Hierarchically Porous Metal–Organic Frameworks: Synthetic Strategies and Applications

Abstract

Metal-organic frameworks (MOFs), assemblies comprised of inorganic nodes (metal ions or clusters) and organic linkers, have attracted widespread interest over the past two decades. [1][2][3][4][5] Different from various classical porous materials, such as zeolite, porous silica, and carbon, MOFs have unique morphological features including high surface areas, ordered crystalline structures, and adjustable pore environments, which enable flexibility in the design of customized configurations. [6][7][8][9] Specifically, by the thoughtful selection of metal ions/clusters and organic ligands/linkers, and using proper synthetic strategies or post-synthetic modifications, it is possible to create custom-designed MOF frameworks that have desired topological structures, pore shapes and sizes, and chemical affinities tailored to specific tasks. Therefore, MOFs have emerged as a new class of multifunctional crystalline porous materials that display outstanding performances in a variety of applications in the mature fields of heterogeneous catalysis, [10][11][12][13][14][15][16] water remediation, [17][18][19] gas storage and separation, [20,21] and also in relatively new fields such as biotechnology, [22] energy storage, [23] and sensing. [24] MOFs with diverse structural topologies and permanent porosities are among the most fascinating classes of materials from both science and engineering perspectives. [25][26][27] Most MOFs reported to date are microporous with pore sizes smaller than 2 nm. The numerous micropores give MOFs high specific surface areas and serve as sites to stabilize or heterogenize small molecules. [28,29] However, despite possessing these unique and advantageous features, traditional microporous MOFs are limited by the small apertures of the pores which inherently prohibits their participation in binding, diffusion, and transfer of large molecules that restricts applications especially. [30][31][32] Therefore, the ability to transform the pore sizes of MOFs to a larger regime including mesopores (2-50 nm) or even macropores (>50 nm) is highly desirable. Consequently, a significant number of studies have been carried out to design and prepare hierarchically porous MOFs (HP-MOFs) to meet the increasing and diverse demands.HP-MOFs possess a multiple of porosity ranges, including those with two or all three pore categories to form hierarchical systems with interconnected pores and entirely properties for desired applications. Although there are some special cases, [33,34] most of the mesoporous MOFs are still HP-MOFs, [35,36] because in addition to the mesopores, they also have intrinsic micropores. The development of HP-MOFs has attracted considerable interest because these materials have exceptional advantages

Improved stability and activity of laccase through de novo and post-synthesis immobilization on a hierarchically porous metal–organic framework (ZIF-8)

“…[44][45][46] Second, the high surface energy enables the HZIF-8 to accelerate the diffusion of the laccase from solution into catalyst itself by the adsorption to laccase with the high surface energy of structure of HZIF-8. 47 When the capacities of MZIF-8 and HZIF-8 to adsorb 2,4-DCP were studied to conrm the effect of different material structures on the catalyst, it was observed that 17.6% and 45.4% of 2,4-DCP had been adsorbed into the MZIF-8 and HZIF-8 samples aer 15 minutes, respectively. HZIF-8 offers a higher adsorption capacity due to its higher specic surface area, a nding consistent with our ndings in this study and those of Gascon.…”

Pt–C interactions in carbon-supported Pt-based electrocatalysts

“…By using different carbon supports, different Pt-C interactions will take place in electrocatalysts, which will affect both its properties and functions. Thus, the strong Pt-C interactions are generally beneficial for enhancement of the properties and stabilities of the electrocatalysts [31][32][33][34][35][36][37]. Therefore, an understanding of Pt-C interactions will greatly facilitate the design and synthesis of high-performance carbonsupported Pt-based electrocatalysts.…”

Recent progress in porous catalysts for dehydrogenation of ammonia borane

“…[23][24][25][26][27] Porous catalysts are a class of catalytic materials with a large number of pore structures, including micropores (o2 nm), mesopores (2-50 nm), and macropores (450 nm), and have been proven to be highly efficient catalysts for AB solvolysis underpinned by their unique physical and chemical properties. [28][29][30] Apart from their porosity tunability, tailorability, and favorable transport properties, [31][32][33] particularly, the large surface area of porous materials promotes the uniform dispersion of metallic atoms and exposes more active sites, which maximizes the utilization of active materials. 34,35 Furthermore, the porous nanostructure facilitates the contact between the catalyst and the reactant, enabling controlled mass and electronic transfer, consequently improving the catalytic activity.…”