Ni-Modified Monolithic Dual-Interface TiO2 Nanotube Arrays for Enhanced Photocatalytic Degradation

TiO 2 -based photocatalysts are often constrained by inefficient charge utilization during the degradation of refractory organic pollutants. Their activity can be improved by promoting charge separation through phase junction construction and defect engineering. In this study, anatase/rutile (A/R) heterojunctions with controlled phase composition were fabricated by calcining anodic TiO 2 nanotube arrays, followed by Ni 2+ incorporation via electrodeposition to modulate the interfacial electronic structure. XRD and XPS results indicated that Ni introduction increases the oxygen vacancy concentration. Under UV irradiation, the optimized A/R-TiO 2 achieved 89.56% degradation of methylene blue within 3 h, corresponding to an apparent rate constant of 0.01057 min -1 . After Ni 2+ modification, the degradation efficiency and rate constant were further improved to 94% and 0.01561 min -1 , respectively. Transient photocurrent measurements showed the highest photo-response for the Ni 2+ -modified A/R-TiO 2 , indicating more efficient charge separation and transfer. DFT calculations revealed that Ni 2+ introduced defect states near the conduction band, facilitating electron trapping and enabling stepwise charge transfer across the A/R interface rather than forming a metallic Schottky junction. This work provides fundamental insight into charge-transfer behavior in TiO 2 heterojunctions and presents a practical design strategy for high-performance photocatalysts targeting refractory pollutants. • Ni 2+ -modified A/R TiO 2 nanotubes show enhanced methylene blue degradation. • Controlled A/R heterojunctions and Ni 2+ defects improve charge separation. • Ni 2+ defect states enable electron trapping without forming Schottky junctions. • Optimized photocatalysts achieved 94% MB degradation under UV irradiation. • Experiments and DFT reveal interfacial charge-transfer mechanisms.