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Activated carbon filter: untangling the true from the false

Activated carbon filter: untangling the true from the false

Our second article on air purification technologies focuses on activated carbon filters. Find out the whole truth about them.

Activated carbon

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).

How does an activated carbon filter work?

The activated carbon filter acts by adsorption, and more precisely by physisorption. This means that certain gases present in the air get lodged in the pores of the coal and. The air leaving the filter is then purified of these adsorbed gases.

Adsorption or absorption?

Adsorption should not be confused with absorption. Absorption is a process by which gas or liquid molecules, when brought into contact with a solid material, become incorporated into its entire volume. Adsorption is when this process only affects the surface of the solid.



Activated carbon filtration is a complex and difficult technology to master. It depends on many factors, hence its effectiveness is often uncertain. *german consumer organisation carrying out comparative tests of products and services on the market.

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