Reduced Graphene Oxide Films Research Articles

Flexible and free-standing reduced graphene oxide thick films with PMMA stabilized silver nanoparticles, as a potential probe for cancer thermal therapy

Thermal therapy is an efficient, cost-effective method for treating different types of cancers and hence flexible, light weight, biocompatible heating materials with low power consumption are of utmost importance. Partially reduced flexible, robust and bio-compatible thick graphene oxide films with, mostly edge functionalized Polymethyl methacrylate (PMMA) and in situ grown silver nanoparticles were prepared using simple soak and dry strategy. Larger distribution of silver nanoparticles with a mean diameter of 2.5 nm were anchored towards the edges of these thick films. The electrothermal (Joule heating) performance were found to increase in the presence of silver nanoparticles due to decrease in sheet resistance (0.33 × 104 Ωm) and increase in electron-phonon interaction. These free-standing, flexible films exhibited stable Joule heating behavior under repeated voltage on/off cycles. In-vitro studies performed on breast cancer cells in the presence of the prepared films, with an external applied voltage of 10 VDC, shows 67% cell death. This work proves the potentiality of thick heterogeneous (partially) reduced graphene oxide films towards site specific destruction of solid tumors by utilizing its Joule heating properties.

A rapid heat pressing strategy to prepare fluffy reduced graphene oxide films with meso/macropores for high-performance supercapacitors

Among the various graphene-based macroscopic architectures, paper-like graphene films exhibit outstanding superiority such as high power output, good malleability and scale-up production. However, the two dimensional graphene nanosheets can easily restack to form dense lamellar microstructures especially in paper-like film, which lose most of the accessible surface and fade the performance of films. In this study, a simple yet high efficient heat pressing method is successfully developed to prepare reduced graphene oxide (RGO) nanosheets with crumpled topography, which can weaken the π-π and van der Waals interactions between nanosheets and inhibit the restacking of nanosheets. Therefore, the resultant RGO film exhibits fluffy layered and meso/macroporous structure (this RGO film is named as f-RGOF). Additionally, the chemical reduction combined with iodine doping reaction endow f-RGOFs with high conductivity of 3000–3300 S m−1. Electrochemical studies demonstrate that the f-RGOF exhibits a high gravimetric capacitance (CM) of 238.4 F g−1 at current density of 0.5 A g−1, and ∼67% retention (158.8 F g−1) with a small IR drop (0.16 V) even up to 80 A g−1. Moreover, the electrochemical performance of f-RGOFs only shows a slight decay (85% CM retention and almost no decay for rate capability) with the increase of areal mass loading, indicating the high utilization rate of electrode material. For practical applications, the flexible solid-state supercapacitors (FSSCs) based on f-RGOFs are also fabricated, which exhibit comparable volumetric energy density of 1.7 mW h cm−3 to 4 V/500 µA h Li thin-film batteries as well as excellent mechanical flexibility. These results demonstrate that the strategy can be potentially applied for fabricating restacking-inhibited and high-performance RGO films using in flexible electronic devices.

Defect-engineered reduced graphene oxide sheets with high electric conductivity and controlled thermal conductivity for soft and flexible wearable thermoelectric generators

The direct use of graphene for potential thermoelectric material requires the opening of its bandgap without loss of its high electric conductivity. We herein demonstrate a synchronous reduction and assembly strategy to fabricate large-area reduced graphene oxide films with high electric conductivity and optimized low thermal conductivity assembly. The reduced graphene oxide films have a high electric conductivity and low thermal conductivity, which results from high longitudinal carrier mobility of the lattice domains as well as the enhanced scattering of phonons in the defects and their boundary that substantially reduces the mean phonon free path and the thermal conductivity. Flexible thermoelectric generators were prepared by assembling reduced graphene oxide film on 3D printed polydimethylsiloxane grids, demonstrating a remarkable output voltage of 57.33 mV/g at a temperature difference of 50 K. A wristband-type flexible thermoelectric generator with 7 repeating units generated a maximum power density of 4.19 µW/g at ambient temperature of 15 °C. The 3D printed generator is promising in providing power autonomy to wearable microwatt electronic devices. In addition, we believe that this work can be easily scaled up and can offer the pathway to produce large-scale manufacturing of graphene based materials for future microelectronics and large-scaled flexible and wearable energy harvesting systems.

Reinforced heat dissipation by simple graphene coating for phosphor-in-glass applied in high-power LED

A well dispersed graphene oxide sol was prepared by the improved Hummer method. The atomic force micrographs showed a monolayer structure and larger sheet area. Aiming at improving the poor heat dissipation ability of Phosphor-in-glass (PiG)for remote packaged LED, the reduced graphene oxide film was prepared by photoreduction that after the sol was coated on PiG. UV–Vis spectra showed that the degree of reduction of graphene oxide was related to the illumination time, while the reduced graphene film had high transmittance without affecting the luminescent properties of the fluorescent material. At the same time, the excellent thermal conductivity of the film significantly enhanced the cooling capacity of the PiG, which has a lower stable operating temperature and a higher luminous intensity under high-power excitation compared with the uncoated ones. Software simulation also showed similar results of heat dissipation.

Broadband Microwave Absorbing Composites with a Multi-Scale Layered Structure Based on Reduced Graphene Oxide Film as the Frequency Selective Surface.

A broadband microwave absorbing composite with a multi-scale layered structure is proposed, in which a reduced graphene oxide (RGO) film sandwiched between two layers of epoxy glass fiber laminates serves as the frequency selective surface (FSS). RGO films with the desired electrical properties were synthesized directly by hydrothermal reaction, vacuum filtration, and heat treatment without subsequent processing. With the novel layer-by-layer structure ranging from micro to macro scale, the optimized composite exhibits excellent microwave absorption performance with a total thickness of 3.2 mm. Its reflection coefficient (RC) is less than −10 dB in the entire X and Ku band, reaching a minimum value of −32 dB at 10.2 GHz and an average RC of −22.8 dB from 8 to 18 GHz. Enhanced microwave absorption of the composites is achieved through the optimization of layer thickness in the sandwich structure to promote destructive interference. Improved impedance matching by the introduction of FSS along with the polarization and conduction loss of layered graphene films also contribute to the increased absorption.

Films of Reduced Graphene Oxide with Percolation Networks of Nanographenes

Percolation networks of electrically connected nanographenes are the promising structures for solving the problem of the transfer of their peculiar quantum properties to the macroscopic level. In this work we report the results of investigations, conducted with using a set of complementary physical methods, on the origin, structural motifs and properties of such networks revealed in thermally reduced graphene oxide films. The presence of zero modes, which may be π-electronic states stabilized at the zigzag edges of network elements, has been established.

Efficient and scalable synthesis of highly aligned and compact two-dimensional nanosheet films with record performances

It is crucial to align two-dimensional nanosheets to form a highly compact layered structure for many applications, such as electronics, optoelectronics, thermal management, energy storage, separation membranes, and composites. Here we show that continuous centrifugal casting is a universal, scalable and efficient method to produce highly aligned and compact two-dimensional nanosheets films with record performances. The synthesis mechanism, structure control and property dependence of alignment and compaction of the films are discussed. Significantly, 10-μm-thick graphene oxide films can be synthesized within 1 min, and scalable synthesis of meter-scale films is demonstrated. The reduced graphene oxide films show super-high strength (~660 MPa) and conductivity (~650 S cm−1). The reduced graphene oxide/carbon nanotube hybrid-film-based all-solid-state flexible supercapacitors exhibit ultrahigh volumetric capacitance (407 F cm−3) and energy density (~10 mWh cm−3) comparable to that of thin-film lithium batteries. We also demonstrate the production of highly anisotropic graphene nanocomposites as well as aligned, compact films and vertical heterostructures of various nanosheets.

Ultra-fast charging–discharging planar on-chip micro-supercapacitors based on reduced graphene oxide films by modified liquid–air interface self-assembly

Planar on-chip micro-supercapacitor (POMS), as a new energy storage device, can be easily used for integration with micro/nano electronic devices to provide an effective power source. In this work, a modified liquid–air interface self-assembly method is introduced to fabricate reduced graphene oxide (RGO) films on the silicon wafer for POMSs. The RGO films have good surface morphologies, uniform thickness (31 ± 3.073 nm) and high conductivity (640.3 S cm−1) after hydroiodic acid treatment. The POMS exhibits a maximum stack capacitance of 351.59 mF cm−3 and 98.17% capacitance of POMSs was retained after charging and discharging for 2000 cycles at a scan rate of 1000 V s−1. Specially, there is still a high power density (587.85 mW cm−3) at an ultra-high scan rate of 5000 V s−1 as well as an ultra-fast charging–discharging time (14 ms). The demonstrated POMS has a good application foreground in the preparation of high-performance integrated micro-devices.

Flexible micro-supercapacitors assembled via chemically reduced graphene oxide films assisted by a laser printer

Flexible micro-supercapacitors (MSCs) as power suppliers are important for portable and wearable electronic devices. Despite enormous efforts made, a simple, inexpensive high-throughput technique of graphene-based MSCs is still challenging. In this work, flexible MSCs are fabricated through commercial laser printing of the interdigital configuration of reduced graphene oxide–graphene oxide–reduced graphene oxide (rGO–GO–rGO) where the conductive rGO works as the electrode and the insulated GO serves as the separator. We demonstrate that the as-fabricated MSC devices show high-energy storage capacities, good cyclic stability and remarkable flexibility. The relationship between the geometric parameters (integration level and coverage fraction) and the capacitive performance of the MSCs is studied systematically to build better theoretical guidance for the design of future in-plane MSCs.

In–situ hybridization of polyaniline nanofibers on functionalized reduced graphene oxide films for high-performance supercapacitor

High-performance hybrid supercapacitor is still hampered by lacking of proper electrode materials of desired nanostructures. However, the hybridization of polyaniline (PANI) on functionalized reduced graphene oxide (FrGO) could form such desired nanostructure with uniform graphene distribution, high carriers density and significantly improved cycling stability and rate capability of PANI. Here we report a facile process for the hybridization of polyaniline nanofibers (PANI NFs) on functionalized reduced graphene oxide (FrGO) films by filtering the hybrid suspension of graphene oxide (GO) and in-situ polymerized PANI NFs followed by hydrothermal treatment to reduce GO and sulfur functionalization of rGO. The as-prepared PANI NFs/FrGO composite films were uniform, flexible and stable with a high specific capacitance of 692.0 F/g at 1 A g−1 and an excellent capacitance retention of 53.5% at 40 A g−1. Furthermore, the assembled all-solid-state supercapacitor using the as-prepared composite films as electrodes exhibited a high capacitance of 324.4 F/g at 1 A g−1 and an energy density ∼16.3 Wh kg−1 at a power density of 300 W kg−1, showing a great promising in the applications for portable power and flexible supercapacitor.

The study of wettability in reduced graphene oxide film on copper substrate using electrostatic spray deposition technique

We report the preliminary study of wettability properties of reduced-graphene oxide (rGO) film prepared by electrostatic spray deposition technique. Wettability is an important property in surface material that can drive the direction of development for various applications. The experiments were performed using copper plate as substrate and graphene oxide (GO) solution of 4 mg/ml as coating material. We examined and investigated the effect of various high voltages to surface morphology and wettability of rGO. The voltages are varied at 1.0 and 1.5 kV and substrate temperature was fixed at 150°C. The rGO film was obtained through thermal treatment of GO film at 200°C for 1 hour. The surface morphology of rGO films were examined using optical microscope and scanning electron microscope. The wettability was examined using static contact angle method to determine water contact angle. The results show that the surface roughness and water contact angle of rGO film was affected by deposition voltage. The highest water contact angle of rGO film of 123.98° that indicated good hydrophobic properties was obtained for deposition condition on 1.5 kV.

Electrical and electrochemical properties of reduced graphene oxide film for secondary battery electrode

We prepared thin layer of reduced graphene oxide (rGO) from reduced graphene oxide powder that dispersed in deionized water and dimethylformamide (DMF) using drop-casting technique. We used carboxymethyl cellulose (CMC) as a binder in order to obtain better surface of rGO film with varied concentration of rGO. We obtained that rGO film prepared using rGO dispersed in deionized water has better surface compare to the ones dispersed in DMF. An addition of CMC into rGO has improved its film surface and increasing amount of rGO resulted higher conductivity of the sample. The cyclic voltammogram (CV) of the rGO film has shown a hysteresis curve that correspond to charging and discharging process. From CV measurement we obtain that rGO-CMC film that prepared using 3 mg/ml rGO dispersed in DI water and blend with CMC has higher specific capacitance of 400 mF/g.

Comparative study on chemical reduction of free-standing flexible GO films and their cyclic voltammetry performance

Chemical reduction of graphene oxide (GO) is one of the most practical methods to recover the properties of graphene. However, these properties vary with the reduction agents. Understanding these differences is fundamental to applications related to reduced graphene oxide (RGO). In this work, six different reduction agents were used to make flexible and free-standing RGO films, resulting in different properties such as surface morphology, inner structure, surface C/O ratio, electrical conductivity, and wettability. We found that not all the six reduction agents were suitable for making flexible and free-standing films. Then, we further studied the electrochemical behavior of these samples and found that the electrochemical properties of the RGO films depend on all the properties but electrical conductivity played the most important role in determining the pseudocapacitance behavior.

Fabrication of free-standing graphene oxide films using a facile approach toluene swollen paraffin peeling and green reduction of these films into highly conductive reduced graphene oxide films

Free-standing films of graphene oxide (GO) are regarded as potential materials for numerous applications in different fields. However, fabricating macroscopic free-standing GO films with high throughput is a bottleneck in large-scale application of these films. Here we introduce a method suitable for the mass-scale fabrication of free-standing GO films by exploring paraffin film (Parafilm M®) as a sacrificial substrate. The method involves deposition of GO on a paraffin film and peeling of the paraffin film after swelling it with toluene to obtain free-standing film of GO. Furthermore, the GO films were reduced into highly conductive RGO films using a green reducing agent ascorbic acid. A strategy of treating GO films with CuSO4 solution prior to reduction is also designed to avoid the possible disintegration of GO films in ascorbic acid solution. A detailed comparative study on the properties of RGO films prepared via thermal and chemical treatment and through the combination of both is also reported. An investigation of the variation in the electrical conductivity of the RGO films based on the reduction method is also carried out. The hydrophobic nature of the thermally reduced RGO films is explored for the oil/water separation.

Corrosion protection of mild steel by graphene-based films

We explore the ability of reduced graphene oxide (RGO) and titanium dioxide-decorated RGO (RGO-TiO2) films to protect mild steel from corrosion in 3.5% NaCl. Graphene oxide (GO), prepared using a Modified Hummers method, was reduced using sodium borohydride. TiO2 nanostructures were generated on RGO in a dispersion. The synthesized materials were characterized using UV-visible spectroscopy (UV–vis), Fourier Transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), Thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The obtained results confirm the exfoliation of graphite, reduction of graphene oxide, and formation of predominantly anatase phase of TiO2, grown as nanotubes. Corrosion behaviour of mild steel, with coatings of GO, RGO and RGO-TiO2, was studied using Tafel polarization studies and Electrochemical Impedance Spectroscopy (EIS). Tafel results showed that GO, RGO and RGO-TiO2 shifted the corrosion potential anodically, indicating that they prevent the anodic dissolution of iron. A six order-of-magnitude reduction in the corrosion current was observed with GO-film-coated mild steel coupons, with further reduction resulting in the use of RGO and RGO-TiO2 composite films. Impedance analysis showed that the films exhibited significantly enhanced charge transfer resistance for corrosion of mild steel by more than an order of magnitude compared to uncoated mild steel.

Encapsulated hollow Na2Ti3O7 spheres in reduced graphene oxide films for flexible sodium-ion batteries

The binder-free films of hollow Na2Ti3O7 (NTO) spheres and reduced graphene oxide were employed as anodes for sodium ion batteries. The films were assembled by vacuum filtration of the pre-prepared hollow NTO spheres and reduced graphene oxide nanosheets (NTO-rGO). The ultrathin nanosheets, as the building blocks of hollow spheres, optimize the sodium ion transportation at the particle level. Furthermore, the hollow spheres were employed to prevent the restacking of reduced graphene oxide nanosheets and optimize the sodium ion transportation at electrode level. Thanks to the optimized ion transportation on both particle and electrode levels, the as-prepared NTO-rGO film showed enhanced rate performance of a high capacity of 135 mA h g−1 under the current density of 500 mA g−1 and over 650 cycles, demonstrating the superiority of this unique structure.

In Situ Observation of Resistive Switching in an Asymmetric Graphene Oxide Bilayer Structure.

Graphene oxide decorated with oxygen functional groups is a promising candidate as an active layer in resistive switching devices due to its controllable physical-chemical properties, high flexibility, and transparency. However, the origin of conductive channels and their growth dynamics remain a major challenge. We use in situ transmission electron microscopy techniques to demonstrate that nanoscale graphene oxide sheets bonded with oxygen dynamically change their physical and chemical structures upon an applied electric field. Artificially engineered bilayer reduced graphene oxide films with asymmetric oxygen content exhibit nonvolatile write-once-read-many memory behaviors without experiencing the bubble destruction due to the efficient migration of oxygen ions. We clearly observe that a conductive graphitic channel with a conical shape evolves from the upper oxygen-rich region to the lower oxygen-poor region. These findings provide fundamental guidance for understanding the oxygen motions of oxygen-containing carbon materials for future carbon-based nanoelectronics.

All-solid-state planar on-chip supercapacitors based on reduced graphene oxide by liquid-air interfacial assembly

ABSTRACTAll-solid-state planar on-chip supercapacitors (APCSs) was prepared based on reduced graphene oxide films obtained by liquid-air interfacial assembly method and hydroiodic acid treatment. The reduced graphene oxide films (495.44 S cm−1) have good surface morphologies, uniform thickness and a higher carbon to oxygen atomic ratio (C/O = 11.5) after hydroiodic acid treatment. The APCSs based on reduced graphene oxide delivered an area capacitance 69.57 μF cm−2 and a stack capacitance 2.34 F cm−3. Moveover, they show an energy density of 324.23 μWh cm−3 and a power density of 1167.21 μW cm−3. The demonstrated APCSs provide an important reference for the study of planar supercapacitors.

One-Step Laser Patterned Highly Uniform Reduced Graphene Oxide Thin Films for Circuit-Enabled Tattoo and Flexible Humidity Sensor Application.

The conversion of graphene oxide (GO) into reduced graphene oxide (rGO) is imperative for the electronic device applications of graphene-based materials. Efficient and cost-effective fabrication of highly uniform GO films and the successive reduction into rGO on a large area is still a cumbersome task through conventional protocols. Improved film casting of GO sheets on a polymeric substrate with quick and green reduction processes has a potential that may establish a path to the practical flexible electronics. Herein, we report a facile deposition process of GO on flexible polymer substrates to create highly uniform thin films over a large area by a flow-enabled self-assembly approach. The self-assembly of GO sheets was successfully performed by dragging the trapped solution of GO in confined geometry, which consisted of an upper stationary blade and a lower moving substrate on a motorized translational stage. The prepared GO thin films could be selectively reduced and facilitated from the simple laser direct writing process for programmable circuit printing with the desired configuration and less sample damage due to the non-contact mode operation without the use of photolithography, toxic chemistry, or high-temperature reduction methods. Furthermore, two different modes of the laser operating system for the reduction of GO films turned out to be valuable for the construction of novel graphene-based high-throughput electrical circuit boards compatible with integrating electronic module chips and flexible humidity sensors.

Fabricating reduced graphene oxide films with high volumetric capacitive performances via thermal and acid treatment

Considering the growing requirement for high-performance energy storage devices, active electrode materials with high volumetric performance are urgently needed, but only few reports devote to the preparation of reduced graphene oxide (rGO) with high gravimetric specific capacitance (Cg) and volumetric specific capacitance (Cv). Here, the thermally treated dense rGO films are further treated with concentrated sulfuric acid to achieve the high Cg, Cv and cycling stability. The optimal film possesses high density of about 2.04 g cm−3 and exhibits the maximal Cg and Cv of about 242.3 F g−1 and 494.3 F cm−3 in 1.0 mol L−1 H2SO4 electrolyte based on the two-electrode testing system. Furthermore, the optimal film shows excellent cycling stability in 1.0 mol L−1 H2SO4 (90.2% capacitance retention after 10000 cycles) and excellent rate capability. It is believed that this strategy can be developed as an effective process to prepare rGO-based materials with high capacitive performance for compact energy storage device.