Regenerable Mg/Fe bimetallic hydroxide for remarkable removal of low-concentration norfloxacin from aqueous solution

Abstract

The widespread existence of antibiotics in aquatic environments has gained much concern due to their non-biodegradability and eco-toxicity, which would easily destroy the ecological balance. In this work, the synthesized Mg/Fe layered bimetallic hydroxides (Mg/Fe LDHs) was first used to adsorb low concentration norfloxacin (NOR) antibiotics in water. It was found that the LDH adsorbent with a Mg/Fe molar ratio of 5:1 (MF5:1) exhibited superior adsorption properties for the removal of low concentration (20 mg·L-1) of Norfloxacin (NOR). The adsorption capacity could reach to ~ 97.07 mg·g-1 at neutral pH. Kinetic fitting shows that it could be well described by Pseudo-second-order models, indicating that chemical adsorption dominants the process. Also, the isothermal adsorption data could be well fitted by Freundlich isotherm model, which suggests a multilayer adsorption process. The adsorbent has good properties of salt resistance with ~ 5% and 30% decrease of removal efficiencies in 0.1 mol·L-1 KCl and CaCl2 solution, respectively. By contrasting the structural variation of the adsorbent before and after adsorption, it could be inferred that coordination and hydrogen bonding rather than electrostatic interaction might be the main forces between NOR and Mg/Fe5:1 nanocrystal. In addition, the recover of the adsorbent could be easily achieved by pyrolysis and rehydration circle with little decrease of adsorption property. Our finding suggests that Mg/Fe LDHs can be severed as a promising candidate for the removal of antibiotics, especially for the low concentrations of NOR.