Magnetic MgAl-LDH for Adsorptive Removal of Malachite Green from Water

Malachite Green removal from water using Layered Double Hydroxide/iron oxide nanoparticles as magnetic adsorbent was investigated due to the environmental risk that the difficulty of treatment and incorrect disposal of colored pollutants entail. Characterization, adsorption capacity, kinetics and equilibrium studies of the materials were carried out. The adsorbents reaching equilibrium showed MG adsorbed amounts (q(e)) of 198.94 and 172.13 mg g(-1) for LDH and LDH/Iron oxides, respectively. Furthermore, for the three materials, in the kinetic study at low concentrations for metal oxides, a rapid adsorption was observed, with more than 80% of equilibrium reached in 200 min, while LDH took almost 400 min for the same performance. The composite kinetic behavior highlighted that the metallic oxides ensured that 80% adsorption was achieved below 200 min, and the pseudo-first order model was the one that best fitted for all materials. In addition, through the adsorption isotherms, a better fit to the Sips model was observed. Although LDH and the composite (LDH/Iron oxides) have shown excellent efficiency for pollutant removal, the difference lies in the adsorbent recovery process. LDH are well known as effective adsorbents for pollutant removal, but they have disadvantages linked to their mechanical properties and the costs related to material losses through the processes. The magnetic composite presented was able to improve the adsorbent material properties without losing its excellent adsorptive capacity, being a new competitive material against other adsorbents present in the current global market and showing superiority above 100% of removal when compared with biochar-LDH composites and isolated LDH's.{graphical abstract)