Cleaner remediation of antibiotic wastewater: From efficient photocatalytic degradation to reduced ecological risk via Cd-doped Bi2MoO6/Bi5O7I S-scheme heterojunction coupled with interfacial engineering.

The growing contamination of water bodies by antibiotics necessitates the development of efficient and environmentally sustainable treatment technologies. Herein, a novel Cd-doped S-scheme Bi5O7I/Cd-Bi2MoO6 heterojunction was constructed for the sustainable remediation of doxycycline hydrochloride (DH). The optimal composite achieved 92.6 % removal of DH and 59.2 % mineralization (TOC removal) within 60 minutes under visible light. Notably, Bi/Cd-Bi-40 exhibited the highest reaction rate constant (0.03939 min-1), surpassing pristine Bi5O7I (0.00832 min-1) and 1Cd-Bi2MoO6 (0.01905 min-1) by 4.73 and 2.07 times, respectively. The catalyst retained excellent stability and maintained high efficiency over five cycles, confirming its practical application potential. The performance enhancement was attributed to the S-scheme charge transfer mechanism, which was validated by experimental characterization and DFT calculations. This mechanism, driven by a built-in electric field (IEF), significantly boosted carrier separation and generated dominant reactive species (•O2‾ and •OH). Furthermore, possible degradation pathways were proposed based on LC-MS analysis and DFT calculations. For actual water treatment scenarios, the resistance of the catalyst to common anions and humic acids were evaluated. More importantly, the environmental sustainability was confirmed through a combined ecotoxicity assessment: degradation intermediates exhibited significantly reduced ecological toxicity, as evidenced by wheat germination bioassays and quantitative structure-activity relationship predictions. The study not only presents a high-performance photocatalyst but also offers a sustainable and clean strategy for mitigating the ecological risks posed by antibiotic pollution.