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Lightweight, flexible, and thin nanocomposite structures providing enhanced electromagnetic interference (EMI) shielding in the desired frequency band are required for future generations of curved and bendable electronic devices. The present work deals with designing and developing such types of nanocomposite structures based on 2–8 wt% graphene nanoplatelets (GNPs) embedded in the polyurethane matrix. The GNP in the present situation is synthesized through the microwave intercalation technique followed by ultrasonication. It is observed that the 6 wt% of GNP (GNP6) having a density of 0.74 g/cc provides enhanced conductive and dielectric properties in the specified frequency band. The maximum value of total shielding effectiveness (SET) achieved here is 22.11 dB for GNP6 at 0.35 mm thickness. The strength of the proposed flexible structure is ascertained by measuring the SET of GNP6 after mechanically bending it for 500 cycles. The mechanism contributing to the high SET is explained based on their microstructure and frequency-dependent dielectric profile. The SET is numerically analyzed by simulation using the CST microwave studio in 8–18 GHz for broadband electromagnetic shielding application. The fabricated lightweight flexible nanocomposite structures show high EMI shielding, making them appropriate for conformal electronic packaging and thin coating in military and space applications. [ABSTRACT FROM AUTHOR]

In recent years, heteroatoms-doped graphene, with its exceptional properties, has generated significant advances in many fields of modern nanoscience and nanotechnology. With the rapid progress in doped graphene research, advanced graphene materials have been developed and frequently used in electromagnetic shielding applications. In this context, heteroatom-doping of graphene materials has been considered as an efficient strategy for the development of novel electromagnetic interference (EMI) shielding materials. This article aims to provide a timely update on the synthesis and EMI shielding applications of doped graphene materials. Heteroatom-doped and co-doped graphene-based materials (n-type and p-type doping) have been synthesized using various chemical and physical routes. Extensive approaches and strategies have been applied for achieving the intended doping/co-doping levels in graphene-based materials. Doping in graphene and its derivatives induces the formation of defects, changing the electrical conductivity as well as the mechanical properties. This results in an increase of reflection, and an improvement of absorption, enhancing shielding effectiveness. This review article provides a comprehensive overview of doping strategies for graphene and related composites, their EMI shielding performance, as well as comments on the future perspectives and possible challenges for doped graphene-based materials. We hope this review article offers a valuable starting point for researchers entering the field, providing an overview of synthesis approaches and EMI shielding applications. [ABSTRACT FROM AUTHOR]

In the present study, low defect density graphene nanosheets (GNs) have been synthesized via chemical reduction of exfoliated graphite (EG) in the presence of a green reducing agent, oxalic acID. EG has been synthesized via chemical intercalation of natural flake graphite followed by exfoliation through microwave irradiation at 800?W for 50?s. 50?mg/mL concentration of oxalic acID helps to extract low defect density GNs from EG. As-synthesized GNs have been characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV-Visible spectroscopy, field emission scanning electron microscopy, and X-ray photon spectroscopy. Raman analysis confirms the removal of oxygen functional groups from EG and achieved an ID/IG ratio of ∼0.10 with low defect density (∼1.12?×?1010?cm-2). Elemental analysis supports the Raman sIGnature of the removal of oxygen functionalities from EG, and a hIGh C/O ratio of ∼15.97 is obtained. Further, transparent conducting films (TCFs) have been fabricated by spray coating. The optical and electrical properties of fabricated TCFs have been measured after thermal graphitization. Thermal graphitization helps to improve the optical and electrical properties of TCFs by tuning the optical bandgap in a controlled way. TCF shows best performance when the film is annealed at 900?°C for 1?h in vacuum. It shows a sheet resistance of ∼1.10?kΩ/? and a transmittance of ∼71.56% at 550?nm. [ABSTRACT FROM AUTHOR]

The integration of nanomaterials with the micro-wave technology is a significant step toward the development of low-cost and low-power RF gas sensors. But, the issues associated with materials like insignificant surface area and poor conductivity, are barriers for the rapid detection of wide range of gas concentrations. In this paper, we demonstrate the proof-of concept using an RF complementary split ring resonator (CSRR) integrated ZnO/N-doped graphene (NGN) nano-hybrid to study the gas sensing properties. This RF device senses the presence of ammonia based on the change in the electrical conductivity of the nanohybrid material upon gas exposure. For this, we have designed and fabricated various new CSRR structures, namely, the meander (M-CSRR) and the CSRR, with the concentric-etched square pattern (SP-CSRR) other than the conventional CSRR (C-CSRR). The fabricated CSRRs are coated with the solvothermal methodically prepared ZnO/NGN nanomaterials and a comparison among them is also made. The comparison revealed that the SP-CSRR coated ZnO/NGN sensor had the maximum shift in the S21 resonance frequency ($\Delta \text {f}_{\mathbf {S21}} = 13$ MHz at 100 ppm) among all at room temperature. Furthermore, the SP-CSRR-ZnO/NGN sensor exhibited a large-S21 frequency shift of 133 MHz for 500 ppm of ammonia and has shown excellent reproducibility with 0.05% of variation. We have also projected the plausible sensing mechanism for this RF sensing device. [ABSTRACT FROM AUTHOR]

Composite prepared by mixing of different forms of carbon or other reinforcing fillers with polymer, is one of the possible ways to enhance the performance of polymeric materials. The present work focuses on the study of viscoelastic, thermal, electrical and mechanical properties of graphite flake-reinforced high-density polyethylene composites. The composites are processed by melt mixing using vertical twin-screw micro-compounder followed by final sample preparation via micro injection moulding. The reinforcing filler, graphite flake, is varied from 0 to 50 vol.% with respect to the polymer matrix. Dynamic mechanical thermal analysis reveals an increase in the storage modulus (E′) as well as loss modulus (E″) throughout the temperature range; however, damping (tan δ) shows a mixed behaviour. There is 550% and 479% increase of E′ and E″ in the rubbery region. Degree of entanglement, reinforcement efficiency and C factor are also calculated and correlated with the mechanical properties. On comparison, high-density polyethylene /graphite flake composite having 50 vol.% graphite flake with pure high-bcdensity polyethylene shows 52% increase in melt viscosity, whereas bulk density increases by 38%. This graphite flake is also responsible for the increase in the thermal stability (shift in the onset degradation temperature of ∼7℃ and the degradation temperature is more than 400℃), thermal conductivity (175% improvement) and electrical conductivity (∼6125% improvement, as the conductivity of pristine high-density polyethylene is ∼9.67 E-08 S/m). Mechanical properties determined by tensile and flexural tests show an initial increase and then a slight decrease in the tensile and flexural strength. Therefore, the graphite flake-reinforced high-density polyethylene composite with improved thermal conductivity, electrical conductivity, heat stability, viscoelastic behaviour and flexural modulus can be a promising as well as suitable composite material for making of various electronic and electrical accessories including bipolar plate for fuel cell applications. [ABSTRACT FROM AUTHOR]

In the present work, silver nanoparticles (Ag NPs)/graphene nanocomposite has been synthesized successfully by simple solvothermal method via green route. Citric acid is used as green reducing agent for the reduction of graphene oxide (GO) and Ag ions. Silver nitrate is used as a precursor material for Ag NPs. As synthesized Ag NPs/graphene nanocomposite has been characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infra-red spectroscopy, UV–vis spectroscopy, thermal gravimetric analysis, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Experimental results confirm the reduction of GO and the successful formation of Ag NPs decorated graphene nanosheets. In addition, spray coating technique is employed for the fabrication of transparent conducting films. Enhancement in the optoelectrical signatures has been achieved using thermal graphitization of fabricated films. Thermal graphitization at 800 °C for 1 h marks the best performance of fabricated film with sheet resistance of ~3.4 kΩ/□ and transmittance (550 nm) of ~66.40%, respectively. [ABSTRACT FROM AUTHOR]

In the present study, nitrogen doped graphene sheets (NGNs) have been synthesized by solvothermal reaction using cow urine as a natural dopant of N atoms, which is an alternative of highly toxic chemicals with excellent reducing capability. As synthesized NGNs have been characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), UV–visible spectroscopy (UV–vis), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), surface area (Brunauer-Emmett–Teller (BET)) and X-ray photon spectroscopy (XPS). Raman analysis reveals that the reduction of oxygen occurs from graphene oxide (GO) by cow urine, and reaches Raman D to G band intensity ratio of ∼1.23. XPS analysis validates the Raman signature of removal of oxygen functional groups, simultaneously N-atoms are successfully doped into honeycomb lattice, and produces GNs with high C/O ratio of ∼5.25 having N content ∼3.4 at.%. The presence of N atoms produces defect morphology in graphene structure that eventually enhances the overall electrical properties of NGNs. The NGN-epoxy nanocomposites have been fabricated for the investigation of the electromagnetic responses generated exclusively in the X band (8.2–12.4 GHz). A maximum absorption value of −40.8 dB (99.992% absorption) as well as 1.5 GHz of −10 dB effective bandwidth is observed with 2 wt.% of NGNs loadings. The strong microwave absorption is due to the electric, dielectric, interfacial polarization, and nitrogen generated defect polarization canters. Moreover, NGNs with unique disordered structure can regulate the electromagnetic properties to attain the best impedance matching criteria. This investigation opens a novel useful eco-friendly approach for the development of NGNs structure for highly efficient, light weight and low cost microwave absorber. [ABSTRACT FROM AUTHOR]

Laser-based methodologies for synthesis, reduction, modification and assembly of graphene-based materials are highly demanded for energy-related electrodes and devices for portable electronics. Laser technologies for graphene synthesis and modification exhibit several advantages when compared to alternative methods. They are fast, low-cost and energy saving, allowing selective heating and programmable processing, with controlled manipulation over the main experimental parameters. In this review, we summarize the most recent studies on laser-assisted synthesis of graphene-based materials, as well as their modification and application as electrodes for supercapacitor and battery applications. After a brief introduction to the physical properties of graphene and a discussion of the different types of laser processing operations, the practical uses of laser techniques for the fabrication of electrode materials are discussed in detail. Finally, the review is concluded with a brief discussion of some of the outstanding problems and possible directions for research in the area of laser-based graphene materials for energy storage devices. [ABSTRACT FROM AUTHOR]

In the present study, the green approach has been adopted for the reduction of graphene oxide (GO) using cow urine and urea, which were further spray-coated to fabricate graphene nanosheets (GNs) based transparent conducting films (TCFs). Raman analysis reveals the I D /I G intensity ratio of ~1.25, 1.39 for synthesized GNs by cow urine and urea, respectively. It indicates the removal of oxygen spices from GO, which is further confirmed by elemental analysis and FTIR. XRD, Raman and Urbach energy confirm the enhanced defects and lattice disorders, which are attributed to nitrogen incorporation, vacancies, and other structural defects. The presence of pyridinic-N defects as revealed by XPS and other structural defects has changed the electrical and optical properties of GNs. A detailed comparative study has been done to compare the electrical and optical properties of spray-coated TCFs over the quartz substrate. The enhanced conductivity in CGF (coated film using GN synthesized by cow urine) and UGF (coated film using GN synthesized by urea) might be due to presence of pyridinic-N and oxygen species removal, while enhanced transmissivity is due to presence of less number of graphene layers. UGF, which is thermally annealed at 900 °C shows the best performance with sheet resistance ~1.78 kΩ/□ and transmittance ~71.16%. Image 1 • GNs have been synthesized via green route avoiding hazardous chemicals. • Structural defects affect electrical conductivity and optical transparency. • Spray coating technique has been used for the one step fabrication of GNs based TCFs. • Best performance of TCF exhibits sheet resistance ~1.78 kΩ/□ and transmittance ~71.16%. [ABSTRACT FROM AUTHOR]