Surface microenvironment engineering of black V₂O₅ nanostructures for visible light photodegradation of methylene blue

Utilization of photocatalysis as a promising strategy for environmental and energy applications has been widely considered. Herein, we report a novel black V₂O₅ material (bV₂O₅) synthesized using a controllable and environmentally benign physicochemical reduction method. HRTEM, ESEM, EDX. Raman, XPS, XRD, and BET textural characterization, as well as computational density functional theory (DFT) techniques were employed to understand the chemical and electronic changes obtained through modulation of the surface microenvironment. DFT analyses reveal that tuning a high degree of surface oxygen vacancies considerably ameliorated visible light photoactivity of practically inactive pristine V₂O₅. The optimized bV₂O₅ sample yielded 92% photodegradation of 20 mg/L cationic methylene blue (MB) in 60 min under visible light irradiation – corresponding to a 58-fold increase in photodegradation efficiency over pristine V₂O₅. Neutral quinoline yellow (QY) and anionic methyl orange (MO) photodegradation were also investigated to examine the photocatalytic efficacy of bV₂O₅ for degradation of other organic contaminants with different charges. DFT calculations show a clear thermodynamic stability towards reduction of the predominant polar (001) facet at 1-coordinated oxygen surface site. A staggered (type-II) heterostructure between pristine and reduced V₂O₅ was determined from band edge positions which is believed to promote the enhancement in photoactivity of the reduced sample by offering favorable electron-hole separation and allowing both hydroxyl and superoxide radical formation. The mechanism behind the formation of surface defects on bV₂O₅ was proposed based on configurational changes.