Preparation of functionalized graphene sheets by a low-temperature thermal exfoliation approach and their electrochemical supercapacitive behaviors

Two kinds of functionalized graphene sheets were produced by thermal exfoliation of graphite oxide. The first kind of functionalized graphene sheets was obtained by thermal exfoliation of graphite oxide at low temperature in air. The second kind was prepared by carbonization of the first kind of functionalized graphene sheets at higher temperature in N₂. Scanning electron microscopy images show that both two kinds of samples possess nanoporous structures. The results of N₂ adsorption-desorption analysis indicate that both of two kinds of samples have high BET surface areas. Moreover, the second kind of functionalized graphene sheets has a relatively higher BET surface area. The results of electrochemical tests is as follows: the specific capacitance values of the first kind of functionalized graphene sheets in aqueous KOH electrolyte are about 230 F g⁻¹; the specific capacitance values of the second kind of functionalized graphene sheets with higher BET surface areas are only about 100 F g⁻¹; however, compared with the first kind of functionalized graphene sheets, the second kind has a higher capacitance retention at large current density because of its good conductive behaviors; furthermore, in non-aqueous EC/DEC electrolyte, the specific capacitance values of the first kind sample and the second kind sample are about 73 F g⁻¹ and 36 F g⁻¹, respectively.     

Preparation of scrolled graphene oxides with multi-walled carbon nanotube templates

A simple and efficient wet-chemical strategy was developed to form graphene oxide scrolls around multi-walled carbon nanotube templates through covalent bond formation. Scanning electron microscopy, atomic force microscopy, transmission electron microscopy and dynamic light scattering measurements confirmed the scrolled conformation of graphene oxide sheets while Fourier transform infrared spectroscopy and X-ray photoelectron data indicated the formation of covalent bonds between the scrolled sheets and the nanotubes. Conformational changes of the graphene oxide sheets were also monitored by Raman spectroscopy. All the data suggested successful formation of graphene oxide scrolls with multi-walled carbon nanotube templates.     

Efficient synthesis of graphene sheets using pyrrole as a reducing agent

The efficient synthesis of graphene sheets using pyrrole as a reducing agent was explored. The obtained graphene sheets were dispersible in organic solvents such as ethanol, isopropanol, N,N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, tetrahydrofuran, and acetone. During this reduction reaction, pyrrole was oxidized, forming oxidation product of pyrrole and adsorbed on the graphene sheets surface by π–π interaction. The oxidation product of pyrrole acted as a capping agent for graphene sheets by preventing re-stacking and formed organically dispersible graphene. The formation of graphene and its crystalline nature was indicated by the transmission electron microscopy and the atomic force microscopy analysis. Raman, X-ray photoelectron spectroscopy and X-ray diffraction provided the evidence for graphene formation from graphene oxide precursor. Furthermore, the reduced oxygen content and N 1s peak observed by the X-ray photoelectron spectroscopy analysis of graphene sheets confirmed the reduction reaction and presence of adsorbed oxidation product on the surface of graphene sheets. The resulting graphene sheets were readily dispersible in solvents and easily to process.     

A general strategy for the synthesis of reduced graphene oxide-based composites

Well-exfoliated graphene oxide sheets were initially fabricated through a modified pressurized oxidation method with powdered flake graphite as raw material. A variety of inorganic-reduced graphene oxide composites have been then successfully synthesized through a general solvothermal strategy with the graphene oxide sheets as supports, ethanol as solvent, and metal salts as precursors. After the solvothermal reactions, Ni(OH)₂ nanoparticles, Fe₂O₃ nanorods, W₁₈O₄₉ nanowires, ZnO nanoparticles, and Ag nanoparticles were in situ grown on the surfaces of the graphene oxide sheets, accompanied by effective reduction of graphene oxide to reduced graphene oxide. The as-prepared products have been systematically characterized by electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, and Raman spectroscopy. The present work opens up a versatile route for preparing the reduced graphene oxide-based composites.     

Graphene-supported carbonaceous dielectric sheets and their electrorheology

Two-dimensional dielectric sheets composed of graphene-supported amorphous carbon were prepared by annealing polyaniline-coated graphene oxide sheets in vacuum. The morphology and structure were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy. This showed that annealing the polyaniline-coated graphene oxide had little influence on its plate-like morphology but transformed the graphene oxide core into conducting graphene and the polyaniline shell into insulating nitrogen-enriched amorphous carbon. An electrorheological suspension was prepared by dispersing the graphene-supported carbonaceous sheets in silicone oil and its electrorheological property was investigated by rhelogical tests under electric fields. The suspension demonstrated a strong electrorheological effect. Its yield stress and shear stress were about three times as large as those of a suspension of pure carbonaceous particles at equal electric field strengths. The storage modulus of the suspension was also higher than that of a suspension of pure carbonaceous particles, indicating stronger electrorheological activity. Dielectric measurements indicated that the presence of the graphene core had increased the polarization property, and this is responsible for the increased electrorheological activity.     

石墨烯负载二氧化钛复合材料及光催化降解甲基橙

以天然鳞片石墨为原料,用改进的Hummers法氧化制备氧化石墨烯,然后用葡萄糖还原制得石墨稀,再用溶胶一凝胶法复合制备了TiO2／2;墨烯的复合材料。用FI-IR、Raman、AFM、SEMvR）3LTGA对石墨烯和TiO2／2;墨烯复合材料进行了表征,并在紫外光照射条件下对比石墨烯、TiO2、TiO：／2;墨烯复合材料对甲基橙的降解效果。结果表明,在紫外光照射下,TiO2的负载率为35％时,TiO2／2;墨烯复合材料光催化降解甲基橙的催化效率明显大于单纯TiO2及石墨烯,光催化4小时后,脱色率达到85％。TiO2／2;墨烯复合材料不失为一种有潜力的光催化降解染料废水催化材料。     

高电活性石墨烯/聚苯胺纳米复合材料的制备和表征

采用了一种简单有效地方法制备了高电活性的石墨烯/聚苯胺复合材料。首先,将苯胺在氧化石墨烯（GO）的水性分散液中氧化聚合,制备了氧化石墨烯/聚苯胺（GO/PANI）,再将GO/PANI与水合肼反应,制得还原-氧化石墨烯/聚苯胺（R（GO/PANI））。利用透射电子显微镜（TEM）,热失重分析（TGA）和循环伏安法（CV）对GO/PANI和R（GO/PANI的形貌,热稳定性和电化学性能进行了分析研究。结果表明,GO表面存PANI,且R（GO/PANI）的热稳定性和电活性都明显高于GO/PANI。     

Electrochemically exfoliated graphene oxide/iron oxide composite foams for lithium storage,produced by simultaneous graphene reduction and Fe(OH)3 condensation

We describe the production of graphene-based composites for energy storage, obtained by a combination of electrochemical and solution processing techniques. Electrochemically exfoliated graphene oxide sheets (EGO) are produced using an original setup that allows fast expansion of graphite flakes and efficient exfoliation of expanded graphite via an electrochemical route. The sheets are deposited on a sacrificial nickel foam together with an iron hydroxide colloidal precursor. Calcination treatment simultaneously renders the EGO foam conductive and transforms Fe(OH)₃ into hematite (α-Fe₂O₃), yielding a nanoporous Fe₂O₃ layer on the surface of the mesoporous EGO foam, creating an ideal structure for lithium storage. The obtained graphene/metal oxide hybrid is a continuous, electrically conductive three-dimensional (3D) composite featuring a hierarchical meso–nano porous structure. A systematic study of these composites, varying the Fe₂O₃:EGO ratio, is then performed to maximize their performance as nanostructured electrodes in standard coin cell batteries.     

Synthesis of graphene-like nanosheets and their hydrogen adsorption capacity

Graphene-like nanosheets have been synthesized by the reduction of a colloidal suspension of exfoliated graphite oxide. The morphology and structure of the graphene powder sample was studied using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The graphene sheets are found to be in a highly agglomerated state, with many wrinkles. The sample has a BET surface area of 640 m²/g as measured by nitrogen adsorption at 77 K. Hydrogen adsorption-desorption isotherms were measured in the temperature range 77-298 K and at pressures of up to 10 bar. This gives hydrogen adsorption capacities of about 1.2 wt.% and 0.1 wt.% at 77 K and 298 K, respectively. The isosteric heat of adsorption is in the range of 5.9-4 kJ/mol, indicating a favourable interaction between hydrogen and surface of the graphene sheets. The estimated room temperature H₂ uptake capacity of 0.72 wt.% at 100 bar and the isosteric heat of adsorption of our sample are comparable to those of high surface area activated carbons, however significantly better than the recently reported values for graphene and a range of other carbon and nanoporous materials; single and multi walled carbon nanotubes, nanofibers, graphites and zeolites.     

In Situ Synthesis of Reduced Graphene Oxide and Gold Nanocomposites for Nanoelectronics and Biosensing

In this study, an in situ chemical synthesis approach has been developed to prepare graphene–Au nanocomposites from chemically reduced graphene oxide (rGO) in aqueous media. UV–Vis absorption, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy were used to demonstrate the successful attachment of Au nanoparticles to graphene sheets. Configured as field-effect transistors (FETs), the as-synthesized single-layered rGO-Au nanocomposites exhibit higher hole mobility and conductance when compared to the rGO sheets, promising its applications in nanoelectronics. Furthermore, we demonstrate that the rGO-Au FETs are able to label-freely detect DNA hybridization with high sensitivity, indicating its potentials in nanoelectronic biosensing.     

Photovoltaic and UV detector applications of ZnS/rGO nanocomposites synthesized by a green method

The effect of graphene concentration on the photovoltaic and UV detector applications of ZnS/graphene nanocomposites was investigated. The nanocomposites were synthesized by a green, cost-effective, and simple co-precipitation method with different graphene concentrations (5, 10, and 15 wt%) using L-cysteine amino acid as a surfactant and graphene oxide (GO) powder as a graphene source. Transmission electron microscopy (TEM) images showed that the ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in ZnS diameter size. The results of X-ray diffraction (XRD) patterns, Raman, and Fourier transform infrared (FTIR) spectroscopy indicated that the GO sheets were changed into reduced graphene oxide (rGO) during synthesis process. Therefore, L-cysteine amino acid played its role as a reducing agent to reduce the GO. Photovoltaic measurements showed that the graphene caused to increase the efficiency of solar-cell application of ZnS/rGO nanocomposites. In addition, our observation showed that the nanocomposites were suitable as ultraviolet (UV) detectors and graphene concentration increased the responsibility of the detectors.     

Exfoliated graphene sheets decorated with metal/metal oxide nanoparticles: Simple preparation from cation exchanged graphite oxide

We produced carbon hybrid materials of graphene sheets decorated with metal or metal oxide nanoparticles of gold, silver, copper, cobalt, or nickel from cation exchanged graphite oxide. Measurements using powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectra revealed that the Au and Ag in the materials (Au–Gr and Ag–Gr) existed on graphene sheets as metal nanoparticles, whereas Cu and Co in the materials (Cu–Gr and Co–Gr) existed as a metal oxide. Most Ni particles in Ni–Gr were metal, but the surfaces of large particles were partly oxidized, producing a core–shell structure. The Ag–Gr sample showed a catalytic activity for the oxygen reduction reaction in 1.0 M KOH aq. under an oxygen atmosphere. Ag–Gr is superior as a cathode in alkaline fuel cells, which should not be disturbed by the methanol cross-over problem from the anode. We established an effective approach to prepare a series of graphene-nanoparticle composite materials using heat treatment.     

Graphene-enhanced visible-light photocatalysis of large-sized CdS particles for wastewater treatment

The hybrid composites of graphene decorated by large-sized CdS particles (G/M-CdS) were prepared by a one-pot solvothermal route in which the reduction of graphite oxide into graphene was accompanied by the generation of microsized CdS particles. The structure and composition of the obtained nanocomposites were studied by means of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The CdS particles with the average sizes of approximately 640 nm were formed on graphene sheets. The as-prepared composite was used as adsorbent to remove dye from wastewater using the organic dye Rhodamine B as the adsorbate. The G/M-CdS composite reveals a high photodegradation rate under visible light irradiation. Our results demonstrate that the G/M-CdS is very promising for removing organic dyes from wastewater.     

Physical wrapping of reduced graphene oxide sheets by polyethylene wax and its modification on the mechanical properties of polyethylene

A facile method to encapsulate the reduced graphene oxide (RGO) sheets physically with polyethylene (PE) wax was developed. The graphene oxide sheets were first wrapped with polyethylene wax, and reduced by hydrazine hydrate. The structure of the wrapped RGO was confirmed by means of Fourier transform infrared spectroscopy, X‐ray diffraction (XRD), and Raman spectroscopy. The PE wax‐wrapped RGO sheets were melt blended with PE to prepare PE/RGO nanocomposites. Transmission electron microscopy and XRD studies showed that this method could provide uniform dispersion of RGO sheets in the PE matrix. Scanning electron microscopy and Raman spectroscopy indicated that there was a strong interfacial interaction between the PE wax‐wrapped RGO sheets and PE matrix. Addition of 1 wt % RGO sheets in PE matrix led to a 48% increment in the yield stress and 118% increment in the Young's modulus, respectively. However, the elongation at break decreased with increasing RGO sheets loading content. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

One-pot synthesis of CdS sensitized TiO2 decorated reduced graphene oxide nanosheets for the hydrolysis of ammonia-borane and the effective removal of organic pollutant from water

A hybrid material of reduced graphene oxide (RGO) sheets decorated with CdS-TiO₂ NPs was prepared through a facile one-pot hydrothermal method. The assembly of CdS-TiO₂ nanoparticles (NPs) on RGO sheets was in-situ produced. As-synthesized nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy disperse X-ray spectrum (EDS), fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The obtained nanocomposites exhibited a good photocatalytic activity for the visible-light-induced decomposition of methylene blue (MB) dye and hydrolysis of ammonia borane. The results showed that by incorporation of CdS and TiO₂ NPs on graphene oxide sheets the photocatalytic efficiency was enhanced. The significant enhancement in the photocatalytic activity of CdS-TiO₂/RGO nanocomposites under visible light irradiation can be ascribed to the effect of CdS by acting as electron traps in TiO₂ band gap. Reduced graphene oxide worked as the adsorbent, electron acceptor and a photo-sensitizer to efficiently enhance the dye photo decomposition. Such nanocomposite photocatalyst might find potential application in a wide range of fields, including hydrogen energy generation, air purification, and wastewater treatment.     

Chemical Functionalization of Graphene Oxide by Poly(styrene sulfonate) Using Atom Transfer Radical and Free Radical Polymerization: A Comparative Study

Poly(sodium styrenesulfonate)-functionalized graphene was prepared from graphene oxide, using atom transfer radical polymerization and free radical polymerization. In atom transfer radical polymerization route, the amine-functionalized GO was synthesized through hydroxyl group reaction of GO with 3-amino propyltriethoxysilane. Atom transfer radical polymerization initiator was grafted onto modified GO (GO-NH₂) by reaction of 2-bromo-2-methylpropionyl bromide with amine groups, then styrene sulfonate monomers were polymerized on the surface of GO sheets by in situ atom transfer radical polymerization. In free radical polymerization route, the poly(sodium 4-styrenesulfonate) chains were grafted on GO sheets in presence of Azobis-Isobutyronitrile as an initiator and styrene sulfonate monomer in water medium. The resulting modified GO was characterized using range of techniques. Thermal gravimetric analysis, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy results indicated the successful graft of polymer chains on GO sheets. Thermogravimetric analysis showed that the amount of grafted polymer was 22.5 and 31?wt% in the free radical polymerization and atom transfer radical polymerization methods, respectively. The thickness of polymer grafted on GO sheets was 2.1?nm (free radical polymerization method) and 6?nm (atom transfer radical polymerization method) that was measured by atomic force microscopy analysis. X-ray diffractometer and transmission electron microscopy indicated that after grafting of poly(sodium 4-styrenesulfonate), the modified GO sheets still retained isolated and exfoliated, and also the dispersibility was enhanced.     

镍负载二氧化钛/PEI/石墨烯纳米复合催化剂的制备与研究

首先采用改进的Hummers法制备了氧化石墨烯(GO),再以聚乙烯亚胺(PEI)修饰的氧化石墨烯为载体,并以硫酸钛和氯化镍为前驱体,利用水热法在180 ℃下以PEI为交联剂制得镍负载的TiO2/PEI/石墨烯纳米复合催化剂。通过紫外可见分光光度计(UV-vis)、傅里叶变换红外光谱(FTIR)、扫描电镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)等测试手段对催化剂进行了表征。结果表明,Ni-TiO2/PEI/RGO纳米复合催化剂中镍负载TiO2纳米粒子与石墨烯能够均匀复合,并具有较小的晶粒尺寸。以对硝基苯酚(4-NP)为降解目标物,考察了该催化剂在NaBH4存在下还原4-NP的催化活性。结果表明,镍负载的TiO2/PEI/石墨烯纳米复合催化剂具有良好的重复催化活性,其降解率为98%,催化剂重复使用10次后,降解率仍能保持90%以上。     

Cytotoxicity and variant cellular internalization behavior of water-soluble sulfonated nanographene sheets in liver cancer cells

Highly exfoliated sulfonated graphene sheets (SGSs), an alternative to graphene oxide and graphene derivatives, were synthesized, characterized, and applied to liver cancer cells in vitro. Cytotoxicity profiles were obtained using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, WST-1[2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, and lactate dehydrogenase release colorimetric assays. These particles were found to be non-toxic across the concentration range of 0.1 to 10 μg/ml. Internalization of SGSs was also studied by means of optical and electron microscopy. Although not conclusive, high-resolution transmission and scanning electron microscopy revealed variant internalization behaviors where some of the SGS became folded and compartmentalized into tight bundles within cellular organelles. The ability for liver cancer cells to internalize, fold, and compartmentalize graphene structures is a phenomenon not previously documented for graphene cell biology and should be further investigated.     

Synergetic Effects of Graphene Oxide and Clay on the Microstructure and Properties of HIPS/Graphene Oxide/Clay Nanocomposites

In this paper, double-network structure nanocomposite with improved mechanical and thermal properties were prepared using high-impact polystyrene as a matrix phase, clay and graphene oxide as effective reinforcing fillers through a facile solution intercalation method. The structure and morphology of nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction analysis, and the synergetic effects of clay and graphene oxide on the final properties were investigated using tensile, dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA) analysis. Mechanical analysis showed that the combination of graphene oxide and clay exerted a favorable synergistic effect on the tensile modulus and the yield strength of the ternary composite that are greatly improved as compared with neat high-impact polystyrene, high-impact polystyrene/graphene oxide, and high-impact polystyrene/clay binary composites due to the double-network structure formation between the nanofillers as confirmed by the direct morphological observations using transmission electron microscopy and scanning electron microscopy analysis. The viscoelastic behavior showed that storage modulus of ternary composite significantly improvement over than that of the pure matrix, high-impact polystyrene/graphene oxide and high-impact polystyrene/clay while network structure made. TGA and DMTA measurements also demonstrated that thermal stability of high-impact polystyrene matrix modified by graphene oxide and clay slightly enhanced during the creation of dual network structure of graphene oxide and clay. Our data suggest a potential application for the combination of graphene oxide and clay in graphene-based composite materials.     

Nanoscale charge distribution and energy band modification in defect-patterned graphene

Defects were introduced precisely to exfoliated graphene (G) sheets on a SiO(2)/n(+) Si substrate to modulate the local energy band structure and the electron pathway using solution-phase oxidation followed by thermal reduction. The resulting nanoscale charge distribution and band gap modification were investigated by electrostatic force microscopy and spectroscopy. A transition phase with coexisting submicron-sized metallic and insulating regions in the moderately oxidized monolayer graphene were visualized and measured directly. It was determined that the delocalization of electrons/holes in a graphene "island" is confined by the surrounding defective C-O matrix, which acts as an energy barrier for mobile charge carriers. In contrast to the irreversible structural variations caused by the oxidation process, the electrical properties of graphene can be restored by annealing. The defect-patterned graphene and graphene oxide heterojunctions were further characterized by electrical transport measurement.