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With more and more applications, the mechanical strength of graphene paper (GP) has attracted significant attention in recent years. In this report, GPs were prepared by flow-induced filtration of electrochemical exfoliated graphene sheets. By adjusting the concentration of solution, we found graphene sheets fabricated in 0.1 M K2SO4 have the thinnest average thickness. And by uniaxial in-plane tensile tests operated on a self-developed in situ scanning electron microscopy (SEM) tensile stage, the corresponding GP has the best fracture strength of 192 MPa. This is due to that the thickness decrease of exfoliated graphene will increase the quantity of interlayer crosslinks, thus improving the mechanical properties of GPs. This research may open a new way to obtain high-strength GPs for applications.

Free-standing graphene-based composite paper electrodes with various active materials have attracted tremendous interest for next-generation lithium-ion batteries (LIBs) due to advantages such as their light weight, excellent mechanical flexibility, and superior electrochemical performance. However, despite its high theoretical energy density, SnS2 is rather difficult to composite with the graphene paper, because conventional reduction procedures for graphene oxide (GO) induce either decomposition or oxidation of SnS2. Herein, a novel solid/gas two-phase interface hydrothermal process is reported to fabricate flexible free-standing SnS2/graphene nanocomposite papers (SGP) assisted by a reducing and stabilizing agent thioacetamide aqueous solution. Such hydrothermal process not only successfully reduces SnS2/graphene oxide paper (SGOP) to SGP, but more importantly, keeps intact the paper configuration as well as the phase stability of SnS2. The as-prepared SGP electrode exhibits high reversible discharge capacity, outstanding cyclic stability and rate capability, which can be attributed to the synergistic effect of the conductive and flexible graphene matrix for accommodation of the volumetric changes of SnS2 upon cycling and the planar SnS2 nanospacers between the graphene layers introducing nanopores for penetration of electrolyte and inhibition of graphene nanosheets restacking. This report demonstrates a new strategy for more active materials with promising lithium storage properties joining the flexible graphene-based paper electrode family.

Free-standing graphene (FSG) paper plays a vital role in a wide variety of applications as an electrode material. Specifically, the electrical properties of FSG are the most important factor affecting its use as an electrode material. Herein, the vacuum filtration technique is utilized to fabricate GO paper, which is then reductively treated with HI. Initially, the electrical conductivity is measured for GO papers with different thicknesses by varying the concentration of GO precursor as well as the reduction time. The FSG paper with a thickness of 3 microns exhibits the lowest sheet resistance and further characterization is carried out to reveal the origin of this enhancement of electrical properties. The low resistance is attributed to its crystalline nature, stacking height (Lc), in-plane crystallite size (La) and defect density (nD). Meanwhile, iodide ions intercalated into the graphene layers act as hole-carriers, and their intercalation is favoured over adsorption at the surface.

In this research, we demonstrate a facile approach for the synthesis of a graphite-analogous layer-by-layer heterostructured CuO/ZnO/carbon paper using a graphene oxide paper as a sacrificial template. Cu2+ and Zn2+ were inserted into the interlayer of graphene oxide papers via physical absorption and electrostatic effects and then, the Mn+-graphene oxide paper was annealed in air to generate 2D nanoporous CuO/ZnO nanosheets. Due to the graphene oxide template, the structure of the obtained CuO/ZnO nanosheets with an average size of ∼50 nm was duplicated from the graphene oxide paper, which displayed a layer-by-layer structure on the microscale. The papers composed of nanosheets had an average pore size of ∼10 nm. Moreover, the as-prepared CuO-ZnO papers displayed high hybridization on the nanoscale. More importantly, the thickness of the single-layer CuO/ZnO nanosheet was about 2 nm (3-4 layer atom thickness). The as-synthesized nano-hybrid material with a high specific surface area and conjunct bimodal pores could play key roles for providing a shorter diffusion path and rapid electrolyte transport, which could further facilitate electrochemical reactions by providing more active sites. As an electrode material, it displayed high performances as a non-enzymatic sensor for the detection of glucose with a low potential (0.3 V vs. SCE), high sensitivity (3.85 mA mM-1 cm-2), wide linear range (5 μM to 3.325 mM), and low detection limit of 0.5 μM.

A graphene oxide paper (GOP) was irradiated with 500 keV proton for total fluence of 2 × 1013 cm−2 to 2 × 1015 cm−2 in a ground-based irradiation simulator. The spacing of layer, surface chemical composition, structural defects, thermal conductivity and electrical property of the GOP before and after irradiation was measured. The results indicated that the spacing of layer decreased after irradiation. The ratio of total carbon atom and total oxygen atom increased from 2.40 to 4.31 as well as the sp2 hybridized carbons obviously increased after 2 × 1015 cm−2 irradiation. The XPS analysis suggested the occurrence of reduction, and the Raman spectra indicated that the defects were produced after proton irradiation. Furthermore, the thermal conductivity of GOP decreased, and then increased smoothly as the irradiation fluences were increased, and the electrical property showed the similar trend. The change in the thermal and electrical properties for GOP could be attributed to the defects and the removal of oxygen-containing functional groups, which lead to the phonon conduct path and scattering centers changed under proton irradiation. This study could promote the application of GOP in future space expeditions.

Flexible energy storage devices have received great interest due to the increasing demand for wearable and flexible electronic devices with high-power energy sources. Herein, a novel hybrid flexible hexagonal boron nitride integrated graphene paper (BN/GrP) is fabricated from 2D hexagonal boron nitride (h-BN) nanosheets integrated with graphene sheets dispersion via a simple vacuum filtration method. FE-SEM indicated that layered graphene nanosheets tightly confined with h-BN nanosheets. Further, the Raman spectroscopy confirmed successful integration of BN with graphene. As-prepared BN/GrP free-standing flexible conductive paper showed high electrical conductivity of 5.36 × 104 S m−1 with the sheet resistance of 8.87 Ω sq−1. However, after 1000 continuous bending cycles, the BN/GrP sheet resistance increased just about 8.7% which indicated good flexibility of the paper. Furthermore, as-prepared BN/GrP showed excellent specific capacitance of 321.95 F g−1 at current density of 0.5 A g−1. In addition, the power and energy densities were obtained as 3588.3 W kg−1, and 44.7 W h kg−1, respectively. The stability of the prepared flexible electrode was tested in galvanostatic charge/discharge cycles, where the results showed the 96.3% retention even after 6000 cycles. These results exhibited that the proposed BN/GrP may be useful to prepare flexible energy-storage systems.

In this study, to achieve a compatible and good dispersion of graphene in polyimide matrix, we synthesized an aromatic diamine, aniline trimer, as a polymerizable graphene dispersant. Polyimide/graphene nanocomposites with 0.25–2% mass fraction of graphene were prepared by in situ condensation of pyromellitic dianhydride, 4,4′-oxydianiline, and aniline trimer (AT) functionalized graphene in DMAc, following subsequent thermal imidization at elevated temperatures. UV-vis and Raman spectroscopy verified the π–π interactions between AT and graphene. The microstructure analysis using XRD, SEM, and TEM were performed to investigate the morphology of graphene in the polyimide matrix. The thermal, mechanical, and tribological properties of polyimide/graphene nanocomposites were investigated by TGA, DMA, and friction and wear tests. In view of the ease of preparation and their superior physical properties over neat polyimide, PI/G composites prepared in this study showed promising applications as wear-resistant and self-lubricating materials.

The catalytic activity of transition metals with regard to carbo-hydroxyl molecules (CxHy) has triggered new technological developments in graphene growth. Both the opening of the Dirac-point by controlling the number of graphene layers as well as the patterning of the graphene are critical for applications such as transistor-based electronics. In this work, we have developed a method to control the position and number of layers (n = 0, 1, and more than 2) during graphene growth based on our previous key ideas. This was achieved by using pre-patterned (Ni pre-patterned for more than 2 layers due to its high carbon solubility compared to Cu and MgO pre-patterned for 0 layer graphene due to the low catalytic activity and carbon solubility) ultra-flat Cu foils made using the peeled off method from a c-plane sapphire substrate.

A graphene/silicon composite paper is considered as a promising anode material for flexible batteries. Herein, a highly conductive, flexible, self-supporting, and binder-free graphene/Si composite paper has been prepared via in situ iodine doping and simultaneous reduction of a graphene oxide/silicon composite slice with a solution of hydrohalic (HI) acid as a reducing agent. The in situ iodine doping not only increases the electrical conductivity of the graphene/silicon composite paper, but also improves the strength of the graphene matrix; this results in high capacity and enhanced cycling stability. The in situ iodine-doped composite paper is used as a flexible, self-supporting, and binder-free electrode. The composite paper exhibits a stable capacity retention of 805 mA h g−1 after 100 cycles and an enhanced rate capability, which shows superior performance as compared to the common thermally reduced rGO/Si composites. The high flexibility and high conductivity as well as improved electrochemical performance of this binder-free self-supporting paper anode make it attractive for LIB applications in flexible storage devices.

A new and facile method for the fabrication of polysulfone-graphene oxide composite membranes is reported, where after casting, phase inversion is carried out with graphene oxide flakes (GO) in a coagulation bath. The membranes were characterized and the morphology was analysed using scanning electron microscopy. A bacterial inhibition ratio of 74.5% was observed with membranes fabricated from a very low concentration of di-water-GO non-solvent (0.048% of GO). The membranes were successfully tested for permeate flux and fouling resistance using activated sludge filtration from an MBR system. The observed trend shows that GO can operate as a protective barrier for membrane pores against the bacterial community. To our knowledge this is the first time where the immersion precipitation mechanism was carried out in a coagulation bath with GO flakes under continuous stirring. Using this method, a very low concentration of GO is required to fabricate membranes with conventional GO composite membrane properties and better selectivity. © The Royal Society of Chemistry.

A novel composite catalyst based on in situ synthesis of W1+49 nanorods on reduced graphene oxide sheets was successfully fabricated through a one-pot solvothermal route. The as-prepared W18O49–reduced graphene oxide (rGO) composite has been systematically characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman microscopy, X-ray photoelectron spectra, and a rotating disk electrode. Compared to W18O49 nanorods or reduced graphene oxide alone, or their physical mixture, the composite catalyst exhibited unexpectedly high ORR activity with a more positive onset-potential (close to that of Pt/C) and a higher kinetic current density (JK), which is mainly attributed to the nanorod morphology, surface oxygen vacancies of W18O49, and strong coupling interaction between the W18O49 nanorods and reduced graphene oxide sheets. These results raise the possibility of developing low-cost and efficient ORR electrocatalysts.

We demonstrate confinement of CVD grown MoS2 to a patterned graphene area, forming a vertically stacked 2D heterostructure. The CVD-grown graphene had been transferred onto a Si wafer and patterned using photolithography. Raman mapping and spectral analysis reveal few-layer MoS2 grew selectively on graphene regions, and not on the surrounding SiO2 substrate surface. We also report CVD growth of WS2 directly on transferred graphene. Unlike MoS2, no few-layer regions were found; the WS2 was found to be either monolayer or at least five layers (bulk). The WS2 coverage was only partial, but selectivity to graphene is apparent. These findings have the potential to significantly advance fabrication of vertical 2D heterostructures and related devices, and suggest the selective growth on graphene may be applicable to TMDCs in general.

Recently, nitrogen-doped graphene has attracted significant attention for application as an anode in lithium-ion batteries due to effective modulation of the electronic properties of graphene. Herein, we report a facile route to successfully synthesize a series of tin-based materials (including Sn, SnO2, and SnS2) supported on N-doped reduced graphene oxide (N-rGO). Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images indicated that the Sn-based materials were uniformly and tightly dispersed on the surface of N-rGO. When used as an anode in LIBs, the electrochemical performances of the proposed electrodes were systematically investigated and compared. The results show that among these electrodes, SnS2/N-rGO with a matched layered structure delivers the best performance with not only high specific capability but also excellent cycling stability.

Controlling the neutral plane of a multilayer structure is crucial in designing a reliable flexible display, where the bending strain imposed on the individual layers that are positioned closer to the neutral plane can be significantly reduced. In this study, we explore the usage of polymer/graphene composites with different concentrations of graphene flakes to systematically vary the modulus in attempt to control the location of the neutral plane to the desirable position. Nanoindentation of the PMMA/graphene composite film on Si substrate revealed that increasing the graphene flake content led to the enhancement in hardness and modulus of the composite. The increased Young's modulus caused a shift in the neutral plane position towards the organic emissive layers by ∼2.2 μm that resulted in a reduction of bending strain in the organic light emitting diodes with a typical multilayer structure. Furthermore, gas permeability against O2 and water molecules showed that the gas transmission rate of PMMA/graphene composites decreased as the content of graphene flakes increased since the randomly mixed graphene in PMMA can efficiently hinder the O2 and water molecules from transporting through the thickness of the composite, thereby enhancing the barrier properties.

Graphene/Co3O4 nanowire composite films were successfully synthesized using a simple, three-step treatment, and the effect of the Co3O4 nanowire content on the electrochemical properties of the composite films was studied. The one-dimensional Co3O4 nanowires were homogeneously embedded and dispersed between prepared graphene papers, forming a layered graphene/Co3O4 nanowire hybrid structure. These composite films exhibited better electrochemical properties than previously reported ones, such as graphene/CNT, where carbon spheres existed in the graphene composites, which were fabricated using the same method but without the Co3O4 nanowires. The addition of a small amount of Co3O4—typically 8 : 1 by weight (reduced graphene oxide (RGO) : Co3O4)—to form thick RGO/Co3O4 sandwiches in the form of papers resulted in an excellent specific charge capacity of 278.936 C g−1 at a scan rate of 5 mV s−1. These results indicate the potential of the composite for the development of highly capacitive energy storage devices for practical applications.

Binder-free and free-standing electrodes have been regarded as an attractive and promising structure in lithium–sulfur batteries. In this work we describe how a free-standing sulfur/reduced graphene oxide with embedded carbon nanotubes electrode has been synthesized by a novel, facile and eco-friendly method taking advantage of the solubility difference of polar and nonpolar materials. First, the nonpolar elemental sulfur is dissolved in a weak polar solvent (ethanol) by intensive ultrasonication. During a subsequent heavy polar solvent (deionized water) drop-wise procedure, nano-sized sulfur particles are precipitated from the ethanol and deposited on the dispersed carbon nanotubes and graphene oxide. Noticeably, since ascorbic acid is taken as the reducing agent for graphene oxide at 75 °C, the process produces no toxic byproducts. Besides, the ‘as-designed’ sulfur/reduced graphene oxide with embedded carbon nanotubes graphene oxide displays a unique structure with both the sulfur and carbon nanotubes embedded in the basal plane of reduced graphene oxide. The manufactured electrode is found to exhibit excellent rate capability and cyclability, with the maximum capacity of 1025 mA h g−1 observed in the third cycle and a stable capacity of 704 mA h g−1 after 100 cycles.

Copper/graphene composites are lightweight and possess many attractive properties such as improved mechanical, electrical, and thermal properties. The organization of copper atoms at the copper/graphene interface highly influences the abovementioned properties. In this study, the organization of copper atoms and applied force-induced desorption of copper from a graphene substrate were studied via molecular dynamics (MD) simulation. The copper atoms were organized in face-centred cubic (fcc) and hexagonal close-packed (hcp) lattices over the graphene substrate. However, at the copper/graphene interface, copper atoms were organized in the {111} facet of the fcc lattice. The applied force-induced desorption of copper atoms from a graphene substrate was studied at high temperature (T = 1000 K). A critical force was required to be exceeded before the detachment of copper atoms from the substrate. It was found that a higher critical force was required to remove copper atoms from the graphene substrate in the z-direction (perpendicular to the substrate) compared to that in the x-direction. The outcome of this study may provide useful scientific information about the metal/graphene interface properties, which will help enhance the performance of graphene-based metallic nanocomposites.

III–V semiconductor/graphene tubular structures with diameters of 4.5–5.4 μm have been fabricated on a silicon platform by rolling up monolayer CVD graphene together with heteroepitaxial InGaAs/GaAs bilayers. Scanning electron microscopy (SEM) reveals that transferred graphene adheres to the wall of the Si-based InGaAs/GaAs microtube. Micro-Raman spectroscopy measurements show remarkable redshifts of the G and 2D bands of graphene after planar graphene totally rolls up, reflecting that rolled-up graphene is under uniaxial tensile strain and the strain originates from the rolled-up InGaAs/GaAs microtube. We also fabricated GaAs-based III–V semiconductor/graphene tubular structures with diameters of 3.7 and 4.7 μm, respectively, thus finding an approach to graphene strain engineering (i.e., the Raman redshift and tensile strain of rolled-up graphene increase with the decrement of microtube diameter). Obviously, assembling strained graphene with III–V semiconductors in rolled-up form on a Si platform will bring about a variety of Si-based electronic and optical applications in the future.

In this paper, a novel and scalable method to fabricate graphene/carbon nanotube (CNT) hybrid transparent conductive films on Cu substrates, which combines electroplating and chemical vapor deposition (CVD) is proposed and demonstrated. The Cu substrate was electroplated with electrolyte containing conductive CNTs; then, a uniform graphene film was grown on Cu. After a commonly utilized polymethyl methacrylate assisted transfer process, a hybrid graphene/CNT transparent conductive film was obtained at the target substrate. Conventional graphene grown on electropolished Cu was used as the reference sample. The comprehensive characterization using scanning electron microscopy (SEM), Raman microscopy system, and transmission electron microscopy (TEM) selected area electron diffraction pattern show that the CNTs are uniformly covered by a monolayer graphene with comparable quality to graphene grown on electropolished Cu. The hybrid thin films exhibit outstanding surface morphology (RMS of 1.26), obviously enhanced electrical properties (the square resistance decreases from 490 to 394 Ω sq−1), better surface wettability (7° decrease in contact angle), and a negligible transmittance loss (1.3% reduction at 550 nm) compared to CVD graphene that was grown on electropolished Cu. It is anticipated that the graphene/CNT hybrid films that are fabricated using the proposed approach can be a promising alternative to ITO to realize the emerging, particularly flexible optoelectronic devices.

Multi-quaternary ammonium surfactants are assembled co-operatively with graphene oxide (GO) to generate two-dimensional (2D) silicalite-1. The hybrid composites behave with controllable electrical conductivity and exhibit a specific surface area (SBET) as high as 643 m2 g−1.

Nitrogen-doped activated carbon/reduced graphene oxide composites are prepared by pre-carbonization of the precursors (mixture of graphene oxide and nitrogen-doped activated carbons) and KOH activation of the pyrolysis products. Nitrogen-doped activated carbons were prepared from waste particleboard bonded with ureaformaldehyde resin adhesives. Graphene oxide was prepared from graphite according to the modified Hummers' method. The effects of the mass ratio of KOH and the precursor and the mass radio of graphene oxide in the precursor on electrochemical properties are investigated, respectively. The results demonstrated that graphene oxide as precursor was activated and reduced via high temperature and wrapped on the outer surface of the active carbon particles. The thermally reduced graphene oxide sustains the activated carbon particles as a wrinkled carrier after activation. The electrode of GO–AC–KOH 1–4–4 has achieved the highest specific capacitance of 265 F g−1 and increased 17.8% comparing with the activated carbon (225 F g−1) under a current density of 50 mA g−1 in a 7 mol l−1 KOH electrolytic solution. Moreover, the symmetrical supercapacitor show an excellent cycling stability with capacitance retention 92% of the initial capacitance after 3000 cycles at a current density of 5 A g−1. It is also found that KOH activation of disused composite panels is an efficient and straightforward approach to production of low-cost GO–AC composite for electrochemical capacitors.

Nanocomposites of MnS anchored on graphene, nitrogen-doped graphene and boron-doped graphene have been prepared by a simple wet chemical process. The effect of graphene concentration in MnS and the effect of doping type in the composites are studied through the use of various characterization techniques. An electrochemical performance better than that of pure MnS has been observed in the graphene based composites. The doping of N and B atoms in graphene can further enhance the electrochemical activities of the nanocomposites. The present study demonstrates that MnS with doped graphene has large electrode/electrolyte interfaces, which offers more active sites and ensures a high charge storage capacity of the composite. A maximum specific capacitance of 696.6 and 353.8 F g−1 are measured for MnS/BG-9 and MnS/NG-9 composite, respectively, at a 5 mV s−1 scan rate, whereas the pure graphene composite (MnS/G-9) exhibits only a maximum specific capacitance of 156 F g−1.

A novel scotch tape assisted direct transfer of graphene onto different flexible and rigid substrates, including paper, polyethylene terephthalate, flat and curved glass, SiO2/Si, and a solution-processed high-k dielectric layer is presented. This facile graphene transfer process is driven by the difference in adhesion energy of graphene with respect to tape and a target substrate. In addition, the graphene films transferred by scotch tape are found to be cleaner, more continuous, less doped and higher-quality than those transferred by PMMA. Based on that, the tape transferred graphene is employed as a carrier transport layer in oxide thin-film transistors (TFTs) with different gate dielectrics (i.e., SiO2 and high-k ZrO2). The In2O3/graphene/SiO2 TFTs exhibit a high electron mobility of 404 cm2 V−1 s−1 and a high on/off current ratio of 105, while the counterpart In2O3/graphene/ZrO2 TFTs exhibit improved electron transport properties at an ultra-low operating voltage of 3 V, which is 20 times lower than that of SiO2-based devices. In contrast, the ZrO2-based TFTs with PMMA-transferred graphene exhibit no detective electrical properties. Therefore, the proposed scotch tape assisted transfer method will be particularly useful for the production of graphene films and other two-dimensional materials in more cost-effective and environmentally friendly modes for broad practical applications beyond graphene-based field-effect transistors (GFETs).

An efficient strategy is developed for the fabrication of graphene-filled polypropylene (PP) nanocomposites with graphene nanosheets orderly oriented in the in-plane direction. The nanocomposites with an anisotropic coefficient as high as 35 000 in electrical resistivity were fabricated by a sequential biaxial stretching process. Polymethylmethacrylate (PMMA) was employed to bridge graphene to the non-polar PP matrix, which facilitates the homogeneous dispersion and the orientation of the chemically converted graphene nanosheets. A PMMA/graphene masterbatch was firstly prepared and blended into the PP matrix. During the biaxial stretching, the PMMA/graphene phase was transformed from beads to sheets, which induced the in-plane orientation of the graphene nanosheets. As a consequence, the storage modulus and the conductivity of the nanocomposites were improved in the in-plane direction. The effects of graphene content and draw ratio on the anisotropy of the PP/PMMA/graphene nanocomposites were discussed in detail. This strategy of orientation-effectiveness and cost-effectiveness can be potentially integrated with commercialized biaxial stretching processes to produce high-quality anisotropic polyolefin/graphene composite films.

To address the poor dispersibility and incompatibility of graphene toward potential applications, we propose an approach to prepare high-density modified graphene sheets by combining solvent exfoliation of graphite with chemical modification of ionic liquids (ILs). Graphite is exfoliated into graphene sheets along with in situ modification in ILs-containing solution, and ILs–modified multilayer graphene (MLG) is formed because as-exfoliated graphene sheets with the charged groups of ionic liquids can undergo self-assembly together through electrostatic interaction. Here, three ILs–modified MLG was prepared using different alkyl imidazolium ILs, and their structures and tribological properties were investigated in detail. High-density coverage of IL cation and anion moieties is achieved, remarkably enhancing the dispersibility of the graphene in lubricant. MLG hybrid nanofluids show excellent friction-reducing and anti-wear ability for the contact of steel/steel because of the synergistic effect of a physical adsorption film and a tribo-chemical reaction film on the sliding surfaces.

Printing of electronic devices on a paper substrate using 2D graphene-based ink is an opening gate to innovative applications, where devices would be biodegradable, eco-friendly and can be disposed of with negligible impact on the environment. A resistor is a key element of electronic devices and their application area depends upon its power rating and temperature coefficient of resistance (TCR). In this work, in house developed graphene ink is successfully utilized to fabricate a paper-based resistor using a bar coating technique. Dimensional patterning with precise known values of resistance is achieved using a laser with freedom of shape and size which has been explored for the first time on a paper substrate. The resistor has potential to handle ∼7 W power at room temperature with capacity to withstand up to 200 V which is the highest among reported printed resistors. A dual, low and high TCR is observed, correspondingly in cold (173 K to 300 K) and hot (300 K to 373 K) temperature regions with an activation energy Ea of ∼8 meV for the cold region which is 375 percent lower than the hot region (∼30 meV). The dual TCR behaviour is of great importance for application as a stable resistor up to room temperature, and as a thermistor above room temperature.

Reduction of graphene oxide with different reduction degrees was carried out using a hydrothermal reduction method at 130–190 °C. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectrometry, Raman spectroscopy, and electrochemical testing methods were conducted to investigate the effect of reduction of the graphene oxide gel on the Li–S battery electrochemical performance. The results indicated that the reduced graphene oxide gel was a 3D network graphite structure. The sulfur-based composite material was uniformly embedded, and sulfur polymer loss was suppressed. The reduction degree of graphene oxide (GO) gel increased with increasing water fluid temperatures. In contrast, when the water fluid temperature was 190 °C, the best rate performance of the electrode was observed.

Fe3O4/graphene composites were synthesized as an advanced electromagnetic wave absorption material by a solvothermal method in a system of ethylene glycol. The Fe3O4 nanoparticles were homogeneously anchored on the graphene sheets and the structures of the nanoparticles could be experimentally controlled from ring-like spheres, flower-like spheres to solid spheres by changing the concentration of the oxide graphene. Microwave absorption tests demonstrated that the structures of the nanoparticles had a positive influence on the microwave absorption properties. Especially, for the Fe3O4/graphene composite with a flower-like structure, the minimum reflection loss value (RL) could reach −53.2 dB and the bandwidth of RL less than 10 dB (90% absorption) ranged from 8.1 to 16 GHz at a thickness of 2.5 mm, which is among the best-reported performances of Fe3O4/graphene materials, showing a huge potential to be used as a candidate for microwave absorbing materials.

Till now, several innovative methods have been developed for the synthesis of graphene materials including mechanical exfoliation, epitaxial growth by chemical vapor deposition, chemical reduction of graphite oxide, liquid-phase exfoliation, arc discharge of graphite, in situ electron beam irradiation, epitaxial growth on SiC, thermal fusion, laser reduction of polymers sheets and unzipping of carbon nanotubes etc. Generally large scale graphene nanosheets are reliably synthesized utilizing other forms of graphene-based novel materials, including graphene oxide (GO), exfoliated graphite oxide (by thermal and microwave), and reduced graphene oxide. The degree of GO reduction and number of graphene layers are minimized mainly by applying two approaches via chemical or thermal treatments. The promising and excellent properties together with the ease of processability and chemical functionalization makes graphene based materials especially GO, ideal candidates for incorporation into a variety of advanced functional materials. Chemical functionalization of graphene can be easily achieved, by the introduction of various functional groups. These functional groups help to control and manipulate the graphene surfaces and help to tune the properties of the resulting hybrid materials. Importantly, graphene and its derivatives GO, have been explored in a wide range of applications, such as energy generation/storage, optical devices, electronic and photonic devices, drug delivery, clean energy, and chemical/bio sensors. In this review article, we have incorporated a general introduction of GO, its synthesis, reduction and some selected frontier applications.

Titania nanotubes (TNTs) synthesized by an anodization process were used as a basic substrate material to create different morphologies of quasi-1D (nanoribbons), 2D (nanoflakes), and 3D (nanoparticles) structures via an alkali-controlled hydrothermal route. Graphite oxide was introduced to the hydrothermal unit to fabricate graphene oxide/reduced graphene oxide–titania nanostructure hybrid materials. The presence of NaOH and graphene oxide in the hydrothermal environment had a profound effect on the surface morphology of the nanostructures. NaOH acted as both an etchant to convert TNT surfaces into low-dimensional structures and as a reducing agent to convert graphene oxide into reduced graphene oxide. Graphene oxide inhibited the etching rate to tune the surface morphologies into 1D, 2D, and 3D nanostructures. The electrochemical supercapacitance of all the nanostructures was characterized. Among the prepared samples, the nanostructured hybrid sample of reduced graphene oxide, titania nanoflakes, and TNT exhibited enhanced electrochemical performance with quite high specific capacitance. This superior electrochemical performance is attributed to the specific nanostructure, which provides short pathways for fast transport of salt ions and improved specific surface area for more adsorption sites for the formation of an electrical double layer, which leads to fast charge transfer.

Graphene based composites usually show unique interior structures, extraordinary properties and diverse applications. In this work, with waterborne epoxy resin and an aqueous suspension of graphene oxide (GO) as raw materials, composites of graphene oxide and epoxy resin (GO/ER) with different GO to ER ratios were prepared. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the as-obtained composites have unique structures in which the GO sheets assemble into three-dimensional (3D) networks. It was also illustrated that the mechanical properties, the glass transition temperatures (Tg) and thermal conductivities could be tuned by varying the content of GO in the composites. For instance, the mechanical strength and elastic modulus of the GO/ER composites containing 2% (in weight) GO were increased by 50% and 19.6%; the Tg was increased by 15.59 °C; the thermal conductivity was improved by 1.4 fold in comparison to the bare epoxy resin.

A universal method for the fabrication of graphene composite modified carbon fiber is reported. This method contains two consecutive electrochemical steps. Firstly, the compact and corrugated graphene film is coated onto the carbon fiber (graphene coated carbon fiber, GCF) by electrochemically reducing graphene oxide (GO) dispersion followed by drying in air. Subsequently, the second components are electrochemically deposited on the graphene film, forming the graphene composite modified carbon fiber. The amount of both the graphene and the second components can be easily controlled by the electrochemical parameters. Double salt/GCF, noble metal nanoparticles/GCF, conducting polymer/GCF and layered double hydroxide/GCF were successfully prepared, suggesting the versatility of this method. The PB/GCF showed a good electro-catalytic activity towards H2O2 and can be used in the detection of H2O2 with a wide linear range from 10 to 1310 μM and high sensitivity of 2.2 mA cm−2 mM−1. This method developed here may open a new way to the fabrication of high performance CF-based electrochemical microsensors.

In this work, covalently crosslinked nanocomposite hydroxide conducting membranes were developed on the basis of functionalized graphene oxide and quaternized polysulfone. Fourier transform infrared attenuated total reflection spectroscopy and transmission electron microscopy were employed to characterise the structure and morphology. The properties of AEMs including water uptake, swelling ratio, mechanical properties and ionic conductivity were measured. The resultant nanocomposite membrane containing 2% functionalized graphene oxide is tough and flexible, demonstrating a water uptake of 19.44% and an ionic conductivity of 1.27 × 10−2 S cm−1 at 60 °C, a tensile strength of 14.90 MPa and a moderate elongation rate at break. Furthermore, it still maintained its flexibility and toughness after treatment in 1 M NaOH solution for 744 h at 50 °C.

Precise assembly of exfoliated graphene sheets on electrode surfaces plays a major role for next generation electrodes to be used in sensors, batteries, fuel cells, supercapacitors and other types of energy storage devices. Here, we achieve vertical assembly of sulfonated, few-layer graphene on a metal surface. The few layer graphene flakes were extensively decorated with dopamine capped iron oxide nanoparticles utilizing electrostatic interactions between the nanoparticles and the graphene sheets. The attached nanoparticles drived the assembly of the graphene nanosheets into a vertical orientation on a gold surface under the effect of a moderate external magnetic field.

A simple method, i.e. the calcination of a mixture of Co(NO3)2, PEG-PPG-PEG Pluronic® P-123, and melamine in the presence of graphene oxide (GO), has been adopted for the synthesis of Co3O4 nanoparticles encapsulated in a graphene supported carbon matrix (Co3O4@C/graphene). It shows that the co-existence of P123, melamine, and GO was crucial to obtain the small sized Co3O4 nanoparticles encapsulated in the graphene supported carbon matrix. The resulting Co3O4@C/graphene was found to be highly active for the oxygen reduction reaction and exhibited higher electrocatalytic activity and better stability than the commercial Pt/C with 20 wt% Pt loading. Their high electrocatalytic activity could be attributed to the synergistic coupling between Co3O4 and the nitrogen-doped carbon matrix/graphene, the small Co3O4 nanoparticle size, and the presence of the nitrogen doped porous carbon matrix and the carbon encapsulated structure, which make the Co3O4@C/graphene kinetically facile and highly stable during complicated electrochemical processes.

The present work is focused on the electrical characterization of laser-assisted reduced graphene oxide by point-contact techniques. The aim is twofold: firstly, the careful investigation of in-line two and four point-contact techniques applied to macroscopic samples of reduced graphene oxide. The combination of both methods has shed light on the role of the point-contact when extracting the intrinsic resistivity of the material. Secondly, once the measurement protocol is well understood, it is applied to improve the conductivity of the samples by the adjustment of the initial colloid concentration and the photothermal power intensity used for the reduction. The final optimized samples present promising conductivity, comparable to that of large graphene sheets obtained by chemical vapor deposition methods.

Transition metal carbonates with high energy density of lithium storage via conversion reactions as anode materials for lithium-ion batteries are a hot research focus. However, the large volume changes during the processes of insertion/extraction of Li+ ions and low electronic conductivity are great challenges. Herein, a nano-layered MnxCoyNizCO3/graphene composite and micro-spherical MnxCoyNizCO3 are synthesized via a facile hydrothermal route in the presence and absence of graphene, respectively. As an anode material, the prepared MnxCoyNizCO3/graphene composite delivers a final 500th reversible discharge specific capacity of 1046 mA h g−1 at 100 mA g−1 and furthermore presents a high value of 711 mA h g−1 at 1000 mA g−1 after 500 cycles, which shows prominent superiority in comparison with MnxCoyNizCO3 (517 mA h g−1 at 100 mA g−1 after 500 cycles) and other reported works about transition metal carbonates. The high reversible capacity, long-term cycling stability and perfect rate performance of the MnxCoyNizCO3/graphene composite should be ascribed to the existence of graphene, which plays an important role in keeping the nanostructure of the sample, enhancing the electronic conductivity of the sample, preventing the aggregation of particles and accommodating volume changes of the electrode during the cycling process. Hence, the prepared MnxCoyNizCO3/graphene composite is a promising anode material for lithium-ion batteries.

The reinforcement of rubber by graphene has generated great interest in recent years. The dispersion of graphene in a rubber matrix, however, remains a challenge. In this study, ferroferric oxide (Fe3O4) was used as a carrier to prepare graphene/Fe3O4 hybrid particles, in order to improve the dispersion of graphene in nitrile rubber (NBR). The graphene hybrid particles prepared by co-precipitation synthesis was added into NBR solution to prepare composites. Results show that there was about 90% improvement in tensile strength when 4 phr of graphene hybrid particles (equally only 0.5 phr of graphene in NBR) were added to the matrix. In contrast, the tensile strength of NBR decreased when 4 phr of Fe3O4 were added. SEM and XRD both explained the mechanism for the reinforcement of graphene hybrid particles. The DMA results show higher Tg and a higher value of tanδ for the modified NBR, further proving the reinforcement mechanism, i.e. the hybridization of graphene and Fe3O4 improves the dispersion of graphene in NBR and the interfacial action of graphene with NBR. Moreover, addition of graphene hybrid particles gives NBR extra properties such as surface wettability and magnetism, providing a useful guide for the preparation of functional graphene/rubber composites.

Controllable integration of platinum nanoparticles (PtNPs) and a carbonaceous material is a promising strategy to obtain cost-effective and highly efficient nano-catalysts. Three-dimensional (3D) graphene-based aerogel is considered as an ideal catalyst support because it not only possesses the superior properties of graphene, but also can provide a high loading volume with hierarchical 3D porous architectures. In this paper, PtNP-decorated 3D nitrogen-doped graphene aerogel was prepared through a one-pot hydrothermal route for the first time. Compared to PtNP-decorated 3D graphene aerogel or PtNP-decorated 2D graphene, this nanocomposite shows excellent electrocatalytic activity because of the nitrogen doping and 3D porous structure.

The objective of this study was to investigate Joule heating/electric swing adsorption (ESA) as a mode of regeneration and to compare the carbon dioxide (CO2) adsorption capacity of pristine graphene films and reduced graphene oxide (rGO) aerogels. Joule heating/ESA has not been previously demonstrated in graphene based structures. Various forms of graphene have been previously evaluated for their use as a CO2 adsorbent, but most of these studies have focused on graphene oxide powders and films. We utilize both pristine graphene and rGO; we also highlight regeneration through Joule heating in contrast to heating under vacuum or by pressure swing. The amount of CO2 captured by graphene films and rGO aerogels was 0.52 ± 0.02 and 0.94 ± 0.02 g of CO2 per g of adsorbate, respectively. This adsorption capacity of pristine graphene films and rGO aerogels was found to be stable over multiple samples and multiple cycles of adsorption and electrical current stimulated desorption.

The effects of the hydrocarbon chain-length of aliphatic surfactants on the preparation of graphene oxide from mildly-oxidized graphite oxide through intercalation and the intercalating mechanism have been studied in this work. This study was performed on a mildly-oxidized graphite oxide and its exfoliated products through the measurements of X-ray diffraction, ultraviolet visible spectrophotometer, atomic force microscopy, cyclic voltammetry, zeta potential, Fourier transformed infrared spectra and X-ray photoelectron spectrometer. The experimental results have shown that the in-plane graphitic order remained unaltered after intercalating surfactants into the graphite oxide. The yield and quality of prepared graphene oxide were proportional to the hydrocarbon chain-length of the aliphatic surfactants. Also, it was found that the aliphatic surfactants were intercalated into the lamellas of graphite oxide by means of hydrogen bonding and hydrophobic attractive force instead of electrostatic attraction or chemical bonding.

Developing synthetic methods for graphene based cathode materials, with low cost and in an environmentally friendly way, is necessary for industrial production. Although the precursor of graphene is abundant on the earth, the most common precursor of graphene is graphene oxide (GO), and it needs many steps and reagents for transformation to graphite. The traditional approach for the synthesis of GO needs many chemicals, thus leading to a high cost for production and potentially great amounts of damage to the environment. In this study, we develop a simple wet ball-milling method to construct a V2O5/graphene hybrid structure in which nanometre-sized V2O5 particles/aggregates are well embedded and uniformly dispersed into the crumpled and flexible graphene sheets generated by in situ conversion of bulk graphite. The combination of V2O5 nanoparticles/aggregates and in situ graphene leads the hybrid to exhibit a markedly enhanced discharge capacity, excellent rate capability, and good cycling stability. This study suggests that nanostructured metal oxide electrodes integrated with graphene can address the poor cycling issues of electrode materials that suffer from low electronic and ionic conductivities. This simple wet ball-milling method can potentially be used to prepare various graphene based hybrid electrodes for large scale energy storage applications.

We report a simple and efficient approach for graphene production, by electrochemical exfoliation of graphite rods, in acidic solutions. The applied bias and electrolyte concentration were optimized. The X-ray powder diffraction (XRD) patterns of nanosheets reveal the decreasing, or even the disappearance, of the graphene oxide peak by reducing the electrochemical exfoliation bias from +6 to +2.5 V. Thus, graphene with different oxidation degrees can be obtained by controlling the applied bias. An optimal graphene sample was prepared in a mixture of H2SO4 : HNO3 (3 : 1 ratio; 1 M each) at a bias of +3 V. The interlayer spacing, crystallite size and the average number of layers were determined by XRD. The structural and morphological characteristics of the prepared samples were also investigated by Raman Spectroscopy, FTIR Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM).

In tissue engineering, magnetic nanoparticle based polymeric nanocomposites are attractive due to some superior properties that are demonstrated in monitoring the nature of cell proliferation, differentiation and the activation of cell construction in the tissue regeneration phase. Herein, we have developed a non-toxic, antimicrobial, biocompatible and biodegradable magnetic Fe3O4/RGO-g-PHBV composite based porous 3D scaffold. The facile and cost-effective green pathways were chosen to reduce the exfoliated graphite oxide using a new microbial strain, Lysinibacillus fusiformis at room temperature. The reduction of exfoliated graphite oxide and the fabrication of iron nanoparticle embedded Fe3O4/RGO-g-PHBV nanocomposite were confirmed by X-ray powder diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The analysis of the stretching vibrations by Raman spectroscopy indicated that both the graphite oxide and reduced graphene oxide exhibit frequencies at nearly 1560 cm−1 (G-band) and 1307 cm−1 (D-band). Field Emission Scanning Electron Microscopy (FESEM) and high-resolution transmission electron microscopic studies demonstrated the exfoliated nano sheets of the graphite oxide and the uniform distribution of the deposited ferrite nanoparticles. The inclusion of magnetite nanoparticles and reduced graphene oxide in the network of the PHBV matrix revealed the improvement of the mechanical strength of the nanocomposite, in comparison to the pure PHBV copolymer. The magnetic properties measured by vibrating sample magnetometer (VSM) and magnetic imaging resonance (MRI) confirmed the super-paramagnetic behavior of the nanocomposite, evidenced by the saturation magnetization having low coercive field and dark contrast images in the presence of applied magnetic fields. The confocal and scanning electron microscopy analyses demonstrated the excellent fibroblast cell infiltration, adhesion and proliferation into the micro-porous 3D scaffold, indicating the biocompatibility of the Fe3O4/RGO-g-PHBV nanocomposite based supporting biomaterials.

Enhancing the thermal stability of different epoxy acrylates is a critical step towards development of thermally stable organic coating materials. Herein, we examine the thermal properties of a model system based on bisphenol A tetraacrylate by a graphite oxide induced space confinement. Studies related to understanding the critical role of anisotropic particles like graphite and its derivatives in improving the thermal properties of commercially important different epoxy acrylates is still obscure. The samples with 2% (AP2) and 4% (AP4) of graphite oxide loading were found to significantly delay the onset of the thermal degradation of bisphenol A tetraacrylate by 17 °C and 28 °C respectively. Scanning electron microscopy and X-ray diffraction studies of the composites indicated that the bisphenol A tetraacrylate was intercalated between the graphite oxide sheets, resulting in the formation of a nano brickwall type super structure. The d-spacing of graphite oxide was noted to be 0.8 nm, while in the composite, the d-spacing value obtained for AP4 was 1.2 nm. Thermodynamic calculations indicated significant perturbation in the radius of gyration of the pre-polymer in the presence of graphite oxide sheet. Such a finding can be readily extended to other layered like filler materials to understand the physical properties of the pre-polymers under space confinement.

The rolling of semiconductor thin films with graphene layers on top is carried out to integrate distinct material classes. Tubular structures obtained can span from the nanometer to the micrometer range, providing controlled and homogeneous curvature on few-layer CVD graphene systems. Scanning electron microscopy measurements reveal an increase in the tube radius for larger amounts of stacked/rolled graphene sheets. The relation between the retrieved radii for different layered configurations and total layer thickness is fitted with continuum elasticity theory, directly providing elastic parameters such as Young modulus and Poisson's ratio for few-layer graphene systems. X-ray diffraction and Raman spectroscopy evidence that surface modifications due to the transferring methods are negligible and that layer-to-layer registry (graphitization) is not observed. The concept of rolling up layered materials for direct evaluation of elastic properties can be extended to other two-dimensional systems.

Three different architectural designs are developed for manufacturing advanced multi-scale reinforced epoxy based composites in which graphene sheets and carbon fibers are utilized as nano- and micro-scale reinforcements, respectively. In the first design, electrospraying technique as an efficient and up-scaleable method is employed for the selective deposition of graphene sheets onto the surface of carbon fabric mats. Controlled and uniform dispersion of graphene sheets on the surface of carbon fabric mats enhances the interfacial strength between the epoxy matrix and carbon fibers and increases the efficiency of load transfer between matrix and reinforcing fibers. In the second design, graphene sheets are directly dispersed into the hardener-epoxy mixture to produce carbon fiber/epoxy composites with graphene reinforced matrix. In the third design, the combination of the first and the second arrangements is employed to obtain a multi-scale hybrid composite with superior mechanical properties. The effect of graphene sheets as an interface modifier and as a matrix reinforcement as well as the synergetic effect due to the combination of both arrangements are investigated in details by conducting various physical–chemical characterization techniques. Graphene/carbon fiber/epoxy composites in all three different arrangements of graphene sheets show enhancement in in-plane and out of plane mechanical performances. In the hybrid composite structure in which graphene sheets are used as both interface modifier and matrix reinforcing agent, remarkable improvements are observed in the work of fracture by about 55% and the flexural strength by about 51% as well as notable enhancement on other mechanical properties.

In this report we show that the photochemical oxidation of monolayer graphene is strongly dependent on its underlying substrate. It was found that chemical vapor deposition-grown monolayer graphene transferred onto a silicon wafer is more easily oxidized compared to graphene that was left on the copper substrate or transferred onto a H2-annealed copper foil. The differences in the degree of oxidation were tentatively attributed to the varying energies of adhesion between the graphene and the underlying substrate. Our result has significant implications for the outdoor use of graphene as a transparent conducting material.

The short time fabrication of graphene layers on glassy carbon (GCE) and indium tin oxide (ITO) electrodes by simultaneous electroreduction of graphene oxide (GO) and diazonium salts was described for the first time. Initially, aminotriazine groups were introduced on the electrode surface by an in situ process of a diazotization protocol using melamine. Subsequent electrochemical reduction of diazonium groups immersed in GO solution leads to the formation of graphene layers on the electrode surface. Using this methodology, stable graphene layers were fabricated within 10 min on the electrode surface. The simultaneous reduction of triazine diazonium cations and GO and the formation of graphene layers on the electrode surface were confirmed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and cyclic voltammetry (CV). The absence of characteristic peaks in XPS for the diazonium group (403.7 and 405.6 eV) and oxygen functionalities confirmed the reduction of the triazine diazonium cations and GO on the electrode surface. Raman spectra reveal that the intensity ratio of D and G bands (1340 and 1584 cm−1) was increased after the electrochemical reduction of GO. The SEM image shows the formation of thin layers of graphene. Impedance studies indicate that the electron transfer reaction of [Fe(CN)6]3−/4− was higher at the graphene modified electrode (4.10 × 10−4 cm s−1) than at bare (3.77 × 10−5 cm s−1) GC electrode. The electrocatalytic activity of the graphene modified electrode was examined by studying the oxidation of dopamine (DA). The graphene modified electrode not only increased the oxidation current of DA enormously but also shifted its potential towards a less positive potential when compared to bare and GO modified GC electrodes. The present strategy of modification of graphene is simple and requires a very short time.

We present a simple and convenient route to freestanding graphene nanosheets and large-area/patterned graphene nanofilms by thermal annealing of an indium (In) and graphite mixture. In particles mixed with graphite powder catalytically oxidize the graphite powder and produce carbon oxide gases. The carbon oxide gases are then catalytically graphitized to form graphene nanostructures on In. The morphologies of the graphene nanostructures can be controlled by the In geometry: vertically-standing graphene nanosheets are synthesized using In particles and a graphene nanofilm is grown on a thin In layer. In is then completely removed, and thus high-purity graphene is finally produced. The graphene nanosheets exhibited excellent field-emission performance due to high-density edges. In addition, the graphene nanofilms show electrical conductivities comparable to or better than that of reduced graphene oxide. Furthermore, a large-area or a patterned graphene nanofilm is synthesized using a uniform or a pre-patterned In layer, respectively.