Hybrid Metal-Organic Framework-Reduced Graphene Oxide Nanomaterial for Selective Removal of Chromate from Water in an Electrochemical Process.

Hexavalent chromium Cr(VI) is a highly toxic groundwater contaminant. In this study, we demonstrate a selective electrochemical process tailored for removal of Cr(VI) using a nanocomposite electrode material [email protected] synthesized by in situ growth of a nanocrystalline, mixed ligand octahedral metal-organic framework with cobalt metal centers, [Co2(btec)(bipy)(DMF)2]n (Co-MOF), on the surface of reduced graphene oxide (rGO). The rGO provides the electric conductivity necessary for an electrode, while the Co-MOF endows highly selective adsorption sites for CrO42-. When used as an anode in the treatment cycles, the [email protected] electrode exhibits strong selectivity for adsorption of CrO42- over competing anions including Cl-, SO42- and As(III), and achieves charge efficiency >100% due to the strong physisorption of CrO42- by Co-MOF; both electro- and physi- sorption capacity is regenerated with a reversal of the applied voltage, when highly toxic Cr(VI) is reduced to low toxicity, reduced Cr species and subsequently released into the brine. This approach allows easy regeneration of the nonconducting Co-MOF without any chemical addition while simultaneously transforms Cr(VI), inspiring a novel electrochemical method for highly selective degradation of toxic contaminants using tailor designed electrodes with high affinity adsorbents.