Porous carbon materials

Nanoporous materials as a subset of nanostructured materials possess unique surface, structural, and bulk properties that underline their important uses in various fields such as catalysts, hemosorbents, adsorbents for chromatography and gas storage systems, carbon-carbon composite materials, etc. Nanoporous materials are also of scientific and technological importance because of their vast ability to adsorb and interact with atoms, ions and molecules on their large internal surfaces and in the nanometer sized pore space.

Porous carbon materials due to their high sorption activity are widely used in various technological processes of separation in liquid and gaseous media.

Distinctive features of porous carbon materials are high specific adsorption and catalytic activity with sufficient stability in non-oxidative media, the possibility of varying the specific surface in the range 0.1-10³ m²/g and pore size from an angstrom to hundreds of microns, as well as a wide range of forms of the final product, which includes powders, granules, block products, film, fibrous and woven materials.

The large internal surface area and voidvolumes with extremely narrow pore size distributionas well as functional centers homogeneously dispersedover the surface make microporous solids highlyactive materials.

Increasing production volumes and expanding the range of porous carbon materials is facilitated by the fact that any types of carbon-containing raw materials can be used for their production: wood, stone and brown coals, various types of agricultural waste, peat, polymeric materials, liquid and gaseous hydrocarbons, and carbon-containing industrial and household waste.

To obtain porous carbon materials used as adsorbents and catalyst carriers, methods of physical or chemical activation are usually used. The preparation of porous carbon materials using physical activation includes the following steps: preparation of raw materials (separation, crushing, drying, etc.); pyrolysis (heat treatment without oxidizer access at a temperature of 550-1000 ⁰C, activation (heat treatment in the presence of an oxidant, CO2 or water vapor at 700-1000 °C). The production of porous carbon materials by thermochemical activation is based on the introduction of chemical additives into the starting material, followed by carbonization in an inert medium or in the presence of a gaseous oxidant. The transformation of the raw material into a porous carbon material is carried out under the action of acid-base or oxidation-reduction catalysts (ZnCl₂, Al₂O₃, H₃PO₄, carbonates or oxides of alkali metals, etc.). Catalysts activate the transformation of aliphatic fragments, practically without affecting aryl C-C bonds, remove oxygen, hydrogen and other heteroatoms with simultaneous carbonization and activation at temperatures generally below 700 °C. As a result, porous carbon materials with a developed porous structure are obtained.

For effective use of porous carbon materials, knowledge of their structural and texture characteristics, such as the specific surface area, pore volume and size, pore size distribution, is required. There are data on the study of porous carbon materials obtained by chemical modification of various types of natural carbonaceous raw materials: anthracites, brown coals, plant biomass.