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

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.

New Supercage Metal–Organic Framework Based on Allopurinol Ligands Showing Acetylene Storage and Separation

“…Q st for C 2 H 2 , CO 2 and CH 4 were in the range of 31.1–26.9, 32.3–26.5 and 23.6–20.9 kJ mol −1 , respectively (Figure 3 d). The Q st value of C 2 H 2 in 1 is higher than many of reported MOFs, such as 1‐mim (16.13 kJ mol −1 ), [42] FIR‐51 (24.48 kJ mol −1 ), [43] and Zn‐F‐DATRZ (20.8 kJ mol −1 ) [44] …”

Regulation on Topological Architectures and Gas Adsorption for Cadmium-Azolate-Carboxylate Frameworks by the Ligand Flexibility

“…However, most of the current flexible MOFs only choose a single flexible or rigid organic ligand in the synthesis process, which greatly hinders the development of flexible MOFs. In addition, since the metal azolate framework mainly constructed by triazole or tetrazole and transition metals have functional groups of aromatic −N­(H) donors to strengthen the MOF skeleton and acidic gas molecules interactions, the development of such MOFs has also attracted much attention. − Although many metal azolate frameworks have been reported, it is still a challenge to construct a skeleton with as many N-donor sites as possible. Compared with individual triazole or tetrazole, organic ligands containing multiple triazole or tetrazole groups have more N-donor sites and the coordination models are more diverse.…”

A microporous, amino acid functionalized Zn(ii)-organic framework nanoflower for selective CO2capture and solvent encapsulation

“…[14][15][16] As the landfill-gas is a combination of polar (CO 2 ) and non-polar (CH 4 ) gas, the criteria for the selectivity of CO 2 are: (a) an access to open metal sites and polar N-containing basic functional groups, which show adsorbateadsorbent interaction due to quadrupole interaction of CO 2 molecules with the framework, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] and (b) an appropriate pore diameter of the framework for size/shape exclusion. [31][32][33][34][35][36] It should be noted that initial efforts with zeolitic and zeoliticlike metal imidazolate framworks (ZIFs) that have excellent affinity for CO 2 due to the presence of -N(H) donors on the imidazole moieties have suffered for less uptake capacity and selectivity for CO 2 for not having open metal sites. 37 On the other hand, flue gases also have water vapour apart from CO 2 .…”