Construction of OH sites within MIL-101(Cr)-NH2 framework for enhanced CO2 adsorption and CO2/N2 selectivity

The MIL-101(Cr)-NH2 framework was effectively modified by 2,5-dihydroxyterephthalic acid ((HO)(2)BDC) guest molecules to obtain (HO)(2)BDC-incorporated MIL-101(Cr)-NH2 adsorbent, namely (HO)(2)BDC@CrN. The CO2-temperature programmed-desorption (TPD) analysis indicated that the incorporation of (HO)(2)BDC into the MIL-101(Cr)-NH2 framework generated new OH sites besides unsaturated Cr- metal sites and NH2 sites. The formed OH sites improved CO2 adsorption and separation on the prepared adsorbent. The highest CO2 uptake capacity of similar to 3.58 mmol g(-1) obtained over the novel (HO)(2)BDC@CrN adsorbent was higher 40% than that of the parent MOF, and also surpasses that of other previously reported adsorbents, including activated carbon, nitrogen-doped hollow carbon, zeolite, ZIF-68, MOF-5, ZIF-8, UiO-66(Zr), and MIL-100(Cr). The highest ideal adsorbed solution theory (IAST) CO2/N-2 selectivity of similar to 67 was obtained over the (HO)(2)BDC@CrN adsorbent at 100 kPa. The achieved selectivity was six times greater than that of pure MIL-101(Cr)-NH2. In addition, the synthesized (HO)(2)BDC@CrN adsorbent displayed good regenerability after six consecutive adsorption-desorption cycles.