A single gram of activated carbon can hide 3,000 square metres of surface
Ordinary charcoal offers just a few square metres of surface per gram. Activation riddles it with microscopic pores, a bit like popping corn, until one gram exposes more than 3,000 square metres for molecules to cling to. That vast hidden area is why the black powder cleans water, air, vodka and more.
The key process is adsorption, where atoms or molecules stick to a surface rather than soaking into a material. Before activation, charcoal has roughly 2 to 5 square metres of area per gram. Treating it with steam or carbon dioxide at high temperature, or with chemicals, opens a sponge-like network of tiny pores. Researchers at Cornell University produced a version measuring 4,800 square metres per gram, the highest figure reported for the material. Much of the raw feedstock is agricultural waste such as coconut husks, olive stones and nutshells, first turned into charcoal and then activated.
Its uses are strikingly varied: decaffeination, gold purification, respirator filters, radon measurement and stripping impurities from nickel plating baths. Nuclear boiling water reactors pass air through large charcoal beds that hold radioactive gases until they decay into harmless solids. Filtering an impure vodka through it at the right rate leaves the alcohol content unchanged while removing compounds that spoil its smell and taste. Organic winemakers may use it to pull brown pigments from white grape concentrates.
Some applications create headaches of their own. Carbon laced with sulfur or iodine traps mercury from coal-fired power stations, but in the United States spent material above 260 parts per million of mercury is barred from landfill and piles up in warehouses and old mines at an estimated 100 tons a year. The Netherlands instead recovers most of the mercury and burns the carbon. In the 1970s, a proposed US rule requiring drinking water plants to use granular activated carbon was abandoned after utilities objected to the cost.
In medicine it features on the World Health Organization's essential medicines list for certain swallowed poisons, yet it does nothing against many substances, including cyanide, iron, lithium and alcohols, and it shows no effect on intestinal gas despite being sold for it. Food-grade charcoal became a trend in 2016, blackening ice cream and bagels, prompting warnings that it can stop medicines such as birth control pills from working.
Source: Activated carbon
