Promotional effect of Ca doping on BiFeO as peroxymonosulfate activator for gatifloxacin removal.

A series of Ca-doped bismuth ferrite was prepared at various %w/w of Ca via a facile hydrothermal method to obtain BiCaFeO (denoted as BFOCa-X, where X = 1, 0.95, 0.90, 0.80, 0.50). The BFOCa-X catalysts were characterized, and the results showed that they consist of pure phase BFO with nanosheet-like morphology. The as-prepared BFOCa-X catalysts were used as peroxymonosulfate (PMS) activator for gatifloxacin (GAT) removal. It was found that the catalytic activity decreased in the following order: BFOCa-0.8 (90.2% GAT removal efficiency in 45 min, k = 0.084 min)>BFOCa-0.95 > BFOCa-0.9 > BFOCa-0.5 > BFO indicating that BFOCa-0.8 has the optimized active sites for catalysis. The Ca dopant contributed to the increased oxygen vacancies and surface hydroxyl groups, promoting the catalytic PMS activation process. The k value increased gradually with increasing catalyst loading and PMS dosage while pH 9 presented the highest GAT removal rate. The GAT degradation rate was inhibited by PO-, humic acid and NH but promoted in the presence of Cl-, NO- and HCO-. It was also found that the GAT can undergo several degradation pathways in the catalytic PMS system, which eventually mineralized into innocuous compounds. The dominant reactive oxygen species (ROS) were identified using chemical scavengers, revealing that SO-, O and OH contributed significantly to GAT degradation. Based on the XPS study, PMS was activated by the Fe/Fe redox cycling and oxygen vacancies to produce SO-/OH and O, respectively. Overall, the BFOCa-0.8 also showed excellent reusability up to at least 4 cycles with low Bi and Fe leaching (<7 and 62 μg L, respectively), indicating that it has promising potential for application as PMS activator for antibiotics removal.