Reduced Graphene Oxide Films Research Articles

Formation and Characterization of Copper Nanocube-Decorated Reduced Graphene Oxide Film

In this study, we present a new approach for the formation and deposition of Cu nanocube-decorated reduced graphene oxide (rGO-CuNCs) nanosheet on indium tin oxide (ITO) electrode using very simple method. Cubic Cu nanocrystals have been successfully fabricated on rGO by a chemical reduction method at low temperature. The morphologies of the synthesized materials were characterized by ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy (AFM). The as-formed CuNCs were found to be homogeneously and uniformly decorated on rGO nanosheets. We demonstrated that the individual rGO sheets can be readily reduced and decorated with CuNCs under a mild condition using L-ascorbic acid (L-AA). Such novel ITO/rGO-CuNCs represent promising platform for future device fabrication and electrocatalytic applications.

Electroanalytical Approach for Determination of Tanshinone IIA Based on Electrochemically Reduced Graphene Oxide Modified Gold Nanoparticles-Incorporated Carbon Paste Electrode

In this work, a novel electrochemical sensor was presented for Tanshinone IIA determination. The as-prepared electrode was prepared by electrodepositing a reduced graphene oxide film onto a carbon paste electrode modified with gold nanoparticles, which combined the advantages of both gold nanoparticles and electrochemically reduced graphene oxide. It was characterized with scanning electron microscopy and cyclic voltammetry. The electrochemical behavior of Tanshinone IIA at the modified electrode was investigated for the first time. Results revealed that the modified electrode can effectively increase response toward Tanshinone IIA by significantly enhancing the redox peak currents and decreasing the peak-to-peak separation. Under the optimized conditions, the modified electrode showed a linear voltammetric response to Tanshinone IIA at concentrations ranging from [Formula: see text][Formula: see text]mol L[Formula: see text] to [Formula: see text][Formula: see text]mol L[Formula: see text], with a detection limit of [Formula: see text][Formula: see text]mol L[Formula: see text] ([Formula: see text]). The proposed method was successfully applied in determination of Tanshinone IIA in pharmaceutical samples with satisfactory results.

Fabrication and molecular dynamics analyses of highly thermal conductive reduced graphene oxide films at ultra-high temperatures.

Thin films with high thermal conductivity are urgently needed as heat dissipation materials for electronic devices. In this study, we developed a readily scalable roller coating method followed by ultra-high temperature annealing to prepare large-sized, free-standing, and flexible reduced graphene oxide (rGO) films with high thermal conductivity. The in-plane thermal conductivity measured by a laser flash method for the sample annealed at 2800 °C was 826.0 W m-1 K-1, which was much higher than that of copper foil. X-ray diffraction, Raman, and SEM analyses indicated that, different from common chemical reduction, heat treatment at high temperature could not only remove O, H, and other impure elements but also develop the in-plane crystal size of graphene and decrease the interlayer spacing of graphene sheets. Meanwhile, tight embedding during annealing and concomitant mechanical impaction was indispensable for retaining the shape and raising the density of the films. Furthermore, molecular dynamics analyses demonstrated that point defects, pentagonal/heptagonal defects, or even large in-plane holes in graphene could be rehabilitated to a great extent during ultra-high temperature annealing. In addition, real-time temperature monitoring demonstrated that the rGO films could act as an excellent thermal dissipation material in LED packages by reducing 10%-15% of the temperature increase.

Highly sensitive airflow sensors with an ultrathin reduced graphene oxide film inspired by gas exfoliation of graphite oxide

A highly-sensitive, novel airflow sensor is demonstrated with an ultrathin reduced graphene oxide film with tunable interlayer gaps.

Electrodeposited Reduced Graphene Oxide Films on Stainless Steel, Copper, and Aluminum for Corrosion Protection Enhancement

The enhancement of corrosion protection of metals and alloys by coating with simple, low cost, and highly adhered layer is still a main goal of many workers. In this research graphite flakes converted into graphene oxide using modified Hammers method and then reduced graphene oxide was electrodeposited on stainless steel 316, copper, and aluminum for corrosion protection application in seawater at four temperatures, namely, 20, 30, 40, and 50°C. All corrosion measurements, kinetics, and thermodynamics parameters were established from Tafel plots using three-electrode potentiostat. The deposited films were examined by FTIR, Raman, XRD, SEM, and AFM techniques; they revealed high percentages of conversion to the few layers of graphene with confirmed defects.

Controlling the Thickness of Thermally Expanded Films of Graphene Oxide

"Paper-like" film material made from stacked and overlapping graphene oxide sheets can be exfoliated (expanded) through rapid heating, and this has until now been done with no control of the final geometry of the expanded graphene oxide material, i.e., the expansion has been physically unconstrained. (As a consequence of the heating and exfoliation, the graphene oxide is "reduced", i.e., the graphene oxide platelets are deoxygenated to a degree.) We have used a confined space to constrain the expanding films to a controllable and uniform thickness. By changing the gap above the film, the final thickness of expanded films prepared from, e.g., a 10 μm-thick graphene oxide film, could be controlled to values such as 20, 30, 50, or 100 μm. When the expansion of the films was unconstrained, the final film was broken into pieces or had many cracks. In contrast, when the expansion was constrained, it never cracked or broke. Hot pressing the expanded reduced graphene oxide films at 1000 °C yielded a highly compact structure and promoted graphitization. Such thickness-controlled expansion of graphene oxide films up to tens or hundreds of times the original film thickness was used to emboss patterns on the films to produce areas with different thicknesses that remain connected "in plane". In another set of experiments, we treated the original graphene oxide film with NaOH before its controlled expansion resulted in a different structure featuring uniformly distributed pores and interconnected layers as well as simultaneous activation of the carbon.

Direct electrochemistry and electrocatalysis of lobetyolin via magnetic functionalized reduced graphene oxide film fabricated electrochemical sensor

A novel lobetyolin electrochemical sensor based on a magnetic functionalized reduced graphene oxide/Nafion nanohybrid film has been introduced in this work. The magnetic functionalized reduced graphene oxide was characterized by fourier transform infrared spectroscopy, atomic force microscope, X-ray diffraction, transmission electron microscopy and thermogravimetric analysis. The scanning electron microscopy characterized the morphology and microstructure of the prepared sensors, and the electrochemical effective surface areas of the prepared sensors were also calculated by chronocoulometry method. The electrochemical behavior of lobetyolin on the magnetic functionalized reduced graphene oxide/Nafion nanohybrid modified glassy carbon electrode was investigated by cyclic voltammetry and differential pulse voltammetry in a phosphate buffer solution of pH6.0. The electron-transfer coefficient (α), electron transfer number (n), and electrode reaction rate constant (Κs) were calculated as 0.78, 0.73, and 4.63s−1, respectively. Under the optimized conditions, the sensor based on magnetic functionalized reduced graphene oxide/Nafion showed a linear voltammetric response to the lobetyolin concentration at 1.0×10−7 to 1.0×10−4mol/L with detection limit (S/N=3)of 4.3×10−8mol/L. The proposed sensor also displayed acceptable reproducibility, long-term stability, and high selectivity, and performs well for analysis of lobetyolin in real samples. The voltammetric sensor was successfully applied to detect lobetyolin in Codonopsis pilosula with recovery values in the range of 96.12%–102.66%.

Nano-tribology studies of reduced graphene oxide films in air and in aqueous solutions with different pH values

Abstract

Nanoscale Perforation of Graphene Oxide during Photoreduction Process in the Argon Atmosphere

We present a study of the process of reduction of thin graphene oxide (GO) films consisting of flakes with lateral size of up to 100 μm through soft ultraviolet irradiation in the argon atmosphere. It was found out that the reduction process leads to a significant decrease in the overall content of the basal-plane functional groups, namely, epoxides and hydroxyls, but with simultaneous increase in the total number of the edge-located carboxyl groups. Obtained transmission electron microscopy images showed that this effect is related to formation of nanoscale holes in the course of reduction. Based on the data obtained, we have proposed a mechanism of the observed GO structural modification in terms of photoinduced chemical reactions between the carbon network and functional groups. These reactions result in progressive growth of the initially existing and newly formed vacancies with formation of the nanoholes with size of up to 100 nm. Thus, reduced graphene oxide films with the restored conjugated networ...

Self-assembled and intercalated film of reduced graphene oxide for a novel vacuum pressure sensor.

We report a new method for measuring vacuum pressures using Van der Waals (VDW) interactions between reduced graphene oxide (RGO) sheets. For this purpose, we utilized a reaction-based self-assembly process to fabricate various intercalated RGO (i-RGO) films, and monitored their electrical behavior with changing pressure and temperature. Pumping to remove gas from a vacuum chamber produced a decrease in the sheet resistance of i-RGO. With further pumping, distinctly different sheet resistance behaivors were observed depending on the measurement temperature. With increasing vacuum pressure, the resistance increased at 100 °C, whereas it decreased at 30 °C. Two types of VDW interactions are proposed to explain these features: a local VDW interaction between RGO sheets that resulted in V-shaped curves of sheet resistance with pressure changes and broad VDW interactions that occur between RGO sheets when the elastic force required to bend carbon clusters on an RGO sheet exceeds their vibrational energy at low temperatures. On the basis of the results, we propose that the resistance behavior of i-RGO as a function of vacuum pressure can be interpreted as the sum of the two different VDW interactions.

Corrigendum: Lateral photovoltaic effect in flexible free-standing reduced graphene oxide film for self-powered position-sensitive detection.

Scientific Reports 6: Article number: 33525; published online: 16 September 2016; updated: 11 November 2016

Study of reduced graphene oxide film incorporated of TiO2 species for efficient visible light driven dye-sensitized solar cell

The hybrid reduced graphene oxide (rGO) with titanium dioxide (TiO2) species photoelectrodes forming a TiO2–rGO nanocomposite (TiO2–rGO NC) was prepared using a simple hydrothermal technique to enhance their visible light dye-sensitized solar cells (DSSCs) performances compared with the pure reduced graphene oxide (rGO) photoelectrodes. This study aims to determine the optimum loading content of TiO2 species on the rGO photoelectrodes for improving their visible response in terms of conductivity as well as photoconversion efficiency. A low content of TiO2 (0.3 wt%) species was successfully incorporated into the rGO photoelectrodes lattice and formed a Ti–O–C bond, which significantly maximized the photocurrent generation efficiency and promoted a charge separation by trapping the photo-induced electrons with 7.2%, which is relatively high compared to the pure rGO photoelectrodes (0.67%). However, the excess TiO2 species of 0.4 and 0.5 wt% resulted in poor photoconversion efficiency performance attributed to the over photocatalytic reaction occurred leaving extra holes on the counter electrode. Herein, a novel hybrid formation between rGO and TiO2 nanomaterials by using the one-step hydrothermal technique in order to improve the DSSCs performance which brought a better conductivity, higher photoconversion efficiency (0.67–7.20%), and lower recombination of rGO material was introduced.

A Sensitive Reduced Graphene Oxide-Antimony Nanofilm Sensor for Simultaneous Determination of PGMs

Electrochemical kinetics of Platinum Group Metals was studied by cyclic voltammetry and the concentration of these metal ions was successfully detected by adsorptive differential pulse cathodic stripping voltammetry using a GCE/rGO-SbNPs sensor. The sensor constructed in this work consisted of a reduced graphene oxide film that was impregnated with antimony nanoparticles. The constructed nanosensor provided an excellent platform for the simultaneous determination of Pd (II), Pt (II) and Rh (III) metal ions. The analytical curve was linear in the concentration range from 0 - 0.40 ng L-1, and 0 - 0.56 ng L-1 for Pd (II)-Rh (III) and Pt (II)-Rh (III), respectively. The detection limits of Pd (II) and Rh (III) were found to be 0.46 ng L-1and 0.55 ng L-1, respectively while for Pt (II) and Rh (III) it was 0.52 ng L-1and 0.48 ng L-1, respectively. The relative standard deviation from 5 measurements for 0.4 ng L-1 Pd (II)-Rh (III) and Pt (II)-Rh (III) by using the GCE/rGO-SbNPs sensor was found to be 6.21% and 3.96%, respectively. Interferences by other metal ions were also studied.

Thermally reduced graphene oxide film on soda lime glass as transparent conducting electrode

Abstract Here we report application of commercially available soda lime glass as transparent, conducting electrodes. Transparent glass substrate, without any surface preparation, was coated with reduced graphene oxide (rGO), through a simple, scalable, easy-to-operate and low-cost deposition technique to render conductivity to it. The process involved dip coating of graphene oxide (GO) solution on soda lime glass, followed by reduction of GO to rGO by thermal annealing process at 500 °C in Ar or Ar + H2 atmosphere. Though there was no significant effect of atmosphere (Ar or Ar + H2 gases) on the transmittance of the electrode, lower sheet resistance was observed in the films reduced under Ar + H2 cover, as compared to those reduced in only Ar atmosphere. The highest transmittance of 97.98% and lowest sheet resistance of 12.55 × 103 Ω/sq was achieved under different processing conditions. De-bonding energy of GO and rGO (Ar and Ar + H2 treated) with the soda lime glass was also quantified using nanoscratch technique to throw light on the adhesion behavior of the film with the substrate.

Preparation and characterization of reduced graphene oxide using ascorbic acid and sodium citrate as binary reductant

ABSTRACTIn this article, we successfully prepared transparent and gauze-like reduced graphene oxide (RGO) film with the thickness of only 1.32 nm using modified Hummers method and binary reductant consisting of ascorbic acid and sodium citrate. SEM, TEM, AFM, XRD, UV-Vis, and FTIR results all convincingly demonstrated that the reduction of graphite oxide using binary reductant is a feasible method to prepare RGO. In addition, the results also revealed that extending the oxidation time and increasing the ultrasonic oscillation reasonably might improve the oxidation degree of the graphite oxide, the ratio of the D-band Raman intensity to that of the G band (ID/IG) reached up to 1.244 in the as-obtained graphite oxide. Moreover, sodium citrate not only increased the reducibility of binary reduction system but also improved the dispersion of graphite oxide. Furthermore, reasonable annealing treatment could reduce the defects of RGO. It is a potential route to prepare RGO films and increase practical applications in large-scale production of graphene.

Laser direct 3D patterning and reduction of graphene oxide film on polymer substrate

The graphene oxide (GO) film embossing and reduction was demonstrated under femtosecond laser pulses. The best conductivity of laser reduced GO film of 200Ω/□ was achieved for fs laser pulses energy of 35–45nJ and 10–25 pulses per µm. We demonstrate the patterned laser reduction over the embossed GO film that holds it integrity and conductivity. Laser reduced GO properties was studied by Raman, SEM and sheet resistance measurements.

Controllable Laser Reduction of Graphene Oxide Films for Photoelectronic Applications.

This article presents a new simple method of creating light-absorbing carbon material for optical devices such as bolometers. A simple method of laser microstructuring of graphene oxide is used in order to create such material. The absorption values of more than 98% in the visible and more than 90% in the infrared range are achieved. Moreover thermal properties of the films, such as temperature dependence and the thermal response of the samples, are studied. The change in resistance with temperature is 13 Ohm K-1, temperature coefficient of resistance (TCR) is 0.3% K-1, and the sensitivity is 0.17 V W-1 at 300 K. Thermal conductivity is rather high at ∼104 W m-1 K-1 at 300 K. The designed bolometer operates at room temperature using incandescent lamp as a light source. This technique suggests a new inexpensive way to create a selective absorption coating and/or active layer for optical devices. Developed GO and rGO films have a large surface area and high conductivity. These properties make carbon coatings a perfect candidate for creating a new type of optoelectronic devices (gas sensors, detectors of biological objects, etc.).

Electrocatalytic Sensing with Reduced Graphene Oxide: Electron Shuttling between Redox Couples Anchored on a 2-D Surface

The electron storage and shuttling capabilities of reduced graphene oxide (RGO) have been explored by anchoring two redox couples, methyl viologen (MV2+) and ferrocene (Fc). When an RGO modified glassy carbon electrode (GCE/RGO) was subjected to a cathodic scan, a quasi-reversible reduction of MV2+ was seen indicating a loss of electrons contributed to “charging” of RGO. These stored electrons can then be transported to oxidized Fc during the anodic scan through the C–C network of RGO. The recycling and peak current magnitude of oxidized and reduced forms of Fc during the anodic scan is strongly dependent on the scan rate, concentration, and extent of MV2+ reduction, either complete or partial, during the cathodic scan. This electrocatalytic property of RGO film enables the design of sensors and catalysts with the capacity to capture, store, and shuttle electrons and corroborate a boost in sensitivity for the electrochemical detection and conversion of low level analytes.

Surface modification of reduced graphene oxide film by Ti ion implantation technique for high dye-sensitized solar cells performance

Titanium (Ti) ion implantation approach was used in the present study to modify the reduced graphene oxide nanosheet (rGO NS) by incorporating the Ti4+ ion (at various applied powers ranging from 50 to 250W) onto the rGO NS to prepare photoanodes for Dye-Sensitized Solar Cell (DSSC). The surface morphologies, functional groups, optical properties and surface chemical states of the modified rGO based photoanode (rGO-TiO2 nanocomposite (NC)) were studied. Fourier transform infrared (FTIR) spectra coupled with the elemental/chemical states in X-ray photoelectron spectroscopy (XPS) analysis revealed the presence of Ti–O–C functional groups after the modification process. Besides, the average size of Ti ion was found to be 70–80nm as incorporated with rGO NS. The spacing of anatase TiO2 onto rGO NS were reported as 0.35nm and 0.34nm under HRTEM analysis, respectively. Experimental result implied that 150W was the optimum applied power for the surface modification to take place ascribed to the lowest possibility for the recombination to occur and the smallest energy band gap. On top of that, at 150W, the electron transfer rate was also found to be the highest due to the highest availability of the carbon-atom vacancy holes for Ti4+ replacement. It was also discovered that the optimized power conversion efficiency (PCE) of 8.51% could be achieved in DSSC by implanting the Ti ion onto rGO NS-based photoanode using 150W. Further increase of the applied power to 200W or 250W led to the undesirable recombination of the Ti ions and rGO NS due to the exceptional photocatalytic activity among N719 dye/rGO/TiO2 interfaces which interfered the charge transportation at the KI electrolyte/N719 dye/rGO/TiO2 interfaces.

Dye-sensitized solar cell (DSSC) utilizing reduced graphene oxide (RGO) films counter electrode: effect of graphene oxide (GO) content

This paper reports the preliminary work on the DSSC utilizing reduced graphene oxide (RGO) films counter electrode. The effect of graphene oxide (GO) content on the performance of the DSSC has been investigated. The FESEM images show that the sample contains conductive RGO and non-conductive GO. The RGO samples are crystalline with the diffraction peak at 22.5°. It was found that the short-circuit current density (JSC) and power conversion efficiency (η) of the device are significantly affected by the GO content. The DSSC utilizing RGO film counter electrode prepared using 2.5 mg GO performed the highest JSC, Voc and η of 0.77 mA cm−2, 0.613 V and 0.09 %, respectively. The highest performance of the device is due to highest electronic conductivity, the lowest leak current, bulk resistance (Rb), charge transfer resistance (Rct) and longest charge carrier lifetime. The lower leak current, Rb and Rct, the longer carrier lifetime resulted in the higher JSC and η.