Heterogeneous photocatalysis is one of the most versatile and widely studied photochemical approaches for the degradation of recalcitrant pollutants. Owing to its favorable physicochemical properties, titanium dioxide (TiO2) remains one of the most investigated semiconductor photocatalysts. However, its wide band-gap energy (3.2 eV) restricts its photoactivity to the UV region, which represents only a small fraction of the solar spectrum. A major challenge in this field is therefore the development of TiO2-based materials capable of operating efficiently under visible light irradiation, enabling the use of solar energy as a sustainable primary source. Several strategies have been explored to extend the optical response of TiO2, among which elemental doping remains one of the most effective and commonly applied. In this work, we conducted systematic comparative analysis to evaluate the photocatalytic performance of TiO2 modified through different doping approaches. Sixty-one scientific reports published between 2015 and 2025 were analyzed, comparing three categories of dopants: (i) metal dopants, (ii) non-metal dopants, and (iii) co-doping systems. In the first section, we discuss fundamental concepts of photocatalysis and recent advances in doping strategies and surface modifications aimed at enhancing the photocatalytic performance of TiO2. In the second section, we present a comparative analysis based on 61 scientific reports focusing on TiO2 doping and co-doping processes. Finally, this study summarizes the different categories of doped TiO2 photocatalysts by comparing the photocatalytic performance employing an alternative performance metric.
Vallejo et al. (Thu,) studied this question.