In a webinar on activated carbon adsorption, it was mentioned that AC can adsorb organics/complex compounds with several ring formations more easily than the simple/inorganic compounds. Why is that?
Not sure, but probably it is due to the extremely large specific surface area of activated carbons?
Because the affinity by organic compounds combined with the large surface area. The surface of activated carbons contains several organic groups that increase the affinity with certain organic compounds. Generally, the activated carbons are structurally similar to graphite with terminal groups. These groups can generate specific interactions, so, the graphite structure can generate, for example, pi-pi interaction. In a activated carbon, is very interesting measure the acidity and basicity properties, the Boehm method or TPD are a interesting tool for this purpose.
Inorganic compound are generally ionic. The ions have charges, and the surface of activated carbon is more favourable as non-ionic surface for non-ionic physisorption interactions than ionic interactions.
basically it is "Like dissolves like"concept, where the oragnics are more preferred than inorganics onto activated carbons having pure "inert" surface.
you have to be careful with the matter of inorganics being ionic, because, in aqueous solution, the carbon surface functional groups will have charges themselves, negative or positive, depending on the pH of the point of zero charge and on the pH of the solution. Also, the surface may present a diversity of oxygenated and nitrogenated functional groups that will behave differently, depending on the pH of the solution. The charges developed at the surface will facilitate approximation of the adsorbate to the surface groups by Coulomb attraction. The answer to your question is probably more related to the possibility of multilayer adsorption in the case of organics (physisorption), which rarely occurs with inorganics. I would not go as far as generalyzing it that way (the way it was conveyed in the webnar you took).
Adsortion of simple organic compounds on AC is due to superficial groups interactions, but in complex compound with several ring formation pi-pi interactions play a significant role because the AC structure at pore scale is formed by graphene sheets normally