Thermodynamics of Equilibrium Adsorption of Antibiotics at Solid-Liquid Interface

摘要

The presence of pharmaceuticals in the environment is an emerging concern in the environmental community. Sorption interactions of three high - use antibiotics (cefotxime, ciprofloxacin and oxytetracycline) with soils from Erbil governorate were investigated using batch equilibrium technique. This study was aimed to find out the fate and the behavior of antibiotics in our local environment, no such study has been done here. Adsorption equilibrium data were correlated with linear distribution, Freundlich and Langmuir models. Freundlich model being found to provide the best fit of the experimental data (R~2≥0.856). Our results showed that the three studied antibiotics were found to adsorb strongly to the soils with 50-76% adsorbed under all experimental conditions. Values of equilibrium constant (K_o) were increased with temperature, confirming that the antibiotics had a high preference for adsorption at high temperature. The results of effect of temperature and thermodynamic parameters confirm the adsorption process to be endothermic in nature. Values of ΔG were in the range -10.412 to -2.089, -14.102 to -2.721, and -25.952 to-1.414 Kjmol~(-1), for cefotxime (Cef), ceprofloxacine (Cip) and oxytetracycline (OTC) respectively. Values of △G~o were negative and increased with temperature, indicating that at all experimental temperatures: the interactions of antibiotics with soils were spontaneous with a high preference of the soil surface and the adsorption occurred through a bonding mechanism. Values of △H followed the range 51.043-74.081, 38.535-85.476, and 52.561- 73.512 Kjmol~(-1), for Cef, Cip and OTC respectively. High values of △H~o pointed towered chemisorption mechnism, it may be through the coordination and/or protonation, hydrogen bonding and dipole association or Van der Waal's forces, and metal ion bridge mechanism between the soil and organic molecules occur with or without a water bridge.