In this work, we prepared thin films of titanium dioxide (TiO2) using the atomic layer deposition (ALD) method. We studied the controlled introduction of defects in TiO2 anatase and rutile by low-energy H2+ and Ar+ ion bombardment. Our goal was to modify their chemical, structural, optical, electrical, photocatalytic and other properties. XPS analysis showed that all TiO2 surfaces are reduced under the influence of ion bombardment so that the Ti4+ oxidation state partially reduces to Ti3+ and Ti2+ states. However, the oxide reduction mechanism is different in the case of H2+ and Ar+ bombardment. In addition, the detected states within the band gap of anatase and rutile, which arise due to ion bombardment, indicate the metallization of their surface. SIMS in-depth analysis showed that the Ar+ ion beam significantly etches the surface of the samples, while the film thickness remained unchanged after H2+ bombardment. Additionally, in the case of films modified by hydrogen reduction, a characteristic hydrogen implantation profile is observed in the SIMS depth spectra of both anatase and rutile, in accordance with the TRIM simulations performed as part of this work. GIXRD analysis indicated a possible partial amorphization of the surface layers of anatase and rutile. From the SEM analysis of the modified samples, changes in the surface morphology of anatase and rutile are observed, resulting from the etching of the surface by Ar+ ion beam. In contrast, the H2+ ion beam does not significantly change the surface morphology of anatase, while the formation of protrusions on the grains is observed in the case of rutile. By determining the optical band gap of the samples before and after ion bombardment, we showed that the band gap of both anatase and rutile increases after the modification. By measuring the photocatalytic activity of anatase and rutile films before and after H2+ or Ar+ bombardment, we showed that it significantly decreases in modified samples compared to unmodified ones.