Hydrothermal synthesis of facet-engineered Cu-doped rutile TiO₂ films for photocatalytic decolorization of methylene blue

Cu-doped rutile TiO₂ microstructured films were synthesized through a controlled hydrothermal route to elucidate the influence of Cu incorporation on dopant-induced lattice distortion and facet restructuring, which influence the electronic properties of rutile TiO₂. Increasing Cu incorporation promoted a progressive transformation from aggregated rods toward well-defined flowerlike architectures, accompanied by the preferential exposure of the (111) and (220) facets. XRD, Raman, and HR-TEM analyses revealed lattice expansion and defect formation consistent with Cu²⁺ substitution, thereby narrowing the bandgap from 3.05 to 2.89 eV. UV–vis and kinetic studies showed that the optimized Cu-doped rutile TiO₂ films (1–5 wt% Cu) achieved the highest photogenerated carrier utilization. The 5 wt% Cu-doped TiO₂ film exhibited the highest photocatalytic activity. Kinetic studies showed that the TiO 2 –Cu 5 wt% film achieved a decolorization rate constant approximately 1.2 times that of undoped TiO 2, consistent with the trend of increasing decolorization efficiency across the Cu-doping series. The enhanced photocatalytic decolorization performance may be associated with Cu-induced defect states, facet-dependent electron transport pathways, and possible oxygen-vacancy formation, which may contribute to improved charge separation and reduced electron–hole recombination. These findings establish a clear structure-property relationship between dopant chemistry, facet engineering, and charge-transport behavior in rutile TiO₂, offering a feasible strategy for tuning semiconductor functionality in thin-film electronic and photoactive devices.