Preparation and photocatalytic properties of La ³⁺ -CDs modified TiO ₂ nanotubes

La 3+ -CDs modified TiO 2 nanotubes were prepared using a combination of anodisation, electrochemistry and electrophoresis. Their phase structure, morphology and light absorption properties were characterised using XRD, SEM, UV-Vis, EDS, XPS and PL, and photocatalytic degradation experiments were conducted on methylene blue and phenol. The results indicate that La 3+ -CDs modification inhibits the transformation of the anatase phase into the rutile phase. The diameter of the La 3+ -CDs modified TiO 2 nanotubes ranged between 60 and 80 nm, with La and C distributed uniformly within the nanotubes. The La 3+ -CDs modification did not cause a change in the valence state of Ti 4+ , and La existed in the form of La 3+ . La 3+ -CDs modification caused a significant red shift in the light absorption peak of the TiO 2 nanotubes, broadened their light absorption range, and suppressed the recombination of photo-generated carriers. When the CDs composite concentration was 0.1 mg/mL and the La 3+ doping concentration was 0.005 mol/L, the red shift of the light absorption band edge was most pronounced, and the bandgap width decreased to a minimum of 2.89 eV. As the concentration of CDs or the La 3+ doping concentration increased, the degradation rate of methylene blue by the TiO 2 nanotubes first increased and then decreased. When the concentration of CDs was 0.1 mg/mL and the La 3+ doping concentration was 0.005 mol/L, the photocatalytic activity of the TiO 2 nanotubes was optimal, with a degradation rate of up to 93.61% after 8 hours, representing an increase of approximately 58% compared to pure TiO 2 nanotubes. Hydroxyl radicals were identified as the primary active species in the photocatalytic reaction. Furthermore, this sample achieved a phenol degradation rate of 89.92% after 8 hours. After three cycles of reuse, the sample with a CDs composite concentration of 0.1 mg/mL and a La 3+ doping concentration of 0.005 mol/L still exhibited a degradation rate of over 90% for methylene blue, indicating that the catalyst prepared in this study possesses both high catalytic activity and high stability.