Activated charcoal is a highly porous form of carbon with an incredibly large surface area, making it effective at adsorbing substances.
What is Activated Charcoal?
Unlike the charcoal used for grilling, activated charcoal is specifically processed to increase its adsorption capabilities. It is a fine black powder produced from carbon-rich materials such as wood, coconut shells, or peat. Its structure is honeycombed with millions of tiny pores, which is the key to its ability to trap chemicals.
How is Activated Charcoal Prepared?
Activated charcoal is prepared by the process of Carbonization or Calcination, followed by an activation step.
Step-by-Step Preparation
The preparation involves two primary stages:
-
Carbonization or Calcination: This initial step involves burning a carbon-rich source material, such as wood, at a very high temperature (typically between 600°C and 900°C) in an inert atmosphere (without oxygen). This process, as referenced, produces charcoal, which is a nearly pure form of carbon (C). This heating drives off water and volatile compounds, leaving behind a char structure.
-
Activation: Once the charcoal is obtained, it is passed through a variety of chemical or physical processes in order to activate it.
- Physical Activation: The char is exposed to oxidizing gases (like steam, carbon dioxide, or air) at high temperatures (800°C to 1100°C). This etches away the carbon surface, creating and expanding the internal pore network.
- Chemical Activation: The char is impregnated with chemicals (such as phosphoric acid, potassium hydroxide, zinc chloride, or calcium chloride) before carbonization. The material is then heated to lower temperatures (400°C to 900°C). The activating chemicals act as dehydrating agents and pore-enlarging substances, preventing tar formation and creating a highly porous structure during carbonization.
The activation process significantly increases the internal surface area of the charcoal, sometimes exceeding 1,000 square meters per gram, which allows it to effectively adsorb a wide range of molecules.
Key Properties Resulting from Preparation
The specific methods used in carbonization and activation dictate the pore size distribution and overall surface area of the final activated charcoal product, tailoring it for different applications.
