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Nanotubes in real life

New applications for carbon nanodevices are generated in Ribeirão Preto

Photos José Maurício Rosolen/USP Felt, electric conductor, on the left, and examples of nanotubes and carbon compositesPhotos José Maurício Rosolen/USP

Nanotechnology has become an extensive field of study all over the world and carbon nanotubes are among the major exponents of this field. Electronic engineering and industrial chemistry are the most promising areas for the use of these devices, as attested to by the work of a group of researchers from the Chemistry Department at the School of Philosophy, Sciences and Literature in Ribeirão Preto, the University of São Paulo (USP). These researchers developed nanomaterials to produce more efficient lithium ion batteries to be used in electric cars; for sophisticated filters with the capacity to retain hazardous toxic gases and volatile composites; and for sensors to detect glucose levels in blood. The nanometric-scale material developed by the researchers – one nanometer corresponds to one millimeter divided by one million – is a composite formed of carbon nanotubes, a carbon atom sheet rolled like a tube, grown on carbon felt – the higher substrate – on a micromere scale, available commercially and manufactured from commercial polymers such as polyacrylonitrile and polyamide.

The nanomaterial is scheduled for production this year on a post-laboratory scale at a pilot plant in the process of being built at the university. In addition to the possibility of new technological applications, the research project headed by physicist and USP professor José Maurício Rosolen, in partnership with chemist Elaine Yoshiko Matsubara, has led to two patent requests filed with the National Industrial Property Institute (INPI) and to a number of scientific articles published in international scientific journals. The development of composites – a product characterized as being comprised of two or more materials – within the scope of nanotechnology normally includes a nanotube as one of the components. The researchers from Ribeirão Preto used these devices, grown over special felt, an electronic conductor substrate similar to traditional felt, except that it is made of carbon instead of cotton or synthetic fibers. This was the solution found by the researchers to overcome the existing limitations and difficulties related to the use of carbon nanotubes on a large industrial scale.

According to Rosolen, the problem in using nanotubes is the difficulty in handling these products, which normally come in powder form, together with other materials, and control the compacting or agglomeration which occurs at random. “The carbon nanotubes interact with each other, forming beams and agglomerates with properties that differ from the original properties. This situation may lead to problems related to the reproduction of devices and materials in the industrial scope, whose properties depend on the agglomeration or dispersion of the nanotubes, such as capacitors, sensors, filters, electrodes, and batteries,” says Rosolen.

By incorporating the nanotubes in a carbon felt substrate, the researchers were able to assemble pre-established geometries, thus avoiding the problems found in particulate matter. In addition, micrometric devices are easier to be manipulated and it is simpler to mix them with other materials. “We created a new material, but we maintained all the potential of the carbon nanotubes,” says the physicist from USP. The composite is in the shape of a blanket or cloth, with these devices impregnated on the surface. This characteristic reduces the risk of the nanotubes being inhaled by researchers and workers that handle them in powder form. One of the most advanced applications of this new material is for the manufacturing of industrial filters and masks. In the first case, the composite can be used to manufacture filters for air conditioning equipment installed in automotive vehicles. In addition, this filter can retain the toxic gases released into the air through the vehicles’ exhaust pipe. “The filters on the market prevent drivers from inhaling the fine particles emitted by automobiles, but they do not retain various toxic gases of molecular dimensions,” says Rosolen.

Cigarette filter
This nanomaterial can also be used in the manufacturing of individual protection masks to keep out toxic organic solvents released by certain industrial processes. Likewise, the material can be useful as a nicotine filter in cigarettes. The first patent obtained by the researcher is related to the development of filters for volatile organic composites and for nicotine. The second patent is related to the production of carbon composites and carbon nanotubes with hydrophilic surface (which interacts with water); these composites and nanotubes are well-dispersed in aqueous mediums. As such, they could be used for the manufacturing of pigments for water-based paints. The nanomaterial created at the USP laboratories also opens up interesting perspectives for the manufacturing of big lithium ion batteries, lighter than the existing ones, to equip electric vehicles. “As our compound is a good electronic conductor, battery manufacturers would not have to use huge quantities of aluminum sheets and mesh, which make the batteries very heavy,” he explains. By reducing the weight of the device, it would also be possible to manufacture electric cars equipped with longer-lasting batteries to achieve higher autonomy. “Several big companies have already shown interest in the battery-producing technology and in the use of this material to manufacture filters. We are talking to these companies,” says Rosolen. Another promising application for the carbon nanotube composite is the manufacturing of amperometric sensors. Studies conducted together with professor Susana Inês Cordoba Torresi, from the Chemistry Institute of USP/ São Paulo, have demonstrated that the composite allows for the production of highly sensitive sensors capable of detecting glucose in a sodium and potassium medium. “The device proved to be highly sensitive, with speedy response time, within a much broader concentration band than that of conventional sensors,” says Rosolen.

The Projects
1. Carbon Nanotechnology applied to the development of sensors, photovoltaic cells, pseudo capacitors, and polymer composites (nº 04/07085-2); Modality Regular Research Awards; Coordinator
José Maurício Rosolen – USP; Investment R$ 174,124.21 and US$ 18,558.95 (FAPESP)
2. Carbon nanotube composite and carbon felt (nº 06/06129-1); Modality Support Program for Intellectual Property; Coordinator
José Maurício Rosolen – USP; Investment R$ 6,000.00 (FAPESP)

Scientific articles
ROSOLEN, J. M. et al. Electron field emission of carbon nanotubes on carbon felt. Chemical Physics Letters. v. 424, p.151-55. 2006.
ROSOLEN, J. M. et al. Carbon nanotube/felt composite electrodes without polymer binders. Journal of Power Sources. v. 162, p. 620-28. 2006.