Preparation of rGO/MoSe2 nanocomposites for enhanced microwave absorption of whole X and Ku bands.

rGO-MoSe2 nanocomposites were prepared via a one-pot hydrothermal method in which MoSe2 microspheres (MS) were decorated on rGO sheets. Three nanocomposites named F1, F2, and F3 were prepared using different weight ratios of MoSe2 MS to rGO: (3 : 1), (4 : 1), and (5 : 1), respectively. FESEM images showed a flower-like porous morphology of the MoSe2 microspheres. All the rGO-MoSe2 nanocomposites exhibited remarkable microwave absorption properties as demonstrated by strong reflection loss (-58 dB to -99 dB) and an ultrabroad effective absorption bandwidth (equivalent to 90% attenuation), which covers whole X and Ku frequency bands at matching thicknesses of 2.8-3.2 mm. The minimum reflection loss reached -98, -99, and -75 dB for F1, F2 and F3, respectively. The excellent absorption properties of the rGO-MoSe2 nanocomposites is related to the unique morphology and micro size of MoSe2 in which incident waves are attenuated by multiple reflections and scattering.

GO-decorated chain-like Fe2O3/FeMn2O4 NPs (GO-Fe2O3/FeMn2O4 nanocomposites) with ultrabroad band microwave absorption.

In this study, GO-Fe2O3/FeMn2O4 nanocomposites were synthesized in which the chain-like Fe2O3/FeMn2O4 NPs were decorated on GO sheets. The crystalline phases of Fe2O3 and FeMn2O4 were recognized from the XRD pattern. TEM images showed that the oval-shaped Fe2O3/FeMn2O4 NPs with an almost narrow size distribution (60-80 nm) were connected to form chains. The Fe2O3/FeMn2O4 NP chains were decorated on the GO sheets in different weight ratios and GO-Fe2O3/FeMn2O4 (1 : 3), GO-Fe2O3/FeMn2O4 (1 : 4), and GO-Fe2O3/FeMn2O4 (1 : 5) nanocomposites, which were respectively named S1, S2, and S3, were finally produced. The microwave attenuation performance of all samples was investigated based on their EM parameters. The results demonstrated the superior attenuation ability of S1 and S2 in terms of reflection loss and absorption bandwidth. The minimum reflection losses (RLmin) for S1 and S2 reached over -85 dB and -88 dB and at the rest of the frequency band, the RL varied from -10 dB to -40 dB for samples thicker than 2.4 mm. The effective bandwidth (RL ≤ -10 dB) was 10 GHz, which covered the entire Ku and X bands for S1, and was -8.3 GHz, which eliminated the entire Ku band and half of the X band, for S2 at 2.4-3.6 mm with matching thicknesses. S3 exhibited a relatively weaker absorption performance. The results confirmed that achieving the maximum EM absorption performance of GO-based composites is guaranteed by optimizing the weight ratio of the decorative material (Fe2O3/FeMn2O4 NPs).

Superior microwave absorption ability of CuFe2O4/MWCNT at whole Ku-band and half X-band.

Recently, with the increasing progress of telecommunication systems and the development of high-range antennas, especially microwave antennas, the pollution caused by them has become very worrying. So, many efforts are being made to design absorbents which protect the environment from electromagnetic waves. Many reports have proved the extraordinary effect of absorbents containing carbon and ferrites. Here, the microwave absorption capabilities of two samples of CuFe2O4/MWCNT composites (annealed at 400 °C and unannealed) were studied in which CuFe2O4 nanoparticles (NPs) were decorated on multiwalled carbon nanotubes (MWCNTs) via a two-step method. First, CuFe2O4 NPs were synthesized at an optimum condition to have narrow size distribution (<10 nm) and high saturation magnetization of 47 emu g-1. Then, the CuFe2O4 NPs were used to decorate MWCNTs affording CuFe2O4/MWCNT. Half of CuFe2O4/MWCNT was annealed at 400 °C for 3 h and the rest of CuFe2O4/MWCNT remained nonannealed. The minimum reflection loss (RLmin) in the nonannealed sample was -46.4 dB at 16 GHz for a 2.8 mm thickness. While, for the annealed sample, RLmin reached -69 dB at 10 GHz for a 3.4 mm thickness. In the nonannealed sample, the effective absorption bandwidth was 3.8 GHz, but this value was significantly increased to 8.5 GHz for the annealed sample at 3.2 and 3.4 mm thickness, which covered whole X and Ku bands.

Microwave absorption property of GO-Fe/FeO-NiO HNFs: GO decorated Fe/FeO-NiO hexagonal flakes with a 2D/0D/2D structure.

In this study, Fe/FeO-NiO HNFs in which 2D NiO hexagonal nanoflakes (NiO HNFs) were decorated by 0D Fe/FeO NPs were prepared by a facile hydrothermal method. Then, 0D/2D Fe/FeO-NiO HNFs were loaded on 2D GO sheets in three different weight ratios of GO (1 : 3), (1 : 4), and (1 : 5) to Fe/FeO-NiO HNFs and a novel GO-Fe/FeO-NiO HNF composite with a 2D/0D/2D structure was successfully produced. TEM images revealed the interesting morphology of the GO-Fe/FeO-NiO HNF composite in which individual FeO NPs with a narrow size distribution (∼15 nm) were arranged in hexagonal NiO nanoflakes, decorated on the GO substrate. Since the morphology of nanomaterials has an important effect on their microwave absorption properties, designing a composite with an asymmetric morphology, which is the combination of zero, one, and two-dimensional nanostructures can be very efficient for adjusting the microwave absorption property. The microwave absorption ability of GO-Fe/FeO-NiO HNF composites was surveyed. All samples of Fe/FeO-NiO HNF composites exhibited superior microwave attenuation performance in terms of reflection loss with a suitable bandwidth. The minimum reflection losses for GO-Fe/FeO-NiO HNFs (1 : 3), (1 : 4), and (1 : 5) reached -75.22, -53, and -18 dB, respectively, and the effective absorption bandwidths (RL ≤ -10 dB) for GO-Fe/FeO-NiO HNFs (1 : 3), (1 : 4), and (1 : 5) were 2, 3 and 3.2 GHz, respectively.

Synthesis and microwave absorption characterization of SiO2 coated Fe3O4-MWCNT composites.

This study investigated the microwave absorption properties of core-shell composites containing; iron oxide decorated carbon nanotubes (CNTs) and silica (SiO2@Fe3O4-MWCNTs) with various thicknesses of silica shells (7, 20 and 50 nm). Transmission electron microscopy (TEM) and X-ray diffraction results confirmed the formation of these core-shell structures. Microwave absorption characterization of the samples at the ranging band under consideration (the X-band) showed increased absorption and shifting of the peaks to lower frequencies compared to the uncoated sample (Fe3O4-MWCNTs). The minimum reflection loss decreased with increasing SiO2 thickness. The minimum reflection loss of the composite with an optimized thickness of the silica shell (7 nm) exceeded -41 dB at 8.7-9 GHz.