Avanish Pratap Singh

Encapsulation of γ-Fe2O3 decorated reduced graphene oxide in polyaniline core–shell tubes as an exceptional tracker for electromagnetic environmental pollution

The ultimate goal of the development of a new material γ-Fe2O3 decorated reduced graphene oxide (rGO)–polyaniline (PANI) core–shell tubes has been done for absorbing electromagnetic interference (EMI) pollution. Herein, we report on the synthesis and characterization of PANI tubes consisting of rGO decorated with iron oxide nanoparticles (RF). The intercalated RF was synthesized by thermal decomposition of ferric acetyl acetonate in a reducing atmosphere. Furthermore, RF was encapsulated through oxidative polymerization of aniline in the presence of β-naphthalene sulphonic acid which results in RF–PANI core–shell morphology. Scanning electron microscopy results confirm the formation of tubular core–shell morphology having 5–15 μm length and 1–5 μm diameter. The presence of rGO–γ-Fe2O3 in PANI core enhances the interfacial polarization and the effective anisotropy energy of the composite which contributes to more scattering and leads to high shielding effectiveness (SET ∼ 51 dB) at a critical thickness of 2.5 mm. Additionally, the effective complex permeability and permittivity parameters of the composites have been evaluated from the experimental scattering parameters (S11 & S21) using theoretical calculations given in Nicholson–Ross and Weir algorithms.

Graphene oxide/ferrofluid/cement composites for electromagnetic interference shielding application

This paper deals with the preparation of graphene oxide-ferrofluid-cement nanocomposites to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) in the 8.2-12.4 GHz frequency range. It has been observed that incorporation of graphene oxide (30 wt%) along with an appropriate amount of ferrofluid in the cement matrix leads to a shielding effectiveness of 46 dB (>99% attenuation).The presence of graphene oxide and ferrofluid in the cement leads to strong polarizations and magnetic losses that consequently result in higher shielding effectiveness compared to pristine cement. The resulting nanocomposites have shown Shore hardness of 54 and dc conductivity of 10.40 S cm( - 1). SEM reveals the homogeneous dispersion of graphene oxide and ferrofluid in the cement matrix.

MnO2 decorated graphene nanoribbons with superior permittivity and excellent microwave shielding properties

Microwave shielding properties of chemically synthesized MnO2 decorated graphene nanoribbons (GNRs) are reported for the first time. The nature of MnO2 decoration on the GNRs has been investigated using scanning electron microscopy, X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. The electromagnetic interference (EMI) shielding effectiveness of this material was investigated in the microwave region (Ku-band, 12.4–18 GHz). The presence of MnO2 on GNR enhances the interfacial polarization, multiple scattering, natural resonances and the effective anisotropy energy, which leads to absorption dominated high shielding effectiveness of −57 dB (blocking >99.9999% radiation) by a 3 mm thick sample. Dielectric attributes (e′ and e′′) were evaluated to understand the mechanism of the excellent shielding effectiveness. The material will be an excellent choice for radar absorbing applications.

Conducting ferrofluid: a high-performance microwave shielding material

Conducting materials based on reduced graphene oxide (RGO) sheets have become the focus of considerable research interest in recent years because of the scientific and technological significance of these materials. Herein, we report the fabrication of conducting ferrofluid composites of reduced graphene oxide and nanoscale Fe3O4 (5–20 nm) particles made using a simple yet versatile co-precipitation method. Raman spectroscopy was performed to elucidate the graphitic structure of RGO and interaction between ferrofluid nanoparticles and RGO, which shows a slight shift in the peak position of RGO (shifting from 1360 to 1348 cm−1 in the D band and 1604 to 1593 cm−1 in the G band) and ferrofluid. This shift in the bands is an evidence of a strong interaction between these two components. The magnetic and electromagnetic shielding properties of these conducting ferrofluid composites having different loadings of reduced graphene oxide sheets were investigated. In addition, the high value of microwave shielding, 41 dB (99.9% attenuation) results from the combined effect of magnetic losses (natural resonance and eddy currents) due to ferrofluid and dielectric losses (natural resonance, dipole relaxation, electron polarization related relaxation, interfacial polarization, residual defects in RGO sheets and higher conductivity) due to reduced graphene oxide. The as-synthesized conducting ferrofluid could be a promising candidate for the next generation building block material in microwave shielding applications with vast utilities in the radio frequency range.

Microwave shielding properties of Co/Ni attached to single walled carbon nanotubes

Cobalt/nickel nanoparticles attached to single-walled carbon nanotubes (Co/Ni@SWCNTs) were prepared by dc-arc discharge technique. Co/Ni@SWCNTs were characterized by scanning electron microscopy, high resolution transmission electron microscopy (HRTEM), Raman spectroscopy and energy dispersive X-ray analysis techniques. HRTEM results confirmed attachment of magnetic nanoparticles onto SWCNTs having 1.2 nm diameter. A microwave shielding effectiveness value of 24 dB (blocking >99% radiation) by a 1.5 mm thick sample in the frequency range of 12.4–18 GHz was observed. In order to understand the mechanism of shielding, dielectric and magnetic attributes of the shielding effectiveness of Co/Ni@SWCNTs have been evaluated. Eddy currents and natural resonances due to the presence of magnetic nanoparticles, electronic polarization and their relaxation, interfacial polarization and unique composition of the shield contributed significantly in achieving good shielding effectiveness. The observed microwave shielding crossed the limit required for commercial applications which suggests that these nanocomposites are promising microwave shielding materials in the Ku band.

Conduction mechanism in Polyaniline-flyash composite material for shielding against electromagnetic radiation in X-band & Ku band

β–Naphthalene sulphonic acid (β–NSA) doped polyaniline (PANI)–flyash (FA) composites have been prepared by chemical oxidative polymerization route whose conductivity lies in the range 2.37–21.49 S/cm. The temperature dependence of electrical conductivity has also been recorded which shows that composites follow Motts 3D–VRH model. SEM images demonstrate that β–NSA leads to the formation of the tubular structure with incorporated flyash phase. TGA studies show the improvement in thermal stability of composites with increase in loading level of flyash. Complex parameters i.e. permittivity (ɛ* = ɛ′- iɛ″) and permeability (μ*=μ′- iμ″) of PANI-FA composites have been calculated from experimental scattering parameters (S11 & S21) using theoretical calculations given in Nicholson–Ross and Weir algorithms. The microwave absorption properties of the composites have been studied in X-band (8.2 – 12.4 GHz) & Ku–Band (12.4 – 18 GHz) frequency range. The maximum shielding effectiveness observed was 32dB, which strongly depends on dielectric loss and volume fraction of flyash in PANI matrix.

Tailored polyaniline/barium strontium titanate/expanded graphite multiphase composite for efficient radar absorption

The present paper reports the synthesis of a high-performance microwave absorbing material using a simple, cost-effective and scalable method by encapsulating barium strontium titanate (BST) and expanded graphite (EG) in a polyaniline (PANI) matrix. One of the formulations (higher content of BST) shows shielding effectiveness due to absorption of more than 50 dB (>99.9999% attenuation) with minimum reflection loss (≤1 dB) in the Ku-band (12.4–18 GHz) frequency range. Another formulation (higher content of EG) shows a total shielding effectiveness of more than 81 dB with a reflection loss of 10 dB. In order to probe the relationship between the observed shielding response and the electromagnetic attributes, dielectric and permeability parameters have been calculated from the measured scattering parameters (S11, S22, S12, S21) using the Nicolson–Ross–Weir algorithm. The synthesised formulations were characterized thoroughly using XRD, FTIR, TGA, UV, Raman spectroscopy, SEM and HRTEM.

Lightweight and Easily Foldable MCMB-MWCNTs Composite Paper with Exceptional Electromagnetic Interference Shielding

Lightweight and easily foldable with high conductivity, multiwalled carbon nanotube (MWCNT)-based mesocarbon microbead (MCMB) composite paper is prepared using a simple, efficient, and cost-effective strategy. The developed lightweight and conductive composite paper have been reported for the first time as an efficient electromagnetic interference (EMI) shielding material in X-band frequency region having a low density of 0.26 g/cm(3). The investigation revealed that composite paper shows an excellent absorption dominated EMI shielding effectiveness (SE) of -31 to -56 dB at 0.15-0.6 mm thickness, respectively. Specific EMI-SE of as high as -215 dB cm(3)/g exceeds the best values of metal and other low-density carbon-based composites. Additionally, lightweight and easily foldable ability of this composite paper will help in providing stable EMI shielding values even after constant bending. Such intriguing performances open the framework to designing a lightweight and easily foldable composite paper as promising EMI shielding material, especially in next-generation devices and for defense industries.

Multifunctional, robust, light-weight, free-standing MWCNT/phenolic composite paper as anodes for lithium ion batteries and EMI shielding material

Energy density of Li-ion batteries is marred due to the additional weight of copper, which is used as a current collector. In this work, fabrication of strong, graphitized, multiwalled carbon nanotubes (G-CNTs)/phenolic composite paper using a new dispersion technique is reported. The composite paper has been used as a free-standing current collector, as well as an anode material for Li-ion batteries, because of its good electrical conductivity of 76 S cm−1. This highly thin conductive composite paper (thickness 140 μm) also shows efficient electromagnetic interference (EMI) shielding effectiveness of 32.4 dB in Ku-band (12.4–18 GHz). Moreover, structural and morphological studies were carried out using TEM and SEM. The flexural strength of the composite paper was 30 MPa, which is good enough for use as an electrode in batteries. The electrochemical properties of the composite paper were investigated by galvanostatic charge–discharge test. It exhibits a stable reversible specific capacity for more than 45 cycles. EMI shielding effectiveness (SE) was measured using a vector network analyzer, and the total EMI-SE surpasses the value needed for commercial applications.

Improved microwave absorption in lightweight resin-based carbon foam by decorating with magnetic and dielectric nanoparticles

Carbon foams (CFoams) are sponge-like high performance lightweight engineering materials that possess excellent electrical and mechanical properties as well as thermal stability. CFoams possess bulk density in the range from 0.30 to 0.40 g cm−3 and open porosity of more than 70%. The CFoam consists of pore walls, i.e., ligaments, which are responsible for the conduction path and hence the electrical conductivity due to mobile charge carrier (delocalized π electron), are interconnected to each other. The high value of electrical conductivity causes the CFoam to act as an electromagnetic radiation reflector rather than an absorber; however, in certain applications, shielding materials must be able to absorb the maximum electromagnetic radiation. Therefore, to improve the absorptivity of electromagnetic radiation in lightweight CFoams, the CFoams are decorated by Fe3O4 and ZnO nanoparticles. It is observed that coating with Fe3O4 and Fe3O4–ZnO nanoparticles not only improved the absorption losses but also enhanced the compressive strength of CFoam by 100%. This modified CFoam demonstrated excellent shielding response in the frequency range from 8.2 to 12.4 GHz, in which the total shielding effectiveness (SE) was dominated by absorption losses. The total SE is −45.7 and −48.5 dB of Fe3O4 and Fe3O4–ZnO-coated CFoam, respectively, and it is governed by absorption losses of −34.3 dB and −41.5 dB, respectively. Moreover, the absorption losses increased by 236% in Fe3O4-coated CFoam and 281% in Fe3O4–ZnO-coated CFoam without much enhancement in the bulk density. This is due to the high level of magnetic and dielectric losses of nanoparticles with high surface area. Note that the absorption losses are 80% higher than any value reported for CFoam; thus, lightweight CFoam decorated with magnetic and dielectric nanoparticles is an excellent material for stealth technology.