Construction of direct Z-scheme Bi5O7I/UiO-66-NH2 heterojunction photocatalysts for enhanced degradation of ciprofloxacin: Mechanism insight, pathway analysis and toxicity evaluation

Direct Z-scheme Bi5O7I/UiO-66-NH2 (denoted as BU-x) heterojunction photocatalysts were successfully constructed through ball-milling method. Photocatalytic activities of the as-prepared BU-x samples were determined by using a typical fluoroquinolone antibiotic, ciprofloxacin (CIP). All BU-x heterojunctions exhibited better CIP removal performances than that of pristine Bi5O7I and UiO-66-NH2 upon exposure to white light irradiation. In comparison, the heterojunction with UiO-66-NH2 content of 50 wt% (BU-5) showed excellent structural stability and the optimal adsorption-photodegradation efficiency for the CIP removal. The removal efficiency of CIP (10 mg/L) over BU-5 (0.75 g/L) achieved 96.1% within 120 min illumination. Meanwhile, the effect of photocatalyst dosage, pH and inorganic anions were systemically explored. Reactive species trapping experiments, electron spin resonance (ESR) signals, Mott-Schottky measurements and density functional theory (DFT) simulation revealed that the photo-generated holes (h(+)), hydroxyl radical (center dot OH) and superoxide radical (center dot O-2(-)) played crucial roles in CIP degradation. This result can be ascribed to that the unique Z-scheme charge transfer configuration retained the excellent redox capacities of Bi5O7I and UiO-66-NH2. Meanwhile, the CIP degradation pathways and the toxicity of various intermediates were subsequently analyzed. This work provided a feasible idea for removing antibiotics by bismuth-rich bismuth oxyhalide/MOF-based heterostructured photocatalysts.

Automated summary

Z-scheme Bi5O7I/UiO-66-NH2 heterojunction photocatalysts were successfully constructed via ball-milling, showing superior CIP removal efficiency compared to pristine Bi5O7I and UiO-66-NH2. Among them, the heterojunction with 50 wt% UiO-66-NH2 content (BU-5) exhibited excellent structural stability and optimal CIP removal efficiency, achieving 96.1% removal within 120 minutes of illumination.