Effects of surface oxygen functional groups on activated carbon on the adsorption and photocatalytic degradation activities of a TiO₂-AC hybrid for methylene blue and methylene orange

A series of activated carbons (AC) with different amounts of surface oxygen functional groups was obtained by nitric acid oxidation and heat treatment at different temperatures, and these were used as supports for a TiO₂ photocatalyst. The nature and number of the surface oxygen functional groups were determined by Boehm titration. The pore texture and morphology of the ACs and the TiO₂-AC hybrid were characterized by nitrogen adsorption and scanning electron microscopy. The adsorption and photocatalytic activity of the material under ultraviolet light irradiation were investigated using methylene blue (MB, cation dye) and methylene orange (MO, anion dye) as the model compounds. Results show that the oxidation and heat treatment change the surface oxygen functional groups much more than they do the pore texture. The surface oxygen functional groups, especially the surface carboxylic acid, control the adsorption and photocatalytic activities for MB and MO over the TiO₂-AC hybrid. The surface oxygen functional groups have a much greater influence on MB degradation than that on MO. The photocatalytic degradation activity for MB decreases at all heat treatment temperatures while that for MO is increased by heat treatment at 250℃.