NanoCarbon 2011

This paper is a review of the research on field emission properties of carbon nanotubes (CNTs), the basic properties of CNTs, the main emission properties with highlighting in energy spread and the work done in applying CNTs for field emission microscopy (FEM). In this work there are explanations about the density of states (DOS) of the conduction electrons responsible for the emission; comparison of the characteristics of CNTs emission from single nanotube or films; comparison of the different types of electron sources and the introduction of CNTs electron sources applying in retarding field analyzer (RFA).

Carbon nanocomposites have received more attention in the last years in view of their special properties such as low density, high specific surface area, and thermal and mechanical stability. Taking into account the importance of these materials, many studies aimed at improving the synthesis process have been conducted. However, the presence of impurities could affect significantly the properties of these materials, and the characterisation of these compounds is an important challenge to assure the quality of the new carbon nanocomposites. Thus, in this work are presented the characteristics of carbon nanocomposites, the improvements and developments in the synthesis process, as well as the most used characterisation techniques of these compounds.

This paper describes the synthesis of Ni/MgAl₂O₄ catalysts using a method developed by our group with the objective of obtaining a material with more homogeneous composition, more porous structure and greater surface area compared with other spinel preparation methods. The performance of the material obtained was evaluated in the catalytic decomposition of methane, which is a potential alternative route for obtaining pure hydrogen and valuable carbonaceous materials. The textural properties of the catalyst were investigated by X-ray diffraction (XRD), N₂ adsorption/desorption isotherms (BET and BJH methods), and temperature-programmed reduction (TPR) analysis. The nature of the carbon deposits was investigated by thermogravimetric analysis (TGA), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The influence of the operating conditions on the characteristics of the carbon deposited was studied. The results demonstrated the efficiency of the catalyst in this reaction with the formation of CNTs, irrespective of the operating conditions employed. In general, multiple-walled nanotubes (MWCNTs) were preferentially obtained, and when a diluted flow of CH₄ was used the CNTs presented a greater degree of graphitization.

The interaction between nanostructured materials and living systems is of fundamental and practical interest and will determine the biocompatibility, potential utilities and applications of novel nanomaterials in biological settings. The pursuit of new types of molecular transporters is an active area of research, due to the high impermeability of cell membranes and other biological barriers to foreign substances and the need for intercellular delivery of molecules via cell-penetrating transporter for drug, gene or protein therapeutics. Here, is described the novel nanostructure-based transfection systems. The transfection uses of nanopolymers, nanoparticles and nanotubes are the main focus of this review. In addition are described the technique called NanoSMGT that uses nanostructures for DNA transfection in sperm cells that could be used for transgenic animal generation or human gene therapy.

Nanooncology is based on the use of nanoscale materials to provide tools for cancer detection, prevention, diagnosis and treatment. Due to their unique physical and chemical properties, carbon nanotubes (CNTs) are among newly developed products and are currently of much interest, with a large amount of research dedicated to their novel applications. In cancer research, many advantages of CNTs in drug delivery systems, cellular Imaging, and Cancer Photothermal therapy draw attention. Their physicochemical features enable introduction of several pharmaceutically relevant entities and allow for rational design of novel candidate nanoscale constructs. Thus, a detailed understanding of recent progress in nanooncology, focusing on biomedical research exploring possible application of carbon nanotubes, is required to consider the medical applications of these materials.

Titanium dioxide (TiO₂) is a semiconductor material that is widely used in many different areas, such as gas sensors, air purification, catalysis, solar to electric energy conversion, photoelectrochemical systems and photocatalyst for degrading a wide range of organic pollutants because of its nontoxicity, photochemical stability, and low cost. There are reports that show that the heterojunction of TiO₂ and carbon nanotubes (CNTs) improves the efficiency of the photocatalytic activity, mainly because the recombination of the photogenerated electron–hole pairs becomes more difficult in the presence of nanotubes. Multi-wall carbon nanotubes/TiO₂ (MWCNT/TiO₂) composite materials have been attracting attention in relation to their use in the treatment of contaminated water and air by heterogeneous photocatalysis, hydrogen evolution, CO₂ photo-reduction, and dye sensitized solar cells. Nevertheless, functionalization routes to aggregate these materials and characterization methods need to be studied; since they have direct influence on properties and potential applications.

Vertically aligned carbon nanotubes are bundles of carbon nanotubes that grow perpendicular to a substrate, assembling a bamboo forest. They are dense and orderly arranged, and can be very long. The unique properties of carbon nanotubes along with the ability to produce yarns from these nanotubes forests enable vertically aligned nanotubes to be used in various fields. The most used method to synthesize these nanotubes is the CVD technique. According to the parameters used, carbon nanotubes forests will grow longer or shorter, more or less aligned. This review explores the CVD method used to obtain vertically aligned nanotubes as well as the process parameters that determine the morphology, orientation and growth size of nanotubes and the applications of these materials.

In this chapter, a brief review on three-component composites comprised of a (micro) fibrous reinforcement and a thermoset polymer resin filled with nanoparticles is presented. For this type of composite, carbon nanotubes (CNT) and carbon nanofibers are more commonly used and the focus usually lies on resin-dominated properties, such as interlaminar shear strength, and interlaminar fracture toughness. Many three-component systems comprised of fiber/epoxy/CNT have been produced using resin transfer molding (RTM) or VARTM. However, there are major difficulties associated with the impregnation of a dry fibrous reinforcement using a highly viscous suspension of resin/nanofiller, especially for high content of nanofillers or highly packed fibrous systems. In such harsh circumstances, an alternative and recent approach to enable processing comprises the production/use of three-component prepregs containing nanofillers, although they are usually associated with high cost. The presented case study focused on an alternative route to produce glass-fiber composites with high content of CNT via RTM. A practical, low-cost and effective methodology for the direct deposition of an acetone/CNT/epoxy suspension on glass-fiber cloths was developed, achieving up to 4.15 % wt. in overall CNT content in the composite. The mechanical properties of the composites produced with non-functionalized CNT increased, in general, up to 10 % compared to the reference epoxy/glass-fiber composite. However, the high CNT content obtained was of uttermost importance for the development of electromagnetic characteristics on the material, absorbing much of the radiation in the microwave frequency range. The reflectivity properties reached a maximum of approximately - 14 dB (c.a. 95 % of electromagnetic absorption) and this excellent performance was obtained using a comparatively low cost (glass fiber) and thin (»2.2 mm) polymer composite material. Thus, the developed composites showed great potential to be used as microwave-absorption materials, replacing conventional ones employed for this aim. With further improvement in the manufacturing process, these materials could become of interest as high performance composites in a wide range of engineering applications, from telecommunications to aerospace.