Mechanically Flexible and Weavable Hybrid Aerogel Fibers with Ultrahigh Metal–Organic Framework Loadings for Versatile Applications

Abstract

Flexible and weavable metal−organic framework (MOF)-based hybrid fibers can enable many potential applications, particularly for wearable functional devices. However, the fabrication of composite textiles with high MOF loadings, a large specific surface area, and outstanding mechanical flexibility is still very challenging. Herein, we demonstrate the preparation of mechanically strong MOF@ ANF (aramid nanofiber) hybrid aerogel fibers with gradient distribution of MOF crystals along the radial direction through in situ growth of MOFs on the skeletons of three-dimensional (3D)-printed aramid nanofiber (ANF) aerogel fibers. The deprotonation of poly(p-phenylene terephthalamide) networks increases the local concentration of cobalt ions and enables the in situ growth of MOF crystals inside the ANF filaments, the mechanism of which was revealed by computational simulations. As a result, an ultrahigh ZIF-67 loading of 63.4 wt % and a large specific surface area of 756.6 m 2 g −1 were achieved by the hybrid ZIF-67@ANF aerogel fibers, the highest specific surface area among macroscopic and weavable MOF-based composite fibers ever reported. These aerogel textiles show excellent mechanical flexibility and exhibit fast adsorption kinetics, high adsorption capacity, and recycling stability for addressing various hazardous pollutants, including formaldehyde vapor, heavy metal ions, and organic dyes. This work takes a further step toward wearable-MOF-based textile development for broad applications in wearable devices.

Strong, Tough, and Recyclable Aramid Aerogel Fibers with Homogeneous Nanoscale Structures for High-Temperature Thermal Insulation Applications

“…The modulus and strength achieved in HAAF-5 with a C s of 4 wt % were 257 and 36.1 MPa, respectively, and these values further increased to 483 and 39.7 MPa with a C s of 5 wt % (Figure g,h and Table S2). Notably, the strength is much higher than previously reported aramid or its composite aerogel fibers by phase separation (0.5–8.1 MPa) ,− and is even comparable to aramid aerogel fibers from highly concentrated (10 wt %) aramid nanofiber liquid crystal with further drafting treatment (41 MPa) . Our HAAFs also possess superior strength to recently reported other aerogel fibers, such as polyimide aerogel fibers (2.1–22 MPa), ,,, cellulose aerogel fibers (5.8–30.0 MPa), − and core–shell structured chitosan-TPU aerogel fibers (12.7 MPa) .…”

“…Our HAAFs also possess superior strength to recently reported other aerogel fibers, such as polyimide aerogel fibers (2.1–22 MPa), ,,, cellulose aerogel fibers (5.8–30.0 MPa), − and core–shell structured chitosan-TPU aerogel fibers (12.7 MPa) . Noteworthily, our HAAF-5 achieves a large elongation at break of 99.1% with a C s of 4 wt %, which surpasses all previously reported aramid aerogel fibers (10–40%). − The comparison of the strength, elongation, and thermal conductivity properties with other aerogel fibers in Figure S8.The calculated toughness is as high as 23.14 MJ/m 3 , rivaling that of high-toughness cellulose aerogel fibers in a very recent work . The good ductility and high toughness of our HAAFs are also attributed to the homogeneous cross-linking and porous structures.…”

“…Furthermore, a small fraction of flexible poly-2,2′- p -oxidiphenylene-5,5′-dibenzimidazole (OPBI) that acted as ropes was added into the PABI system to bind the rigid PABI rods, thus promoting the oxidation-induced gelation of the PABI/Co 2+ system and strengthening the cross-linked networks of HAAFs on the nanoscale level, which facilitated the continuous spinning of HAAFs on commonly used wet spinning equipment. In contrast to the previously reported wet spinning − or freeze spinning − method, the in situ constructed 3D cross-linked networks in gel fibers in this approach have fixed the porous structure firmly after subsequent solvent-exchange and drying process; thus, the obtained aerogel fibers demonstrated homogeneous porous structure across the whole fiber, which gives rise to high mechanical strength and superior toughness than other reported AAFs. The critical factors that affect the structure and properties of HAAFs were systematically investigated, the thermal protective performance of HAAFs was evaluated, and the recyclability of HAAFs after chemical reduction was also assessed.…”

“…The wet gel fiber was then subjected to solvent exchange and a freeze-drying treatment to afford HAAFs (Figure a). SEM images show that the cross section and surface (Figure b 1 ,c 1 ) of the obtained aerogel fibers (HAAF-5) were all regular in shape, and it was observed from the magnified images (Figure b 2 ,c 2 ) that the cross section and surface of the fiber were composed of uniform pores ranging from tens to hundreds of nanometer, which was in sharp contrast to the previously reported dense sheath of aerogel fibers, where the formation mechanism of the porous structure was nonsolvent phase separation, ,− suggesting our oxidation induced cross-linking has preserved the 3D porous structure of gel fibers in subsequent solvent exchange and drying treatments, leading to homogeneous porous structure across the whole aerogel fiber. Strikingly, a single HAAF-5 can load a weight of 200 g (Figure d), and it can be knotted without breaking (Figure e, Figure S4) and woven into fabric without causing the leaf to bend when the fabric is placed at the edge (Figure f), indicating its good mechanical properties, flexibility, and lightweight characteristics.…”

“…The resultant AAFs demonstrated excellent thermal insulation properties under extreme temperatures. Various kinds of AAFs were then reported in recent years with the aim of improving the mechanical strength of AAFs , or introducing functional materials such as phase change materials, carbon nanotubes, , silver nanowires, and MOFs into AAFs to widen their functionalities. However, all reported AAFs were exclusively fabricated by wet-spinning, using ANFs as precursors.…”