Multifunctional SiC@SiO_(2) Nanofiber Aerogel with Ultrabroadband Electromagnetic Wave Absorption

Traditional ceramic materials are generally brittle and not flexible with high production costs,which seriously hinders their practical applications.Multifunctional nanofiber ceramic aerogels are highly desirable for applications in extreme environments,however,the integration of multiple functions in their preparation is extremely challenging.To tackle these challenges,we fabricated a multifunctional SiC@SiO_(2) nanofiber aerogel(SiC@SiO_(2) NFA)with a threedimensional(3D)porous cross-linked structure through a simple chemical vapor deposition method and subsequent heat-treatment process.The as-prepared SiC@SiO_(2) NFA exhibits an ultralow density(~11 mg cm^(-3)),ultra-elastic,fatigue-resistant and refractory performance,high temperature thermal stability,thermal insulation properties,and significant strain-dependent piezoresistive sensing behavior.Furthermore,the SiC@SiO_(2) NFA shows a superior electromagnetic wave absorption performance with a minimum refection loss(RL_(min))value of-50.36 d B and a maximum effective absorption bandwidth(EAB_(max))of 8.6 GHz.The successful preparation of this multifunctional aerogel material provides a promising prospect for the design and fabrication of the cutting-edge ceramic materials.

Preparation of Polyaniline/Cellulose Nanofiber Aerogel for Efficient Removal of Cr(Ⅵ) from Aqueous Solution

Aerogel composed of polyaniline/cellulose nanofiber(PANI/CNF)was synthesized by a two-step method and used as an adsorbent to remove Cr(Ⅵ)from wastewater in this study.Adsorption results showed that PANI/CNF aerogel adsorbent exhibited a high adsorption capacity of 298.5 mg·g-1 for Cr(Ⅵ)(318 K,pH=2.0).Meanwhile,the adsorption process can be fitted well with the pseudo-second-order model and the Freundlich model.Moreover,the Cr(Ⅵ)removal efficiency of the adsorbent remained above 85%after ten recycling experiments,indicating that PANI/CNF aerogel had excellent stability and reusability.Therefore,PANI/CNF aerogel showed a potential application in the treatment of chromium-containing wastewater.

Ultralight and hyperelastic SiC nanofiber aerogel spring for personal thermal energy regulation

Multifunctionalization is the development direction of personal thermal energy regulation equipment in the future.However,it is still a huge challenge to effectively integrate multiple functionalities into one material.In this study,a simple thermochemical process was used to prepare a multifunctional SiC nanofiber aerogel spring(SiC NFAS),which exhibited ultralow density(9 mg/cm3),ultralow thermal conductivity(0.029 W/(m·K)at 20℃),excellent ablation and oxidation resistance,and a stable three-dimensional(3D)structure that composed of a large number of interlacing 3C-SiC nanofibers with diameters of 300–500 nm and lengths in tens to hundreds of microns.Furthermore,the as-prepared SiC NFAS displayed excellent mechanical properties,with a permanent deformation of only 1.3%at 20℃after 1000 cycles.Remarkably,the SiC NFAS exhibited robust hyperelasticity and cyclic fatigue resistance at both low(~-196℃)and high(~700℃)temperatures.Due to its exceptional thermal insulation performance,the SiC NFAS can be used for personal thermal energy regulation.The results of the study conclusively show that the SiC NFAS is a multifunctional material and has potential insulation applications in both low-and high-temperature environments.

Highly Porous Yet Transparent Mechanically Flexible Aerogels Realizing Solar-Thermal Regulatory Cooling

The demand for highly porous yet transparent aerogels with mechanical flexibility and solar-thermal dual-regulation for energy-saving windows is significant but challenging.Herein,a delaminated aerogel film(DAF)is fabricated through filtration-induced delaminated gelation and ambient drying.The delaminated gelation process involves the assembly of fluorinated cellulose nanofiber(FCNF)at the solid-liquid interface between the filter and the filtrate during filtration,resulting in the formation of lamellar FCNF hydrogels with strong intra-plane and weak interlayer hydrogen bonding.By exchanging the solvents from water to hexane,the hydrogen bonding in the FCNF hydrogel is further enhanced,enabling the formation of the DAF with intra-layer mesopores upon ambient drying.The resulting aerogel film is lightweight and ultra-flexible,which pos-sesses desirable properties of high visible-light transmittance(91.0%),low thermal conductivity(33 mW m^(-1) K^(-1)),and high atmospheric-window emissivity(90.1%).Furthermore,the DAF exhibits reduced surface energy and exceptional hydrophobicity due to the presence of fluorine-containing groups,enhancing its durability and UV resistance.Consequently,the DAF has demonstrated its potential as solar-thermal regulatory cooling window materials capable of simultaneously providing indoor lighting,thermal insulation,and daytime radiative cooling under direct sunlight.Significantly,the enclosed space protected by the DAF exhibits a temperature reduction of 2.6℃ compared to that shielded by conventional architectural glass.

Recyclable Joule heated low shrinkage carbon nanofiber aerogels for microscale oil/water separation

Aerogels have shown great potential as oil adsorbents but their application to the removal of microscale oil from water and their recycling remains problematic.The present work proposed a freeze-shaping method for fabricating carbon nanofiber aerogels(CNFAs)based on the direct use of one-dimensional(1D)carbon nanofibers(CNF)rather than carbonization of polymer aerogels.This technique greatly reduces volume shrinkage and increases the three-dimensional(3D)structural stability of the material.Carbon nanotubes(CNT)and gelatinized starch were incorporated in these aerogels as a conductive enhancement agent and binder,respectively,forming a“vine(CNT)-wrapped tree(CNF)”structure that improved mechanical and Joule-heating performance.The effects of glutaraldehyde added to aerogels as a crosslinking agent on mechanical properties and microstructure were also systematically investigated.The optimized CNFAs combined with low density,high porosity,good elasticity,and superior Joule-heating efficiency along with suitable adsorption capacity,excellent selectivity,and cycling stability.This material was able to selectively remove 87%and 92%of microscale acetone and dimethylformamide(DMF),respectively,from the water after nine cycles of adsorption and Joule-heating.The present work demonstrates a novel means of designing and fabricating a low shrinkage CNFA with outstanding Joule-heating performance having potential practical applications in the remediation of organic pollution.

Progress on the Structures and Functions of Aerogels

Aerogel materials possess a wide variety of excellent functions,hence a striking number of applications have developed for them.In this paper,we present a historic review of the aerogel materials,showing the main concepts,research methods,important scientific problems,formation mechanism,structure characteristics and essence of aerogel.More applications are evolving as the scientific and engineering community,which becomes familiar with the unusual and exceptional physical properties of aerogels.In addition,we also discuss the huge development potential and prospect of polysaccharide aerogels as the research trend in the future.

Superhydrophobic polyvinylidene fluoride/polyimide nanofiber composite aerogels for thermal insulation under extremely humid and hot environment

Excellent thermal insulating materials are highly demanded in various applications including buildings, aerospace and sport equipment. However, in practical applications,the performance of thermal insulating materials usually deteriorates under diverse temperature and humidity conditions.Therefore, it is highly essential to construct a bulk material that exhibits outstanding thermal insulation performance under extremely humid and hot environment. In this work, we have conceived a green and effective strategy to fabricate a superhydrophobic and compressible polyvinylidene fluoride/polyimide(PVDF/PI) nanofiber composite aerogel via electrospinning and freeze-drying technique. Interestingly, the PVDF nanofibers and PI nanofibers function as the hydrophobic fibrous framework and mechanical support skeleton,respectively, forming a robust three-dimensional framework with good mechanical flexibility. The PVDF/PI aerogel possesses outstanding superhydrophobic feature(water contact angle of 152°) and low thermal conductivity(31.0 m W m^(-1)K^(-1))at room temperature. Significantly, even at 100% relative humidity(80℃), the PVDF/PI aerogel still exhibits a low thermal conductivity of only 48.6 m W m^(-1)K^(-1), which outperforms the majority of commercial thermal insulating materials. Therefore, the novel PVDF/PI aerogel is promising as an excellent thermal insulating material for the applications in high-temperature and humid environment.

Highly Dispersive Co@N-C Catalyst as Freestanding Bifunctional Cathode for Flexible and Rechargeable Zinc–air Batteries

The design of efficient cathode with great cycle performance,high flexibility,and low cost is essential for the commercialization of zinc–air battery(ZAB).Herein,we report the exploration of freestanding bifunctional cathode with rationally designed structures,namely,tiny Co nanoparticles embedded in Ndoped carbon nanofiber aerogels,which have desired features including uniform Co dispersity,balanced distribution of N-C species,hierarchically porous structure with increased fraction of meso-to micropores,and moderate amounts of defects.Accordingly,the as-fabricated cathodes exhibit positive half-wave potential of 0.82 V for oxygen reduction and small overpotential of 350 mV at 10 mA cm^(−2) for oxygen evolution,respectively,which deliver smaller reversible oxygen electrode index(0.76 V)than the commercial Pt/C+RuO_(2)(0.80 V)and most Co-based electrocatalysts ever reported.Impressively,the as-constructed liquid rechargeable ZAB behaves high peak power density(160 mW cm^(−2)),large specific capacity(759.7 mAh g^(−1) at 10 mA cm^(−2),tested after 120 h of OCV tests),and robust stability over 277 h.Moreover,the as-assembled quasi-solid-state ZAB using such freestanding cathode represents excellent mechanical flexibility and outstanding cycle performance,regardless of being serviced under extremely bending conditions from 0°to 180°,underscoring their promising applications as durable bifunctional cathode for portable metalair batteries.

Self-reinforcement of Light, Temperature-Resistant Silica Nanofibrous Aerogels with Tunable Mechanical Properties

Silica aerogels have attracted significant interest in thermal insulation applications because of their low thermal conductivity and great thermal stability,however,their fragility has limited their application in every-day products.Herein,a self-reinforcing strategy to design silica nanofibrous aerogels(SNFAs)is proposed using electrospun SiO2 nanofibers as the matrix and a silica sol as a high-temperature nanoglue.Adopting this approach results in a strong and compatible interfacial interaction between the SiO_(2) fibers and the silica sol,which results in the SNFAs exhibiting high-temperature-resistant and tunable mechanical properties from elastic to rigid.Furthermore,additional properties such as low density,high thermal insulation performance,and fire-resistance are still retained.The self-reinforcing method described herein may be extended to numerous other new ceramic aerogels that require robust mechanical properties and high-temperature resistance.