Graphene Nanosheet Composites Research Articles

Enhanced Reversible Sodium‐Ion Intercalation by Synergistic Coupling of Few‐Layered MoS2 and S‐Doped Graphene

AbstractSodium‐ion batteries (SIBs) are regarded as the best alternative to lithium‐ion batteries due to their low cost and similar Na+ insertion chemistry. It is still challenging but greatly desired to design and develop novel electrode materials with high reversible capacity, long cycling life, and good rate capability toward high‐performance SIBs. This work demonstrates an innovative design strategy and a development of few‐layered molybdenum disulfide/sulfur‐doped graphene nanosheets (MoS2/SG) composites as the SIB anode material providing a high specific capacity of 587 mA h g−1 calculated based on the total composite mass and an extremely long cycling stability over 1000 cycles at a current density of 1.0 A g−1 with a high capacity retention of ≈85%. Systematic characterizations reveal that the outstanding performance is mainly attributed to the unique and robust composite architecture where few‐layered MoS2 and S‐doped graphene are intimately bridged at the hetero‐interface through a synergistic coupling effect via the covalently doped S atoms. The design strategy and mechanism understanding at the molecular level outlined here can be readily applied to other layered transition metal oxides for SIBs anode and play a key role in contributing to the development of high‐performance SIBs.

Synthesis and superior lithium storage performances of hybrid hollow urchin-like silicate constructed by nanotubes wrapped in reduced graphene oxides

Hybrid hollow urchin-like cobalt and copper silicate constructed by nanotubes encapsulated in graphene nanosheets composites were successfully prepared using graphene oxide as carrier and silica spheres as template, which were done through a well-known Stȍber process and a hydrothermal method. In fact, the synthesis of hybrid urchin-like silicate constructed by nanotubes through onestep hydrothermal reaction has rarely been reported.The electrochemical performances of the composites as lithium-ion battery anode materials were studiedfor the first time. As novel anode materials of Li-ion batteries, the special hollow urchin-like structure not only could facilitate the Li+ diffusion and electron transport but alsocouldaccommodate the volume variation during the conversion reactions. In addition, the introduction of graphene can make the electrical conductivity better. Graphene wrapped hollow urchin-like silicate compositespossesses superior electrochemical cycling properties. The first discharge capacity is1955.2mAh/g with a current density of 300mA/g. The unique well-designed configuration presents a beneficial method to synthesize efficient and high performance electrode materials for advanced power applications.

Fabrication of NiCo2-Anchored Graphene Nanosheets by Liquid-Phase Exfoliation for Excellent Microwave Absorbers.

Graphene nanosheets (GNSs) were prepared by an efficient liquid-phase exfoliation method, and then the NiCo2/GNS nanohybrids were fabricated using the single-mode microwave-assisted hydrothermal technique. The NiCo2/GNS composites with different GNS proportions were investigated as microwave absorbers. Morphology investigation suggested that NiCo2 nanocrystals were uniformly anchored on the GNS without aggregation. The electromagnetic parameters of NiCo2/GNS nanohybrids could be artificially adjusted by changing the GNS proportion, which led to an exceptional microwave-absorbing performance. A reflection loss (RL) exceeding -20 dB was obtained in the frequency range of 5.3-16.4 GHz for the absorber thicknesses of 1.2-3.2 mm, while an optimal RL of -30 dB was achieved at 11.7 GHz for a thickness of 1.6 mm. The enhanced microwave-absorbing performance indicated that the NiCo2/10 wt % GNS composite has great potential for use as an excellent microwave absorber.

Development of a Novel Electrochemical Sensor for Determination of Matrine in Sophora flavescens.

A simple and sensitive electrochemical sensor fabricated with graphene nanosheets (GNs) and a hydroxyapatite (HA) nanocomposite–modified glassy carbon electrode (GCE) was developed for the determination of matrine (MT). The as-prepared electrode (GNs/HA/GCE) was verified to outperform bare a GCE and GNs-modified electrode with increased oxidation peak currents and the decreased over-potential in the redox process of MT, indicating the great enhancement of electrocatalytic activity toward the oxidation of MT by the composite of GNs and HA. Under the optimized conditions, the oxidation peak currents were related linearly with the concentration of MT, ranging from 2 μM to 3 mM, and the detection limit (S/N = 3) was 1.2 μM. In addition, the proposed electrochemical sensor can be successfully applied in the quantitative determination of MT in Sophora flavescens extract.

Preparation of chitosan–graphene nanosheet composites with enhanced electrochemical and mechanical properties

ABSTRACTIn this study, we proposed an alternative way to produce graphene nanosheet (GNS)/chitosan (CS) composites. Graphite‐intercalating compounds (GICs) were prepared by graphite and m‐chloroperbenzion acid (M‐CPBA) as starting materials. The GNS–CS composites were produced through the mixing of the GICs into CS and the removal of impurities in the final step. X‐ray diffraction, atomic force microscopy, and transmission and scanning electron microscopy analyses showed that graphite could be effectively exfoliated by an intercalating agent (M‐CPBA) and the GNSs were homogeneously dispersed into the CS matrix. Furthermore, we demonstrated that the electrochemical behavior and mechanical properties of the GNS–CS composites were significantly improved with a low level of GNSs in CS. The redox peak current increased 509%, and the modulus and hardness of the GNS–CS composites increased by 2.7 and 0.15 GPa, respectively, when the GNSs addition was 0.6 wt %. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45104.

Electrochemical sensing platform for tetrabromobisphenol A at pM level based on the synergetic enhancement effects of graphene and dioctadecyldimethylammonium bromide

Graphene nanosheets (GS) were prepared via solvent exfoliation, and then hybridized with dioctadecyldimethylammonium bromide (DDAB). On the single surface of DDAB and GS film, the direct oxidation activities of tetrabromobisphenol A (TBBPA) are improved effectively, and consequently the oxidation signals enhance obviously. Interestingly, the composite of DDAB and GS exhibits remarkable synergetic effects toward the oxidation of TBBPA, and the peak currents of TBBPA further increase greatly on the DDAB-GS composite film. The signal enhancement mechanism was studied using chronocoulometry. It is found that the greatly-increased accumulation efficiency is the main reason. As a result, a novel electrochemical sensing platform was developed for TBBPA. The linear range is from 0.1 to 400 μg L−1, and the detection limit is as low as 41.8 ng L−1 (76.8 pM). The practical applications in water samples manifest that this new determination system is accurate and feasible.

Improvement in Mechanical Properties and Electromagnetic Interference Shielding Effectiveness of PVA‐Based Composites: Synergistic Effect Between Graphene Nano‐Sheets and Multi‐Walled Carbon Nanotubes

In this study, polyvinyl alcohol (PVA)/graphene nano-sheets (GNs) composites are produced via solution mixing and melt compounding methods, where multi-walled carbon nanotubes (MWCNTs) are added during process. After that, the test results show that PVA/GNs composites composed of 0.25 wt% GNs possess the optimal tensile strength, while the others composed of 2 wt% GNs have a higher thermal stability, electrical conductivity, and electromagnetic interference shielding effectiveness (EMI SE). The addition of MWCNTs provides the PVA/GNs composites with better synergy that can enhance the tensile properties, thermal stability, electrical conductivity, and EMI SE of composites. In comparison to the melt compounding method, the solution mixing method can yield improved properties.

Inhibited grain growth in hydroxyapatite–graphene nanocomposites during high temperature treatment and their enhanced mechanical properties

Nanostructured hydroxyapatite (HA)–graphene nanosheet (GN) composites have been fabricated by spark plasma sintering consolidation. Nanostructual evolution of the bioceramic-based composites during further high temperature heat treatment is characterized and enhanced mechanical strength is assessed. GN keeps intact after the treatment and its presence at HA grain boundaries effectively inhibits HA grain growth by impeding interconnection of individual HA grains. Microstructural characterization discloses strong coherent interfaces between GN and the (300) plane of HA crystals. This particular matching state in the composites agrees well with the competitive theoretical pull-out energy for single graphene sheet being departed from HA matrix. The toughening regimes that operate in HA–GN composites at high temperatures give clear insight into potential applications of GN for ceramic matrix composites.

Facile surfactant- and template-free synthesis and electrochemical properties of SnO2/graphene composites

In this work, we demonstrate a facile and green hydrothermal process without using any surfactant or template to synthesize SnO2 nanoflowers (NFs)/graphene nanosheets (GNSs) composites as a high-performance electrode material for electric double layer capacitors (EDLCs). The crystal structure and morphology of the products were characterized by X-ray diffraction, scanning electron microscopy, and transition electron microscopy. The electrochemical properties were investigated by galvanostatic charge/discharge cycling and cycling voltammetry in a voltage range of −0.2–0.8 V. The results exhibit that the addition of GNSs did not change the tetragonal crystal structure of SnO2, and the GNSs were successfully coated on the flower-like surface of SnO2. The grain morphology of SnO2@GNSs composites has a flower-like appearance suggesting excellent electrochemical properties which were confirmed by electrochemical techniques. Compared with the GNSs, the SnO2@GNSs composites exhibit a high specific discharge capacitance of 126 F g−1 at 0.2 A g−1 and remains 98.2% after 2000 charge–discharge cycles. The combination of GNSs and SnO2 could significantly improve the electrical conductivity, enhance the interactions between GNSs and SnO2 NFs and provide more reaction sites, thereby resulting in improved electrochemical properties for the SnO2@GNSs composites in contrast with the pristine GNSs sample. The high specific capacity and long stability make the SnO2@GNSs nanocomposite as a electrode material for high-performance supercapacitors.

Performance of palladium nanoparticle–graphene composite as an efficient electrode material for electrochemical double layer capacitors

Palladium nanoparticle–graphene nanosheet composite (PdNP–GN) is demonstrated as an efficient electrode material in energy storage applications in supercapacitors. Palladium nanoparticle (PdNP) decorated graphene nanosheet (GN) composite was synthesized via a chemical approach in a single step by the simultaneous reduction of graphene oxide (GO) and palladium chloride from the aqueous phase using ascorbic acid as reducing agent. The materials were characterized by scanning and high resolution transmission electron microscopy, Raman, X-ray diffraction and energy dispersive X-ray spectroscopy which demonstrate that the metal nanoparticles have been uniformly deposited on the surface of graphene nanosheets. The synthesized material has been analyzed by cyclic voltammetry, electrochemical impedance spectrometry and chronopotentiometry using 1M KCl as the supporting electrolyte for its application in electrochemical double layer supercapacitors. PdNPs-GN composite showed improved electron transfer kinetics and superior capacitive performance with large specific capacitance of 637Fg−1, excellent cyclic performance and maximum energy and power densities of 56 Wh kg−1 and 1166Wkg−1, respectively at a current density of 1.25Ag−1. This highlights the importance of the synergetic effects of electrochemically efficient Pd nanoparticles and graphene for energy storage applications in supercapacitors.

Anchoring Nanostructured Manganese Fluoride on Few-Layer Graphene Nanosheets as Anode for Enhanced Lithium Storage.

Manganese fluoride (MnF2)/few-layer graphene nanosheets (GNS) composites are successfully prepared via a facile solvothermal method. It is found that in situ formed tetragonal MnF2 submicron crystals (50-200 nm) with good crystallinity anchoring homogeneously onto conducting GNS, allows the electrically insulating MnF2 particles to be wired up to the current collector with enhanced electron transport pathway. The MnF2/GNS composites act as anode in LIBs and display prominently improved electrochemical performance in comparison to that of pure MnF2, on account of the close interactions between the underlying graphene nanosheets and MnF2 particles grown atop. Distinctly enhanced capacity as high as 489 mAh g(-1) after 100 cycles can be obtained at 600 mA g(-1), while the self-activation process can be greatly accelerated at 6000 mA g(-1) with a maximum specific capacity of 530 mAh g(-1). With long cycling stability for 4000 cycles at 6000 mA g(-1), the MnF2/GNS composite can be deemed as an attractive candidate anode for high-capacity, long cycle life, and environmentally friendly LIBs.

An impedimeric biosensor based on a composite of graphene nanosheets and polyaniline as a suitable platform for prostate cancer sensing

A simple and new electrochemical biosensor was designed based on a glassy carbon electrode (GCE) modified with polyaniline (PANI) and graphene oxide (GO) nanocomposite for DNA detection.

LiMn2O4/graphene composites as cathodes with enhanced electrochemical performance for lithium-ion capacitors

The LiMn2O4microspheres (LMO-MSs)/graphene nanosheets (GNSs) composites have been synthesized using γ-MnO2microspheres as precursor.

Facile Synthesis of Graphene–Enwrapped Ag3PO4 Composites with Highly Efficient Visible Light Photocatalytic Performance

In this work, thermally exfoliated graphene nanosheets (GNS) were employed to prepare novel Ag3PO4–GNS composite photocatalysts by a facile chemical precipitation approach. The as-prepared Ag3PO4–GNS composite photocatalysts were characterized by X-ray diffraction (XRD) pattern, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetric (TG) analysis, ultraviolet-visible diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectra. It was found that the Ag3PO4 particles were well deposited on the surfaces of GNS. Compared with bare Ag3PO4 and Ag3PO4–rGO composite, the Ag3PO4–GNS composite exhibited enhanced photocatalytic activity for the photodegradation of rhodamine B (RhB) under visible light irradiation. The photocatalytic degradation rate of Ag3PO4–GNS composite was 1.7 times that of bare Ag3PO4 and about 1.3 times that of Ag3PO4–rGO for the degradation of RhB. Furthermore, the photocatalytic stability of Ag3PO4–GNS composite was also greatly enhanced. This enhanced photocatalytic activity and stability could be ascribed to the positive synergetic effects between the Ag3PO4 particles and GNS sheets, which could provide a greater number of active adsorption sites, suppress charge recombination and reduce the serious photocorrosion of Ag3PO4. Moreover, the photocatalytic degradation of RhB over Ag3PO4–GNS composites was also optimized, suggesting that the optimal amount of GNS in the composites was 11.4[Formula: see text]wt.%. This work shows a great potential of Ag3PO4–GNS composite for environmental treatment of organic pollutants.

Cobalt oxide (Co3O4)/graphene nanosheets (GNS) composite prepared by novel route for supercapacitor application

Cobalt oxide (Co3O4)–graphene nanosheets (GNS) composite was prepared using a novel route. Room temperature prepared graphite oxide was exfoliated at low temperature and subsequently reduced to GNS by chemical method. Successful compound formation was confirmed and structural details were obtained from XRD studies. Cobalt oxide was found to crystallize in spinel fcc structure with average crystallite size of 9 nm in the composite. FTIR and XPS study confirms the removal of oxygen containing functional group in reduced graphene and spinel formation of cobalt oxide in the composite. Raman spectra depict the reestablishment of sp2 conjugated network of carbon atoms, on reduction to graphene. FESEM images reveal the nanosheet like morphology of the graphene being retained in the composite and promoting ion diffusion channels. Electrochemical characterization discloses the pseudocapacitive behaviour of the composite material. Higher specific capacitance of 650 F/g was exhibited by GNS–Co3O4 at 5 mV/s scan rate. Symmetrical supercapacitor fabricated using GNS–Co3O4 demonstrated superior power characteristics. Graphene in the composite has substantially increased the electron and ion transport in the electrode material leading to enhanced performance.

Hierarchical electromagnetic absorption in micro-waveguide stuffed with magnetic media for resin-based composites of graphene nanosheets and manganese oxides

Waveguide configurations of hierarchical system are proposed as new microstructures for composites in absorbing enhancement. Supercritical fluid (SCF) one-pot exfoliation of layered graphite and manganese oxide mixing materials is developed to obtain a hierarchical system, containing graphene nanosheets (GNS) and exfoliated manganese oxides (EMO) in different sizes. Composites with GNS–EMO embedded in epoxy resin matrix are produced for a design of dielectric and magnetic loss integrated absorber. Volume fraction of GNS–EMO in composites is given for an optimal quantity of resin epoxy in fixation and formation. The effect of mixing ratios between electric and magnetic components is provided for the design of dielectric and magnetic loss integrated absorbers. Frequency shifting phenomena are revealed in the component adjusting course. Excluding the offsetting sizes, reflection loss of composites is enhanced as thickness increases. Synergistic effect of electric and magnetic coordinated materials demonstrates the superiority of micro-waveguide structures in GNS–EMO composite absorber.

Pyrolyzed polyaniline and graphene nano sheet composite with improved rate and cycle performance for lithium storage

Pyrolyzed poly-aniline graphene nano sheets (PAGNS) composite was investigated serving as a novel anode material for lithium storage. The composite material with carbon coating and nitrogen doping on graphene were synthesized by heat treatment of polyaniline and graphite oxide precursors under an Ar/H2 atmosphere at 850°C. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy techniques were employed to characterize the PAGNS composites with various contents of carbon and nitrogen doping on graphene in comparison with pristine graphene nanosheets (GNS). The PAGNS composites show defects resulting from nitrogen doping in graphene lattice, and carbon is coated on graphene surface causing vertical alignment of nanosheets which leads to improved electronic conductivity. Electrochemical tests show that the PAGNS composites exhibit enhanced rate performance and cycle capability. The PAGNS is also examined at a 1.6Ag−1 high rate and at 55°C high temperature, and the material demonstrates 282mAhg−1 capacity after 500 cycles, which is superior over that of GNS. The enhanced Li-ion storage properties could be attributed to the synergetic effect of carbon-coating and nitrogen-doping in graphene nanosheets.

Atomic layer deposition derived amorphous TiO2 thin film decorating graphene nanosheets with superior rate capability

Composites consisting of graphene nanosheets (GNSs) decorated with amorphous TiO2 thin films were synthesized by an atomic layer deposition (ALD) technique. It was revealed that the TiO2 thin films were uniformly deposited onto the worm-like GNSs. When used as anode materials in lithium ion batteries (LIBs), the TiO2–GNS composites deliver a stable capacity of ~ 140 mAh g− 1 after 100 cycles at a specific current of 100 mA g− 1 as well as superior rate capability, accounting for a sustainable 95 mAh g− 1 capacity at a specific current of 1200 mA g− 1. It is believed that the remarkable electrochemical performance lied in the unique features of the composites, i.e., the amorphous nature of the TiO2 films and the large surface area of GNSs. The former rendered short Li+ diffusion pathways in TiO2 thin film, while the latter offered excellent electronic conductivity as well as a large intimate contact area between the electrolyte and TiO2. This work laid a venue for designing new electrodes for high-performance LIBs.

Modification of Chemically Exfoliated Graphene to Produce Efficient Piezoresistive Polystyrene–Graphene Composites

We report the chemical exfoliation of grapheneoxide from graphite and its subsequent reduction to graphene nanosheets (GN) to obtain highly conducting composites of graphene sheets in a polymer matrix. The effect of using graphite nanoparticles or flakes as precursors, and different drying methods, was investigated to obtain multilayer graphene sheets of atomically controlled thickness, which was essential to optimizing their dispersion in a polystyrene (PS) polymer matrix. In situ emulsion polymerization of the styrene monomer in the presence of GN was performed to obtain thin composite films with highly uniform dispersion and fewer graphene layers when GN were obtained from graphite flakes then freeze drying. The highest electrical conductivity of PS–GN composites was ~0.01 S/m for a graphene filling fraction of 2%. The piezoresistance of the PS–GN composites was evaluated and used in pressure sensor arrays with pressure field imaging capability.

A stable and high-capacity anode for lithium-ion battery: Fe2O3 wrapped by few layered graphene

Fe2O3 wrapped by few layered graphene nanosheets composites (Fe2O3-FLG) have been synthesized via a facile and massive one-step P-milling method, which is effective in reducing the particle size of Fe2O3 and exfoliating the graphite into FLG. The composite shows good electrochemical performance due to the tight wrapping of FLG nanosheets, which is beneficial to electric conductivity and integrity of the electrode. The sample treated under 20 h retains a reversible capacity of 758 mAh g−1 at 200 mA g−1 after 300 cycles, which equals to 88% of its theoretic capacity. With the superior electrochemical performance, Fe2O3-FLG composites prepared via the P-milling method could be promising as anode materials for high performance lithium-ion batteries.