A novel bimetallic MIL-101(Cr, Mg) with high CO2 adsorption capacity and CO2/N2 selectivity

• A novel bimetallic MIL-101(Cr, Mg) was successfully synthesized.
• New CO2 adsorptive sites on MIL-101(Cr, Mg) surfaces were formed due to Mg doping.
• The bimetallic MIL-101(Cr, Mg) exhibits higher CO2 uptake than MIL-101(Cr).
• MIL-101(Cr, Mg) shows high CO2/N2 adsorption selectivity up to 86.
• Isosteric heat of CO2 adsorption on MIL-101(Cr, Mg) is higher than that on MIL-101(Cr).

A novel bimetallic MIL-101(Cr, Mg) was successfully synthesized for the first time by doping Mg during the solvothermal synthesis of MIL-101(Cr), and then characterized. The doped magnesium was homogeneously dispersed in the crystals of MIL-101(Cr, Mg). The magnesium ions had successfully coordinated with the carboxylic group in BDC through Mg–O. The synthesized MIL-101(Cr, Mg) remained excellent moisture-stability after exposed to humid air with 90% relative humidity for 30 days. Importantly, Mg doping not only made MIL-101(Cr, Mg) had higher surface area than MIL-101(Cr), but also created new and strong adsorptive sites for CO2 confirmed by TPD experiments. As a result, CO2 adsorption capacity of MIL-101(Cr, Mg) was significantly improved, and reached 3.28 mmol/g at 298 K and 1 bar, having an increase of 40% in comparison with MIL-101(Cr). More importantly, the CO2/N2 adsorption selectivity of MIL-101(Cr, Mg) was significantly enhanced up to 86 at 100 kPa, being ~4 times of that of MIL-101(Cr). The strategy of doping metal ions can be an effective way to improve the adsorption performance of MOFs.

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