In this work, we study the effect of doping depth profile on the photocatalytic and surface properties of TiO₂ films. Two thin film layers of TiO₂ (200 nm) and Co (5 nm), respectively, were deposited by physical evaporation on glass substrate. These films were annealed for 1 s at 100 and 400 °C and the Co layer was removed by chemical etching. Atomic force microscopy (AFM) phase images showed changes in the surface in function of thermal treatment. The grazing-incidence X-ray fluorescence (GIXRF) measurements indicated that the thermal treatment caused migration of Co atoms to below the surface, the depths found were between 19 and 29 nm. The contact angle showed distinct values in function of the doped profile or Co surface concentration. The UV–vis spectra presented a red shift with the increasing of thermal treatment. Photocatalytical assays were performed by methylene blue discoloration and the higher activity was found for TiO₂–Co treated at 400 °C, the ESI-MS showed the fragments formed during the methylene blue decomposition.