Quantifying Graphene Oxide Reduction Using Spectroscopic Techniques: A Chemometric Analysis.

Here we report a highly conductive polypropylene-graphene nonwoven composite via direct coating of melt blown polypropylene (PP) nonwoven fabrics with graphene oxide (GO) dispersions in N,N-dimethylformamide (DMF), followed by the chemical reduction of GO with hydroiodic acid (HI). GO as an amphiphilic macromolecule can be dispersed in DMF homogeneously at a concentration of 5 mg/mL, which has much lower surface tension (37.5 mN/m) than that of GO in water (72.9 mN/m, at 5 mg/mL). The hydrophobic PP nonwoven has a surface energy of 30.1 mN/m, close to the surface tension of GO in DMF. Therefore, the PP nonwoven can be easily wetted by the GO/DMF dispersion without any pretreatment. Soaking PP nonwoven in a GO/DMF dispersion leads to uniform coatings of GO on PP-fiber surfaces. After chemical reduction of GO to graphene, the resulting PP/graphene nonwoven composite offers an electrical conductivity of 35.6 S m-1 at graphene loading of 5.2 wt %, the highest among the existing conductive PP systems reported, indicating that surface tension of coating baths has significant impact on the coating uniformity and affinity. The conductivity of our PP/graphene nonwoven is also stable against stirring washing test. In addition, here we demonstrate a monolithic supercapacitor derived from the PP-GO nonwoven composite by using a direct laser-patterning process. The resulted sandwich supercapacitor shows a high areal capacitance of 4.18 mF/cm2 in PVA-H2SO4 gel electrolyte. The resulting highly conductive or capacitive PP/graphene nonwoven carries great promise to be used as electronic textiles.

Graphene, a single layer of sp2-hybridized carbon atoms in a hexagonal (two-dimensional honey-comb) lattice, has attracted strong scientific and technological interest due to its novel and excellent optical, chemical, electrical, mechanical and thermal properties. The solution-processable chemical reduction of Graphene oxide (GO is considered as the most favorable method regarding mass production of graphene. Generally, the reduction of GO is carried out by chemical approaches using different reductants such as hydrazine and sodium borohydride. These components are corrosive, combustible and highly toxic which may be dangerous for personnel health and the environment. Hence, these reducing agents are not promising choice for reducing of graphene oxide (GO). As a consequence, it is necessary for further development and optimization of eco-friendly, natural reducing agent for clean and effective reduction of GO. Ascorbic acid, an eco-friendly and natural reducing agents, having a mild reductive ability and nontoxic property. So, the aim of this research was to green synthesis of GO with ascorbic acid. For this purpose, the required amount of NaOH and ascorbic acid were added to GO solution (0.5 mg/ml) and were heated at 95 °C for 1 hour. According to the X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electrochemical results, GO were reduced with ascorbic acid like hydrazine with better electrochemical properties and ascorbic acid is an ideal substitute for hydrazine in the reduction of graphene oxide process.

As a novel two‐dimensional carbon material, graphene has fine potential applications in the fields of electron transfer agent and supercapacitor material for its excellent electronic and optical property. However, the challenge is to synthesize graphene in a bulk quantity. In this paper, graphite oxide was prepared from natural flake graphite by Hummers’ method through liquid oxidization, and the reduced graphene oxide was obtained by chemical reduction of graphene oxide using NH3·H2O aqueous solution and hydrazine hydrate. The raw material graphite, graphite oxide, and reduced graphene oxide were characterized by X‐ray diffraction (XRD), attenuated total reflectance‐infrared spectroscopy (ATR‐IR), and field emission scanning electron microscope (SEM). The results indicated that the distance spacing of graphite oxide was longer than that of graphite and the crystal structure of graphite was changed. The flake graphite was oxidized to graphite oxide and lots of oxygen‐containing groups were found in the graphite oxide. In the morphologies of samples, fold structure was found on both the surface and the edge of reduced graphene oxide.

A simple, effective, and environmentally benign approach for the reduction of graphene oxide (GO) using apple juice as a reducing agent has been reported in this work. The advantage of this approach is that it eliminates the need for using toxic reducing agents or external stabilizers to carry out the chemical reduction of GO. The reduction, mediated by the extracted maleic acid from apple juice, was found to take place under mild conditions in the aqueous medium. The formation of layered graphitic structure and random orientation of graphene was confirmed by X-ray diffraction study. Appearance of a broad band at 24.9°, corresponds to d-spacing of ~0.342 nm) elucidates successful reduction. Successful reduction of GO was further confirmed by UV–visible spectroscopy. The plasmon peak at 230 nm has been red-shifted to 263 nm corroborating the electronic conjugation in MRGO nanosheets was restored. Raman spectroscopy revealed the formation of graphene with defects. Since the method proposed is economical, it can be used for the large-scale production of reduced GO.

The reduction of graphene oxide (GO) thin films deposited on substrates is crucial to achieve a technologically useful supported graphene material. However, the well-known thermal reduction process cannot be used with thermally unstable substrates (e.g., plastics and paper), in addition photo-reduction methods are expensive and only capable of reducing the external surface. Therefore, solid-state chemical reduction techniques could become a convenient approach for the full thickness reduction of the GO layers supported on thermally unstable substrates. Here, a novel experimental procedure for quantitative reduction of GO films on paper by a green and low-cost chemical reductant (L-ascorbic acid, L-aa) is proposed. The possibility to have an effective mass transport of the reductant inside the swelled GO solid (gel-phase) deposit was ensured by spraying a reductant solution on the GO film and allowing it to reflux in a closed microenvironment at 50 °C. The GO conversion degree to reduced graphene oxide (r-GO) was evaluated by Fourier transform infrared spectroscopy (FT-IR) in attenuated total reflectance (ATR) mode and X-ray Diffraction (XRD). In addition, morphology and wettability of GO deposits, before and after reduction, were confirmed by digital USB microscopy, scanning electron microscopy (SEM), and contact angle measurements. According to these structural characterizations, the proposed method allows a bulky reduction of the coating but leaves to a GO layer at the interface, that is essential for a good coating-substrate adhesion and this special characteristic is useful for industrial exploitation of the material.

Chemical reduction of graphene oxide (GO) using nontoxic reductants is a promising and green approach to produce graphene with versatile functionalities in large scale. However, the relatively low reduction extent of the reduced graphene oxide (RGO) is the main hindrance for many applications. In the present work, significantly enhanced reduction of aqueous RGO suspension is achieved by the chemical reduction with combination of tea polyphenols (TPs) and aluminum flake. In comparison with the RGO reduced by TPs only, the defect of the RGO achieved by the combination of TPs and aluminum flake decrease by 6.70%. The sp 2 structure fraction in the RGO increases by 9.67% due to the synergistic effect between TPs and aluminum flake. In addition, a possible mechanism for the synergistic effect between TPs and aluminum flake on the enhanced reduction of RGO is proposed. This approach provides new significant insights on the efficient and environmentally friendly preparation of RGO with much improved quality.

The unique properties of graphene oxide (GO) have attracted the attention of the research community and cost-effective routes for its production are studied. The type and percentage of the oxygen groups that decorate a GO sheet are dependent on the synthesis path, and this path specifies the carbon content of the sheet. The chemical reduction of GO results in reduced graphene oxide (rGO) while the removal of the oxygen groups is also achievable with thermal processes (tpGO). This review article introduces the reader to the carbon allotropes, provides information about graphene which is the backbone of GO and focuses on GO synthesis and properties. The last part covers some characterization techniques of GO (XRD, FTIR, AFM, SEM-EDS, N2 porosimetry and UV-Vis) with a view to the fundamental principles of each technique. Some critical aspects arise for GO synthesized and characterized from our group.

Thermo-oxidative resistance of crosslinked polyethylene (XLPE) coated by hybrid coatings containing graphene oxide

Solubility study on the surfactants functionalized reduced graphene oxide

Novel carbon nanomaterials such as reduced graphene oxide (rGO) and graphene oxide (GO) can be easily incorporated into the undergraduate curriculum to discuss basic chemistry and nanotechnology concepts. This paper describes a laboratory experiment designed to study the differences between GO and rGO regarding their physicochemical properties (e.g., color, hydrophobicity, type of functional groups, electrical conductivity, etc.). In this course, students carry out the chemical reduction of GO using ascorbic acid, a mild and environmentally friendly reducing agent. The differences between GO and rGO can be spotted by the naked eye and can be further evaluated by spectroscopic methods, as Fourier transform infrared and UV–vis spectroscopy and X-ray diffraction. Simple and applicable in all laboratories, use of the multimeter to measure resistance was proposed to reveal the different electrical properties of GO and rGO. Moreover, the proposed laboratory experiment is an ideal pretext to discuss the definition of graphene in the context of the overuse of this term in the literature.

Chemical reduction of graphene oxide is one of the main routes of preparation for large quantities of graphenes. A wide range of reducing agents was described for this task, such as hydroquinone, ascorbic acid, saccharides, proteins, hydrazine, or sodium borohydride. With exception of sodium borohydride and hydrazine, no “standard” organic chemistry agents have been described for reduction of graphene oxides. Lithium aluminum hydride (LAH) is a very powerful reducing agent frequently used in organic synthetic methodologies to convert several types of oxygen containing carbon moieties with a well-known reduction mechanism. Here, we describe, for the first time, the use of LAH toward the reduction of graphene oxide and compare its reduction strength to that of hydrazine and sodium borohydride, which are generally adopted in such application. We show that LAH is far more efficient in reducing oxygen functionalities present on graphene oxide. This is a step forward toward applicability of “standard” organic chemistry reducing agents for reduction of graphene oxides.

The current fabrication methods of pristine graphene are not feasible for bulk production. The closest approach, which is through chemical reduction of graphene oxide to chemically reduced graphene oxide that resembles pristine graphene, has been widely adopted instead. Herein, we report a new methodology for the reduction of graphene oxide to chemically reduced graphene oxide using a common industrial reductant, thiourea dioxide. The final product has been fully characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, electrochemical impedance spectroscopy (EIS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and cyclic voltammetry. The microscopy techniques revealed reduced graphene of few-layered sheets. Based on the XPS analyses, a C/O ratio as high as 16.0 was achieved. The reduced graphene oxide product demonstrated a good electrochemical performance with a charge transfer resistance as low as 0.11 kΩ based on EIS measurements and a low overpotential for the oxidation of ascorbic acid. Since thiourea is a common industrial reductant, standard protocols are already in place for the waste produced from this methodology. As such, we foresee that this methodology holds the potential for industrial scale reduction of graphene oxide.

Chemical reduction of graphene oxide (GO) in an aqueous polymer/GO dispersion invariably causes restacking and precipitation of reduced GO (rGO) sheets leading to spontaneous phase separation. This has been a significant challenge limiting the commercial production of aqueous polymer/rGO paints and coatings. In this study, we developed in situ reduction strategies to chemically reduce GO while maintaining the colloidal stability of an aqueous polymer/rGO dispersion. An aqueous polymer/GO latex was prepared using miniemulsion polymerization, which was subsequently reduced in situ using four different chemical reducing agents (hydroiodic acid, sodium borohydride, ascorbic acid, and hydrazine hydrate) to obtain colloidally stable polymer/rGO dispersions. The reduction of GO was confirmed using X-ray photoelectron spectroscopy (XPS), Raman, and X-ray diffraction (XRD). The colloidal stability of the reduced dispersions was maintained for over 6 months under ambient storage conditions. Stable polymer/rGO dispersions were drop cast to form nanocomposite films at ambient temperature. Finally, the electrical conductivity measurement of polymer/rGO films revealed the highest conductivity for hydrazine hydrate-reduced films (∼6.6 S m–1), which was marginally higher than for hydroiodic acid-reduced films (∼3.4 S m–1). The electrical conductivity of sodium borohydride- and ascorbic acid-reduced films was two orders of magnitude lower than for hydrazine hydrate- and hydroiodic acid-reduced films. Overall, the present results pave a path for the commercial production of colloidally stable aqueous polymer/rGO composite paints and coatings.

Influence of the reduction strategy in the synthesis of reduced graphene oxide

A facile production of highly porous graphene foam by using flame treatment of graphene oxide (GO) is proposed. Highly porous architectures with randomly distributed micro-crack and micro-slit were produced due to the high temperature induced ruinous reduction and rapid expansion of GO. Synchronously, abundant oxygen-containing groups (OCGs) on GO sheets could be effectively removed after flame treatment, which renders significantly increased conductivity to the resultant flame reduced GO (FR-GO). The synergistic effect of micro/nanostructuring and the OCGs removal makes FR-GO a promising candidate for electrode materials. Compared with chemically reduced GO (CR-GO), FR-GO delivers much higher specific capacity. It gives us some hints that flame treatment of graphene-based material is a smart strategy for cost-effective production of anode materials for commercial application.