The photocatalytic features of TiO2 doped with ferric oxides or mixed with activated carbon (AC-TiO2) are compared with those of the unmodified Degussa P-25 TiO2. These new catalysts show specific structural features that alter catechol and resorcinot photo-degradabilities, according to their chemical structures. For instance, we have observed that Fe oxides located on the TiO2 particle surface hamper these dihydroxybenzenes degradation. Likewise, AC-TiO2 catalysts have shown improved catechol photodegradability with respect to that of TiO2, while that of resorcinol is not altered. These studies show that catechol and resorcinol adsorption patterns are different, i.e., they have different adsorption centres on the catalyst surface and are differently affected by photonic flux variations.