Organic dye removal from aqueous solutions by hierarchical calcined Ni-Fe layered double hydroxide: Isotherm, kinetic and mechanism studies

Hierarchically porous nickel-iron-layered double hydroxide (NiFe-LDH) with a Ni2+/Fe3+ molar ratio of 3 was successfully synthesised through a simple hydrothermal route. After calcination at 400 degrees C, NiFe-LDH transformed into nickel-iron-layered double oxides (NiFe-LDO). The as-prepared samples were characterised through X-ray powder diffraction, field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption. The calcined and uncalcined NiFe-LDH was used as adsorbents to remove Congo red (CR) dye in an aqueous solution. The equilibrium adsorption data of NiFe-LDH and NiFe-LDO samples were well fitted to Langmuir model and were characterised by excellent adsorption capacities of 205 and 330 mg/g, respectively. Pseudo-second-order kinetic and intra-particle diffusion models indicated that CR was well adsorbed on the adsorbent. The underlying adsorption mechanism was investigated and observed as anion exchange and reconstruction.(C) 2017 Elsevier Inc. All rights reserved.