Design of Highly Connected Cd-Tetrazolate-Dicarboxylate Frameworks with Enhanced CO2/CH4 and C-2 Hydrocarbons/CH4 Separation Performance

摘要

Highly connected crystalline porous materials are rare but promising for gas adsorption and separation since varying pore shape and size as well as high framework stability may be achieved by tuning the framework connectivity. We demonstrate herein two highly connected frameworks, namely, {[Cd-7(BDC)(6)(MTAZ)(2)(DMF)(6)].3DMF}(n) (SNNU-11) and {[ Cd-5(BDC) (PTAZ)(8)(DMF)(2)].4DMF}(n) (SNNU-12) (BDC = 1,4-benzenedicarboxylic acid, MTAZ = 5-methyl-tetrazole, and PTAZ = 5-(4-pyridyl)-tetrazole). In SNNU-11, BDC ligands link S-shaped [Cd-7(MTAZ)(2)] motifs to form a novel 10-connected framework, which is related to but different from the reported 10-connected bct and gpu nets. Under the similar synthesis condition, the utilization of 5-(4-pyridyl)-tetrazole produced SNNU-12, which is constructed from zigzag Cd5 clusters and exhibits a 12-connected fcu net. Notably, SNNU-12 decorated with uncoordinated nitrogen sites shows not only high CO2 uptake capacity (87.9 crn(3) g(-1), 1 atm, and 273 K) but also high CO2 over CH4 and C-2 hydrocarbons over CH4 selectivity, which is among the highest values of highly connected MOF materials (connectivity >= 10) including famous UiO-66 and rare-earth fcu-MOFs under the same temperature and pressure.