Towards efficient ciprofloxacin adsorption using magnetic hybrid nanoparticles prepared with κ-, ι-, and λ-carrageenan

The efficient removal of the antibiotic ciprofloxacin (CIP) from aqueous samples using magnetic nanosorbents prepared using three sulfated polysaccharides, kappa-, iota-, and lambda-carrageenan and an alkoxysilane agent containing a reactive epoxide ring is described. The prepared nanosorbents were characterized in detail using FTIR spectroscopy, solid-state Si-29 and C-13 NMR spectroscopy and elemental microanalysis. The synthesis method was more effective for incorporating higher amounts of kappa-carrageenan in the siliceous shells. Although being less sulfated, kappa-carrageenan is cheaper than the other carrageenan tested. The CIP adsorption was a cooperative process, well described by the Dubinin-Radushkevich isotherm, with maximum adsorption capacities of 878, 969 and 865 mg/g for kappa-, iota-, and lambda-carrageenan sorbents, respectively. Overall, the produced magnetic nanosorbents are among the best magnetic systems with high adsorptive efficiency for CIP. It is suggested that protonated CIP molecules are exchanged with ester sulfate counterions of carrageenan at the particles' surface as the main pathway for CIP adsorption. The adsorption process was exothermic and entropically favorable for the three sorbents. However, at 298 K, the adsorption was spontaneous for kappa-carrageenan-based sorbents and non-spontaneous for iota- and lambda-carrageenan particles. The magnetic sorbents could be reused and maintained their ability towards CIP removal up to four cycles. The removal efficiency in wastewater was enhanced with the sorbent dose. [GRAPHICS] .