gh NANOPOROUS CARBON – TO BE PRODUCED AND USED

Researchers have to invent surprising technologies to produce a nanoporopus carbonic material with predetermined pore size. But, if they succeed – and specialists of the legendary St. Petersburg A.F.Ioffe Applied-Physics Institutes, Russian Academy of Sciences, manage to do that successfully – there will be a lot of enthusiasts for applying this remarkable nanoporous material because its capabilities are very extensive, if not unlimited. It can help to remove supertoxicants from water, or supercondensers can be made based on this material. At that, the prefix “super” is meaningful in both cases.

The essence of the method is as follows if described in a very simplified way. Carbide powder is moistened by spirits and compressed to impart the necessary shape to the future articles. Then, it is “impregnated with pyrocarbon”. These words imply a rather complicated process, in the course of which the half-finished product gets heavily heated, the methane natural gas is being passed through the half-finished product. Part of methane is decomposed into hydrogen, which naturally flies away, and carbon, which precipitates on the surface of the carbide particles. But this is only the beginning. The worst and the most interesting is still to come.

The “impregnated” half-finished product is heated once again, but this time – in the chlorine atmosphere. More active chlorine literally “pushes out” from carbides the carbide former atoms in the form of their volatile chlorides and leaves the scene of action thus leaving the reaction sphere. But carbon remains.

Of course, carbon atoms immediately assemble together forming a rather complicated structures, individual components of which resemble plain layers likewise in graphite but only of a smaller size – these are macromolecules. After that the article can be annealled once again – it is kept at a high temperature but this time in the inert gas atmosphere to avoid burning down. At that, amorphous carbon has a chance to “re-form” into crystal structures in the form of the same monolayers similar to graphite. As a result, the entire article constitutes a carbonic framework penetrated by pore of three kinds: micro-, meso- and macro-pores.

When developing the method, the authors used both well-known approaches and their own know-how. Neither published articles nor patents generally contain fine points, which enable to implement chemical reactions written on paper. Therefore, in the course of work, the researchers had to carry out enormous investigation work in order to find out how parameters of certain technological stages influence the product properties and to learn how to manage the process to get the product with required properties at the output: porosity, pore size and pore distribution, specific surface area and strength-to-weigth ratio. Besides, the authors even had to develop new methods for X-ray structure analysis to determine parameters of resulting nanostructures. On top of that, the process should be performed in such a way that the predetermined quantity of pores remained “open” – the closed pores are unfit for adsorption.

In the end, the researchers managed to develop scientific foundations of technology, which enables to get nanoporous carbonic materials with predetermined properties and of preset shape – tablets, membranes, pipes, powders and so on. The authors have already tested capabilities of some types of articles made of similar materials. For example, they have found out that nanoporous carbon enables to purify water from admixtures asymmetric dimethylhydrazins – extremely toxic rocket propellant. The toxicant is sorbed in the nanoporous carbon pores. If contaminated water is passed through them for two or three times, it can be purified at least to the maximum allowable concentration level. As for supercondensers (electrochemical high-value capacitors), their most important part is nanoporous electrode made of carbon with highly developed surface.

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