Substantial Turnover Frequency Enhancement of MOF Catalysts by Crystallite Downsizing Combined with Surface Anchoring

Abstract

We report on the preparation of surface-anchored nanoparticles of the metal–organic framework (MOF) UiO-66 (Universitet i Oslo; Zr6O4(OH)4(bdc)6; bdc2– = 1,4-benzene dicarboxylate). The surface-anchored nano-MOFs (SA-NMOFs) were prepared by covalent anchoring of a presynthesized, functionalized UiO-66 nano-MOF (NMOF) on surface-modified poly­(dimethylsiloxane). The SA-NMOFs exhibit discrete NMOFs (<30 nm) which do not aggregate. The SA-NMOFs retain a high surface area, rendering them interesting catalysts. We compared the catalytic activities of SA-NMOFs in the cyanosilylation of benzaldehyde with those of the bulk UiO-66 and colloidal-dispersed UiO-66 NMOFs (size: 22 ± 3 nm). The SA-NMOFs exhibit a boost in activity by a factor of 100,000–1,000,000 owing to (a) the generally larger surface area of NMOFs and (b) the suppressed aggregation of the nanoparticles by surface immobilization. In contrast, colloidal NMOFs rapidly aggregate, as shown by dynamic light scattering. The general applicability of our approach for other Lewis acid-catalyzed reactions is demonstrated by comparing the activities of the three catalyst systems for the cycloaddition of CO2 and propylene oxide to propylene carbonate, where SA-NMOFs by far outperform the bulk MOFs and defect-engineered MOFs, respectively. This discovery paves the way for application of SA-NMOFs as efficient catalyst materials.

Postsynthetic Modification: An Enabling Technology for the Advancement of Metal–Organic Frameworks

“…Drawing inspiration from this study, other biomolecules were attached to the surface of nanoparticles through coordinative PSM. 102 , 103 As it pertains to MOFs, Mirkin and co-workers have played a pioneering role in attaching biomolecules to MOF particles. 104 , 105 In one report, phospholipids ( Figure 6 ), 1,2-dioleoyl- sn -glycero-3-phosphate (DOPA), were tethered to the surface of three Zr 4+ -based MOFs (UiO-66, UiO-67, and BUT-30).…”

From Macro- to Nanoscale: Finite Size Effects on Metal–Organic Framework Switchability

“…Nanostructures are essential for many applications (Figure 1 and Box 1). The increased outer active surface and mass transport in nanocrystals is advantageous for catalytic applications [38][39][40][41][42]. Ultrathin nanosheets offer a high density of active centers [43,44].…”

Impact of Crystal Size and Morphology on Switchability Characteristics in Pillared-Layer Metal-Organic Framework DUT-8(Ni)

“…This dynamic nature of flexible MOFs makes them attractive for several potential applications such as sensors, molecular separation, gas storage, drug delivery, and catalysis (Mason et al, 2015;Majewski et al, 2017;Allendorf et al, 2020;Hou et al, 2020;Semrau et al, 2020;Wang et al, 2020). Applications of MOFs, however, often require material downsizing, especially for integration into the operating systems.…”

“…The so-called “third generation” of MOFs represents a subset of these materials, showing reversible stimuli-responsive structural transitions upon adsorption/desorption of fluids, temperature or pressure change (Boutin et al, 2013 ; Gagnon et al, 2013 ; Wieme et al, 2018 ; Collings and Goodwin, 2019 ; Krause et al, 2020 ). This dynamic nature of flexible MOFs makes them attractive for several potential applications such as sensors, molecular separation, gas storage, drug delivery, and catalysis (Mason et al, 2015 ; Majewski et al, 2017 ; Allendorf et al, 2020 ; Hou et al, 2020 ; Semrau et al, 2020 ; Wang et al, 2020 ). Applications of MOFs, however, often require material downsizing, especially for integration into the operating systems.…”