Ni-Fe/Reduced Graphene Oxide Nanocomposites for Hexavalent Chromium Reduction in an Aqueous Environment.

We designed and synthesized a novel high efficiency Cr(VI) removal material using reduced graphene oxide (RGO) as a support with high specific surface area and a mixture of Fe and Ni nanoparticles (NPs) as a catalytic reducing agent. Such a design enables the composite particle to be integrated with three functions of adsorption, catalysis, and reduction, where RGO could enhance Cr(VI) adsorption, while Fe/Ni NPs increase the catalytic reducing efficiency. The application of a microchip mixer guaranteed a better mixing of GO and subsequent decoration of Fe and Ni NPs on RGO. Cr(VI) removal experiments with various materials are performed, and the results demonstrated that the Ni-Fe/RGO achieved an adsorption capacity of 150.45 mg/g at pH = 7 and 197.43 mg/g at pH = 5 for Cr(VI), which is higher than those of other reported materials at a pH of ∼7. To the best of our knowledge, this is the first example of Ni-Fe/RGO for efficient Cr(VI) removal by using the synergistic effects of increased adsorption, catalysis-assisted reduction, and enhanced mixing effect of a microchip mixer. This work also provides us with a simple and low-cost method for the fabrication of an effective Cr(VI) removal material.