rGO Film Research Articles

Honeycomb-patterned porous graphene film for electrochemical detection of dopamine

Development of simple, low-cost and facile electrochemical sensor for DA detection is of great significance for the study and treatment of several neurological and psychiatric disorders. Herein, an innovative integration of honeycomb-patterned ordered porous structure with conductive reduced graphene oxide (rGO) was realized through the convenient breath figure method, in which the self-assembly of nontoxic and inexpensive water droplets were involved. Graphene oxide (GO) can be transferred to organic phase by surfactant via a simple self-assembly process to acquire the GO/surfactant complex, which was used as the casting solution in the breath figure method, and thus the skeleton of the porous structure. After electrochemical reduction, honeycomb-patterned porous rGO film was obtained. The prepared rGO-based porous structure modified electrode exhibited a high sensitivity of 1.18 μA/μM and low detection limit of 0.12 μM to DA detection, which are 2.5 and 0.07 folds to corresponding flat films, and are also comparable or even exceeding several functionalized graphene, GO or rGO composites sensor. In addition, excellent anti-interference, reproducibility, repeatability, long-term stability and good accuracy for DA detection in real samples were shown. Importantly, the porous structure can be easily adjusted by changing the preparation conditions, thereby regulating or optimizing the electrochemical sensing performance.

Self-powered photosensor based on curcumin:reduced graphene oxide (CU:rGO)/n-Si heterojunction in visible and UV regions

This study proposes a novel photosensor that uses curcumin:reduced graphene oxide/silicon (CU:rGO)/ n -Si heterojunction, prepared at different molar ratios of rGO with CU. The CU:rGO was deposited on an n-Si by electrochemically. The EDX, XRD, SEM and absorbance analyses of CU:rGO film were investigated. From the I-V measurements, the all CU:rGO/ n -Si devices showed excellent rectification characteristics both in the dark and under various illumination intensities. The device with higher rGO ratio (labelled D1) had better performance overall having the rectification ratio of 86094, the ideality factor of 2.15 and photosensitivity of 198 (at 150 mW/cm 2 ), which was attributed to the extraordinary electro-optical properties of rGO. Hence, the electrical and optical properties of D1 device were analyzed in detailed. The typical I-V measurements were conducted both in dark and under AM 1.5 G illumination of various light intensities. The intensity of the incident light varied from 10 to 150 mW/cm 2 . The photocurrent exhibited a strong dependence on the light intensity. The I-V measurements of another device (labelled D4) prepared under the same conditions were achieved at 365 nm and 395 nm wavelengths and it showed good sensitivity to light even in the UV region. Furthermore, both D1 and D4 devices operated in self-powered mode in visible and UV light without the need for any external voltage. According to the experimental results, the produced CU:rGO/n-Si devices can be potential devices for photosensor applications in a wide spectral region. • A curcumin:reduced graphene oxide(CU:rGO/n-Si heterojunction photosensor, prepared at different molar ratios of rGO with CU. • The EDX, XRD, SEM and absorbance analyses of CU:rGO film were investigated. • The CU:rGO/ n -Si device showed excellent rectification characteristics both under visible and UV light illumination. • Both under visible light and at 365 nm and 395 nm, the device showed self-powered mode. • The photosensitivity reached to 1.0 × 10 5 at the zero biased point for 150 mW/cm 2 illumination power.

Fabricating Graphene Oxide/h-BN Metal Insulator Semiconductor Diodes by Nanosecond Laser Irradiation.

To employ graphene’s rapid conduction in 2D devices, a heterostructure with a broad bandgap dielectric that is free of traps is required. Within this paradigm, h-BN is a good candidate because of its graphene-like structure and ultrawide bandgap. We show how to make such a heterostructure by irradiating alternating layers of a-C and a-BN film with a nanosecond excimer laser, melting and zone-refining constituent layers in the process. With Raman spectroscopy and ToF-SIMS analyses, we demonstrate this localized zone-refining into phase-pure h-BN and rGO films with distinct Raman vibrational modes and SIMS profile flattening after laser irradiation. Furthermore, in comparing laser-irradiated rGO-Si MS and rGO/h-BN/Si MIS diodes, the MIS diodes exhibit an increased turn-on voltage (4.4 V) and low leakage current. The MIS diode I-V characteristics reveal direct tunneling conduction under low bias and Fowler-Nordheim tunneling in the high-voltage regime, turning the MIS diode ON with improved rectification and current flow. This study sheds light on the nonequilibrium approaches to engineering h-BN and graphene heterostructures for ultrathin field effect transistor device development.

Pseudocapacitance-rich carbon nanospheres with graphene protective shield achieving favorable capacity-cyclability combinations of K-ion storage

Pseudocapacitance points out a new direction for the recent research and development of potassium ion anode materials because of its fast energy storage kinetics, which has yielded lots of successful pseudocapacitance-rich examples by introducing more active sites such as doped heteroatoms. However, the negative reactions with the electrolyte in electrochemical process often cause the serious inactivation of active sites, giving a hit for seeking higher pseudocapacitance. In this work we proposed a new strategy to wrap the protective shield for the pseudocapacitance-rich materials to alleviate this matter. By the ultrasonic-induced rGO self-encapsulation of S, N dual-doped carbon spheres, the directional contact between active sites and the electrolyte is blocked, while the rGO films with enlarged interlayer spacing and lots of defects also like filter membrane, accelerate the K+ desolvation and fast diffusion into carbon matrix. Benefiting from the synergistic effect of rGO shielding and filtrating, the pseudocapacitance of S, N dual-doping carbon spheres is fully activated. As the potassium-ion battery anode, the obtained S, N dual-doping carbon sphere@rGO delivers a state-of-the-art capacity of 596 mAh g−1, which achieves a 52.5 % capacity enhancement in contrast to that without rGO shield. As a proof of application, the resultant high-pseudocapacitance carbon anode is incorporated into a potassium ion hybrid capacitor, showing the most favorable capacity-cyclability combinations with the high energy–density of 83 Wh kg−1 after 6500 cycles at 5A g−1.

Highly stable GO/formamide based GOLLCs for free standing film fabrication and their photodegradation applications against organic dyes

In this context, formamide is explored as an efficient solvent for the dispersion of GO sheets and preparation of graphene oxide lyotropic liquid crystals (GOLLCs). Polarizing optical microscopy (POM) studies confirm that GO/formamide dispersion shows smectic phase at lower concentration (< 2 mg/mL) and nematic phase up to 300 mg/mL. GOLLCs are found stable for up to 24 months. Probably it is the first report on the formation of GOLLCs in formamide and their long-term stability up to 24 months. GOLLCs are studied for steady and dynamic rheological behavior at room temperature. All the GOLLCs exhibit shear-thinning fluid behavior under the shear rate 1–100 s−1. Dynamic rheology reveals that GOLLCs follow solid viscoelastic behavior till 20 mg/mL concentration and then depict long range viscoelastic behavior at higher concentrations. Complex moduli behavior of GOLLCs has been studied to predict their elasticity. The scaling analysis of tunable viscoelastic GOLLCs is computed from Er=Ax−xc4.43. The free-standing film is prepared via thermal treatment method from 2 mg/mL GOLLCs and studied for structural and photocatalytic degradation behavior. rGO film shows 99.18% and 97.87% degradation efficiency for malachite green and methyl orange organic dyes respectively under UV light and is found stable up to 3 cycles.

A 2D Ultrathin Nanopatterned Interlayer to Suppress Lithium Dendrite Growth in High-Energy Lithium-Metal Anodes.

A novel strategy for robust and ultrathin (<1 µm) multilayered protective structures to address uncontrolled Lithium (Li) dendrite growth at Li-metal battery anodes is reported. Synergetic interaction among Ag nanoparticles (Ag NPs), reduced graphene oxide (rGO) films, and self-assembled block-copolymer (BCP) layers enables effective suppression of dendritic Li growth. While Ag NP layer confines the growth of Li metal underneath the rGO layer, BCP layer facilitates the fast and uniformly distributed flux of Li-ion transport and mechanically supports the rGO layer. Notably, highly aligned nanochannels with ≈15nm diameter and ≈600nm length scale interpenetrating within the BCP layer offer reversible well-defined pathways for Li-ion transport. Dramatic stress relaxation with the multilayered structure is confirmed via structural simulation considering the mechanical stress induced by filamentary-growth of Li metal. Li-metal anodes modified with the protective layer well-maintain stable reaction interfaces with limited solid-electrolyte interphase formation, yielding outstanding cycling stability and enhanced rate capability, as demonstrated by the full-cells paired with high-loading of LiFePO4 cathodes. The idealized design of multilayer protective layer provides significant insight for advanced Li-metal anodes.

Highly Sensitive Electrochemical Pb(II) Sensors Based on MoS2/rGO Nanocomposites by Square Wave Voltammetry

Currently, heavy metal ion contamination in water is becoming more and more common, especially Pb(II), which is a serious threat to human health. In this experiment, MoS2/rGO nanocomposites were used to modify glassy carbon electrodes and square wave voltammetry(SWV) electrochemical detection method was selected to detect trace Pb(II) in water. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) showed that MoS2 nanoparticles were uniformly distributed on the rGO films. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) showed that MoS2/rGO has higher sensitivity and conductivity. After determining the optimal experimental parameters, the MoS2/rGO modified glassy carbon electrodes exhibited high sensitivity (57.57 μA μM−1) and low limit of detection (0.060 μM) for Pb(II) as well as good interference resistance and stability.

A flexible free-standing FeF3/reduced graphene oxide film as cathode for advanced lithium-ion battery

High-capacity cathode materials of metal fluorides generally undergo low conductivities and sluggish kinetics derived from a multielectron-transfer conversion reaction mechanism, which severely hinder the cycling stability and rate performance towards their commercialization. Herein, a flexible free-standing FeF3/chitosan pyrolytic carbon/reduced graphene oxide (FeF3/C/RGO) film as an additive-free cathode was designed and prepared by a facile hydrothermal strategy followed by sequential freeze-drying, thermal reduction and fluorination post-treatments. The ultrafine FeF3 nanoparticles (NPs, ~30 nm) are confined within highly ordered RGO film, effectively reducing the Li+ diffusion pathway while the RGO sheets act as a matrix to restrict the complicated interlamination reaction (Fe3+⇄Fe2+⇄Fe) between adjacent interlayers with the spacing of ~30 nm. Benefiting from the free-standing structure, the FeF3/C/RGO film can achieve an admirable capacity up to 220 mAh g–1 over 200 cycles at 100 mA g–1, showing great potential for wearable and flexible electronic devices.

Efficient design and optimization of multifunctional N-F-TiO2/rGO films via orthogonal composite approach

An orthogonal composite approach is proposed to study the multielement synergistic modified TiO2 photocatalytic films. The relationship between different preparation factors and photocatalytic evaluation indexes including photo-degradation activities, antibacterial properties, light transmittance and hydrophilicity, is revealed by the correlation and difference analysis. The increase of F content improves the photocatalytic and antibacterial activities. While the increase of Fe content and calcination temperature are not conducive to the transmittance. Additionally, reduced graphene oxide (rGO) is beneficial to improve the antibacterial properties, but it is not conducive to the self-cleaning performance. The interaction between different factors cannot be ignored in the design of multifunctional TiO2 films from Pareto analysis. The optimal state shows that the glass coated with multifunctional F(9%)-N(1%)-TiO2/rGO(0.5%)-300 ℃ film exhibits the highest photo-degradation (59.8%) and antibacterial activities (87.1%) with superior transmittance (84.1%) and hydrophilicity (7.0°) under visible-light irradiation condition.

Vitamin C-reduced graphene oxide improves the performance and stability of multimodal neural microelectrodes

SummaryNanocarbons are often employed as coatings for neural electrodes to enhance surface area. However, processing and integrating them into microfabrication flows requires complex and harmful chemical and heating conditions. This article presents a safe, scalable, cost-effective method to produce reduced graphene oxide (rGO) coatings using vitamin C (VC) as the reducing agent. We spray coat GO + VC mixtures onto target substrates, and then heat samples for 15 min at 150°C. The resulting rGO films have conductivities of ∼44 S cm−1, and are easily integrated into an ad hoc microfabrication flow. The rGO/Au microelectrodes show ∼8x lower impedance and ∼400x higher capacitance than bare Au, resulting in significantly enhanced charge storage and injection capacity. We subsequently use rGO/Au arrays to detect dopamine in vitro, and to map cortical activity intraoperatively over rat whisker barrel cortex, demonstrating that conductive VC-rGO coatings improve the performance and stability of multimodal microelectrodes for different applications.

Reduced graphene oxide films for reducing hotspot temperatures of electronic devices

The increase in the number of transistors in electronic circuits has increased the power density of electronic devices, which leads to the formation of hotspots on the microchips of the electronic devices. Hotspots deteriorate the lifespan and reliability of electronic devices. With the advantages of high thermal conductivity (κ), low cost, and feasibility for mass production, reduced graphene oxide (rGO) films have become a promising candidate for dispersing the excessive heat at the hotspots and alleviating the adverse effects caused by the hotspots. In this study, a chemical–thermal method combining the chemical reduction and thermal annealing process at a relatively low temperature of 1200 °C was utilized for the synthesis of rGO films. The synthesis method lowered the annealing temperature and yielded a high-quality rGO film. A high κ of 1653.9 ± 214.7 W/m-K was derived for the rGO film annealed at 1200 °C for 90 min. In addition, by bonding the rGO film on the Si chip, the hotspot temperature and thermal spreading resistance were reduced by 12 °C and 20%, respectively. The results indicate that the rGO films synthesized in this study retain a superior thermal property and can be employed for the thermal management of electronic devices.

Optimization of Nanofiber Wearable Heart Rate Sensor Module for Human Motion Detection.

In order to further improve the detection performance of the wearable heart rate sensor for human physiological and biochemical signals and body kinematics performance, the wearable heart rate sensor module was optimized by using nanofibers. Nanoparticle-doped graphene films were prepared by adding nanoparticles to a graphene oxide solution. The prepared film was placed in toluene, and the nanoparticles were removed to complete the preparation of a graphene film with a porous microstructure. The graphene film and the conductive film together formed a wearable heart rate sensor module. The strain response test of the porous graphene film wearable heart rate sensor module verifies the validity of the research in this paper. The resistance change of the wearable heart rate sensor module based on the PGF-2 film is 8 to 16 times higher than that of the RGO film, and the sensitivity is better, proving that the sensor module designed by this method shows significant application potential in human motion detection.

Fabrication of multilayer film with graphene oxide of different surface charge through electrospray deposition

Due to its notable mechanical and electrical properties, graphene has high-value-added applications in future flexible electronics. The preparation of ultrathin uniform graphene oxide (GO) multilayer film through simple and cost-effective technique still is concern. Herein, we have demonstrated the electrospray deposition (ESD) method to prepare the uniform alternative GO multilayer film with controlled thickness by alternatively depositing the different surface charge. It is a solution-processed technique that can be applied in a variety of practical applications due to low-cost and high-speed processing time. Colloidal nanoparticles, which is deposited through ESD technique, have different physical and optical properties based on surface charge. Owing to the electrostatic repulsion between the functional groups, GO can be well soluble, homogeneous and stable dispersion. The prepared alternated rGO films enhanced the sheet resistance because of improving electrical conductivity. Furthermore, alternated rGO film is utilized in the symmetric supercapacitor and the device exhibit a larger capacitance of 103.5 F/g at 0.5 A/g and good cycling stability (94%) on the account of high conductivity than that of other prepared rGO based films. These attributes of ultra-thin rGO film underscore the potential of the current method towards the understanding of film-based supercapacitors in a numerous energy storage applications.

Ultrasensitive sandwich-type photoelectrochemcial oxytetracycline sensing platform based on MnIn2S4/WO3 (Yb, Tm) functionalized rGO film

• A PEC detection platform based on MnIn 2 S 4 /WO 3 (Yb, Tm) functionalized rGO film was constructed. • The fast charge separation and great optical absorption were beneficial to amplify detection signal. • The sandwich-type recognition model was applied to promote specificity and increase sensitivity. • The PEC sensing system showed great property for detecting oxytetracycline in water. A novel photoelectrochemical (PEC) detection system was constructed based on reduced oxide graphene (rGO) film as substrate and MnIn 2 S 4 /WO 3 (Yb, Tm) Z-scheme heterojunction as signal matrix. Benefiting from the accelerated photo-generated carrier separation and enhanced optical absorption, the application of MnIn 2 S 4 /WO 3 (Yb, Tm) as photoactive material is propitious to boost the photocurrent detection signal. With great electron transfer property, rGO further promotes the separation of photo-generated carrier, resulting in the amplification of detection signal. The sandwich-type detection mode is introduced to increase the sensitivity and enhance the specificity. Under the optimal conditions, the PEC detection system presented great property in oxytetracycline (OTC) detection with a linear range from 4 × 10 - 5 nM to 5 × 10 - 2 nM and a low limit of detection as 1.3 × 10 - 5 nM (5.99 × 10 - 3 ng L - 1 ). Give these merits, the proposed PEC sensing system provides a new horizon for sensitive detection of environmental contaminants and biological targets.

Electrodeposition of CoxNiVyOz Ternary Nanopetals on Bare and rGO-Coated Nickel Foam for High-Performance Supercapacitor Application.

We report a simple strategy to grow a novel cobalt nickel vanadium oxide (CoxNiVyOz) nanocomposite on bare and reduced-graphene-oxide (rGO)-coated nickel foam (Ni foam) substrates. In this way, the synthesized graphene oxide is coated on Ni foam, and reduced electrochemically with a negative voltage to prepare a more conductive rGO-coated Ni foam substrate. The fabricated electrodes were characterized with a field-emission scanning electron microscope (FESEM), energy-dispersive X-ray spectra (EDX), X-ray photoelectron spectra (XPS), and Fourier-transform infrared (FTIR) spectra. The electrochemical performance of these CoxNiVyOz-based electrode materials deposited on rGO-coated Ni foam substrate exhibited superior specific capacitance 701.08 F/g, which is more than twice that of a sample coated on bare Ni foam (300.31 F/g) under the same experimental conditions at current density 2 A/g. Our work highlights the effect of covering the Ni foam surface with a rGO film to expedite the specific capacity of the supercapacitors. Despite the slightly decreased stability of a CoxNiVyOz-based electrode coated on a Ni foam@rGO substrate, the facile synthesis, large specific capacitance, and preservation of 92% of the initial capacitance, even after running 5500 cyclic voltammetric (CV) scans, indicate that the CoxNiVyOz-based electrode is a promising candidate for high-performance energy-storage devices.

Electromagnetic Interference Shielding by Reduced Graphene Oxide Foils

The pursuit of materials to avoid problems associated with electromagnetic pollution has become a relevant research topic. Here, we report the exceptional electromagnetic interference (EMI) shielding performance of freestanding reduced graphene oxide (rGO) foil produced by thermal reduction of graphene oxide (GO). The rGO foil with a thickness of 93.1 ± 12.4 μm reaches an efficient EMI shielding effectiveness (SE) value of 61.6 dB at 12.4 GHz. The excellent performance of the rGO foil is attributed to the thermal reduction of the GO foil, which restores the electrically conductive network, resulting in the electrical conductivity of 1.17 × 104 S m–1. To obtain a more complete profile of the EMI shielding performance of the rGO foil, measurements are performed in G- and C-bands, thus becoming the first study on the EMI shielding performance of an rGO film on a broad frequency range beyond the so-called X-band. The material sustains an EMI shielding efficiency higher than 99.999% over the frequency bands investigated, greatly desired in a wide range of commercial applications in this field.

Effective reduction and doping of graphene oxide films at near-room temperature by microwave-excited surface-wave plasma process

The effective reduction of graphene oxide (GO) and incorporation of dopant elements on flexible soft substrates, such as plastics, polymers, papers etc. are of significant importance for energy-related devices and flexible wearable electronics. Here, we demonstrate a novel microwave-excited surface-wave plasma (MW-SWP) process to reduce insulating GO to highly conducting reduced graphene oxide (rGO) on the polyethylene terephthalate (PET) substrate as well as achieving reduction of free-standing GO paper at a near-room temperature. It is also observed that the GO coated on the both top and back surface of a PET substrate reduce simultaneously to obtain conducting rGO films. Most effective reduction was achieved using an argon-hydrogen gas mixture, whereas addition of nitrogen in the gas mixture enabled to incorporate nitrogen dopant in the rGO layers. The GO coated PET and freestanding GO films showed a sheet resistance in the range of MΩ/□, which reduced to an average value of 1.075 kΩ/□ and 134 Ω/□, respectively after the plasma treatment. Thus, the developed MW-SWP process can be significant to produce highly conducting rGO-based graphene films on a soft substrate as well as enabling fabrication of highly conducting freestanding rGO papers.

The Effect of Thin Film Fabrication Techniques on the Performance of rGO Based NO2 Gas Sensors at Room Temperature

Reduced graphene oxide (rGO) has attracted enormous interest as a promising candidate material for gas detection due to its large specific surface areas. In our work, rGO films were fabricated on a large scale using dip-coating and spin-coating methods for the detection of nitrogen dioxide (NO2) gas at room temperature. The influence of different test environments on the sensing performance, including the test atmosphere, gas flow and gas pressure was evaluated. The response time of the dip-coating method was 573 s with a long recovery period of 639 s and for the spin-coating method, the response time and recovery time was 386 s and 577 s, respectively. In addition, the spin-coated sensor exhibited high selectivity to NO2, with the response increasing by more than 20% (for 15 ppm NO2) as compared with that for HCHO, NH3, and CH4. Our results indicated that the spin coating method was more suitable for rGO-based gas sensors with higher performance.

Low‐Power Photodetectors Based on PVA‐Modified Reduced Graphene Oxide Hybrid Solutions

Photodetectors based on reduced graphene oxide (rGO) have attracted much attention owing to their simple and low-cost fabrication process. However, the aggregation and defects of rGO flakes still limit the performance of rGO photodetectors. Controlling the composition of rGO has become a vital factor for its prospective applications. For example, the interconnection between rGO and polymers for modified morphologies of rGO films leads to an enhanced performance of devices. In this work, a practical approach to engineer surface uniformity and enhance the performance of a photodetector by modifying the rGO film with hydrophilic polymers poly(vinyl alcohol) (PVA) is reported. Compared with the rGO photodetector, the on/off ratio for the PVA/rGO photodetector shows 3.5 times improvement, and the detectivity shows 53% enhancement even when the photodetector is operated at a low bias of 0.3V. This study provides an effective route to realize PVA/rGO photodetectors with a low-power operation which shows promising opportunities for the future development of green systems.

Multilayer structured CNF/rGO aerogels and rGO film composites for efficient electromagnetic interference shielding

The development of efficient electromagnetic interference (EMI) shielding materials with high electromagnetic waves (EMWs) absorption capacity is of great significance to alleviate secondary EMWs pollution. Herein, multilayered composites were prepared by stacking cellulose nanofibril (CNF)/reduced graphene oxide (rGO) aerogels and rGO film together. The porous aerogels and the dense film serve as the EMWs absorbing layer and reflecting layer, respectively. When the EMWs enter the multilayer composites, they go through the process of absorption-reflection-reabsorption, resulting in a high EMI shielding effectiveness (SE) of ~32 dB. Furthermore, both experimental and theoretical analyses were adopted to explore the effect of arrangement order of CNF/rGO aerogels on EMI shielding performance. The results indicate that composites with progressively higher graphene content exhibit a higher EMWs absorption capacity at the same total EMI SE. This work offers a feasible design for improving EMWs absorption without affecting the overall EMI shielding performance of the material.