CIPROFLOXACIN ADSORPTION ON MAGNETITE-WATER INTERFACE

Ciprofloxacin (CIP), an important class of fluoroquinolone antibiotics, is known to cause ecotoxicological hazards when present at an elevated concentration in aquatic and soil environments. Recent fate and transport studies of CIP have highlighted its affinity towards iron- oxides. However, there are no reports of interaction of CIP with a common Fe-oxide mineral such as magnetite. The main objective of this research was to investigate the sorption mechanism of CIP with magnetite. Both spectroscopic and surface complexation modeling (SCM) approaches were undertaken to understand the interaction mechanism at the molecular level. A sorption envelop was created at pH ranging from 3.44-8.39 at magnetite solid solution ratio of 10 gL^-1 and CIP initial concentration of 100 µM. Desorption envelop was also generated to understand the reversibility of the sorption process. Sorption isotherm with initial CIP concentration of 1-500 µM was created at three different ionic strengths (0.5, 0.1, and 0.01 M NaCl). In situ-FTIR techniques were applied to study the sorption envelop with a pH range of 3-9. Preliminary results from macroscopic experiments indicated a bell-shaped sorption envelop where sorption of CIP on magnetite increased from 45 -80% at pH 3.44 -5.97; beyond that sorption gradually decreased to a value of 25% at pH 8.39. Desorption envelop indicated negligible amount of desorption a pH range of 4-7. Above and below this pH range, greater amount of desorption was observed. Sorption isotherm indicated negligible dependence on ionic strengths until 200 µM initial CIP concentrations. Ongoing in-situ FTIR experiments indicate inner-sphere nature of the sorption. In addition, data suggest that carboxylic acid groups of CIP participate in the sorption process. SCM modeling using FITEQL is ongoing to isolate the probable surface complexation reactions.