Fabrication of CQDs/Bi5Nb3O15 nanocomposites for photocatalytic degradation of veterinary pharmaceutical sarafloxacin

The unabated release of fluoroquinolone compounds into surface water led to environmental problems. In this contribution, the heterogeneous photocatalytic technology was employed utilizing carbon quantum dot CQDs/Bi5Nb3O15 nanocomposites for degrading the veterinary pharmaceutical sarafloxacin as a model pollutant. A simple hydrothermal method was used to synthesize CQDs/Bi5Nb3O15 nanocomposites with different CQDs amount (1-4 wt%). X-ray diffraction and Fourier transform infrared spectra revealed the formation of CQDs/Bi5Nb3O15 nanocomposites. UV-vis spectra of CQDs/Bi5Nb3O15 nanocomposites displayed a marked absorption enhancement in the range of 400-700 nm. Transmission electron microscopy images demonstrated the as-prepared CQDs having small particle size were successfully coupled with Bi5Nb3O15. X-ray photoelectron spectra indicated the presence of C, O, Bi and Nb in CQDs/Bi5Nb3O15 nanocomposites. Brunauer-Emmett-Teller measurements confirmed that the surface area of 3 wt% CQDs/Bi5Nb3O15 nanocomposites was higher than that of Bi5Nb3O15. The photocatalytic decomposition of sarafloxacin was investigated using these novel nanocomposites under irradiation of 250W Xe lamp. The prepared 3 wt% CQDs/Bi5Nb3O15 nanocomposites exhibited better degradation efficiency than pure Bi5Nb3O15 nanoparticles. In addition, the degradation products were identified by UHPLC/MS/MS and possible degradation pathways were proposed. Four new intermediates were found, featuring a series of steps including cleavage of piperazine ring and oxidation.