In-situ grown Ni Co bimetal anchored on porous straw-derived biochar composites with boosted microwave absorption properties

With the gradually increasing protection awareness about electromagnetic pollution,the demand for absorbing materials with renewability and environmental friendliness has attracted widespread attention.In this work,composites consisting of straw-derived biochar combined with NiCo alloy were successfully fabricated through high-temperature carbonization and subsequent hydrothermal reaction.The electromagnetic parameters of the porous biocarbon/NiCo composites can be effectively modified by altering their NiCo content,and their improved absorbing performance can be attributed to the synergy effect of magnetic-dielectric characteristics.An exceptional reflection loss of-27.0 dB at 2.2 mm thickness and an effective absorption bandwidth of 4.4 GHz(11.7-16.1 GHz)were achieved.These results revealed that the porous biocarbon/NiCo composites could be used as a new generation absorbing material because of their low density,light weight,excellent conductivity,and strong absorption.

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.

Enhanced electromagnetic wave absorption via optical fiber-like PMMA@Ti_(3)C_(2)T_(x)@SiO_(2) composites with improved impedance matching

Ti_(3)C_(2)T_(x) nanosheets have attracted significant attention for their potential in electromagnetic wave absorption(EWA).However,their inherent self-stacking and exorbitant electrical conductivity inevitably lead to serious impedance mismatch,restricting their EWA application.Therefore,the optimization of impedance matching becomes crucial.In this work,we developed polymethyl methacrylate(PMMA)@Ti_(3)C_(2)T_(x)@SiO_(2) composites with a sandwich-like core–shell structure by coating SiO_(2) on PMMA@Ti_(3)C_(2)T_(x).The results demonstrate that the superiority of the SiO_(2) layer in combination with PMMA@Ti_(3)C_(2)T_(x),outperforming other relative graded distribution structures and meeting the requirements of EWA equipment.The resulting PMMA@Ti_(3)C_(2)T_(x)@SiO_(2) composites achieved a minimum reflection loss of-58.08 dB with a thickness of 1.9 mm,and an effective absorption bandwidth of 2.88 GHz.Mechanism analysis revealed that the structural design of SiO_(2) layer not only optimized impedance matching,but also synergistically enhanced multiple loss mechanisms such as interfacial polarization and dipolar polarization.Therefore,this work provides valuable insights for the future preparation of high-performance electromagnetic wave absorbing Ti_(3)C_(2)T_(x)-based composites.

Construction of hydrangea-like core-shell SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi microspheres for tunable electromagnetic wave absorbers

Ti_(3)C_(2)T_(x)MXene shows great potential in the application as microwave absorbers due to its high attenuation ability.However,excessively high permittivity and self-stacking are the main obstacles that constrain its wide range of applications.To tackle these problems,herein,the microspheres of SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi with the hydrangea-like core-shell structure were designed and prepared by a combinatorial electrostatic assembly and hydrothermal reaction method.These microspheres are constructed by an outside layer of CoNi nanosheets and intermediate Ti_(3)C_(2)T_(x)MXene nanosheets wrapping on the core of modified SiO_(2),engendering both homogenous and heterogeneous interfaces.Such trilayer SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi microspheres are“magnetic microsize supercapacitors”that can not only induce dielectric loss and magnetic loss but also provide multilayer interfaces to enhance the interfacial polarization.The optimized impedance matching and core-shell structure could boost the reflection loss(RL)by electromagnetic synergy.The synthesized SiO_(2)@Ti_(3)C_(2)T_(x)@CoNi microspheres demonstrate outstanding microwave absorption(MA)performance benefited from these advantages.The obtained RL value was-63.95 dB at an ultra-thin thickness of 1.2 mm,corresponding to an effective absorption bandwidth(EAB)of 4.56 GHz.This work demonstrates that the trilayer core-shell structure designing strategy is highly efficient for tuning the MA performance of MXene-based microspheres.

Construction of dual heterogeneous interface between zigzag-like Mo–MXene nanofibers and small CoNi@NC nanoparticles for electromagnetic wave absorption

Two-dimensional(2D)transition metal carbides(MXene)possess attractive conductivity and abundant surface functional groups,providing immense potential in the field of electromagnetic wave(EMW)absorption.However,high conductivity and spontaneous aggregation of MXene suffer from limited EMW response.Inspired by dielectric–magnetic synergy effect,the strategy of decorating MXene with magnetic elements is expected to solve this challenge.In this work,zigzag-like Mo_(2)TiC_(2)–MXene nanofibers(Mo-based MXene(Mo–MXene)NFs)with cross-linked networks are fabricated by hydrofluoric acid(HF)etching and potassium hydroxide(KOH)shearing processes.Subsequently,Co-metal–organic framework(MOF)and derived CoNi layered double hydroxide(LDH)ultrathin nanosheets are grown inside Mo–MXene NFs,and the N-doped carbon matrix anchored by CoNi alloy nanoparticles formed by pyrolysis is firmly embedded in the Mo–MXene NFs network.Benefiting from synergistic effect of highly dispersed small CoNi alloy nanoparticles,a three-dimensional(3D)conductive network assembled by zigzag-like Mo–MXene NFs,numerous N-doped hollow carbon vesicles,and abundant dual heterogeneous interface,the designed Mo–MXene/CoNi–NC heterostructure provides robust EMW absorption ability with a reflection loss(RL)value of−68.45 dB at the thickness(d)of 4.38 mm.The robust EMW absorption performance can be attributed to excellent dielectric loss,magnetic loss,impedance matching(Z),and multiple scattering and reflection triggered by the unique 3D network structure.This work puts up great potential in developing advanced MXene-based EMW absorption devices.

Oscillatory pressure-assisted sinter forging for preparation of high-performance SiC whisker reinforced Al_(2)O_(3) composites

In this work,a novel process,oscillatory pressure-assisted sinter forging(OPSF),for the preparation of high-performance ceramic composites was reported.Compared with the samples made by conventional sinter forging(SF)and hot oscillatory pressing(HOP),the SiC whisker reinforced Al_(2)O_(3) composites(SiCw–Al_(2)O_(3))prepared by OPSF at the same temperature exhibited a higher density and significantly improved the mechanical properties.The improvements in densification and performance are attributed to simultaneous enhanced shear deformation at both macro-and micro-scales,resulting from the combination of die-free configuration and oscillatory pressure of OPSF.And the strength of grain boundary is greatly increased when the temperature reaches 1600℃ of OPSF,due to that the grain-boundary sliding became pronounced at higher temperatures.The current results shed light on a powerful technique for preparing ceramic composites,which is likely applicable to other systems.

From binary to ternary and back to binary:Transition of electromagnetic wave shielding to absorption among MAB phase Ni_(3)ZnB_(2)and corresponding binary borides Nin+1Bn(n=1,3)

Due to chemical inertness of nickel and boron,the preparation of nickel borides and corresponding layered ternary transition metal borides Ni_(3)ZnB_(2)(MAB phase)has always required high-temperature and/or high-pressure conditions.Yet,an innovative and efficient approach to preparing Ni_(3)ZnB_(2)at only 600℃and without applied pressure is presented in this study.It is discovered that by simply adjusting the temperature,a phase transition from Ni_(3)ZnB_(2)to Ni4B3 with a layered structure could be induced.This transition between the binary-component and the ternary-component brings about significant variation in electromagnetic wave(EMW)shielding/absorption performance of prepared borides.For instance,Ni2B has good EMW shielding performance(42.54 dB in X band)and Ni_(3)ZnB_(2)is of weak EMW shielding(13.43 dB in X band);Ni_(3)ZnB_(2)has poor EMW absorption performance(−5 dB)while Ni4B3 has excellent EMW absorption performance(−45.19 dB)at a thickness of 2.7 mm with effective absorption bandwidth(10.4 GHz).

Ultrabroad band microwave absorption from hierarchical MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)Tx hybrids via annealing treatment

Two-dimensional(2D)transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave(EMW)absorbers.However,the application of MXenes in the field of electromagnetic wave absorption(EMA)is limited by the disadvantages of poor impedance matching,single loss mechanism,and easy oxidation.In this work,MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids were prepared by the annealing-treated Mo_(2)TiC_(2)T_(x)MXene and uniform MoO_(3)and TiO_(2)oxides in-situ grew on Mo_(2)TiC_(2)T_(x)layers.At the annealing temperature of 300℃,the minimum reflection loss(RLmin)value of MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)reaches-30.76 dB(2.3 mm)at 10.18 GHz with a significantly broadening effective absorption bandwidth(EAB)of 8.6 GHz(1.8 mm).The in-situ generated oxides creating numerous defects and heterogeneous interfaces enhance dipolar and interfacial polarizations and optimize the impedance matching of Mo_(2)TiC_(2)T_(x).Considering the excellent overall performance,the MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids can be a promising candidate for EMA.

Growth of magnetic metals on carbon microspheres with synergetic dissipation abilities to broaden microwave absorption

Microwave absorption(MA) materials have been captured extensive attentions due to the serious electromagnetic(EM) pollution. Numerous interests focus on the MA performances of core-shell structural composites with magnetic constituents as cores and dielectric constituents as shells, which inevitably suppressed the magnetic coupling causing the decrease of magnetic loss to some extent. Herein, the coreshell structural carbon(C) microsphere/magnetic metal composites were fabricated through the combination of an electrostatic assembly approach and subsequent in-situ reduction reaction. The complex permittivity and permeability of core-shell C@magnetic metal composite system can be effective adjusted by the constituent and microstructure of shells. Thanks to the distinct magnetic coupling from the subtle designed structures and the promotion of the magnetic-dielectric synergy, the C@magnetic metal composite exhibited enhanced MA properties. The optimal reflection loss(RL) of C@Ni composite was-54.1 dB with a thickness of 3.4 mm, meanwhile the effective absorbing band could reach over 5.5 GHz at only a1.8 mm thickness. Broad absorption bandwidth with RL below-10 d B could achieve 6.0 GHz and 6.7 GHz for C@Co and C@Ni Co composites with a thin 2.1 mm thickness, respectively. Our exciting findings might lead a guide on the novel structure design for the functional core-shell structural composites used for microwave absorption.

(Ca,Sr,Ba)ZrO_(3):A promising entropy-stabilized ceramic for titanium alloys smelting

A novel entropy-stabilized(ES)(Ca,Sr,Ba)ZrO_(3) ceramic has been designed and synthesized by pressureless sintering of CaZr03,SrZr03 and BaZr03 powders mixtures at 1450℃,1500℃and 1550℃for 3 h.X-ray diffraction,scanning electron microscopy and transmission electron microscopy analyses collectively indicate that a single solid solution is formed with a homogeneous distribution of metal elements after sintering at 1550℃.The relative density and hardness of the ES(Ca,Sr,Ba)ZrO_(3) ceramic sintered at 1550℃are 97.79%and 10.840.33 GPa,re s pectively.This ES(Ca,Sr,Ba)ZrO_(3) exhibits lower thermal conductivity from 373 K to 1073 K than their constituting zirconates,CaZrO_(3),SrZrO_(3) and BaZrO_(3).Most importantly,the ES(Ca,Sr,Ba)ZrO_(3) ceramic possesses good corrosion resistance to TiNi alloy melt and no distinct reaction layer exists between TiNi alloy and ES(Ca,Sr,Ba)ZrO_(3) ceramic in the contact region.The combination of these properties indicates that ES(Ca,Sr,Ba)ZrO_(3) ceramic is promising for use as a novel crucible material for the melting of titanium alloys.

Novel hierarchical structure of MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites for dramatically enhanced electromagnetic absorbing properties

In order to prevent the microwave leakage and mutual interference,more and more microwave absorbing devices are added into the design of electronic products to ensure its routine operation.In this work,we have successfully prepared MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) hierarchical composites by one-pot hydrothermal method and focused on the relationship between structures and electromagnetic absorbing properties.Supported by comprehensive characterizations,M0S_(2) nanosheets were proved to be anchored on the surface and interlayer of Ti_(3)C_(2)T_(x) through a hydrothermal process.Additionally,TiO_(2) nanoparticles were obtained in situ.Due to these hierarchical structures,the MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites showed greatly enhanced microwave absorbing performance.The MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites exhibit a maximum reflection loss value of -33.5 dB at 10.24 GHz and the effective absorption bandwidth covers 3.1GHz(13.9-17 GHz)at the thickness of 1.0 mm,implying the features of wide frequency and light weight.This work in the hierarchical structure of MoS_(2)/TiO_(2)/Ti_(3)C_(2)T_(x) composites opens a promising door to the exploration of constructing extraordinary electromagnetic wave absorbents.

Facile synthesis of yolk-shell Ni@void@SnO2（Ni3Sn2） ternary composites via galvanic replacement/Kirkendall effect and their enhanced microwave absorption properties

Yolk-shell ternary composites composed of a Ni sphere core and a SnO2（Ni3Sn2） shell were successfully prepared by a facile two-step method. The size, morphology, microstructure, and phase purity of the resulting composites were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy （TEM）, high-resolution TEM, selected-area electron diffraction, and powder X-ray diffraction. The core sizes, interstitial void volumes, and constituents of the yolk-shell structures varied by varying the reaction time. A mechanism based on the time-dependent experiments was proposed for the formation of the yolk-shell structures. The yolk-shell structures were formed by a synergistic combination of an etching reaction, a galvanic replacement reaction, and the Kirkendall effect. The yolk-shell ternary SnO2 （Ni3Sn2）@Ni composites synthesized at a reaction time of 15 h showed excellent microwave absorption properties. The reflection loss was found to be as low as -43 dB at 6.1 GHz. The enhanced microwave absorption properties may be attributed to the good impedance match, multiple reflections, the scattering owing to the voids between the core and the shell, and the effective complementarities between the dielectric loss and the magnetic loss. Thus, the yolk-shell ternary composites are expected to be promising candidates for microwave absorption applications, lithium ion batteries, and photocatalysis.

Green rapid synthesis of Cu_(2)O/Ag heterojunctions exerting synergistic antibiosis

Semiconductor-noble metal composite has become a research focus due to its superior performance compared with its respective component.Although various methods have been developed to synthesize semiconductor-noble metal heterostructures,most of them are relatively complex multistep and use toxic reactants of high cost and risk.In this work,a series of Cu_(2)O/Ag heterojunctions were quickly prepared in one step via simple microwave-assisted green route.XRD,SEM,TEM,EDS,XPS,etc.were used to characterize obtained products,and the results indicate a Cu_(2)O/Ag metal-semiconductor heterojunction in micro-nano size was fabricated successfully.In addition,antibacterial behavior of Cu_(2)O/Ag heterojunctions against E.coli and S.aureus were investigated.Owing to the synergistic effect of Cu_(2)O and Ag,the heterojunction exhibits much better antibacterial performance than the pristine Cu_(2)O does.This work provides new insights into the green design and fabrication of surface-modified Cu_(2)O hybrid multifunctional materials for antibacterial applications.

Structure-dependent electromagnetic wave absorbing properties of bowl-like and honeycomb TiO_(2)/CNT composites

Materials that can efficiently absorb electromagnetic waves(EMWs)are required to deal with electromagnetic pollution.Structure design appears to be an efficient way to improve the EMW-absorption performance of such materials,particularly when adjustment of the constitution or mixing ratio is limited.In this study,bowl-like and honeycomb titanium dioxide/carbon nanotube(TiO_(2)/CNT)composites with different CNT contents were fabricated using the methods of hierarchical and mixing vacuum-assisted filtration,respectively.Compared to the honeycomb structure,the bowl-like structure simultaneously facilitated greater interfacial polarization and conduction loss in favor of dielectric polarization,and augmented multiple reflections.The high porosity of the honeycomb structure was conducive to optimizing the impedance matching characteristics.The bowl-like TiO_(2)/CNT composite exhibited a minimum reflection loss(RL_(min))of-38.6 dB(1.5 mm)with a wide effective absorption band(EAB;<-10 dB)of4.2 GHz,while the honeycomb TiO_(2)/CNT composite showed an RLminof-34.8 dB(2.1 mm)with an EAB of 4.3 GHz.The required mixing ratio in the matrix was only 15 wt%,outperforming that of the most closely related composites.Thus,both the bowl-like and honeycomb TiO_(2)/CNT composites are ideal candidates for light-weight and highly efficient EMW-absorbing materials.

Perylene Bisimides as efficient electron transport layers in planar heterojunction perovskite solar cells

Two perylene bisimides based non-fullerene small molecules, H-DIPBI and B-DIPBI, are applied into inverted planar heterojunction perovskite solar cells. The power conversion efficiency up to 11.6% has been achieved for device with B-DIPBI,indicating that non-fullerene acceptor can function as the electron transport layer to replace PCBM in perovskite solar cells.

Microwave synthesis of chain-like zircona nanofibers through carbon-induced self-assembly growth

Chain-like zircona （ZrO2） nanofibers were prepared by microwave sinter- ing without any surfactants or solid templates. Microwave sintering was conducted in a multimode microwave cavity with TE666 resonant mode at 2.45 GHz. Carbon particles were used to activate unique thermal processes when mixed with ZrO2 precursor. The sintering condition was at 1300℃ for 10 min. Samples were characterized by XRD, SEM, TEM techniques. It was found that both monolithic and tetragonal ZrO2 co-existed in samples prepared from the mixture of ZrO2 precursors and carbon by either microwave or conventional sintering. Only m-ZrO2 exists in samples prepared by ZrO2 precursors without carbon. ZrO2 appeared as chain-like nanofibers, which might be attributed to a so- called carbon-induced self-assembly growth mechanism.

Sintering behavior of alumina whisker reinforced zirconia ceramics in hot oscillatory pressing

Alumina whisker reinforced zirconia ceramic composite was prepared by both hot oscillatory pressing(HOP)and conventional hot pressing(HP).The results show that compared with HP,HOP can significantly increase the final density and densification rate of the material.Analysis of densification kinetics reveals that the predominant densification mechanism transits from grain boundary sliding in the beginning to the diffusion in the later stage.The main effect of the oscillating pressure is to increase the densification rate in the process of grain boundary sliding.The current study suggests that HOP is a promising technique for densifying whisker reinforced ceramics.

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.

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°C,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°C 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.