Self-assembled nickel cocoon-like structure and its superior adsorption for Cr(VI) pollutants

In this work, a unique nickel cocoon-like structure was synthesized by a facile water-bath reaction. The agitation modes adopted during its synthesis were of utmost importance to its formation. To obtain this structure, less reaction time was needed when magnetic stirring was employed, while less amount of hydrazine hydrate was needed after long-time reaction under mechanical agitation. Moreover, the saturation magnetization of this structure was 48-108 emu g(-1) depending on the reaction time and the dosage of hydrazine hydrate in its synthesis. The as-obtained nickel cocoon-like structure was then investigated as a potential magnetic adsorbent for Cr(VI) removal in wastewater. Its adsorption process could be depicted using pseudo-second-order model and intra-particle diffusion model. The numerous hydroxyl groups anchored on the adsorbent would sufficiently exchange with Cr(VI) species (e.g., Cr2O72- and HCrO4- anions) in water to promote the chemisorption process, resulting in a high adsorption capacity of 345 mg g(-1) and high regeneration efficiencies above 95% after six adsorption-desorption cycles. (C) 2018 Elsevier B.V. All rights reserved.