A facile approach has been developed to construct a composite of magnetic Fe3O4 (MNPs) and regular hexagon Mg-Al layered double hydroxide (MNPs/MgAl-LDH) via a two-step hydrothermal method combined with the urea hydrolysis reaction for the removal of Orange II. The scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy results showed MNPs and MgAl-LDH have been combined successfully, providing the combination of the superior properties of fast separation and high adsorption capacity. The pH values, contact time, initial dye concentration and temperature were investigated in detail. The kinetics and isotherm study showed the adsorption of Orange II on MNPs/MgAl-LDH obeyed the pseudo-second-order and Langmuir model respectively and the adsorption processes were spontaneous and endothermic in nature. Also, some coexisting anions such as Cl−, NO3−, CO3− and SO42− had no significant effect on the removal of Orange II. The mechanism study revealed that the adsorption of Orange II on MNPs/MgAl-LDH mainly involves surface adsorption through electrostatic force and the layer anion exchange. Moreover, Orange II could be desorbed from MNPs/MgAl-LDH using 100 mg L−1 NaOH and used for four cycles without any adsorption performance loss, demonstrating MNPs/MgAl-LDH prepared in this work could be used as a cost-effective and efficient material for the removal of Orange II.

adsorption, layered double hydroxide, magnetic nanoparticles, Orange II
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