An adsorption and thermodynamic study of ofloxacin on marine sediments

Abstract

Environmental contextOfloxacin, a widely used fluorinated antibiotic, is resistant to biodegradation and hence can accumulate in the environment. A systematic investigation of ofloxacin on marine sediments showed that sediment organic carbon and heterogeneous sites on sediments play important roles in adsorption processes. The results help our understanding of the environmental behaviour and fate of ofloxacin in marine systems. AbstractThe adsorption behaviour of ofloxacin (OFL) on marine sediments treated by different methods was investigated using batch experiments. Three factors (sediment organic carbon content, salinity and temperature) that may affect the adsorption behaviour of OFL were analysed. The equilibrium time for OFL adsorption on marine sediment in natural seawater was ~4–5h. The adsorption of OFL on all sediments with different treatments fitted the Freundlich model well. The adsorption parameter Kf value was in the order of Kf (H2O2 treatment)<Kf (H2O treatment)<Kf (HCl treatment) over the studied concentration range. The adsorption of OFL was influenced not only by the sediment organic carbon content but also by external factors such as salinity of media and temperature. The adsorption was favourably influenced by decreased salinity and temperature of seawater. The adsorption capacity of OFL on marine sediments decreased with an increase of temperature and salinity. The Kf values decreased from 33.73±1.66 to 22.54±1.12(Lkg−1)1/n when the temperature increased from 283 to 313K. The changes in standard Gibbs free energy (ΔG0) and enthalpy (ΔH0) were −6.62±0.34kJmol−1 and −7.58±0.38kJmol−1 respectively, indicating that the adsorption process of OFL was spontaneous and exothermic. The positive value of the entropy change ΔS0 (i.e. 3.38±0.17JK−1mol−1) suggests that the degree of freedom increased during the adsorption process.