Activated carbon filter: untangling the true from the false

Activated carbon is a material consisting essentially of carbonaceous material with a porous structure. It can be produced from any carbon-rich plant organic matter: wood, bark, coconut shells, etc. Once activated (physically or chemically), the surface area of the activated carbon can reach 400 to 2,000 m².g-1. The coal then retains the molecules of gases and liquids. Therefore, the effectiveness of an activated carbon on gases can depend on the ambient humidity. The pore diameter depends on the method of activation and the pores present in the raw material used. Coconut shells thus give micro-pores ( < 2 nm). Woods can have pores larger than 50 nanometres. To purify the air of polluting gases, activated carbons with pores measuring 1 to 2 nanometres are the most suitable. Activated carbons with different pore diameters will have different gas efficiencies. In general, however, the pore size of activated carbons is not regular, so they are called "unstructured" porous materials. Their behaviour is therefore highly variable depending on volatile organic compounds and ambient conditions (temperature and humidity).