Heterojunction engineering in titanium dioxide/NH2-MIL-125(titanium)/polyaniline cathodes enhances visible light-driven Photoelectrocatalytic rhodamine B degradation

The rational design of charge-transfer interfaces is essential for high-performance photoelectrocatalytic (PEC) wastewater remediation. Herein, a novel ternary n-n-p heterojunction electrode, titanium dioxide/NH 2 -MIL-125(titanium)/polyaniline (TiO 2 /Ti-MOF/PANI), was successfully fabricated via a two-step hydrothermal and chemical polymerization strategy, followed by electrophoretic deposition. The optimized electrode exhibited a superior Rhodamine B (RhB) degradation efficiency of 96.1% and a total organic carbon mineralization rate of 67.19% within 70 min under visible light with a −0.8 V bias, significantly outperforming the individual photocatalytic and electrocatalytic processes. The superior performance originates from the synergistic integration of the ternary components. Ti-MOF and PANI broaden the visible-light response, promoting the generation of photogenerated electron-hole pairs under visible-light irradiation. Within this heterostructure, PANI functions as a narrow-band-gap sensitizer and p-type hole-transport layer, while n-type Ti-MOF provides a continuous pathway for rapid interfacial charge transfer. Meanwhile, n-type TiO 2 serves as a robust electron-transport backbone and offers stable surface active sites for subsequent redox reactions. The resulting n-n-p heterojunction establishes an internal electric field that, in conjunction with the applied negative bias, accelerates charge-carrier migration and accumulation at the electrode surface, thereby facilitating RhB degradation. Furthermore, PANI acts as an efficient conductive bridge, shortening electron-transport distances and reducing interfacial resistance. Mechanistic insights from radical trapping and electron spin resonance analysis confirm that •O 2 − and •OH are the predominant reactive species driving the oxidative cleavage of the xanthene chromophore. Overall, this work provides valuable design principles for multi-component PEC electrodes, offering insights into efficient environmental remediation. • A novel TiO 2 /Ti-MOF/PANI electrode was prepared by electrophoretic deposition. • A ternary n-n-p heterostructure was successfully constructed. • TiO 2 /Ti-MOF/PANI exhibits significant enhancement in PEC RhB degradation. • A possible PEC mechanism of the TiO 2 /Ti-MOF/PANI electrode was proposed.