Synthesis and characterization of electrochemically-reduced graphene

Graphene has superior electrical conductivity than graphite and other allotropes of carbon because of its high surface area and chemical tolerance. Electrochemically processed graphene sheets were obtained through the reduction of graphene oxide from hydrazine hydrate. The prepared samples were heated to different temperatures such as 673 and 873 K. X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM), Raman spectra and conductivity measurements were made for as-prepared and heat-treated graphene samples. XRD pattern of graphene shows a sharp and intensive peak centred at a diffraction angle (2θ) of 26·350. FTIR spectra of as-prepared and heated graphene were used to confirm the oxidation of graphite. TEM results indicated that the defect density and number of layers of graphene sheets were varied with heating temperature. The hexagonal sheet morphology and purity of as-prepared and heat treated samples were confirmed by SEM–EDX and Raman spectroscopy. The conductivity measurements revealed that the conductivity of graphene was decreased with an increase in heating temperature. The present study explains that graphene with enhanced functional properties can be achieved from the as-prepared sample.     

Synthesis of mono layer graphene oxide from sonicated graphite flakes and their Hall effect measurements

Graphene, a single atom thick sheet is considered a key candidate for the future nanotechnology, due to its unique extraordinary properties. Researchers are trying to synthesize bulk graphene via chemical route from graphene oxide precursor. In the present work, we investigated a safe and efficient way of monolayer graphene oxide synthesis. To get a high degree of oxidation, we sonicated the graphite flakes before oxidation. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results confirmed graphene oxide formation and high degree of oxidation. Raman spectroscopy and atomic force microscopy (AFM) results revealed a monolayer of graphene oxide (GO) flakes. The sheet like morphology of the GO flakes was further confirmed by scanning electron microscopy (SEM). The Hall effect measurements were performed on the GO film on a silica substrate to investigate its electrical properties. The results obtained, revealed that the GO film is perfectly insulating, having electrical resistivity up to 8.4 × 10⁸ (Ω·cm) at room temperature.     

Synthesis and characterization of stable aqueous dispersions of graphene

A stable aqueous dispersion (5 mg ml^?1) of graphene was synthesized by a simple protocol based on three-step reduction of graphene oxide (GO) dispersion synthesized using the modified version of Hummers and Offeman method. Reduction of GO was carried out using sodium borohydride, hydrazine hydrate and dimethyl hydrazine as reducing agents. The chemically synthesized graphene was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible absorption spectroscopy, Fourier transform infrared (FTIR) and Raman spectroscopy, thermogravimetric analysis (TGA), optical microscopy. The stability of aqueous dispersions of graphene was confirmed through zeta potential measurements and the negative zeta potentials of 55–60 mV were obtained indicating the high stability of aqueous graphene dispersions.     

氧化石墨烯表面稀土改性机理

石墨烯独特的物理、化学和力学性能为复合材料的开发奠定了重要基础,是各种复合材料的理想增强体,但石墨烯分散性和湿润性差的问题严重限制了其在复合材料中的进一步应用。采用浸润法和加热改性剂法制备了稀土改性氧化石墨烯(RE-M-GO),利用X射线衍射(XRD)和扫描电子显微镜(SEM),能谱仪(EDS)对RE-M-GO的形貌和相结构进行表征;并结合傅里叶变换红外(FTIR)和紫外光谱仪器(UV),分析改性氧化石墨烯的官能团结构的变化,探讨其改性机理。结果表明:稀土改性的氧化石墨烯的分散性有明显的改善,主要是由于稀土元素与氧化石墨烯的含氧官能团进行反应形成配位键,生成了新的官能团,降低了氧化石墨烯的界面能及表面能,从而改善了氧化石墨烯的分散性。     

Rapid and effective functionalization of graphene oxide by ionic liquid

Functionalized graphene oxide (DDIB-GO) sheets, which can be homogeneously distributed into ortho-dichlorobenene, were obtained via rapid and effective covalent functionalization with imidazolium ionic liquids (1,3-didodecylimidazolium bromine) through ion exchange. The resulting DDIB-GO sheets were characterized by Fourier transform infrared spectroscopy (FTIR), UV Vis NIR spectroscopy, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), Atomic force microscopy (AFM). Furthermore, FTIR, XPS and TGA show that the 1,3-didodecylimidazolium have been covalently attached to the GO sheets. UV Vis NIR, TEM, and AFM demonstrate that after functionalization, the size and shape of DDIB-GO sheets had little change compared with GO sheets and it was mostly dispersed in single layer. And good electronic conductivity of the film prepared from DDIB-GO in ODCB was obtained after high temperature annealing.     

Facile route to preparation of positively charged GO using poly (diallyldimethylammoniumchloride)

Abstract

In the present study, positively charged graphene oxide (GO) was prepared by a simple method under mild reaction conditions. The samples were characterized via Zeta potential, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and Scanning electron microscope. The results showed that GO was successfully modified by Poly (diallyldimethylammoniumchloride) (PDDA). The obtained sample (PDDA-GO) still had a lamellar structure; however, it clearly presented wavy wrinkles appearance in the surface microscopy morphology. When the ratio of GO to PDDA was 1:13, the fabricated PDDA-GO sheets possessed a high positive charge value and a good dispersion in water. Also, to study the interaction between PDDA and GO in PDDA-GO, GTA modified GO was selected as a comparative experiment. The Fourier transform infrared spectroscopy, UV/vis spectroscopy, and Fluorescence spectroscopy results indicate that the π-π interactions played a leading role in the process of PDDA modified GO sheets. While the electrostatic interactions played an inferior role in the same process.     

Study on preparation and performance of Ru-Fe/GO catalyst for sodium borohydride alcoholysis to produce hydrogen

Abstract

Ru-Fe bimetallic alloy nanoparticle catalyst (Ru-Fe/GO) was prepared by chemical reduction method on graphene oxide prepared using Hummers modified method. The structure and morphology of both GO and Ru-Fe/GO were analyzed using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS).The effect of catalyst components on hydrogen generation rate for NaBH₄ methanolysis was investigated. When Ru:Fe is 6:1, the catalytic activity is the highest, and the average rate is about 473?mL·min^?1·g^?1. The effect of temperature, Sodium hydroxide concentration, and sodium borohydride concentration on reaction rate is also discussed, and the activation energy for the methanolysis of sodium borohydride is 59.33?kJ·mol^?1 based on the data.     

Facile fabrication of functionalized graphene sheets (FGS)/ZnO nanocomposites with photocatalytic property

Functionalized graphene sheets (FGS)/ZnO nanocomposites were fabricated via thermal treatment method, using graphene oxide as a precursor of graphene, Zn(NH(3))(4)CO(3) as a precursor of zinc oxide, and poly(vinyl pyrrolidone) as an intermediate to combine zinc with carbon materials. Thermogravimetric analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize crystal structure and morphology of FGS/ZnO nanocomposites. It was shown that the well-dispersed ZnO nanoparticles were deposited on FGS homogeneously. The composites exhibited photocatalytic activity to decompose rhodamine 6G efficiently under low-power ultraviolet (UV) light. This facile and low-cost method makes the composite a perfect candidate in applications of catalysis and other areas.     

Thermally assisted semiconductor-like to insulator transition in gold-poly(methyl methacrylate) nanocomposites

Gold-polymethylmethacrylate (PMMA) nanocomposites were fabricated by mixing gold nanoparticles capped with oleylamine in polymethylmethacrylate. The samples were analysed using UV-vis absorption spectroscopy, transmission electron microscopy, small angle x-ray scattering, Fourier transform infrared spectrometry (FTIR) and x-ray photoelectron spectroscopy (XPS). Electrical resistivity of nanocomposite samples was measured by a four-probe technique in the 70-300?K range. The nanocomposites showed a transition with an onset at ～160-165?K. They exhibited a semiconductor-like conductivity at higher temperatures and nearly temperature independent conductivity at lower temperatures. The interfacial interaction of Au nanoparticles and PMMA polymer is investigated using FTIR and XPS. A ligand-exchange process occurs when capped gold nanoparticles are incorporated in PMMA polymer.     

Continuous microwave assisted flow synthesis and characterization of calcium deficient hydroxyapatite nanorods

Synthetic calcium deficient hydroxyapatite (CDHA) nanorods (<100?nm) were rapidly prepared with the help of a new continuous microwave assisted flow synthesis (CMFS) reactor in 5?min only from aqueous solution of calcium hydroxide and orthophosphoric acid at pH 8.5. The effect of various reaction parameters like, pH, concentration, temperature, residence time, degree of crystallinity and particle surface area were studied in detail. The phase purity, particle size and morphology of the powder samples were characterised by techniques such as X-ray diffraction analysis, transmission electron microscopy, scanning electron microscopy and FTIR and Raman spectroscopy. With the help of X-ray photoelectron spectroscopy, the chemical analysis was completed. Measurements were taken into account to estimate the particle size following the dynamic light scattering. The results showed that the employed synthesis procedure offered an efficient and economical route to achieve high quality nano-sized products with suitable size and low level of impurities.     

Differential antibacterial response exhibited by graphene nanosheets toward gram‐positive bacterium Staphylococcus aureus

Two different morphological forms of graphene nanosheets: improved reduced graphene oxide (IRGO) and modified reduced GO (rGO) (MRGO) have been synthesised by improved and modified methods, respectively. Physical characterisations of these graphene nanosheets were carried out using X‐ray diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. Colloidal stability of these nanosheets toward a selected bacterium (e.g. Staphylococcus aureus) was ascertained by zeta potential. In the present study, the authors for the first time made an attempt to study and compare the potentialities of these two different forms of graphene nanosheets as efficient bactericidal agents. Field‐emission scanning electron microscopy and TEM with energy dispersive X‐ray spectroscopy (EDAX) studies of IRGO and MRGO have been carried out to explore their underlying mechanism of antibacterial responses through physical as well as chemical interactions with the selected bacterial species.Inspec keywords: scanning electron microscopy, X‐ray diffraction, graphene, Raman spectra, field emission electron microscopy, microorganisms, colloids, X‐ray chemical analysis, antibacterial activity, electrokinetic effects, nanofabrication, Fourier transform infrared spectra, nanobiotechnologyOther keywords: graphene nanosheets, differential antibacterial response, gram‐positive bacterium, reduced graphene oxide, Staphylococcus aureus, X‐ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, colloidal stability, field‐emission scanning electron microscopy, TEM, EDAX, C     

Graphene-SnO(2) composites for highly efficient photocatalytic degradation of methylene blue under sunlight

Graphene sheets decorated with SnO(2) nanoparticles (RGO-SnO(2)) were prepared via a redox reaction between graphene oxide (GO) and SnCl(2). Graphene oxide (GO) was reduced to graphene (RGO) and Sn(2+) was oxidized to SnO(2) during the redox reaction, leading to a homogeneous distribution of SnO(2) nanoparticles on RGO sheets. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show uniform distribution of the nanoparticles on the RGO surface and high-resolution transmission electron microscopy (HRTEM) shows an average particle size of 3-5?nm. The RGO-SnO(2) composite showed an enhanced photocatalytic degradation activity for the organic dye methylene blue under sunlight compared to bare SnO(2) nanoparticles. This result leads us to believe that the RGO-SnO(2) composite could be used in catalytic photodegradation of other organic dyes.     

The effect of Ag loading on supercapacitor performance of graphene based nanocomposites

In the present study, we prepared reduced graphene oxide (rGO) decorated with Ag nanoparticles by a one pot, simultaneous reduction method. The effect of AgNO₃ amount on the chemical, morphological and electrochemical properties of binary rGO-Ag nanocomposite for supercapacitor application was investigated. The chemical and morphological characterization of prepared rGO-Ag nanocomposites was realized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). For supercapacitor application, electrochemical performance of the nanocomposites was investigated with cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. As a result of their excellent conductivity and spacer role which prevent aggregation of rGO nanosheets and maintain the electroactive surface area, Ag nanoparticles significantly enhance the electrochemical performance of the nanocomposite. The rGO-Ag nanoparticle nanocomposite exhibited a maximum specific capacitance of 34.2?mF?cm^?2 at 0.6?A?cm^?2 current density. The nanocomposite electrode also has excellent rate capability and cycle life. The capacitance retention of rGO-Ag electrode is 98% after 1000 charge-discharge cycle. The results showed that rGO-Ag nanocomposite is a building block for ternary or other multicomponent nanocomposites.     

MEMS超级电容器膜电极材料的表面改性

为了改善MEMS超级电容器膜电极的致密性,通过在聚吡咯(PPy)中引入苯磺酸钠(BSNa)和氧化石墨烯(GO)表面改性功能薄膜,实现聚吡咯薄膜在MEMS超级电容器三维微结构上的均匀沉积.借助扫描电镜(SEM)、循环伏安测试(CV)、交流阻抗谱测试(EIS)、恒流充放电测试(CP)等手段对表面改性后的样品进行电化学性能测试.结果表明:当吡咯单体(Py)与BSNa摩尔比为1∶2,GO含量为0.4%时,在-0.4~1.0 V电压范围内,以100 m V/s速率扫描56圈,PPy薄膜的致密性最佳;表面改性可以在很大程度上减轻PPy颗粒的团聚,使得聚合后的PPy分子链排布紧密,形成了规整的网状立体结构;在放电电流为2 m A时,比容量可以达到13.3 m F/cm2,MEMS超级电容器的电化学性能得到改善.     

Triethylenetetramine/hydroxyethyl cellulose-functionalized graphene oxide monoliths for the removal of copper and arsenate ions

Nitrogen-doped graphene oxide monoliths (GOMs) were readily constructed by crosslinking graphene oxide (GO) using triethylenetetramine (TETA) and hydroxyethyl cellulose (HEC). The addition of HEC was beneficial to the formation of a network structure compared to that in the absence of HEC. The generated monoliths have shown various morphologies with different d spacing, layer thickness, and micropore size. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses provided evidences for the formation of covalent C–N bonds and some nitrogen-containing heterocyclic composition inside the graphene oxide sheet, indicating that the interaction of GO with the amine crosslinker involved the crosslinking reaction between GO epoxides and amine groups. HEC was also involved in the N-doping reaction via the partial reduction of oxygen in HEC molecules. Analysis of X-ray diffraction (XRD) results indicated that the lattice distance between GO sheets increased after TETA/HEC crosslinking. Thermogravimetric analysis (TGA) confirmed the successful incorporation of crosslinker moieties on the surface of GO sheets. The fabricated GOMs could be used to efficiently adsorb metal ions and arsenate by the introduced polar functional groups on GO sheets and porous structures based on hydrogen bonds, whose morphologies and compositions were confirmed via XRD, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).     

Preparation of covalently functionalized graphene using residual oxygen-containing functional groups

When fabricated by thermal exfoliation, graphene can be covalently functionalized more easily by applying a direct ring-opening reaction between the residual epoxide functional groups on the graphene and the amine-bearing molecules. Investigation by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) all confirm that these molecules were covalently grafted to the surface of graphene. The resulting dispersion in an organic solvent demonstrated a long-term homogeneous stability of the products. Furthermore, comparison with traditional free radical functionalization shows the extent of the defects characterized by TEM and Raman spectroscopy and reveals that direct functionalization enables graphene to be covalently functionalized on the surface without causing any further damage to the surface structure. Thermogravmetric analysis (TGA) shows that the nondestroyed graphene structure provides greater thermal stability not only for the grafted molecules but also, more importantly, for the graphene itself, compared to the free-radical grafting method.     

A facile approach to the synthesis of graphene nanosheets under ultra-low exfoliation temperature

High specific surface area graphene nanosheets have been obtained from graphite oxide by using an effective modified exfoliation method under vacuum, the exfoliation temperature (135 degrees C) is much lower than that conventionally applied (1050 degrees C) to obtain monolayer graphene sheets via rapid thermal shock. These products have fluffy and highly porous structure and with a lateral size typically of a few micrometers. Transmission electron microscopy (TEM) observation shows that it looks like a wrinkled transparent ultrathin film consisting of single or few-layer graphene sheets, and their Brunauer-Emmett-Teller surface area is as large as 750 m2/g. Simultaneously, X-ray photoelectron spectroscopy analysis revealed that considerable amount of oxygen-containing groups (C/O ratio, 5:1) retained on the graphene sheets after exfoliation process, which would provide convenience for further modification of the surface properties and chemistry of graphene sheets. This work offers a facile and scalable approach to fabricate graphene oxide and opens up a new vista of various potential applications electronics and composite materials.     

Ni2CoS4/还原氧化石墨烯/多孔还原氧化石墨烯的制备及其在超级电容器中的应用

采用水热法制备Ni_2CoS_4活性材料,通过物理过程和水热反应将其与氧化石墨烯(GO)、水热多孔氧化石墨烯(HHGO)复合得到Ni_2CoS_4/还原氧化石墨烯/多孔还原氧化石墨烯(Ni_2CoS_4/RGO/HRGO)复合电极材料。采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、循环伏安测试、恒流充放电测试和交流阻抗测试等,对复合材料的形貌结构、电化学性能进行了表征。研究结果表明:在1 A/g的电流密度下,其比电容为1 684 F/g,在5 A/g的电流密度下循环2 000次后,其比电容保持率为91.8%。Ni_2CoS_4/RGO/HRGO优良的电化学行为归因于这种复合结构使电解液对电极材料的润湿程度提高,进而提高了离子和电荷的传输速率,同时也缓解石墨烯、Ni_2CoS_4的团聚和循环过程中的体积变化。因此,Ni_2CoS_4/RGO/HRGO是一种有良好应用前景的高性能超级电容器电极材料。     

Excellent photocatalytic performance under visible-light irradiation of ZnS/rGO nanocomposites synthesized by a green method

ZnS/graphene nanocomposites with different graphene concentrations (5, 10 and 15 wt.%) were synthesized using L-cysteine as surfactant and graphene oxide (GO) powders as graphene source. Excellent performance for nanocomposites to remove methylene blue (MB) dye and hexavalent chromium (Cr(VI)) under visible-light illumination was revealed. TEM images showed that ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in the ZnS diameter size. XRD patterns, XPS and FTIR spectroscopy results indicated that GO sheets changed into reduced graphene oxide (rGO) during the synthesis process. Photocurrent measurements under a visiblelight source indicated a good chemical reaction between ZnS NPs and rGO sheets.     

Wafer scale homogeneous bilayer graphene films by chemical vapor deposition

The discovery of electric field induced band gap opening in bilayer graphene opens a new door for making semiconducting graphene without aggressive size scaling or using expensive substrates. However, bilayer graphene samples have been limited to μm(2) size scale thus far, and synthesis of wafer scale bilayer graphene poses a tremendous challenge. Here we report homogeneous bilayer graphene films over at least a 2 in. × 2 in. area, synthesized by chemical vapor deposition on copper foil and subsequently transferred to arbitrary substrates. The bilayer nature of graphene film is verified by Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Importantly, spatially resolved Raman spectroscopy confirms a bilayer coverage of over 99%. The homogeneity of the film is further supported by electrical transport measurements on dual-gate bilayer graphene transistors, in which a band gap opening is observed in 98% of the devices.