pH-dependent adsorption and desorption of phenol and aniline on basic activated carbon

The interaction of phenol and aniline with the surface of highly microporous ash-free carbon was systematically studied in aqueous solutions in the pH range 3–11 under oxic conditions. The irreversible acid/base response obtained by continuous cyclic titration in a CO2-free medium can be governed by porosity-controlled diffusion, multi-step surface reactions involving oxygen trapped in the micropores, or incomplete equilibrium. Phenol and aniline are adsorbed most strongly in unbuffered conditions. Due to competitive adsorption of water and the buffer ions only part of the surface area is utilized. According to thermal desorption measurements, physisorption takes place in the whole pH range studied. Chemisorption was detected only when electrostatic interaction is possible. Thermal desorption removes only part of the adsorbed species, leaving behind a morphologically and chemically modified surface.