Carbon filtering is a method of filtering that uses a piece of activated carbon to remove contaminants and impurities, utilizing chemical adsorption. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. When certain chemicals pass next to the carbon surface, they attach to the surface and are trapped.
Each piece of carbon is designed to provide a large section of surface area, in order to allow contaminants the most possible exposure to the filter media. One pound (454g) of activated carbon contains a surface area of approximately 100 acres (1 km/kg). This carbon is generally activated with a positive charge and is designed to attract negatively charged water contaminants. Carbon filtering is commonly used for water purification, but is also used in air purifiers.
There are two predominant types of carbon filters used in the filtration industry: powdered block filters and granular activated filters.
Activated Carbon
Activated carbon, also called activated charcoal or activated coal, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions. The word activated in the name is sometimes substituted by active. Due to its high degree of microporosity, just one gram of activated carbon has a surface area in excess of 500 m (or about 2 tennis courts), as determined typically by nitrogen gas adsorption. Sufficient activation for useful applications may come solely from the high surface area, though further chemical treatment often enhances the adsorbing properties of the material. Activated carbon is usually derived from charcoal. Properties of activated carbon include:
Has a capacity for virtually any vapor contaminant; it will adsorb some of almost any vapor.
Has a large capacity for organic molecules, especially solvents.
Will adsorb and retain a wide variety of chemicals at the same time.
Has an extremely large capacity to catalytically destroy ozone, a major component of smog.
Works well under a wide range of temperature and humidity conditions.
Adsorbs odors and chemicals preferentially to moisture. It is not a desiccant and will release moisture to adsorb chemicals.
Can be used as a carrier of one material to attract and hold or react with another material.
Is inert and safe to handle and use.