In the rapidly evolving landscape of materials science, covalent organic frameworks (COFs) have emerged as a beacon of promise, captivating researchers worldwide with their remarkable structural tunability and unparalleled potential across various applications. These crystalline, porous polymers, constructed via strong covalent bonds between organic building blocks, have been heralded for their ability to revolutionize areas ranging from gas storage and catalysis to electronic devices and environmental remediation. Nonetheless, despite their theoretical appeal and demonstrated functionalities, the practical utilization of COFs has been consistently undermined by the inherent challenges of their synthesis. Traditionally, the creation of highly crystalline COFs is an arduous endeavor, involving toxic solvents, protracted reaction times, labor-intensive procedures, and resulting predominantly in powders of microcrystalline nature, which are far from ideal for real-world implementations.
Such synthesis bottlenecks have confined COFs largely to academic curiosities rather than scalable functional materials, constraining their integration into devices or industrial processes. The reliance on solvothermal or ionothermal methodologies demands elevated temperatures sustained over several hours or days, often in sealed reactors under inert atmospheres, while intricate purification protocols are mandatory to isolate the products. These procedures not only compromise the environmental sustainability of the COF production but also impede rapid iteration and large-scale manufacturing. Crucially, efforts to circumvent these issues by developing alternative synthesis routes have frequently culminated in compromised crystallinity and pore architecture—two fundamental attributes underpinning the superior performance of COFs.
In a groundbreaking study published in Nature Chemical Engineering, Jin, Wang, Cheng, and colleagues have introduced an innovative solid-phase hot-pressing technique that promises to reconfigure the synthetic paradigm for COFs. This approach sidesteps the limitations of solvent-based reactions, enabling the fabrication of highly crystalline, porous COF platelets in mere minutes—a dramatic reduction from the conventional multi-hour protocols. Through this method, 15 different COFs encompassing diverse linkage chemistries, such as imine, hydrazone, β-ketoenamine, and imide bonds, were successfully synthesized, showcasing the technique’s versatility and broad applicability.
The essence of the solid-phase hot-pressing strategy lies in intimately mixing the monomeric powders and subjecting them to controlled heat and pressure within a solid matrix, thereby accelerating the polymerization process without necessitating solvents. This shift not only enhances the sustainability profile of COF synthesis but also yields platelet-shaped products with superior crystallinity evident through sharp diffraction peaks and enlarged surface areas as verified by nitrogen adsorption measurements. Importantly, the crystallinity and porosity are preserved or even enhanced compared to their conventionally synthesized counterparts, overcoming the historic trade-off encountered in rapid or solvent-free syntheses.
One of the most compelling advantages of this methodology is its capacity to accommodate complex COF architectures. The researchers demonstrated the fabrication of COFs with sophisticated chemical topologies, including a rare three-dimensional COF and frameworks assembled from multiple monomer components. Such complexity often bedevils traditional approaches due to difficulties in maintaining uniform reaction conditions and achieving complete polymerization. The hot-pressing technique’s ability to homogenize the reaction environment at the solid phase evidently mitigates these challenges, allowing precise control over the framework geometry.
Moreover, the process duration astonishingly spans only between 30 seconds and 5 minutes, representing an unprecedented acceleration in COF assembly. This rapid reaction kinetics stem from the synergy of heat and mechanical pressure in promoting imine condensation and other covalent bond formations at the intimate contact interfaces of monomers. Consequently, this facilitates immediate framework nucleation and growth, producing platelet morphologies that are highly suited for thin-film technologies and facile device integration.
Beyond the synthetic triumphs, the practical ramifications of this development are exemplified through a proof-of-concept application. The team assembled a β-ketoenamine-linked COF platelet directly into an atmospheric water harvesting device, demonstrating robust water absorption and collection performance. This real-world demonstration underscores the COF platelet’s enhanced surface accessibility and structural robustness—traits essential for cyclic operation under variable humidity conditions. Atmospheric water harvesting technologies benefit immensely from such materials, as their pore structures and chemical stability dictate efficiency and longevity.
The atmospheric water harvesting device exemplifies a class of applications where the morphological uniformity, high crystallinity, and porosity of COF platelets are particularly advantageous. Unlike powders or irregularly shaped aggregates, platelet structures can reliably form continuous and defect-minimized films, facilitating optimal vapor diffusion and condensate release. This tangible translation from synthetic methodology to applied technology reaffirms the hot-pressing solid-phase approach not only as an academic curiosity but also as an industrially relevant innovation.
The implications of this method extend well beyond water harvesting. The universal applicability to different COF linkage chemistries suggests potential breakthroughs in fields relying on COF-based membranes, sensors, energy storage devices, and heterogeneous catalysis. The easy scalability and rapid turnaround time reduce production costs and environmental burdens, which are critical considerations for deployment in commercial and environmental contexts. Moreover, the elimination of hazardous solvents aligns with green chemistry principles, fostering safer laboratory practices and reducing ecological footprints.
Technical characterization of the COF platelets synthesized via hot-pressing revealed exceptional crystallographic fidelity. X-ray diffraction patterns display sharp, well-defined peaks consistent with the anticipated framework topologies. Brunauer-Emmett-Teller (BET) surface areas often surpass those obtained through conventional solvothermal synthesis, indicating well-preserved or enhanced porosity. Scanning electron microscopy images illustrate uniform platelet morphology with consistent thickness and lateral dimensions, further reinforcing the high quality of the materials generated. Such detailed structural analyses validate the robustness of the synthesis protocol and provide insights into the role of solid-phase conditions in dictating framework order.
From a mechanistic standpoint, the solid-phase hot-pressing environment likely introduces unique reaction kinetics compared to solution-based methods. The absence of solvent molecules, which traditionally mediate diffusion and monomer mobility, necessitates direct contact between reacting species under pressure and heat. This enforced proximity accelerates bond formation while limiting defects and undesirable side reactions. Furthermore, the brief processing times prevent framework degradation or uncontrolled side reactions that can plague longer, high-temperature syntheses. These mechanistic advantages translate directly into the high crystallinity and pore uniformity that define the quality of COFs for functional use.
It is also notable that the newly developed methodology opens avenues for combinatorial materials science within the COF domain. By permitting multiple monomers and complex chemistries to polymerize rapidly under uniform conditions, researchers can systematically explore vast chemical space to design frameworks with tailored properties. This capability will accelerate discovery in functional COFs targeting selective adsorption, electronic properties, and catalytic activities. The integration of hot-pressing with in situ characterization techniques might further elucidate growth mechanisms and enable real-time optimization of synthetic parameters.
Given the burgeoning interest in sustainable technologies and materials, the ability to synthesize COFs rapidly, cleanly, and with outstanding structural control represents a milestone. This work bridges the gap between laboratory-scale curiosity and scalable application, potentially catalyzing a paradigm shift in the manufacturing of porous, crystalline organic frameworks. Future explorations may optimize hot-pressing parameters further, expand the library of accessible COF chemistries, and demonstrate integrated devices harnessing the full structural advantages of platelet morphologies.
In summary, the introduction of a rapid, solid-phase hot-pressing method to produce highly crystalline COF platelets signifies a powerful advancement in materials chemistry. By overcoming longstanding synthetic barriers—long reaction times, toxic solvents, and suboptimal morphologies—this strategy paves the way for the next generation of COF-enabled technologies. As researchers worldwide strive for materials solutions that are both effective and practical, such innovations promise to unlock the latent potential of COFs and inspire a new era of functional porous materials tailored for the needs of modern society.
Subject of Research: Synthesis and fabrication of highly crystalline covalent organic framework (COF) platelets via a rapid solid-phase hot-pressing method.
Article Title: Rapid solid-phase synthesis of highly crystalline covalent organic framework platelets.
Article References:
Jin, Y., Wang, H., Cheng, H. et al. Rapid solid-phase synthesis of highly crystalline covalent organic framework platelets. Nat Chem Eng (2025). https://doi.org/10.1038/s44286-025-00277-9
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