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

Abstract

The self-assembly of colloidal metal–organic framework (MOF) particles enables the development of novel ordered, porous superstructures for diverse applications. Herein, we discuss the strategies for the self-assembly of colloidal MOF particles.

Macroscopic alignment of metal–organic framework crystals in specific crystallographic orientations

“…In pre-formed polyhedral MOF particles, when specific facets align and join with those of neighboring particles, they ultimately unveil identical facets in a particular direction, resulting in an oriented structure. 50,104 Consequently, the driving forces of colloidal self-assembly proved to be highly effective in the creation of novel-oriented MOF structures.…”

“…Typically, oriented MOFs with a specific direction can be achieved through direct growth on substrates or by aligning pre-formed crystals. 49,50 Substrate-assisted methods involve precursor molecule adsorption on substrates, guiding the growth of MOF crystals based on factors like substrate lattice parameters, 51 surface interactions, 52 and differential growth rates of crystal facets. 53,54 This approach assembles building blocks directly onto functional substrates, yielding tailored structures and novel architectures when integrated with other substrates.…”

“…Another approach utilizes external forces like electric and magnetic fields, interfacial tension, and capillary and depletion forces to guide the orientation of pre-formed MOF crystals. 49,50,55 Using pre-formed crystals offers flexibility in material selection and ensures consistent starting points for size, shape, and morphology, enabling the fabrication of highly ordered orientations in large quantities. 39,55 Self-assembly of polyhedral MOF particles with distinct facets leads to the formation of oriented structures, allowing full utilization of directional anisotropic properties over a large area.…”

“…Aligned MOF crystals selectively expose specific facets, maximizing their anisotropic properties and leading to improved characteristics, such as permeability, diffusivity, selectivity, conductivity, catalytic properties, optical properties, and wettability. 49,50 One prominent example is the improved molecular separation achieved through controlled alignment. 56–58 By aligning MOF crystals in a specific direction, precise pathways for guest molecules can be engineered, resulting in superior selectivity and mass transport.…”

Alignment of Breathing Metal–Organic Framework Particles for Enhanced Water-Driven Actuation

“…Controlled alignment of MOF crystals is, therefore, a key focus to harnessing and translating the directional functionality of individual crystals to the macroscale; − this can be achieved through various strategies, such as entropically driven or modulator-driven MOF ordering, in situ solvothermal growth on substrates that favor directional crystal growth, or secondary growth crystallization, or via external stimuli to obtain superlattices or directionally aligned MOF materials. ,− Many of these methods require substrates, which hinder applicability, with few works utilizing these approaches to fabricate free-standing films. − Furthermore, entropically driven assembly is often limited by demanding requirements such as a high degree of MOF crystal uniformity in terms of size and shape, while in situ growth may require carefully controlled synthetic conditions specifically tailored to the MOF of interest, which can be time-consuming to optimize. A new way to align MOF particles is via an electric-field (E-field)-assisted assembly.…”