Ming-Ming Lu

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.

Graphene/polyaniline nanorod arrays: synthesis and excellent electromagnetic absorption properties

In the paper, we find that graphene has a strong dielectric loss, but exhibits very weak attenuation properties to electromagnetic waves due to its high conductivity. As polyaniline nanorods are perpendicularly grown on the surface of graphene by an in situ polymerization process, the electromagnetic absorption properties of the nanocomposite are significantly enhanced. The maximum reflection loss reaches −45.1 dB with a thickness of the absorber of only 2.5 mm. Theoretical simulation in terms of the Cole–Cole dispersion law shows that the Debye relaxation processes in graphene/polyaniline nanorod arrays are improved compared to polyaniline nanorods. The enhanced electromagnetic absorption properties are attributed to the unique structural characteristics and the charge transfer between graphene and polyaniline nanorods. Our results demonstrate that the deposition of other dielectric nanostructures on the surface of graphene sheets is an efficient way to fabricate lightweight materials for strong electromagnetic wave absorbents.

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.

Multi-wall carbon nanotubes decorated with ZnO nanocrystals: mild solution-process synthesis and highly efficient microwave absorption properties at elevated temperature

Light weight and high efficiency are two key factors for microwave absorption materials. In particular, it is extremely important that absorption materials meet the harsh requirements of thermal environments. In this work, multi-wall carbon nanotubes decorated with ZnO nanocrystals (ZnO@MWCNTs) were synthesized by a mild solution-process synthesis. The high-temperature dielectric and microwave absorption properties of SiO2-based composites loaded with ZnO@MWCNTs (ZnO@MWCNTs/SiO2) are investigated in 8.2–12.4 GHz and in the 373–673 K temperature range. The imaginary permittivity e′′ of the composite with 5 wt% loading presents a weak downward trend, while those of the composites with 10 and 15 wt% loading show an upward trend with increasing temperature, which reveals different temperature dependences of e′′. The e′′ for 15 wt% loading is about 10 times that for 5 wt% loading. The maximum loss tangent tan δ values of the composites with 10 and 15 wt% loading exceed 0.8, while that of the composites with 5 wt% loading is less than 0.3. High tan δ is mainly attributed to the conductivity of ZnO@MWCNTs, which is dominated by the hopping of electrons in the ZnO@MWCNT network, which increases with elevated temperature. The addition of ZnO properly adjusts the complex permittivity to endow the ZnO@MWCNT/SiO2 composites with highly efficient and thermally stable microwave absorption coupled with a broad attenuation bandwidth, which almost covers the full X-band for RL ≤ −10 dB. A series of outstanding properties of ZnO@MWCNTs imply that it is a promising functional material in the world of microwave absorption.

Multiscale Assembly of Grape-Like Ferroferric Oxide and Carbon Nanotubes: A Smart Absorber Prototype Varying Temperature to Tune Intensities

Ideal electromagnetic attenuation material should not only shield the electromagnetic interference but also need strong absorption. Lightweight microwave absorber with thermal stability and high efficiency is a highly sought-after goal of researchers. Tuning microwave absorption to meet the harsh requirements of thermal environments has been a great challenge. Here, grape-like Fe3O4-multiwalled carbon nanotubes (MWCNTs) are synthesized, which have unique multiscale-assembled morphology, relatively uniform size, good crystallinity, high magnetization, and favorable superparamagnetism. The Fe3O4-MWCNTs is proven to be a smart microwave-absorber prototype with tunable high intensities in double belts in the temperature range of 323-473 K and X band. Maximum absorption in two absorbing belts can be simultaneously tuned from ∼-10 to ∼-15 dB and from ∼-16 to ∼-25 dB by varying temperature, respectively. The belt for reflection loss ≤-20 dB can almost cover the X band at 323 K. The tunable microwave absorption is attributed to effective impedance matching, benefiting from abundant interfacial polarizations and increased magnetic loss resulting from the grape-like Fe3O4 nanocrystals. Temperature adjusts the impedance matching by changing both the dielectric and magnetic loss. The special assembly of MWCNTs and magnetic loss nanocrystals provides an effective pathway to realize excellent absorbers at elevated temperature.

3D Fe3O4 nanocrystals decorating carbon nanotubes to tune electromagnetic properties and enhance microwave absorption capacity

We fabricated a novel dielectric–magnetic nanostructure by hybridizing 3D Fe3O4 nanocrystals and multi-walled carbon nanotubes through a simple co-precipitation route. The 3D Fe3O4-MWCNTs composites demonstrate enhanced microwave absorption with tunable strong-absorption wavebands in the frequency range of 2–18 GHz. Double-band microwave absorption appears in the investigated frequency range and at various thicknesses. This depends on the loading concentration of 3D Fe3O4-MWCNTs. Minimum reflection loss values at 20 wt% loading of −23.0 dB and −52.8 dB are observed at 4.1 GHz and 12.8 GHz, respectively, which are superior to those of pure MWCNTs as well as other hybrids of Fe3O4. The improved absorption capacity arises from the synergy of dielectric loss and magnetic loss, as well as the enhancement of multiple interfaces among 3D Fe3O4 nanocrystals. All of these factors increase the flexibility of tuning microwave absorption. These results provide a new strategy to tune electromagnetic properties and enhance the capacity of high-efficient microwave absorbers.

Synthesis and growth mechanism of 3D α-MnO2 clusters and their application in polymer composites with enhanced microwave absorption properties

α-MnO2 hollow-sphere-like clusters composed of nanotubes have been synthesized on a large scale by a simple hydrothermal method. The results show that the 3D hollow-sphere-like clusters are assembled by 1D nanotubes (HSC-nanotubes) with diameter of around 80–100 nm and length of around 2–3 μm. The influences of reaction time and temperature on the morphology of the final products are investigated, while the formation mechanism is also discussed. The α-MnO2 hollow-sphere-like clusters possess much better dielectric properties than the bulk material, which is directly related to their special nanostructures. Besides, the synthesized α-MnO2 hollow-sphere-like clusters were used as fillers in the fabrication of α-MnO2/PVDF nanocomposites, which have excellent wave-absorption properties with low filler loading. The enhanced properties are caused by a synergic effect between α-MnO2 and PVDF, as explained in this research.