TiO2-based visible-light-sensitive nanomaterials are widely studied for photocatalytic applications under UV-Vis radiation. Among the mechanisms of visible light sensitization, extrinsic oxygen vacancies have been introduced into TiO2 and charge transfer complexes (CTCs) have been formed between chelating ligands, such as acetylacetone, and nanocrystalline TiO2 (TiO2-ACAC). On the other hand, it was found in the literature that nanocrystalline anatasecoupled glutaric acid (TiO2-GA) exhibits high photocatalytic efficiency under UV due to its high surface area. However, the influence of extrinsic oxygen vacancies on the photocatalytic performance of TiO2-based CTCs is unknown and the sensitization of TiO2 to visible light by functionalization with glutaric acid (TiO2-GA) and its photocatalytic performance under visible light radiation have not yet been investigated. In this work, surface/bulk extrinsic oxygen vacancies were introduced into TiO2-ACAC through calcination at 270 °C under static air, Ar and H2 atmospheres and visible-light-sensitive TiO2- GA nanomaterials were synthesized via sol-gel and calcined under static air at 270 °C. TiO2-ACAC and TiO2-GA CTCs were characterized by XRPD, FTIR, TGA, DRS, PL, EPR and XPS techniques. FTIR results proved the formation of the CTC through bidentate chelating interaction between TiO2 and GA. TiO2-GA CTCs calcined at 270 °C under static air exhibited a long absorption tail in the visible light spectrum due to the formation of F+ centers and bulk Ti3+ defects. Tetracycline (TC) photodegradation using scavengers and the correlation with EPR-spin trapping highlighted the key role of the superoxide radical in the TC degradation by TiO2-ACAC and TiO2-GA CTCs under low-power visible light radiation. The increased extrinsic oxygen vacancies concentration was not beneĄcial for photocatalytic performance of TiO2-ACAC CTCs, since bulk extrinsic oxygen vacancies additionally acts as recombination centers. In fact, the TiO2-ACAC CTC with the lowest extrinsic oxygen vacancies concentration exhibited the highest photocatalytic performance for TC degradation due to an adequate distribution of extrinsic bulk oxygen vacancies, which led to the trapped electrons undergoing repeated hopping, reducing the recombination rates and improving the efficiency in the superoxide radicals production. On the other hand, the high content of GA organic molecule ineffectively bounded to the TiO2 surface were not beneĄcial for photocatalytic performance of TiO2-GA CTCs, since the organic molecule that is not effectively bounded to the TiO2 surface reduced the active sites in the TiO2-GA nanostructure. Our Ąndings indicated that TiO2-ACAC and TiO2-GA CTCs are able to degrade pollutants via interactions with electronic holes and principally superoxide radicals and also, provided fundamental information about the influence of surface/bulk extrinsic oxygen vacancies on photocatalytic performance, lattice parameters, optical and photochemical properties of TiO2- based CTCs.