Graphene nanofl akes and hybrid nanocomposites with gold and silver nanoparticles: optical and thermal properties

Russian Chemical Bulletin - New technologies for the preparation of graphene nanofl akes (GNF) with noble metal nanoparticles (NPs), specifi cally Au and Ag, as well as hybrid nanocomposites...     

Carbon nanostructure-derived polyaniline metacomposites: electrical, dielectric, and giant magnetoresistive properties

Polyaniline (PANI) nanocomposites incorporating different loadings of graphene and various other carbon nanostructures including carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have been synthesized using a surface-initiated polymerization (SIP) method. Transmission electron microscopy (TEM) results indicate that the graphene has been exfoliated into a few layers (typically one, two, and three layers) during polymerization and has been uniformly dispersed in the PANI matrix. The graphene layer dispersion degree is quantified by a free-path spacing measurement (FPSM) method based on the TEM microstructures. The SIP method also demonstrates its feasibility for coating PANI on one-dimensional (1D) CNFs and CNTs without introducing additional surface functional groups. The effects of graphene size, loading level, and surface functionality on the electrical conductivity and dielectric permittivity of their corresponding nanocomposites have been systematically studied. The temperature-dependent conductivity behavior revealed a quasi-3D variable range hopping (VRH) electron transport mechanism for all the nanocomposites. Giant magnetoresistance (GMR) at room temperature is observed in pure PANI, which can be enhanced by the incorporation of a high loading of graphene (5%) due to the π-π stacking-induced efficient electron transport at the PANI/graphene interface. More interestingly, negative permittivity is found in each composite which can be easily tuned by adjusting the filler loading, morphology, and surface functionality.     

Theoretical Design and Experimental Realization of Quasi Single Electron Enhancement in Plasmonic Catalysis

By a combination of theoretical and experimental design, we probed the effect of a quasi‐single electron on the surface plasmon resonance (SPR)‐mediated catalytic activities of Ag nanoparticles. Specifically, we started by theoretically investigating how the E‐field distribution around the surface of a Ag nanosphere was influenced by static electric field induced by one, two, or three extra fixed electrons embedded in graphene oxide (GO) next to the Ag nanosphere. We found that the presence of the extra electron(s) changed the E‐field distributions and led to higher electric field intensities. Then, we experimentally observed that a quasi‐single electron trapped at the interface between GO and Ag NPs in Ag NPs supported on graphene oxide (GO‐Ag NPs) led to higher catalytic activities as compared to Ag and GO‐Ag NPs without electrons trapped at the interface, representing the first observation of catalytic enhancement promoted by a quasi‐single electron.     

SnS2–graphene nanocomposites as anodes of lithium-ion batteries

SnS₂–graphene nanocomposites are synthesized by a hydrothermal method, and their application as anodes of lithium-ion batteries has been investigated. SnS₂ nanosheets are uniformly coating on the surface of graphene. SnS₂–graphene nanocomposites exhibit high cyclability and capacity. The reversible capacity is 766 mAh/g at 0.2C rate and maintains at 570 mAh/g after 30 cycles. Such a high performance can be attributed to high electron and Li-ion conductivity, large surface area, good mechanical flexibility of graphene nanosheets and the synergetic effect between graphene and SnS₂ nanostructures. The present results indicate that SnS₂–graphene nanocomposites have potential applications in lithium-ion battery anodes.     

High strain rate compression testing of intra-ply and inter-ply hybrid thermoplastic composites reinforced with Kevlar/basalt fibers

In this study, the influence of hybridization on the compression response of thermoplastic matrix-based composites under high strain rate loading was investigated. The intra-ply and inter-ply hybrid composites were manufactured with Kevlar/Basalt yarns as the reinforcements with Polypropylene as a matrix. Cylindrical composite specimens were laser cut from the flat compression moulded laminates. The composite specimens were loaded under high strain rate using split-Hopkinson pressure bar setup at strain rates ranging from 2815/s to 5481/s. The study revealed differences in the rate-dependent growth of peak stress, peak strain and toughness with the strain rate. Intra-ply hybrid composites with alternate weaving of Kevlar and basalt yarns exhibited highest peak stress as compared to the Inter-ply hybrid composites (alternate layers of Kevlar and basalt fabrics) and another intra-ply composite containing Kevlar in the warp and basalt in the weft direction. Whereas in inter-ply hybrid composite, with Kevlar as the loading face attained higher stress, while composite with Basalt as the loading face attained higher strain. SEM micrographs revealed that Kevlar on the loading face can bear the impact with lesser delamination as compared to the Basalt on the loading face. Damage studies revealed that Kevlar fiber surface loading results in higher stress as compared to basalt (brittle) surface loading with lower overall damage.     

Fe3O4 nanoparticle-integrated graphene sheets for high-performance half and full lithium ion cells

We synthesized Fe(3)O(4) nanoparticle/reduced graphene oxide (RGO-Fe(3)O(4)) nanocomposites and evaluated their performance as anodes in both half and full coin cells. The nanocomposites were synthesized through a chemical co-precipitation of Fe(2+) and Fe(3+) in the presence of graphene oxides within an alkaline solution and a subsequent high-temperature reduction reaction in argon (Ar) environment. The morphology and microstructures of the fabricated RGO-Fe(3)O(4) nanocomposites were characterized using various techniques. The results indicated that the Fe(3)O(4) nanoparticles had relatively homogeneous dispersions on the RGO sheet surfaces. These as-synthesized RGO-Fe(3)O(4) nanocomposites were used as anodes for both half and full lithium-ion cells. Electrochemical measurement results exhibit a high reversible capacity which is about two and a half times higher than that of graphite-based anodes at a 0.05C rate, and an enhanced reversible capacity of about 200 mAh g(-1) even at a high charge/discharge rate of 10C (9260 mA g(-1)) in half cells. Most important of all, these fabricated novel nanostructures also show exceptional capacity retention with the assembled RGO-Fe(3)O(4)/LiNi(1/3)Mn(1/3)Co(1/3)O(2) full cell at different C rates. This outstanding electrochemical behavior can be attributed to the unique microstructure, morphology, texture, surface properties of the nanocomposites, and combinative effects from the different chemical composition in the nanocomposites.     

LDPE/EVA/graphene nanocomposites with enhanced mechanical and gas permeability properties

In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low‐density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1‐nm thickness and good transparency was synthesized using the well‐known Hummers's method. Fourier transform infrared and X‐ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are improved 65% and 92% by adding 7 wt% of GO and RGO, respectively. The tensile measurements showed that maximum tensile strength emerged in 3 wt% of loading for RGO and 5 wt% for GO. The measured oxygen and carbon dioxide permeability represented noticeably the attenuation of gas permeability in composite films compared with pristine LDPE/EVA blend. Copyright © 2015 John Wiley & Sons, Ltd.     

石墨烯负载新型π-共轭聚合物纳米复合电极材料的合成及其超级电容特性

采用γ射线辐照还原技术获得易分散石墨烯(GNS),并以其为载体,以樟脑磺酸为掺杂剂和软模板,借助化学氧化聚合方法制备出分级孔结构的石墨烯负载聚(1, 5-二氨基蒽醌)(GNS@PDAA)纳米复合材料。运用傅里叶变换红外(FTIR)光谱、拉曼光谱(Raman)、原子力显微镜(AFM)、能谱仪(EDS)、场发射扫描电镜(FE-SEM)和电化学测试等手段研究了不同GNS/DAA质量比对GNS@PDAA复合材料的形貌、结构及超级电容特性的影响。研究表明,当DAA/GNS质量比为6/1时,借助π-π堆叠和网络限域作用, PDAA以20-40 nm纳米颗粒的形式牢固沉积于石墨烯表面,材料内部存在大量10-30 nm尺寸的介孔。该GNS@PDAA复合材料在0.5 A·g^-1时呈现最高的比电容(398.7 F·g^-1),优异的倍率特性(在50 A·g^-1下比电容保持率为71%)和非常好的循环性能(20000次循环后比电容损失仅为8.3%)。进而证实了GNS@PDAA复合材料所组装的超级电容器具有优异的串并联特性。     

石墨烯及其聚合物复合材料

近些年来,石墨烯以其独特的结构和优异的性质成为备受瞩目的研究前沿和热点。石墨烯作为纳米增强组分,少量添加可以使聚合物的物理性能得到大幅地提高。本文就石墨烯及其在聚合物复合材料的研究进展进行了综述,着重阐述了现已工业化制备石墨烯的氧化还原法,以及石墨烯/聚合物复合材料的制备方法(溶液共混、原位聚合和熔融共混)和性能(电学性能、导热性能、力学性能、热性能以及气体阻隔性能),并指出其待解决的关键技术及工业化前景。     

C−N Coupling Reactions on Graphene with Aromatic Macromolecules and the Spatial Conformation of Grafted Macromolecules

The fabrication of advanced graphene-based nanocomposites with high-performance polymers requires covalent modification of graphene with aromatic macromolecules. Herein, C−N coupling reactions between fluorinated graphene (FG) and aromatic polyamides containing the benzimidazole moiety are successfully achieved. The optimized conditions are presented based on the nucleophilic behavior of the C−N coupling reaction on graphene. Different from the C−N coupling reaction between two small aromatic molecules, the conformation of grafted aromatic polyamide after reaction changes from torsional to paralleled alignment on graphene with the molecular length increment. Non-covalent interactions between graphene and aromatic polyamides result in this conformational change owing to the extended π systems of graphene and aromatic polyamides, and the synergistic effect of covalent and non-covalent interactions is put forward. As a consequence, graphene dispersibility is greatly enhanced in the solution of aromatic polyamide.     

One-step hydrothermal synthesis of nitrogen doped reduced graphene oxide-silver nanocomposites: Catalytic performance

The aim of this study is to efficiently utilize catalytic properties of silver nanoparticles and nitrogen doped graphene and their combined synergistic effect. For this purpose, nitrogen doped reduced graphene oxide-silver (NrGO-Ag) nanocomposites were synthesized by a facile, environmentally friendly, one-pot hydrothermal method for the first time and characterized by UV–Vis, FTIR, XRD, XPS, SEM, and TEM. Catalytic activity of the synthesized nanocomposites was tested against 4-nitrophenol (4-NP) and methylene blue (MB) reduction reactions in the presence of NaBH₄. Total degradation was achieved in both reactions in 210 and 44 s, and pseudo first order reaction rate constants were calculated as 0.0071 and 0.0322 s⁻¹ for 4-NP and MB reduction reactions, respectively.     

Novel Zn-Fe LDH/MWCNTs and Graphene/MWCNTs Nanocomposites Based Potentiometric Sensors for Benzydamine Determination in Biological Fluids and Real Water Samples

Two sensitive and selective potentiometric sensors based on zinc-iron layered double hydroxides/multiwalled carbon nanotubes (Zn−Fe LDH/MWCNTs) (sensor I) and graphene/multiwalled carbon nanotubes (Gr/MWCNTs) (sensor II) nanocomposites were developed for benzydamine hydrochloride (Benz) determination. The investigated sensors displayed excellent Nernstian slopes 58.5±0.7 and 59.5±0.5 mV decade⁻¹, detection limits 8.3×10⁻⁷ and 1.9×10⁻⁷ mol L⁻¹, long lifetimes, adequate selectivity, high chemical, and thermal stability within pH range of 2.4–8.5 for sensors І and ІІ, respectively. The surface morphology of sensors was analyzed using a Transmission Electron Microscope (TEM). The analytical method was efficiently implemented for Benz determination in biological fluids and surface water samples.     

Gas-Phase Deposited Plasmonic Nanoparticles Supported on 3D-Graphene/Nickel Foam for Highly SERS Detection

In this work, we proposed a novel three-dimensional (3D) plasmonic nanostructure based on porous graphene/nickel foam (GNF) and gas-phase deposited Ag nanoparticles (NPs).Ag NPs with high density were directly deposited on the surface of 3D GNF by performing a novel cluster beam deposition approach. In comparison with traditional Ag substrate(SiO₂/Ag), such hot-spots enriched 3D nanostructure showed extremely high electromag-netic field enhancement under incident light irradiation which could be used as a sensitive chemical sensor based on surface enhanced Raman scattering (SERS). The experimental results demonstrated that the proposed nanostructure showed superior SERS performance in terms of Raman signal reproducibility and sensitivity for the probe molecules. 3D full-wave simulation showed that the enhanced SERS performance in this 3D hierarchical plasmonic nanostructure was mainly obtained from the hot-spots between Ag NPs and the near-field coupling between Ag NPs and GNF sca olds. This work can provide a novel assembled SERS substrate as a SERS-based chemical sensor in practical applications.     

Effect of molecular interactions on the performance of poly(isobutylene-co-isoprene)/graphene and clay nanocomposites

Poly(isobutylene-co-isoprene) (IIR)/graphene and cloisite10A nanocomposites were prepared successfully and the resulting mechanical, rheological and barrier properties were carefully evaluated and compared. Chemical treatments like maleic anhydride grafting were used to improve the dispersion of the clay in the IIR matrix. Blends with different loading (20, 40, 60, and 80 %) of maleic anhydride grafted poly(isobutylene-co-isoprene) (MA-g-IIR) and IIR were made to maintain a balance between the beneficial polarity induced by MA grafting and the inevitable decrease in molecular weight (due to chain scission) induced by the free radical grafting process. The highest moduli, tensile strength and elongation at break were achieved in the case of a 60:40 ratio of MA-g-IIR (grafting degree 0.75)/IIR mixture with 5 phr of cloisite 10A. IIR/graphene nanocomposites exhibited higher reinforcement (Young’s moduli) and lower gas permeability compared to the optimized clay nanocomposites with same weight percentage. The filler–elastomer and filler–filler interactions deduced from rheology, stress relaxation and Payne effect experiments emphasize the reinforcing ability in IIR/graphene and MA-g-IIR/clay. XRD, SEM and TEM results further substantiated the results from the obtained micro structure of the nanocomposites. The improved performances of IIR/MA-g-IIR/clay and IIR/graphene were successfully correlated with interactions between the filler platelets and elastomer chains occurring in the nanocomposites.     

Reversal and activation of physical aging by applied deformations in simple compression and extension

The differential (incremental) storage modulus E′ was measured intermittently at 1 Hz during the stress relaxation of cylindrical specimens of polycarbonate subjected to finite static strains in both simple compression and extension. (In measuring E′, the amplitude of the applied sinusoidal strain was 0.2%.) Application of each static strain gave a value of E′/E′₀ less than unity, where E′₀ is the storage modulus at 1 Hz of the undeformed specimen. This behavior results from an increase in the mobility of short molecular segments; it signifies a partial erasure of the state of physical aging, a change also termed de-aging or rejuvenation. After a static strain had been applied, E′ increased continuously, a reflection of physical aging that results from a progressive decrease in segmental mobility. Plots of E′/E′₀ at an aging time of 100 s against the absolute value of the static strain show that simple extension de-ages a specimen somewhat more than does a strain of the same magnitude in compression. This difference results from the increase or decrease in volume (or free volume) effected by strains in extension or compression, respectively. The dominant cause of de-aging, however, is the deviatoric (shear) component of the strain tensor. The increase or decrease in volume produced by an applied strain modifies only slightly the segmental mobility.     

High strain rate in-plane shear behavior of composites

Studies are presented on in-plane shear properties of a typical plain weave E-glass/epoxy composite under high strain rate loading. In-plane shear properties were determined with ±45 degree off-axis compression and tension tests using a split Hopkinson pressure bar apparatus. In-plane shear properties are presented as a function of axial and shear strain rates. The range of axial strain rates for off-axis compression tests was 819–2003 per sec, and for off-axis tension tests was 91–180 per sec, whereas the range of shear strain rates for off-axis compression tests was 1388–3442 per sec and for off-axis tension tests was 153–303 per sec. In general, it was observed that in-plane shear strength was enhanced at high strain rate loading compared to that at quasi-static loading. Also, it was observed that in-plane shear strength increased with increasing strain rate within the range of strain rates considered.     

Microwave-assisted synthesis of BiOBr/graphene nanocomposites and their enhanced photocatalytic activity

BiOBr/graphene nanocomposites were synthesized by a green single-step microwave strategy and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity of the as-prepared BiOBr nanoplates and BiOBr/graphene nanocomposites for the photodegeneration of organic dyes in aqueous solution under visible light irradiation was investigated. The results show that BiOBr/graphene nanocomposites have a higher photocatalytic activity than bare BiOBr nanoplates.     

Synthesis of polydopamine‐coated graphene–polymer nanocomposites via RAFT polymerization

Graphene‐polymer nanocomposites have significant potential in many applications such as photovoltaic devices, fuel cells, and sensors. Functionalization of graphene is an essential step in the synthesis of uniformly distributed graphene‐polymer nanocomposites, but often results in structural defects in the graphitic sp² carbon framework. To address this issue, we synthesized graphene oxide (GO) by oxidative exfoliation of graphite and then reduced it into graphene via self‐polymerization of dopamine (DA). The simultaneous reduction of GO into graphene, and polymerization and coating of polydopamine (PDA) on the reduced graphene oxide (RGO) surface were confirmed with XRD, UV–Vis, XPS, Raman, TGA, and FTIR. The degree of reduction of GO increased with increasing DA/GO ratio from 1/4 to 4/1 and/or with increasing temperature from room temperature to 60 °C. A RAFT agent, 2‐(dodecylthiocarbonothioylthio)?2‐methylpropionic acid, was linked onto the surface of the PDA/RGO, with a higher equivalence of RAFT agent in the reaction leading to a higher concentration of RAFT sites on the surface. Graphene‐poly(methyl methacrylate), graphene‐poly(tert‐butyl acrylate), and graphene‐poly(N‐isopropylacrylamide) nanocomposites were synthesized via RAFT polymerization, showing their characteristic solubility in several different solvents. This novel synthetic route was found facile and can be readily used for the rational design of graphene‐polymer nanocomposites, promoting their applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3941–3949     

Synthesis and characterization of graphene oxide/modified poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) nanocomposite

In this study, the graphene oxide/poly(N-isopropylacrylamide) nanocomposite modified with 2-mercaptoethanol (GO/MPNIPAM) was synthesized in three stages. N-Isopropylacrylamide polymerization was firstly performed in the presence of azobisisobutyronitrile as an initiator, which was discovered by Homer, and 2-mercaptoethanol as a modifier. Then, the graphene oxide/modified polymer nanocomposite was synthesized by the covalent interactions between carboxylic acids of the graphene oxide and hydroxyl groups of the modified polymer during the esterification reaction. The GO/MPNIPAM nanocomposite includes some percentage of the polymer that improves solubility and stability of the GO sheets in physiological applications; due to the interaction between the MPNIPAM and the modified GO polymer, a bridge-like connection is formed between the GO sheets and the process that leads to remove a large number of hydrophilic groups on the GO nanocomposite and therefore, the GO/MPNIPAM is well dissolved in organic solvents. This property is beneficial for anti-cancer drug delivery as well as π–π interactions between the nanocomposite and aromatic drugs. The nanocomposite is not a toxic material for human body at all and has high capacity for drug delivery. Structure and morphology of the nanocomposite were studied by FTIR, SEM, XRD, UV, TGA and Raman analysis. The analysis done by X-ray diffraction pattern confirmed the presence of graphene oxide in nanocomposites and improved crystalline polymer in nanocomposites.     

Graphene anchored with ZnFe2O4 nanoparticles as a high-capacity anode material for lithium-ion batteries

Heterostructured ZnFe₂O₄–graphene nanocomposites are synthesized by a facile hydrothermal method. The as-prepared ZnFe₂O₄–graphene nanocomposites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis and galvanostatic charge and discharge measurements. Compared with the pure ZnFe₂O₄ nanoparticles, the ZnFe₂O₄–graphene nanocomposites exhibit much larger reversible capacity up to 980 mAh g⁻¹, greatly improved cycling stability, and excellent rate capability. The superior electrochemical performance of the ZnFe₂O₄–graphene nanocomposites could be attributed to the synergetic effect between the conducting graphene nanosheets and the ZnFe₂O₄ nanoparticles.