Sliding wear behavior of copper-based composites reinforced with graphene nanosheets and graphite

The mechanical and tribological properties of hot-pressed copper-based composites containing different amounts of graphene nanosheets（GNSs） are compared with those of copper-graphite（Gr） composites fabricated by the same method.The results show that the Cu-GNSs composites exhibit higher relative density,microhardness and bending strength compared with Cu-Gr composites with the same volume fraction of GNSs and Gr.Moreover,the friction coefficients and wear rates reduce significantly by the addition of GNSs,whereas the limited impact on reducing friction and wear is found on graphite.The abrasive and delamination wear are the dominant wear mechanisms of the composites.It is believed that the superior mechanical and tribological performances of Cu-GNSs composites are attributed to the unique strengthening effect as well as the higher lubricating efficiency of graphene nanosheets compared with those of graphite,which demonstrates that GNS is an ideal filler for copper matrix composites,acting as not only an impactful lubricant but also a favorable reinforcement.

Development of an Ultra-Sensitive and Flexible Piezoresistive Flow Sensor Using Vertical Graphene Nanosheets

This paper suggests development of a flexible,lightweight,and ultra-sensitive piezoresistive flow sensor based on vertical graphene nanosheets(VGNs) with a mazelike structure.The sensor was thoroughly characterized for steady-state and oscillatory water flow monitoring applications.The results demonstrated a high sensitivity(103.91 mV(mm/s)-1) and a very low-velocity detection threshold(1.127 mm s-1) in steady-state flow monitoring.As one of many potential applications,we demonstrated that the proposed VGNs/PDMS flow sensor can closely mimic the vestibular hair cell sensors housed inside the semicircular canals(SCCs).As a proof of concept,magnetic resonance imaging of the human inner ear was conducted to measure the dimensions of the SCCs and to develop a 3D printed lateral semicircular canal(LSCC).The sensor was embedded into the artificial LSCC and tested for various physiological movements.The obtained results indicate that the flow sensor is able to distinguish minute changes in the rotational axis physical geometry,frequency,and amplitude.The success of this study paves the way for extending this technology not only to vestibular organ prosthesis but also to other applications such as blood/urine flow monitoring,intravenous therapy(Ⅳ),water leakage monitoring,and unmanned underwater robots through incorporation of the appropriate packaging of devices.

The Effect of Thermal Exfoliation Temperature on the Structure and Supercapacitive Performance of Graphene Nanosheets

Graphene nanosheets(GSs) were prepared from graphite oxide by thermal exfoliation method. The effect of thermal exfoliation temperature on the structure and supercapacitive performance of GSs has been investigated. The results show that the GSs with pore sizes center around 4.0 nm. With an increase of thermal reduction temperature, the number of stacking layers and the structure disorder degree increase, while the oxygen-containing groups content, BET surface area,and electrical resistivity of GSs decrease. The results indicate that 673 K is the preferable thermal exfoliation temperature to acquire good supercapacitive performance. In this case, the GSs have the best supercapacitive performance(233.1 F g-1) in a 6 mol L-1KOH electrolyte. The prepared GSs at the preferable thermal exfoliation temperature have good rate performance and cycle stability.

Atomic Layer Coated Al_(2)O_(3) on Nitrogen Doped Vertical Graphene Nanosheets for High Performance Sodium Ion Batteries

Heteroatom doped graphene materials are considered as promising anode for high-performance sodium-ion batteries(SIBs).Defective and porous structure especially with large specific surface area is generally considered as a feasible strategy to boost reaction kinetics;however,the unwanted side reaction at the anode hinders the practical application of SIBs.In this work,a precisely controlled Al_(2)O_(3)coated nitrogen doped vertical graphene nanosheets(NVG)anode material has been proposed,which exhibits excellent sodium storage capacity and cycling stability.The ultrathin Al_(2)O_(3)coating on the NVG is considered to help construct an advantageous interface between electrode and electrolyte,both alleviating the electrolyte decomposition and enhancing sodium adsorption ability.As a result,the optimal Al_(2)O_(3)coated NVG materials delivers a high reversible capacity(835.0 mAh g^(-1))and superior cycling stability(retention of 92.3%after 5000 cycles).This work demonstrates a new way to design graphene-based anode materials for highperformance sodium-ion batteries.

Co-synthesis of vertical graphene nanosheets and high-value gases using inductively coupled plasma enhanced chemical vapor deposition

One-step controllable synthesis of vertical graphene nanosheets （VGs） and high-value gases was achieved using inductively coupled plasma enhanced chemical vapor deposition （ICPECVD）. The basic physical properties of the ICPECVD process were revealed via electrical diagnosis and optical emission spectroscopy. The coil current and voltage increased linearly with the augmenting of injected power, and CH, C2, H2 and H were detected at a wavelength from 300 to 700 nm, implying the generation of abundant graphene-building species. The morphology and structure of solid carbon products, graphene nanosheets, were systemically characterized in terms of the variations of operating conditions, such as pressure, temperature, gas proportion, etc. The results indicated that an appropriate operating condition was indispensable for the growth process of graphene nanosheets. In the present work, the optimized result was achieved at the pressure, heating temperature, applied power and gas proportion of 600 mTorr, 800 ~C, 500 W and 20：20：15, respectively, and the augmenting of both CH4 and H2 concentrations had a positive effect on the etching of amorphous carbon. Additionally, H2 and C2 hydrocarbons were detected as the main exhaust gases. The selectivity of H2 and C2H2, measured in exhaust gases, reached up to 52% and 8%, respectively, which implied a process of free radical reactions and electron collision dissociation. Based on a comprehensive investigation of spectral and electrical parameters and synthesized products, the reaction mechanism of collision, dissociation, diffusion, etc, in ICPECVD could be speculated, providing a probable guide for experimental and industrial applications.

Secondary electron emission yield from vertical graphene nanosheets by helicon plasma deposition

The secondary electron emission yields of materials depend on the geometries of their surface structures.In this paper,a method of depositing vertical graphene nanosheet(VGN)on the surface of the material is proposed,and the secondary electron emission(SEE)characteristics for the VGN structure are studied.The COMSOL simulation and the scanning electron microscope(SEM)image analysis are carried out to study the secondary electron yield(SEY).The effect of aspect ratio and packing density of VGN on SEY under normal incident condition are studied.The results show that the VGN structure has a good effect on suppressing SEE.

High-performance solid-solution potassium-ion intercalation mechanism of multilayered turbostratic graphene nanosheets

The solid-solution reaction between an alkali cation and an active host material is known as a singlephase redox mechanism,and it is typically accompanied by a continuous voltage change.It is distinct from the typical alkali cation intercalation reaction at an equivalent site of the active host material,which exhibits a voltage plateau.Herein,we report an unusual solid-solution potassium-ion intercalation mechanism with a low-voltage plateau capacity on multilayered turbostratic graphene nanosheets(T-GNSs).Despite the disordered graphitic structure with a broad range of d-spacings(3.65–4.18À),the T-GNSs showed a reversible plateau capacity of~200 m A h g^(-1),which is higher than that of a well-ordered graphite nanoplate(~120 m A h g^(-1)).In addition,a sloping capacity of~220 m A h g^(-1)was delivered with the plateau capacity,and higher rate capabilities,better reversibility,and a more stable cycling performance were confirmed on the turbostratic microstructure.First-principles calculations suggest that the multitudinous lattice domains of the T-GNSs contain diverse intercalation sites with strong binding energies,which could be the origin of the high-performance solid-solution potassium-ion intercalation behavior when the turbostratic graphene stacks have a d-spacing smaller than that of equilibrium potassium–graphite intercalation compounds(5.35À).

Direct synthesis of graphene nanosheets support Pd nanodendrites for electrocatalytic formic acid oxidation

We report a solvothermal method preparation of dendritic Pd nanoparticles （DPNs） and spherical Pd nanoparticles （SPNs） supported on reduced graphene oxide （RGO）. Drastically different morphologies of Pd NPs with nanodendritic structures or spherical structures were observed on graphene by controlling the reduction degree of graphene oxide （GO） un- der mild conditions. In addition to being a commonplace substrate, GO plays a more important role that relies on its surface groups, which serves as a shape-directing agent to direct the dendritic growth. As a result, the obtained DPNs/RGO catalyst exhibits a significantly enhanced electro-catalytic behavior for the oxidation of formic acid compared to the SPNs/RGO catalyst.

Auxiliary ball milling to prepare WS_(2)/graphene nanosheets composite for lithium-ion battery anode materials

A novel nano-WS_(2)/graphene nanosheets(GNSs)composite is obtained by ball milling with xylitol as auxiliary agent and hightemperature sintering.Xylitol improves the shear force during ball milling and well overcomes the van der Waals interactions between the interlayer of graphite and WS_(2).Through high-temperature calcination,GNSs and WS_(2) nanosheets can form tight interface contact.The produced WS_(2)/GNSs composites can be used as anode materials for lithium-ion batteries,while maintaining a high reversible specific capacity of 705 mAh·g^(-1)with the capacity retention of 95%at a current density of 250 mA·g^(-1)after 200 cycles,mainly because WS_(2)/GNSs composites have a higher Li^(+)diffusion coefficient of 2.2×10^(-9)cm^(2)·s^(-1)and a higher specific surface area of 70.10 m^(2)·g^(-1).As a result,the xylitol-assisted ball milling method designed in this work is suitable for extended preparation of peeling of two-dimensional layer materials into nanosheets.

Corrosion Behavior of Graphene Nanosheets Reinforced Magnesium Matrix Composites in Simulated Body Fluids

Magnesium(Mg)alloy is considered as a promising biodegradable implant material but restricted to rapid degradation.Here,the new strategies based on thixomolding process had been explored to utilize the outstanding anti-permeability of graphene nanosheets(GNPs)while inhibit its galvanic corrosion with the matrix,so as to improve the corrosion resistance of composites.The agglomerate of GNPs with 0.9 wt%content is the main reason for the deterioration of corrosion performance due to the formation of micro-galvanic corrosion.The grain refinement of composites with 0.6 wt%content had positive effects on the better corrosion resistance.After process adjusting,the unique distributions of GNPs along grain boundaries play a vital role in improving the corrosion resistance.It can be ascribed to the following mechanisms:(I)The barriers can be established between the Mg matrix and corrosive medium,hence blocking the charge transfer at the interface;(II)The GNPs can effectively promote apatite deposition on the Mg matrix,leading to form dense apatite layers and prevent the further invasion of SBF;(III)The GNPs acting as reinforcements exists in the corrosion layer and apatite layer,impede the apatite layer falling off from the Mg matrix.These findings broaden the horizon for biomedical applications in Mg matrix composites to realize desired performances.

Polyurethane foam-supported three-dimensional interconnected graphene nanosheets network encapsulated in polydimethylsiloxane to achieve significant thermal conductivity enhancement

Polyurethane(PU)foams are widely used in thermal management materials due to their good flexibility.However,their low thermal conductivity limits the efficiency.To address this issue,we developed a new method to produce tannic acid(TA)-modified graphene nanosheets(GTs)-encapsulated PU(PU@GT)foams using the soft template microstructure and a facile layer-by-layer(L-B-L)assembly method.The resulting PU@GT scaffolds have ordered and tightly stacked GTs layers that act as three-dimensional(3D)highly interconnected thermal networks.These networks are further infiltrated with polydimethylsiloxane(PDMS).The through-plane thermal conductivity of the polymer composite reaches 1.58 W·m^(−1)·K^(−1) at a low filler loading of 7.9 wt.%,which is 1115%higher than that of the polymer matrix.Moreover,the mechanical property of the composite is~2 times higher than that of the polymer matrix while preserving good flexibility of the polymer matrix owing to the retention of the PU foam template and the construction of a stable 3D graphene network.This work presents a facile and scalable production approach to fabricate lightweight PU@GT/PDMS polymer composites with excellent thermal and mechanical performance,which implies a promising future in thermal management systems of electronic devices.

Tribological properties of copper matrix composites reinforced with homogeneously dispersed graphene nanosheets

Graphene reinforced copper matrix composites （Gr/Cu） were fabricated by electrostatic self-assembly and powder metallurgy. The morphology and structure of graphene oxide, graphene oxide-Cu powders and Gr/Cu composites were characterized by scanning electronic microscopy, transmission electronic microscopy, X-ray diffraction and Raman spectroscopy, respectively. The effects of graphene contents, applied loads and sliding speeds on the tribological behavior of the composites were investigated. The results indicate that the coefficient of friction of the composites decreases first and then increases with increasing the graphene content. The lowest friction coefficient is achieved in 0.3 wt~ Gr/Cu composite, which decreases by 65% compared to that of pure copper. The coefficient of friction of the composite does not have significant change with increasing the applied load, however, it increases with increasing the sliding speed. The tribological mechanisms of the composite under different conditions were also investigated.

Vertical graphene nanosheetsmodiBed Al current collectors for high-performance sodium-ion batteries

Rechargeable sodium-ion batteries(SIBs)are promising candidates for large-scale energy storage owing to their excellent high-power performance.However,Al-based current collectorsat both anodes and cathodes of SIBs,which widely influence the power properties of a variety of electrodes in SIBs,have rarely been investigated.Here,we demonstrate that vertical graphene nanosheets grown on commercial Al foil by the plasma-enhanced chemical vapor deposition(PECVD)method,form a robust connection with the carbon-based conductive network of the electrode,thereby significantly reducing the electrode current collector interfacial resistance.For sodium vanadium phosphate(NVP)anodes with vertical graphenenanosheetmodified Al foil(G-AI)current collectors,the interfacial resistance between the electrode and current collector is reduced 20-fold compared with that in the case of Al foil.The G-AI current collector reduces the polarization and improves the rate capability compared with that of Al current collectors within both cathodes and anodes of SIBs.At a high rate of 5 C,the capacity retention of NVP cathode with G-AI current collector is 74%,which is much higher than that with AI foil(22%).We believe that the obtained results support the prospect for the widespread use of G-AI current collectors in the further improvement of high-power profiles of SIBs.

Direct fabrication of flexible tensile sensors enabled by polariton energy transfer based on graphene nanosheet films

A fundamental problem in the direct manufacturing of flexible devices is the low melting temperature of flexible substrates,which hinders the development of flexible electronics.Proposed here is an electron-cyclotron-resonance sputtering system that can batch-fabricate devices directly on flexible substrates under a low temperature by virtue of the polariton energy transfer between the plasma and the material.Flexible graphene nanosheet-embedded carbon(F-GNEC)films are manufactured directly on polyimide,polyethylene terephthalate,and polydimethylsiloxane,and how the substrate bias(electron energy),microwave power(plasma flux and energy),and magnetic field(electron flux)affect the nanostructure of the F-GNEC films is investigated,indicating that electron energy and flux contribute to the formation of standing graphene nanosheets in the film.The films have good uniformity of distribution in a large size(17 mm×17 mm),and tensile and angle sensors with a high gauge factor(0.92)and fast response(50 ms)for a machine hand are obtained by virtue of the unique nanostructure of the F-GNEC film.This work sheds light on the quantum manufacturing of carbon sensors and its applications for intelligent machine hands and virtual-reality technology.

Construction of SnS-Mo-graphene nanosheets composite for highly reversible and stable lithium/sodium storage

Sn-based chalcogenides are considered as one of the most promising anode materials for lithium-ion batteries(LIBs)because of their high capacities through both conversion and alloying reactions.However,the realization of full capacities of Sn-based chalcogenides is mainly hindered by the large volume variation and inferior reversibility of conversion reaction during cycling.In present work,a new ternary Sn SMo-graphene nanosheets(Sn S-Mo-GNs)composite is fabricated by a simple and scalable plasma milling method,in which Sn S nanoparticles are tightly bonded with Mo and GNs.The Mo and GNs additives can effectively alleviate the large volume change of Sn S upon cycling,which leads to a stable electrochemical framework.Moreover,they can significantly suppress the Sn agglomeration in lithiated Sn S,which enables highly reversible conversion reaction during cycling.As anode for LIBs,the Sn S-Mo-GNs composite exhibits a high initial coulombic efficiency of 86.9%(almost complete reversibility of Sn S,~97.3%),high cyclic coulombic efficiency after initial three cycles(>99.5%),and long lifespan(up to 600 cycles).Moreover,it also demonstrates superior electrochemical performance for sodium storage.Thus,this work demonstrates a potential anode for batteries application and provides a viable strategy to obtain highly reversible and stable anodes for lithium/sodium storage.

High dielectric permittivity and low dielectric loss nanocomposites based on poly(VDF-TrFE-CTFE)and graphene nanosheets

In this work,nanocomposites(poly(vinylidenefluoride
trifluoroethylene
chlorotrifluoroethylene)/Graphene nanosheets)(P(VDF-TrFE-CTFE)/GNS)were fabricated via solution cast process.GNS were covalently functionalized with KH550 to improve their interfacial interactions with the terpolymer matrix P(VDF-TrFE-CTFE).Compared to neat terpolymer,significantly improved dielectric permittivity and low loss were observed for the composites.For instance,at 1 kHz the P(VDF-TrFE-CTFE)/GNS composites with 4%GNS possessed a dielectric permittivity of 144,over 14 times larger than that of neat terpolymer,while the loss was only 0.56.These findings represent an effective route to design potential dielectric polymer films for high-charge storage capacitors.

Graphene Nanosheets Decorated with Copper Oxide Nanoparticles for the Photodegradation of Methylene Blue

Textile industries extensively use colorants,such as methylene blue,and if disposed off untreated,they contaminate the effluent streams,causing a severe impact on the environment and aquatic life.Photocatalytic degradation has been found as an inevitable approach to treat them.Herein,we decorated the copper oxide nanoparticles on graphene nanosheets during the reflux process.The resultant copper oxide/graphene nanocomposites were analyzed for structural and functional attributes.It was observed that on increasing the copper oxide contents,the z-average size of the resultant nanocomposites decreased.The X-ray diffraction analysis demonstrated the crystalline nature of the nanocomposite.The surface morphology of the copper oxide nanoparticles appeared to be spherical and that of the copper oxide/graphene composite somehow wrinkled.The infrared analysis indicated successful intercalation of precursors in the nanocomposite.The bandgap of copper oxide/graphene nanocomposites varied in the range of 1.03—1.30 eV,which indicated their effective photocatalytic activity.The results demonstrated that after 120 min of exposure,the methylene blue removal efficiency reached 94.0%,92.2%,and 89.4%(mass fraction)on the copper oxide/graphene nanocomposite at copper oxide nanoparticles to graphene nanosheets ratios of 1:1,1.5:1,and 2:1(mass ratio),respectively.The photodegradation performance of the prepared nano-catalyst was found satisfactory even after five cycles.

NON-ISOTHERMAL CRYSTALLIZATION OF ETHYLENE-VINYL ACETATE COPOLYMER CONTAINING A HIGH WEIGHT FRACTION OF GRAPHENE NANOSHEETS AND CARBON NANOTUBES

The effect of the different geometrical dimensionality of two dimensional graphene nanosheets （2D GNSs） and one dimensional carbon nanotubes （1D CNTs） on the non-isothermal crystallization of an ethylene-vinyl acetate （EVA） copolymer at high loading （5 wt%） was studied. Transmission electron microscopy indicated a homogeneous dispersion of GNSs and CNTs in EVA obtained by a solution dispersion process. Fourier-transform infrared spectroscopy and differential scanning calorimetry measurements showed that 1D CNTs and 2D GNSs acted as effective nucleating agents, with a noticeably increased onset crystallization temperature of EVA. A high weight fraction of nano-fillers slowed the overall crystallization rate of composites. At the same crystallization temperatute, the crystallization behavior of GNS/EVA composites was slowed compared to that of the CNT/EVA ones owing to larger nucleus barrier and activation energy of diffusion. Dynamic mechanical relaxation and rheology behavior of CNT/EVA and GNS/EVA composites demonstrated that the planar structure of the GNSs had an intensively negative effect on EVA chain mobility due to interactions between nano- fillers and polymer chains, as well as spatial restriction.

Functional graphene oxide nanosheets modified with cyclodextrins for removal of Bisphenol A from water

A novel type of functional graphene oxide nanosheets(GNs)modified with b-cyclodextrins(b-CDs)have been developed by coating dopamine-functionalized cyclodextrin(DACD)molecules on GNs for removing Bisphenol A(BPA)molecules from water.The DACD molecules with both b-CD groups for achieving adsorption property and dopamine(DA)groups for achieving adhesion property are synthesized by grafting DA onto carboxymethyl-b-cyclodextrin(CmbCD).The proposed DACD molecules can be firmly coated on the surfaces of various inorganic and organic substrates.Due to the large specific surface area of GNs,DACD-coated GNs(DACD@GNs)are proposed for efficient adsorption separation of BPA molecules from water.Due to the host-gust complexation between the BPA molecules in water and b-CDs on DACD@GNs,the fabricated DACD@GNs exhibit excellent adsorption performances.The adsorption kinetics can be explained via the pseudo-second-order model effectively.The experimental adsorption capacity of DACD@GNs is 11.29 mg·g^(-1) for BPA.Furthermore,after the adsorption process,the DACD@GNs can be easily separated from aqueous solutions via vacuum filtration with porous membranes,and then regenerated by simply washing with ethanol.The proposed strategy in this study can be used for effectively functionalizing the surfaces of various substrates with functional b-CDs,which is highly promising in applications in the field of adsorption separations,especially water treatments.

Effect of graphene addition on the physicomechanical and tribological properties of Cu nanocomposites

This paper presents an experimental investigation of the mechanical and tribological properties of Cu-graphene nanosheets(GN)nanocomposites.We employed the electroless coating process to coat GNs with Ag particles to avoid its reaction with Cu and the formation of intermetallic phases.We analyzed the effect of GN content on the structural,mechanical,and tribological properties of the produced nanocom-posites.Results showed that the electroless coating process is an efficient technique to avoid the reaction between Cu and C and the formation of intermetallic phases.The addition of GNs significantly improves the mechanical and tribological properties of Cu nanocomposites.However,the addition of GNs needs to be done carefully because,after a certain threshold value,the mechanical and tribological properties are negatively affected.The optimum GN content is determined to be 0.5vol%,at which hardness,wear rate,and coefficient of friction are im-proved by 13%,81.9%,and 49.8%,respectively,compared with Cu nanocomposites.These improved properties are due to the reduced crys-tallite size,presence of GNs,and homogenous distribution of the composite constituents.