Efficient accumulation of photogenerated holes on BiOI-modified TiO2 n-n type heterojunction for enhanced photocatalytic water treatment under visible light

Avoiding electron and hole recombination was always widely concerned during the design and synthesis of photocatalyst in photocatalytic water treatment, while the laws and strategies of individual hole interactions and accumulation have been rarely studied. In this study, a novel photocatalyst featuring a BiOI-modified n-n type heterojunction (TiO2@BiOI-OVs) has been introduced for efficient photocatalytic water treatment under visible light irradiation. The photocatalyst demonstrates a remarkable capability for accumulating photogenerated holes, crucial for effective water treatment processes. Upon photoexcitation, carriers swift traverse through the TiO2@BiOI-OVs structure via the n-n heterojunction transfer pathway, propelled by a directional interfacial electric field. This mechanism significantly curtails carrier recombination rates, as evidenced by the notably shortage average radiative lifetime of recombination on TiO2@BiOI-OVs (14.114 ns) compared to TiO2 (43.412 ns). Furthermore, the introduction of oxygen vacancies within TiO2@BiOI-OVs serve as electron traps, proficiently capturing photogenerated electrons. This action aids in the separation of charge carriers and fosters the accumulation holes endowed with potent oxidation capabilities. Density functional theory calculations demonstrated the formation of heterojunction effectively reduces the band gap of TiO2@BiOI-VOs and improves its responsiveness to visible light. Consequently, the kinetic constants for the photodegradation of tetracycline hydrochloride by TiO2@BiOI-OVs (0.0791 min-1) were observed 5.8 times higher than those exhibited by pristine TiO2. The photogenerated holes was mainly responsible for the TCH removal by radical quenching experiments and EPR measurements analyses. This investigation unveils a compelling strategy for systematic design of BiOI-modified n-n type heterojunction photocatalysts tailored for environmental remediation applications.