Adsorption of ciprofloxacin on 2:1 dioctahedral clay minerals

Frequent detection of antibiotics in natural environment and wastewater effluent requires systematic investigations of various clay minerals. Dioctahedral 2:1 clay minerals are major constituents of soil and sediments. Interaction of these clay minerals and ciprofloxacin (CIP) was studied. The CIP adsorption capacities on montmorillonite, rectorite, and illite were 1.19, 0.41, and 0.10 mmol/g, corresponding to 1.0, 1.0, and 0.9 CEC. Desorption of the equivalent amounts of exchangeable cations suggested that the cation exchange was mainly responsible for the CIP adsorption on montmorillonite and rectorite. The expansion of the basal spacing and shifts of characteristic FTIR bands indicated the intercalation of CIP ions with tilted orientation in montmorillonite and rectorite. The displacement of exchangeable cations and associated FTIR band shifts also indicated the cation exchange as important for CIP adsorption on illite but hydrogen bonding between CIP carboxylic groups and basal oxygen atoms on external surface apparently made a significant contribution to the adsorption.