A durable MOF-nanofiber composite overcomes the fragility of reactive materials, enabling real-world systems that capture and break down nerve agents and toxic industrial gases under harsh conditions.
(Nanowerk Spotlight) Some of the most dangerous chemical threats cannot be seen or smelled and take effect before their presence is even known. Nerve agents like soman, industrial gases like chlorine, and blistering compounds such as sulfur mustard are toxic in minute quantities and difficult to counter once released. While filters and protective gear can trap these substances, most rely on passive absorption. Under the wrong conditions, toxins can be re-released into the air, posing a renewed risk.
Neutralizing hazardous chemicals on contact requires materials that combine precision at the molecular scale with strength and stability in real-world conditions. These materials must offer vast internal surface areas, be chemically reactive, and hold up under pressure, humidity, and repeated mechanical stress. Some of the most effective lab-scale materials fail when moved into practical formats like air filters, protective suits, or field-ready decontamination systems.
Metal-organic frameworks, or MOFs, are one class of materials that show promise. These are porous crystals made from metal clusters and organic linkers, engineered to attract and interact with specific molecules. MOFs have been studied for their ability to break down toxic compounds, but in powdered form they are fragile, difficult to handle, and prone to clumping, making them impractical for most applications.
The team developed a method for combining MOFs with flexible nanofiberaerogels to create a lightweight, durable composite that can both capture and chemically degrade toxic agents. These materials remain stable under compression, resist water, and function effectively with live nerve agents and industrial gases. The approach avoids complex processing steps and opens the door to scalable, multifunctional systems for chemical protection and environmental remediation.
Schematic illustration of the solvothermal synthesis process for mesoporous UiO-66-NH2 MOF powder. (Image: reprinted from DOI:10.1002/adfm.202516872, CC BY) (click on image to enlarge)
The composite materials developed in this study are based on two well-known MOFs: UiO-66-NH₂, a zirconium-based structure with known catalytic activity, and HKUST-1, a copper-based MOF commonly used for gas adsorption. Both materials offer high internal surface area and reactive sites suitable for interacting with hazardous compounds. However, on their own, they suffer from mechanical fragility and poor handling properties.
To overcome this, the researchers first focused on modifying UiO-66-NH₂ to introduce mesopores, which are larger than typical MOF pores and help improve diffusion of bulky molecules like chemical warfare agents. They achieved this using a mild water-based synthesis method with cocamidopropyl betaine, or CAPB, a surfactant that acts both as a pore template and a stabilizing agent. Using 0.5 grams of CAPB, the team produced UiO-66-NH₂ with a surface area of approximately 1100 square meters per gram and a broad distribution of pore sizes ranging from 6 to over 200 angstroms.
Once synthesized, the MOF powders were combined with polymer nanofibers made from polyacrylonitrile and polyvinylpyrrolidone. The nanofibers were created by electrospinning, then chopped and dispersed in tert-butanol along with the MOF particles. This mixture was frozen and freeze-dried to form an aerogel, followed by thermal treatment to improve structural stability. MOF loadings ranged from 50 to 90 percent by weight.
Despite some reduction in surface area due to heating, the composites maintained their porous structure and showed strong mechanical performance. Even at 90 percent MOF content, the materials could be compressed and re-expanded with minimal loss of height. Adhesion between the MOFs and the nanofiber network remained strong, and no MOF particles were lost during water immersion, agitation, or manual compression. This mechanical durability is critical for protective applications, where materials must withstand handling and repeated stress.
The materials were tested for their ability to degrade dimethyl 4-nitrophenyl phosphate, or DMNP, a standard simulant for nerve agents. The reaction followed first-order kinetics. The 90 percent UiO-66-NH₂ composites achieved nearly complete DMNP conversion within 15 minutes, with half-lives as low as three minutes.
Composites with 50 percent MOF content showed slower but still effective degradation. The variability in performance across samples was attributed to thermal gradients during fabrication, which may have created local differences in MOF activity.
Live-agent tests confirmed the composites’ ability to degrade soman and sulfur mustard. The 90 percent UiO-66-NH₂ aerogels converted around 62 percent of soman and 36 percent of sulfur mustard in 24 hours under solid-state conditions. These results are significantly better than those for activated carbon cloth, which typically reaches only 20 percent soman degradation under the same conditions. The improved performance is linked to the presence of reactive amino groups on the MOF surface, which catalyze the breakdown of phosphorus and sulfur bonds in these agents.
To extend the utility of the composites, the researchers also incorporated HKUST-1 and ZIF-8 into the same nanofiber aerogel matrix. The team evaluated MOFs for their ability to capture ammonia, chlorine, and 2-chloroethyl ethyl sulfide, a simulant for sulfur mustard. Thermally treated HKUST-1 achieved the highest ammonia adsorption at 10.8 moles per kilogram. ZIF-8 performed best for chlorine and CEES, with adsorption capacities of 5.0 and 6.2 moles per kilogram, respectively.
The study investigated the interactions between these gases and the MOF structures. Ammonia binds strongly to copper centers in HKUST-1 through coordination and hydrogen bonding. Chlorine shows weaker physical interactions and can form copper-chloride complexes that reduce the MOF’s structural stability. CEES interacts both physically and chemically, forming bonds with metal centers and fitting into the mesoporous structure.
Breakthrough tests showed that thermally treated HKUST-1 had the longest ammonia retention times. Composites with 90 percent MOF loading retained more gas than those with 50 percent loading, though in some cases the higher MOF content led to reduced performance due to diffusion limitations. The results highlight the importance of optimizing both MOF content and pore accessibility when designing adsorbent systems.
Mechanical testing confirmed that the composites remained structurally sound under repeated compression. The 50 to 80 percent MOF-loaded aerogels retained elasticity and height after multiple loading cycles. At 90 percent loading, the material became more brittle but still performed well under moderate strain. These properties suggest the composites could function in settings where compressive forces are common, such as in wearable filters or packed cartridges.
The fabrication approach used in this study avoids many limitations of earlier methods. By physically mixing pre-synthesized MOF powders with nanofiber dispersions, the researchers eliminated the need for solvent exchange, in situ crystal growth, or toxic reagents. The method is compatible with large-scale production and allows for customization depending on the target application or chemical threat.
While thermal treatment reduced surface area and porosity compared to untreated powders, the overall performance of the composites remained strong. The researchers suggest future work could refine the thermal protocols to better preserve pore structure and MOF activity. Additional studies will also focus on mechanical fatigue testing and environmental stability over time.
By integrating porous MOFs with structurally robust nanofiber aerogels, this work demonstrates a route to multifunctional materials that are both chemically effective and mechanically resilient. The composites combine high adsorption capacity with catalytic detoxification and can be tailored for specific chemical threats. Their durability and processability make them promising candidates for protective systems in defense, industrial safety, and environmental cleanup.
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