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Conducting two-dimensional (2D) materials of MXene have exhibited great potential for high-performance flexible supercapacitor applications. However, MXene-based flexible supercapacitors are difficult to balance the electrochemical performance and mechanical stability, due to a low operating voltage window of MXene-based symmetric supercapacitors configuration and the absence of suitable flexible positive electrodes. For this, we design a novel asymmetric device, where the active materials are totally based on the conducting 2D materials with electrochemically covalent active groups on the surface. The covalently modified graphene materials grafted with p-phenylenediamine (PPD) (PrGO) and MXene materials are used as the positive and negative electrodes, respectively. Besides, one-dimensional (1D) aramid nanofibers (ANFs) are introduced into the flexible electrode for reinforcing the mechanical strength and structure stability. Benefited from the excellent nanostructure of ANFs and rich amide active groups, multiple interactions are formed at the interface of 2D pseudocapacitive materials and 1D ANFs, including van der Waals forces and hydrogen bonds. As a result, excellent performance is achieved in the fabricated flexible composite film electrodes of PrGO (7:6)/ANFs (404 F g−1, 82.2 MPa) and MXene/ANFs (370 F g−1,90.8 MPa). Notably, the assembled flexible asymmetric supercapacitors (ASCs) maintained about 100 % capacitance after 10,000 cycles and exhibited a superior quality energy density of 24.5 Wh kg−1, exceeding the majority of MXene-based flexible supercapacitors. It can be subjected to thousands of folding and deformation tests without any damage, demonstrating that devices assembled in this manner are highly efficient and have excellent potential for application in flexible wearable energy storage devices.

Nanocomposite conductive fiber has been newly developed as a lightweight material with high flexibility and strong weavability, which can meet the requirements of flexible wearable devices. Herein, lightweight porous aramid nanofibers (ANF) and carbon nanotube (CNT) aerogel fibers coated with polypyrrole (PPy) layers are prepared by a wet spinning method for motion detection and information transmission. The ANF/CNT/PPy aerogel fiber with low density (56.3 mg/cm3), conductivity (6.43 S/m), and tensile strength (2.88 MPa) were used as motion sensors with high sensitivity (0.12) and long life (1000 cycles). At the same time, the differential conductivity of aerogel fibers is utilized to reduce the information transmission time (up to 46%). High- and low-temperature-resistant (−196 to 100 °C) aerogel fibers are also available as a quick heater and ionic solution detector. In summary, the prepared ANF/CNT/PPy aerogel fiber can be used as a multifunctional sensor for human-health detection and motion monitoring.

Benefiting from its superior thermal stability, polyimide (PI) fiber-based composites have attracted wide attention in the field of high-temperature filtration and separation. However, the trade-off between filtration efficiency and pressure drop of traditional PI filters with single morphology and structure still remains challenging. Herein, the electrospun PI high-temperature-resistant air filter was fabricated via thermal-induced phase separation (TIPS), employing polyacrylonitrile (PAN) as a template. The PI nanofibers exhibited special wrinkled porous structure, and the filter possessed a high specific surface area of 304.77 m2/g. The removal of PAN changed the chemical composition of the fiber and induced PI molecules to form complex folds on the surface of the fiber, thus forming the wrinkled porous structure. Additionally, the wrinkled porous PI nanofiber filter displayed a high PM0.3 removal efficiency of 99.99% with a low pressure drop of 43.35 Pa at room temperature, and the filtration efficiency was still over 97% after being used for long time. Moreover, the efficiency of the filter could even reach 95.55% at a high temperature of 280 °C. The excellent filtration performance was attributed to the special wrinkled porous surface, which could limit the Brownian motion of PMs and reinforce the mechanical interception effect to capture the particulate matters (PMs) on the surface of the filter. Therefore, this work provided a novel strategy for the fabrication of filters with special morphology to cope with increasingly serious air pollution in the industrial field.

Herein, we discovered that using the mixed aqueous solution of hydroxyethyl cellulose (HEC) and sodium hydroxide (NaOH) as ball-milling medium of hexagonal boron nitride (h-BN) could exfoliate larger lateral size boron nitride nanosheets (BNNSs) than using HEC solution alone due to the salting-out effects of Na+to HEC that aggregated the polymer molecules and in turn enhanced the impact resistance to milling balls. Through centrifugal separation and reduced ball-to-h-BN ratios, different lateral size BNNSs were obtained and further assembled into films with aramid nanofibers (ANFs) to investigate their thermal conduction performances. The results indicated that the larger lateral size BNNS-based films show higher thermal conductivities (TCs) owing to the reduced phonon scattering at boundaries, but BNNSs with overlarge lateral sizes are difficult to be stacked into compact microstructures and in turn result in the much lowered TC for the assembled film. Meanwhile, the interfacial interactions and BNNS defects also have some influences on TCs of the composites. Overall, this study provides a novel route to the fabrication of large-area BNNSs and reveals their scale laws on thermal conduction, and the fabricated ANF/BNNS heat spreader has a high TC of 31.88 W·m–1·K–1, which is promising for use in thermal management of high-power electronic devices and batteries.

Herein, Fe3+, Co2+, and Ni2+were respectively introduced into the splitting of aramid fibers, and then the metal hydroxide nanoparticles (NPs) were formed on the aramid nanofibers (ANFs). The nanofilm assembled from NP-grafted ANFs shows high stress, toughness, and dielectric breakdown strength. The results indicate that the ANF nanofilm contained 5 wt% Fe3+presents the highest enhancing capacity to the mechanical properties of ANF film, with a strength of 312 MPa and a toughness of 61.9 MJ m−3, increased by 73.3% and 215.8%, respectively. The NPs increase the ANF film's dielectric breakdown strength by 40.8%–60.2%. Different from the previous studies, we have not observed the densification of the nanofilm, and the enhanced mechanical properties may be caused by the strong electrostatic and coordinate interactions between NPs and ANFs, evidenced by the large numbers of fiber pull-out on fracture cross-sections. Because of the hydrophilicity of the NPs and the un-densified structures, the composite films show both high flux and rejection to methylene blue (MLB).

Solvothermal techniques are widely used to exfoliate many two-dimensional materials, but the formation mechanisms of these nanomaterials have not been clearly revealed. Herein, we discovered the dissociation of hexagonal boron nitride (h-BN) in solvothermal exfoliation evidenced by the formation of B(OH)3, NH4B5O8·4H2O, and (NH4)2B10O16·8H2O. In the selected solvents, the lateral sizes of the formed boron nitride nanosheets (BNNSs) are increased in the order of N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), acetonitrile (MeCN), and isopropanol (IPA), suggesting the decreased dissolving abilities of these solvents to h-BN in turn. The dissociation behaviors are the properties of solvents themselves, but the inclusion of lithium chloride (LiCl) and cetyltrimethylammonium bromide (CTAB) can elevate the dissociation degree and yield BNNSs with smaller lateral sizes due to the intercalating effects. The cation−π interactions make CTAB more effective in obtaining uniform BNNSs than using the neutral halogenated hydrocarbons as assistant reagents. The dissociation abilities of the solvents have strong relationships with the surface tension, Hansen solubility parameters distances (Ra), and polarities, whereas there is little relevance with the pressures. Meanwhile, we also observed the cracking of CTAB and the polymerization of MeCN in these reactions. Our findings indicate that the impurities are prone to be attached to the BNNSs exfoliated by the solvothermal route.

TEMPO-oxidized cellulose nanofibers (TOCNs) derived from the TEMPO-mediated oxidation of macro cellulose fibers have plentiful hydroxyls (-OH) and carboxyl anions (-COO−) on their surface, which are prone to form strong hydrogen bonding (HB) interactions with HB acceptor/donor contained polymers. In this work, polyvinylpyrrolidone (PVP), polyacrylamide (PAM), polyvinyl alcohol (PVA), polyacrylic acid (PAA), and carboxymethyl cellulose (CMC) were selected as HB acceptor/donor to fabricate composite films with TOCNs, and the influences of HB interactions on the mechanical properties of the as-prepared composites were thoroughly analyzed. It was found that polymers containing both HB donor and acceptor have better mechanical enhancement abilities than the polymer only containing HB acceptor. Among the selected polymers, TOCN/PAA shows the best comprehensive mechanical properties with a stress of 185.5 MPa, a strain of 7.62%, and a toughness of 9.54 MJ m−3, which are 79.7%, 67.5%, and 223.4% higher than the pure TOCN film, respectively.