Preparation of Ti1-xO2-x with Di-vacancies Using N-Methylpyrrolidone Bifunctional Modifier and Its Deep Photodegradation Mechanism

Abstract

N-methylpyrrolidone (NMP) was employed as the doping and induced-defect modifier to prepare titanium dioxide based photocatalytic materials via a solvothermal process. The substitution of N for O introduces localized negative charges; following the removal of N at high temperatures, the resulting localized charge imbalance leads the system to spontaneously form positive charge defects to achieve electrical neutrality. This represents a novel in-situ defect formation strategy, rather than a traditional method involving external reduction, and utilized for efficient remediation of tetracycline (TC) through synergistic adsorption and photocatalysis. Oxygen vacancies (OVs) are the dominant defects governing photocatalytic activity, while titanium vacancies (TiVs) assist in enhancing charge separation efficiency. The localized built-in electric field induced by the dual defect structure not only boosts the visible-light response of the material but also facilitates the efficient separation of photogenerated electrons and holes. After 30 min dark adsorption period, the photocatalytic removal of TC (20 mg·L-1) reached 90.21% under 60 min of visible-light illumination. Notably, Ti1-xO2-x exhibited a first-order rate constant that was 1.98-fold and 2.41-fold greater than those of an-TiO2 and the commercial P25, respectively. The results from radical-trapping experiments, corroborated by electron spin resonance (ESR) analysis, underscore the predominant role of ·O2- in driving the photocatalytic degradation of TC. Moreover, the material proved effective in the mineralization of various antibiotics and dyes, highlighting its wide applicability for environmental remediation. The interaction between conduction band electrons and oxygen vacancies creates dual-pathway electron supply, effectively promoting the multi-channel generation of superoxide radicals. This work delineates the synergistic dynamics of electron migration and active species generation in defect-engineered Ti1-xO2-x, establishing an experimental foundation for the development of advanced TiO2-based semiconductors.