Chemical Reduction Of Graphene Oxide Research Articles

Magnetically induced anisotropic orientation of graphene oxide locked by in situ hydrogelation.

A general method to prepare polymer gels containing anisotropically oriented graphene oxide (GO) or reduced graphene oxide (RGO) was developed, by using the magnetically induced orientation of GO. Under a magnetic field, an aqueous dispersion of GO was gelated by in situ cross-linking polymerization of an acryl monomer and a cross-linker. In the resultant hydrogel, the orientation of GO was retained even in the absence of the magnetic field, because the gel network trapped GO via noncovalent interactions and efficiently suppressed the structural relaxation of GO. The locked structure enabled quantitative investigation on the magnetic orientation of GO using 2D small-angle X-ray scattering, which revealed that GO nanosheets orient parallel to the magnetic field with an order parameter of up to 0.80. Systematic studies with varying gelation conditions indicate that the present method can afford a wide range of GO-hybridized anisotropic materials, in terms of GO alignment direction, sample shape, and GO concentration. Also by virtue of the locked structure, the orientation of GO in the hydrogel was well preserved throughout the in situ chemical reduction of GO, yielding an RGO-hybridized anisotropic hydrogel, as well as the conversion of the hydrogel into organo- and ionogels through the replacement of the internal water with solvents. As a preliminary demonstration of the present method for practical application, a polymer-composite film containing RGO oriented vertical to the film surface was prepared, and its anisotropically enhanced electroconductivity along the orientation direction of RGO was confirmed by the flash-photolysis time-resolved microwave conductivity measurement.

Hydrogen uptake of reduced graphene oxide and graphene sheets decorated with Fe nanoclusters

Graphene oxide (GO) has been prepared by employing modified Staudenmaier's method through thermal exfoliation of graphite oxide. High pressure hydrogen sorption isotherms up to 50 bar of GO, reduced by thermal reduction (TR-GO), chemical reduction (CR-GO) and graphene sheets decorated with Fe nanoclusters (Fe-GS) have been investigated. Thermal reduction of GO at 623 K under high vacuum yields TR-GO. Chemical reduction of GO using hydrazine forms CR-GO. Fe-GS was synthesized through arc-discharge between the ends of two graphite rods with one rod carrying Fe nanoparticles. The surface areas of these graphene samples were determined from the nitrogen adsorption isotherm employing Brunauer, Emmett and Teller (BET) method. Kelvin's equation was used to determine the pore size distribution of all graphene based samples. Hydrogen pressure-composition isotherms (PCI) were determined at 300 K and at 77 K, between 0.1 and 50 bar. Further, in this paper, we present a comparative adsorption isotherm analysis of hydrogen and helium on TR-GO. This reveals that the volume of hydrogen and helium adsorbed by TR-GO is nearly equal. The similar uptake volume determined for both hydrogen and helium indicates the possibility of monolayer adsorption of hydrogen and also nearly similar binding energy between TR-GO and H2/He.

Green preparation of reduced graphene oxide for sensing and energy storage applications.

Preparation of graphene from chemical reduction of graphene oxide (GO) is recognized as one of the most promising methods for large-scale and low-cost production of graphene-based materials. This study reports a new, green, and efficient reducing agent (caffeic acid/CA) for GO reduction. The CA-reduced GO (CA-rGO) shows a high C/O ratio (7.15) that is among the best rGOs prepared with green reducing reagents. Electronic gas sensors and supercapacitors have been fabricated with the CA-rGO and show good performance, which demonstrates the potential of CA-rGO for sensing and energy storage applications.

Effect of combined chemical and electrochemical reduction of graphene oxide on morphology and structure of electrodeposited ZnO

This study reports a novel method of tailoring the properties of ZnO nanostructures by electrodeposition in presence of chemically-reduced graphene oxide (rGO). The coupled electrochemical and chemical reduction of graphene oxide resulted in few-layer graphene-based material. The presence of rGO in the electrolytic bath showed a marked influence on the morphology and structure of the hybrid nanostructures. The results indicated the presence of 5mgL−1 rGO results in a 42.9% decrease in resistivity of the hybrid material with respect to the pure ZnO. The proposed approach shows very promising for the fabrication of transparent conductive oxide electrodes.

Preparation and Properties of a Graphene Oxide Intercalation Compound Utilizing Hydrocalumite Layered Double Hydroxide as Host Structure

AbstractParticularly small graphene oxide (GO) nano sheets were synthesized and intercalated into a hydrocalumite type layered double hydroxide (Ca2Al‐LDH) host structure. Synthesis of the GO intercalation compound was performed via controlled rehydration of tricalcium aluminate (Ca3Al2O6) in the presence of GO. Formation of Ca2Al‐GO‐LDH was evidenced from elemental, thermogravimetric, IR spectroscopy, XRD, and SAXS analysis. From the latter, an interlayer distance of 1.05 nm (d value) was found, indicating that one GO sheet is sandwiched by [Ca2Al(OH)6]+ main sheets. SAXS analysis revealed a length of the lamellar structure of 109 nm and presence of agglomerates of randomly stacked nanosized LDH fragments. The carbon content of the Ca2Al‐GO‐LDH particles (thickness ca. 30 nm) was significantly higher than that found for Ca2Al‐OH‐LDH holding surface adsorbed GO only (14 wt % vs. < 2 wt %). GO can be released easily from the inorganic host structure by anion exchange, e.g. with sulfate. The novel compound could present an interesting precursor for electronic applications after chemical reduction of GO to graphene.

Synthesis of silanized maghemite nanoparticles onto reduced graphene sheets composites

Novel γ-Fe2O3@APTES@rGO composites are successfully synthesized by using graphene oxide and silanized maghemite nanoparticles. Graphene oxide and maghemite were obtained by Hummers and Massart methods, respectively. The silanization process was done to functionalize maghemite surface with a controllable quantity of amino groups. Then, by adding aqueous graphene oxide suspension, the bonding between graphene oxide and silanized maghemite nanoparticles was done in refluxing conditions. Afterwards, chemical reduced graphene oxide reaction was realized by addition of hydrazine solution. The characterization of γ-Fe2O3@APTES@rGO composites was studied by X-ray Diffraction, Fourier Transformed Infrared Spectroscopy, thermogravimetric analysis and scanning electron microscopy.

Regeneration of a Conjugated sp2 Graphene System through Selective Defunctionalization of Epoxides by Using a Proven Synthetic Chemistry Mechanism

Graphene is a promising material capable of driving technological advancement. It is, however, a challenge to obtain pristine graphene in large quantities given the limitation of current synthetic methods. Among the numerous methods available, the chemical approach provides an optimistic outlook and has garnered much interest within the graphene community as a potential alternative. One of the most crucial steps of the chemical approach is the chemical reduction of graphene oxide as this dictates the final quality of the graphene sheets. In recent years, much of the focus has shifted to the usage of established reducing agents or oxygen removal reagents, frequently applied in organic chemistry, onto a graphene oxide platform. Herein, the selective removal of epoxide groups and subsequent regeneration of disrupted conjugated sp(2) system is highlighted, based on the synergistic effect of indium and indium(I) chloride. The morphological, structural, and electrical properties of the resulting graphene were fully characterized with X-ray photoelectron, Fourier transform IR, solid-state (13)C NMR, and Raman spectroscopy; thermogravimetric analysis; scanning electron microscopy; and conductivity measurements. The as-prepared graphene showed a tenfold increase in conductivity against conventional graphene treated with hydrazine reducing agent and demonstrated a high dispersion stability in ethanol. Moreover, the selective defunctionalization of the epoxide groups provides opportunities for potential tailoring of graphene properties for prospective applications.

Graphene-Supported, Iron-Based Nanoparticles for Catalytic Production of Liquid Hydrocarbons from Synthesis Gas: The Role of the Graphene Support in Comparison with Carbon Nanotubes

Fischer–Tropsch synthesis (FTS) is a potentially attractive technology for the production of clean liquid fuels from synthesis gas. The efficiency and selectivity of FTS can be enhanced by the design of new active catalyst systems with improved selectivity for long-chain hydrocarbons and low methane production. In this paper, we introduce a new class of FT catalysts supported on the high surface area graphene nanosheets and report on their high activity and selectivity for the production of long-chain hydrocarbons. The chemical reduction of graphene oxide in water in the presence of the metal salts under microwave irradiation allows the deposition of well-dispersed surface-oxidized metal nanoparticles on the defect sites of the graphene nanosheets. The Fe–K-nanoparticle catalyst supported on graphene exhibits high activity and selectivity toward C8 and higher hydrocarbons with excellent stability and recyclability. In comparison with other carbon supports, such as carbon nanotubes, the graphene support sh...

Graphene–platinum nanocomposite as a sensitive and selective voltammetric sensor for trace level arsenic quantification

A simple protocol for the chemical modification of graphene with platinum nanoparticles and its subsequent electroanalytical application toward sensitive and selective determination of arsenic has been described. Chemical modification was carried out by the simultaneous and sequential chemical reduction of graphene oxide and hexachloroplatinic acid in the presence of ethylene glycol as a mild reducing agent. The synthesized graphene–platinum nanocomposite (Gr–nPt) has been characterized through infrared spectroscopy, x-ray diffraction study, field emission scanning electron microscopy and cyclic voltammetry (CV) techniques. CV and square-wave anodic stripping voltammetry have been used to quantify arsenic. The proposed nanostructure showed linearity in the concentration range 10–100 nM with a detection limit of 1.1 nM. The proposed sensor has been successfully applied to measure trace levels of arsenic present in natural sample matrices like borewell water, polluted lake water, agricultural soil, tomato and spinach leaves.

Chemical reduction of graphene oxide: a synthetic chemistry viewpoint

The chemical reduction of graphene oxide is a promising route towards the large scale production of graphene for commercial applications. The current state-of-the-art in graphene oxide reduction, consisting of more than 50 types of reducing agent, will be reviewed from a synthetic chemistry point of view. Emphasis is placed on the techniques, reaction mechanisms and the quality of the produced graphene. The reducing agents are reviewed under two major categories: (i) those which function according to well-supported mechanisms and (ii) those which function according to proposed mechanisms based on knowledge of organic chemistry. This review will serve as a valuable platform to understand the efficiency of these reducing agents for the reduction of graphene oxide.

Recyclable catalyst for catalytic hydrogenation of phenylacetylene by coupling Pd nanoparticles with highly compressible graphene aerogels

Highly compressible graphene aerogels were made by chemical reduction of graphene oxide with HI, which act as recyclable catalyst to exhibit excellent catalytic performance towards selective semi-hydrogenation reaction after loading Pd nanoparticles.

Flexible TCO-free counter electrode for dye-sensitized solar cells using graphene nanosheets from a Ti–Ti(III) acid solution

A rapid and simple route to synthesize highly conductive graphene-based nanosheets for use as a flexible counter electrode in dye-sensitized solar cells is presented. The flexible counter electrode is free of transparent conductive oxide layer, i.e., TCO-free. A clean graphene with high quality is obtained by the chemical reduction of graphene oxide (GO) using titanium metallic powders in a hydrochloric acid solution. The Ti+3 ions that dissociated from metallic Ti particles in a hydrochloric acid solution result in a clean graphene material with no formation of TiO2 nanoparticles, which are always present on graphene when only Ti+3 ions are used for the reduction, i.e., an anatase TiO2 nanoparticle by-product will be always left on the graphene product when not using metallic Ti particles. The chemical reaction mechanisms for these differences are revealed in this report. The reduced materials are characterized by field emission scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, thermo-gravimetric analysis, Fourier transform infrared spectrometry, UV–vis spectroscopy and X-ray photoelectron spectroscopy. The four-point probe method is also employed to characterize the surface conductivity of the graphene films. This high quality graphene film exhibits comparable or better performance than those obtained using conventional sputtered Pt counter electrode when used as a flexible counter electrode of dye-sensitized solar cells.

A polymer composite consists of electrochemical reduced graphene oxide/polyimide/chemical reduced graphene oxide for effective preparation of SnSe by electrochemical atomic layer deposition method with enhanced electrochemical performance and surface area

A novel polymer electrode is prepared by incorporating polyimide (PI) with chemical reduced graphene oxide (rGO). Then modified this PI/RGO electrode with a layer of electrochemical-reduced graphene oxide (EGO), and by this way the expected EGO/PI/RGO electrode is obtained. Compared with bare PI/RGO film, the hybrid EGO/PI/RGO electrode own large active area and excellent conductivity, which offers more extensive field to prepare compound and more sensitive surface to detect electrochemical signal. SnSe is prepared on this modified substrate by electrochemical atomic layer deposition (EC-ALD) technology. Moreover, SnSe deposit on bare PI/RGO electrode by EC-ALD method is also done for comparison. Open-circuit potential (OCP) and Mott–Schottky measurement indicated the obtained SnSe is a p-type semiconductor. Moreover, the semiconductor appears more excellent photoelectric property on modified electrode.

Reaction mechanisms of graphene oxide chemical reduction by sulfur-containing compounds

We used density functional theory to study the reaction mechanisms of chemical reduction of graphene oxide (GO) by the sulfur-containing compounds HSO3− and H2SO3. We studied the reaction energy profiles for the following reactions: dehydroxylation of GO with one and two hydroxyl groups, de-epoxidation of GO with one or two epoxy groups and decarboxylation and decarbonylation of GO with carboxyl and carbonyl groups. We found that hydroxyl and epoxide groups could be easily reduced because of the lower energy barriers, whereas decarboxylation and decarbonylation reactions are not kinetically and thermodynamically easy because of the higher energy barriers. These reaction mechanisms at the atomistic level are not only supported by Chen’s experimental results [J. Phys. Chem. C 2010, 114, 19885], but are also beneficial for the development of new agents that could efficiently reduce GO.

Synthesis of carboxylate-functionalized graphene nanosheets for high dispersion of platinum nanoparticles based on the reduction of graphene oxide via 1-pyrenecarboxaldehyde

A one-step reduction/functionalization strategy for the synthesis of carboxylate-functionalized graphene nanosheets is reported in this paper. 1-pyrenecarboxaldehyde (PCA) is introduced as a new reductant for the chemical reduction of graphene oxide (GO), serving three roles: reducing GO to graphene nanosheets (GNs), stabilizing the as-prepared GNs due to the electrostatic repulsion of the oxidation products of PCA (1-pyrenecarboxylate, PC−) on the surface of the GNs and anchoring Pt nanoparticles (Pt NPs) with high dispersion and small particle size. Transmission electron microscopy shows that Pt NPs with an average diameter of 1.3 ± 0.2 nm are uniformly dispersed on the surface of the PC−-functionalized GNs (PC−-GNs). The obtained Pt NPs/PC−-GNs nanohybrids have higher electrocatalytic activity and stability towards methanol oxidation in comparison with Pt NPs supported on GNs obtained by the chemical reduction of GO with the typical reductant, hydrazine.

Graphene-encapsulated silicon nanoparticles as an anode material for lithium-ion batteries

Silicon particles have been embedded into graphene sheets via a novel method combining the electrostatic interaction and chemical reduction of graphene oxide, and the electrochemical properties of the composite anode material have been evaluated.

Reduced graphene oxide/CoSe2 nanocomposites: hydrothermal synthesis and their enhanced electrocatalytic activity

Reduced graphene oxide (RGO)/CoSe2 nanocomposites were synthesized by self-assembly of CoSe2/DETA (DETA: diethylenetriamine) onto the surface of graphene oxide (GO), followed by subsequent chemical reduction of GO during a hydrothermal process. The as-synthesized products were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectra, scanning electron microscopy, and transmission electron microscopy. The morphology of the CoSe2 on the RGO nanosheets can be well controlled by adjusting the reaction time during the hydrothermal process. The catalytic activities of the RGO/CoSe2 nanocomposites were investigated for oxygen evolution reaction (OER) in alkaline conditions. It was found that the as-formed RGO/CoSe2 nanocomposites show higher catalytic activity compared with the unsupported CoSe2. In addition, the loading amounts and morphologies of CoSe2 on RGO sheets have a great influence on the catalytic performance of RGO/CoSe2. Our studies raise promising possibilities for designing effective OER electrocatalysts for energy conversion.

Spontaneous Reduction and Assembly of Graphene oxide into Three-Dimensional Graphene Network on Arbitrary Conductive Substrates

Chemical reduction of graphene oxide (GO) is the main route to produce the mass graphene-based materials with tailored surface chemistry and functions. However, the toxic reducing circumstances, multiple steps, and even incomplete removal of the oxygen-containing groups were involved, and the produced graphenes existed usually as the assembly-absent precipitates. Herein, a substrate-assisted reduction and assembly of GO (SARA-GO) method was developed for spontaneous formation of 3D graphene network on arbitrary conductive substrates including active and inert metals, semiconducting Si, nonmetallic carbon, and even indium-tin oxide glass without any additional reducing agents. The SARA-GO process offers a facile, efficient approach for constructing unique graphene assemblies such as microtubes, multi-channel networks, micropatterns, and allows the fabrication of high-performance binder-free rechargeable lithium-ion batteries. The versatile SARD-GO method significantly improves the processablity of graphenes, which could thus benefit many important applications in sensors and energy-related devices.

Scalable preparation of three-dimensional porous structures of reduced graphene oxide/cellulose composites and their application in supercapacitors

Controlling the assembled structures of graphene has recently attracted enormous attention due to intriguing properties of the resultant structures. In this study, three-dimensional (3D) porous structures of reduced graphene oxide (RGO) with various ratios of RGO to cellulose have been fabricated by a scalable, but simple and efficient, approach that consists of ball milling assisted chemical reduction of GO, template shaping, coagulating, and lyophilization. The efficient mechanical shearing of ball milling and the hydrogen bond interactions between RGO and cellulose molecules contribute to the formation of a homogeneous RGO/cellulose hydrogel, improved thermal stability of the resultant composites, and enhanced crystallinity of the cellulose in the composites. The coagulation effect of cellulose maintains the RGO sheets in the 3D structures of cellulose; on the other hand, the RGO sheets facilitate the preservation of the 3D structures during freeze-drying, leading to the formation of 3D porous structures of RGO/cellulose composites. Benefiting from the continuous RGO network in the composites, the 3D porous structures of RGO(70)/cellulose(100) (GO:cellulose=70:100 in weight) show an electrical conductivity of 15.28Sm−1. Moreover, the 3D porous structures show potential application in supercapacitors due to the fact that they provide high specific surface area and fast charge propagation.

Mechanically Robust, Electrically Conductive Biocomposite Films Using Antimicrobial Chitosan‐Functionalized Graphenes

An effective way of covalently functionalizing graphene with a chitosan polymer via a nitrene chemistry is demonstrated. The biofunctionalized graphene is prepared by the chemical reduction of graphene oxide using a nitrene chemistry, and then covalently grafting chitosan to the graphene surface. The effectiveness of the biofunctionalized graphene as a reinforcing filler (4 wt%) in a chitosan polymer matrix is verified by the dramatic enhancement of the mechanical properties (breaking stress = 330%, Young's modulus = 243%) and the electrical conductivity (0.3 S m−1) without much loss in the elongation‐at‐break. The reinforcing effect can be explained by both the homogeneous dispersion of graphene within the matrix and the strong bond arising from the intrinsically intimate contact between the graphene and the matrix. The high antimicrobial activity of the biofunctionalized graphene compared with graphene oxide and chemically reduced graphene may be because of the presence of chitosan polymer on the edges of the graphene. The strong, antimicrobial graphene‐filled composite film can be used for food packaging and for coating various biomedical devices, where bacterial surface colonization is undesirable.