Enhanced visible-light photoelectrocatalysis over TiO2 NTs/Cu2O-CuO: Mechanistic insights into charge separation and pollutant degradation

Addressing the escalating contamination of aquatic ecosystems by industrial dyes and heavy metals such as Cr(VI), this study presents a novel TiO 2 NTs/Cu 2 O-CuO hybrid photoelectrocatalytic system. By integrating anodic oxidation with a controlled hydrothermal process, Cu 2 O-CuO dual-phase heterojunctions were successfully anchored onto TiO 2 nanotube arrays, establishing a cascade-like band alignment for efficient charge carrier separation. The characterization confirms that the energy band structure-comprising TiO 2 NTs (3.08 eV), Cu 2 O (2.11 eV), and CuO (1.77 eV)-significantly extends visible-light absorption and suppresses the recombination of photogenerated electron-hole pairs. Under combined visible-light irradiation and external bias, the system exhibits superior photoelectrocatalytic performance, achieving removal efficiencies of 96.92% for Congo red (CR), 74.87% for methylene blue (MB), and 93.64% for Cr(VI). Mechanistic insights reveal that the mineralization of pollutants is dominated by a synergistic pathway involving direct hole (h + ) oxidation and superoxide radicals (•O 2 − ) derived from O 2 reduction. Furthermore, an ecological toxicity assessment using Vigna angularis seedlings demonstrates that this photoelectrocatalytic process effectively detoxifies treated wastewater, promoting plant growth and restoring ecological safety. This work provides both a robust design principle for high-performance heterojunction photoanodes and a critical framework for evaluating the real-world environmental safety of water purification technologies.