Magnetic nanosorbents with siliceous hybrid shells of alginic acid and carrageenan for removal of ciprofloxacin.

Water contamination with antibiotics is a serious environmental threat. Ciprofloxacin (CIP) is one of the most frequently detected antibiotics in water. Herein, silica-based magnetic nanosorbents prepared using three seaweed polysaccharides, alginic acid, κ- and λ-carrageenan, were developed and evaluated in the uptake of ciprofloxacin. The sorbents were firstly characterized in detail to assess their morphology and composition. A systematic investigation was conducted to study the adsorption performance towards CIP, by varying the initial pH, contact time and initial CIP concentration. The maximum adsorption capacity was 464, 423 and 1350 mg/g for particles prepared from alginic acid, κ- and λ-carrageenan respectively. These high values indicate that these materials are among the most effective sorbents reported so far for the removal of CIP from water. The kinetic data were consistent with the pseudo-second-order model. The CIP adsorption on λ-carrageenan particles followed a cooperative process with sigmoidal isotherm that was described by the Dubinin-Radushkevich model. The high charge density of λ-carrageenan and the propensity of CIP molecules to self-aggregate may explain the cooperative nature of CIP adsorption. The sorbents were easily regenerated in mild conditions and could be reused in CIP removal up to 4 times without a significant loss of adsorptive properties.