What is activated charcoal?

We put the question to University of Texas chemist Kate Biberdorf, who let Chris Smith in on the answer...

Kate - So activated charcoal is essentially a chunk of carbon, which is just what charcoal is, that has been ground up to a really fine powder. And so when we throw the word activated on it, it just means that it has a lot of surface area. So for example, 1 gram of activated carbon has a surface area of around 3000 metres squared, or for Americans 32,000 square feet. So it's a lot, it's a huge surface area. And so when you use activated carbon like a filter, which is what we do when we try to purify water, it acts exactly like a face mask does - it lets the small molecules go through, like oxygen when we're breathing or in this case water, but the big, bad molecules or the bad pollutants can't go through the face mask and they can't go through the filter. And so your clean little water molecules go through the bottom, but the bigger molecules or those pollutants - things we're trying to filter out - get trapped in the pores of the carbon and they get kind of stuck there, and so it's a really beautiful way to purify water and I'm a big fan.

Chris - So it's not a chemical trick, it's not doing any additional novel chemistry, it's just a structural trick. It's like a fine grain filter with a big surface area.

Kate - Yeah, that is exactly what it is. Now, there are going to be people who are moth chemists or PCM chemists who are going to argue with that because there can be some adhesive properties that happen. And depending on the molecules you can spike it with, you can take this in a whole different direction. But pure, plain, activated carbon is just carbon that's going to trap bigger molecules, that's it.