Double-solvent-assisted synthesis of bimetallic CuFe-incorporated MIL-101(Cr) for improved CO-adsorption performance and oxygen-resistant stability

Abstract

In this study, a bimetallic CuFe-incorporated MIL-101(Cr) adsorbent was developed with enhanced CO-adsorption capacity and oxygen resistance. Different compositions of bimetallic Cu(II)–Fe(II) were incorporated into the MIL-101(Cr) framework with ultrahigh porosity by the double-solvent (DS) method, followed by facile reduction at a low temperature of 250 °C. By employing formate (HCOO−), Cu(II) was selectively reduced to Cu(I) at 250 °C. Moreover, the presence of the reducing agent, Fe(II), enhanced the reduction of Cu(II) in the adsorbent. The obtained results indicated that the synergistic effect of utilizing Fe(II) and employing the DS method significantly enhanced the dispersion of the formed Cu(I) in the support. The DS-assisted CuFe (4 mmol g−1 of CuCl and 1.0 mmol g−1 FeCl2)-incorporated MIL-100(Fe) adsorbent exhibited a high CO-adsorption capacity of ca. 3.24 mmol g−1 and CO/N2 selectivity of 428 at 25 °C and 100 kPa, which were superior to those of the counterpart that was prepared by the wetness impregnation method. Additionally, the CO-adsorption capacity of the prepared CuFe-incorporated MIL-100(Fe) was still 90–65% after it was exposed to atmospheric humidity for 15–30 days, thereby demonstrating its superior oxygen-resistant stability compared to those of the benchmark π-complexation adsorbents containing Cu(I).