Graphene-based Functional Materials Research Articles

Combustion Characteristics of r-GO/g-C3N4/LaFeO3 Nanohybrids Loaded Fuel Droplets

ABSTRACT Graphene oxide (GO), reduced graphene oxide (r-GO) and graphitic carbon nitride (g-C3N4) are two-dimensional carbon-based nanosheets that show promise in reducing emissions with their superior catalytic activity in capturing species such as NOx and CO2 thanks to their oxygen-based functional groups and active edges on their surfaces. These active surfaces also provide a scheme for the substitution of materials with high calorific value or high catalytic activity for combustion. This study focuses on the fabrication of functional nanohybrid structures customized for combustion with LaFeO3 metal oxide nanoparticles substituted on these nanosheets and their effect on the combustion behavior of gasoline. The fabrication of r-GO/g-C3N4/LaFeO3 nanohybrid structures was carried out by a two-step hydrothermal method. The structural characterizations of the samples were confirmed by SEM and XRD analyses and their chemical states were confirmed by Raman and XPS techniques. Combustion experiments were carried out by droplet scale combustion of gasoline-based nanofuel droplets containing dilute (0.2 wt.%) and high (0.7 wt.%) concentrations of GO, r-GO, g-C3N4, g-C3N4/LaFeO3 and r-GO/g-C3N4/LaFeO3 nanoparticles. The experimental process was recorded with a high-speed camera and a thermal camera. The nanofuel droplets containing 0.2 wt.% g-C3N4/LaFeO3 nanohybrid structures had the highest maximum flame temperature of 519 K, and the nanofuel droplets containing 0.7 wt.% r-GO/g-C3N4/LaFeO3 particles had the highest maximum aggregate temperature of 1177 K. The ignition delay time decreased for all droplets with 0.2 wt.% and 0.7 wt.% particle loadings. At 0.2 wt.% concentration, g-C3N4 doped fuel droplets exhibited the lowest extinction time, while at 0.7 wt.% concentration, the lowest extinction time was measured for r-GO/g-C3N4/LaFeO3 doped fuel droplets. Fuel droplets containing g-C3N4 particles had the highest burning rate and were the fastest extinguishing fuel droplets in the electric field. In this study, it has been demonstrated that the combustion rate and energy value of hydrocarbon fuels can be increased and soot formation can be reduced at the same time with the new generation of graphene-based functional materials to be created, and thus, many combustion problems can be solved simultaneously with these functional particles.

Self-Assembly of a Graphene Oxide Liquid Crystal for Water Treatment.

Adsorbents, especially those with high removal efficiency, long life, and multi-purpose capabilities, are the most crucial components in an adsorption system. By taking advantage of the liquid-like mobility and crystal-like ordering of liquid crystal materials, a liquid crystal induction method is developed and applied to construct three-dimensional graphene-based adsorbents featuring excellent shape adaptability, a distinctive pore structure, and abundant surface functional groups. When the monoliths are used for water restoration, the large amount of residual oxygen-containing groups is more susceptible to electrophilic attack, thus contributing to cation adsorption (up to 705.4 mg g-1 for methylene blue), while the connected microvoids between the aligned graphene oxide sheets facilitate mass transfer, e.g., the high adsorption capacity for organic pollutants (196.2 g g-1 for ethylene glycol) and the high evaporation rate for water (4.01 kg m-2 h-1). This work gives a practical method for producing high-performance graphene-based functional materials for those applications that are sensitive to surface and mass transfer properties.

Facile preparation of graphene/polyaniline composite hydrogel film by electrodeposition for binder-free all-solid-state supercapacitor

The combination of graphene and polyaniline (PANI) as electrodes for supercapacitors has attracted dramatic interests due to their synergistic effects. However, the preparation of the electrode materials usually involves complicated process and other additives. In this work, we report the facile fabrication of the graphene/PANI composite hydrogel film as the symmetric all-solid-state supercapacitor electrode. The free-standing reduced graphene oxide (rGO) hydrogel film is hydrothermally synthesized from a GO solution layer, which is used for subsequent electropolymerization of PANI. The electrochemical measurements of the resulting rGO/PANI hydrogel film present the capacitance of 853.7 F g−1 at 1 A g−1 with good rate capability and cycling stability. In addition, the hydrogel composite film is assembled into the symmetric all-solid-state capacitor without any additives and attains the capacitance of 741.8 F g−1 with a high capacitance retention of 92.6% after 8000 cycles. These excellent electrochemical properties of the composite film are ascribed to the joint effort of superior conductivity and porous structure of rGO matrix with the outstanding pseudocapacitive property of PANI. The convenient method could be considered for the preparation of graphene-based functional composite materials.

Drop-on-demand printing of edge-enhanced and conductive graphene twin-lines by coalescence regulation and multi-layers overwriting

Fabrication of straight and highly conductive graphene lines, the cornerstones of high-performance graphene-based printed electronics, still faces considerable challenges. We have developed a convenient and effective way to print edge-enhanced highly conductive graphene twin-lines by coalescence regulation and multi-layers overwriting (CRMO), which enhances both outline accuracy and electrical conductivity. The overlapping traces and wavy edges were eliminated by droplets coalescence at the expense of introducing discrete footprints, which were transformed into continuous lines by multi-layers overwriting. We successfully fabricated the edge-enhanced graphene twin-line with an edge width of 72.33 ± 7.96 μm and a linear resistivity of 0.188 ± 0.160 kΩ μm−1, yielding the coinstantaneous enhancement of outline accuracy, printing efficiency, and electrical conductivity. Printed graphene twin-lines achieve one of the lowest relative linear resistivity reported so far and a conductivity of 359.88 S m−1. We attributed the highly concentrated and tightly interconnected graphene flakes at the edge to the synergetic effect of CRMO. Finally, we have demonstrated the feasibility of CRMO by printing graphene line resistors with excellent linearity and broad resistance ranges. Such findings establish relationships among the printing method, line morphologies, flakes distribution, and electrical conductivity. This work will be of great significance for the self-assembly of graphene-based functional materials and graphene-based printed electronics development.

Defect-Driven Heterogeneous Electron Transfer between an Individual Graphene Sheet and Electrode.

Understanding the heterogeneous electron-transfer (ET) kinetics on graphene is essential for its extensive applications. Here, on the basis of the redox-induced fluorescence variation of monolayer graphene itself, the heterogeneous ET kinetics at the interface between the electrode and the monolayer graphene was studied label-freely at the single-sheet level. By tuning the defect density on graphene, an optimal heterogeneous ET rate was observed at a moderate defect density, indicating defect-driven ET kinetics. The heterogeneities of both the intrasheet and intersheet ET kinetics were revealed at the single-sheet level. With the optimal defective graphene sheets as a sensing material for oxygen gas, a cost-effective electrochemical oxygen sensor was obtained with high sensitivity, fast response/recovery, and remarkable durability. The results obtained here deepen our understanding of the electrochemical properties of graphene and imply that rational defect control can enhance the ET process between the electrode and graphene and then improve the performance of graphene-based functional materials or devices.

Efficient synthesis of graphene oxide by Hummers method assisted with an electric field

An electric field-assisted Hummers method for the synthesis of graphene oxide (GO) is reported which can enhance the efficiency of oxidation processes, while decreasing destructive effects on the resultant graphite lattice. The electric field varies from 0 ∼ 167 V cm−1 was applied outside the reaction system and operated on three temperature stages of Hummers method which use a low dose of oxidizer. The as-prepared GO nanoplate has a layer spacing of 1 nm. This improved method may be important for preparing high-quality GO with low cost and light pollution. Furthermore, it is a promising improvement to the efficiency of reduction processes and optimization of the structure of GO or reduced graphene oxide (rGO), allowing them to be applied to various graphene-based functional materials.

Graphene aerogel derived by purification-free graphite oxide for high performance supercapacitor electrodes

Graphite oxide (GO), often being used as a precursor of graphene-based materials, can be prepared through a modified Hummers' method. The last step of GO synthesis, i.e. the removal of hydrogen chloride (HCl), is generally time-consuming, costly and polluting. Herein, the HCl-containing graphite oxide (H-GO) and pure GO aqueous suspensions were respectively hydrothermally treated followed by freeze-drying, leading to two graphene aerogels (H-GA and GA). Characterization results show that the two aerogels possess similar microstructure but distinct surface chemistry properties. When used as the active electrode materials in supercapacitors, GA and H-GA show comparable electrochemical properties in KOH aqueous electrolyte. In EMIMBF4 ionic liquid electrolyte, H-GA shows larger specific capacitance (243 F g−1 at 1 A g−1), better rate capability, and higher energy density (135 Wh kg−1 at 1 kW kg−1) compared with GA (216 F g−1, 120 Wh kg−1), which is attributed to its higher O/C ratio and better electrolyte wettability. We propose that it is not always necessary to conduct the HCl removal, and H-GO could be directly used as a precursor, which not only saves the time and cost remarkably but also may open up a relatively facile route to fabricate some graphene-based functional bulk materials.

Synthesis of graphene-based nanostructures by the combined method comprising sol-gel and sonochemistry techniques

Nanocomposites based on graphene and Co3O4, MoO3, NiO and WO3 have been synthesized by a combination of sol-gel and sonochemical techniques. N,N-Dimethyloctylamine was used for the formation and stabilization of metal-containing sols and for stabilization of graphene suspension. The structure, morphology and composition of graphene-based nanocomposites were investigated by means of transmission electron microscopy, X-ray diffraction, Raman and FT-IR spectroscopy. It has been shown that the proposed method allows obtaining the hybrid nanoparticles with 10 to 200 nm size consisting of Co3O4, MoO3, NiO or WO3 crystallites coated with the graphene layers. This method enables preparing chemically homogeneous composite nanopowders for the production of high performance (photo)catalysts and fine-grained ceramics for the energy sector with uniform distribution of components within a volume. It has beens proven experimentally that graphene sheets are involved in the formation of hybrid nanoparticles based on metal oxides as structuring and texturing agents. These results show promise in the synthesis and fabrication of well-defined graphene-based functional materials, including graphene-ceramic hybrids, with a broad scope of applications.

Graphene oxide liquid crystals: a frontier 2D soft material for graphene-based functional materials.

Graphene, despite being the best known strong and electrical/thermal conductive material, has found limited success in practical applications, mostly due to difficulties in the formation of desired large-scale highly organized structures. Our discovery of a liquid crystalline phase formation in graphene oxide dispersion has enabled a broad spectrum of highly aligned graphene-based structures, including films, fibers, membranes, and mesoscale structures. In this review, the current understanding of the structure-property relationship of graphene oxide liquid crystals (GOLCs) is overviewed. Various synthetic methods and parameters that can be optimized for GOLC phase formation are highlighted. Along with the results from different characterization methods for the identification of the GOLC phases, the typical characteristics of different types of GOLC phases introduced so far, including nematic, lamellar and chiral phases, are carefully discussed. Finally, various interesting applications of GOLCs are outlined together with the future prospects for their further developments.

Preparation of graphene oxide-coated silk fibers through HBPAA [a molecular glue]-induced layer-by-layer self-assembly

Carbon nanomaterials recently gained extensive interests for their good application potential in composite nanomaterials because of their unique physicochemical properties. In this study, graphene oxide (GO)-coated silk fibers were fabricated through HBPAA-induced layer-by-layer (LbL) self-assembly technology. The closely adhered GOs coatings were achieved by circular incubation with solutions of hyperbranched poly (amidoamine) (HBPAA) and GOs, with HBPAA serving as the “molecular glue” that could bind single or mutilayered GOs to the surface of silk fibers. In the experiments, GOs nanosheets were synthesized by a modified Hummers method and were characterized by atomic force microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Our developed technology was able to tightly bind GOs to the silk surface and control their loading capacity. Owing to the positive charges and abundant amino end groups of HBPAA, GOs were found to be completely adsorbed onto silk surface. Therefore, their assembly would be green and controllable. The Fourier transform infrared (FTIR) spectroscopy, XPS, XRD, Thermogravimetric analyses (TGA) confirmed the attachment of HBPAA and GOs. Field mission scanning electron microscopy (FESEM) indicated that GOs closely spread on the surface of silk fibers without any self-folding though excessive stacking were observed in a small part of a silk surface with the increased density of GOs coatings. The developed LbL self-assembly technology may provide a controllable approach to coat GOs on the surface of biological fibers and graphene-based functional materials.

A method for selective bromination of graphene and its use for subsequent functionalization with aromatic molecules

A novel method for selective bromination of graphene was proposed. The reduced graphene oxide (denoted as graphene) used as the raw material, was brominated with 1,3-dibromo-5,5-dimethylhydantoin in the mixture of trifluoromethanesulfonic acid and CH2Cl2 at room temperature. The success of bromination was confirmed by x-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive x-ray analysis, and Fourier transform-infrared spectroscopy. Moreover, it was found that the bromine concentration of the brominated graphene increased up to 10% Br/C with increasing bromination duration for the first 24 h; then the concentration unexpectedly decreased. The brominated graphene was further functionalized with 4-pyridinyl boronic acid through the Suzuki-coupling reaction. The atomic concentration of Br greatly decreased, whereas the atomic concentration of N increased significantly. This indicated that the functionalization was successful. This proposed bromination method is easy and well-suited for graphene and its derivatives. Additionally, the brominated graphene can be a starting material for constructing other graphene-based functional materials.

Advances in Subcritical Hydro-/Solvothermal Processing of Graphene Materials.

Many promising graphene-based materials are kept away from mainstream applications due to problems of scalability and environmental concerns in their processing. Hydro-/solvothermal techniques overwhelmingly satisfy both the aforementioned criteria, and have matured as alternatives to wet-chemical methods with advances made over the past few decades. The insolubility of graphene in many solvents poses considerable difficulties in their processing. In this context hydro-/solvothermal techniques present an ideal opportunity for processing of graphenic materials with their versatility in manipulating the physical and thermodynamic properties of the solvent. The flexibility in hydro-/solvothermal techniques for manipulation of solvent composition, temperature and pressure provides numerous handles to manipulate graphene-based materials during synthesis. This review provides a comprehensive look at the subcritical hydro-/solvothermal synthesis of graphene-based functional materials and their applications. Several key synthetic strategies governing the morphology and properties of the products such as temperature, pressure, and solvent effects are elaborated. Advances in the synthesis, doping, and functionalization of graphene in hydro-/solvothermal media are highlighted together with our perspectives in the field.

Progress in research on preparation of graphene-based functional materials using gamma-ray irradiation technology

Progress in research on preparation of graphene-based functional materials using gamma-ray irradiation technology

Preparation and Application of Water-in-Oil Emulsions Stabilized by Modified Graphene Oxide.

A series of alkyl chain modified graphene oxides (AmGO) with different alkyl chain length and content was fabricated using a reducing reaction between graphene oxide (GO) and alkyl amine. Then AmGO was used as a graphene-based particle emulsifier to stabilize Pickering emulsion. Compared with the emulsion stabilized by GO, which was oil-in-water type, all the emulsions stabilized by AmGO were water-in-oil type. The effects of alkyl chain length and alkyl chain content on the emulsion properties of AmGO were investigated. The emulsions stabilized by AmGO showed good stability within a wide range of pH (from pH = 1 to pH = 13) and salt concentrations (from 0.1 to 1000 mM). In addition, the application of water-in-oil emulsions stabilized by AmGO was investigated. AmGO/polyaniline nanocomposite (AmGO/PANi) was prepared through an emulsion approach, and its supercapacitor performance was investigated. This research broadens the application of AmGO as a water-in-oil type emulsion stabilizer and in preparing graphene-based functional materials.

Super-stretchable graphene oxide macroscopic fibers with outstanding knotability fabricated by dry film scrolling.

Graphene oxide (GO) has recently become an attractive building block for fabricating graphene-based functional materials. GO films and fibers have been prepared mainly by vacuum filtration and wet spinning. These materials exhibit relatively high Young's moduli but low toughness and a high tendency to tear or break. Here, we report an alternative method, using bar coating and drying of water/GO dispersions, for preparing large-area GO thin films (e.g., 800-1200 cm(2) or larger) with an outstanding mechanical behavior and excellent tear resistance. These dried films were subsequently scrolled to prepare GO fibers with extremely large elongation to fracture (up to 76%), high toughness (up to 17 J/m(3)), and attractive macroscopic properties, such as uniform circular cross section, smooth surface, and great knotability. This method is simple, and after thermal reduction of the GO material, it can render highly electrically conducting graphene-based fibers with values up to 416 S/cm at room temperature. In this context, GO fibers annealed at 2000 °C were also successfully used as electron field emitters operating at low turn on voltages of ca. 0.48 V/μm and high current densities (5.3 A/cm(2)). Robust GO fibers and large-area films with fascinating architectures and outstanding mechanical and electrical properties were prepared with bar coating followed by dry film scrolling.

An Overview with Applications to Graphene-Based Composites

In recent years, graphene has been increasingly studied due to its good performance, low prices and accessible materials in recent years. In addition, the scaled-up and reliable production of graphene derivatives provides a large range of opportunity to synthesize graphene-based functional materials for various applications. This paper summarizes the graphene-based composites in various fields of applications.

Graphene in Copper Catalyzed Azide-Alkyne Cycloaddition Reactions: Evolution from [60]Fullerene and Carbon Nanotubes Strategies

Graphene possesses outstanding electronic and structural properties and the possibility to functionalize it with different functional moieties has greatly broadened the scope of its applications. The copper (I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction has been recently adopted as a universal coupling process with applications that extend far beyond organic synthesis to further challenging goals in chemistry, polymer science, and biology. In this article we critically examine the progress in the use of the CuAAC reaction with different carbon nanostructures and show how this research is merging now in the development of novel graphene-based functional materials. We believe that the selective functionalization of graphene using the CuAAC click reaction may play an important role in improving the integration of graphene in multicomponent systems, and consequently their applications. Keywords: Graphene, Carbon Nanostructures, Chemical Modification, Copper Catalyzed Azide-Alkyne Cycloaddition.

Factors that Affect Pickering Emulsions Stabilized by Graphene Oxide

Stable Pickering emulsions were prepared using only graphene oxide (GO) as a stabilizer, and the effects of the type of oil, the sonication time, the GO concentration, the oil/water ratio, and the pH value on the stability, type, and morphology of these emulsions were investigated. In addition, the effects of salt and the extent of GO reduction on emulsion formation and stability were studied and discussed. The average droplet size decreased with sonication time and with GO concentration, and the emulsions tended to achieve good stability at intermediate oil/water ratios and at low pH values. In all solvents, the emulsions were of the oil-in-water type, but interestingly, some water-in-oil-in-water (w/o/w) multiple emulsion droplets were also observed with low GO concentrations, low pH values, high oil/water ratios, high salt concentrations, or moderately reduced GO in the benzyl chloride-water system. A Pickering emulsion stabilized by Ag/GO was also prepared, and its catalytic performance for the reduction of 4-nitrophenol was investigated. This research paves the way for the fabrication of graphene-based functional materials with novel nanostructures and microstructures.

Self-assembled hydrothermal synthesis for producing a MnCO3/graphene hydrogel composite and its electrochemical properties

As ultrathin and flexible materials, graphene sheets are versatile building blocks for fabricating graphene-based functional composite materials for widespread applications. In this paper, we demonstrated a facile approach to prepare MnCO3/graphene hydrogel (MGH) composites via a hydrothermal process. The MnCO3 nanoparticles are 50–100 nm in size and are deposited on graphene sheets’ surfaces as spacers to prevent graphene sheets from restacking. A combination of deposited MnCO3 nanoparticles and hydration of the hydrogel could effectively keep the neighboring graphene sheets separated. The obtained MGH nanocomposite presents a high specific capacitance (Cs) of 645.5 F g−1 at 0.5 A g−1 in a three-electrode system, suggesting that it is a robust candidate as a supercapacitor electrode material.

ChemInform Abstract: Nanocomposites and Macroscopic Materials: Assembly of Chemically Modified Graphene Sheets

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