Highly dispersed ultrafine Pt and PtRu nanoparticles on graphene: formation mechanism and electrocatalytic activity

We demonstrate a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene by exploiting the nucleation of a metal precursor phase on graphite oxide surfaces. Our method opens up new possibilities to engineer graphene-based hybrids for applications in multifunctional nanoscale devices.

Hydrothermal synthesis of a monoclinic VO2 nanotube-graphene hybrid for use as cathode material in lithium ion batteries

The hydrothermal reaction of a mixture of a colloidal dispersion of graphite oxide and ammonium vanadate yielded a hybrid made of graphene and a nanotubular metastable monoclinic polymorph of VO2, known as VO2(B). The formation of VO2(B) nanotubes is accompanied by the reduction of graphite oxide. Initially the partially scrolled graphite oxide layers act as templates for the crystallization of VO2(B) in the tubular morphology. This is followed by the reduction of graphite oxide to graphene resulting in a hybrid in which VO2(B) nanotubes are dispersed in graphene. Electron microscopic studies of the hybrid reveal that the VO2(B) nanotubes are wrapped by and trapped between graphene sheets. The hybrid shows potential to be a high capacity cathode material for lithium ion batteries. It exhibits a high capacity (similar to 450 mAh/g) and cycling stability. The high capacity of the hybrid is attributed to the interaction between the graphene sheets and the VO2(B) tubes which improves the charge-transfer. The graphene matrix prevents the aggregation of the VO2(B) nanotubes leading to high cycling stability. (C) 2012 Elsevier Ltd. All rights reserved.

Na0.33V2O5 center dot 1.5H(2)O nanorings/nanorods and Na0.33V2O5 center dot 1.5H(2)O/RGO composite fabricated by a facile one pot synthesis and its lithium storage behavior

In this work, Na0.33V2O5 center dot 1.5H(2)O nanorings/nanorods and Na0.33V2O5 center dot 1.5H(2)O/reduced graphene oxide (RGO) composites have been prepared through a facile hydrothermal route in acidic medium at 200 degrees C for 2 days. The hydrothermally derived products have been characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, UV-Visible spectroscopy, Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and electrochemical discharge-charge cycling in lithium ion battery. XRD pattern exhibits the layered structure of Na0.33V2O5 center dot 1.5H(2)O and the composite shows the presence of RGO at 2 theta = 25.8 degrees. FTIR spectrum shows that the band at 760 cm(-1) could be assigned to a V-OH2 stretching mode due to coordinated water. Raman spectrum shows that the band at 264 cm(-1) is due to the presence of water molecules between the layers. FESEM/TEM micrographs reveal that the products consist of nanorings of inner diameter 5 mu m and thickness of the ring is found to be 200-300 nm. Addition of exfoliated graphene oxide (EGO) destroys the formation of rings. The reduction of EGO sheets into RGO is also evidenced by the red shift of the absorbance peak from 228 nm to 264 nm. In this composite Na0.33V2O5 center dot 1.5H(2)O nanorods may adhere to the surface of RGO and/or embedded in the RGO nanosheets. As a result, an effective three-dimensional conducting network was formed by bridging RGO nanosheets, which can facilitate electron transport effectively and thus improve the kinetics and rate performance of Na0.33V2O5 center dot 1.5H(2)O nanorings/nanorods. The Na0.33V2O5 center dot 1.5H(2)O/RGO composites exhibited a discharge capacity of 340 mAh g(-1) at a current density of 0.1 mA g(-1) and also an improved cyclic stability. RGO plays a `flexible confinement' function to enwrap Na0.33V2O5 center dot 1.5H(2)O nanorods, which can compensate for the volume change and prevent the detachment and agglomeration of pulverized Na0.33V2O5 center dot 1.5H(2)O, thus extending the cycling life of the electrode. A probable reaction mechanism for the formation of Na0.33V2O5 center dot 1.5H(2)O nanorings is also discussed. (C) 2012 Elsevier B.V. All rights reserved.

Strategies for the Synthesis of Graphene, Graphene Nanoribbons, Nanoscrolls and Related Materials

Single-layer graphene (SLG), the 3.4 angstrom thick two-dimensional sheet of sp(2) carbon atoms, was first prepared in 2004 by mechanical exfoliation of graphite crystals using the scotch tape technique. Since then, SLG has been prepared by other physical methods such as laser irradiation or ultrasonication of graphite in liquid media. Chemical methods of synthesis of SLG are more commonly used; the most popular involves preparation of single-layer graphene oxide followed by reduction with a stable reagent, often assisted by microwave heating. This method yields single-layer reduced graphene oxide. Other methods for preparing SLG include chemical vapour deposition over surfaces of transition metals such as Ni and Cu. Large-area SLG has also been prepared by epitaxial growth over SIC. Few-layer graphene (FLG) is prepared by several methods; arc discharge of graphite in hydrogen atmosphere being the most convenient. Several other methods for preparing FLG include exfoliation of graphite oxide by rapid heating, ultrasonication or laser irradiation of graphite in liquid media, reduction of few-layer graphene oxide, alkali metal intercalation followed by exfoliation. Graphene nanoribbons, which are rectangular strips of graphene, are best prepared by the unzipping of carbon nanotubes by chemical oxidation or laser irradiation. Many graphene analogues of inorganic materials such as MoS2, MoSe2 and BN have been prepared by mechanical exfoliation, ultrasonication and by chemical methods involving high-temperature or hydrothermal reactions and intercalation of alkali metals followed by exfoliation. Scrolls of graphene are prepared by potassium intercalation in graphite or by microwave irradiation of graphite immersed in liquid nitrogen.

Electrochemiluminescence from tris(2,2 '-bipyridyl)ruthenium(II)-graphene-Nafion modified electrode

An electrochemiluminescence (ECL) sensor based on Ru(bpy)(3)(2+)-graphene-Nafion composite film was developed. The graphene sheet was produced by chemical conversion of graphite, and was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy. The introduction of conductive graphene into Nafion not only greatly facilitates the electron transfer of Ru(bpy)(3)(2+), but also dramatically improves the long-term stability of the sensor by inhibiting the migration of Ru(bpy)(3)(2+) into the electrochemically inactive hydrophobic region of Nafion. The ECL sensor gives a good linear range over 1 x 10(-7) to 1 x 10(-4) M with a detection limit of 50 nM towards the determination of tripropylamine (TPA), comparable to that obtained by Nafion-CNT.

Water-Soluble Graphene Covalently Functionalized by Biocompatible Poly-L-lysine

Graphene sheets functionalized covalently with biocompatible poly-L-lysine (PLL) were first synthesized in all alkaline solution. PLL-functionalized graphene is water-soluble and biocompatible, which makes it a novel material promising for biological applications. Graphene sheets played an important role as connectors to assemble these active amino groups Of Poly-L-lysine, which provided a very biocompatible. environment for further functionalization, such as attaching bioactive molecules. As an example, an amplified biosensor toward H2O2 based on linking peroxidase onto PLL-functionalized graphene was investigated.

Direct Electrochemistry of Glucose Oxidase and Biosensing for Glucose Based on Graphene

We first reported that polyvinylpyrrolidone-protected graphene was dispersed well in water and had good electrochemical reduction toward O-2 and H2O2. With glucose oxidase (GOD) as an enzyme model, we constructed a novel polyvinylpyrrolidone-proteeted graphene/polyethylenimine-ftmctionalized ionic liquid/GOD electrochemical biosensor, which achieved the direct electron transfer of GOD, maintained its bioactivity and showed potential application for the fabrication of novel glucose biosensors with linear glucose response up to 14 mM.

Identifying the trend of reactivity for sp2 materials: an electron delocalization model from first principles calculations

The reactivity of sp² carbon materials is studied using the adsorption and dissociation of O₂ on graphene and graphene oxide as model systems. The reactions on the basal plane, zigzag and armchair edges of graphene and graphene oxide with different oxygen-containing groups are calculated using first principles calculations. Two Brønsted-Evans- Polanyi relationships are identified and an electron delocalization model is suggested to understand the general trend of reactivity for sp² carbon materials.

Observation of active sites for oxygen reduction reaction on nitrogen-doped multilayer graphene

Active sites and the catalytic mechanism of nitrogen-doped graphene in an oxygen reduction reaction (ORR) have been extensively studied but are still inconclusive, partly due to the lack of an experimental method that can detect the active sites. It is proposed in this report that the active sites on nitrogen-doped graphene can be determined via the examination of its chemical composition change before and after ORR. Synchrotron-based X-ray photoelectron spectroscopy analyses of three nitrogen-doped multilayer graphene samples reveal that oxygen reduction intermediate OH(ads), which should chemically attach to the active sites, remains on the carbon atoms neighboring pyridinic nitrogen after ORR. In addition, a high amount of the OH(ads) attachment after ORR corresponds to a high catalytic efficiency and vice versa. These pinpoint that the carbon atoms close to pyridinic nitrogen are the main active sites among the different nitrogen doping configurations.

RAFT controlled synthesis of graphene/polymer hydrogel with enhanced mechanical property for pH-controlled drug release

A pH-sensitive, mechanically strong and thermally stable graphene/poly (acrylic acid) (graphene/PAA) hydrogel was prepared via reversible addition fragmentation transfer (RAFT) polymerizations in the presence of a cross-linking agent. The RAFT agent was covalently coupled onto graphene basal planes via an esterification reaction, with benzoic acid functionalities pre-attached on graphene with its aryl diazonium salt precursor. AFM and SEM analysis revealed the successful preparation of single layered graphene sheets and graphene/polymer hydrogels with pH controlled porous structures. Attenuated total reflection infrared (ATR-IR) and thermogravimetric analyzer (TGA) verified the successful stepwise preparation of graphene/PAA hydrogel. This graphene/PAA hydrogel was pH-sensitive and more mechanically elastic than the PAA hydrogel prepared without graphene. The pH sensitivity of the hydrogel was further utilized for controlled drug release. Doxorubicin was chosen as a model drug and loaded into the hydrogels. The drug loading and release experiment indicated that this hydrogel can be used to efficiently control drug release in the intestine environment (pH = 7.4), better than release in a more acidic environment.© 2013 Elsevier Ltd. All rights reserved.

High-performance multifunctional graphene yarns: toward wearable all-carbon energy storage textiles

The successful commercialization of smart wearable garments is hindered by the lack of fully integrated carbon-based energy storage devices into smart wearables. Since electrodes are the active components that determine the performance of energy storage systems, it is important to rationally design and engineer hierarchical architectures atboth the nano- and macroscale that can enjoy all of the necessary requirements for a perfect electrode. Here we demonstrate a large-scale flexible fabrication of highly porous high-performance multifunctional graphene oxide (GO) and rGO fibers and yarns by taking advantage of the intrinsic soft self-assembly behavior of ultralarge graphene oxide liquid crystalline dispersions. The produced yarns, which are the only practical form of these architectures for real-life device applications, were found to be mechanically robust (Young's modulus in excess of 29 GPa) and exhibited high native electrical conductivity (2508 ± 632 S m(-1)) and exceptionally high specific surface area (2605 m(2) g(-1) before reduction and 2210 m(2) g(-1) after reduction). Furthermore, the highly porous nature of these architectures enabled us to translate the superior electrochemical properties of individual graphene sheets into practical everyday use devices with complex geometrical architectures. The as-prepared final architectures exhibited an open network structure with a continuous ion transport network, resulting in unrivaled charge storage capacity (409 F g(-1) at 1 A g(-1)) and rate capability (56 F g(-1) at 100 A g(-1)) while maintaining their strong flexible nature.

Graphene and graphitic derivative filled polymer composites as potential sensors

Graphite and numerous graphitic-derived micro- and nano-particles have gained importance in current materials science research. These two-dimensional sheets of sp(2)-hybridized carbon atoms remarkably influence the properties of polymers. Graphene mono-layers, graphene oxides, graphite oxides, exfoliated graphite, and other related materials are derived from a parental graphite structure. In this review, we focus primarily on the role of these fillers in regulating the electrical and sensing properties of polymer composites. It has been demonstrated that the addition of an optimized mixture of graphene and or its derivatives to various polymers produces a record-high enhancement of the electrical conductivity and achieved semiconducting characteristics at small filler loading, making it suitable for sensor manufacture. Promising sensing characteristics are observed in graphite-derived composite films compared with those of micro-sized composites and the properties are explained mainly based on the filler volume fraction, nature and rate of dispersion and the filler polymer interactions at the interface. In short, this critical review aims to provide a thorough understanding of the recent advances in the area of graphitic-based polymer composites in advanced electronics. Future perspectives in this rapidly developing field are also discussed.

Desenvolvimento de revestimentos siloxano-PMMA reforçados por nanotubos de carbono, óxido de grafite e óxido de grafite reduzido para aplicações anticorrosivas

Pós-graduação em Química - IQ

Synthesis and characterization of CeO2-graphene composite

The synthesis and characterization of graphite oxide (GO), graphene (GS), and the composites: GS-CeO2 and GO-CeO2 are reported. This synthesis was carried out by mixing aqueous solutions of CeCl3 center dot 7H(2)O and GO, which yields the oxidized composite GO-CeO2. GO-CeO2 was hydrothermally reduced with ethylene glycol, at 120 A degrees C, yielding the reduced composite GS-CeO2. GO, GS ,and the composites with CeO2 were characterized by CHN, TG/DTG, BET, XRD, SEM microscopy, FTIR, and Raman spectroscopy. The estimation of crystallite size of CeO2 anchored on GO and on GS by Raman, XRD, and SEM agreed very well showing diameters about 5 nm. The role of particles of CeO2 coating carbon sheets of GO and GS was discussed.

SYNTHESIS OF GRAPHENE AND ITS APPLICATIONS FOR DYE-SENSITIZED SOLAR CELLS

Graphene, which is a two-dimensional carbon material, exhibits unique properties that promise its potential applications in photovoltaic devices. Dye-sensitized solar cell (DSSC) is a representative of the third generation photovoltaic devices. Therefore, it is important to synthesize graphene with special structures, which possess excellent properties for dye-sensitized solar cells. This dissertation research was focused on (1) the effect of oxygen content on the structure of graphite oxide, (2) the stability of graphene oxide solution, (3) the application of graphene precipitate from graphene oxide solution as counter electrode for DSSCs, (4) the development of a novel synthesis method for the three-dimensional graphene with honeycomb-like structure, and (5) the exploration of honeycomb structured graphene (HSG) as counter electrodes for DSSCs. Graphite oxide is a crucial precursor to synthesize graphene sheets via chemical exfoliation method. The relationship between the oxygen content and the structures of graphite oxides was still not explored. In this research, the oxygen content of graphite oxide is tuned by changing the oxidation time and the effect of oxygen content on the structure of graphite oxide was evaluated. It has been found that the saturated ratio of oxygen to carbon is 0.47. The types of functional groups in graphite oxides, which are epoxy, hydroxyl, and carboxylgroups, are independent of oxygen content. However, the interplanar space and BET surface area of graphite oxide linearly increases with increasing O/C ratio. Graphene oxide (GO) can easily dissolve in water to form a stable homogeneous solution, which can be used to fabricate graphene films and graphene based composites. This work is the first research to evaluate the stability of graphene oxide solution. It has been found that the introduction of strong electrolytes (HCl, LiOH, LiCl) into GO solution can cause GO precipitation. This indicates that the electrostatic repulsion plays a critical role in stabilizing aqueous GO solution. Furthermore, the HCl-induced GO precipitation is a feasible approach to deposit GO sheets on a substrate as a Pt-free counter electrode for a dye-sensitized solar cell (DSSC), which exhibited 1.65% of power conversion efficiency. To explore broad and practical applications, large-scale synthesis with controllable integration of individual graphene sheets is essential. A novel strategy for the synthesis of graphene sheets with three-dimensional (3D) Honeycomb-like structure has been invented in this project based on a simple and novel chemical reaction (Li2O and CO to graphene and Li2CO3). The simultaneous formation of Li2CO3 with graphene not only can isolate graphene sheets from each other to prevent graphite formation during the process, but also determine the locally curved shape of graphene sheets. After removing Li2CO3, 3D graphene sheets with a honeycomb-like structure were obtained. This would be the first approach to synthesize 3D graphene sheets with a controllable shape. Furthermore, it has been demonstrated that the 3D Honeycomb-Structured Graphene (HSG) possesses excellent electrical conductivity and high catalytic activity. As a result, DSSCs with HSG counter electrodes exhibit energy conversion efficiency as high as 7.8%, which is comparable to that of an expensive noble Pt electrode.