Reusable composite membranes for highly efficient chromium removal from real water matrixes

Abstract

Hexavalent chromium water contamination is still a worldwide concern because this highly mobile ion can cause carcinogenic effects on animals and humans. Therefore, there is an intense research on new active and cost-effective sorbents for Cr(VI), but most of them still exhibit a critical limitation: their powdered nature makes their recovery from water cost and energyconsuming. In this work, Cr(VI) nano-sorbents (i.e., Al(OH)3, MIL-88-B(Fe), and UiO-66- NH2) have been immobilized into a poly (vinylidene fluoride-co-hexafluoropropylene) (PVDFHFP) polymeric substrate to develop an easily reactivable and reusable Cr(VI) filtering technology. The microstructure, morphology, and surface properties of the active nanoparticulated sorbents and the corresponding nanocomposite membranes (NCM) have been characterized from the macrometric to the nanometric scale. The immobilization of the nano sorbent into the PVDF-HFP porous matrix induces a templating effect of the porous structure and allows to tune the hydrophobic/hydrophilic nature of the NCMs. Although a partial blocking of the Cr(VI) adsorptive capacity for Al(OH)3 and MIL-88-B(Fe) based membranes with respect to the pristine nanosorbents was observed, UiO-66-NH2 composite filters maintain the full capacity of the active material to trap Cr(VI), achieving a maximum adsorption capacity of 59.9 mg/g. Despite the slow-down of the Cr(VI) adsorption kinetics of the UiO-66- NH2/PVDF-HFP NCM compared to the active material in suspension, the hybrid system allows easy recovery and activatation, is functionally stable over adsorption-desorption cycling, and is highly robust in terms of efficiency when applied in real effluent water samples.