Calcined MgFe layered double hydroxides for magnetic separation and enhanced adsorption performance of methyl orange: Mechanism based on the memory effect

Abstract

This study successfully synthesized magnetic MgFe-layered double oxides (MgFe-LDO-500 °C) by calcining MgFe-layered double hydroxides (MgFe-LDHs) at 500 °C. Calcination temperature was identified as a critical factor for optimizing adsorption capacity and activating a memory effect, with 500 °C being particularly effective. The adsorption performance of MgFe-LDO-500 °C towards methyl orange (MO) in aqueous solutions was evaluated across varying pH levels (2–12), initial MO concentrations (50–1800 mg/L), contact times (0–1440 min), and temperatures (25–45 °C). The results indicated that MgFe-LDO-500 °C adsorption conforms to the pseudo-second-order kinetic and Langmuir models, achieving a theoretical maximum adsorption capacity of 5087.76 mg/g. Characterization through scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Zeta potential analysis revealed that the outstanding adsorption performance of MgFe-LDO-500 °C towards MO involves a combination of electrostatic attraction, memory effect, and surface complexation. Moreover, after four regeneration cycles, the material maintained a 73 % MO removal efficiency and could be efficiently separated using magnetic separation technology. In conclusion, MgFe-LDO-500 °C represents a promising adsorbent for wastewater treatment.