Reversing Internal Electric Field Direction at BiVO₄/TiO₂ Heterostructure Interface by a Thin W‐VO₂ Layer: Turning Waste Charge Carriers into Wealth

Abstract In heterojunction photocatalysts, the band edge alignment and internal electric field (IEF) direction significantly affect the charge carrier separation, thus the photoconversion efficiency. For example, because of an unfavorable band alignment and compared to BiVO₄ alone, BiVO₄/TiO₂ results in ≈24% reduction in photocurrent density in this study. Herein, a tungsten‐doped VO₂ (W‐VO₂) thin film is inserted between BiVO₄ and TiO₂ to modify unfavorable spike‐like conduction band offset and IEF direction in ternary heterojunction. After reversing the IEF direction and engineering the band edges through W‐VO₂ insertion, the photocurrent density is enhanced by ≈145% and ≈91% compared to BiVO₄/TiO₂ and BiVO₄, respectively at 1.23 V versus RHE. Besides, under visible light irradiation, the kinetics rate constant for tetracycline removal by BiVO₄/W‐VO₂/TiO₂ photocatalyst is 225% higher than that of BiVO₄/TiO₂, due to utilizing charge carriers before being recombined, without doping the BiVO₄ and TiO₂ structures. Lastly, LC‐HR‐MS/MS analysis followed by the Toxicity Estimation Software Tool (T.E.S.T.) reveals the high importance of the band alignment on the detoxification of the solution. The tunability of the VO₂ work function with a low bandgap, yet distinctive valence and conduction bands (which distinguished it from metals) opens new avenues for designing high‐performance heterojunction‐based devices.