Two-Dimensional Metal–Organic Framework Superstructures from Ice-Templated Self-Assembly

Abstract

Here, we report the synthesis of two-dimensional (2D) layered metal–organic framework (MOF) nanoparticle (NP) superstructures via an ice-templating strategy. MOF NP monolayers and bilayers can be obtained by regulating the concentration of colloidal MOF NPs without any external fields during self-assembly. Adjacent polyhedral MOF NPs are packed and aligned through crystalline facets, resulting in the formation of a quasi-ordered array superstructure. The morphology of the MOF layers is well preserved when subjected to pyrolysis, and the obtained carbon NPs have hollow interiors driven by the outward contraction of MOF precursors during pyrolysis. With the advantages of large surface areas, hierarchical porosity, high exposure of active sites, and fast electron transport of the 2D layered structure, the mono- and bilayered carbon NP superstructures show better oxygen reduction activity than isolated carbon particles in alkaline media. Our work demonstrates that ice-templating is a powerful strategy to fabricate superstructures of various MOFs and their derivatives.

Self-assembly of colloidal metal–organic framework (MOF) particles

“…Using this strategy, mono- and bilayer 2D quasi-ordered superstructures could be created depending on the initial concentration of the MOF colloids. 94 Remarkably, these layers could be calcinated without losing their initial 2D shape, to form mono- and bilayers of 2D hollow carbon particles that exhibited a high oxygen-reduction catalytic activity in alkaline media. Given the assemblies obtained at the air–liquid interfaces, 81 emulsion droplets, 59 capillaries, 76 and ice-templates, 94 one can conclude that these approaches performed by confining MOF particles to pre-engineered interfaces provide a high level of control over self-assembly.…”

“…94 Remarkably, these layers could be calcinated without losing their initial 2D shape, to form mono- and bilayers of 2D hollow carbon particles that exhibited a high oxygen-reduction catalytic activity in alkaline media. Given the assemblies obtained at the air–liquid interfaces, 81 emulsion droplets, 59 capillaries, 76 and ice-templates, 94 one can conclude that these approaches performed by confining MOF particles to pre-engineered interfaces provide a high level of control over self-assembly. Importantly, these methodologies allow for free movement of MOF particles within the interface, which in turn serves to correct any defects, thereby leading to the formation of energetically favourable ordered superstructures.…”

“…90 In another, very recent example, TRD-ZIF-8, C-ZIF-8, O-UiO-66 and hexagonal nanorods of MIL-88B(Fe)-NH 2 were self-assembled into 2D quasi-ordered superstructures using an ice-templating strategy. 94 Aqueous suspensions of MOF particles were initially frozen in liquid N 2 and, during this freezing stage, the formed polycrystalline ice pushed the MOF particles into the channels between adjacent ice crystals. Then, self-assembly of MOF particles was induced by freeze-drying.…”

Photoswitchable Nanoporous Metal–Organic Framework Monolayer Film for Light-Gated Ion Nanochannel

“…To address the above difficulties, Cohen and co-workers reported the first self-assembled MOF monolayer (SAMM) film, a new type of MOF monolayer film formed by the self-assembly of MOF nanoparticles (NPs), which is a dense, highly ordered, large-area, free-standing monolayer film with nanoscale thicknesses (∼200 nm), and 87 wt % MOF, providing an efficient method to prepare MOF monolayer films with high particle loadings without necessitating a readily modifiable MOF ligand. Unlike usual monolayer films with single molecule scale, the thickness of this SAMM film is comparable to the size of MOF NPs, which provides better mechanical strength and makes it easier to form large-area and free-standing monolayer films. − The regular 2D arrangement in SAMMs offers multiple structural advantages, such as highly exposed interaction sites, accelerated mass transfer, and enhanced charge transfer between NPs. Furthermore, functional SAMM films can be prepared only by modifying the surface of MOF NPs without changing the structure of NPs.…”

A hybridization cage-confinement pyrolysis strategy for ultrasmall Ni3Fe alloy coated with N-doped carbon nanotubes as bifunctional oxygen electrocatalysts for Zn–air batteries

“…4,5 However, the kinetics of the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) of ZABs in the process of charging and discharging is sluggish, resulting in high overpotential, low roundtrip efficiency, low cycle life, and energy conversion efficiency, which are the major bottlenecks for large-scale commercial applications of ZABs. [6][7][8] Noble metal Pt-based and Ru-and Irbased catalysts are considered to be effective catalysts for the ORR and OER, respectively. However, the scarcity of global reserves, high cost, insufficient bifunctional catalytic activity, and limited catalytic selectivity and stability of precious metals have hindered their large-scale application.…”