Effect of purification conditions on gas storage and separations in a chromium-based metal-organic framework MIL-101

The effect of purification condition of a chromium terephthalate MIL-101 on gas storage (H-2, CO2, and C2H2) and C2 hydrocarbon separations was investigated for MIL-101a, MIL-101b, and MIL-101c, which were obtained by three-step sequential purification using hot water/ethanol and aqueous NH4F solution treatments. MIL-101c was the best in terms of gas storage capacities among the three samples possibly due to the removal of free and coordinated terephthalic acids. Remarkably, MIL-101c exhibits among the highest total hydrogen uptake at 50 bar and 77 K (9.9 wt%) and shows considerably large deliverable capacity between 1.5 and 50 bar (7.6 wt%). Moreover, MIL-101c shows among the highest C2H2 storage capacity (6.4 mmol g(-1)) and deliverable capacity (4.3 mmol g(-1)) at 1 bar and 313 K. For C2H2/C2H6, C2H2/C2H4, and C2H4/C2H6 separations, MIL-101c exhibits higher adsorption capacities, working capacities and adsorption figure of merit (AFM) values while MIL-101b shows higher selectivities and sorbent selection parameters. These results clearly show that a proper purification of MIL-101 is important for gas storage and gas separations. (C) 2014 Elsevier Inc. All rights reserved.