State of the Art and Prospects in Metal-Organic Framework-Derived Microwave Absorption Materials

Microwave has been widely used in many fields,including communication,medical treatment and military industry;however,the corresponding generated radiations have been novel hazardous sources of pollution threating human’s daily life.Therefore,designing high-performance microwave absorption materials(MAMs)has become an indispensable requirement.Recently,metal-organic frameworks(MOFs)have been considered as one of the most ideal precursor candidates of MAMs because of their tunable structure,high porosity and large specific surface area.Usually,MOF-derived MAMs exhibit excellent electrical conductivity,good magnetism and sufficient defects and interfaces,providing obvious merits in both impedance matching and microwave loss.In this review,the recent research progresses on MOF-derived MAMs were profoundly reviewed,including the categories of MOFs and MOF composites precursors,design principles,preparation methods and the relationship between mechanisms of microwave absorption and microstructures of MAMs.Finally,the current challenges and prospects for future opportunities of MOF-derived MAMs are also discussed.

A Review on Metal-Organic Framework-Derived Porous Carbon-Based Novel Microwave Absorption Materials

The development of microwave absorption materials(MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human’s health.And MAMs are also used in radar stealth for protecting the weapons from being detected.Many nanomaterials were studied as MAMs,but not all of them have the satisfactory performance.Recently,metal-organic frameworks(MOFs) have attracted tremendous attention owing to their tunable chemical structures,diverse properties,large specific surface area and uniform pore distribution.MOF can transform to porous carbon(PC) which is decorated with metal species at appropriate pyrolysis temperature.However,the loss mechanism of pure MOF-derived PC is often relatively simple.In order to further improve the MA performance,the MOFs coupled with other loss materials are a widely studied method.In this review,we summarize the theories of MA,the progress of different MOF-derived PC-based MAMs,tunable chemical structures incorporated with dielectric loss or magnetic loss materials.The different MA performance and mechanisms are discussed in detail.Finally,the shortcomings,challenges and perspectives of MOF-derived PC-based MAMs are also presented.We hope this review could provide a new insight to design and fabricate MOF-derived PC-based MAMs with better fundamental understanding and practical application.

Progress in MXene-based materials for microwave absorption

Due to the rapid development of radar technology,the demand for absorbing stealth materials is increas-ing,and ultra-broadband absorption(effective absorption bandwidth>8 GHz)has become an inevitable requirement.As a new type of two-dimensional material,MXene material possesses the characteristics of excellent wave absorbing material due to its easy preparation,easy modulation of defects and sur-face functional groups,and high conductivity.This work summarizes the absorbing theory and research progress on MXene-based absorbing materials in recent years,including pure MXene absorbing materials and MXene-based magnetic or dielectric composite materials with multiple losses.Some shortcomings and research directions of MXene-based materials were pointed out.Currently,research on MXene-based absorbent materials is thriving and in a state of vigorous development.Excellent absorbent materials have been reported,but their shortcomings are also apparent.The factors that affect the performance of MXene-based absorbent materials are complex,and the absorption mechanism is relatively simple.Further systematic and detailed research is needed to clarify these influencing mechanisms,broaden the absorption bandwidth,and reduce the matching thickness to meet practical usage requirements in the future.

Review and Perspective of Tailorable Metal-Organic Framework for Enhancing Microwave Absorption

Metal-organic frameworks(MOFs)and their pyrolytic derivates,displaying diverse chemical compositions and microstructures,pro-vide the infinite potential for preparing high-performance microwave absorption materials(MAMs)and have attracted extensive at-tention.In this review,we systematically reviewed the recent progress of MOF-based MAMs,including three types of MOF-based MAMs(MOF-derived metal/carbon nanocomposites,MOF-based hybridization materials and conductive MOF).Besides that,the microwave absorption properties and their related physical and chemical appearance were also analyzed.On behalf of synergistic effects between microstructures,dielectric components and magnetic response,the MOF-based MAMs show excellent microwave absorption performance,which is superior to that of traditional single metal,metal alloy and pure carbon-based MAMs.Further-more,the novel conductive MOF with tunable electrical conductivity shows great potential in MAMs due to the fact that it can dra-matically simplify the synthesis process.

Why Sustainable Porous Carbon Should be Further Explored as Radar-Absorbing Material? A Comparative Study with Different Nanostructured Carbons

Radar Absorbing Materials(RAM)are a class of composites that can attenuate incident electromagnetic waves to avoid radar detection.Most carbon allotropes that have the potential to be used as RAM are either carbon nano-tubes(CNTs),graphene,carbon black(CB)and ultimately,sustainable porous carbon(SPC).Here,black wattle bark waste(following tannin extraction)was used as a sustainable source to produce SPC made from biomass waste.It was characterized and used as afiller for a silicone rubber matrix to produce aflexible RAM.The elec-tromagnetic performance of this composite was compared with composites made with commercial CB and CNT through reflection loss(RL),where-10 dB is equivalent to 90%of attenuation.These composites were evaluated in single-layer,double-layer,and as radar absorbing structures(RAS)with the aim of improving their effective absorption bandwidth(EAB)performances and a reduction in costs.The CNT composite presented a RL of-26.85 dB at 10.89 GHz and an EAB of 2.6 GHz with a 1.9 mm thickness,while the double-layer structures using CNT and SPC provided a RL of-19.74 dB at 10.75 GHz and an EAB of 2.51 GHz.Furthermore,the double-layer structures are~42%cheaper than the composite using only CNT since less material is used.Finally,the largest EAB was achieved with a RAS using SPC,reaching~2.8 GHz and a RL of-49.09 dB at 10.4 GHz.Summarizing,SPC made of black wattle bark waste can be a competitive,alternative material for use as RAM and RAS since it is cheaper,sustainable,and suitable for daily life uses such as absorbers for anechoic chambers,sensors,and elec-tromagnetic interference shields for electronics,wallets,vehicles,and others.

Review of wave mechanics theory for microwave absorption by film

The film and the material have been confused in current microwave absorption theory.This confusion has led to the establishment of the wrong theory of impedance matching and the wrong absorption mechanism.Progress on this subject has been reviewed in this work,and it shows that the wave mechanics theory which was proposed recently in the field of microwave absorption can be used to explain all aspects of the behavior of microwave absorption in film.Important aspects of the theory have been reviewed in detail involving the different absorption properties between film and material,the inverse relationship between frequency and film thickness that is related to the quarter-wavelength theory.