Colloidal Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) are two- or three-dimensional (2D or 3D) polymer networks with designed topology and chemical functionality, permanent porosity, and high surface areas. These features are potentially useful for a broad range of applications, including catalysis, optoelectronics, and energy storage devices. But current COF syntheses offer poor control over the material’s morphology and final form, generally providing insoluble and unprocessable microcrystalline powder aggregates. COF polymerizations are often performed under conditions in which the monomers are only partially soluble in the reaction solvent, and this heterogeneity has hindered understanding of their polymerization or crystallization processes. Here we report homogeneous polymerization conditions for boronate ester-linked, 2D COFs that inhibit crystallite precipitation, resulting in stable colloidal suspensions of 2D COF nanoparticles. The hexagonal, layered structures of the colloids are confirmed by small-angle and wide-angle X-ray scattering, and kinetic characterization provides insight into the growth process. The colloid size is modulated by solvent conditions, and the technique is demonstrated for four 2D boronate ester-linked COFs. The diameter of individual COF nanoparticles in solution is monitored and quantified during COF growth and stabilization at elevated temperature using in situ variable-temperature liquid cell transmission electron microscopy imaging, a new characterization technique that complements conventional bulk scattering techniques. Solution casting of the colloids yields a free-standing transparent COF film with retained crystallinity and porosity, as well as preferential crystallite orientation. Collectively this structural control provides new opportunities for understanding COF formation and designing morphologies for device applications.

Design Principles for Covalent Organic Frameworks in Energy Storage Applications

“…Colloidal synthesis methods have also now been developedt hat allow COFs to be conveniently formed into films ands heets through solution processing. [95] Despite the challenges, these advancements are encouraging for the eventual development of COFs into practical, commerciallyp roduced materials and devices.…”

Covalent Organic Frameworks and Cage Compounds: Design and Applications of Polymeric and Discrete Organic Scaffolds

“…by exfoliation of presynthesized bulk materials by immersing powder samples in various solvents, [229] mechanical grinding, [230] or chemical delamination, for example,b yD iels-Alder reactions of anthracene moieties. [231] Self-exfoliation was observed for guanidinium-based ionic COFs [232] and for COFs containing flexible C 3v symmetric vertices [233] that induce significant weakening of the interlayer stacking interactions.F ree-standing COF membranes were obtained from colloidal COF suspensions [234] by mechanical pressing of COF-5 bulk samples, [235] by baking of the molecular precursors, [236] or interfacial crystallization. [237] A2 Dc ovalent organic monolayer was obtained at the air/water interface by using the Langmuir-Blodgett method.…”

A MOF@COF Composite with Enhanced Uptake through Interfacial Pore Generation

“…[6] Archetypal examples are mixed-matrix membranes (MMMs) in which aporous material (e.g.,zeolite or metal-organic framework [MOF]) is incorporated into an amorphous porous polymeric film. [7] Researchers have recently developed ac lass of crystalline porous polymers known as covalent-organic frameworks (COFs), [8] which can be used as components in porous composites.For example,Fu et al recently developed an ew class of membranes by interfacing aM OF (Zn(bdc) 2 (dabco) or ZIF-8) layer on top of aCOF (COF-300) layer. Theresulting membranes showed synergistic enhancement of selective separation of H 2 over CO 2 relative to the summed separation capacity of the MOF and COF components.…”