Activated carbon

Derived from vegetable or animal materials by roasting in a vacuum furnace. Its porous nature gives it a very high surface area per unit mass, as much as 1,000 m2/g, which is 10 million times the surface area of 1g of water in an open container. Used in adsorption (see definition), activated carbon adsorbs substances that are not or are only slightly adsorbed by other methods.

Source: Handbook of water and wastewater treatment plant operations