The BiOCl/diatomite composites for rapid photocatalytic degradation of ciprofloxacin: Efficiency, toxicity evaluation, mechanisms and pathways

The activity and separation performance of nano-structure photocatalyst have always been the focus in the field of environmental pollutant removal. In this work, BiOCl/diatomite composites were successfully fabricated via a simple hydrolysis method, which could meet the above two requirements. The superior performance of composites was explained by using X-ray diffractometer (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results revealed that the tetragonal phase BiOCl and diatomite coexisted in the composites, producing the synergistic effect. The diatomite had the high adsorption and silicon hydroxyl groups while the BiOCl had the exposed (0 0 1) facets. Diatomite as a carrier was actually equivalent to a solid dispersant, which could immobilize BiOCl microspheres evenly on its surface and prevent their aggregation, guaranteeing more active sites of BiOCl be exposed and promoting the transfer and separation of photo-induced carriers. The prepared BiOCl/60%D presented 94% removal efficiency for ciprofloxacin (CIP) under simulated solar light within 10 min irradiation, and also presented a 42.9% of total organic carbon (TOC) removal after 240 min. Despite the mineralization of CIP was incomplete, toxicity assessment indicated effective elimination of CIP antibacterial property by BiOCl/60%D in a short time. Moreover, the BiOCl/60%D exhibited good stability and reusability. The formation mechanism of BiOCl/diatomite composites was speculated, meanwhile, the photocatalytic degradation mechanism and pathways of CIP were also deduced by using radicals trapping experiments, electron spin resonance (ESR), high performance liquid chromatography (HPLC) and mass spectrometry (MS). This study provided a simple method of building efficient BiOCl/diatomite composites for fast degradation of CIP in water, which had substantial attraction for application.