# How does activated carbon bind the adsorbate?

I read some articles and journals about activated carbon and found a problem about how the adsorbate could bind to the activated carbon. Some said it is because of intramolecular forces (van der Waals) and some said it is because of chemisorption. If chemisorption plays a role, what would the bonding be? And if the bonding is just caused by intramolecular forces, what is the active site of the activated carbon? An answer or illustration for better understanding is greatly appreciated.

## 2 Answers

Activated carbon works by enlarging the surface area of elemental carbon. Activated carbon can reach surface areas of several hundred square meters to several thousand square meters per gram. Also elemental carbon is fairly non reactive, non toxic and cheap.

As seen in the picture, activated carbon forms a micro structure with incredibly small pores, so that many molecules can be adsorbed (the forces involved decrease with a factor $1/r^{6}$ with distance). The adsorption itself is an application of the London dispersion force (one of the Van der Waals forces).

I don't believe chemisorption has anything to do with this.

Chemisorption means chemical reaction occurs during absorption process, and any bond type other than intermolecular forces (dipole-dipole, H-bond, Van Der Waals) is possible. Activated carbon absorb using intermolecular forces, and I do not think it is chemisorption. The absorption is strong because the surface area is huge, not because of any real chemical bonds.

• So what inter-molecular force is responsible? And why carbon and not sulfur for example? I think if you discuss these points too, this would greatly improve your answer. – Jori May 25 '14 at 9:33
• Not all solid can have such a big surface area like activated carbon. Sulfur for example as find powder do absorb but it is reactive, and not as cheap as activate carbon. If you do a search, there are a lot of physical absorbent that utilize intermolecular forces to absorb. Activated carbon is just the most commonly used one. – Ian Fang May 29 '14 at 2:33