Synthesis of metal organic frameworks based on multiazole ligands for adsorption and separation of acetylene
Acetylene(C2H2)production using the calcium carbide method produces several impurities,such as nitrogen,oxygen,and carbon dioxide.To obtain high-purity acetylene,research regarding the corresponding purification and separation is vital.Metal organic framework(MOF)materials have ultrahigh porosity and easy functionalization.Based on the specific characteristics of their pores,these materials typically possess large surface areas,abundant functional sites,and flexible and tunable pore structures.Thus,these materials demonstrate excellent performance in gas adsorption and separation.This study is based on MOF material construction using multiple nitrogen-containing imidazole ligands.A novel MOF material(Cu(Hptz)),named TYUT-15,was successfully synthesized using copper acetate monohydrate and 5-(4-pyridyl)-lH-tetrazole as raw materials.TYUT-15 has a basic structural unit comprising five-coordinated copper atoms linked to three different ligand units and two bridging oxygen atoms.Moreover,these units form a one-dimensional square channel structure with pore openings of approximately 6.0A×6.0Å and have a BET(Brunauer,Emmett and Teller)specific surface area of approximately 416 m2/g.Considering the unique square-shaped pore structures and multiple nitrogen adsorption sites,TYUT-15 triggers the dipole moment synergistic adsorption among acetylene molecules in the pores,and it improves the adsorption capacity of acetylene under the joint action of host and guest.Single-crystal X-ray diffraction,thermogravimetric analysis,single-component gas adsorption,and a breakthrough test were performed to characterize the sample structure and gas adsorption/separation performance.The results indicate that TYUT-15 is structurally stable and possesses numerous microporous structures.The single-component gas adsorption test reveals that this material has a high C2H2 adsorption capacity.The desorption isotherm of C2H2 exhibits certain hysteresis compared to the desorption isotherms of other gases,indicating a stronger interaction between TYUT-15 and C2H2.GCMC simulation calculations also support this observation by demonstrating that the adsorption heat of C2H2 is higher than that of CO2,providing further evidence of the stronger interaction between TYUT-15 and C2H2.Furthermore,TYUT-15 exhibits remarkably better adsorption capacity for C2H2 compared to CO2/N2/O2,and its adsorption capacity surpasses those of many previously reported MOF materials,including BSF-1(52.6 cm3/g),PCPs-mal(56.4 cm3/g),NTU-72(41 cm3/g),andNbOFFIVE-l-Ni(53.8 cm3/g).The IAST selectivity calculation results for TYUT-15 at 298 K and 1 bar for the equimolar gas mixture of C2H2/CO2(V/V=1/1)show that this material exhibits excellent C2H2/CO2 selectivity(11.3).Moreover,the selectivity is superior to that of most C2H2/CO2 separation materials,such as JNU-1(3.6),UTSA-74(9),DZU-11(3.6),FJU-112(4.2),and Ni-pz(10.3).The separation experiment results of the multicomponent mixed gas(C2H2/CO2/N2/O2)show that the retention time of C2H2 is approximately twice that of CO2,indicating that TYUT-15 can directly capture C2H2 from the four-component mixed gas of C2H2/CO2/N2/O2.Based on the structure construction of TYUT-15,this study utilizes the material's special square-shaped cavity characteristics and multiple nitrogen adsorption sites to achieve efficient C2H2 separation from mixed gases.This study proves that using multiazole ligands is feasible for building MOF materials for C2H2 recognition and separation.
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