Antimonene fabricated by mechanical exfoliation is highly stable under atmospheric conditions over periods of months and even when immersed in water. Density functional theory confirms the ...experiments and predicts an electronic gap of ≈1 eV. These results highlight the use of antimonene for optoelectronics applications.
The use of covalent organic frameworks (COFs) in practical applications demands shaping them into macroscopic objects, which remains challenging. Herein, we report a simple three‐step method to ...produce COF aerogels, based on sol‐gel transition, solvent‐exchange, and supercritical CO2 drying, in which 2D imine‐based COF sheets link together to form hierarchical porous structures. The resultant COF aerogel monoliths have extremely low densities (ca. 0.02 g cm−3), high porosity (total porosity values of ca. 99 %), and mechanically behave as elastic materials under a moderate strain (<25–35 %) but become plastic under greater strain. Moreover, these COF aerogels maintain the micro‐ and meso‐porosity of their constituent COFs, and show excellent absorption capacity (e.g. toluene uptake: 32 g g−1), with high removal efficiency (ca. 99 %). The same three‐step method can be used to create functional composites of these COF aerogels with nanomaterials.
A three‐step method produces COF aerogel monoliths, based on sol–gel transition, solvent‐exchange, and supercritical CO2 drying. 2D imine‐based COF sheets link together to form hierarchical porous structures. The aerogels have extremely low densities, high porosity, and mechanically behave as elastic or plastic materials under different strain. They show excellent absorption capacity with high removal efficiency.
We present the novel potential application of imine-based covalent organic frameworks (COFs), formed by the direct Schiff reaction between 1,3,5-tris(4-aminophenyl)benzene and ...1,3,5-benzenetricarbaldehyde building blocks in m-cresol or acetic acid, named RT-COF-1 or RT-COF-1Ac/RT-COF-1AcB. The post-synthetic treatment of RT-COF-1 with LiCl leads to the formation of LiCl@RT-COF-1. The ionic conductivity of this series of polyimine COFs has been characterized at variable temperature and humidity, using electrochemical impedance spectroscopy. LiCl@RT-COF-1 exhibits a conductivity value of 6.45 × 10–3 S cm–1 (at 313 K and 100% relative humidity) which is among the highest values so far reported in proton conduction for COFs. The mechanism of conduction has been determined using 1H and 7Li solid-state nuclear magnetic resonance spectroscopy. Interestingly, these materials, in the presence of controlled amounts of acetic acid and under pressure, show a remarkable processability that gives rise to quasi-transparent and flexible films showing in-plane structural order as confirmed by X-ray crystallography. Finally, we prove that these films are useful for the construction of proton exchange membrane fuel cells (PEMFC) reaching values up to 12.95 mW cm–2 and 53.1 mA cm–2 for maximum power and current density at 323 K, respectively.
Covalent organic frameworks (COFs) are an emerging class of new organic polymers showing tuneable permanent porosity and crystallinity. They are formed, using modular chemistry concepts, by ...condensation reactions between their molecular precursors based on the formation of dynamic bonds. Despite much effort having been devoted towards the design of the physical and/or chemical properties of these materials by selecting their initial building blocks, the importance of processability for their applications has only recently emerged. This tutorial review article rationalizes the strategies used so far on COF processability leading to the formation of thin-films, membranes, or individual particles with controlled shape and size as well as composite fabrication. We aim to provide a rational perspective of the importance of COF processability towards potential applications of COFs in many different fields which are at the forefront of research in materials science.
This tutorial provides a perspective on the processability of covalent organic frameworks, an emerging class of new organic polymers, towards their potential applications.
Covalent organic frameworks (COFs) are commonly synthesized under harsh conditions yielding unprocessable powders. Control in their crystallization process and growth has been limited to studies ...conducted in hazardous organic solvents. Herein, we report a one-pot synthetic method that yields stable aqueous colloidal solutions of sub-20 nm crystalline imine-based COF particles at room temperature and ambient pressure. Additionally, through the combination of experimental and computational studies, we investigated the mechanisms and forces underlying the formation of such imine-based COF colloids in water. Further, we show that our method can be used to process the colloidal solution into 2D and 3D COF shapes as well as to generate a COF ink that can be directly printed onto surfaces. These findings should open new vistas in COF chemistry, enabling new application areas.
Abstract Covalent organic frameworks (COFs) have witnessed outstanding developments in the past 15 years, particularly in optimizing their pore structures, linkages, and variety of monomers used in ...their synthesis. Yet, a significant challenge remains unaddressed: the processability of COFs into macroscopic architectures with arbitrary shapes, as they are typically obtained as unprocessable powders. This study presents a novel strategy to address this issue by developing a 3D printable ink comprising a colloidal water suspension of COF nanoparticles. A microfluidic device is engineered that provides precise control over the gelation process of the COF‐based ink, allowing for a layer‐by‐layer fabrication. As a result, the direct production of large‐scale binder‐free COF architectures from digital designs is achieved at room temperature and atmospheric pressure while eliminating the use of toxic organic solvents.
2D materials have opened a new field in materials science with outstanding scientific and technological impact. A largely explored route for the preparation of 2D materials is the exfoliation of ...layered crystals with weak forces between their layers. However, its application to covalent crystals remains elusive. Herein, a further step is taken by introducing the exfoliation of germanium, a narrow‐bandgap semiconductor presenting a 3D diamond‐like structure with strong covalent bonds. Pure α‐germanium is exfoliated following a simple one‐step procedure assisted by wet ball‐milling, allowing gram‐scale fabrication of high‐quality layers with large lateral dimensions and nanometer thicknesses. The generated flakes are thoroughly characterized by different techniques, giving evidence that the new 2D material exhibits bandgaps that depend on both the crystallographic direction and the number of layers. Besides potential technological applications, this work is also of interest for the search of 2D materials with new properties.
α‐Germanium crystals are exfoliated using a wet ball‐milling technique to produce α‐germanium nanolayers (α‐Ge NLs) in a process that is upscaled to gram production. The α‐Ge NLs can be redispersed using a shear‐mixer, yielding very stable suspensions. Theoretical calculations predict a thickness‐dependent bandgap of these NLs that is confirmed by electron energy‐loss spectroscopy of α‐Ge NLs with different orientations.
In this study, we present a novel approach for the synthesis of covalent organic frameworks (COFs) that overcomes the common limitations of non‐scalable solvothermal procedures. Our method allows for ...the room‐temperature and scalable synthesis of a highly fluorinated DFTAPB‐TFTA‐COF, which exhibits intrinsic hydrophobicity. We used DFT‐based calculations to elucidate the role of the fluorine atoms in enhancing the crystallinity of the material through corrugation effects, resulting in maximized interlayer interactions, as disclosed both from PXRD structural resolution and theoretical simulations. We further investigated the electrocatalytic properties of this material towards the oxygen reduction reaction (ORR). Our results show that the fluorinated COF produces hydrogen peroxide selectively with low overpotential (0.062 V) and high turnover frequency (0.0757 s−1) without the addition of any conductive additives. These values are among the best reported for non‐pyrolyzed and metal‐free electrocatalysts. Finally, we employed DFT‐based calculations to analyse the reaction mechanism, highlighting the crucial role of the fluorine atom in the active site assembly. Our findings shed light on the potential of fluorinated COFs as promising electrocatalysts for the ORR, as well as their potential applications in other fields.
Covalent organic frameworks (COFs) are a class of crystalline polymers. Herein we report the room temperature and scalable synthesis of two isostructural COFs, modulated by the introduction of fluorine atoms, obtaining an extended framework with record number of F per pore. The substitution produces a dramatical increase of selectivity for the oxygen reduction reaction electrocatalysis, with a response comparable to other noble electrocatalysts.
To date, crystallization studies conducted in space laboratories, which are prohibitively costly and unsuitable to most research laboratories, have shown the valuable effects of microgravity during ...crystal growth and morphogenesis. Herein, an easy and highly efficient method is shown to achieve space‐like experimentation conditions on Earth employing custom‐made microfluidic devices to fabricate 2D porous crystalline molecular frameworks. It is confirmed that experimentation under these simulated microgravity conditions has unprecedented effects on the orientation, compactness and crack‐free generation of 2D porous crystalline molecular frameworks as well as in their integration and crystal morphogenesis. It is believed that this work will provide a new “playground” to chemists, physicists, and materials scientists that desire to process unprecedented 2D functional materials and devices.
How to achieve simulated microgravity conditions on Earth? The art of growing and processing 2D porous crystalline molecular frameworks in simulated microgravity is presented.
Covalent organic frameworks (COFs) are crystalline materials with intrinsic porosity that offer a wide range of potential applications spanning diverse fields. Yet, the main goal in the COF research ...area is to achieve the most stable thermodynamic product while simultaneously targeting the desired size and structure crucial for enabling specific functions. While significant progress is made in the synthesis and processing of 2D COFs, the development of processable 3D COF nanocrystals remains challenging. Here, a water‐based nanoreactor technology for producing processable sub‐40 nm 3D COF nanoparticles at ambient conditions is presented. Significantly, this technology not only improves the processability of the synthesized 3D COF, but also unveils exciting possibilities for their utilization in previously unexplored domains, such as nano/microrobotics and biomedicine, which are limited by larger crystallites.
Herein, a water‐based nanoreactor technology that allows for the controlled generation of sub‐40 nm 3D covalent organic frameworks (COF) nanoparticles, boosting processability, and opening new frontiers in nano/microrobotics and biomedicine is presented. This breakthrough clearly overcomes the limitations posed by larger reported 3D COF crystal structures, unlocking exciting possibilities for previously unexplored domains.
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