“Hard” Emulsion-Induced Interface Super-Assembly: A General Strategy for Two-Dimensional Hierarchically Porous Metal–Organic Framework Nanoarchitectures
Ji Han, Haidong Xu, Bin Zhao, Ruigang Sun, Guangrui Chen, Tianyu Wu, Guiyuan Zhong, Yanjing Gao, Song Lin Zhang, Yusuke Yamauchi, Buyuan Guan
Abstract
Two-dimensional (2D) hierarchically porous metal–organic framework (MOF) nanoarchitectures with tailorable meso-/macropores hold great promise for enhancing mass transfer kinetics, augmenting accessible active sites, and thereby boosting performance in heterogeneous catalysis. However, achieving the general synthesis of 2D free-standing MOF nanosheets with controllable hierarchical porosity and thickness remains a challenging task. Herein, we present an ingenious “hard” emulsion-induced interface super-assembly strategy for preparing 2D hierarchically porous UiO-66-NH 2 nanosheets with highly accessible pore channels, tunable meso-/macropore sizes, and adjustable thicknesses. The methodology relies on transforming the geometric shape of oil droplet templates within appropriate oil-in-water emulsions from conventional zero-dimensional (0D) “soft” liquid spheres to 2D “hard” solid sheets below the oil’s melting/freezing point. Subsequent surfactant exchange on the surface of 2D “hard” emulsions facilitates the heterogeneous nucleation and interfacial super-assembly of in situ formed mesostructured MOF nanocomposites, serving as structural units, in a loosely packed manner to produce 2D MOF nanosheets with multimodal micro/meso-/macroporous systems. Importantly, this strategy can be extended to prepare other 2D hierarchically porous MOF nanosheets by altering metal-oxo clusters and organic ligands. Benefiting from fast mass transfer and highly accessible Lewis acidic sites, the resultant 2D hierarchically porous UiO-66-NH 2 nanosheets deliver a fabulous catalytic yield of approximately 96% on the CO 2 cycloaddition of glycidyl-2-methylphenyl ether, far exceeding the yield of approximately 29% achieved using conventional UiO-66-NH 2 microporous crystals. This “hard” emulsion-induced interface super-assembly strategy paves a new path toward the rational construction of elaborate 2D nanoarchitecture of hierarchical MOFs with tailored physicochemical properties for diverse potential applications.