Tuning the CO2 and C1/C2 Hydrocarbon Capture and Separation Performance for a Zn-F-Triazolate Framework through Functional Amine Groups

Hai-Peng Li, Shu-Ni Li, Hua-Ming Sun, Man-Cheng Hu, Yu-Cheng Jiang, Quan-Guo Zhai

Index: 10.1021/acs.cgd.8b00389

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Abstract

Functionalization by amine groups has been recognized as an effective route to promote the gas capture and separation performance of MOF materials; however, it remains elusive to date what is the optimal number of functional amine groups and which specific MOFs are suitable to be functionalized. To answer these questions, systemic investigations on the interactions between gas molecules and NH2-functionalized MOFs are necessary. Here a microporous Zn-F-triazolate framework which can be easily decorated by different −NH2 groups is selected (Zn-F-TRZ, Zn-F-ATRZ, and Zn-F-DATRZ; TRZ = 1,2,4-triazole, ATRZ = 3-amino-1,2,4-triazole, DATRZ = 3,5-diamino-1,2,4-triazole) to discuss the effect of amine groups on CO2 and C1/C2 hydrocarbon capture and separation. When the pressure is lower than about 0.15 atm, the CO2 uptakes increase directly with the number of anime groups (Zn-F-TRZ < Zn-F-ATRZ < Zn-F-DATRZ). However, at 1 atm, the decoration of one amine group effectively improves the CO2 adsorption of the Zn-F-triazolate framework, and the addition of a second amine group clearly decreases the CO2 uptakes. A similar uptake trend has been observed for C1/C2 hydrocarbons except for C2H2, which decrease dramatically with the number of amine groups. These results show that the combination of amine functional groups and appropriate pore size is responsible for the low-pressure binding and uptake of CO2 and C1/C2 hydrocarbon molecules in Zn-F-triazolate MOFs. Furthermore, thanks to the functionalization by amine groups, these Zn-F-triazolate frameworks all show excellent gas separation performance. Especially, the initial C2H2/CH4 selectivity (107.0) for Zn-F-ATRZ and initial CO2/CH4 (115.7), C2H4/CH4 (78.9), and CO2/C2H2 (5.9) selectivities for Zn-F-DATRZ at room temperature all surpass those of most of the MOFs reported up to now.