Electrochemical treatment of phenol-containing wastewater by facet-tailored TiO2: Efficiency, characteristics and mechanisms

Abstract Electrochemical oxidation is widely used for water and wastewater treatment. Anodic material is crucial and the shape-tailored {001}-exposed TiO2 has been proven to be an ideal electrode material for pollutant oxidation. In this work, the electrochemical treatment of wastewater containing typical p-substituted phenols by facet-tailored TiO2 is studied in terms of efficiency, characteristics and mechanisms. Experimental results demonstrate that the anodic oxidation of p-substituted phenols becomes more difficult with the increasing Hammett's constant (σ) of phenols, while their degradation rates (k) increase continuously with the initial surface concentration (Γ). Phenols are degraded mainly by surface-bound ·OH and direct electron transfer on the TiO2/Ti electrode, rather than by bulk-free ·OH suspended in the aqueous phase. Theoretical calculations reveal that the surface-bound ·OH-mediated oxidation mechanism is attributed mainly to the strong surface bond strength between shape-tailored TiO2 and water molecule as well as the reactive ·OH. Such strong interactions are associated with the higher density of atomic steps, edges and kinks of low-coordinate surface atoms with a large number dangling bonds on the high-energy {001} polar facet. For practical treatment of real wastewater with different matrixes, the facet-tailored TiO2/Ti electrode exhibits both a high efficiency and a fast kinetics. Our findings provide a new chance to degrade phenolic pollutants in wastewater and offer atomic-scale insights into the preparation, modification and application of TiO2-based anodic materials for electrochemical water treatment.