Synthesis of novel nano-layered double hydroxide by urea hydrolysis method and their application in removal of chromium(VI) from aqueous solution: Kinetic, thermodynamic and equilibrium studies

Wastewater contaminated with chromium(VI) ions was released in the aquatic environment during different industrial processes and is considered dangerous, since chromium(VI) is a powerful epithelial irritant and a human carcinogen. It is therefore required to develop new materials that can effectively used to remove metallic species from liquid phase. In this perspective layered double hydroxides (LDHs) with Co/Bi = 3 were synthesized via urea hydrolysis method. The as-prepared LDH material was further characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The adsorption behavior of Cr (VI) was studied at different initial concentrations (100-500 mg/L), contact time (15-120 min), pH (2.0-12.0), temperature (298-318 K) and adsorbent dose (0.1-0.5 g) by batch equilibrium technique. Adsorption experiments indicate that the maximum adsorption capacity of Cr(VI) reached to 277.7 mg/g on the optimum adsorption conditions (dosage of 0.1 g, contact time for 120 min., pH at 7 and temperature at 283 K). The kinetic data agrees well with pseudo-second order (R-2 = 0.995). The adsorption isotherm study reveals that experimental data fitted well in both Freundlich and Redlich-Peterson model. The study of thermodynamic parameters indicated that adsorption of Cr(VI) is spontaneous and exothermic in nature. Desorption study recommends that adsorbent can be easily regenerated by 0.1 M NaHCO3. (C) 2014 Elsevier B.V. All rights reserved.