Ti³⁺ self-doped TiO₂ nanotube arrays revisited as Janus photoelectrodes for persulfate activation and water treatment

This study investigates the binary role of Ti³⁺ self-doped TiO₂ nanotubes (bl-TNA) as an anode as well as a cathode in the photoelectrochemical (PEC) oxidative treatment of organic contaminants. Compared to the Ti cathode-based asymmetric system, the symmetric PEC system with Janus bl-TNA photoelectrodes demonstrated higher interfacial charge transfer, photoresponsive activity, and kinetic constant for bisphenol-A (BPA) degradation. The bl-TNA photocathode enhanced the formation of radicals by providing additional reaction sites for photocatalytic reactions and cathodic peroxydisulfate (PDS) activation. Additionally, the rate constant ratio for BPA degradation between the anode and cathode in the symmetric system changed from 7.5:1–1.3:1 under PEC and PEC/PDS conditions, indicating that PDS addition enhanced the photoactivity of the electrodes, with a higher rate at the cathode. Finally, only 2.4% performance decline was observed after 64 h with the periodic polarity reversal operation, demonstrating the long-term stability of the proposed PEC system.