Engineering oxygen vacancy-enriched S-scheme ZnIO(OH)/BiOIO heterojunction architectures for enhanced charge separation and photocatalytic efficiency.

Tetracycline (TC), a commonly used antibiotic, is often classified under pharmaceuticals and personal care products (PPCPs), and its extensive use poses significant risks including ecotoxicity, antimicrobial resistance (AMR), and gut microbiota imbalance, among others. The composite photocatalyst ZCZIH/BIO (ZnCO/ZnIO(OH)/BiOIO) with S-scheme heterojunction was fabricated through a simplified two-stage hydrothermal approach for the degradation of TC in aqueous environment. The optimal photocatalyst showed excellent photocatalytic performance for TC degradation, achieving a reaction rate constant of around 8.0 × 10 min, which was 1.43 and 1.33 times of the original ZCZIH (5.6 × 10 min) and BIO (6.0 × 10 min), respectively. The electronic structure characterization techniques were employed to investigate the band structure properties of the materials, and the composites were found to form an S-type heterojunction. The existence of oxygen vacancies (OVs) was confirmed by electron spin resonance (ESR) and other characterization methods. OVs could effectively promote the separation of bulk charges and provide more active sites, while the formation of S-type heterojunction could promote the effective separation of interface photogenerated charges through the built-in electric field. All these enhanced the photocatalytic performance of the material. Radical trapping experiments and ESR analysis confirmed that superoxide radicals and singlet oxygen were the primary active species in TC degradation, while holes and hydroxyl radicals also contributed to some extent. The catalyst underwent five cycles of testing, and its structural and morphological characteristics were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and Raman techniques. The results confirmed that the catalyst exhibited excellent photostability. Further optimization of OVs concentration and interfacial coupling in S-scheme heterojunctions could unlock superior solar-driven photocatalytic applications, including pollutant degradation and clean energy production.