One-step synthesis,electromagnetic and microwave absorbing properties of α-FeOOH/polypyrrole nanocomposites

One-step synthesis of α-FeOOH/polypyrrole (PPy) nanocomposites is reported for the first time via a facile one-step chemical method in the presence of OH⁻, Fe²⁺, Fe³⁺ and pyrrole monomer. α-FeOOH nanorods are in situ formed in PPy matrix and the content of α-FeOOH nanorods increases with decreasing the molar ratio of pyrrole to Fe²⁺ ([Py]/[Fe²⁺] ratio). The electromagnetic and microwave absorbing properties of the nanocomposites are investigated as a function of the [Py]/[Fe²⁺] ratio. The results show that the PPy nanocomposites exhibit good conductivity (up to 16.10 S/cm) and antiferromagnetic behavior. The reflection loss evaluation based on the absorbing wall theory at the thickness of 2 mm shows that the nanocomposite at [Py]/[Fe²⁺] = 1.0 exhibits the best microwave absorbing property in the 2–18 GHz. And the corresponding reflection frequency range under −10 dB and −5 dB is 4.2 GHz and 5.8 GHz, respectively.     

Low-temperature synthesis of manganese oxide–carbon nanotube-enhanced microwave-absorbing nanocomposites

Noting that the dielectric properties of manganese oxide make it a promising microwave-absorbing material, a low-temperature method to deposit crystalline MnO₂ over carbon nanotubes (CNTs) is developed. Adjusting the pH of the precursor solution allows control over the phases and morphologies of the synthesized manganese oxides MnO₂ and Mn₃O₄ that have minimum reflection losses of ??11 dB and ??6 dB, respectively. The synthesized CNT–MnO₂ and CNT–Mn₃O₄ nanocomposites are superior microwave absorbers than simpler physical mixtures of CNTs and manganese oxides, with reflection losses as high as ??19 dB at 9.5 GHz and ??34 dB at 4 GHz, and have wider absorption bands than pure manganese oxides. Coating CNTs with manganese oxide not only increases dielectric and magnetic losses, but also improves the impedance match between free space and the absorber. The addition of CNTs to pure MnO₂ and Mn₃O₄ improves impedance matching by enhancing the relaxation polarization and conductivity losses, magnetic loss, including contributions form eddy current and natural resonance. This facile, low-cost, scalable, high-yield method produces an enhanced microwave-absorbing nanocomposite.     

One-step synthesis of mesoporous silica–graphene composites by simultaneous hydrothermal coupling and reduction of graphene oxide

Silica–graphene oxide composites were synthesized by hydrothermal method with simultaneous functionalization and reduction of graphene oxide (GO) in the presence of mesoporous silica. Two types of silica were used in the study, mesoporous synthetic silica (MSU-F) synthesized by sol-gel method and mesoporous mineral silica (meso-celite) from pseudomorphic synthesis. The infrared spectra of the composites showed the disappearance of the carboxyl peak at 1735 cm^-1 which could be due to the reduction of the –COOH group. The enhancement of the band at 1385 cm^–1 is attributed to the vibration of the Si–O–C=O moiety formed by reaction of the –COOH group of GO and the silanol (Si–OH) of silica. The Raman spectra of the composites show a diminished intensity ratio of D to G band indicating that GO was reduced to graphene sheets. The TEM images demonstrate the coupling of silica to GO surface revealing dense loading of silica on GO in planar structure.     

One-step synthesis of Co–Ni ferrite/graphene nanocomposites with controllable magnetic and electrical properties

Co_1−xNi_xFe₂O₄/graphene nanocomposites were synthesized through a one-step solvothermal method. The as-synthesized products were characterized by X-ray powder diffraction, field emission scanning microscopy, transmission electron microscope, and high-resolution transmission electron microscope. The results show that the Co_1−xNi_xFe₂O₄ nanoparticles are uniformly dispersed on graphene sheets. The dependence of structure, magnetic and electrical properties of Co_1−xNi_xFe₂O₄/graphene nanocomposites on the Ni²⁺ concentration and the graphene content were also studied. The saturation magnetization and electrical conductivity of the as-prepared products reached 51.82 emu/g and 1.00 × 10² S/m, respectively.     

Thermal decomposition of β-FeOOH

β-FeOOH particles were prepared by a forced hydrolysis of the 0.1 M FeCl₃ + 5·10⁻³ M HCl solution, whereas sulfated β-FeOOH particles were prepared by forced hydrolysis of the 0.1 M FeCl₃ solution containing 5·10⁻³ M quinine hydrogen sulfate (QHS). β-FeOOH particles, as well as sulfated β-FeOOH particles, were thermally treated up to 600 °C. The samples were characterized using DTA, XRD, FT-IR and TEM. β-FeOOH particles showed a cigar-type morphology, whereas bundles of β-FeOOH needles were obtained in the presence of QHS. Heating of β-FeOOH particles at 300 °C and above yielded α-Fe₂O₃ particles. Specific adsorption of sulfate groups showed a strong effect on the thermal decomposition of β-FeOOH particles. Upon heating of sulfated particles between 300 and 500 °C the formation of an amorphous phase and a small fraction of α-Fe₂O₃ were observed. Needle-like morphology of amorphous particles in these samples was preserved. At 600 °C, α-Fe₂O₃ particles were obtained; however, they were much smaller than those obtained by heating a pure β-FeOOH.     

Fabrication of reduced graphene oxide nanosheets reinforced Sn–Bi nanocomposites by electro-chemical deposition

Novel Sn–Bi/reduced graphene oxide nanosheets (RGOS) nanocomposites were fabricated using electro-chemical deposition process at room temperature. The RGOS dispersed and distributed in Sn–Bi alloy. Nano-sized Sn–Bi grain clusters grew on the surface of RGOS and the Sn–Bi grains became finer after the incorporation of RGOS. The mechanical properties including micro-hardness and shear strength were enhanced by the incorporation of RGOS. The enhance mechanism of RGOS in Sn–Bi/RGOS nanocomposites was proposed by finite element method simulation. The graphene with extra-thin thickness and huge aspect ratio lead to an effective stress transfer and stress concentration occurs near the edge of graphene. The Sn–Bi/RGOS nanocomposites are promising in application as TIM of high power electronics, integrated circuits.     

The sensitive electrical response of reduced graphene oxide–polymer nanocomposites to large deformation

In this paper, the reduced graphene oxide (rGO)–polymer nanocomposite films were prepared by two comparable methods, and their electrical performances at large deformation were measured and analyzed. It is concluded that the gauge factor (GF) value of strain-sensing composite strongly depends on rGO’s content and preparing process. The composites with rGO’s content between percolation threshold and the content which rGO conducting as a complete network show better sensitive electrical response. What’s more, strong interface interaction between conducting filler and matrix benefits the improvement of GF value. The composites we prepared display significant and consistent changes in their GF values when subjected to large deformation, which are suitable for large structural deformation monitoring in advanced civil engineering.     

Preparation and characterization of epoxy/γ-aluminum oxide nanocomposites

Epoxy/γ-Al₂O₃ nanocomposites were prepared with a homogenizer and followed by a stepwise thermal curing process in this study. The dispersion of γ-Al₂O₃ nanoparticles was examined with a transmission electron microscopy (TEM). Meanwhile, the effects of γ-Al₂O₃ nanoparticles on thermal, dynamic mechanical and tensile properties of epoxy/γ-Al₂O₃ nanocomposites were also investigated and discussed. When the γ-Al₂O₃ content was increased from 1phr to 5phr, results revealed that γ-Al₂O₃ nanoparticles were effective to enhance both the stiffness and toughness of epoxy resin. Meanwhile, the maximum properties of glass transition temperature (T_g), T_d5%, storage modulus, tensile modulus, and elongation at break were observed in the epoxy/5phr γ-Al₂O₃ nanocomposite.     

Size-controlled synthesis of Rod-like α-FeOOH nanostructure

One-dimensional goethite (α-FeOOH) nanorods were successfully fabricated by a hydrothermal route without any template. Experimental results reveal that concentrations of Fe^3 + and ethylenediaminetetraacetic disodium salt (Na₂EDTA) affect the phase composition and size of the as-synthesized products. The size of the rod-like α-FeOOH increased when the concentration of Na₂EDTA was increased, where Na₂EDTA acts as a nucleation inhibitor. α-Fe₂O₃ nanoparticles were produced when the concentration of Fe^3 + was increased from 0.02 to 0.08 and 0.40 M. A possible formation mechanism was proposed based on the results of the time dependent experiments. Different electrolytes and surfactants can affect the size and the aspect ratio of the as-prepared nanorod-like α-FeOOH. Na₂SO₄ induced the decreasing of the size of the as-prepared sample. KCl and PVP affected the aspect ratio of the nanorods.     

Facile synthesis of α-MnO2/graphene nanocomposites and their high performance as lithium-ion battery anode

α-MnO₂/graphene nanocomposites are synthesized via a facile wet-chemical route, and α-MnO₂ nanosheets are uniformly distributed on the surface of graphene. Their high performance as lithium ion battery anodes is obtained. Their reversible capacity at C/10 rate is up to 726.5 mA h/g, and maintains up to 635.5 mA h/g after 30 cycles. Such a performance can be partly attributed to high electron conductivity, excellent flexibility and high specific surface area of graphene. Also, α-MnO₂ nanostructures can play a role in preventing the pile of graphene nanosheets with the loss of their active surface area. The present results indicate that α-MnO₂/graphene nanocomposites have potential applications in lithium-ion battery anodes.     

In situ controllable synthesis of Ag@AgCl core–shell nanoparticles on graphene oxide sheets

Graphene oxide-supported uniform Ag@AgCl core–shell nanoparticle composites have been successfully prepared by a facile two-step synthetic process. First, graphene oxide sheets were used as carriers to anchor and disperse Ag nanoparticles on their surface. Then these fixed Ag nanoparticles on carbon sheets are utilized as precursors, around which AgCl nanocrystals form in situ using FeCl₃ as oxidant, forming graphene oxide-supported Ag@AgCl core–shell nanoparticle composites. The composition of these attached Ag@AgCl core–shell nanoparticles can be easily controlled by adjusting the usage of FeCl₃, resulting in the formation of controllable core–shell nanostructures. Furthermore, these as-prepared graphene oxide–Ag@AgCl nanoparticle composites display effective photodegradation of methylene orange dye under visible light irradiation, which indicates their potential applications in environmental areas.     

Tribological performance of carbon nanotube–graphene oxide hybrid/epoxy composites

An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr.     

Facile synthesis of reduced graphene oxide–gold nanohybrid for potential use in industrial waste-water treatment

Here, we report a facile approach, by the photochemical reduction technique, for in situ synthesis of Au-reduced graphene oxide (Au-RGO) nanohybrids, which demonstrate excellent adsorption capacities and recyclability for a broad range of dyes. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) data confirm the successful synthesis of Au-RGO nanohybrids. The effect of several experimental parameters (temperature and pH) variation can effectively control the dye adsorption capability. Furthermore, kinetic adsorption data reveal that the adsorption process follows a pseudo second-order model. The negative value of Gibbs free energy (ΔG⁰) confirms spontaneity while the positive enthalpy (ΔH⁰) indicates the endothermic nature of the adsorption process. Picosecond resolved fluorescence technique unravels the excited state dynamical processes of dye molecules adsorbed on the Au-RGO surface. Time resolved fluorescence quenching of Rh123 after adsorption on Au-RGO nanohybrids indicates efficient energy transfer from Rh123 to Au nanoparticles. A prototype device has been fabricated using Au-RGO nanohybrids on a syringe filter (pore size: 0.220 μm) and the experimental data indicate efficient removal of dyes from waste water with high recyclability. The application of this nanohybrid may lead to the development of an efficient reusable adsorbent in portable water purification.     

How can graphene reduce the flammability of polymer nanocomposites?

Nanocomposites based on poly(vinyl alcohol) (PVA) and graphene nanosheets have been prepared by polymer solution blending and their flame retardant properties have been evaluated by a cone calorimetry test. It has been shown that there is a strong influence of graphene nanosheets on the fire behaviour of the composites with a significant reduction in peak heat release rate (PHRR) and a much longer time to ignition. Compared to pure PVA, the PHRR of PVA filled with 3 wt.% graphene is reduced by 49%. The flame retardancy of graphene for PVA matrix surpasses that of both Na-MMT and MWNTs with the same addition content. Such a remarkable behaviour might be explained by the forming of a compact, dense and uniform char during combustion.     

A novel combined molecular dynamics–micromechanics method for modeling of stiffness of graphene/epoxy nanocomposites with randomly distributed graphene

In this paper, by combining molecular dynamics and micromechanics methods, a new approach for prediction of the stiffness of the nanocomposites with randomly distributed nanoparticles in the macro level is presented. The molecular dynamics method is used to model the stiffness of the graphene/epoxy nanocomposites containing one layer of an aligned nano graphene embedded in epoxy resin. By considering the large sizes of the length and width of the nano graphene in comparison with its thickness and the shortcomings of the available hardware and software for simulation purposes, a new approach for modeling is also developed. This new approach, by using the moduli of different graphene sheets with different sizes embedded in a representative volume element, can predict the moduli of a real size graphene embedded in the matrix along the longitudinal, transverse and normal directions in the nano-scale. In order to consider the effect of the random distribution of graphene sheets in epoxy resin, a micromechanical approach is used. The results obtained by the molecular dynamics method are used by the micromechanics approach and the stiffness of graphene/epoxy nanocomposites with randomly distributed graphene in the macro-scale is predicted. An experimental program is conducted to evaluate the capability of the model. The result of the modeling is in a very good agreement with the experimental data.     

Preparation and supercapacitive performance of manganese‐cobalt sulfide/silver nanowires/graphene ternary nanocomposites

Journal of Materials Science: Materials in Electronics - Bimetallic sulfides are potential and attractive electrode materials for high-performance supercapacitors. In this study, the...     

Effect of zinc oxide concentration on the core–shell ZnS/ZnO nanocomposites

In this work, synthesis and characterization of core–shell zinc sulphide (ZnS)/zinc oxide (ZnO) nanocomposites has been reported to see the effect of ZnO concentration in core–shell combination. The nascent as well as core–shell nanostructures were prepared by a chemical precipitation method starting with the synthesis of nascent ZnS nanoparticles. The change in morphological and optical properties of core–shell nanoparticles was studied by changing the concentration of ZnO for a fixed amount of ZnS. The nascent ZnS nanoparticles were of 4–6 nm in diameter as seen from TEM, each containing primary crystallites of size 1.8 nm which was estimated from the X-ray diffraction patterns. However, the particle size increases appreciably with the increase in ZnO concentration leading to the well known ZnO wurtzite phase coated with FCC phase of ZnS. Band gap studies were done by UV–visible spectroscopy and it shows that band gap tunability can be achieved appreciably in case of ZnS/ZnO core–shell nanostructures by varying the concentration of ZnO. Fourier transform infrared analysis also proves the formation of core–shell nanostructures. Photoluminescence studies show that emission wavelength blue shifts with the increase in ZnO concentration. These core–shell ZnS/ZnO nanocomposites will be a very suitable material for any type of optoelectronic application as we can control various parameters in this case in comparison to the nascent nanostructures.