Synthesis of novel magnetic rhamnolipid-activated layered double hydroxides nanocomposite for simultaneous adsorption of Cu(II) and m-cresol from aqueous solution

Abstract

A novel magnetic rhamnolipid (RL)-activated layered double hydroxides (LDH) nanocomposite (Fe3O4/RL-LDH) was prepared by coprecipitation and ion exchange method for the simultaneous adsorption of Cu(II) and m-cresol from aqueous solution. The physical and chemical properties of Fe3O4/RL-LDH were characterized using various techniques, and it was found that Fe3O4/RL-LDH exhibited platelet-like morphology, i.e., tiny Fe3O4 particles with diameter of approximately 40 nm were dispersed over the RL-LDH lamella. Adsorption experiments were carried out to remove Cu(II) and m-cresol by changing the adsorption conditions such as adsorbent dosage (0.2–2 g·L−1), pH (5–10), initial Cu(II) and m-cresol concentrations (10–200 mg·L−1 and 5–100 mg·L−1), adsorption time (0–180 min), temperature (25–45 °C) and coexisting anions (SO42− and NO3−). The optimum adsorbent dosage, pH and contact time to reach equilibrium were 0.8 g·L−1, 5.5 and 120 min, respectively. The experimental results showed that the adsorption kinetics of Fe3O4/RL-LDH for Cu(II) and m-cresol agreed well with the pseudo-second-order kinetic equation, and the adsorption isotherms were well depicted by the Freundlich equation. According to the results obtained from adsorption kinetics and thermodynamic studies, powder X-ray diffractometer (PXRD) and X-ray photoelectron spectroscopy (XPS) analysis of Fe3O4/RL-LDH before and after adsorption, it could be inferred that the adsorption mechanism of Cu(II) mainly involved the complexation between RL anions (intercalated in the interlayers of LDH) with Cu(II) ions and that of m-cresol involved the hydrophobic interaction between RL anions and m-cresol. Both Cu(II) and m-cresol adsorptions were spontaneous and exothermic. The magnetic property of Fe3O4/RL-LDH enabled the separation and recovery of Cu(II) and m-cresol from aqueous solution using an external magnet. Thus, the novel magnetic adsorbent Fe3O4/RL-LDH has a potential for simultaneous remediation of organic and heavy metal pollutants.