Enhancing light hydrocarbons storage and separation through introducing Lewis basic nitrogen sites within a carboxylate-decorated copper-organic framework

Xiuping Liu, Weidong Fan, Minghui Zhang, Guixia Li, Haijun Liu, Daofeng Sun, Lianming Zhao, Houyu Zhu, Wenyue Guo

Index: 10.1039/C8QM00105G

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Abstract

A novel nanoporous Cu metal-organic framework (NEM-4) with open CuII sites, Lewis basic nitrogen sites, and uncoordinated -COO- groups, exhibits both outstanding uptake capacities (in cm3 (STP) g-1) for C2H2 (204), C2H4 (164.1), C2H6 (172.2), C3H6 (197.4), and C3H8 (196.1) and high selectivities for C2H2/CH4 (63.2), C3H6/CH4 (174.8), C3H8/CH4 (168.3) at ambient conditions. After eight cycles of adsorption-desorption tests, only 8.2% and 10.3% of acetylene and propene storage capacities decrease, indicating an excellent repeatability. Compared with 1 (carboxylate decorated NOTT-101), when nitrogen sites are inserted, the C2−C3 hydrocarbons uptakes of NEM-4 can be significantly enhanced. Grand Canonical Monte Carlo and first-principle calculations reveal that not only the open CuII sites but also the uncoordinated -COO- groups and the nitrogen sites play the significant roles in its high C2−C3 hydrocarbons uptakes. Moreover, the adsorption and separation of cationic dye in NEM-4 are highly size and charged state dependence, and the adsorbed methylene blue (MB+) in NEM-4 can be efficiently released in NaCl-containing CH3OH solution. This study reveals that the combination of open metal sites, carboxylate groups, Lewis basic pyridyl sites, and appropriate pore geometry is responsible for the high adsorption/separation of light hydrocarbons in NEM-4.