Russian scientists develop an effective technique for making nanoporous carbon materials with predetermined properties and shape. Such materials have a variety of applications: from sorbent for water purification to supercondenser elements and catalyst carriers.

In plain words the essence of the technique is following. Carbide power is soaked with alcohol and given a necessary shape in press. Then future product is “treated with pyrolyzed carbon”. The whole process is not as simple as its description. Raw piece is heated with methane flowing through it. Methane partly splits into hydrogen, which flies away, and carbon, which precipitated on the surface of carbide particles. Then the most interesting part starts.

“Treated” raw piece is heated one more time, but now in chlorine-saturated atmosphere. Chlorine, being very active, “kicks” atoms of carbide-forming elements in the form of highly volatile chlorides out from carbides and leaves the “battle scene”. Carbon is the one who stays.

Needless to say, carbon atoms immediately get together and form complicated structures, some elements of which remind of flat layers, similar to that of graphite, but smaller in size – something like macromolecules. After that future product should once more be annealed – treated with high temperature in an inert gas to prevent burning. All this may cause amorphous carbon to “rearrange” in crystal structures looking the same as abovementioned graphite-like monolayers. And finally the product is ready – a carbon framework, pierced with three types of pores – micro-, meso- and macropores.

While developing this technique, authors used both well-known approaches and their own “know-how”. Researchers performed an enormous work in order to find out how parameters of various technological stages influence product properties and to learn how to control all processes for resulting in a product with wanted properties: porosity, pore size and their distribution, surface area and durability. Moreover, authors had to develop new technology of X-ray crystal structure analysis, since there was no other way to measure parameters of forming nanostructures. Another difficulty was keeping pores open – closed pores are useless for adsorption.

All hard work was behind – and Russian scientists succeeded in developing scientific base for a technology, which allows synthesizing nanoporous carbon materials with predetermined properties and shape – pellets, membranes, tubes, powders and etc. Authors have already tested some items, made of their materials. For instance, scientists found out that nanoporous carbon could purify water from unsymmetrical dimethylhydrazines, highly toxic fuel for rockets. Toxic agent is stuck in pores of nanoporous carbon, and after filtering contaminated water through such carbon material two or three times, toxicity level falls to MPC (maximum permissible concentrations). As for supercondensers (high-capacity electrochemical capacitors), main element – nanoporous electrode – is made from the Russian development.

Source: Russian Science News

Kizilova Anna