Mao-Sheng Cao

Reduced graphene oxides: light-weight and high-efficiency electromagnetic interference shielding at elevated temperatures.

Chemical graphitized r-GOs, as the thinnest and lightest material in the carbon family, exhibit high-efficiency electromagnetic interference (EMI) shielding at elevated temperature, attributed to the cooperation of dipole polarization and hopping conductivity. The r-GO composites show different temperature-dependent imaginary permittivities and EMI shielding performances with changing mass ratio.

Ferroferric Oxide/Multiwalled Carbon Nanotube vs Polyaniline/ Ferroferric Oxide/Multiwalled Carbon Nanotube Multiheterostructures for Highly Effective Microwave Absorption

Light-weight nanocomposites filled with carbon nanotubes (CNTs) are developed for their significant potentials in electromagnetic shielding and attenuation for wide applications in electronics, communication devices, and specific parts in aircrafts and vehicles. Specifically, the introduction of a second phase into/onto CNTs for achieving CNT-based heterostructures has been widely pursued due to the enhancement in either dielectric loss or magnetic loss. In this work, ferroferric oxide (Fe(3)O(4)) was selected as the phase in multiwalled carbon nanotube (MWCNT)-based composites for enhancing magnetic properties to obtain improved electromagnetic attenuation. A direct comparison between the two-phase heterostructures (Fe(3)O(4)/MWCNTs) and polyaniline (PANI) coated Fe(3)O(4)/MWCNTs, namely, three-phase heterostructures (PANI/Fe(3)O(4)/MWCNTs), was made to investigate the interface influences of Fe(3)O(4) and PANI on the complex permittivity and permeability separately. Compared to PANI/Fe(3)O(4)/MWCNTs, Fe(3)O(4)/MWCNTs exhibited enhanced magnetic properties coupled with increased dielectric properties. Interfaces between MWCNTs and heterostructures were found to play a role in the corresponding properties. The evaluation of microwave absorption of their wax composites was carried out, and the comparison between Fe(3)O(4)/MWCNTs and PANI/Fe(3)O(4)/MWCNTs with respect to highly efficient microwave absorption and effective absorption bandwidth was discussed.

Enhanced Microwave Absorption Property of Reduced Graphene Oxide (RGO)-MnFe2O4 Nanocomposites and Polyvinylidene Fluoride

MnFe2O4 nanoparticles have been synthesized on a large scale by a simple hydrothermal process in a wild condition, and the RGO/MnFe2O4 nanocomposites were also prepared under ultrasonic treatment based on the synthesized nanoparticles. The absorption properties of MnFe2O4/wax, RGO/MnFe2O4/wax and the RGO/MnFe2O4/PVDF (polyvinylidene fluoride) composites were studied; the results indicated that the RGO/MnFe2O4/PVDF composites show the most excellent wave absorption properties. The minimum reflection loss of RGO/MnFe2O4/PVDF composites with filler content of 5 wt % can reach -29.0 dB at 9.2 GHz, and the bandwidth of frequency less than -10 dB is from 8.00 to 12.88 GHz. The wave absorbing mechanism can be attributed to the dielectric loss, magnetic loss and the synergetic effect between RGO+MnFe2O4, RGO+PVDF and MnFe2O4+PVDF.

Ultrathin graphene: electrical properties and highly efficient electromagnetic interference shielding

Ultrathin graphene, a wonder material, exhibits great promise in various fields with its unique electronic structure and excellent physical, chemical, electrochemical, thermal and mechanical properties. Graphene presents great progress in electromagnetic interference (EMI) shielding. Herein, we review the advance in graphene-based EMI shielding materials. Towards graphene composites, we intensively evaluate EMI shielding efficiency and meaningfully describe the mechanism, such as polarization, hopping conduction and interface scattering. Moreover, we highlight an important direction for enhancing EMI shielding, the architectures, including alignment, paper, film and foam. Following that, the problems are summarized and the prospect is also highlighted for significant applications of ultrathin graphene in the field of EMI shielding.

Dual nonlinear dielectric resonance and nesting microwave absorption peaks of hollow cobalt nanochains composites with negative permeability

The permittivity and permeability behaviors of the hollow cobalt nanochains composites have been investigated in 2–18 GHz. The permittivity presents two dielectric resonance peaks at about 12.3 and 14.5 GHz, respectively, which mainly results from the cooperative consequence of the hollow structure and the one-dimensional structure of the as-synthesized Co nanochains. The negative permeability behavior within 12.3–18 GHz is attributed to radiation of the magnetic energy according to the as-established equivalent circuit model. Two strong absorption peaks of the composites nest at the resonance frequencies due to the effect of the dual nonlinear dielectric resonance and the negative permeability behavior.

Graphene–Fe3O4 nanohybrids: Synthesis and excellent electromagnetic absorption properties

Graphene (G)–Fe3O4 nanohybrids were fabricated by first depositing β-FeOOH crystals with diameter of 3–5 nm on the surface of the graphene sheets. After annealing under Ar flow, β-FeOOH nanocrystals were reduced to Fe3O4 nanoparticles by the graphene sheets, and thus G–Fe3O4 nanohybrids were obtained. The Fe3O4 nanoparticles with a diameter of about 25 nm were uniformly dispersed over the surface of the graphene sheets. Moreover, compared with other magnetic materials and the graphene, the nanohybrids exhibited significantly increased electromagnetic absorption properties owing to high surface areas, interfacial polarizations, and good separation of magnetic nanoparticles. The maximum reflection loss was up to −40.36 dB for G–Fe3O4 nanohybrids with a thickness of 5.0 mm. The nanohybrids are very promising for lightweight and strong electromagnetic attenuation materials.

Controllable fabrication of mono-dispersed RGO–hematite nanocomposites and their enhanced wave absorption properties

Novel RGO–hematite nanocomposites have been successfully fabricated using a surfactant-governed approach in the presence of polyvinylpyrrolidone (PVP) under mild wet chemical conditions (105 °C). A series of characterization methods including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the as-prepared single-crystal hematite particles with relatively uniform size are embedded in RGO layers to form unique quasi shell–core nanostructures. The microwave absorption properties of the RGO–hematite composites were studied in detail; as an absorber, the RGO–hematite nanocomposites possess excellent microwave absorbing properties. The enhanced microwave absorbing properties were also explained based on the structures of the nanocomposites.

Enhanced wave absorption of nanocomposites based on the synthesized complex symmetrical CuS nanostructure and poly(vinylidene fluoride)

Complex symmetrical CuS nanostructures were synthesized in large scale by a simple wet chemical method at low temperature. As a semiconductor material with superstructure, CuS was well characterized and firstly introduced into PVDF to form nanocomposites. The substantial enhancement of wave absorption (−102 dB at 7.7 GHz) was observed by addition of CuS with a low filler loading (5 wt%). The mechanism for the enhanced wave absorbing properties was explained in detail.

NiO Hierarchical Nanorings on SiC: Enhancing Relaxation to Tune Microwave Absorption at Elevated Temperature

We fabricated NiO nanorings on SiC, a novel hierarchical architecture, by a facile two-step method. The dielectric properties depend on temperature and frequency in the range from 373 to 773 K and X band. The imaginary part and loss tangent increase more than four times and three times with increasing temperature, respectively. The architecture demonstrates multirelaxation and possesses high-efficient absorption. The reflection loss exceeds -40 dB and the bandwidth covers 85% of X band (approximately -20 dB). The synergistic effect between multirelaxation and conductance is beneficial to the microwave absorption. Our findings provide a novel and feasible strategy to tune microwave absorption.

Temperature dependent microwave absorption of ultrathin graphene composites

Ultrathin, lightweight graphene composites exhibit high-efficiency microwave absorption at elevated temperatures as well as thermal-stability permittivity. The minimum reflection loss reaches −42 dB and the widest bandwidth covers the entire X-band (−10 dB). More significantly, the composites possess one high-efficiency absorption belt with a value ≤−15 dB, as well as two ‘islands’ of reflection loss of ≤−17 dB and −30 dB. These excellent properties arise from the synergistic effect of polarization and conductivity. Our finding demonstrates that ultrathin graphene is a promising microwave absorber for microwave attenuation devices, information security and electromagnetic pollution defense.