Cost-effective and eco-friendly synthesis of MIL-101(Cr) from waste hexavalent chromium and its application for carbon monoxide separation

Abstract

Conventionally, MIL-101(Cr) has been directly prepared from analytically pure trivalent chromium (Cr(III)) with the assistance of hydrofluoric acid (HF). Here, we report a novel approach of HF-free synthesis of MIL-101(Cr) using a waste Cr source. A wastewater model containing a high concentration of hexavalent Cr (Cr(VI)) was first reduced by sulfite to obtain Cr(III) at room temperature and subsequently, the resulting solution was directly used as a precursor for MIL-101(Cr) synthesis without HF. The synthesized MIL-101(Cr) had surface area of 2850 m2/g and pore volume of 1.54 cm3/g which are comparable to the one conventionally prepared with analytically pure Cr(III). The MIL-101(Cr) after Cu(I) loading became CO-selective π complexation adsorbents, showing much higher CO adsorption capacity (2.82 mmol/g) than CO2 (0.85 mmol/g) and N2 (0.08 mmol/g).