Z-scheme heterojunction photocatalyst formed by MOF-derived C-TiO 2 and Bi 2 WO 6 for enhancing degradation of oxytetracycline: Mechanistic insights and toxicity evaluation in the presence of a single active species.

In the work, Bi2 WO6 /C-TiO2 photocatalyst was successfully synthesized for the first time by loading narrow bandgap semiconductor Bi2 WO6 on MOF-derived carboxyl modified TiO2 . The phase structure, morphology, photoelectric properties, surface chemical states and photocatalytic performance of the prepared photocatalysts were systematically investigated using various characterization tools. The degradation efficiency of oxytetracycline by 6BT Z-scheme heterojunction photocatalyst under visible light could reach 93.6 % within 100 min, which was related to the high light harvesting and effective separation and transfer of photo-generated carriers. Furthermore, the effects of various environmental factors in actual wastewater were further investigated, and the results showed that 6BT exhibited good adaptability, durability and resistance to interference. Unlike most works, the degradation system with a different single active species were designed and constructed based on their formation mechanism. In addition, for the first time, a positive study was conducted on the priority attack sites, intermediate products, and degradation pathways for the photocatalytic degradation of oxytetracycline by a single active species through HPLC-MS and Fukui index calculations. The toxicity changes of intermediate products produced in three different single active species oxidation systems were evaluated using toxicity assessment software tools (T.E.S.T.), Escherichia coli growth experiments, and wheat growth experiments. Among them, the intermediate products formed through O2 - oxidation had the lowest toxicity and the main active sites it attacked were the 20C, 38O, 18C, 41O, and 55O atoms with high f+ values in the oxytetracycline molecular structure. This work provided the insight into the role of each active species in the degradation of antibiotics and offered new ideas for the design and synthesis of efficient and eco-friendly photocatalysts.