Why is Charcoal such an excellent adsorbent? Charcoal (also activated charcoal) is known to adsorb a huge variety of substances including a variety of paints, dyes and many different kinds of ions. Moreover, the amount of adsorption at normal pressure and temperature is high. I know physisorption requires high capacity of Van-der-waal bonding with the adsorbate which is favoured by surface atoms with large, easily-dispersed electron clouds and chemisorption requires actual chemical bond formation which requires highly reactive surface atoms. Charged species get adsorbed to form a double layer when the surface is charged, either due to ionization or due to polarity.  


  But charcoal possesses none of the structural specialities required to
  be a great adsorbent. Neither it has charged centres (unlike colloidal
  proteins, or metal sols) nor it has a very high reactivity (Charcoal
  is almost the final product of combustion of wood, bone, sugar etc and
  is supposed to be immune to further oxidation even at considerable
  temperature). Why is it then an excellent adsorbent?
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.