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.

Surface functionalized N-C-TiO_(2)/C nanocomposites derived from metal-organic framework in water vapour for enhanced photocatalytic H generation

Surface-functionalized nitrogen/carbon co-doped polymorphic TiO_(2) phase junction nanoparticles uniformly distributed in porous carbon matrix were synthesized by a simple one-step pyrolysis of titanium based metal-organic framework(MOF),NH_(2)-MIL^(-1)25(Ti) at 700℃ under water vapour atmosphere.Introducing water vapour during the pyrolysis of NH_(2)-MIL^(-1)25(Ti) not only functionalizes the derived porous carbon matrix with carboxyl groups but also forms additional oxygen-rich N like interstitial/intraband states lying above the valence band of TiO2 along with the self-doped carbo n,which further narrows the energy band gaps of polymorphic TiO2 nanoparticles that enhance photocatalytic charge transfer efficiency.Without co-catalyst,sample N-C-TiO2/CArW demonstrates H_(2) evolution activity of 426 μmol gcat-1h^(-1),which remarkably outperforms commercial TiO_(2)(P-25) and N-C-TiO_(2)/CAr with a 5-fold and 3-fold H_(2) generation,respectively.This study clearly shows that water vapour atmosphere during the pyrolysis increases the hydrophilicity of the Ti-MOF derived composites by functionalizing porous carbon matrix with carboxylic groups,as well as enhancing the electrical conductivity and charge transfer efficiency due to the formation of additional localized oxygen-rich N like interstitial/intraband states.This work also demonstrates that by optimizing the anatase-rutile phase composition of the TiO2 polymorphs,tuning the energy band gaps by N/C co-doping and functionalizing the porous carbon matrix in the N-C-TiO2/C nanocomposites,the photocatalytic H_(2) generation activity can be further enhanced.

Ternary layered boride MoAlB:A novel thermo-regulation microwave absorbing ceramic material

In the context of the fifth-generation(5G)smart era,the demand for electromagnetic wave(EMW)-absorbing materials has become increasingly prominent,so it is necessary to explore promising candidate materials.This work focuses on the exploration of the material absorbing properties of a MoAlB MAB(MAB represents a promising group of alternatives,where M stands for a transition metal,A typically denotes Al,and B is boron)phase system.First,the first-principles calculations were performed to reveal the unique crystal and layered structure of the MoAlB ceramics and to predict their potential for use as an EMW absorption material.Subsequently,a series of MoAlB ceramics were synthesized at temperatures ranging from 800 to 1300℃,and the influence of temperature on the phase compositions and microstructures of the obtained MoAlB ceramics was characterized and analyzed.Finally,the practical EMW absorption performance of the prepared MoAlB ceramics was evaluated via a combination of experiments and radar cross-sectional calculations.The MoAlB sample synthesized at 900℃ exhibits superior EMW absorption performance,achieving an impressive minimum reflection loss(RL)of−50.33 dB.The unique layered structure and good electrical conductivity of the MoAlB samples are the main reasons for their enhanced wave absorption performance,which provides interfacial polarization and multiple dielectric loss mechanisms.Therefore,this study not only contributes to the understanding of the preparation of MoAlB materials but also provides potential guidance for their utilization in the realm of electromagnetic wave absorption.

Tribological properties of Al-GNP composites at elevated temperature

Lighter and more powerful next generation vehicles and other rotary machinery demand bearings to operate in harsher conditions for higher efficiency,and the continuous development of advanced low-wear and friction materials is thus becoming even more important to meet these requirements.New aluminium composites reinforced with high performance lubricate phases such as graphene nanoplatelets(GNPs)are very promising and have been vigorously investigated.By maintaining a low coefficient of friction(COF)and offering great strength against wear due to their self-lubricating capability,the solid lubricant like GNPs protect the bearing surface from wear damage and prevent change in metallurgical properties during temperature fluctuations.This paper first studies the high-temperature tribological performance of aluminium matrix composites reinforced with GNP,consolidated via powder metallurgy,then elucidates their tribological mechanism.We report that the best tribological performance is achieved by the composite containing 2.0 wt%GNP,with an extraordinarily low COF of 0.09 and a specific wear rate of 3.5×10^(−2)mm^(3)·N^(−1)·m^(−1),which represent 75%and 40%reduction respectively,against the plain aluminium consolidated under identical conditions.The in-track and out-of-track Raman analysis have confirmed the role of GNPs in creating a tribofilm on the counterpart surface which contributed to the excellent performance.

Metal-organic framework derived multi-functionalized and co-doped TiO_(2)/C nanocomposites for excellent visible-light photocatalysis

Multi-functionalized and co-doped TiO_(2)/C nanocomposites were derived from the pyrolysis of Ti-MOFs at 800℃under different gaseous atmospheres and their photocatalytic performance were investigated.The gaseous atmosphere during pyrolysis plays a critical role in determining the structural,textural,optical and physicochemical properties of the derived TiO_(2)/C composites due to the synergistic effect of nitrogen-containing species,carboxylate and sulfur functionalized porous carbon as well as N/S co-doped TiO_(2)nanoparticles.All the Ti-MOFs derived TiO_(2)/C composites exclusively possess homogeneously distributed TiO_(2)nanoparticles in a functionalized disc-like porous carbon matrix and demonstrate much enhanced adsorption and photodegradation performance than commercial TiO_(2)under the same conditions.The adsorption of methylene blue(MB)in dark on these TiO_(2)/C composites are dominated with pseudo second-order kinetic model and the high adsorption capacity of MB in dark on composite TiO_(2)/C derived from MIL-125(Ti)in argon is due to its high surface area with predominant mesoporous carbon matrix in the composite.The composite N-O-TiO_(2)/C derived from NH2-MIL-125(Ti)in water vapor exhibited the highest photodegradation activity with 99.7%MB removal in 3 h under visible light due to the optimal anatase/rutile phasejunction,together with the formation of photoactive oxygen-rich N-O like interstitial/intraband states above the valence band of TiO_(2),as well as the presence of N-containing species and-OH/-COOH multi-functional groups with superhydrophilic nature of the composite.This simple one-step and easily modifiable approach can be further employed to modulate homogeneously dispersed multi-functionalized and co-doped metal oxide/carbon nanocomposites for various environment and energy-related applications.

Bimetallic Fe-Mo sulfide/carbon nanocomposites derived from phosphomolybdic acid encapsulated MOF for efficient hydrogen generation

To tackle the energy crisis and achieve more sustainable development,hydrogen as a clean and renewable energy resource has attracted great interest.Searching for cheap but efficient catalysts for hydrogen production from water splitting is urgently needed.In this report,bimetallic Fe-Mo sulfide/carbon nanocomposites that derived from a polyoxometalate phosphomolybdic acid encapsulated metal-organic framework MIL-100(PMA@MIL-100)have been generated and their applications in electrocatalytic hydrogen generation were explored.The PMA@MIL-100 precursor is formed via a simple one-pot hydrothermal synthesis method and the bimetallic Fe-Mo sulfide/carbon nanocomposites were obtained by chemical vapor sulfurization of PMA@MIL-100 at high temperatures.The nanocomposite samples were fully characterized by a series of techniques including X-ray diffraction,Fourier-transform infrared analysis,thermogravimetric analysis,N2 gas sorption,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy,and were further investigated as electrocatalysts for hydrogen production from water splitting.The hydrogen production activity of the best performed bimetallic Fe-Mo sulfide/carbon nanocomposite exhibits an overpotential of-0.321 V at 10 m A cm^(-2)and a Tafel slope of 62 m V dec^(-1)with a 53%reduction in overpotential compared to Mo-free counterpart composite.This dramatic improvement in catalytic performance of the Fe-Mo sulfide/carbon composite is attributed to the homogeneous distribution of the nanosized iron sulfide,MoS_(2)particles,and the formation of Fe-Mo-S phases in the S-doped porous carbon matrix.This work has demonstrated a potential approach to fabricate complex heterogeneous catalytic materials for different applications.

Ultralight three-dimensional,carbon-based nanocomposites for thermal energy storage

Polymer based nanocomposites consisting of elastic three-dimensional(3 D)carbon foam(CF),paraffin wax and graphene nanoplatelets(GNPs)have been created and evaluated for thermal energy storage.The ultralight,highly porous(~98.6%porosity),and flexible CFs with densities of2.84-5.26 mg/cm^3 have been used as the backbone skeleton to accommodate phase change wax and nanoscale thermal conductive enhancer,GNP.Low level of defects and the ordered sp2 configuration allow the resulting CFs to exhibit excellent cyclic compressive behavior at strains up to 95%,while retaining part of their elastic properties even after 100 cycles of testing.By dispersing the highly conductive GNP nanofillers in paraffin wax and infiltrating them into the flexible CFs,the resultant nanocomposites were observed to possess enhanced overall thermal conductivity up to 0.76 W/(m K),representing an impressive improvement of226%,which is highly desirable for thermal engineering.

Graphene-reinforced metal-organic frameworks derived cobalt sulfide/carbon nanocomposites as efficient multifunctional electrocatalysts

Developing cost-effective electrocatalysts for oxygen reduction reaction(ORR),oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)is vital in energy conversion and storage applications.Herein,we report a simple method for the synthesis of graphene-reinforced CoS/C nanocomposites and the evaluation of their electrocatalytic performance for typical electrocatalytic reactions.Nanocomposites of CoS embedded in N,S co-doped porous carbon and graphene(CoS@C/Graphene)were generated via simultaneous sulfurization and carbonization of one-pot synthesized graphite oxide-ZIF-67 precursors.The obtained CoS@C/Graphene nanocomposites were characterized by X-ray diffraction,Raman spectroscopy,thermogravimetric analysis-mass spectroscopy,scanning electronic microscopy,transmission electronic microscopy,X-ray photoelectron spectroscopy and gas sorption.It is found that CoS nanoparticles homogenously dispersed in the in situ formed N,S co-doped porous carbon/graphene matrix.The CoS@C/10Graphene composite not only shows excellent electrocatalytic activity toward ORR with high onset potential of 0.89 V,four-electron pathway and superior durability of maintaining 98%of current after continuously running for around 5 h,but also exhibits good performance for OER and HER,due to the improved electrical conductivity,increased catalytic active sites and connectivity between the electrocatalytic active CoS and the carbon matrix.This work offers a new approach for the development of novel multifunctional nanocomposites for the next generation of energy conversion and storage applications.