MIL-101 was prepared from hydrothermal reaction of Cr(NO 3 ) 3 9H 2 O (2.00 g, 5 mmol), HF (48 wt %, 5 mmol), terephthalic acid (0.823 g, 5 mmol), and 24 ml deionized water at 220 C for 8 h. The mixture was cooled first to 150 C in 1 h, and then slowly to room temperature in 12 h. Upon the slow cooling procedure, most of the residual carboxylic acid was in large crystals that can be easily isolated from the solution and MIL-101 powder by using a large pore fritted glass filter (n2, Schott).

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... The free terephthalic acid was eliminated and the green MIL-101 powder was isolated from the solution using a small pore paper filter (1, Whatman). The powder was washed thoroughly with deionized water and ethanol, and then soaked in ethanol (95% EtOH with 5% water) at 80 C for 24 h. The solid was finally dried overnight at 150 C under vacuum. Synthesis of EN-MIL-101 S2 MIL-101 grafted with ethylenediamine (EN) was prepared according to the following procedures. MIL-101 (0.5 g) dehydrated at 423 K for 12 h was suspended in anhydrous toluene (30 ml). To this suspension, ethylenediamine (0.045 g) was added and the mixture was stirred under reflux for 12 h. The product was recovered by filtration and washed with de-ionized water/ethanol, and then dried at room temperature for 24 h.