Metal–Organic Gel Material Based on UiO‐66‐NH₂ Nanoparticles for Improved Adsorption and Conversion of Carbon Dioxide

Abstract

Metal-organic frameworks (MOFs) including the UiO-66 series show potential application in the adsorption and conversion of CO2 . Herein, we report the first tetravalent metal-based metal-organic gels constructed from Zr(IV) and 2-aminoterephthalic acid (H2 BDC-NH2 ). The ZrBDC-NH2 gel materials are based on UiO-66-NH2 nanoparticles and were easily prepared under mild conditions (80 °C for 4.5 h). The ZrBDC-NH2 -1:1-0.2 gel material has a high surface area (up to 1040 m(2) g(-1) ) and showed outstanding performance in CO2 adsorption (by using the dried material) and conversion (by using the wet gel) arising from the combined advantages of the gel and the UiO-66-NH2 MOF. The ZrBDC-NH2 -1:1-0.2 dried material showed 38 % higher capture capacity for CO2 at 298 K than microcrystalline UiO-66-NH2 . It showed high ideal adsorbed solution theory selectivity (71.6 at 298 K) for a CO2 /N2 gas mixture (molar ratio 15:85). Furthermore, the ZrBDC-NH2 -1:1-0.2 gel showed activity as a heterogeneous catalyst in the chemical fixation of CO2 and an excellent catalytic performance was achieved for the cycloaddition of atmospheric pressure of CO2 to epoxides at 373 K. In addition, the gel catalyst could be reused over multiple cycles with no considerable loss of catalytic activity.

Self‐Assembly of Metal–Organic Frameworks into Monolithic Materials with Highly Controlled Trimodal Pore Structures

“…The mesopore size distributions are depending on the size of the primary particles, and the larger size of the primary particles should result in the larger mesopore size. In addition, it has been reported that the crystallization and grain growth behavior of UiO‐66 are critically influenced by the solvent composition . In this case, therefore, it is considered that the grain growth is more significantly impeded in the solvent containing PPG than in the solvent without PPG, and as a result, the difference in the mesopore size distribution was observed.…”

“…However, in general, the high crystallization tendency of MOFs impedes such uniform gelation. Opaque gels composed of aggregated crystallites coarse enough to scatter the visible light thus have been obtained in previous works . Macroporous structure is not controllable in such cases because the formation of macropores relies on the uncontrolled aggregation of coarse crystallites.…”

“…In this study,a saproof of concept, we focused on Zrbased UiO-66 type MOF,which undergoes sol-gel transition by self-assembly of Zr clusters and terephthalic acid. [11,22,23] TheM OF UiO-66, with the formula [Zr 6 O 4 (OH) 4 (bdc) 6 ] (bdc = 1,4-benzenedicarboxylate), is one of the most important MOFs owing to its high thermal, chemical, and mechanical stabilities, [24,25] and has been increasingly studied for av ariety of applications for example,c atalyst, [26,27] catalyst support, [28,29] adsorbent, [30] gas storage medium, [11] and liquid or gas separation medium. [31,32] We used 2-aminoterephthalic acid (BDC-NH 2 )a so rganic linker to obtain UiO-66-NH 2 because of its good solubility in solvents such as N,Ndimethylformamide (DMF).…”

Gel-based morphological design of zirconium metal–organic frameworks

“…47–51 For example, the synthesis of UiO-66-(COOH) 2 from ZrCl 4 in water proceeds through the formation of a white gel. 48,49 Gelation during the synthesis scale-up of UiO-66, using zirconyl chloride octahydrate (ZrOCl 2 ·8H 2 O) as precursor, was also reported by Ragon and coworkers.…”

“…50 Finally, Liu et al described a MOF gel synthesized from an ethanol–DMF mixture using 2-aminoterephthalic acid and ZrCl 4 . 51 However, detailed investigations into the synthesis or structure of such gels are sparse; there are no reports on formation of crystalline monolithic materials or hierarchically porous architectures from these gels.…”