Now, a team of researchers in China reports a strategy that directly confronts this processing challenge. Writing in Nature Communications, Meidi Wang, Guan-Zheng Zhou, and colleagues describe a dual-drive transformation that converts COF powders into coherent membranes through the interplay of two forces: an internal driver based on framework reconstruction and an external driver based on acid attack. The work, carried out at China Three Gorges University with collaborators at the Harbin Institute of Technology and Huazhong University of Science and Technology, demonstrates that dynamic covalent chemistry, the same reversible bond-forming behavior that allows COFs to self-correct during synthesis, can be harnessed at the macroscopic scale to reshape an entire material.

The central insight is that COF frameworks are not as chemically inert as they might appear. Under the right conditions, the linkages that hold the network together can break and reform, allowing the structure to reorganize. The researchers exploited this plasticity deliberately. By subjecting COF powders to acid attack, they destabilized the existing bonds, while the intrinsic tendency of the framework to reconstruct drove the material to reassemble into a continuous membrane rather than remaining a collection of disconnected crystallites. The result is a transformation that operates at the macroscopic scale, converting bulk powder into a free-standing or supported film without the need for elaborate layer-by-layer assembly or high-temperature processing.

What makes the approach especially striking is its scalability. The team produced both two-dimensional and three-dimensional COF membranes, with the largest reaching an area of 225 square centimeters. For a field where many reported membranes measure only a few square centimeters, that figure represents a meaningful leap toward practical dimensions. The dual-drive strategy also achieved high conversion ratios and fabrication efficiency, outperforming conventional membrane-making methods on several fronts. Because the transformation relies on chemical driving forces rather than energy-intensive deposition techniques, the authors describe it as a green and versatile route to COF membranes, one that could in principle accommodate the wide structural diversity that reticular chemistry already provides.

The performance of the resulting membranes is where the work becomes truly compelling. The team’s optimum membrane, built from the TpPa framework, a combination of a triphenylene-based aldehyde and a phenylenediamine linker that forms imine-linked 2D layers, delivered impressive molecular sieving results. In filtration tests, the membrane rejected 99 percent of dye molecules and 98 percent of pharmaceutical molecules, while maintaining a pure water permeance of 179.0 liters per square meter per hour per bar. That combination of high selectivity and high flux is the holy grail of membrane science, since the two properties usually trade off against each other: membranes that filter more precisely tend to let water through more slowly, and vice versa.

The implications for water treatment are considerable. Dyes from textile manufacturing and active pharmaceutical compounds from municipal and industrial wastewater are among the most troublesome classes of aquatic pollutants, being small enough to slip through many conventional membranes yet harmful at low concentrations. A membrane that can reject these molecules at the 98 to 99 percent level while sustaining fast water transport could reduce the energy and cost of advanced treatment processes. The authors position the technology within chemical engineering separations broadly, suggesting applications that extend beyond pollution remediation to areas such as solvent purification and resource recovery.

To appreciate why the powder-to-membrane problem has been so persistent, it helps to consider the alternatives. Researchers have tried to grow COF membranes directly on supports through interfacial polymerization, to exfoliate 2D COFs into nanosheets and restack them into laminates, and to blend COF particles into polymer matrices as mixed-matrix films. Each route has drawbacks. Direct growth can be slow and difficult to control over large areas, often leaving pinholes that destroy selectivity. Exfoliation and restacking depend on delicate assembly steps that are hard to scale. Mixed-matrix membranes suffer from poor interface compatibility between the inorganic-like framework and the polymer. The dual-drive transformation sidesteps many of these issues by starting from the fully formed, crystalline powder and letting dynamic covalent chemistry do the assembly work.

The strategy also speaks to a broader trend in materials chemistry: the recognition that synthesis and processing should not be treated as separate stages. Reticular chemistry has excelled at designing structures atom by atom, but the history of materials science shows that a material only matters industrially when it can be shaped into the form a device requires. Graphene, metal-organic frameworks, and zeolites have all faced similar processing bottlenecks, and breakthroughs in shaping them, such as scalable graphene films or zeolite membranes, unlocked entire application domains. The COF community has been waiting for its own processing breakthrough, and a powder-to-membrane transformation that is green, efficient, and general enough to span 2D and 3D frameworks may prove to be exactly that.

There are, of course, questions that will shape the road ahead. The reported work is at an early stage, and the authors note that the published version is subject to further editorial refinement. Long-term stability under continuous operation, mechanical robustness, performance in complex real-world feed streams, and the economics of scale-up all remain to be demonstrated beyond the laboratory. The acid attack step, while central to the transformation, will need careful engineering in industrial settings. Still, the fundamentals are encouraging: the membranes are defect-free, the areas achieved are the largest reported for this class of material by a wide margin, and the underlying chemistry is inherently modular, meaning new COF chemistries could be plugged into the same transformation pipeline as they are invented.

The study, published open access on 30 September 2026 with support from the National Natural Science Foundation of China and the Hubei Three Gorges Laboratory, arrives at a moment when demand for advanced separation technology is rising across water purification, chemical manufacturing, and energy storage. If the dual-drive transformation proves as general and scalable as the authors suggest, the vast library of COF powders accumulated over the past two decades could suddenly become a library of usable membranes. That would be a quiet revolution in separation science, achieved not by inventing a new material, but by finding the chemistry that lets an existing one take the shape the world needs.

Subject of Research: Transformation of covalent organic framework powders into 2D/3D membranes for molecular separation

Article Title: Powder-to-membrane transformation affording 2D/3D COF membranes for molecular separations

Article References: Wang, M., Zhou, G.-Z., Zhou, Z., Shao, L., Shu, C., Ma, T.-Y., Wu, X.-Q., & Li, D.-S. (2026). Powder-to-membrane transformation affording 2D/3D COF membranes for molecular separations. Nature Communications. https://doi.org/10.1038/s41467-026-78068-w

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78068-w

Keywords: covalent organic frameworks, COF membranes, molecular separations, dynamic covalent chemistry, water purification, membrane technology, reticular chemistry, dye rejection, pharmaceutical pollutants, framework reconstruction, porous materials, chemical engineering

Forward osmosis works on a deceptively simple principle. Water spontaneously flows from a feed solution of lower osmotic pressure toward a concentrated draw solution on the other side of a semipermeable membrane. Because the process requires no external pumping pressure, it fouls less than pressure-driven reverse osmosis and can be paired with draw solutes that are easily recovered, or run as a pretreatment stage ahead of reverse osmosis. The heart of any such system is the membrane itself, typically a thin polyamide active layer formed on a porous support. The polyamide layer is created by interfacial polymerization, in which an aqueous amine monomer, usually m-phenylenediamine, meets an organic acyl chloride monomer, usually trimesoyl chloride, at the support’s surface. The reaction is fast and self-limiting, producing an ultrathin but dense film whose thickness, roughness and crosslinking density dictate how fast water moves and how well it rejects solutes.

For years, membrane scientists have tried to tune that film by embedding nanomaterials, a approach known as thin-film nanocomposite design. Nanoparticles of zeolites, metal-organic frameworks, carbon nanotubes, graphene oxide and MXenes have all been slipped into or beneath the polyamide layer, with mixed results. Additives can create extra water pathways and increase hydrophilicity, but they can also introduce defects, agglomerate into clumps that wreck selectivity, or leach out over time. The Iranian team chose a different class of additive altogether: a polyamide-based hyper-crosslinked polymer. Hyper-crosslinked polymers are amorphous, permanently porous networks built from rigid aromatic building blocks locked together by extensive covalent crosslinks. Their high internal surface area, tunable chemistry and chemical stability have made them popular in gas storage and catalysis, and this study puts them to work as a nanofiller for water membranes.

The synthesis itself was characterized with a battery of analytical techniques. Attenuated total reflectance Fourier-transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy confirmed that the hyper-crosslinked polymer had formed successfully, revealing a layered morphology rather than a granular one. Elemental mapping of the material showed that nitrogen-bearing groups were distributed uniformly throughout the structure, a detail that matters because those amide and amine groups interact strongly with water and with the monomers used in membrane fabrication. The high nitrogen content and even dispersion suggested the polymer would integrate well into the polyamide chemistry rather than sitting inertly inside it as a foreign body.

The genuinely clever part of the study is how the polymer gets into the membrane. Rather than blending it into the support or into the aqueous monomer solution, the researchers used what they call an intermediate strategy. The hyper-crosslinked polymer was dispersed in hexane, an organic solvent in which the polymer can be spread as a coating, and that dispersion was applied to the membrane support surface precisely between the aqueous amine phase and the organic acyl chloride phase. The polymer thus occupies the very frontier where interfacial polymerization happens. As the two monomers diffuse toward each other and react, they must contend with a porous, nitrogen-rich, layered material sitting at the reaction zone. The result is a polyamide film whose growth has been sculpted from the inside out.

That sculpting shows up clearly in the membrane’s final properties. The presence of the hyper-crosslinked layer changed the dynamics of monomer diffusion and film nucleation, and the modified active layers came out smoother, thinner and more hydrophilic than films polymerized without the additive. Each of those three attributes pushes performance in the right direction. A thinner film shortens the path water must travel. Greater hydrophilicity improves wetting and reduces the energetic penalty water pays entering the polymer network. Reduced roughness matters for fouling, because contaminants preferentially snag on peaks and valleys, so a smoother surface resists the accumulation of organic matter and dye molecules during long filtration runs. Chemical characterization confirmed the hyper-crosslinked polymer was stably embedded within the polyamide matrix rather than loosely deposited on top of it.

The performance numbers are the study’s headline. An unmodified forward osmosis membrane delivered a water flux of 12.2 liters per square meter per hour, a common benchmark unit abbreviated LMH. At the optimal loading of hyper-crosslinked polymer, flux rose to 23.4 LMH, an increase of more than 90 percent. Pushing the additive loading higher actually backfired, with flux declining again because excess polymer drove the formation of a thicker polyamide layer, which added resistance faster than the extra pathways added permeability. That dose-dependent behavior is typical of nanocomposite membranes and underscores why loading optimization is the central design variable. Importantly, the modified membrane also showed enhanced specific reverse salt flux, meaning that the salt that inevitably leaks backward from the draw solution did so at a rate disproportionately low relative to the water gained, an indicator that selectivity had not been sacrificed for speed.

To test the membrane under realistic and demanding conditions, the team ran a 24-hour continuous process concentrating reactive black B, a widely used anionic dye responsible for much of the colored effluent discharged by the textile industry. The membrane rejected more than 99.9 percent of the dye throughout the run and displayed an anti-fouling tendency, resisting the flux decline that usually plagues dye concentration processes as molecules build up on the membrane surface. The authors attribute this resilience to the combination of smoothness, hydrophilicity and stable integration of the hyper-crosslinked polymer within the active layer. Sustained performance over a full day of operation is a meaningful demonstration that the additive does not wash out, degrade or progressively separate from the polyamide, concerns that have undermined other nanofiller systems.

Why does a porous polymer interlayer boost flux so dramatically? The mechanistic picture, supported by the characterization data, centers on how the intermediate layer reshapes interfacial polymerization itself. Interfacial polymerization is governed by the diffusion of monomers into the reaction zone; anything that moderates that diffusion changes the film’s architecture. The hexane-dispersed hyper-crosslinked coating likely slows the amine monomer’s transport toward the organic phase and provides abundant hydrogen-bonding and amide interaction sites, yielding a film that is simultaneously thinner and more uniformly crosslinked. Related interlayer strategies in the literature, using materials from chitosan and cyclodextrins to covalent organic frameworks and MXene-carbon nanotube assemblies, have shown similar gains, confirming that controlling the reaction frontier is one of the most powerful levers in membrane design. What distinguishes the present work is the use of a permanently porous, polymer-based network rather than an inorganic nanoparticle, which sidesteps problems of particle agglomeration and interfacial incompatibility.

The broader significance lies in what the result says about the permeability-selectivity trade-off, the长久-standing constraint that forces membrane designers to choose between fast and clean. By growing a thinner, smoother, more hydrophilic polyamide film without opening defects, the hyper-crosslinked interlayer improved water transport while preserving rejection of salts and dyes, suggesting the trade-off is not an immutable law but a consequence of how films are made. For desalination, higher flux at equal selectivity translates directly into less membrane area and lower capital cost. For textile wastewater treatment, a membrane that concentrates reactive dyes with near-total rejection and low fouling could enable water reuse and dye recovery in one of the world’s most water-intensive industries. The study, published in Polymer Bulletin with financial and instrumental support from the University of Tehran, adds a versatile new tool, a synthetically tunable porous polymer, to the membrane engineer’s toolkit, and points toward a generation of forward osmosis membranes that no longer ask designers to choose between speed and selectivity.

Subject of Research: Modification of thin-film nanocomposite forward osmosis membranes with a hyper-crosslinked polymer interlayer to enhance water flux, salt rejection and dye concentration

Article Title: Modification of thin film nanocomposite forward osmosis membranes using hyper-crosslinked polymer via intermediate strategy

Article References: Mirsaeidghazi, E., Shakeri, A., & Salehi, H. (2026). Modification of thin film nanocomposite forward osmosis membranes using hyper-crosslinked polymer via intermediate strategy. Polymer Bulletin, 83(12), Article 652. https://doi.org/10.1007/s00289-026-06710-0

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06710-0

Keywords: forward osmosis, thin-film nanocomposite membrane, hyper-crosslinked polymer, interfacial polymerization, polyamide, water desalination, dye concentration, anti-fouling, membrane modification, water flux, reverse salt flux, textile wastewater treatment