Metal–organic frameworks are renowned for their modularity and tunable porosity, which make them prime candidates for applications ranging from gas storage and separation to catalysis and drug delivery. Central to their design philosophy is the assembly of metal nodes coordinated to organic linkers, leading to highly ordered frameworks with precise control over pore size and shape. However, incorporating infinite organic networks such as COFs, known for their robust covalent bonding and intrinsic order, into MOFs has remained elusive. This is primarily due to the intrinsic disorder and flexibility inherent in organic chains and layers, which tend to disrupt the long-range periodicities essential for MOF crystallinity.

The innovative synthesis reported by Liu, Wu, Wang, and colleagues circumvents these obstacles by carefully selecting boroxine-based COFs as the organic subnet units and pairing them with Zr6O8 or Hf6O8 metal clusters to form stable frameworks. Boroxine rings, formed through the dehydration of boronic acids, provide a rigid and planar building motif conducive to establishing well-defined organic layers and chains. These boroxine-based structures exhibit remarkable stability and structural uniformity, enabling their integration as infinite connectivity units within MOFs.

A critical insight driving this research is the spatial compatibility between the metal clusters and the boroxine COFs. The complementary geometries and bonding preferences effectively lock the continuous organic units into precisely ordered arrangements within the MOF lattice. This interlocking mechanism ensures that the infinite organic chains or layers are not merely embedded as random phases but serve as well-defined, ordered building blocks coexisting with discrete inorganic nodes. The result is a compartmentalized framework architecture, where distinct structural entities and pore environments are spatially segregated yet interconnected along specific crystallographic directions.

This compartmentalization introduces unprecedented control over pore environments within a single crystalline material, allowing for selective interactions and functionalities to be harnessed in separate spatial domains. For instance, the one-dimensional boroxine chains can provide channels of specific chemical environments and conformations, while the two-dimensional layers offer planar domains with unique topologies. Meanwhile, the inorganic Zr6O8 or Hf6O8 clusters maintain the framework’s mechanical strength and facilitate robust metal-ligand coordination, essential for long-term stability.

The synthetic strategy utilized is a one-pot approach, a streamlined method that combines all starting materials in a single reaction vessel, promoting the simultaneous formation and self-assembly of the organic and inorganic subnetworks. This method enhances synthetic efficiency and reproducibility, which is significant for scaling up these complex architectures for practical applications. Moreover, the controlled reaction environment allows for the precise tuning of the resulting framework’s composition, topology, and porosity by adjusting parameters such as reagent stoichiometry, solvent system, and temperature.

Structurally, the new MOFs embody a remarkable duality: they hold both extended covalent organic frameworks, known for their planar and highly conjugated layers or linear chains, alongside isolated inorganic metal-oxo clusters, each retaining their intrinsic identities. Such duality not only enriches the structural diversity but also imbues the material with multifunctionality derived from both organic and inorganic constituents.

This discovery challenges the traditional paradigm where MOFs and COFs existed as separate classes of porous materials. Now, the coexistence of infinite organic subnetworks within metal-containing frameworks opens avenues for synergistic properties. For example, electronic communication might be facilitated across the organic layers while the metal clusters provide active sites for chemical reactions or adsorption, simultaneously enhancing conductivity and catalytic activity—a feat difficult to realize in separate materials.

The authors report that the pore environments within these frameworks show high compartmentalization along specific crystallographic directions, which can influence diffusion and adsorption selectivity of guest molecules. This could translate into advanced molecular sieving capabilities or catalytic site isolation, allowing for tandem reactions or multi-step processes to occur within a single solid material without cross-interference.

Beyond fundamental structural innovation, these compartmentalized MOFs have promising implications in gas storage, sensing, and heterogeneous catalysis. The spatial segregation allows for hosting multiple guest species in different framework regions or creating multi-functional catalysts with reaction zones confined and optimized for specific steps. Additionally, the boroxine linkers’ chemical tunability provides handles for post-synthetic modifications, further customizing the pore chemistry.

The use of Zr6O8 and Hf6O8 clusters as inorganic nodes is noteworthy for imparting exceptional thermal and chemical robustness, a well-recognized advantage of zirconium and hafnium-based MOFs. Their high valency and strong metal-oxo bonds provide stability that enables these frameworks to withstand harsh conditions, a critical consideration for real-world applications where durability often limits MOF deployment.

To summarize, Liu et al. have realized a new class of MOFs that uniquely integrate infinite covalent organic networks as integral building units. By harnessing boroxine-based COFs and compatible metal-oxo clusters, they achieved highly ordered, compartmentalized pore architectures, unlocking avenues for advanced materials with multifunctional capabilities and spatially regulated interactions. These results demonstrate the power of combining the chemical stability and modularity of MOFs with the extended conjugation and covalency of COFs, marking a significant milestone in reticular chemistry.

Future directions inspired by this work may include exploring other infinite subnet moieties such as covalent chains with different functional groups or electronic properties, expanding the repertoire of metal clusters, or investigating stimuli-responsive behaviors resulting from compartmentalized architectures. Furthermore, the precise control over pore environments raises prospects for complex catalysis, selective molecular recognition, and separation technologies tailored at the nanoscale.

The implications of this synthesis strategy extend beyond purely academic interest; they herald new frontiers in the design of porous crystalline materials, blending the best of both worlds—organic framework conjugation and metal cluster robustness—into architecturally complex, chemically resilient, and functionally diverse materials primed for tackling grand challenges in energy, environment, and medicine.

Subject of Research:
Metal–organic frameworks (MOFs) incorporating covalent organic frameworks (COFs) as infinite building units for creating compartmentalized pore structures.

Article Title:
Covalent organic frameworks as infinite building units for metal–organic frameworks with compartmentalized pores.

Article References:
Liu, B., Wu, Y., Wang, L. et al. Covalent organic frameworks as infinite building units for metal–organic frameworks with compartmentalized pores.
Nat. Chem. (2025). https://doi.org/10.1038/s41557-025-01953-2

Image Credits:
AI Generated

The innovative filters are constructed from covalent organic frameworks (COFs), a class of porous materials characterized by nanoscale pores just a few billionths of a meter in diameter. These tiny cavities can effectively trap PFAS molecules, physically capturing them to prevent contamination. What sets this approach apart is not only the filter’s nanostructure but also the groundbreaking mechanochemical synthesis method employed. Unlike traditional chemical manufacturing, which often relies on solvents and heating, this new technique uses a ball mill that grinds powders in the presence of minimal solvent volumes, initiating chemical reactions solely through mechanical energy and frictional heat. This process is notably sustainable, cutting down waste and energy use while producing highly functional materials.

At the core of the mechanochemical synthesis is a compact device roughly the size of a film canister, containing a small quantity of powder, a few drops of solvent, and two steel balls approximately the size of peppercorns. When the mill vibrates at high frequency—up to 36 times per second—the balls grind the powder, generating localized heat and pressure. These conditions trigger reactions that assemble the powders into complex, crystalline framework structures, forming the covalent organic frameworks required for effective filtration. This ancient yet sophisticated method, known as mechanochemistry, bridges a fascinating connection between historical medicinal practices and cutting-edge material science.

Real-time analysis of the synthesis process was made possible through the high-intensity, focused X-ray beams of PETRA III, DESY’s renowned X-ray source. By directing the X-ray beam into the grinding mill while it operated, researchers could monitor the crystalline transformations down to the second. As the ball mill engaged, diffraction patterns revealed diminishing signals from the initial starting materials and the concurrent emergence of the target crystalline frameworks. This direct observation enabled fine-tuning of the synthesis parameters, such as milling frequency and solvent quantity, to optimize the formation of the COF filters.

Through meticulous experimentation, the research group identified optimal synthesis conditions — a milling frequency of 36 Hz, with 266 milligrams of powder and 250 microliters of solvent — that resulted in the highest quality framework structures. Importantly, unlike many prior filtration materials, these new COFs contain no heavy metals, alleviating concerns about toxicity and environmental impact. This characteristic is of significant importance if these materials are to be scaled up for broader commercial use, aligning with global calls for green chemistry and sustainable industrial practices.

The implications of this work extend beyond laboratory success. Though industrial-scale manufacturing protocols have yet to be established, the future applications are tantalizing. Martin Etter, a physicist at DESY and co-leader of the research, envisions deployment in wastewater treatment plants, particularly those serving manufacturing sites producing PFAS chemicals. Such targeted integration could dramatically reduce environmental PFAS loading at the source. Furthermore, the prospect of embedding these filters directly into household water taps points towards a future where consumers might routinely benefit from PFAS-free drinking water, enhancing public health on a wide scale.

This breakthrough is a vivid demonstration of mechanochemistry’s renaissance within modern materials science. While mechanochemical processes undoubtedly have ancient roots—early pharmaceutical compounds were likely formed by grinding plant materials in mortars—their contemporary applications are pushing the boundaries of chemical synthesis. The mechanochemical approach in this research minimizes solvent usage and energy consumption, establishing a paradigm shift towards greener, more sustainable manufacturing methods suitable for a range of pharmaceuticals, catalysts, and functional materials.

Looking forward, the team anticipates further advances enabled by upcoming technological upgrades at DESY, particularly the PETRA IV upgrade. Scheduled as PETRA III’s successor, PETRA IV will produce much sharper, more precisely collimated X-ray beams that vastly increase temporal resolution. This capability will enable researchers to capture rapid, fleeting intermediate structures during mechanochemical reactions, which until now have been elusive. The enhanced temporal resolution—from one scan every ten seconds to potentially ten scans per second—could unlock new fundamental insights, accelerating the optimization of filter fabrication and related materials.

Such rapid, high-precision monitoring will also have broad implications across chemistry and materials science, extending beyond filtration technologies. It opens doors to real-time control of reactions, fine adjustment of parameters on the fly, and better understanding of reaction pathways that can lead to breakthroughs in multiple industrial processes. This synergy between advanced instrumentation, novel synthesis routes, and pressing environmental challenges exemplifies how cutting-edge science can translate into highly impactful solutions.

Ultimately, the successful synthesis of covalent organic frameworks using mechanochemistry as demonstrated in this study is a major milestone in the ongoing battle against environmental pollutants like PFAS. It heralds a future where problematic, persistent chemicals can be effectively captured and removed by materials that are themselves sustainable and non-toxic. This innovation melds centuries-old chemical wisdom with state-of-the-art technology, creating a blueprint for how mechanochemistry might continue to reshape sustainable materials development.

With such promising results published in the journal small, the research group sets a precedent for multidisciplinary collaboration. Scientists, engineers, and environmentalists alike will be watching closely as this technology progresses from bench to potential real-world application. As humanity grapples with persistent organic pollutants and their footprints on ecosystems and health, solutions like these offer hope—and a glimpse of a cleaner, safer tomorrow.

Subject of Research: Mechanochemical synthesis and application of covalent organic frameworks for PFAS filtration

Article Title: Mechanochemically Synthesized Covalent Organic Framework Effectively Captures PFAS Contaminants

News Publication Date: 18-Sep-2025

Web References: 10.1002/smll.202509275

Image Credits: Science Communication Lab for DESY

Keywords

PFAS, covalent organic frameworks, mechanochemistry, ball milling, water filtration, environmental remediation, sustainable materials, DESY, PETRA III, real-time X-ray analysis, green chemistry, environmental pollutants

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

Image Credits: AI Generated

Traditional information recording media have evolved drastically over millennia—from the earliest clay tablets, to paper, compact discs, and ultimately semiconductor memories. As the demand for miniaturization and higher areal density intensifies, the physical elements encoding data continue to shrink to nanometric scales. Non-volatile memories, which retain information without power for extended periods, are indispensable in contemporary computing and data archival systems. Yet, conventional materials approach intrinsic physical boundaries, necessitating revolutionary approaches for overcoming limitations in size, speed, and stability.

Recent advances in molecular technology, particularly the design and synthesis of molecular machines and nanomachines, have revealed entities capable of precise mechanical motions at the molecular level. Among these, molecular rotors—molecules that rotate or flip around defined chemical bonds—present an intriguing avenue for encoding binary information through their orientation states. The potential to exploit such molecules for memory applications, leveraging their minimal dimensions and tailorability, has been a subject of intense research interest. However, achieving simultaneous control over their orientation, long-term stability, and unhindered rotational mobility within solid-state materials has remained a formidable challenge.

The breakthrough achieved by the Tokyo team centers on the strategic incorporation of dipolar rotors into a COF scaffold designed to circumvent prior limitations. To function effectively as memory elements, molecular rotors must meet three rigorous criteria: first, the presence of a permanent dipole moment to enable manipulation via external electric fields; second, thermal robustness ensuring their orientation remains stable at room and elevated temperatures; and third, sufficient spatial freedom within the solid matrix to allow controlled flipping without steric obstruction. Compounding these demands is the necessity for these materials to withstand operational temperatures up to 150°C, reflecting the harsh thermal environment encountered in computing devices.

Addressing these requisites, the researchers devised two novel COFs, denominated TK-COF-P and TK-COF-M, featuring a structural topology classified as “sln” — a geometry characterized by intrinsically low density and spacious three-dimensional connectivity. This topology, previously unreported among COFs, was crucial in providing the dipolar rotors with a sterically permissive environment facilitating reversible molecular rotations. The frameworks are constructed by covalently linking tetrahedral, four-armed molecular nodes with newly synthesized planar, three-armed linkers embedding alternating dipolar 1,2-difluorophenyl groups and aryl units rooted in a central benzene ring, an arrangement meticulously optimized to stabilize rotor orientation at ambient conditions.

Intriguingly, the researchers observed a remarkable shape dimorphism in these COFs, whereby crystallization conditions dictated the formation of either well-defined hexagonal prismatic crystals or extended membrane-like sheets. Such morphological versatility not only underscores the tunability of COF synthesis but may also bear implications for the integration and processability of these materials in device architectures. Moreover, X-ray crystallographic analysis elucidated the detailed framework geometry, validating the targeted sln topology and confirming the periodic distribution of dipolar rotors within the porous network.

From a thermal standpoint, the newly developed COFs exhibit extraordinary stability, maintaining structural integrity and functional rotor dynamics up to temperatures near 400°C—far exceeding the thermal thresholds typical of conventional semiconductor components. This resilience is a direct consequence of the robust covalent bonds constituting the framework and the minimized density afforded by the sln topology, which collectively mitigate thermal degradation and steric locking of the rotors.

Functionally, the dipolar rotors embedded within these COFs demonstrate the ability to flip orientation when subjected to sufficiently strong electric fields or elevated temperatures exceeding 200°C, yet retain their alignment for extended durations at room temperature. This bistable behavior is a quintessential characteristic for non-volatile information storage, where data represented by rotor orientation must remain stable in the absence of power yet be rewritable upon command. The low-density sln framework underpins this performance by minimizing steric hindrance—a critical factor that had previously hampered molecular rotor mobility within dense organic solids.

Professor Yoichi Murakami, leading the project, highlights the significance of their work not only in advancing molecular-machine-based memory materials but also in expanding the taxonomy of COF structures through the novel discovery of sln topology and shape dimorphism. These findings open avenues for further exploration into COF-based devices where molecular precision and solid-state durability coalesce.

Looking ahead, the implications of this research could be transformative. By harnessing the advantages of molecular scale components—vastly smaller than pits in compact discs or transistor features—these COFs offer a prospective path toward ultra-high-density data storage. The organic, modular nature of the materials affords extensive opportunities for chemical customization, potentially enabling tailored functionalities for specific memory applications or integration with existing semiconductor technologies.

While the current studies focus on demonstrating fundamental properties and material synthesis, subsequent developments will need to address scaling up production, device fabrication, and performance benchmarking against extant technologies. Success in these realms could herald the advent of molecular-machine-driven memories, reshaping the landscape of information technology with devices that are more compact, durable, and energy-efficient.

In essence, the pioneering efforts by the Institute of Science Tokyo exemplify how merging condensed matter chemistry, materials science, and molecular machinery can surmount longstanding barriers in data storage technology. Their innovation encapsulates the promise of COFs as versatile platforms where the dynamic behavior of molecular machines can be harnessed and controlled at the macroscopic scale, enabling new paradigms for information science in the coming decades.

Subject of Research:
Not applicable

Article Title:
sln-Topological Covalent Organic Frameworks with Shape Dimorphism and Dipolar Rotors

News Publication Date:
14-Aug-2025

Web References:
http://dx.doi.org/10.1021/jacs.5c10010

References:

• Murakami, Y. et al., “sln-Topological Covalent Organic Frameworks with Shape Dimorphism and Dipolar Rotors,” Journal of the American Chemical Society, 2025.

Image Credits:
Yoichi Murakami

Keywords

Applied sciences and engineering; Materials engineering; Covalent organic frameworks; Diffraction