Synthesis Of Metal-Organic Frameworks And Their Gas Adsorption Capacity

Metal-Organic Frameworks (MOFs) is a new class of porous materials. They have been attracting a great deal of attention for their potential application in many fields such as gas storage and separation, catalysis and drug delivery due to their high specific surface area, tunable pore structure, chemically modifiability and many other characteristics. Numerous researches have been focus on the synthesis of high specific surface area of MOFs. In addition, the post-synthetic modification (PSM) of MOFs could endow the pristine materials many new features and expand their application. Therefore, it is of utmost important for the synthesis of high specific surface area of MOFs as well as the post-synthetic modification of MOFs.MIL-101(Cr) was chosen as the research object in this work. MIL-101(Cr) and MIL-101(Cr)-NH2with high specific surface area were synthesized via the modified hydrothermal method. MIL-101(Cr)-NH2was chemically modification by dual acyl-chloride compound for the first time. The detailed research work is outlined as follows:MIL-101(Cr) with high surface area was synthesized via an acetate-assisted hydrothermal method successfully. Effects of the amount of acetate addition in the reaction mixture on the structure, morphology and surface area of MIL-101(Cr) were investigated. Results show that MIL-101(Cr) particles with size around250nm and the BET specific surface area exceeding3300m2·g-1can be obtained at the optimum condition when the molar ratio of acetate to Cr(NO3)3is0.15:1. Gas adsorption characterization demonstrate that the MIL-101(Cr) sample synthesized by acetate-assisted hydrothermal method exhibits better CO2adsorption capacity and selectivity than that synthesized by traditional hydrothermal method. The CO2adsorption capacity could be47%higher and the selectivity of CO2/N2and CO2/CH4is3and3.7times higher than the latter at298K and0.1MPa.Nano MIL-101(Cr)-NH2particles with high surface area was synthesized via an alkali-assisted hydrothermal method. Effects of the amount of NaOH addition in the reaction mixture on the structure, morphology and surface area of MIL-101(Cr)-NH2were investigated. The results show that when the molar ratio of NaOH to NH2BDC is4:2, the particle size of the resulting sample is estimated to be around40nm with the BET specific surface area and the pore volume up to2594m2-g"’ which is the highest so far. The adsorption of CO2on the MIL-101(Cr)-NH2sample reaches25.9mmol·g-1and the ideal selectivity of CO2over N2is19.4at273.4K.Covalent modification of MIL-101(Cr)-NH2was implemented by the reaction of oxalyl chloride (terephthaloyl dichloride) with the amino group on the skeleton of MIL-101(Cr)-NH2under moderate condition. The results indicate that the functionalized MIL-101(Cr)-NH2samples exhibit smaller pore size distribution and better thermal stability than that of pristine MIL-101(Cr)-NH2sample, which can be stable up to380℃in the air. The Ideal selectivity of CO2to N2for the functionalized MIL-101(Cr)-NH2samples could be50.4%higher than that for pristine MIL-101(Cr)-NH2sample at298K and0.1MPa. We believe that this strategy is also available for the chemical modification of other amino-functionalized MOFs.