Nanoflake-Engineered Zirconic Fibrous Aerogels with Parallel-Arrayed Conduits for Fast Nerve Agent Degradation

Reactive Polymers of Intrinsic Microporous Aerogels for Rapid Mustard Gas Detoxification

Polymers of intrinsic microporosity (PIMs) have broad application prospects in the detoxification of chemical warfare agents (CWAs) due to their unique pore structure, good tunable reactivity, and solution processability. However, its pore structure is relatively homogeneous, resulting in high resistance to mass transfer. Here, inspired by fractal structure in nature, a structure engineering strategy is proposed to develop 3D reactive nanofibrous aerogels featuring hierarchical porous structures to minimize mass transfer resistance. These aerogels are fabricated with amidoxime-modified PIM-1 (AO-PIM-1) nanofibers serving as building units and flexible SiO2 nanofibers acting as reinforcement. The macro/mesopores of amidoxime-modified PIM-1 nanofibrous aerogels (APAs) originating from freeze-shaping and electrospinning provide interconnected channels for the diffusion of CWAs, and the intrinsic micropores of AO-PIM-1 can effectively trap and anchor adsorbate molecules. In addition, the reactivity of the APAs can be activated by chlorine bleaching. This process forms an N-chlorine structure, which effectively oxidizes the adsorbed CWAs simulant 2-chloroethyl ethyl sulfide (CEES) by APAs, converting them into non-toxic products. The resulting aerogels have the properties of ultralight weight (8 mg cm-3), reversible compression strain of 60%, and repeatable sulfur mustard decontamination (half-life of 1.27 min). These characteristics indicate significant potential for the use in protective materials against vesicant CWAs.

Advancing Metal-Organic Framework-Based Composites for Effective Chemical Warfare Agent Detoxification under Real-World Conditions

Threats from toxic chemical warfare agents (CWAs) persist due to war and terrorist attacks, endangering both human beings and the environment. Metal-organic frameworks (MOFs), which feature ordered pore structures and excellent tunability at both metal/metal cluster nodes and organic linkers, are regarded as the best candidates to directly remove CWAs and their simulants via both physical adsorption and chemically catalyzed hydrolysis or oxidization. MOFs have attracted significant attention in the last two decades that has resulted from the rapid development of MOF-based materials in both fundamental research and real-world applications. In this review, the authors focus on the recent advancements in designing and constructing functional MOF-based materials toward CWAs detoxification and discuss how to bridge the gap between fundamental science and real-world applications. With detailed summaries from different points of view, this review provides insights into design rules for developing next-generation MOF-based materials for protection from both organophosphorus and organosulfur CWAs to mitigate potential threats from CWAs used in wars and terrorism attacks.

Building-Envelope-Inspired, Thermomechanically Robust All-Fiber Ceramic Meta-Aerogel for Temperature-Controlled Dominant Infrared Camouflage

The unsatisfactory properties of ceramic aerogels when subjected to thermal shock, such as strength degradation and structural collapse, render them unsuitable for use at large thermal gradients or prolonged exposure to extreme temperatures. Here, a building-envelope-inspired design for fabricating a thermomechanically robust all-fiber ceramic meta-aerogel with interlocked fibrous interfaces and an interwoven cellular structure in the orthogonal directions is presented, which is achieved through a two-stage physical and chemical process. Inspired by the reinforced concrete building envelope, a solid foundation composed of fibrous frames is constructed and enhanced through supramolecular in situ self-assembly to achieve high compressibility, retaining over 90% of maximum stress under a considerable compressive strain of 50% for 10 000 cycles, and showing temperature-invariance when compressed at 60% strain within the range of -100 to 500 °C. As a result of its distinct response to oscillation tolerance coupled with elastic recovery, the all-fiber ceramic meta-aerogel exhibits exceptional suitability for thermal shock resistance and infrared camouflage performance in cold (-196 °C) and hot (1300 °C) fields. This study provides an opportunity for developing ceramic aerogels for effective thermal management under extreme conditions.

Construction of imidazole@defective hierarchical porous UiO-66 and fibrous composites for rapid and nonbuffered catalytic hydrolysis of organophosphorus nerve agents

Hydrolytic destruction of toxic organophosphorus nerve agents by metal-organic framework (MOF) catalysts is commonly reliant on bulk water and volatile liquid base, preventing real-world implementation. Poor accessibility to MOF-based active sites in heterogeneous catalysis is also a crucial factor since reactants diffusion is limited by inherently small micropores. To overcome these practical limitations, a ligand-selective pyrolysis strategy was used to construct unsaturated Zr defects and additional mesopores in UiO-66(Zr). Owing to synergistic effect of Zr defects and hierarchical pores, hydrolysis rate constant (k) of nerve agent simulant DMNP (dimethyl 4-nitrophenyl phosphate) on optimal DHP-UiO-30% (defective hierarchical porous UiO-66) is 3.2 times higher than counterpart UiO-30% in N-ethylmorpholine buffer. Encapsulating imidazole (Im) into DHP-UiO-30% affords Im@DHP-UiO, mimicking phosphotriesterase. Im-72@DHP-UiO exhibits rapid DMNP detoxification with 99% conversion in 12 min and initial half-life (t1/2) of 1.8 min in nonbuffered water. As the first example of 'three-in-one' detoxifier, Im@DHP-UiO is further integrated onto nonwoven fabric to construct Im@DHP/Fiber, achieving solid-phase detoxification at ambient humidity with t1/2 of 19.6 min and final conversion of 91%. This is comparable to many powdered catalysts in aqueous solution buffered by volatile bases. This unified strategy is critical and viable to efficiently hydrolyze nerve agents in practical settings.

Humidity Enhances the Solid-Phase Catalytic Ability of a Bulk MOF-808 Metal-Organic Gel toward a Chemical Warfare Agent Simulant

Zirconium-based metal-organic frameworks have emerged as promising materials for detoxifying chemical warfare agents (CWAs) due to their remarkable stability and porosity. However, their practical application is hindered by issues with their powder form and poor catalytic performance in solid-phase degradation. To address these challenges, herein, a granular MOF-808 metal-organic gel (G808) is prepared under optimized conditions for catalytic degradation of the simulant 2-chloroethyl ethyl sulfide (2-CEES), a sulfide blister agent, in a neat state under different humidity conditions. The detoxification performance of G808 toward 2-CEES is significantly enhanced as the content of water present increases. The half-life of 2-CEES decontaminated by G808 can be shortened to 816 s, surpassing those of many other benchmark materials. To confirm the mechanism of catalytic degradation, we used gas chromatography, gas chromatography-mass spectrometry, and theoretical calculations. The findings revealed that hydrolysis was the predominant route. Additionally, granular G808 was reusable and adaptable to high-moisture environments, making it an excellent protective material with practical potential.

Defective MOF-74 with ancillary open metal sites for the enhanced adsorption of chemical warfare agent simulants

The development of effective porous adsorbents plays a vital role in eliminating hazardous substances from the environment. Toxic chemicals, including chemical warfare agents (CWAs), pose significant risks to both humans and ecosystems, highlighting the urgency to create efficient porous adsorbents. Therefore, substantial attention has been directed towards advancing adsorption techniques for the successful eradication of CWAs from the environment. Herein, we demonstrate a rational approach for enhancing the adsorption capability of a porous metal-organic framework (MOF) by employing ancillary open metal sites within the MOF structure. To generate defective MOF-74 (D-MOF-74) with ancillary open metal sites, some of the 2,5-dihydroxy-1,4-bezenedicarboxylic acid (DHBDC) linkers originally present in the MOF-74 structure were replaced with 1,4-benzenedicarboxylic acid (BDC) linkers. The absence of hydroxyl groups in the BDC linkers compared to the original DHBDC linkers creates ancillary open metal sites, which enhance the adsorption ability of D-MOF-74 for CWA simulants such as dimethyl methyl phosphonate, 2-chloroethyl ethyl sulfide, and methyl salicylate by providing effective interaction sites for the targeted molecules. However, excessive creation of open metal sites causes the collapse of the originally well-developed MOF-74 structure, resulting in a substantial reduction in its empty space and a subsequent decline in adsorption efficiency. Thus, to produce a defective MOF with the best performance, it is necessary to replace an appropriate amount of organic linker and create suitable open metal sites. Moreover, D-MOF-74 displays excellent recyclability during consecutive adsorption cycles without losing its original structure and morphology, suggesting that D-MOF-74 is an effective and stable material for the removal of CWA simulants.

From 1D Nanofibers to 3D Nanofibrous Aerogels: A Marvellous Evolution of Electrospun SiO2 Nanofibers for Emerging Applications

One-dimensional (1D) SiO2 nanofibers (SNFs), one of the most popular inorganic nanomaterials, have aroused widespread attention because of their excellent chemical stability, as well as unique optical and thermal characteristics. Electrospinning is a straightforward and versatile method to prepare 1D SNFs with programmable structures, manageable dimensions, and modifiable properties, which hold great potential in many cutting-edge applications including aerospace, nanodevice, and energy. In this review, substantial advances in the structural design, controllable synthesis, and multifunctional applications of electrospun SNFs are highlighted. We begin with a brief introduction to the fundamental principles, available raw materials, and typical apparatus of electrospun SNFs. We then discuss the strategies for preparing SNFs with diverse structures in detail, especially stressing the newly emerging three-dimensional SiO2 nanofibrous aerogels. We continue with focus on major breakthroughs about brittleness-to-flexibility transition of SNFs and the means to achieve their mechanical reinforcement. In addition, we showcase recent applications enabled by electrospun SNFs, with particular emphasis on physical protection, health care and water treatment. In the end, we summarize this review and provide some perspectives on the future development direction of electrospun SNFs.

Superelastic and Photothermal RGO/Zr-Doped TiO2 Nanofibrous Aerogels Enable the Rapid Decomposition of Chemical Warfare Agents

To date, the reckless use of deadly chemical warfare agents (CWAs) has posed serious risks to humanity, property, and ecological environment. Therefore, necessary materials able to rapidly adsorb and securely decompose these hazardous toxics are in urgent demand. Herein, three-dimensional (3D) reduced graphene oxide/Zr-doped TiO₂ nanofibrous aerogels (RGO/ZT NAs) are synthesized by feasibly combining sol-gel electrospinning technology and a unidirectional freeze-drying approach. Benefiting from the synergetic coassembly of flexible ZT nanofibers and pliable RGO nanosheets, the hierarchically entangled fibrous frameworks feature ultralow density, superior elasticity, and robust fatigue resistance over 10⁶ compressive cycles. In particular, the RGO incorporation is attributed to the achieved increased surface area, stronger light absorption, and decreased recombination of charge-carriers for photocatalysis. The highly porous 3D RGO/ZT NAs deliver enhanced photothermal catalytic activity for CWA degradation as well as excellent recyclability and good photostability. This work opens fresh horizons for developing advanced 3D aerogel-based photocatalysts in a controlled fashion.