Recent progress in MXene and graphene based nanocomposites for microwave absorption and electromagnetic interference shielding

There is widespread use of telecommunication and microwave technology in modern society, and raised the electromagnetic interference (EMI) issue to alarming situation due to apprehensive demand and growth of 5G technology undesirably disturbing the human health. The two dimensional (2D) materials including graphene and MXenes are already been used for variety of electronic devices due to their exceptional electrical, mechanical, optical, chemical, and thermal properties. MXene is composed of metal carbides, in which mainly metals are the building blocks for dielectrics, semiconductors, or semimetals. However, the strong interfaces with electromagnetic waves (EM) are variable from terahertz (THz) to gigahertz (GHz) frequency levels and are widely used in EMI and Microwave absorption (MA) for mobile networks and communication technologies. The use of different organic materials with metal, organic, inorganic fillers, polymers nanocomposite and MXene as a novel material has been studied to address the recent advancement and challenges in the microwave absorption mechanism of 2D materials and their nanocomposites. In this concern, various techniques and materials has been reported for the improvement of shielding effectiveness (SE), and theoretical aspects of EMI shielding performance, as well stability of 2D materials particularly MXene, graphene and its nanocomposites. Consequently, various materials including polymers, conducting polymers, and metal–organic frameworks (MOF) have also been discussed by introducing various strategies for improved MA and control of EMI shieling. Here in this comprehensive review, we summarized the recent developments on material synthesis and fabrication of MXene based nanocomposites for EMI shielding and MA. This research work is a comprehensive review majorly focuses on the fundamentals of EMI/MA.  The recent developments and challenges of the MXene and graphene based various structures with different polymeric composites are described in a broader perspective.     

三维MXene多孔结构的构建与应用研究进展

MXene作为一种新型二维（2D）纳米材料以其独特的高导电性、高电化学表面活性等特性在多个领域引起了广泛关注。然而,MXene纳米片在自组装过程中出现的紧密堆叠现象导致比表面积急剧下降,降低了活性表面积,从而严重阻碍了它们在能源储存、电磁屏蔽、吸附等领域的潜在应用。构建三维多孔结构是解决MXene组装过程中自堆叠问题的一种有效途径,而且通过不同的组装方法可以实现对多孔宏观结构组成成分、孔径分布以及孔径大小的调控,使得MXene多孔材料在机械性能、电学性能以及光热转换性能等方面得到更好的调整,从而满足不同应用领域的需求。本综述以Ti₃C₂T_x MXene为主要研究材料总结了各种多孔MXene宏观结构的制备方法,讨论了其在电池/超级电容器、电磁屏蔽与吸收、海水淡化、光催化以及传感和环境修复等方面的应用,阐述了MXene多孔结构在各种应用中的贡献与意义,并针对MXene多孔结构的制备、结构调控和应用等方面的机遇和挑战作了论述。     

MXene的制备及其复合材料在能源光催化领域的应用进展

MXene作为一种拥有层状结构的二维材料,具有良好的吸附催化性能、较宽的光吸收范围、高导热性、高硬度、高熔点、高导电性以及大比表面积等物理和化学特性,在储能、催化、润滑、抗菌、电磁屏蔽等领域有着较高应用价值。本文着重介绍了由前驱体MAX相获得MXene的制备方法,综述了MXene复合材料在光催化固氮、析氢、CO₂还原等能源光催化领域的应用进展。     

Multifunctional waterproof MXene-coated wood with high electromagnetic shielding performance

Increasing electromagnetic pollution calls for electromagnetic interference (EMI) shielding materials, especially sustainable, lightweight, and environmentally stable, biomass-based materials. MXene-coated wood (M/wood) is prepared by simply spraying MXene sheets on the wood surface. Varying this spray coating manipulates the shielding performance and its application to different wood species. The M/wood exhibits high electrical conductivity (sheet resistance is only 0.65 Ω/sq) with an excellent EMI shielding effectiveness of 31.1 dB at 8.2?~?12.4 GHz and is also fire retardant. Furthermore, waterborne acrylic resin (WA) is coated on M/wood to enhance environmental stability. The WA coating improves EMI shielding performance stability after water-soaking and drying testing and prevents the peeling of MXene from wood. These satisfactory properties of WA-M/wood and the facile manufacturing approach promote the feasibility of wood-based EMI shielding materials.

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Edge Capping of 2D‐MXene Sheets with Polyanionic Salts To Mitigate Oxidation in Aqueous Colloidal Suspensions

MXenes have shown promise in myriad applications, such as energy storage, catalysis, EMI shielding, among many others. However, MXene oxidation in aqueous colloidal suspensions when stored in water at ambient conditions remains a challenge. It is now shown that by simply capping the edges of individual MXene flakes, Ti₃C₂T_z and V₂CT_z, by polyanions such as polyphosphates, polysilicates or polyborates, it is possible to quite significantly reduce their propensity for oxidation even when held in aerated water for weeks. This breakthrough resulted from the realization that the edges of MXene sheets are positively charged. It is thus an example of selectively functionalizing the edges differently from the MXene sheet surfaces.     

大片单层低缺陷MXene的制备及其膜材料的电磁屏蔽性能

采用原位生成氢氟酸法刻蚀Ti₃AlC₂制备了单片层二维过渡金属碳化物(MXene), 用扫描电子显微镜(SEM)、 透射电子显微镜(TEM)及原子力显微镜(AFM)等表征了MXene的微观形貌. 结果表明, 所制备的MXene材料具有大片、 单层及低缺陷等特点. 通过抽滤MXene分散液制备的MXene膜材料具有导电性高(3280 S/cm)及韧性优异等特点. MXene膜的屏蔽性能测试结果表明, 8 μm厚的MXene膜屏蔽效能为60.6 dB, SSE/t值则高达19531.1 dB·cm ²·g ^-1. 推测MXene膜的屏蔽机理是一种以吸收为主的电磁干扰屏蔽机制.     

Progress in the Foaming of Polymer-based Electromagnetic Interference Shielding Composites by Supercritical CO2

As a critical action plan formulated for peaking carbon dioxide emissions, polymeric electromagnetic interference (EMI) shielding materials based on CO₂ foaming technology have recently been attracting widespread attention in both research and industry, attributable to their efficient use of CO₂, high specific strength, corrosion resistance and low-cost characteristics. In the past decade, the emergence of novel design concepts and preparation techniques for CO₂ foaming technology has led to the development of new high-performance EMI shielding materials in this field. This review summarizes the research progress made to date on the fabrication of EMI shielding composite foams by supercritical carbon dioxide (scCO₂) foaming. We also explore the structure-activity relationships between the component/distribution and EMI shielding properties. Additionally, the application prospects and development challenges of new EMI shielding composite foams are described.     

Design and Synthesis Strategies: 2D Materials for Electromagnetic Shielding/Absorbing

Two-dimensional (2D) materials possess special physical and chemical properties. They have been proved to have potential application advantage in the microwave absorption (MA) and electromagnetic interference (EMI) shielding. Particularly, they exhibit positive shielding and absorbing response to EMI. Here, the research progress of preparation, electromagnetic performance and microwave shielding/absorbing mechanisms of 2D composite materials are introduced. Effective preparation routes including introducing heteroatoms, constructing unique structures and 2D composite materials are described. Furthermore, the application prospects and challenges for the development of novel EMI materials are expatiated.     

Electromagnetic interference shielding Ti_3C_2T_x-bonded carbon black films with enhanced absorption performance

The demand for flexible and freestanding electromagnetic interference(EMI) shielding materials are more and more urgent to combat with serious electromagnetic(EM) radiation pollution.Twodimensional Ti_3C_2T_x is considered as promising EMI shielding material to graphenes because of the low cost and high electrical conductivity.However,the shielding performance still needs to be optimized to decrease the reflection effectiveness(SE_R) and increase absorption effectiveness(SEA).Herein,we prepared Ti_3C_2T_x-bonded carbon black films with a porous structure.The SE_R decreased from 20 dB to12 dB and the SEA increased from 31 dB to 47 dB.The best EMI shielding effectiveness can be as high as60 dB with SE_A of 15 dB and SE_R of45 dB.Their calculated specific shielding effectiveness can be as high as8718 dB cm~2/g.These results indicate that the porous structure can enhance the absorption of the EMI shielding films,resulting from the enhanced scattering and reflectio n.Conseque ntly,this work provides a promising MXene-based EMI shielding film with lightweight and flexibility.     

Eco-friendly non-acid intercalation and exfoliation of graphite to graphene nanosheets in the binary-peroxidant system for EMI shielding

The development of the preparation strategy for high-quality and large-size graphene via eco-friendly routes is still a challenging issue. Herein, we have successfully developed a novel route to chemically exfoliate natural graphite into high-quality and large-size graphene in a binary-peroxidant system. This system is composed of urea peroxide (CO(NH₂)₂⋅H₂O₂) and hydrogen peroxide (H₂O₂), where CO(NH₂)₂⋅H₂O₂ is used in preparing graphene for the first time. Benefiting from the complete decomposition of CO(NH₂)₂⋅H₂O₂ and H₂O₂ into gaseous species under microwave (MW) irradiation, no water-washing and effluent-treatment are needed in this chemical exfoliation procedure, thus the preparation of graphene in an eco-friendly way is realized. The resultant graphene behaves a large-size, high-quality and few-layer feature with a yield of ~100%. Then 4 µm-thick ultrathin graphene paper fabricated from the as-exfoliated graphene is used as an electromagnetic interference (EMI) shielding material. And its absolute effectiveness of EMI shielding (SSE/t) is up to 34,176.9 dB cm²/g, which is, to the best of our knowledge, among the highest values so far reported for typical EMI shielding materials. The EMI shielding performance demonstrates a great application potential of graphene paper in meeting the ever-increasingly EMI shielding demands in miniaturized electronic devices.     

Asymmetric Ni/PVC films for high-performance electromagnetic interference shielding

A novel asymmetric Ni/PVC film has been developed by solution casting method. The structure, electrical conductivity, electromagnetic interference(EMI) shielding, and impact resistance were investigated. The results showed that the Ni particles were asymmetrically distributed along the thickness direction in the film. The top surface resistivity increased with film thickness, while the bottom surface exhibited the different trend. EMI shielding effectiveness(SE) depended on formation of closed packed conductive Ni network, which was influenced by both Ni content and film thickness. A linear relationship was observed between EMI SE and film thickness. The films with lower Ni content showed the faster increasing rate of EMI SE with film thickness. Some of the films show appreciably high EMI SE( 40 d B), indicating the promising application in EMI shielding field. Moreover, the films exhibit different impact performance under different impacting directions. All the experimental facts demonstrate that the asymmetric structure endows the film achieving high-performance EMI shielding function.     

Biopolymer-Based Aerogels for Electromagnetic Wave Shielding and Absorbing

The rapid development of communication technology and electronic industry has brought unprecedented serious electromagnetic interference (EMI) and electromagnetic wave (EMW) pollution. Although EMI shields and EMW absorbers based on metal or magnetic materials were used to solve these problems, they have long been criticized for their high price, high density and easy corrosion. In order to achieve low density and efficient dissipation of electromagnetic energy, aerogels stand out among manifold materials. However, constructing aerogels with good EMI shielding or EMW absorption performance and acceptable mechanical properties is not an easy task. Burgeoning biopolymers, such as cellulose, lignin, chitin/chitosan and alginate, breathe new life into aerogels for high-efficiency EMW shielding and absorbing. Here, we reviewed the contributions of biopolymers in the fields of aerogels for EMW shielding and absorbing. At the same time, some challenges and outlook were also pointed out, aiming to promote the advance of aerogel-based EMI shields and EMW absorbers as well as the rational utilization of biopolymers.     

Intrinsically conducting polymers for electromagnetic interference shielding

This paper summarizes and reviews the research on electromagnetic interference (EMI) shielding with intrinsically conducting polymers (ICPs), mainly polyaniline (PANI) and polypyrrole (PPY), and their composites in various frequency ranges. ICPs are new alternative candidates for EMI shielding applications due to their lightweight, corrosion resistance, ease of processing, and tunable conductivities as compared with typical metals. More importantly, the dominant shielding characteristic of absorption other than that of reflection for metals render ICPs more promising materials in applications requiring not only high EMI shielding effectiveness but also shielding by absorption, such as in stealth technology. Copyright © 2005 John Wiley & Sons, Ltd.     

Ku-band EMI shielding effectiveness and dielectric properties of Polyaniline-Y2O3 composites

Electromagnetic interference (EMI) shielding has become a phenomenon of great concern and there is growing demand towards the synthesis of materials with better EMI shielding effectiveness (EMI SE). This work highlights the preparation of Polyaniline-Yttrium Oxide (PANI-Y₂O₃) composites for EMI shielding applications in the frequency range from 12.4 to 18 GHz (Ku-band). The structure and morphology of the composites were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). EMI SE, microwave absorption and reflection, dielectric properties of the composites are discussed in detail. All the computations were based on microwave scattering parameters measured by transmission line waveguide technique. The observed results show absorption dominant EMI shielding in these composites with EMI SE of ?19 to ?20 dB, which mainly depends on the dielectric loss of the composites. Through the results of our observations, we propose these composites to be potential materials for microwave absorption and EMI shielding applications.     

Highly Conductive MXene Film Actuator Based on Moisture Gradients

MXene (Ti₃C₂T_x) is a new 2D material with both hydrophilicity and high electrical conductivity, and it has shown promise in smart electronic devices. Reported herein is a homogeneous MXene film actuator with high electrical conductivity triggered by moisture gradients. The actuator is highly sensitive to moisture and undergoes deformation, with the maximum bending angle as high as 155° at a relative humidity difference of 65 %. Several analysis methods show that the humidity drive and large deformation of the MXene film occur in situ by asymmetric expansion of the bilayer structure. The combination of deformation and electrical conductivity makes this film applicable to flexible excavators, electrical switches, and other fields, applications that are difficult to achieve directly by using other 2D materials. More importantly, this work further expands the new application range of MXene materials and provides new opportunities for building the next generation of high‐conductivity smart actuators.     

EMI shielding and microwave absorption behavior of Au‐MWCNT/polyaniline nanocomposites

Electrically conducting Au‐multiwalled carbon nanotube/polyaniline (Au‐MWCNT/PANi) nanocomposites were synthesized by two different ways: (1) by direct mixing of MWCNT/PANi and Au nanoparticles (Au‐MWCNT/PANi‐1) and (2) by in situ polymerization of aniline in the presence of both MWCNTs and Au nanoparticles (Au‐MWCNT/PANi‐2). The higher electrical conductivity of Au‐MWCNT/PANi‐2 compared with the other samples (PANi, MWCNT/PANi, Au‐MWCNT/PANi‐1) is supported by the red shifts of the UV‐vis bands (polaron/bipolaron), the high value of the –NH+= stretch peak (Fourier transform infrared spectroscopy studies), the high % crystallinity (X‐ray diffraction analysis) and more uniform dispersion of the Au NPs in the material. The performance of the samples in electromagnetic interference (EMI) shielding and microwave absorption was studied in the X‐band (8–12 GHz). For all the samples, absorption was the dominant factor contributing toward the EMI shielding. Au‐MWCNT/PANi‐2 showed the best performance with a total shielding effectiveness of ?16 dB [averaged over the X‐band (GHz)] and a minimum reflection loss of ?56.5 dB. The higher dielectric properties resulting from the heterogeneities because of the presence of nanofillers and the high electrical conductivity lead to the increased EMI shielding and microwave absorption. The results show the significance of both Au nanoparticles and method of synthesis on the EMI shielding performance of MWCNT/PANi composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Two-dimensional hybrid nanomaterials derived from MXenes(Ti_3C_2T_x)as advanced energy storage and conversion applications

The development of two-dimensional hybrid nanomaterial derived from MXenes as high performance electrode material is the key component for the advanced ene rgy storage and conversion systems.In the past decades,MXene derived nanomaterials have attracted greatly interest in scientific activity and potential applications because of their unique synergistic properties such as high thermal stability,excellent electrical conductivity,large surface area,easy to handle and outstanding electro and photo chemical properties.This review is focused on the synthesis of hybrid nanomaterials from MXene(Ti_3C_2T_x) for renewable energy conversion and storage application including hydrogen evolution reaction,supercapacitor,lithium-ion batteries and photocatalysis.Finally,we also summarized the prospect and opportunities of novel two-dimensional hybrid nanomaterials derived MXene(Ti_3C_2T_x) fo r futuristic sustainable energy technology.     

Electromagnetic Interference Shielding Polymers and Nanocomposites - A Review

Intrinsically conducting polymers (ICP) and conductive fillers incorporated conductive polymer-based composites (CPC) greatly facilitate the research in electromagnetic interference (EMI) shielding because they not only provide excellent EMI shielding but also have advantages of electromagnetic wave absorption rather than reflection. In this review, the latest developments in ICP and CPC based EMI shielding materials are highlighted. In particular, existing methods for adjusting the morphological structure, electric and magnetic properties of EMI shielding materials are discussed along with the future opportunities and challenges in developing ICP and CPC for EMI shielding applications.     

Intercalated MXene-based layered composites:Preparation and application

Combining high conductivity,hydrophilicity and excellent electrochemical perfo rmance in one,MXe nes have attracted increasing attention since their inception.However,easy to stack caused by the van der Waals' force between the layers limits their practical application.Fortunately,intercalating other substances between layers of MXe nes and getting intercalated MXene-based layered composites(IMLCs)with open structure can improve their physical and chemical properties effectively.Larger available surface helps expose more active sites and enlarged layer spacing facilitates ion transport.In addition,other substances fixed in the interlayers by MXenes' two-dimensional confinement effect can produce synergistic effect and expand their applicable range greatly.This review is dedicated to summarizing the preparation methods and applications of IMLCs,emphasizing the advantages of them in the fields of energy storage,catalysis,sensors,electromagnetic interference(EMI) shielding and biomedicine.Furthermore,prospects and further developments in these gratifying fields are also commented.     

Effects of diameter and surface area of electrospun nanocomposite fibers on electromagnetic interference shielding

The effects of variation in average diameter and surface area of nanocomposite fibers on electromagnetic interference (EMI) shielding of multi-walled carbon nanotubes (MWCNTs)/polyvinylpyrrolidone (PVP) fibers were investigated in this paper. The EMI shielding effectiveness of electrospun nanocomposite fibers were measured in the X-band frequency range 8.2–12.4 GHz. The electrical conductivity and EMI shielding behaviors of the nanocomposite fibers were reported as function of average diameter and surface area of MWCNTs/PVP nanocomposite fibers. The electrical conductivity measurements demonstrate using thinner nanocomposite fibers results in a lower limit of electrical resistivity, better electrical conductivity performance. The EMI shielding efficiency of thinner nanocomposite fibers increased up to 42 dB. The EMI shielding data for MWCNTs/PVP nanocomposite fibers with various average diameter and surface area showed that absorption was the major shielding mechanism and reflection was the secondary shielding mechanism. It can be related to higher specific surface area of thinner electrospun MWCNTs/PVP nanocomposite fibers that means more surface area for radiative scatter and absorption leading to higher EMI shielding performance.