(521bb) Experimental and Theoretical Investigation on Surface Microenvironment Engineered Novel Black Vanadia Towards Visible Light Photodegradation

Bench-scale treatment facilities that are easy to operate and maintain in remote locations can find wide implementation in curbing the impact of potable water availability. Organic compounds have been found to be some of the most omnipresent and persistent contaminants found in wastewaters. Efficient and cost-effective photodegradation of these contaminants relies on catalysts with high activity in the visible-light region, favorable kinetics, and resilient performance stability. A clear lack of attention has been given towards investigating the photoactivity of other transition metal oxides (TMO) upon chemical reduction after the serendipitous discovery of ‘black’ TiO₂. To this end, some metal oxide photocatalysts such as V₂O₅ exhibit poor intrinsic photoactivity due to a deep conduction band (CB) edge limiting major reduction reactions (i.e., reduction of oxygen to superoxide radicals) from forming which can be paramount to photodegradation abilities. Herein, we report a novel, vacancy rich, black V₂O₅ material (bV₂O₅) synthesized using a controllable and environmentally benign physicochemical reduction method. First principle density function theory (DFT+U) analyses reveal that tuning a high degree of surface oxygen vacancies considerably ameliorated visible light photoactivity of practically inactive pristine V₂O₅ (pV₂O₅). The heterojunction between surface pV₂O₅ and bV₂O₅ crystals on the same homogenously dispersed microstructure allows for the creation of effective trap states. The modest degree of intercalated Na⁺ in bV₂O₅ - introduced through NaBH₄ reduction – is believed to facilitate neighboring photogenerated electrons to transfer along the bridge-Na sites. Both these aid in inhibiting the electron-hole recombination rate, which enhances visible light photodegradation kinetics. The optimized bV₂O₅ photocatalyst was confirmed to actively achieve 92% methylene blue (MB; 20 mg/L) photodegradation in 1 h under 0.7 kW/m² visible-light intensity, after reaching adsorption equilibrium (capacity = 75 mg/L methylene blue (MB)) without light illumination irradiation – corresponding to a 58-fold increase in photodegradation efficiency over pristine V₂O₅.