Preparation and characterization of organo-vermiculite based on phosphatidylcholine and adsorption of two typical antibiotics

In this study, a novel organoclay (PC-VER) was synthesized by modifying vermiculite (VER) with phosphatidylcholine (PC), and the adsorption characteristics of oxytetracycline (OTC) and ciprofloxacin (CIP) on PC-VER were further examined. The structural characteristics of PC-VER were analyzed by XRD, FTIR, TG and SEM/EDS, confirming that PC molecules were successfully introduced into VER. It was found that PC molecules cannot only intercalate into the interlayer space but also can adsorb on the external surface of VER if the solution contains water. This causes the decrease in specific surface area and increase in thermal stability. Zeta potential results show that PC-VER has a positively charged surface when the solution pH below 3. The kinetic study showed that the adsorption process of OTC and CIP both abided by pseudo-second-order model. The film-diffusion was the dominated controlling-step for the adsorption on VER, and both film and intra-particle diffusion controlled the adsorption on PC-VER. The adsorption isotherm could be well described by the Langmuir model, exhibiting an enhanced adsorption of OTC and CIP for PC-VER. Electrostatic attraction is the main mechanism for the adsorption on VER according to the effect of pH values and coexisting cations. For PC-VER, the enhanced adsorption of OTC was mainly controlled by hydrophobic interaction; while electrostatic attraction was a priority for the CIP adsorption. Results obtained from this study displayed that PC-VER could serve as a low-cost, suitable and eco-friendly material for adsorption of antibiotics.