Mechanistic study of direct Mg-Al layered double hydroxide formation for the removal of amphoteric ciprofloxacin(CIP) antibiotics from aqueous media

• Calcined layered double hydroxide(Cal-LDH) is a promising material for antibiotic removal. • Cal-LDH partially removed CIP during the reconstruction of its layered structure by intercalating CIP. • Both CO3 2− and CIP-intercalated LDHs were competitively formed during CIP removal by Cal-LDH. • The reconstruction of Cal-LDH increased the solution pH, resulting in CIP precipitation. • Cal-LDH can remove 640 mg/g of CIP via LDH reconstruction and ∼2500 mg/g via precipitation mechanisms. The direct layered double hydroxide (LDH) formation technique is considered as highly promising method for removal of antibiotics due to its outstanding removal capacity. However, the removal mechanism and antibiotic adsorption behavior was still ambiguous and limited its potential use in practical application into remediation. In this study, we investigated ciprofloxacin(CIP) removal mechanism by calcined Mg-Al LDH (Cal-LDH) and CIP adsorption behavior to enhance the potential applicability for water remediation materials. The Cal-LDH shows MgO and amorphous Al 2 O 3 mixed structure, but it is rapidly reconstructed as layered structure (LDH) in water. The XRD results revealed that both CO 3 2– (or OH – ) and CIP intercalated LDHs were formed during reconstruction reaction of LDH. By increasing solution pH, the portion of CO 3 2– (or OH – ) intercalated LDH formation became increased, resulting in decrease of CIP adsorption capacity on Cal-LDH. Compared with pristine LDH, the Cal-LDH shows much higher CIP adsorption capacity because it is fully reconstructed, and its primary particle size is only 20.24 nm (38.24 nm for LDH). Also, the precipitation of CIP caused by pH raised from 5 to 10 during reconstruction of LDH involved into the CIP removal mechanisms. Approximately 640.1 mg/g of CIP can be adsorbed on Cal-LDH by intercalation reaction at pH 6 but ∼2500 mg/g of CIP can be removed by precipitation caused by pH increase. In the presence of CO 3 2– and PO 4 3− , the CIP adsorption on Cal-LDH was inhibited due to competitive CO 3 or PO 4 type LDH formation. Finally, the CIP adsorbed Cal-LDH was completely regenerated by calcination at 450 ℃ for 2 h and shows more than 99 % reproducibility during 3 adsorption-regeneration cycles.