted by spherical carbon black or silica particles present in the same matrix at a same filler loading, thus highlighting the effect of the high aspect ratio of the nanotubes. 

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