Frustrated defect pairs of oxygen vacancies and doped nitrogen in amorphous titanium dioxide for enhanced photodegradation of tetracycline

Abstract

In this work, a novel nitrogen-doped amorphous titanium dioxide photocatalytic material (N₅@AT) enriched with oxygen vacancies was prepared by a solvothermal method using triethylamine as a dopant. Spectroscopic and electrochemical data indicate that frustrated defect pairs are formed between doped nitrogen and oxygen vacancies, which can efficiently attract and aggregate photogenerated electrons, enhancing the electron–hole separation efficiency of the material. Meanwhile, the steric effect derived from triethylamine promotes the formation of lamellar structures with high specific surface area, and the specific surface area of N₅@AT is 456.17 m² g⁻¹, which is 2.1 times higher than that of the undoped sample AnT (220.25 m² g⁻¹). This characteristic provides a stable path for photogenerated electron transport, accelerates electron migration, and forms more active sites for pollutant degradation. After 60 min of visible light irradiation, the degradation rate of tetracycline by N₅@AT increased to 0.0364 min⁻¹, which was 1.5 and 3.1 times higher than those of AnT and commercial titanium dioxide (P25), respectively. The mineralisation rate reached 70.28%, which was 2.18 and 4.28 times higher than those of AnT and P25, respectively. The conduction band electrons and oxygen vacancy defects in the N₅@AT material form dual electronic supply channels for improving the multi-path generation of ˙O₂⁻, and the active species capture experiments and EPR technique indicate that the dual active species ˙O₂⁻ and h⁺ play major roles in the deep photodegradation mechanism, which enables enhanced oxidative decomposition of TC molecules. This strategy provides new insights and references for the design of novel amorphous titanium dioxide materials.