Chemistry - Why is Charcoal such an excellent adsorbent?

Solution 1:

Activated charcoal is a great adsorbent because of it's huge surface area. While it doesn't bind very many ions/atoms/molecules per surface area (which is the characteristic of a 'good' adsorbent), due to very big surface area per unit of mass it can adsorb a lot of particles. Actually, process of 'activating' charcoal is designed to maximize the surface area to mass ratio.

Solution 2:

Charcoal isn't a particularly good adsorbent even though it is chemically very similar to activated carbon.

Activated carbon is usually made by more specialised processes that guarantee the final product will have a very large surface area (often >1,000m2/g). Manufacture usually involves pyrolysation with hot gasses, but many forms are also further activated by partially oxidising the surface (using gas containing oxygen) or bay adding chemicals such as phosphoric acid or potassium hydroxide before pyrolysis. These activation reactions create some functional groups on the surface that can enhance specific types of adsorption on the surface.

But the primary feature that matters is the high surface area, which normal methods for making charcoal do not achieve.

Solution 3:

I see three reasons:

  • Activated carbon is commonly used to adsorb organics, that should bind well on coal.

  • For many purposes, activated carbon is treated with potassium or iodine to provide ions for charged centers.

  • Charring organic stuff is a cheap and easy way to create large surfaces for adsorption.

Solution 4:

Charcoal is a good absorbent because its quite selective and cheap. Its high surface area means nothing if it doesn't bond to the components that you want absorbed and not a lot else- witness a household sponge which has high surface area and mercury- the mercury just slides off. Charcoal is used in the gold mining/processing industry. The gold(and other metals) is oxidised to form cyanide complexes. The charcoal mostly only absorbs the cyanide complexes not all the other rubbish and water. Charcoal wouldn't be much good for the water purification industry if it absorbed water. Charcoal absorbation processes are a multitudinous- its thousands of papers of primary metallurgy(gold).