Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that greatly increase the surface area[1][2] available for adsorption or chemical reactions[3] that can be thought of as a microscopic "sponge" structure. (Adsorption, not to be confused with absorption, is a process where atoms or molecules adhere to a surface). Activation is analogous to making popcorn from dried corn kernels: popcorn is light, fluffy, and its kernels have a high surface-area-to-volume ratio. Activated is sometimes replaced by active. Because it is so porous on a microscopic scale, one gram of activated carbon has a surface area of over 3, 000 square metres (32, 000 square feet), [1][2][4] as determined by gas adsorption.[1][2][5] For charcoal, the equivalent figure before activation is about 2–5 square metres.[6][7] A useful activation level may be obtained solely from high surface area. Further chemical treatment often enhances adsorption properties. Activated carbon is usually derived from waste products such as coconut husks; waste from paper mills has been studied as a source.[8] These bulk sources are converted into charcoal before being activated. When derived from coal, [1][2] it is referred to as activated coal. Activated coke is derived from coke. Uses[edit] Activated carbon is used in methane and hydrogen storage, [1][2] air purification, [9] capacitive deionization, supercapacitive swing adsorption, solvent recovery, decaffeination, gold purification, metal extraction, water purification, medicine, sewage treatment, air filters in respirators, filters in compressed air, teeth whitening, production of hydrogen chloride, edible electronics, [10] and many other applications. Industrial[edit] One major industrial application involves use of activated carbon in metal finishing for purification of electroplating solutions. For example, it is the main purification technique for removing organic impurities from bright nickel plating solutions. A variety of organic chemicals are added to plating solutions for improving their deposit qualities and for enhancing properties like brightness, smoothness, ductility, etc. Due to passage of direct current and electrolytic reactions of anodic oxidation and cathodic reduction, organic additives generate unwanted breakdown products in solution. Their excessive build up can adversely affect plating quality and physical properties of deposited metal. Activated carbon treatment removes such impurities and restores plating performance to the desired level.