Competitive Adsorption of Dimetridazole and Metronidazole Antibiotics on Carbon Materials from Aqueous Solution

The single and binary adsorptions of metronidazole (MNZ) and dimetridazole (DTZ) on activated carbon (F400) and activated carbon felt (ACF) were studied in this work. The adsorption capacities of both materials towards antibiotics were determined at pH = 7 and 25 °C. The π-π dispersive interactions controlled the adsorption mechanism of both antibiotics. The Prausnitz-Radke isotherm interpreted quite well the single adsorption equilibrium data of DTZ and MNZ on F400 and ACF. DTZ presented higher affinity for both adsorbents because the DTZ had higher electronic density and smaller molecular size than those of MNZ. The capacity of F400 for adsorbing DTZ or MNZ was higher than that of ACF because the ACF presented higher microporosity and surface area, which was unavailable for adsorbing DTZ and MNZ due to pore restriction. The binary equilibrium data on F400 and ACF were interpreted reasonably well with the extended Langmuir multicomponent isotherm and Sheindorf-Rebuhn-Sheintuch isotherm, respectively. The competitive adsorption of MNZ and DTZ was antagonistic, but not cooperative. In the binary adsorption, both antibiotics were adsorbed simultaneously, competed for the same adsorption sites, and both carbon materials presented higher selectivity towards DTZ than MNZ. Moreover, if one antibiotic was adsorbed first, then another antibiotic could be adsorbed on unoccupied sites or by displacing the antibiotic already adsorbed. The results revealed that the binary adsorption equilibrium was independent on the way of contacting the antibiotics.