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Metacomposites with extraordinary electromagnetic (EM) parameters recently offered a brand-new strategy for EM shielding, but still suffered from the unclear paradigm and regulation mechanism for ε′ -negative and ε′ -near-zero response. Herein, we presented an effective paradigm of binary composites consisting of CaCu 3 Ti 4 O 12 (CCTO) and graphitized-multiwall carbon nanotube (g-MWCNT) which was designed by percolation theory. The ε′ switched from positive to negative with increasing frequency was obtained in g-MWCNT/CCTO composites, which could be explained by electrical dipole resonance of interconnected g-MWCNT clusters. Once the percolated g-MWCNT network is formed, Drude-type ε′ -negative response would be obtained due to the low-frequency plasma oscillation. Epsilon-near-zero effect (at ∼385 MHz and ∼135 MHz) were tuned by adjusting g-MWCNT content, which respectively corresponds to the loss peaks. The EM medium of CCTO/g-MWCNT composites with ε′ -negative or ε′ -near-zero response showed great EM shielding performance at specific frequency region. The g-MWCNT/CCTO metacomposites provide a classical paradigm of ceramic matrix composites for ε′ -negative and ε′ -near-zero response which will guide the practical application of metacomposites in dielectric ceramics and metamaterials, and promote the next steps in EM shielding field. [ABSTRACT FROM AUTHOR]

Graphene-carbon nanotube/copper calcium titanate (GR-CNT/CCTO) ceramic nanocomposites were prepared by spark plasma sintering (SPS) technology. The correlation between GR-CNT content and epsilon-negative property was clarified in detail. Electrical percolation behavior was confirmed in nanocomposites with GR-CNT content rising, corresponding to change from hopping conductivity to metal-like conductivity. When three-dimensional (3D) GR-CNT networks were constructed in CCTO ceramics, epsilon-negative property was obtained, originating from low-frequency collective plasma oscillation of delocalized electrons in formed networks. Epsilon-near-zero (ENZ) property was respectively obtained at ~360 MHz and ~255 MHz. The negative value of epsilon ranged from ~103 to ~104, and plasma frequency of the composites increased from 12.8 GHz to 34.6 GHz with GR-CNT content ranging from 10 wt% to 12 wt%, which was analyzed by Drude model. In addition, the dielectric loss behavior and impedance response also were discussed. The inductive character of epsilon-negative materials was expounded via equivalent circuit analysis. We provide an effective paradigm of carbon/ceramic nanocomposites with epsilon-negative property by constructing 3D GR-CNT networks, which facilitates the clarification of regulation mechanism of epsilon-negative materials. [ABSTRACT FROM AUTHOR]

In this work, a type of unique flexible and ultra-stretchable microtextiles was fabricated by coassembly of Ag nanowires (AgNWs) and thermoplastic polyurethane (TPU) microfibers. The microtexiles show tunable and weakly negative permittivity at a low filler content of 1.0–2.4 wt%. The resonance-induced negative permittivity observed in the AgNW/TPU microtextiles below the percolation threshold (f c) is attributed to the electric dipole moment of the isolated AgNWs, and this phenomenon can be explained by the Lorentz model. When the AgNW content exceeds the f c , the low-frequency collective plasma oscillation of the AgNW networks in the composites triggers the tunable plasma-type negative permittivity, which agrees with the Drude model. Additionally, the inductive character of the composites was assessed with the reactance spectra. The as-prepared Ag/TPU microtextiles could be a good candidate for the applications of garment integrated electronic, novel sensors, electromagnetic cloaking, and wearable electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Metacomposites have drawn considerable attention due to their enticing prospect in electronic and dielectric devices, which meanwhile unfortunately suffered from extremely high negative permittivity (ε' < 0). Herein, we put forward a strategy to suppress the plasma oscillation in metacomposites and thereby constrain the value of negative permittivity by introducing the semiconductive polyaniline to construct polyaniline/nickel (PANI/Ni) metacomposites. Weakly negative permittivity was obtained at a magnitude of 102 over the whole test frequency band, which is remarkably lower by at least three orders of magnitude than that of most metacomposites. The ε′ -negative value was resultantly fine-tuned by about 102 with equally adjusting Ni content. Lorentz and Drude models were employed to describe ε′ -negative spectra, indicating that both dielectric resonance and plasma oscillation contributed to negative permittivity. Negative susceptibility of ε′ -negative materials was mainly ascribed to high-frequency diamagnetic response within Ni networks. The well-designed PANI/Ni metacomposites with weakly and fine-tuning negative permittivity can greatly benefit the practical applications on electromagnetic (EM) shielding, microwave absorption and novel EM sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

Here, Ag/CaCu 3 Ti 4 O 12 (Ag/CCTO) percolative nanocomposites were fabricated by an in-situ synthesis, where the percolation-related transitions of dielectric and magnetic properties were investigated at radio-frequency band. Epsilon-negative property (ε′ < 0) and diamagnetic responses (μ′ < 1) were observed in percolated composites, owing to low-frequency plasmonic state and induced eddy currents within formed conductive Ag networks respectively. The competitive effect between polarization response of ε′ -positive CCTO matrix and collective plasma oscillation of ε′ -negative Ag networks leads to the tunable negative permittivity. The clarification of inductive character of ε′ -negative materials benefits constructing effective strategy for adjusting negative value of dielectric constant. [Display omitted] [ABSTRACT FROM AUTHOR]

Ceramic composites with negative permittivity have attracted widespread attention during the development of novel electromagnetic metamaterials. Herein, carbon nanotubes/TiN/CaCu 3 Ti 4 O 12 (CNTs/TiN/CaCu 3 Ti 4 O 12) ternary composites were prepared, and the effects of dual fillers on the dielectric properties of the ternary composites are discussed. The electrical conductivity increased markedly, and the conduction mechanism changed owing to the percolation of the dual conductor fillers. The switching of the reactance, from negative to positive, suggests that the ternary composites underwent a capacitive-inductive transition. The dielectric permittivity was negative owing to the plasmonic state of the free electrons in the percolating conductor fillers. Regulating the electron concentration by changing the filler content or adjusting the microstructure by changing the relative content of the dual fillers proved to be an effective way to tailor the negative permittivity performance of ternary composites. In addition, conduction loss dominated the dielectric loss mechanism of the negative permittivity composites. The realization and regulation mechanism of the negative permittivity of ternary composites are clarified, shedding light on the preparation and development of negative permittivity materials for various electromagnetic applications. [ABSTRACT FROM AUTHOR]

• The aged ZSM-5 is regenerated by a facile and universal activation technology. • The activation technology can partially unblock the aged-Z's channels. • The activation technology can also realuminate with the extraframework aluminum. • The activation technology can thus increase the yields of light olefins of aged-Z. • The aged cracking catalysts can also be regenerated by the activation technology. The green and sustainable re-utilization the deactivated ZSM-5 zeolites is an important concern for their application in the catalytic cracking of naphtha. In the present study, a facile, universal and environmental-friendly hydrothermal activation technology was firstly performed without any chemical reagent to regenerate the ZSM-5 samples hydrothermally deactivated under harsh conditions (Aged-Z). By XRD, N 2 adsorption/desorption, NH 3 -TPD, FT-IR, 1H and 27Al MAS NMR, and TEM characterizations, it has been confirmed that the unblocking of the channels and the realumination of Aged-Z zeolites could be successfully achieved after a simple hydrothermal activation treatment, in which the migration and the reinsertion of extra-framework aluminum into the framework can properly optimize the textural structure, and the number of acid sites. Thus, the regenerated ZSM-5 (Reg-Z) exhibited the better catalytic cracking performance of naphtha than the aged and fresh ZSM-5 samples. Accordingly, the catalytic cracking mechanisms were hence developed and also in good agreement with the distribution of olefins over the fresh, aged and regenerated ZSM-5 zeolites. [ABSTRACT FROM AUTHOR]

Ceramic metacomposites have been substantially investigated to obtain negative permittivity owing to their promising applications in electronics and dielectric devices. However, the modulation of negative permittivity has still been a challenging issue to be investigated. Herein, CaCu 3 Ti 4 O 12 (CCTO) ceramic nanocomposites with varying content of graphene-carbon nanotube (GR-CNT) fillers were fabricated. There are two different types of radio-frequency (RF) negative permittivity in GR-CNT/CCTO metacomposites, i.e. induced dielectric resonance and plasma oscillation, which provided original envisage for tailorable negative permittivity. Resonance-type negative permittivity behavior originated from the abundant electric dipoles in the isolated GR-CNT clusters and interfacial polarization between GR-CNT and CCTO. Strongly dispersion of negative permittivity (~-104) was achieved in the metacomposites with high carbon content, which was ascribed to plasmonic state of extensive free carriers in percolating GR-CNT networks. Weakly negative permittivity (~-102) was obtained in the composites above the epsilon-near-zero frequencies, which were ~860 MHz, ~430 MHz and ~370 MHz, respectively. Inductive character of metacomposites was an intrinsic performance exactly as equivalent circuit analysis demonstrated. This work benefits for clarifying the regulation mechanism of negative permittivity, which can pave the way to expand the applications of ceramic composites in the field of metamaterials. [ABSTRACT FROM AUTHOR]

Ceramic nanocomposites have been developed to provide a feasible and effective strategy in realizing extraordinary electromagnetic properties, such as negative permittivity. Here, copper calcium titanate CaCu 3 Ti 4 O 12 (CCTO) nanocomposites incorporated with multiwall carbon nanotube (MWCNT) were prepared by spark plasma sintering (SPS) technology. It was found that MWCNT clusters were randomly embedded in CCTO matrix, which destroyed the microstructures of internal barrier layer capacitors in CCTO. The composites with low MWCNT content presented a hopping conduction behavior, while a metal-like conduction behavior was observed in the ceramic with 18 wt% MWCNT content. Interestingly, weakly negative permittivity (~ -103) was obtained in the ceramic consisting of interconnected MWCNT networks, as a great number of free electrons in the MWCNTs formed significantly collective oscillation state over 10 MHz-1 GHz range. Macroscopically, leakage current among MWCNT clusters or networks caused strong conduction loss at low frequencies. Equivalent circuit analysis manifested the correlation between low-frequency plasmonic state and inductive character in the composite with negative permittivity. This work could extend the potential applications of ceramic nanocomposites to metamaterials. [ABSTRACT FROM AUTHOR]

Ceramic composites with negative permittivity have provoked considerable interests of researchers in electronic and dielectric devices due to the extraordinary electromagnetic performance in radio-frequency (RF) region. Herein, graphene/CaCu 3 Ti 4 O 12 (GR/CCTO) ceramic composites were spark plasma sintered, of which the dielectric and thermal properties were demonstrated at RF region. An electrical percolation was identified with GR content varying from 10 wt% to 14 wt% which presenting as a dramatic increase of ac conductivity. The conduction mechanism changed from hopping conductivity to metal-like conductivity. Meanwhile, the real permittivity (ε′) turned from positive to negative which indicating an intrinsic transition of dielectric response mechanism. Therefore, Drude model was applied to elucidate the RF negative permittivity (ε' < 0) which manifesting the low-frequency plasmonic state of delocalized electrons in composites. The constructed GR networks in composites also leaded to the enhanced thermal conductivity due to the dominating contribution of phonon vibration in GR sheets. Besides, theoretical models of capacitive and inductive equivalent circuits were used on impedance spectra which successfully clarified the inductive character of negative permittivity. This work benefits expounding the generation and regulation mechanism of negative permittivity and will be favorable to exploring brand-new applications of ceramic composites. [ABSTRACT FROM AUTHOR]

Taking full advantage of interface engineering to strengthen interface polarization is an effective strategy to improve microwave absorption. Therefore, constructing the mixed-dimensional heterostructures and/or three-dimensional (3D) interconnected network structures should be attractive pathways to create the abundant interfaces for enhanced interfacial effect. Herein, mixed-dimensional framework structure carbon foam (CF)/carbon nanotubes (CNTs)@Fe 3 C@Fe 3 O 4 samples consisting of 3D CF, one-dimensional (1D) CNTs and zero-dimensional (0D) Fe 3 C@Fe 3 O 4 nanoparticles were elaborately designed and produced through a simple catalytic chemical vapor deposition process. The as-prepared CF/CNTs@Fe 3 C@Fe 3 O 4 heterostructures with the different contents of CNTs could be selectively produced by regulating the pyrolysis time. Owing to the unique structure and excellent synergistic effects, the obtained mixed-dimensional CF/CNTs@Fe 3 C@Fe 3 O 4 samples presented the excellent comprehensive electromagnetic wave absorption performances (EMWAPs) including strong absorption capabilities, broad absorption bandwidths, thin matching thicknesses and low densities. Furthermore, the obtained results demonstrated that the enhanced content of CNTs greatly boosted their conduction and polarization loss abilities, which resulted in the enhanced comprehensive EMWAPs. Therefore, our findings not only offered a simple strategy to produce the mixed-dimensional framework structure magnetic CF/CNTs-based heterostructures as excellent lightweight high-efficiency microwave absorbers, but also provided an effective pathway to make the best of interface engineering for enhancing interface polarization. Constructing mixed-dimensional lightweight flexible CF/CNTs@Fe 3 C@Fe 3 O 4 heterostructures: an effective strategy to achieve tunable and boosted microwave absorption. [Display omitted] • Mixed-dimensional framework structure CF/CNTs@Fe 3 C@Fe 3 O 4 heterostructures were produced through a simple process. • The CF/CNTs@Fe 3 C@Fe 3 O 4 with different contents of CNTs were produced by regulating the pyrolysis time. • The enhanced content of CNTs greatly boosted their conduction and polarization loss abilities. • Owing to the abundant interfaces, the designed CF/CNTs@Fe 3 C@Fe 3 O 4 presented the excellent EMWAPs. • Our findings provided an effective pathway to make the best of interface engineering for enhanced interface polarization. [ABSTRACT FROM AUTHOR]

The effect of bilayer structure on high- k and low loss in graphene/polyvinylidene fluoride (GR/PVDF) composites, and the bilayer structured composites consist of negative- k and positive- k layers. [Display omitted] • Synergistic effect of negative and positive-k leads to a good dielectric property. • The permittivity 559 and tanδ 0.053 were observed in bilayer structure composites. • Negative-k response can be obtained and tailored in the resulting composites. Polymer matrix composites (PMCs) with high- k and low loss (tan δ) have aroused extensive research due to their significant applications in energy-storage capacitors and novel printed circuit board. In this work, the single layer structured graphene/polyvinylidene fluoride (GR/PVDF) composites were synthesized by hot pressing process, in which the fascinating permittivity transition from positive to negative was attributed to plasma oscillation. Meanwhile, the alternating current conductivity (σ a c ) and reactance behavior were well consistent with Jonscher's power law and equivalent circuit model. More importantly, the GR/PVDF composites consisted of negative- k layer that led to high- k and low tan δ performances. When the GR content of the negative- k layer was 10 wt% and positive- k layer was 2 wt%, the permittivity reached up to 559 and tan δ was just 0.053 at 100 kHz in bilayer structured composite, respectively. Theoretically, the high- k performance originated from strong interfacial polarization between positive- k and negative- k layers, which is beneficial to the synergistic effect of capacitive and inductive characters. Additionally, the low tan δ was attributed to the effectiveness restriction of electron transfer in capacitive layer. Therefore, the multilayer structured GR/PVDF composites by introducing negative- k layer can achieve high- k and low loss that supply a novel strategy for preparing dielectric materials. [ABSTRACT FROM AUTHOR]

When seeking for satisfactory metacomposites with negative permittivity behavior, an important factor which should be taken into consideration is how to realize a weakly negative permittivity (less than 100). A novel strategy has been proposed accordingly to prepare ternary multiwalled carbon nanotubes/titanium nitride/copper calcium titanate (MWCNT/TiN/CCTO) composites by a facile sintering method in an inert atmosphere. The negative permittivity was observed after the TiN-MWCNT network was constructed among the composites. TiN provided sufficient free electrons and MWCNT were regarded as transporter bridge. Under the synergistic effect of TiN and MWCNT, the negative permittivity decreased by several orders of magnitude owing to the dilution of overall electron density in the resulting composites. Exceptionally, when the permittivity switched from positive to negative along with a resonance, a Lorentz-like negative permittivity was observed in low frequency region. Meanwhile, the Drude-like negative permittivity derived from plasma oscillation was also observed in the higher frequency region. Further investigation confirmed that the permittivity was closely related to the reactance. The positive-negative reactance transition was consistent with the negative-positive permittivity transition, and the epsilon-near-zero was achieved near the zero-crossing point of permittivity. Moreover, the influence of different sintering atmospheres (nitrogen and argon) on the negative permittivity behavior was also explored. This work provides an effective approach for the realization of weakly negative permittivity, and presents, to our knowledge, the first investigation into the influence of sintering atmosphere on negative permittivity. [ABSTRACT FROM AUTHOR]

• Mixed-dimensional Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs in high efficiency through a simple method. • By controlling the amount of initial reactants, Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs with different contents of CNTs were produced. • The enhanced contents of MWCNTs and RGO boosted the impedance matching characteristics, polarization and conduction loss capabilities. • Fe 3 O 4 -FeCO 3 /MWCNTs/RGO mixed-dimensional MCNCs exhibited the outstanding comprehensive EMWAPs. • Our findings took full advantage of interface and magnetic-dielectric synergy strategy to develop high-efficiency novel MAs. Interfacial and/or magnetic-dielectric synergistic effects are important avenues to boost microwave absorption properties. In order to simultaneously utilize these effects, we elaborately designed mixed-dimensional Fe 3 O 4 -FeCO 3 /multi-walled carbon nanotubes (MWCNTs)/reduced graphene oxide (RGO) multicomponent nanocomposites (MCNCs) in large scale via a facile process of hydrothermal and freeze-drying. The microstructural investigation revealed that two-dimensional RGO, one-dimensional MWCNTs and zero-dimensional Fe 3 O 4 -FeCO 3 nanoparticles were well bounded to generate the typical mixed-dimensional structure. By controlling the amounts of initial reactants, the Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs displayed improved impedance matching features, polarization and conduction loss abilities, which lead to the evidently improved electromagnetic absorption properties. The Fe 3 O 4 -FeCO 3 /MWCNTs/RGO MCNCs simultaneously exhibited excellent absorption ability, large absorption bandwidth, low density and thin matching thickness. Generally, this work not only proposed an effective route to make the best of magnetic-dielectric synergy and interfacial strategy for exploiting novel microwave absorption materials, but also presented a simple approach to synthesize magnetic MWCNTs/RGO-based mixed-dimensional MCNCs. Interface and magnetic-dielectric synergy strategy to develop Fe 3 O 4 -Fe 2 CO 3 /multi-walled carbon nanotubes/reduced graphene oxide mixed-dimensional multicomponent nanocomposites for tunable and boosted microwave absorption [Display omitted] [ABSTRACT FROM AUTHOR]

Metacomposites which unveil weakly negative permittivity have been regarded as a promising candidate for next-generation electronics. We propose to prepare such metacomposites by developing the core-shell structured WC/PPy composites. The regulation of properties, including reactance, conductivity, and permittivity, has been achieved by controlling the mass ratio of WC in the WC/PPy composite. Conductive networks are constructed when the WC fraction is increased to a certain level, leading to a weakly negative permittivity, which is related to the plasma oscillation of free electrons. Owing to Lorentz dielectric resonance, a frequency-regulated negative permittivity is also realized, which provides an alternative strategy to obtain negative permittivity. This work will push forward further research and applications of metacomposites. Image 1 • Benefiting from the use of WC filler and the dispersion effect of the PPy shell layer, negative permittivity with small absolute value (between −500 and −50) has been realized. • Lorentz-type negative permittivity and plasma oscillation related negative permittivity can be observed respectively by controlling the mass ratio of WC in the WC/PPy composites. • An electrical percolation happens with the increase of WC fraction, leading to a conversion of conductive mechanism from hopping conduction to electron conduction. [ABSTRACT FROM AUTHOR]

Abstract Oxygen reduction reaction and hydrogen evolution reaction are two key reactions involved in several renewable energy technologies. Herein, a nonprecious bifunctional electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction is facilely synthesized through directly pyrolyzing the mixture of Prussian blue analogues, graphene oxide and graphitic carbon nitride in the presence of silica colloids. Post-synthesis removal of silica hard templates leads to a cobalt and nitrogen co-doped reduced graphene oxide composite with Co nanoparticles, which comprises abundant mesoporous textures and a high specific surface area of 703.26 cm2 g−1. The resultant composite shows marked oxygen reduction reaction activity, with a more positive half-wave potential of +0.848 V, a higher limiting current, a stronger immunity to fuel crossover effect and higher operation stability, as compared with commercial Pt/C catalyst in alkaline solution. Besides, such composite can also serve as efficient and stable hydrogen evolution reaction catalyst in alkaline electrolyte, and an overpotential of only 180 mV is required to reach 10 mA cm−2. The remarkable bifunctional catalytic activities are attributed to the synergistic effects of Co nanoparticles and graphene substrate. These results highlight the high potential of present strategy in synthesis of multifunctional nonprecious electrocatalysts. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Titanium nitride (TiN) with high-temperature plasmonic property can be a promising candidate for metamaterials at radio-frequency region. In this paper, pure TiN powders were pretreated by a facile oxidation process. The introduced titanium oxide was in favor of sintering of TiN, and further controlled the dielectric properties of TiN bulks. The radio-frequency (10 MHz-1 GHz) permittivity spectra of the obtained samples were investigated in detail. Negative permittivity was achieved using TiN based ceramic and it was tailorable by the oxidation temperatures of powders before sintering. The negative permittivity induced by plasma oscillations of conductive electrons was analyzed by Drude model. Interestingly, the zero-crossing points of permittivity from negative to positive were depend on the porous microstructure and weakly conductive titanium oxynitride, as well as the scattering effect by grain boundaries and impurity atoms. The conduction loss is dominant in determining the high dielectric loss. The realization of tunable negative permittivity using TiN gives a new and simple method to achieve negative electromagnetic parameters in single-phase materials. [ABSTRACT FROM AUTHOR]

Nowadays, negative parameters have been originally brought up and investigated in the electromagnetic metamaterial, where the epsilon-near-zero (ENZ) response was dominated by collective plasma frequencies and carrier concentration. However, the ENZ response is missing at the radio frequency, leading to limitations on novel antennas and printed circuit board. Therefore, ternary copper/silica coated copper/polyvinylidene fluoride (Cu/Cu@SiO 2 /PVDF) composites were prepared to investigate the ENZ response at the radio frequency. With increasing the content of Cu granules, a transition from positive to negative permittivity was observed in the binary Cu/PVDF composites, in which negative permittivity was related to an inductive character. On the contrary, the binary Cu@SiO 2 /PVDF composites without any uncoated Cu granules exhibit positive permittivity, showing a capacitive character. In fact, negative permittivity was derived from the collective plasma oscillation of percolative Cu networks, and Cu@SiO 2 granules were responsible for diluting effective electron concentration of Cu. For the ternary Cu/Cu@SiO 2 /PVDF composites, values of negative permittivity were suppressed to several orders of magnitude to −178 (measured at 1 MHz) and plasma frequency decreased to radio frequency about 106 rad/s. Besides, with the construction of percolative Cu networks, the Ac conduction mechanism was transformed from hopping conduction to metal-like conduction. Based on the equivalent circuit analysis, it showed that a permittivity transition was responsible for the capacitive to inductive character. In this work, the epsilon-near-zero response was obtained in the ternary copper/silica coated copper/polyvinylidene fluoride (Cu/Cu@SiO 2 /PVDF) composite, where the carrier concentration of Cu granules was further reduced by introducing insulative Cu@SiO 2 granules, resulting in the lower carrier concentration and lower plasma frequency at the radio frequency region. In fact, the lower carrier concentration was responsible for epsilon-near-zero response, and negative permittivity was attributed to the collective plasma oscillation of Cu granules. [Display omitted] [ABSTRACT FROM AUTHOR]