Enhanced electromagnetic wave absorption properties of polyaniline-coated Fe3O4/reduced graphene oxide nanocomposites

Fe₃O₄-reduced graphene oxide-polyaniline (Fe₃O₄–RGO–PANI) ternary electromagnetic wave absorbing materials were prepared by in situ polymerization of aniline monomer on the surface of Fe₃O₄–RGO nanocomposites. The morphology, structure and other physical properties of the nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, vibration sample magnetism, etc. The electromagnetic wave absorbing properties of composite materials were measured by using a vector network analyzer. The PANI–Fe₃O₄–RGO nanocomposites demonstrated that the maximum reflection loss was ?36.5 dB at 7.4 GHz with a thickness of 4.5 mm and the absorption bandwidth with the reflection loss below ?10 dB was up to 12.0 GHz with a thickness in the range of 2.5–5.0 mm, suggesting that the microwave absorption properties and the absorption bandwidth were greatly enhanced by coating with polyaniline (PANI). The strong absorption characteristics of PANI–Fe₃O₄–RGO ternary composites indicated their potential application as the electromagnetic wave absorbing material.     

Graphene-doped polyaniline nanocomposites as electromagnetic wave absorbing materials

Graphene doped polyaniline (G-PANI) nanocomposites with good electromagnetic properties were synthesized using an in situ emulsion polymerization method. Polyaniline was synthesized in ammonium persulfate and hydrochloric acid solution system. Graphene was added during the polymerization of aniline. Scanning electron microscopy and transmission electron microscopy analyses were performed to characterize the morphology of the nanocomposites. X-ray photoelectron spectroscopy provided the evidence for the oxidation of graphene. Conductivity and electromagnetic performances of polyaniline were improved after graphene doping. The reflection loss of G-PANI showed that the best electromagnetic wave absorbing was achieved at the graphene/polyaniline mass ratio of 1.5?×?10^?3.     

Effect of microwave sintering on the structural, optical and electrical properties of BaTiO3 nanoparticles

BaTiO₃ nanoparticles were prepared by high energy ball milling and subjected to conventional and microwave post sintering at 1,000 °C. From the powder X-ray diffraction results, the synthesized material exhibits strong tetragonality with large c/a ratio. Scanning electron microscope results show the formation of tetragonal shaped BaTiO₃ crystals in the nanometer scale and a significant reduction in the particle size for the microwave sintered sample. The reduced d-spacing of 1.741 Å with high crystallinity for the microwave sintered material is revealed by high resolution transmission electron microscopy analysis. Ultraviolet–visible spectroscopy studies confirm the higher optical band gap (E_g) of 4.157 eV for the microwave sintered sample. Microwave sintered sample shows a very high dielectric constant of ε_r = 4,445 with a low dielectric loss as tan δ = 0.0961. Microwave sintered sample exhibit a high polarization maximum of 73 μC/mm² with reduced coercivity to be 0.293 kV/mm.     

MnO nanorods on graphene as an anode material for high capacity lithium ion batteries

The MnO/graphene hybrid nanocomposites were prepared by an in situ reduction method. The MnO₂ nanorods were attached on the graphene oxides (GOs) to form the MnO₂/GO nanocomposites, which were reduced to the MnO/graphene hybrid under argon atmosphere. As the anode material for the lithium ion batteries, the MnO/graphene electrodes delivered a high initial charge capacity up to 747 mAh g^?1 and a stable capacity of 705.8 mAh g^?1 after 100 cycles, which is much superior to pure MnO with initial charge capacity of 456 mAh g^?1 and the stable capacity of 95.6 mAh g^?1 after 100 cycles. The scanning electron microscope images of the MnO/graphene hybrid nanocomposites after cycling demonstrated that the graphene could prevent the MnO from aggregating during the charge/discharge process.     

Preparation of bilayer graphene utilizing CuO as nucleation sites by CVD method

Graphene is an attractive 2D material for optoelectronics applications. However, due to the spontaneous nucleation characteristics of graphene growth on the metal substrates using chemical vapor deposition method, the polycrystalline graphene exhibited many crystal defects, leading to poor crystal quality. Properly controlling the density of nucleation sites is an important and necessary mean to increase the quality of graphene material. In this work, a new method to synthesize high-quality graphene on Cu substrate was reported by utilizing the CuO nanoparticles as nucleation sites. It was found that when annealing the copper substrate at 300 °C for 30 min with Ar:O₂ flow ratio of 64:1, the copper substrate showed the lowest roughness and the density of CuO nucleation sites after hydrogen etching (H₂ 21 sccm at 1035 °C). Bilayer graphene with diagonal length of ~?3 µm was successfully prepared centering on the CuO nucleation sites. This work supplied a new clue for high quality and monocrystalline graphene preparation.     

Preparation of graphene/TiO2 anode materials for lithium-ion batteries by a novel precipitation method

This paper reports a large-scale production route for graphene/TiO₂ nanocomposites using water-based in situ precipitation method. In this method, freshly prepared graphene oxides/TiO₂ obtained by precipitating Ti(SO₄)₂ with NH₃H₂O was subjected to heat treatment in the presence of N₂, which resulted in the formation of graphene/TiO₂ nanocomposites. Graphene/TiO₂ composites prepared by our method were found to be suitable as anode materials for lithium ion batteries because of its stable cycling performance and high capacity.     

Behaviour of multiphase PVDF in (1−x)PVDF/(x)BaTiO<Subscript>3</Subscript> nanocomposite films: structural,optical, dielectric and ferroelectric properties

The present paper deals with the synthesis and characterization of (1?x)PVDF/(x)BaTiO₃ nanocomposite films with x?=?0.1, 0.2, 0.3, 0.4 and 0.5. The samples were synthesized by simple solution mixing method followed by tape casting process. FESEM images show the homogeneous dispersion of BaTiO₃ nanoparticles within the matrix of poly(vinylidene fluoride) (PVDF) with slight agglomeration. An improvement in the thermal stability of nanocomposite film is observed by TGA results. XRD as well as FTIR analysis indicate the α–β phase transition of PVDF in the nanocomposite films. The embedded BaTiO₃ forms an intermediate band among the PVDF structures and thus decreases the band gap of nanocomposite films by absorbing the wavelength of lower energies. The band gap of nanocomposite films for x?=?0.4 decreases to 2.4 eV as compared to 5.0 eV for pristine PVDF. The dielectric constant (?′) of pristine PVDF at 50 Hz is 8.9, which increases to 26.7 for (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film. An increase in the charge storage ability is observed from PE loops, as (0.6)PVDF/(0.4)BaTiO₃ nanocomposite film has highest value of polarization (0.093 µC cm^?2) as compared to pristine PVDF (0.020 µC cm^?2). This shows an increase in the charge storage ability of (1?x)PVDF/(x)BaTiO₃ nanocomposite films as compared to pristine PVDF.     

Enhanced sensitivity and response speed of graphene oxide/ZnO nanorods photodetector fabricated by introducing graphene oxide in seed layer

Graphene/ZnO nanocomposites photodetectors hold great potential for UV detection because of the combination of photosensitive ZnO and high electron-mobility graphene. In this paper, graphene oxide (GO)/ZnO nanorods photoconductive photodetector with seed layer of GO and ZnO nanocrystals (NCs) hybrids is fabricated via a low-cost solution process. Uniform and oriented GO/ZnO nanorods have been obtained due to the positive role of GO in the growth process of ZnO nanorods, which gives rise to less light scattering and thereby stronger absorption and enhanced photocurrent. When the growth time is 1 h, the optimum photocurrent of GO/ZnO nanorods is about 9.4 times than pure ZnO nanorods, meanwhile, the corresponding detectivity reaches 7.17?×?10¹¹ cm Hz^1/2 W^?1. In addition, owing to the high carrier mobility of graphene, the response time t ₉₀ of GO/ZnO photodetector beneficially decreases to ~1 s, which is much faster than many other GO/ZnO hybrid photodetectors.     

Improvement of electrical properties and thermal conductivity of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO<Subscript>3</Subscript>) by carbon blacks and carbon fibers

The aim of the study was to use carbon fibers and carbon blacks to improve the thermal conductivity, mechanical and dielectric properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO₃) composites. It was found that 7.5 vol% carbon blacks, with high specific surface area, can make complex viscosity of EPDM/BaTiO₃ compound to become non-sensitive to varying shear. Due to the sulfuric atom and C=C groups on surface of carbon blacks, 10 vol% carbon blacks can enhance the tensile strength and tear strength of EPDM/BaTiO₃ (70/30) from 9.00 MPa and 21.06 kN m^?1 to 14.32 MPa (59% increase) and 30.02 kN m^?1 (43% increase). It was found that the 10 vol% spherical carbon blacks with high specific area can partially contact BaTiO₃ and fill the gap between BaTiO₃ particles to increase thermal conductivity and dielectric constant of EPDM/BaTiO₃(70/30) from 0.323 W m^?1 K^?1and 7 at 5 MHz to 0.632 W m^?1 K^?1 (95% increase) and 746 (106 times increase) at 5 MHz, respectively. When the filler content was 10 vol%, carbon blacks and carbon fibers can decrease the volume resistivity of EPDM/BaTiO₃ (70/30) from 2.23?×?10¹³ to 6.37?×?10⁵ Ω m (eight order of magnitude drop) and 4.25?×?10¹¹ Ω m (two order of magnitude drop), respectively.     

Electromagnetic properties and microwave-absorption properties of BaTiO3/BaZn2Fe16O27 composite in 2–18 GHz

BaTiO₃/BaZn₂Fe₁₆O₂₇ composites were prepared by traditional solid state method, BaTiO₃ nano particles were coated around with the BaZn₂Fe₁₆O₂₇ ferrite with hexagonal plate structure. The prepared composite particles were characterized with X-ray diffraction, scanning electron microscopy, and vector network analyzer. With the increase of BaTiO₃ content, the complex permittivity of the composites increases, while the complex permeability decreases; The sharp peaks of the magnetic loss appear at 8.72 and 14.0 GHz, and the peak values are 1.64 and 0.69, respectively, when the mole ratio of BaZn₂Fe₁₆O₂₇/BaTiO₃ is 10:5; The matching thickness of BaTiO₃/BaZn₂Fe₁₆O₂₇ composites is 2.5 mm when the mole ratio of BaZn₂Fe₁₆O₂₇/BaTiO₃ is 10:5, and the minimum reflection loss reaches ?33.49 dB at 8.56 GHz; There are more than one loss peak appeared in the reflection loss cures, and the effective absorption frequency (RL < ?10 dB) ranges from 7.92 to 14.96 GHz with a thickness of 3 mm.     

Preparation and characterization of in situ polymerized cyclic butylene terephthalate/graphene nanocomposites

Graphene-reinforced cyclic butylene terephthalate (CBT) matrix nanocomposites were prepared and characterized by mechanical and thermal methods. These nanocomposites containing different amounts of graphene (up to 5 wt%) were prepared by melt mixing with CBT that was polymerized in situ during a subsequent hot pressing. The nanocomposites and the neat polymerized CBT (pCBT) as reference material were subjected to differential scanning calorimetry, dynamical mechanical analysis, thermogravimetrical analysis, and heat conductivity measurements. The dispersion of the grapheme nanoplatelets was characterized by transmission electron microscopy. It was established that the partly exfoliated graphene worked as nucleating agent for crystallization, acted as very efficient reinforcing agent (the storage modulus at room temperature was increased by 39 and 89 % by incorporating 1- and 5-wt% graphene, respectively). Graphene incorporation markedly enhanced the heat conductivity but did not influence the TGA behavior, except the ash content, due to the not proper exfoliation except the ash content.     

Fabrication and characterization of polyamide 6-functionalized graphene nanocomposite fiber

Graphene oxide was prepared by the Hummers’ method and then functionalized with 4-substituted benzoic acid via “direct Friedel–Crafts” acylation in a mild reaction medium of polyphosphoric acid/phosphorous pentoxide (P₂O₅). Raman spectroscopy, differential scanning calorimetry, thermo-gravimetric analysis, and transmission electron microscopy were used to characterize the resultant structure. The results show that 4-substituted benzoic acid functionalized graphene (FG) sheets were achieved without pretreatment of oxidation. Polycaprolactam (PA6)-FG composites were prepared by in situ polymerization of ε-caprolactam in the presence of FG. Nanocomposite fiber with 0.01–0.5?wt% content of FG was prepared with a piston spinning machine and hot-roller drawing machine. A significant enhancement of mechanical properties of the PA6-FG composites’ fiber is obtained at low graphene loading; that is, a 29?% improvement of tensile strength and a three times increase of Young’s modulus are achieved at a graphene loading of only 0.1?wt%. The “graft-from” methodologies pave the way to prepare graphene-based nanocomposites of condensation polymers with promising performance and functionality.     

Novel X8R-type BaTiO3-based ceramics with a high dielectric constant created by doping nanocomposites with Li–Ti–Si–O

A novel system of temperature-stable Electronic Industries Alliance X8R dielectric materials with high dielectric constants can be obtained by doping BaTiO₃-K_0.5Na_0.5NbO₃ ceramic nanocomposites with 0.7 wt% Li–Ti–Si–O. The dielectric constant is greater than 3,960 at 25 °C, with a dielectric loss lower than 0.8 % and a temperature coefficient of capacitance less than ±12 % from ?55 to 150 °C. The doping increased the degree of tetragonality, grain size, and density, thereby increasing the dielectric constant. We provide additional data on the phase composition, microstructure, and dielectric properties of the doped samples. These materials show high potential for applications in X8R-type multilayer ceramic capacitors.     

Active carbon/graphene hydrogel nanocomposites as a symmetric device for supercapacitors

Activated carbons (ACs) are successfully synthesized from Elaeagnus grain by a simple chemical synthesis methodology and demonstrated as novel, suitable supercapacitor electrode materials for graphene hydrogel (GH)/AC nanocomposites. GH/AC nanocomposites are synthesized via hydrothermal process at temperature of 180°C. The low-temperature thermal exfoliation approach is convenient for mass production of graphene hydrogel (GH) at low cost and it can be used as electrode material for energy storage applications. The GH/AC nanocomposites exhibit better electrochemical performances than the pure GH. Electrochemical performance of the electrodes is studied by cyclic voltammetry, and galvanostatic charge-discharge measurements in 1.0 M H₂SO₄ solution. A remarkable specific capacitance of 602.36 Fg^?1 (based on GH/AC nanocomposites for 0.4 g AC) is obtained at a scan rate of 1 mVs^?1 in 1 M H₂SO₄ solution and 155.78 Fg^?1 for GH. The specific capacitance was increased 3.87 times for GH/AC compared to GH electrodes. Moreover, the GH/AC nanocomposites for 0.2 g AC present excellent long cycle life with 99.8% specific capacitance retained after 1000 charge/discharge processes. Herein, ACs prepared from Elaeagnus grain are synthesized GH and AC supercapacitor device for high-performance electrical energy storage devices as a promising substitute to conventional electrode materials for EDLCs.     

The influence of Graphene quality on performance of a Si/Graphene nanocomposite anode

Si/Graphene nanoparticles represent attractive alternative anode materials for Lithium-ion batteries. Graphene nanosheets with different properties, including surface area, defect distance, and charge-transfer resistance, were fabricated and characterised in Si/Graphene nanocomposites formed by static-electric self-assembly then by an in-situ reduction process. Graphene nanosheets that exhibited the highest surface area, the shortest defect distance, and the lowest charge-transfer resistance demonstrated the best overall electrochemical performance, with a high initial discharge capacity of 2692?mAh?g^?1, good cycling performance of 1135?mAh?g^?1, at the 200th cycle at the current rate of 0.5?C. This work shows the preferable graphene quality for Si/Graphene nanocomposite anode and provides insights into the design of graphene nanocomposite electrodes, regardless of the graphene synthesis method.     

High concentration exfoliation of graphene in ethyl alcohol using block copolymer surfactant and its influence on properties of epoxy nanocomposites

In this work, high concentration exfoliation (～0.2 mg/ml) of graphene in ethyl alcohol is achieved in presence of block copolymer of polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) using sonication followed by centrifugation. The obtained graphene solution is used to prepare epoxy nanocomposites. Flexural tests were conducted over epoxy nanocomposites. The 0.018 wt% of PEO–PPO–PEO block copolymer exfoliated graphene in epoxy matrix shows 21.7% and 15.8% enhancement in flexural modulus and flexural strength respectively as compared to pure epoxy. Transmission electron microscopy reveals well dispersion of graphene in epoxy matrix; and fractography of flexural fractured sample shows graphene dispersion restricts the crack propagation. The well-dispersed graphene in epoxy matrix increase the dielectric constant and thermal stability of epoxy nanocomposites. Further, the enhanced graphene dispersion in epoxy nanocomposites reduces the glass transition temperature (T_g). Thus, enhanced mechanical properties achieved by dispersion of block copolymer exfoliated graphene in epoxy nanocomposites make it suitable for several applications.     

Preparation and microwave absorption properties of polyaniline/Mn0.8Zn0.2Fe2O4 nanocomposite in 2–18 GHz

The polyaniline/Mn_0.8Zn_0.2Fe₂O₄(PANI/MZF) nanocomposite was prepared by an in situ polymerization method. The samples were characterized by Fourier transform infrared spectrometer, X-ray diffraction, scanning electron microscope and vibrating sample magnetometer. The complex permittivity and complex permeability for the nanocomposites were measured by wave-guide method with vector network analyzer in 2.0–18.0 GHz. The reflection losses (R _L ) of the nanocomposites were investigated according to the wave transmission theory. The results showed the maximum reflection loss of the PANI/MZF nanocomposite was about ?20.6 dB at 14.4 GHz with a bandwidth of 5.6 GHz. In conclusion, a wider absorption frequency range could be obtained by adding polyaniline contain in the MZF ferrite. The PANI/MZF nanocomposite is a good microwave shielding and absorbing materials at higher frequency.     

P25/Black phosphorus/Graphene hybrid for enhanced photocatalytic activity

A novel P25/Black phosphorus/Graphene hybrid has been successfully prepared by loading two components [P25 and Black phosphorus (BP)] on graphene nanosheets via a simple one-step hydrothermal method. The P25/BP/Graphene hybrids are characterized by scanning electron microscopy (SEM),Raman spectra and X-ray diffraction patterns, which confirm a good crystallized P25 and BP hybridization with graphene. Photoelectrochemical tests verify that the photocurrent density of as-prepared P25/BP/Graphene ternary hybrid (9.32 μA/cm²) is greatly improved at 1 V, which is nearly 34 times higher than that of sole P25 and 4.8 times as much as that of P25/Graphene. The improved photocatalytic activity is proposed to be benefited from the higher carrier mobility and additional accessible sites derive from the special configurations of ternary hybrid, as well as the introduction of the visible and near-infrared-activated BP photocatalyst. More importantly, this work demonstrates that the as-prepared P25/BP/Graphene hybrid would be an attractive candidate as high-performance photocatalyst, and provide positive proof of concept for developing the practical applications of graphene and black phosphorus based composites.     

Ultrasonication and microwave processing of aluminum alloy- Graphene - Al2O3 nanocomposite

Nanocomposites with Graphene and Al₂O₃ (particulates) as reinforcement combinations with various proportions (weight percentage) in aluminum alloy AA 2024 and AA 2219 matrix with 30 to 40?µm are processed through vacuum hot press and microwave processing approach. X-ray diffraction and Raman spectroscopy analysis was done on developed nanocomposites to study the Graphene peaks, carbide formation, and other deformation on added Graphene in the nanocomposites during microwave processing. Microstructural, compressive, and diametrical tensile strength analyses were also carried out on developed composites. Effect of Graphene addition in combination with Al₂O₃, on strengthening mechanism during microwave sintering, had been discussed.     

Titania-reduced graphene oxide nanocomposite as a promising visible light-active photocatalyst for continuous degradation of VVOC in air purification process

Titania-reduced graphene oxide nanocomposites have been prepared through facile hydrothermal method by a reaction between P25 as TiO₂ source and graphene oxide. Reduction of graphene oxide and its reaction with P25 nanoparticles were achieved simultaneously at high temperature and pressure during the hydrothermal process with the minimum organic solvents. Chemical bonds, crystalline structure, morphology, porosity and light absorption of composites along with their photocatalytic activity under UV and visible light irradiation were investigated. Transmission electron microscopy images showed that P25 nanoparticles, with diameters about 25 nm, were dispersed on the sheets of reduced graphene oxide (RGO) homogeneously. A stronger interaction between P25 and RGO provided a red shift about 20 nm in the absorption edge of the composites. To set up a continuous tubular reactor made from thin layer of the prepared material, composite films were coated on the external surface of a steel tube to make an annular reactor. The reactor was equipped with UV or visible light sources to investigate the photocatalytic activity of the prepared composites in a continuous air flow contaminated with specified amount of acetaldehyde as a VVOC (very volatile organic compound) model molecule. Degradation efficiency of P25–RGO with 0.5 wt% RGO was significantly high under visible light irradiation, and about 70% conversion was observed using an air flow at normal conditions with specific flow rate of 17 ml min^?1 and 500 ppm acetaldehyde, by 30 mg of the coated composite in the reactor. Composites with low amount of RGO would be an appropriate photosensitizer and electron acceptor to suppress the recombination of photogenerated electron–hole pairs to enhance the photocatalytic performance.