Graphene Nanosheets Film Research Articles

Solution-Processed Functionalized Graphene Film Prepared by Vacuum Filtration for Flexible NO2 Sensors.

Large-scale production of graphene nanosheets (GNSs) has led to the availability of solution-processable GNSs on the commercial scale. The controlled vacuum filtration method is a scalable process for the preparation of wafer-scale films of GNSs, which can be used for gas sensing applications. Here, we demonstrate the use of this deposition method to produce functional gas sensors, using a chemiresistor structure from GNS solution-based techniques. The GNS suspension was prepared by liquid-phase exfoliation (LPE) and transferred to a polyvinylidene fluoride (PVDF) membrane. The effect of non-covalent functionalization with Co-porphyrin and Fe-phthalocyanines on the sensor properties was studied. The pristine and functionalized GNS films were characterized using different techniques such as Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and electrical characterizations. The morphological and spectroscopic analyses both confirm that the molecules (Co-porphyrin and Fe-phthalocyanine) were successfully adsorbed onto the GNSs surface through π-π interactions. The chemiresistive sensor response of functionalized GNSs toward the low concentrations of nitrogen dioxide (NO2) (0.5-2 ppm) was studied and compared with those of the film of pristine GNSs. The tests on the sensing performance clearly showed sensitivity to a low concentration of NO2 (5 ppm). Furthermore, the chemical modification of GNSs significantly improves NO2 sensing performance compared to the pristine GNSs. The sensor response can be modulated by the type of adsorbed molecules. Indeed, Co-Por exhibited negative responsiveness (the response of Co-Por-GNS sensors and pristine GNS devices was 13.1% and 15.6%, respectively, after exposure to 0.5 ppm of NO2). Meanwhile, Fe-Phc-GNSs induced the opposite behavior resulting in an increase in the sensor response (the sensitivity was 8.3% and 7.8% of Fe-Phc-GNSs and pristine GNSs, respectively, at 0.5 ppm NO2 gas).

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.

Preparation of ultrathin graphene film via capillary liquid bridge for uniform lithium nucleation in anode free lithium metal battery

Construction of graphene nanosheet films (GNF) with different thickness is highly important for their various applications. Construction of uniform GNF with defined thickness in nanoscale and large size remains challenge. Herein, a facile liquid bridge of capillary array is firstly designed to facilitate the oriented self-assembly of GNF. It is found that the self-assembly of GNF can be well controlled by Marangoni coefficient, in which the characteristic length (R) of liquid bridge for rapid spreading of trace solution on the Cu foil can be a controllable factor. As a result, the GNF with large-area (m2 level) and high-precision thickness (tens of nanometers) has been prepared. Taking the GNF on Cu substrate as lithium deposition electrode, the uniform Li nucleation and orientation growth can be realized to eliminate the growth of lithium dendrites, ascribing to the high lithiophilic of graphene. In the anode-free Li-LiFePO4 battery, the Coulombic efficiency (CE) of the first cycle can reach 88% at a cathode loading of 3 mg cm–2 and a current of 1 C, while the average CE can reach 99.1% within 100 cycles.

High thermal conductivity and increased thickness graphene nanosheet films prepared through metal ion-free route

With the miniaturization and integration of electronic devices heat conduction becomes a serious problem. Graphene films catch research's attention because of its excellent thermal performance and graphene oxide (GO) has been used as the most common precursor to prepare graphene films. But mostly film fabricated from GO is thinner than 30 μm and much thicker films are required to meet certain requirements. Also taking GO as raw material has many disadvantages such as the introduction of massive concentrated sulfuric acid and metal ions, huge weight loss in heat treatment and so on. Herein, we propose a new strategy to prepare graphene nanosheet films (GNFs) with a thickness of 100 μm by vacuum filtration of expand graphite through weak oxidation (WEG). Unlike common strategy, WEG without any metal ions introduced instead of GO is chosen as our raw material. The addition of nonionic surfactant and the employment of microfluidization can stabilize WEG dispersion. After graphitization at 2800 °C WEGF is transferred to GNF. The obtained 100 μm-thick film possesses a decent in-plane thermal conductivity (TC) of 760 W/mk and electrical conductivity (EC) of 5.2×10 5 S/m. Thick films with high TC can guarantee passing more heat flux and fill in larger gaps inside devices.

Direct fabrication of high-performance multi-response e-skin based on a graphene nanosheet film

With the increasing popularity of wearable devices, lightweight electronic skin (e-skin) has attracted significant attention. However, current fabrication technologies make it difficult to directly fabricate sensing materials on flexible substrates at low temperatures. Hence, we propose a flexible graphene nanosheet-embedded carbon (F-GNEC) film, which is directly grown on a flexible substrate using an electron cyclotron resonance low-temperature sputtering system. The direct batch manufacturing of e-skin is obtained by the unique plasma generation mode of electron cyclotron resonance and the polariton energy transfer mode between the plasma and substrate surface. The F-GNEC film contains a large number of graphene nanosheets grown vertically and the graphene edges can serve as electron capture centers, thereby enabling the multi-response properties. We achieve a high gauge factor of 14,699 under a tensile strain of ε = 0.5% and the changing rate of the resistance reaches to 113.2% when the e-skin is bent to 120°. Furthermore, the e-skin achieves a photocurrent of 1.2 μA under 532 nm laser illumination. The F-GNEC film exhibits a sensitive temperature response and achieves a coefficient of -0.58%/°C in a wide temperature range (30-100 °C). The directly fabricated F-GNEC film-based e-skin is stable and firm and exhibits multi-response detection capabilities, which enable its potential application in virtual reality technology and flexible robots.

A highly conductive self-assembled multilayer graphene nanosheet film for electronic tattoos in the applications of human electrophysiology and strain sensing.

Highly conductive, conformable and gel-free electrodes are desirable in human electrophysiology. Besides, intimately coupling with human skin, wearable strain sensors can detect numerous physiological signals, such as wrist pulse and breath. In this study, a multilayer graphene nanosheet film (MGNF) with high conductivity was prepared by the Marangoni self-assembly for using in tattoo dry electrodes (TDEs) and in a graphene tattoo strain sensor (GTSS). Compared to commercial Ag/AgCl gel electrodes, TDEs have lower skin-electrode contact impedance and could detect human electrocardiogram for 24-hour wearing more accurately as well as electromyogram. Through designing a slim serpentine ribbon structure, a resistance-type GTSS, without deterioration even after 2000 cycles, is well demonstrated for human wrist pulse and breath sensing. With the advantages of high conductivity and conformability, MGNF provides support to fabricate low-cost, customizable, and high-performance electronic tattoos for human electrophysiology and strain sensing.

Improving the flexibility of graphene nanosheets films by using aramid nanofiber framework

Graphene nanosheet (GNS) films exhibit good thermal and electric conductivities due to low oxygen content and defect density. However, the weak interlayer interaction forces have resulted in poor mechanical properties and flexibility for GNS films. In order to meet this challenge, aramid nanofiber (ANF) is introduced into the GNS films by solution mixing, then a small amount of water is added to adjust the aramid nanofiber framework (ANFF) in the solution. The results indicate that adding a small amount of water into the aramid nanofiber/dimethyl sulphoxide (ANF/DMSO) suspension can recover the hydrogen bonds between ANF, promoting the ANF to form a stable framework. This design strategy leads to a delectate balance between flexibility and electric, thermal conductivities. With the improvement of water or ANFF content, the mechanical properties of GNS/ANFF composite films are gradually increased. And the electric and thermal conductivities are not influenced by the water content but decrease with the increasement of ANFF content. Most importantly, the flexibility of GNS films is greatly improved with little sacrifice of electric and thermal conductivities by adding only 2 wt% ANFF (GNS-2). The tensile toughness of GNS-2 composite films is dramatically improved from 30.8 to 108.7 kJ m−3, while the electric and thermal conductivities of GNS films are slightly dropped from 827 to 569 S cm−1 and from 140 to 131 W m−1 K−1, respectively. Moreover, the excellent flexibility of the composite films can be maintained even after 1000 times of direct bending. The good over-all properties together with its easy preparation process endows GNS/ANFF composite films with potential applications in next-generation flexible electric devices.

Controlling pore structure and conductivity in graphene nanosheet films through partial thermal exfoliation

Thermal exfoliation is an efficient and scalable method for the production of graphene nanosheets or nanoplatelets, which are typically re-assembled or blended to form new macroscopic “graphene-based materials”. Thermal exfoliation can be applied to these macroscopic graphene-based materials after casting to create internal porosity, but this process variant has not been widely studied, and can easily lead to destruction of the physical form of the original cast body. Here we explore how the partial thermal exfoliation of graphene oxide (GO) multilayer nanosheet films can be used to control pore structure and electrical conductivity of planar, textured, and confined GO films. The GO films are shown to exfoliate explosively when the instrument-set heating rates are 100 K/min and above leading to complete destruction of the film geometry. Textured films with engineered micro-wrinkling and crumpling show similar thermal behavior to planar films. Here, we also demonstrate a novel method to produce fairly large size intact rGO films of high electrical conductivity and microporosity based on confinement. Sandwiching GO precursor films between inert plates during partial exfoliation at 250 °C produces high conductivity and porosity material in the form of a flexible film that preserves the macroscopic structure of the original cast body.

High-response heterojunction phototransistor based on vertically grown graphene nanosheets film

Carbon-phototransistor with a structure of vertically grew graphene nanosheets embedded carbon (GNEC) film is fabricated through an electron-assisted sputtering-deposition method. This heterojunction phototransistor of GNEC/n-Si exhibits broad detection range (from 450 nm to 1200 nm), high photoresponsivity (1.298 × 104 A/W), and rapid response to on-off optical signals (4.91 μs). Driven by the source-drain voltage applied to the GNEC film, electrons recycle in the circuit before recombination, which enhance drastically the usage efficiency of photo-induced carriers. Besides, GNEC film contains a large amount of graphene edges, which may serve as electron pump in the photovoltaic process based on the e-h separation in the p-n junction. The GNEC/n-Si phototransistor improves the responsivity of ∼103 order compared with that of photodiode mode.

One-step scalable preparation of graphene nanosheets and high-thermal-conductivity flexible graphene films

It is well known that graphene nanosheets (GNSs) have many excellent properties. However, it has been a difficult thing to exfoliate graphite into GNSs in a controllable and scalable manner. In this research, a new strategy named xylitol-assisted ball milling exfoliation (XABME) was developed for the scalable preparation of GNSs. The experimental results characterized by a series of measurements showed that GNSs were successfully exfoliated by the XABME strategy. The structure of the prepared nanosheets was featured by large lateral size and ultra-small thickness. Furthermore, the prepared GNSs easily achieved high production yield (≈54%). Lastly, the as-obtained GNSs and cellulose nanofibers (CNF) were compounded to form some nanomaterial films. The prepared films exhibited excellent flexibility and higher thermal conductivity, with the in-plane thermal conductivity of 90 wt% GNS film (8.0 W/(m·K)) being 11.4 times higher than that of the film without GNSs. This shows that GNSs could effectively enhance the thermal conductivity of the CNF matrix and indicate that these prepared films have great potentials in the thermal management of portable mobile devices.

NiMn hydroxides supported on porous Ni/graphene films as electrically and thermally conductive electrodes for supercapacitors

Solid-state supercapacitors (SSCs) hold great promise in the application in portable and wearable electronic devices due to their great progress in electrochemical performance and fabrication technique in recent years. However, in consideration of increasingly harsh requirements toward electronic devices in miniaturization and operational security, the management of thermal generation and dissipation in SSC devices, which have been rarely considered at present, are very worthwhile to be investigated. In this work, flexible solid-state supercapacitors are assembled by rationally designed electrodes, which are fabricated layer by layer by using of an electrochemically exfoliated graphene (EG) nanosheet film, a porous metallic Ni layer and a NiMnLDH pseudocapacitive material layer. The ultrathin NiMnLDH nanosheets and the porous metallic Ni layer ensure high electrochemical performance for the NiMnLDH/Ni/EG electrodes (2110.4 mF cm−2) and the assembled SSC energy storage devices (732.5 mF cm−2). The employments of the EG film and the Ni layer avoid the SSC energy storage devices suffering from overheating during operation, because the high thermally conductive EG film could effectively dissipate the heat generated in the energy storage devices and the high electrically conductive metallic Ni layer could achieve low internal resistance to alleviate the Joule heat generation in the devices. This work could provide an effective thermal management strategy to promote future application of high-power energy storage devices in electronic industry.

Superhigh Electromagnetic Interference Shielding of Ultrathin Aligned Pristine Graphene Nanosheets Film.

Ultrathin, lightweight, high-strength, and thermally conductive electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) are highly desired for next-generation portable and wearable electronics. Pristine graphene (PG) has a great potential to meet all the above requirements, but the poor processability of PG nanosheets hinders its applications. Here, efficient synthesis of highly aligned laminated PG films and nacre-like PG/polymer composites with a superhigh PG loading up to 90 wt% by a scanning centrifugal casting method is reported. Due to the PG-nanosheets-alignment-induced high electrical conductivity and multiple internal reflections, such films show superhigh EMI SE comparable to the reported best synthetic material, MXene films, at an ultralow thickness. An EMI SE of 93 dB is obtained for the PG film at a thickness of ≈100 µm, and 63 dB is achieved for the PG/polyimide composite film at a thickness of ≈60 µm. Furthermore, such PG-nanosheets-based films show much higher mechanical strength (up to 145 MPa) and thermal conductivity (up to 190 W m-1 K-1 ) than those of their MXene counterparts. These excellent comprehensive properties, along with ease of mass production, pave the way for practical applications of PG nanosheets in EMI shielding.

Synthesis and characterizations of graphene-based composite film for thermal dissipation

In this study, we develop a series of graphene nanosheets(GNs)/carbon nanotubes(CNTs)/copper(Cu) composite film for heat dissipation. Scanning electronic microscopy (SEM), Raman spectroscopy, X-ray photo spectroscopy (XPS), Laser flash and infrared thermal images of composite film are carried out in this study. We discovered that the content of CNTs in composite film plays an important role on heat dissipation performance. Optimized ratio of GNs to CNTs were found to be 6:4. Raman spectra showed that ID/IG ratio of GNs was 0.23, and the ID/IG ratio would increase to 0.84 by adding CNTs with the ratio of 6:4. Laser flash analysis shows that the thermal conductivity (K) could be enhanced from 520 W/m⋅K of GNs film to 687 W/m⋅K of GNs/CNTs composite film. Infrared thermal images also relative the relationship between the microstructure of composite film and heat dissipation performance. These data indicate that as-synthesized graphene nanosheets/CNTs/Cu composite film is a potential candidate for heat dissipation applications.

A multilayer-graphene nanosheet film deposited on a ceramic substrate without a catalyst for constructing an electrochemiluminescence imaging platform.

Chemically and electrochemically stable conducting films are very desirable in the electrochemical industry and electrochemical sensing. In this work, ethanol was used as the carbon source to synthesize a multilayer-graphene nanosheet (MLGNS) film on ceramic substrates by a catalyst-free chemical vapor deposition (CVD) method at 900 °C and under ambient pressure. The developed CVD method is simple, economical and safe and avoids damage to the graphene nanosheet film during its transfer from the metal substrate to the non-metal substrate. The synthesized MLGNS film was well characterized by various techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Raman spectroscopy. The prepared MLGNS film has good chemical and electrochemical stability and satisfactory electrical conductivity thus can be used as a new type of electrode material. The MLGNS film on the ceramic substrate has been fabricated into an electrochemiluminescence (ECL) imaging platform to investigate the oxygen reduction reaction (ORR) and evaluate the activities of ORR catalysts, such as PtNPs. The established MLGNS film-based ECL imaging platform may have promising applications in the study of catalysts for fuel cells, high throughput immunoassay in the clinic, and fast screening of anti-cancer drugs.

Anchored graphene nanosheet films towards high performance solid lubricants

Graphene nanosheet films with improved durability and load capability are highly desired to realize the engineering application of graphene as solid lubricants. Here, we report a general approach to fabricate anchored graphene nanosheet films (A-GNSF), which is based on the selective electrochemical dissolution of graphene-containing metal matrix composites. A-GNSF are composing of many anchored graphene nanosheets, whose parts of basal plane expose on the graphene-containing metal matrix composite's surface while other parts of their basal plane anchor into the composite. The microstructure evolution of the A-GNSF as a function of the duration of selective electrochemical dissolution and the graphene content in composites is investigated and is correlated with their tribological performance. The mechanism on reduction of friction and wear for A-GNSF is also discussed. The results show the unique architecture of the A-GNSF greatly contributes to the rapid formation and the stability of the in-situ developed graphene sliding against graphene lubricating interface. As a consequent, A-GNSF show a friction coefficient as low as 0.14, excellent wear resistance and long lifetime under a contact pressure that is up to 0.88 GPa.

Three-dimensional graphene nanosheet films towards high performance solid lubricants

Graphene nanosheet films (GNSF) show great potential as solid lubricants. They, however, usually suffer from short lifetime and low load capability, limiting their further engineering application. In this work, we try to address these crucial challenges, for the first time, by inducing a unique three-dimensional microstructure into the GNSF. The as-prepared three-dimensional graphene nanosheet films (3D-GNSF) are composed of many crumpled and partially standing graphene nanosheets (GNS) that overlap with each other and form a three-dimensional interconnected network. The morphology, composition and structure of the 3D-GNSF are investigated in detail using scanning electron microscope, X-ray diffractometer, transmission electron microscope and X-ray photoelectron spectroscopy to deduce their possible formation mechanism. Tribological tests are conducted in air as a function of contact pressure that is up to about 1GPa. The results suggest it is the unique architecture of the 3D-GNSF that quickly produces a compact and stable sliding interface consisting of GNS against GNS, enabling 3D-GNSF as promising solid lubricants with low friction, excellent anti-wear ability, good durability and high load capability.

Simultaneous voltammetric determination of acetaminophen and dopamine using a glassy carbon electrode modified with copper porphyrin-exfoliated graphene.

Graphene nanosheets (GSs) were prepared via liquid-phase non-covalent exfoliation of graphite powder in N,N-dimethylformamide under the assistance of copper(II) meso-tetra(4-carboxyphenyl)porphyrin tetrasodium salt Na4(CuTCPP). A glassy carbon electrode (GCE) was modified with a film of such GSs which, due to the good electrical conductivity of graphene and the electrocatalytic properties of Na4(CuTCPP), is capable of simultaneous determination of acetaminophen (AC) and dopamine (DA). The peak currents, best measured at voltage of 0.2V (for DA) and 0.4V (for AC; both vs. SCE), increase linearly in the 0.0024-3.6μM and 0.004-7.6μM concentration ranges, respectively. The detection limits are 0.8nM for DA and 0.7nM for AC. The sensor was successfully applied to the simultaneous determination of AC and DA in pharmaceutical preparations and spiked human serum. The results were in good agreement with those obtained for the same samples by HPLC. Graphical abstract Graphene nanosheets were prepared via a facile liquid-phase exfoliation of graphite with the assistance of copper(II) meso-tetra(4-carboxyphenyl)porphyrin tetrasodium salt. A graphene nanosheet-film modified glassy carbon electrode was fabricated to determine acetaminophen and dopamine through a simple and effective strategy.

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.

Growth and follow-up of primary cortical neuron cells on nonfunctionalized graphene nanosheet film.

Conductive biomaterials are an ideal biosubstrate for modifying cellular behaviors by conducting either internal or external electrical signals. In this study, based on a simple-preparation graphite exfoliation method in organic reagent, a nonfunctionalized graphene nanosheet film (NGNF) with high conductivity and large size was simply fabricated through spraying coating. The biocompatibility of the NGNF was carefully tested with primary cortical neuron cells, and its biocompatibility properties were compared with a chemical vapor deposition (CVD) graphene film. Nonfunctionalized graphene nanosheet (NGN) was first exfoliated from graphite with a flat-tip ultrasonicator probe, and then spray-coated onto glass slide substrate to form the film. The morphology of NGNF was observed with light microscopy and SEM. The morphology and neuronal network formation of primary cortical neuron cells onto NGNF, as shown by DAPI and Alexa Fluor® 488 staining, were observed with fluorescent microscopy. Cell viability and proliferation were measured with MTT. NGNF had better cell biocompatibility than CVD graphene film. MTT test showed that NGNF exhibited no cytotoxicity. According to neuronal network formation at 7 days of cell culture, primary neuron cells aggregated into 50-μm "nuclei"; the average neurite number and length were 3 and 100 μm, respectively. However, these values were almost doubled after 14 days of cell culture. These results may improve the use of NGNF as a conductive scaffold for nerve regeneration.

Fe3O4 nanoparticle anchored layered graphene films for high performance lithium storage

Fe3O4 nanoparticles homogeneously decorated onto layered graphene nanosheets film exhibit excellent cyclic retention and good rate capability when used as anodes in lithium storage.