Enhanced internal electric field in S-doped BiOBr for intercalation, adsorption and degradation of ciprofloxacin by photoinitiation

A photocatalyst of layered structural BiOBr doped with sulfur (S-BiOBr) was synthesized using a facile hydrothermal method. X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and density functional theory calculation revealed that S-BiOBr consisted of covalent [Bi2O2S]2+ layer and exchangeable bromide ions [Br2]2-. The specific layered structure of S-BiOBr exhibited excellent performance for the intercalation, adsorption and photocatalytic degradation of ciprofloxacin (CIP) by forming interlayer [Bi2O2S]2+--OOC-R complexes. Furthermore, the internal electric field enhanced by polarization effects in the [Bi2O2S]2+ layer was conducive to a lasting electron transfer in the dark condition after photoactivation. The electron of R• radical derived from oxidizing [Bi2O2S]-OOC-R persistently migrated to the S-BiOBr surface and was trapped by O2 to form O2•-, facilitating the degradation of CIP in the dark. Hence, the degradation of CIP could be realized by utilizing the R• radical triggered through transient photoinitiation with low optical energy consumption.