Elucidating the synergistic effect of oxygen vacancies and Z-scheme heterojunction in NU-1000/BiOCl-Ov composites towards enhanced photocatalytic degradation of tetracycline hydrochloride

Although Z-scheme heterojunction composites have been widely studied in photocatalysis, in-depth investigation of oxygen vacancies (Ov) in the Z-scheme photocatalysts is still rare. Herein, an oxygen vacancies modified NU-1000/BiOCl-Ov composite with Z-scheme heterojunction was rationally designed and fabricated. The combination of X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) experiment verified the presence of oxygen vacancies, meanwhile the Z-scheme charge transfer across the heterojunction interface was confirmed in detail by the in situ-XPS, Kelvin probe force microscope (KPFM) studies, ultraviolet photoelectron spectroscopy (UPS), EPR radical capture experiment, as well as density functional theory (DFT) calculation. Importantly, compared to pristine NU-1000 and BiOCl, the optimized NU-1000/BiOCl-Ov composite displayed enhanced photocatalytic performance in the degradation of tetracycline hydrochloride (TCH) under visible light (λ ≥ 400 nm). Theoretical calculations reveal that the oxygen vacancies could induce electron redistribution, facilitating the activation of O₂ and TCH molecules, thereby promoting the photodegradation efficiency. Moreover, mechanism studies suggested that the synergistic effect of oxygen vacancies and Z-scheme heterojunction could facilitate the effective separation of photogenerated carriers. At last, the degradation routes of TCH were proposed and the toxicity of degradation intermediates was assessed. This work underlines the cooperative functions of oxygen vacancies and Z-scheme heterojunction towards improved photocatalytic performance, which offers new perspectives on the design of metal-organic frameworks (MOFs) composites for efficient photocatalysis.