Synthesis Of Graphenes Research Articles

In Situ Synthesis of Doped Bio-Graphenes as Effective Metal-Free Catalysts in Removal of Antibiotics: Effect of Natural Precursor on Doping, Morphology, and Catalytic Activity.

Wastewater contaminated with antibiotics is a major environmental challenge. The oxidation process is one of the most common and effective ways to remove these pollutants. The use of metal-free, green, and inexpensive catalysts can be a good alternative to metal-containing photocatalysts in environmental applications. We developed here the green synthesis of bio-graphenes by using natural precursors (Xanthan, Chitosan, Boswellia, Tragacanth). The use of these precursors can act as templates to create 3D doped graphene structures with special morphology. Also, this method is a simple method for in situ synthesis of doped graphenes. The elements present in the natural biopolymers (N) and other elements in the natural composition (P, S) are easily placed in the graphene structure and improve the catalytic activity due to the structural defects, surface charges, increased electron transfers, and high absorption. The results have shown that the hollow cubic Chitosan-derived graphene has shown the best performance due to the doping of N, S, and P. The Boswellia-derived graphene shows the highest surface area but a lower catalytic performance, which indicates the more effective role of doping in the catalytic activity. In this mechanism, O2 dissolved in water absorbs onto the positively charged C adjacent to N dopants to create oxygenated radicals, which enables the degradation of antibiotic molecules. Light irradiation increases the amount of radicals and rate of antibiotic removal.

Eco-friendly synthesis of sulphur-doped graphenes with applicability in caffeic acid electrochemical assay

A new electrode based on glassy carbon modified with a sulphur-doped graphene material was successfully developed and applied for caffeic acid (CA) voltammetric detection and quantification. The structural features of sulphur-doped graphene (exfGR-S) characterized by different physicochemical and analytical techniques are presented. Cyclic voltammetry (CV) technique was employed to evaluate the electrochemical behavior of both bare glassy carbon (GCE) and modified GCE/exfGr-S electrodes towards CA oxidation. The study revealed that the modified electrode exhibits superior electrochemical performances compared to the bare electrode, with a broad CA detecting range (from 0.1 to 100.0 µM), a low detection limit 3.03 × 10−8 M), excellent anti-interference capabilities, as well as good stability and repeatability. The developed electrochemical sensor appears to be a promising candidate for real sample quality control analysis since it successfully displayed its ability to directly detect CA in commercially available coffee product without any pretreatment.

Synthesis of nanoporous graphenes via decarboxylation reaction.

Two kinds of C-C bonded crystalline nanoporous graphenes (NPGs) have been synthesized by using a newly developed decarboxylation reaction. Both NPGs show good electrocatalytic oxygen evolution reaction (OER) activities. The clear pore-edge structures of the synthesized NPGs provide an ideal platform for further OER investigations.

Insight into the catalytic performance of HER catalysis of noble metal/3D-G nanocomposites

Development of multifunctional materials has shown a great interest in recent years. Herein, we report the simple, cost-effective, one step, and surfactant-free synthesis of three-dimensional graphenes (3D-G) nanocomposites with Pt, Pd, Au and Ag and explore their catalytic activity and investigated the dynamics for the hydrogen evolution reaction (HER). Field emission scanning electron microscopy (FEG-SEM) and high resolution transmission electron microscopy (HRTEM) study reveals the uniform incorporation of noble metal on the 3D-G. The 3D-G with Pt composite (Pt/3D-G) has shown significantly enhanced catalytic performance over the commercially available Pt/C for HER, suggesting significant improvements in catalytic performance on the incorporation of 3D-G. The Temperature dependent HER investigation has been performed and the apparent activation energy (Eaapp) for Pt/3D-G. Pd/3D-G, Au/3D-G, and Ag/3D-G catalysts are obtained as 25.37, 32.36, 16.14, and 24.82 kJ/mol, respectively. Eaapp of Pt/3D-G and Pd/3D-G are found to decrease with increase in the overpotential, and the Eaapp of Au/3D-G and Ag/3D-G is found to increase with overpotential. This variation of Eaapp with the applied potential is correlated with the metal-hydrogen bond energy with respect to the potential of zero charges (PZC). The kinetics of HER on catalysts is explained in terms of temperature variation of the Tafel slope. The Tafel slopes of Pt/3D-G and Pd/3D-G are increased with increase in temperature, and for Au/3D-G and Ag/3D-G, the Tafel slopes are decreased with increase in temperature, which suggests the enthalpy driven process for Pt/3D-G and Pd/3D-G and entropy driven process for Au/3D-G and Ag/3D-G.

Front Cover: Insights into the Scholl Coupling Reaction: A Key Transformation of Relevance to the Synthesis of Graphenes and Related Systems (Eur. J. Org. Chem. 13/2017)

Front Cover: Insights into the Scholl Coupling Reaction: A Key Transformation of Relevance to the Synthesis of Graphenes and Related Systems (Eur. J. Org. Chem. 13/2017)

Insights into the Scholl Coupling Reaction: A Key Transformation of Relevance to the Synthesis of Graphenes and Related Systems

The Scholl‐type reactions of 4,10‐disubstituted chrysene derivatives proceeded by variegated and unexpected oxidation/coupling pathways. These observations serve as a cautionary note when attempting to employ the Scholl reaction in target‐oriented materials synthesis.

Microwave Exfoliation of Graphite Oxides in H2S Plasma for the Synthesis of Sulfur-Doped Graphenes as Oxygen Reduction Catalysts.

Tuning the electronic and chemical properties of graphene can be carried out through heteroatomic doping, enabling its use as an electrocatalyst. Sulfur-doped graphene has been suggested to be a viable alternative to traditional Pt-based catalysts for oxygen reduction under alkaline conditions. Herein we present a fast and efficient route to synthesize S-doped graphenes through the microwave-assisted exfoliation and reduction of three different graphite oxides in the presence of hydrogen sulfide. The materials obtained were characterized using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, combustion elemental analysis, and voltammetry. These S-doped graphenes were found to have good electrochemical performance and were active in the catalysis of the oxygen reduction reaction.

Comparative study on graphene growth mechanism using Ni films, Ni/Mo sheets, and Pt substrates

We demonstrate a comparative study on graphene growth mechanism using various catalytic metal substrates such as Ni thin films, Ni-deposited Mo (Ni/Mo) sheets, and Pt sheets during chemical vapor deposition (CVD). Depending on the substrates, two kinds of graphene growth mechanisms that involve either precipitation or surface adsorption of carbon have been reported. We synthesized graphene, focusing especially on the initial growth stage during CVD, by varying synthesis parameters such as synthesis time, amount of feedstock, and cooling rate after synthesis. We concluded that precipitation-driven synthesis is dominant in the case of Ni substrates whereas adsorption-driven growth is dominant in the Ni/Mo system. In the case of the Pt substrate, which is generally believed to grow by carbon precipitation, graphene growth by adsorption was found to be dominant. We believe that our results will contribute to a clearer understanding of the graphene synthesis mechanism, and development of manufacturing routes for controllable synthesis of high-quality graphenes.

Characteristic spectral patterns in the carbon-13 nuclear magnetic resonance spectra of hexagonal and crenellated graphene fragments.

Nuclear magnetic resonance (NMR) spectroscopy is an important molecular characterisation method that may aid the synthesis and production of graphenes, especially the molecular-scale graphene nanoislands that have gathered significant attention due to their potential electronic and optical applications. Herein, carbon-13 NMR chemical shifts were calculated using density functional theory methods for finite, increasing-size fragments of graphene, hydrogenated graphene (graphane) and fluorinated graphene (fluorographene). Both concentric hexagon-shaped (zigzag boundary) and crenellated (armchair) fragments were investigated to gain information on the effect of different types of flake boundaries. Convergence trends of the (13)C chemical shift with respect to increasing fragment size and the boundary effects were found and rationalised in terms of low-lying electronically excited states. The results predict characteristic behaviour in the (13)C NMR spectra. Particular attention was paid to the features of the signals arising from the central carbon atoms of the fragments, for graphene and crenellated graphene on the one hand and graphane and fluorographene on the other hand, to aid the interpretation of the overall spectral characteristics. In graphene, the central nuclei become more shielded as the system size increases whereas the opposite behaviour is observed for graphane and fluorographene. The (13)C signals from some of the perimeter nuclei of the crenellated fragments obtain smaller and larger chemical shift values than central nuclei for graphene and graphane/fluorographene, respectively. The diameter of the graphenic quantum dots with zigzag boundary correlates well with the predicted carbon-13 chemical shift range, thus enabling estimation of the size of the system by NMR spectroscopy. The results provide data of predictive quality for future NMR analysis of the graphene nanoflake materials.

Nanostructured Palladium-Graphene Materials for Energy Conversion

Carbon nanostructured materials are widely used in different energy applications: fuel cells, supercapacitors, Li-ion batteries etc [1, 2]. Several synthetic approaches can be used for preparation of CNTs, graphene etc, such as: CVD, exfoliation. At the present work we adopted the sacrificial support method (SSM) developed at UNM group [3-12].Several types of 3D structured graphene materials were synthesized by modified SSM. The morphology control was achieved by variation of silica types, graphene oxide to silica ratio etc. After successful synthesis of graphenes the sacrificial support was leatched by means of concentrated HF.Figure 1 represents SEM image of 3D structured graphene synthesized by SSM. Figure 1: SEM image of 3D structured graphene.TEM analysis confirmed the formation of multi-stacks of graphene layers (Fig. 2).The later step involved the deposition on the graphene surface Pd-based materials. Two methods: thermal or chemical reduction of Pd-precursors was used in order to synthesize highly active catalysts for alcohols electrooxidation.It has been observed that Pd-Cu was evenly dispersed on the graphene sheets (Fig.3).Electrochemical performance of Pd-based catalysts in the reaction of alcohols electrooxidation is shown on Figure 4. It was found that addition of second oxophilic metal to the palladium substantially improved it is activity. Peak current generated by Pd-Cu deposited onto the surface of 3D structured graphene was found to be ~1800 A gpd -1. Figure 2: TEM image of 3D structured graphene. Figure 3: TEM image of Pd-Cu/3D structured graphene. Figure 4: Electrooxidation of EtOH in alkaline media by Pd-based catalysts.

Synthesis of graphene films in a flame

The results of studying the synthesis of graphenes in a premixed propane-oxygen-argon flame at atmospheric conditions are reported. The temperature of 900–950°C and exposure time of 5 min are demonstrated to be suitable for the synthesis of graphene films on a nickel substrate, which is preferable to a copper substrate. It is demonstrated that the formation of graphene layers on the substrate occurs vertically along the flame height, with subsequent changeover to a soot structure. It is shown that the minimum number of graphene layers (two or three) is observed at angles of inclination of the substrate relative to the vertical axis of the flame within 0°–30°.

Epitaxial assembly of graphene on face (0001) of silicon carbide: Modeling by semiempirical methods

The epitaxial growth of graphene on silicon face (0001) of silicon carbide is simulated using the semiempirical methods of quantum chemistry. The experimental conditions for the epitaxial growth of graphene on SiC, at which the probability of seams and similar defects appearing is reduced to a minimum, are formulated. Possible ways of the emergence of reconstructions of the singular carbon and silicon SiC faces during the synthesis of graphenes are investigated as a test of the approach’s efficiency. It is noted that simulation reproduces the reconstruction periods experimentally determined for both faces, and yields the most likely atomic arrangements in cases where the experimental formula of the superstructure allows different versions of such arrangements.

Catalytic one-step synthesis of Pt-decorated few-layer graphenes

This study presents the influence of the various reaction parameters (catalyst concentration, reaction temperature, hydrocarbon flow rate, and reaction time) on the one-step growth of few-layer graphenes decorated with metallic platinum (Pt) nanoparticles. The latter were synthesized over a Pt/MgO catalyst using radio-frequency catalytic chemical vapor deposition (CCVD) from methane. A mixture of nanotubes and graphenes in various ratios was produced depending on the synthesis conditions. The nanotubes have a few walls (generally 2 or 3, but the maximum number observed was 7) with diameters in the range of a few to several nanometers (Dmaxext ≈ 7 nm). The graphene structures have a few square-shaped layers with dimensions ranging between 80 and 100 nm, which are decorated with Pt nanoparticles (with 70% having diameters between 4 and 8 nm) both on the flat surfaces as well as on the edges. Our experimental findings demonstrate that it is relatively easy to obtain predominantly graphenes using the Pt/MgO (2 wt% Pt) catalyst system at 1000 °C, with a 100 mL min−1 hydrocarbon flow rate and a reaction time of 30 minutes.

Synthesis of graphenes on Ni foils by chemical vapor deposition of alcohol with IR-lamp heating

We report the synthesis of single-layer graphenes on polycrystalline Ni foils by alcohol-based chemical vapor deposition (CVD) with IR-lamp heating. Heating with an IR lamp allows fast cooling and a reduction in the overall CVD time because of the rapid thermal processes in the heating and cooling stages. Spatially resolved Raman spectroscopy shows that single-layer graphenes are synthesized by CVD of alcohol with IR-lamp heating. The effects of the reaction temperature and alcohol type on the number of layers and graphene quality are investigated.

Toward controlled synthesis of carbon nanotubes and graphenes

A bottom-up synthesis of structurally uniform carbon nanotubes (CNTs) and graphenes is recognized as one of the greatest challenges of primary importance in nanocarbon science. This paper highlights our efforts to address these challenges since 2005. These endeavors have led to (i) modular, size-selective, and scalable synthesis of [n]cycloparapheneylenes (CPPs), the shortest segment of armchair CNTs, (ii) design and synthesis of the shortest segment of chiral CNTs, and (iii) efficient synthesis of carbon nanosheets through catalytic C–H bond arylation of polycyclic aromatic hydrocarbons (PAHs). We consider these works as a possible first step toward a controlled synthesis of structurally uniform CNTs and nanographenes.

Synthesis of few-layer graphene over gold nanoclusters supported on MgO

We present the successful design and synthesis of few-layer graphenes over an Au/MgO catalytic system by chemical vapor deposition with methane as the carbon source. The resulting structures were composed of a few graphitic layers, and the highest synthesis yield was found to be 62% when the methane flow rate was 120mL/min. The dimension of the in-plane crystallites was found to increase with the reaction time. A simple purification step was used to remove the MgO support that resulted in graphene sheets decorated with Au nanoparticles. Such an approach makes it possible to synthesize high purity Au–graphene nanostructured composites by using a single reaction step and without the need for additional functionalization or attachment.

Novel Multicomponent and Biocompatible Nanocomposite Materials Based on Few-Layer Graphenes Synthesized on a Gold/Hydroxyapatite Catalytic System with Applications in Bone Regeneration

We present the synthesis of few-layer graphenes over a novel Au/hydroxyapatite catalytic system by radio-frequency chemical vapor deposition, with acetylene and methane as the carbon sources. The synthesis time was found to influence linearly the dimensions of the graphitic layers and asymptotically their corresponding thermal decomposition temperature. The resulting multicomponent nanocomposite material formed out of graphene layers, Au nanoparticles (AuNPs) supported on the surface of hydroxyapatite nanoparticles, was found to have good biocompatibility and induce excellent bone cellular proliferation. Such multicomponent composites could find numerous applications in the area of bone regeneration given the excellent biocompatibility, 3D structure, and unique composition.

Graphene‐Based Multifunctional Iron Oxide Nanosheets with Tunable Properties

We report the synthesis of graphenes with tunable properties due to the growth of needlelike iron oxide (IO) nanoparticles on their surfaces. The electrical conductivity, flexibility, and magnetic properties of graphene nanosheets (GNSs) could be tuned on demand by fine controlling both the surface coverage and the length of the IO nanoneedles. The degree of coverage of the IO nanoparticles on the surface of the GNSs made it possible to control the resulting properties of the IO/GNSs on demand. As examples of their utility, paperlike materials were generated by simple filtration, and the resulting IO/GNS nanocomposites showed extraordinary removal capacity and fast adsorption rates for As(V) and Cr(VI) ions in water. Another possible application is the preparation of multifunctional films equipped with conductivity, flexibility, and magnetic properties. The fabrication process is easy to scale up at a low cost. In addition, both the colloidal solution and film forms of the resulting IO/GNSs were effective for removal of heavy metal ions, meaning this material could be utilized for actual industrial applications.

A simple alcohol-chemical vapor deposition synthesis of single-layer graphenes using flash cooling

We report the synthesis of single-layer graphenes from ethanol using, what we call, “flash cooling” just after chemical vapor deposition. The single-layer graphenes synthesized are high-quality and several micrometers in grain size as revealed by Raman spectroscopy. Detailed comparison of the cooling processes suggests that the single-layer graphene growth does not occur during the carbon precipitation but rather stems from surface diffusions of carbon on a nickel substrate. Because of the present simple and easiness for the large-scale synthesis under an inert gas atmosphere and at atmospheric pressure, the present method can easily be applied for the future large-scale and low-cost graphene production.

Graphene: The New Two‐Dimensional Nanomaterial

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.