TiO2 Nanoparticles with Mixed Anatase–Rutile Phase Structure Doped with Different Concentrations of Iron for Photocatalytic Activity in Degrading Methylene Blue

The photodegradation of Fe-doped anatase-rutile mixed-phase TiO₂ nanoparticles (NPs) under visible light to degrade methylene blue has been studied. TiO₂ NPs were successfully synthesized using the co-precipitation method. These nanoparticles were characterized using XRD, UV–Vis, FTIR, FESEM, HRTEM, and EDX. The XRD analysis revealed that the diffraction patterns exhibited two-phase structures, namely, anatase and rutile phase structures, where the intensity of the rutile phase structures was greater than that of the anatase phase structures. The UV–Vis result indicated a reduction of the band-gap energy of the Fe-TiO₂ NPs. FESEM micrographs revealed that agglomerations formed clusters, and SEM results showed that the nanoparticles aggregate to create surface structures resembling edelweiss flowers. Based on Kramers–Kronig analysis, there is a reduction in optical phonon \((\Delta ({\text{LO}} - {\text{TO}}))\) cm⁻¹ difference with a decrease in the rutile fraction as a function of Fe. The reduction in the rutile phase fraction correlated with a decrease in photocatalytic activity, indicating that the rutile phase plays a crucial role in the photodegradation process (1wt% achieved. \(k\)_ads rate: 0.00273 min⁻¹). These results suggest that Fe-doped anatase–rutile mixed-phase TiO₂ nanoparticles are suitable as photocatalysts.