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 available for adsorption or chemical reactions that can be thought of as a microscopic "sponge" structure.. 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.
Activated carbon
Activated charcoal for medical use
A micrograph of activated charcoal (R 1) under bright field illumination on a light microscope. Notice the fractal-like shape of the particles hinting at their enormous surface area. Each particle in this image, despite being only around 0.1 mm across, can have a surface area of several square centimetres. The entire image covers a region of approximately 1.1 by 0.7 mm, and the full resolution version is at a scale of 6.236 pixels/μm.
A micrograph of activated charcoal (GAC) under a scanning electron microscope
Carbon is a chemical element; it has symbol C and atomic number 6. It is nonmetallic and tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 electrons. It belongs to group 14 of the periodic table. Carbon makes up about 0.025 percent of Earth's crust. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.
Graphite (left) and diamond (right), two allotropes of carbon
A large sample of glassy carbon
Comet C/2014 Q2 (Lovejoy) surrounded by glowing carbon vapor
Graphite ore, shown with a penny for scale