| Ethylene is the chemical with the largest production and demand in the world.The key step in the production of high-purity ethylene is the separation of acetylene/ethylene.However,the troductional separation methods have the disadvantages of high energy consumption and high cost.The development of green and efficient acetylene/ethylene separation technology is extremely challenging.In this work,a series of novel layered two-dimensional fluorinated metal-organic frameworks with ultra-micro channels and high-density binding sites are designed and synthesized by utilizing the designable structures of the layered framework materials and the strong hydrogen bonding ability of the fluorinated anion.The separation performance of these materials for trace acetylene in ethylene was studied,and its structure-activity relationship and separation mechanism were revealed,expecting to promote the development of acetylene/ethylene separation technology.Firstly,using the V-type 4,4'-bipyridyl sulphur organic ligands,inorganic fluorinated anion and metal ions,7 layered two-dimensional fluorinated MOFs with double ultra-micro intralayer and interlayer channels were synthesized.Their crystal structures,pore characteristics and stability were characterized.The results show that by systematic variancing of ligand atom oxidation state and the type of anions,the regulation of layer stacking pattern,ligand conformation and the aperture size of interlayer and intralayer space can be adjusted at the same time,to obtain the suitable channel size for acetylene/ethylene separation.The layered materials based on 4,4'-bipyridylsulfone,ZUL-100,ZUL-200 and ZUL-3 00 all had the rigid structures with permanent interlayer and intralayer ultra-micro channels,which channel size is similar to acetylene molecular,and excellent water and thermal stability.And then the adsorption equilibriums of acetylene and ethylene and column breakthrough tests for mixture on these materials were determined.The results showed that the oxidation state of the sulfur atom in the ligand can significant affect the acetylene/ethylene separation performance.The layered materials based on 4,4'-bipyridylsulfide and 4,4'-bipyridylsulfoxide had different degrees of "gate-opening" effect in acetylene adsorption,and the acetylene uptakes at low pressure are small.While the layered materials based on 4,4'-bipyridylsulfone can obtain very high acetylene uptakes at low pressure,and have the excellent acetylene/ethylene separation performance.At 298 K,the static acetylene uptake of ZUL-100 at 0.01 bar can reach 2.96 mmol/g,the separation potential of acetylene/ethylene(1/99,v/v)mixture reached 200 mmol/g,the saturation dynamic acetylene uptake from column breakthrough tests was as high as 1.92 mmol/g,and the yield of high-purity ethylene(>99.9999%)was as high as 121.2 mmol/g,which are significantly better than the benchmark.At the same time,ZUL-100 also showed very good recycling performance.The presence of moisture in the gas has no effect on the separation and recycling performance.The adsorption mechanism of acetylene and ethylene in the layered two-dimensional fluorinated MOFs was studied at the molecular level by density functional theory calculation and single crystal X-ray diffraction,revealing the key role of interlayer channels in the trace acetylene adsorption and the synergistic effect of interlayer and intralayer channels.In the bipyridylsulfone-type materials,acetylene molecules can form multiple interactions with two anions and two organic ligands from adjacent layers,arranged in a zigzag shape in the interlayer channel,and the static energy was up to 62-71 kJ/mol,far stronger than ethylene(<44 kJ/mol),thus achieving the high uptake and specific recognition of acetylene. |
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