Sorption of the Antimicrobial Ciprofloxacin To Aluminum and Iron Hydrous Oxides

摘要

Solution chemistry(pH,ionic strength(I),and sorbate-to-sorbent ratio)effects on ciprofloxacin sorption to hydrous oxides of Al(HAO)and Fe(HFO)were investigated using macroscopic and spectroscopic analyses.Sorption to both HAO and HFO showed a strong pH-dependent behavior,following the fraction of zwitterionic species over the entire pH range studied.Increase in I from 0.01 to 0.5 M had an insignificant effect on the extent of ciprofloxacin sorption,and isotherms were well-described by the Langmuir model.HFO possessed a higher sorption capacity(0.066 mmol kg~(-1))than HAO(0.041 mmol kg~(-1)).Ligand-promoted dissolution of hydrous oxides,more pronounced for HAO,was observed in the presence of ciprofloxacin,but at a fairly high initial concentration(0.5 mM).Attenuated total reflectance Fourier transform infrared spectroscopy analysis indicated that different types of ciprofloxacin surface complexes are formed with HAO and HFO;while a monodentate mononuclear complex(with-COO~-)appears likely between ciprofloxacin and HAO,keto O and one O from COO~-seem to be involved in the formation of a six-membered ring with Fe on the HFO surface.The study results are expected to increase our understanding of the environmental reactivity of fluoroquinolones,an important class of antimicrobial compounds.