Iron-doped titanium dioxide nanoparticles are widely employed for photocatalytic applications under visible light due to their promising performance. Nevertheless, the manufacturing process, the role of Fe³⁺ ions within the crystal lattice of titanium dioxide, and their impact on operational parameters are still a subject of controversy. Based on these assumptions, the primary objective of this review is to delineate the role of iron, ascertain the optimal quantity, and elucidate its influence on the main photocatalysis parameters, including nanoparticle size, band gap, surface area, anatase–rutile transition, and point of zero charge. Moreover, an optimized synthesis method based on comprehensive data and insights from the existing literature is proposed, focusing exclusively on iron-doped titanium oxide while excluding other dopant variants.

This study focuses on the synthesis of iron-doped TiO₂ nanoparticles “via solid-state” method, as an alternative to the more common doping strategies, with different iron content (0.5, 1.0, 1.5, and 2.0 wt%) using commercial titania Degussa P25 and TiO₂ synthesized (sTiO₂) via microemulsion method. The samples were characterized by SEM, BET, UV–Vis-DRS, and XRD. The photocatalytic activity was evaluated in terms of methylene blue (MB) degradation in aqueous solution under visible radiation (LED lamp 13 W) and under different conditions (pH, catalyst dosage, pollutant initial concentration, irradiance). The tests showed a big difference between sTiO₂ and Degussa 25. The sTiO₂ with an iron load of 1.0 wt% (1% Fe–TiO₂) has been proven to be the best photocatalyst. This behavior is attributed to the Fe³⁺ species in sTiO₂ crystal lattice whose presence decreases the bandgap. Graphical abstract