Recent progress of applied TiO₂ photoelectrocatalysis for the degradation of organic pollutants in wastewaters

Photoelectrocatalysis (PEC) is a promising powerful electrochemical advanced oxidation process (EAOP) that combines photocatalysis and electrolysis. Upon light irradiation over a semiconductor photocatalyst, electrons of its valence band are promoted to its conduction band giving rise to positively charged holes. The external bias potential applied to the photoanode extracts the photoexcited electrons toward the cathode of the electrolytic cell. Organics can then be oxidized directly by the holes or with hydroxyl radical formed by their reaction with H₂O/OH⁻, and at lesser extent with other reactive oxygen species formed. The extensive study of TiO₂ photoanodic nanomaterials and their applicability in environmental remediation makes necessary a further analysis of the state of the art and the actual understanding of potentials and shortcomings. This paper presents a comprehensive and critical review on the application of PEC with TiO₂ photoanodes to remove organic pollutants from wastewaters from 2017 to May 2022. Fundamentals of this technique with pristine TiO₂ photoanodes are explained, with special emphasis on the understanding of ROS origination mechanisms and the analytical techniques used for their characterization. Typical PEC systems and key operating variables related to the effectiveness of the process are examined. Recent advances obtained by TiO₂ and TiO₂-based photoanodes treatment of chemicals, dyes, pharmaceuticals, and pesticides are described and discussed. The preparation of TiO₂ nanocomposites and their heterojunction mechanism, as well as the application of hybrid processes are detailed. Finally, prospects are proposed for the future research of PEC with perspectives to industrial application at higher technology readiness level.