Porphyrin-Functionalized Titanate Nanotubes: Tuning Charge Separation for Highly Efficient Photocatalytic Activity

Addressing the urgent need for advanced photocatalytic systems in dye wastewater remediation, this study reports the synthesis of a titanate nanotube/tetrakis (hydroxyphenyl) porphyrin (TNT/TCPP) heterostructure through hydrothermal growth coupled with surface functionalization. Comprehensive structural analyses utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) demonstrate the successful integration of TCPP molecules onto the tubular TNT framework while preserving crystalline integrity. X-ray photoelectron spectroscopy (XPS) reveals noncovalent interfacial coupling between the components. The TNT/TCPP-2 sample exhibits remarkable visible-light-driven photocatalytic activity, showing a 35-fold higher degradation efficiency (k = 0.01011 min–1) for rose red dye compared to bare TNT. A systematic investigation of charge dynamics identifies two synergistic pathways: (i) enhanced separation of photogenerated electron–hole pairs at the organic–inorganic interface, and (ii) prolonged radical generation via continuous production of hydroxyl (•OH) and superoxide (•O2–) species. Electrochemical impedance spectroscopy corroborates improved charge carrier density and interfacial charge transfer efficiency. Intriguingly, TCPP loading exhibits a volcanic-type activity trend, with optimal performance at 2.0 wt %, followed by diminished returns attributed to photon absorption limitations. These findings establish fundamental design principles for hybrid photocatalysts, particularly emphasizing the necessity to engineer heterojunction interfaces that maximize both light harvesting efficiency and charge separation kinetics─a critical dual requirement for practical solar-driven water purification systems.