Reduction Of Graphene Research Articles

Recent Advances in the Green Reduction of Graphene Oxide and its Potential Applications

Abstract: Graphene has drawn significant attention due to its commercial usage in various fields. Several methods have been developed for the synthesis of graphene sheets but most of them involve only lab-scale production and are expensive too. So, the production of high-grade graphene on a large scale by cost-efficient and eco-friendly methods is still a challenge for the scientific community. The reduction of graphene oxide to produce high-quality graphene is considered the most eco-efficient and auspicious approach. Various pathways for the reduction of graphene oxide involving chemical reduction, thermal annealing, microwave and photoreduction, solvothermal, electrochemical, and green reduction have been explored. Several of these methods use harmful and toxic reagents that cause adverse effects on human health and the environment. The reduction of graphene oxide by plant extracts is simple, easily accessible, environment-friendly, sustainable, renewable, and economical. This review highlights different approaches for the synthesis of reduced graphene oxide with the main focus on green reduction using plant extracts. Moreover, several applications of reduced graphene oxide in various fields have also been elaborated. The main aim of this review is to provide deep insights for current and future researchers related to the greener methods for the synthesis of reduced graphene oxide along with its potential applications.

Crystallographic parameters of Bi2O3 and reduced Graphene-Bi2O3 nano-composite thin film

The Bi2O3 and reduced graphene (RG)-Bi2O3 nano-composite thin films are synthesized using modified sol-gel process. For structural examination, the samples are analyzed using XRD. Using the Scherrer equation and a modified Scherrer plot, the sample's structural parameters are calculated. The materials' size and strain were estimated from different methods like modified Williamson-Hall (W–H), Halder-Wagner (H–W), and Size Strain Plot (SSP) with logical validity. The different crystallographic parameters obtained are compared and presented in this work.

Experimental and Theoretical Findings of the Concerted Effect of Dual Quantum Dots on a Graphene Matrix for Energy Storage Applications

The construction of composite electrode materials that exhibit superior energy and power densities has stirred rigorous research on supercapacitors. Herein, we have successfully designed nitrogen-doped carbon dots (CDs) and hematite dots (HtDs) functionalized reduced graphene (RG) hybrid ternary composites (RG@CDs/HtDs) by liquid exfoliation followed by the solvothermal method. The hybrid electrode material, RG@CDs/HtDs, exhibits a high specific capacitance of 1566 F/g at a scan rate of 2 mV s–1 and excellent stability up to 10,000 cycles. The DFT calculations have been performed to investigate the capacitance enhancement in the hybrid structure. The enhanced quantum capacitance and intense electronic states near the Fermi level for the ternary structure RG@CDs/HtDs justify the superior charge storage. When HtDs and CDs are introduced into RG, charge transfers from the Fe 3d orbital to the C 2p orbital of RG occur. An asymmetric aqueous supercapacitor device has been fabricated using RG@CDs/HtDs as a cathode and Mn3O4/C as an anode. Remarkably, the assembled aqueous asymmetric supercapacitor operates in a stable and wide potential window of 2.5 V with an ultrahigh energy density (134 Wh kg–1) along with extraordinary rate capability and is stable at 10,000 cycles performance that was validated on powering of the red light-emitting diode (LED).

Asymmetric polysaccharide-bound graphene electrode configuration with enhanced electrosorption performance for uranium (VI) ions

As an energy-saving and facile technology, the potential of capacitive deionization (CDI) starts to surface in enrichment and recovery of uranium (U(VI)) from aqueous solutions. However, co-ion expulsion effect and poor surface wettability of electrode materials limit the eletrosorption performance. Here, polysaccharides xanthan gum (XG)- and chitosan (CS) -bound porous reduced graphene (RGH) electrodes were rationally designed, and then assembled into asymmetrical electrode configuration for U(VI) eletrosorption. Owing to the introduction of polysaccharide binders, the oppositely charged groups on the surface of cathode and anode weaken the co-ions exclusion effect as well as endow their superior surface hydrophilicity and electroconductivity, which facilitates the electrosorption for U(VI). Meanwhile, the negatively charged carboxylate groups could act as extra micro electric fields to attract U(VI) cations, and form stronge complexation between them. As a consequence, asymmetrical polysaccharide-bound RGH configuration gave rise to a larger removal ratio of 97.9% within 4 h at 1.2 V, as well as 2.5 times faster kinetics than symmetrical PVDF-bound RGH electrode configuration. Moreover, the accumulated adsorption capacity in six adsorption–desorption cycles of the former is up to 1413.0 mg g−1, 75% higher than the latter, which is of practical significance and economic benefit for electrosorption application.

Bacteriophage-Based Biosensor for Detection of E. coli Bacteria on Graphene Modified Carbon Paste Electrode

Background:Escherichia coli (E. coli) bacteria is one of the hazardous human pathogens. Consequently, developing the rapid and effective method for identification and quantization of E. coli is popular in biotechnological researches in recent years.Experimental:In this research, a label-free capacitance E. coli biosensor was fabricated based on immobilizing bacteriophage on the carbon paste electrode (Cp). Reduced graphene (RGr) was synthesized and used as a substrate for immobilization of bacteriophage on the Cp surface. E. coli bacteriophage was trapped in graphene modified carbon paste electrodes. The immobilization accuracy was confirmed via electrochemical techniques. The modified electrodes were applied as indicator electrodes for capacitance measurements of E. coli.Results:Through this method, E. coli was detected in a concentration range of 33×10-3 to 330×10-3 N L-1 (number of E. coli per Liter) with a correlation coefficient of 0.99 and a detection limit of 12×10-3 N L-1.Conclusion:The proposed biosensor has a fast response time of about 5 s and good selectivity over other bacteria.

Enhanced Electrocatalytic Activity of Ethanol Oxidation Reaction on Palladium-Silver Nanoparticles via Removable Surface Ligands.

This work developed a facile colloidal route to synthesize BH4--capped PdxAgy nanoparticles (NPs) in water using the reducing ionic liquids of [Cnmim]BH4, and the resulting NPs were prone to form the nanocomposites with [amim]+-modified reduced graphene (RG). The removal of the metal-free inorganic ions of BH4- can create the profoundly exposed interfaces on the PdxAgy NPs during the electrooxidation, and favor the ethanol oxidation reaction (EOR) in lowering energy barrier. The counterions of [Cnmim]+ can gather ethanol, OH- ions, and the reaction intermediates on catalysts, and synergistically interact with RG to facilitate the charge transfer in nanocomposites. The interface-modified RG nanosheets can effectively segregate the PdxAgy NPs from aggregation during the EOR. Along with the small size of 4.7 nm, the high alloying degree of 60.2%, the large electrochemical active surface area of 64.1 m2 g-1, and the great peak current density of 1501 mA cm-2 mg-1, Pd1Ag2@[C2mim]BH4-amimRG nanocomposite exhibits the low oxidation potentials, strong poison resistance, and stable catalytic activity for EOR in alkaline media, and hence can be employed as a promising anodic catalyst in ethanol fuel cells.

Effects of oxygen-containing functional groups on the supercapacitor performance of incompletely reduced graphene oxides

Incompletely reduced graphene (RG) was prepared by reduction of graphite oxides via microwave irradiation at the power of 800 W and 1200 W, respectively. Fourier transform infrared spectra and X-ray photoelectron spectroscopy analyses showed that the RG contains flourish oxygen functional groups such as carboxyl, phenol, carbonyl, and quinone groups. X-ray diffraction, scanning electron microscopy and transmission electron microscopy were employed to investigate the structure, morphology of the RG samples. The electrochemical performance of the RG electrodes were measured in 5 M NaOH, 1 M H2SO4 and 1 M Na2SO4 electrolytes respectively. The supercapacitor performance of oxygen-containing functional group behavior was investigated. The specific pseudocapacitance per unit atomic percentage for either carboxyl or phenol group in 1 M H2SO4 and either carbonyl and quinone group in 5 M NaOH were obtained by galvano-statically charge/discharge measurements

Thermodynamic and Structural Insights into Nanocomposites Engineering by Comparing Two Materials Assembly Techniques for Graphene

Materials assembled by layer-by-layer (LBL) assembly and vacuum-assisted flocculation (VAF) have similarities, but a systematic study of their comparative advantages and disadvantages is missing. Such a study is needed from both practical and fundamental perspectives aiming at a better understanding of structure-property relationships of nanocomposites and purposeful engineering of materials with unique properties. Layered composites from polyvinyl alcohol (PVA) and reduced graphene (RG) are made by both techniques. We comparatively evaluate their structure, mechanical, and electrical properties. LBL and VAF composites demonstrate clear differences at atomic and nanoscale structural levels but reveal similarities in micrometer and submicrometer organization. Epitaxial crystallization and suppression of phase transition temperatures are more pronounced for PVA in LBL than for VAF composites. Mechanical properties are virtually identical for both assemblies at high RG contents. We conclude that mechanical properties in layered RG assemblies are largely determined by the thermodynamic state of PVA at the polymer/nanosheet interface rather than the nanometer scale differences in RG packing. High and nearly identical values of toughness for LBL and VAF composites reaching 6.1 MJ/m(3) observed for thermodynamically optimal composition confirm this conclusion. Their toughness is the highest among all other layered assemblies from RG, cellulose, clay, etc. Electrical conductivity, however, is more than 10× higher for LBL than for VAF composites for the same RG contents. Electrical properties are largely determined by the tunneling barrier between RG sheets and therefore strongly dependent on atomic/nanoscale organization. These findings open the door for application-oriented methods of materials engineering using both types of layered assemblies.

Transparent polyimide nanocomposites with improved moisture barrier using graphene

A facile technique was developed to improve the water barrier properties of transparent polyimide (PI) films. Transparent and organo-soluble PI films were synthesized from an alicyclic tetracarboxylic dianhydride (bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride) and an aromatic diamine (3,4′-oxydianiline) in a co-solvent of dimethylacetamide (DMAc) and γ-butyrolactone via a one-step process. Thermally reduced graphene (RG) was then blended with the PI in DMAc solution to fabricate PI/RG nanocomposite films without the addition of coupling agent. With the incorporation of only 0.1 wt% highly exfoliated RG in the PI matrix, the resultant PI/RG-0.1 nanocomposite exhibited a superior barrier to moisture and retained high transmittance in the visible light region. The surface of PI/RG was more hydrophobic than that of pure PI and simultaneously the water vapor transmission rate was significantly reduced to 13 g m−2 day−1 for the PI/RG-0.1 nanocomposite compared to 181 g m−2 day−1 for pure PI. Notably, the PI/RG-0.1 nanocomposite also exhibited favorable thermal stability with a lower coefficient of thermal expansion and a higher thermal degradation temperature compared to pure PI. The easy processing of PI solution and RG nanosheets, the good orientation of RG in PI and the excellent barrier and thermal properties of PI/RG make the transparent PI nanocomposite films potential substrate materials in flexible electronic applications.

Structure, Thermal Stability and Electrical Properties of Reduced Graphene/Poly(vinylidene fluoride) Nanocomposite Films

The reduced graphene/poly(vinylidene fluoride) nanocomposite films were prepared by the solution casting-thermal reduction process using graphene oxide (GO) and poly(vinylidene fluoride) (PVDF) resin. With the presence of reduced graphene (RG) nano sheets in the nanocomposite, the structure of PVDF is transformed from alpha to beta phase, and the beta phase fraction and its crystallinity are largely affected by the RG content. The PVDF thermal stability is improved by the RG introduction, with about 15 degrees C increase of the half-life of PVDF decomposition temperature. The RG/PVDF nanocomposites show a better electrical conductivity than that for the GO/PVDF nanocomposites. At a low RG content (0.8 wt.%), the dielectric constant of RG/PVDF nanocomposite film with a very low loss tangent is dramatically increased from about 6 to 23. The mechanisms for the thermal stability and electrical property improvements are discussed.

Differentiation between graphene oxide and reduced graphene by electrochemical impedance spectroscopy (EIS)

We report a novel method of differentiating 2 types of graphene nanomaterial: graphene oxide (GO) and reduced graphene (RG). GO, synthesized by modified Hummer's method, was subsequently reduced electrochemically (ERG) and photocatalytically (PRG). GO and RG have typically been discriminated by x-ray diffraction spectroscopy (XRD), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS). Electrochemical impedance spectroscopy (EIS) has usually been used to obtain the electronic transfer properties, based on Nyquist diagrams. However, in this report, we demonstrate that EIS can distinguish GO and RG graphene forms using the impedance modulus and shift-phase angle-versus-frequency Bode diagrams. The impedance modulus Bode diagram exhibits 2 time constants for a glassy carbon electrode (GCE) that has been modified with GO versus only 1 time constant for GCE that is modified with ERG and PRG. Thus, this spectroscopic technique can unambiguously determine whether graphene is in its oxidized or reduced form.

Electrophoretic Deposition of a Reduced Graphene–Au Nanoparticle Composite Film as Counter Electrode for CdS Quantum Dot‐Sensitized Solar Cells

A reduced graphene (RG)-Au nanoparticle composite film is successfully fabricated by electrophoretic deposition and used as counter electrode for quantum dot-sensitized solar cells. The RG-Au composite is prepared by one-step microwave-assisted reduction of chloroaurate in alkaline solution with graphite oxide dispersion. Under one sun illumination (AM 1.5 G, 100 mW cm(-2)), the cell with a RG-Au counter electrode shows an energy conversion efficiency of 1.36 %, which is higher than those of cells employing conventional Pt or Au counter electrodes, due to the superior combination of highly catalytic Au nanoparticles and the conductive graphene network structure.

Multifunctionalization of carbon nanotube fibers with the aid of graphene wrapping

Carbon nanotube (CNT) fibers are promising candidates for developing multifunctional textiles. The direct introduction of functional guests within or around CNT fibers meets problems due to the rough fiber surface and weak interfacial bindings. To improve the functionality and performance stability, we report a new method to modify the surface roughness and level of functionalization of CNT fibers, by wrapping graphene oxide (GO) or reduced graphene (RG) around them. Besides the functional groups on the graphene sheets, the introduction of a graphene layer also has smoothing and shield effects, resulting in higher tensile strength and improved and stabilized performance. The electrochemical and photocurrent applications were exploited by depositing polyaniline around GO-wrapped CNT fibers and TiO2 around RG-wrapped fibers, with a capacitance up to 229.5 F cm−3 and a photocurrent density of 132 μA cm−2, respectively. The present technique has the advantage that the mechanical and functional properties can be optimized by simply modifying the core CNT fiber via polymer infiltration during the fiber spinning.

Electrophoretic deposition of reduced graphene-carbon nanotubes composite films as counter electrodes of dye-sensitized solar cells

Reduced graphene (RG)-carbon nanotubes (CNTs) composite films are successfully fabricated by electrophoretic deposition and used as counter electrodes of dye-sensitized solar cells. RG is obtained by microwave-assisted reduction of graphite oxide dispersion in aqueous solution using a microwave synthesis system. By the optimization of CNTs content, photovoltaic conversion efficiency of the cell with RG-CNTs counter electrode reaches a maximum of 6.17% at one sun (AM 1.5 G, 100 mW cm−2) which is comparable to the cell with conventional Pt counter electrode. The results suggest that the RG-CNTs composite films provide a potential feasibility for replacing conventional Pt counter electrodes for DSSCs.