(660d) Removal of Metronidazole and Dimetridazole from Aqueous Solution By Adsorption on Multiwalled and Singlewalled Carbon Nanotubes

Antibiotics are widely prescribed in human and veterinary medicine to prevent and cure bacterial infections. Antibiotics may not be biodegraded by conventional treatments, and they are being discharged in environmental media in their parent form or as transformation products. It is very well documented that the presence of antibiotics in surface water poses serious risks to human health. Nitroimidazoles are among the most widely produced and prescribed antibiotics in many countries. Metronidazole (MNZ) and dimetridazole (DTZ) are very commonly used nitroimidazoles.

The adsorption of the antibiotics MNZ) and DTZ on multiwalled (MWCNT) and single walled (SWCNT) carbon nanotubes was investigated in this work. The effect of the adsorbent-adsorbate interactions as well as the operating conditions (ionic strength, solution pH, temperature, chemical modification of the adsorbents, presence of other antibiotic) on the adsorption capacity were analyzed to substantiate the adsorption mechanism. The MWCNT were modified using a HNO₃ solution and the modified adsorbent was denoted as MWCNT-Ox. The adsorption capacity towards MNZ and DTZ markedly varied as function of the carbon material, decreasing in the following order: SWCNT > MWCNT > MWCNT-Ox, and depended not only on their surface area and pore size distribution, but also on their chemical nature. The adsorption of MNZ and DTZ was strongly influenced by the solution pH, but was not significantly affected by the ionic strength and temperature. Desorption equilibrium data of MNZ and DTZ on all carbon materials demonstrated that the adsorption was reversible corroborating the weakness of the adsorbent-adsorbate interactions.

The binary adsorption of MNZ and DTZ on SWCNT was studied in this work. The experimental binary adsorption data were interpreted using the following multicomponent adsorption isotherms: non-modified, extended and modified Langmuir, non-modified and modified Redlich-Peterson, extended Freundlich, and Sheindorf-Rebuhn-Sheintuch. The latter model best fitted the adsorption data of MNZ-DTZ on SWCNT. The competitive adsorption of MNZ-DTZ on SWCNT revealed that both antibiotics presented very similar antagonism toward the adsorption of the other antibiotic.