Activated carbon is carbon produced from carbonaceous source materials such as bamboo, coconut husk, willow peat, wood, coir, lignite, coal, and petroleum pitch. It can be produced (activated) by one of the following processes:
1. Physical activation: The source material is developed into activated carbon using hot gases. Air is then introduced to burn out the gasses, creating a graded, screened and de-dusted form of activated carbon. This is generally done by using one or more of the following processes:
Carbonization: Material with carbon content is pyrolyzed at temperatures in the range 600–900 °C, usually in an inert atmosphere with gases such as argon or nitrogen
Activation/oxidation: Raw material or carbonized material is exposed to oxidizing atmospheres (oxygen or steam) at temperatures above 250 °C, usually in the temperature range of 600–1200 °C. The activation is performed by heating the sample for 1 h in a muffle furnace at 450 °C in the presence of air.
2. Chemical activation: The carbon material is impregnated with certain chemicals. The chemical is typically an acid, strong base, or a salt (phosphoric acid 25%, potassium hydroxide 5%, sodium hydroxide 5%, potassium carbonate 5%, calcium chloride 25%, and zinc chloride 25%). The carbon is then subjected to high temperatures (250–600 °C). It is believed that the temperature activates the carbon at this stage by forcing the material to open up and have more microscopic pores. Chemical activation is preferred to physical activation owing to the lower temperatures, better quality consistency, and shorter time needed for activating the material.