'Charcoal' briquetts are not pure charcoal. They have other substances added to them to improve flavor, lighting ability, burn time, etc. of your BBQ.
What you want is something called 'activated carbon'. This is actually the same stuff you get at the aquarium supply store to remove chemicals from fishtank water. Bonus, it is fairly inexpensive.
I'm going to stick this thread over in the cultivation section under 'growroom setup'.