Investigation of Raman and photoluminescence studies of reduced graphene oxide sheets

In this paper, we are investigating the Raman and photoluminescence properties of reduced graphene oxide sheets (rGO). Moreover, graphene oxide (GO) sheets are synthesized using Hummer’s method and further reduced into graphene sheets using D-galactose. Both GO and rGO are characterized by UV-vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Thermogravimetric (TGA) analysis. Raman analysis of rGO shows the restoration of graphitic domains in GO after reduction. The photoluminescence of rGO showed emission in the UV region which is blue shifted along with luminescent quenching as compared to GO. This blue shift and quenching in photoluminescence arises due to the newly formed crystalline sp² clusters in rGO which created percolation pathways between the sp² clusters already present.     

Improvement of water softening efficiency in capacitive deionization by ultra purification process of reduced graphene oxide

Capacitive deionization (CDI) is the next generation of water desalination and softening technology by using relatively low capacitive current of electrochemical double layer. Among various carbon-based materials used for making electrode, reduced graphene oxide (rGO) has been intensively studied due to its excellent electrical conductivity and high surface area. Although Hummer method for making graphene oxide (GO) and rGO is a simple process, it remains some impurities in inherent GO and rGO which affect negatively to the CDI performance. In this work, we successfully prepared ultra purified GO and rGO by modifying Hummer method in order to remove entirely excess elements degrading the CDI performance. The electrosorption capacity of ultra purified rGO is considerably better than that of previous rGO, and maximum removal achieves 3.54 mg g⁻¹ at applied voltage of 2.0 V. Thus, this result could be comparable to other researches in CDI process.     

In situ growth of ultrashort rice-like CuO nanorods supported on reduced graphene oxide nanosheets and their lithium storage performance

A facile refluxing strategy in aqueous solution was engaged to synthesize ultrashort rice-like CuO nanorods/reduced graphene oxide (CuO-NRs/rGO) composite. The result of the high-resolution transmission electron microscopy shows that the as-synthesized rice-like CuO nanorods have a uniform size of about 8 nm in width and 28 nm in length and are homogenously dispersed on rGO nanosheets. The CuO nanorods are uniformly dispersed and immobilized by the graphene nanosheets reduced from GO. The resultant CuO-NRs/rGO composite as anode material for lithium-ion batteries displays better electrochemical properties than those of pure CuO-NRs and rGO nanosheets. The high reversible capacity and good stability can be ascribed to the presence of rGO nanosheets.     

A Self‐Assembly Route to an Iron Phthalocyanine/Reduced Graphene Oxide Hybrid Electrocatalyst Affording an Ultrafast Oxygen Reduction Reaction

Graphene oxide (GO) is an attractive freestanding support that can be decorated with ultrathin organic layers for facile and low‐cost fabrication of novel devices with controllable functional properties and microstructures. Here, it is reported that a hybrid material consisting of an ultrathin iron phthalocyanine (FePc) layer self‐assembled on reduced graphene oxide (rGO) exhibits excellent catalytic activity that is superior to that of commercial Pt/C for an oxygen reduction reaction (ORR). During solution processing, the FePc layer is first self‐organized onto GO sheets and then reduced electrochemically to form an FePc/rGO hybrid electrocatalyst. Kinetics studies reveal that the hybrid architecture affords an ultrafast ORR rate caused by a strongly dominant four‐electron process, and the durability of the catalyst shows significant improvement by forming the hybrid structure. Spectroscopic studies suggest that these advantages are afforded by synergistic effects between FePc and rGO, which are enriched by the hybrid structure and the appropriate reduction step.     

Nanocarbon hybrids of graphene‐based materials and ultradispersed diamond: investigating structure and hierarchical defects evolution with electron‐beam irradiation

We report the influence of electron‐beam (E‐beam) irradiation on the structural and physical properties modification of monolayer graphene (Gr), reduced graphene oxide (rGO) and graphene oxide (GO) with ultradispersed diamond (UDD) forming novel hybrid composite ensembles. The films were subjected to a constant energy of 200 keV (40 nA over 100 nm region or electron flux of 3.9 × 10¹⁹ cm⁻²s⁻¹) from a transmission electron microscope gun for 0 (pristine) to 20 min with an interval of 2.5 min continuously – such conditions resemble increased temperature and/or pressure regime, enabling a degree of structural fluidity. To assess the modifications induced by E‐beam, the films were analyzed prior to and post‐irradiation. We focus on the characterization of hierarchical defects evolution using in situ transmission electron microscopy combined with selected area electron diffraction, Raman spectroscopy (RS) and Raman mapping techniques. The experiments showed that the E‐beam irradiation generates microscopic defects (most likely, interstitials and vacancies) in a hierarchical manner much below the amorphization threshold and hybrids stabilized with UDD becomes radiation resilient, elucidated through the intensity, bandwidth, and position variation in prominent RS signatures and mapping, revealing the defects density distribution. The graphene sheet edges start bending, shrinking, and generating gaps (holes) at ~10–12.5 min owing to E‐beam surface sputtering and primary knock‐on damage mechanisms that suffer catastrophic destruction at ~20 min. The microscopic point defects are stabilized by UDD for hybrids in the order of GO > rGO ≥ Gr besides geometric influence, i.e. the int erplay of curvature‐induced (planar vs curved) energy dispersion/absorption effects. Furthermore, an attempt was made to identify the nature of defects (charged vs residual) through inter‐defect distance (i.e. L_D). The trends of L_D for graphene‐based hybrids with E‐beam irradiation implies charged defects described in terms of dangling bonds in contrast to passivated residual or neutral defects. More importantly, they provided a contrasting comparison among variants of graphene and their hybrids with UDD. Copyright © 2015 John Wiley & Sons, Ltd.     

Reduced graphene oxide foils for ion stripping applications

ABSTRACT

Reduced graphene oxide (rGO) films can be employed as ion strippers in an accelerator. They show some advantages with respect to the graphite foils, due to their high thermal and electrical conductivity, low density, high mechanical resistance and high stability. Thin graphene oxide (GO) films with a sub-micron thickness have been synthesized and transformed into reduced GO (rGO) by ion beam irradiations. Physical characterizations of the pristine and ion irradiated GO films have been performed. Measurements of stripping efficiency have been carried out by using helium, lithium, carbon and oxygen ion beams. The rGO stripper films demonstrate a significantly high charge production, comparable to that of the graphite films but with the advantage of a longer lifetime.     

Laser and ion beams graphene oxide reduction for microelectronic devices

Reduced graphene oxide (rGO) is a two-dimensional material, which is attracting increasing attention due to its special properties. It can be obtained by laser or ion beam irradiations of pristine graphene oxide (GO). It shows high mechanical resistance, considerable electric and thermal conductivity. All these rGO characteristics together with the high number of molecular species that can be embedded between its layers, make graphene oxide a potential material for electronic sensors or efficient support on which conductive strips, condensers, and micrometric electronic devices can be designed. In particular, as it is described in this paper, it is possible to carry out high spatial resolution lithography in GO by using a focused laser or micro ion beam in order to design macro, micro, and submicron geometrical structures. The use of the reduced graphene oxide for the laser and ion beam fabrication of electrical resistances and capacitances is presented.     

NiCoP/rGO复合材料的合成及其性能研究

以六水合氯化镍、七水合硫酸钴、氧化石墨烯(GO)和赤磷为原料,利用原位水热法,在不添加任何表面活性剂的情况下,合成了磷化钴镍/还原氧化石墨烯(NiCoP/rGO)纳米复合材料,并通过XRD、SEM、TEM、IR、Raman等对该复合材料进行了表征.结果表明,所得复合材料由NiCoP纳米颗粒和还原氧化石墨烯片层结构组成,NiCoP纳米颗粒尺寸大约为20 nm,均匀分布在rGO片层结构表面上,同时探讨了复合材料的形成过程.另外,复合材料的吸附脱除实验表明,所得复合材料对多种染料都具有非常好的吸附作用,因此,在污水处理方面有较大的应用价值.     

Synthesis and characterization of nitrogen-doped TiO2 coatings on reduced graphene oxide for enhancing the visible light photocatalytic activity

Nitrogen-doped TiO₂ coatings on reduced graphene oxide were prepared via a sonochemical synthesis and hydrothermal process. The nanocomposites showed improved photocatalytic activity due to their large specific surface areas (185–447 m²/g), the presence of TiO₂ in the anatase phase, and a quenched photoluminescence peak. In particular, GN3-TiO₂ (nitrogen-doped TiO₂ coatings on rGO with 3 ml of titanium (IV) isopropoxide) exhibited the best photocatalytic efficiency and degradation rate among the materials prepared. With nitrogen-doped on the reduced graphene oxide surface, the photocatalytic activity is enhanced approximately 17.8 times compared to that of the pristine TiO₂. The dramatic enhancement of activity is attributed to the nitrogen contents and rGO effectively promoting charge-separation efficiency and providing abundant catalytically active sites to enhance the reactivity. The composites also showed improved pollutant adsorption capacity, electron–hole pair lifetime, light absorption capability, and absorbance of visible light.     

Liquid Crystalline Dispersions of Graphene‐Oxide‐Based Hybrids: A Practical Approach towards the Next Generation of 3D Isotropic Architectures for Energy Storage Applications

We report the use of the spray pyrolysis method to design self‐assembled isotropic ternary architectures made up of reduced graphene oxide (GO), functionalized multiwalled carbon nanotubes, and nickel oxide nanoparticles for cost‐effective high‐performance supercapacitor devices. Electrodes fabricated from this novel ternary system exhibit exceptionally high capacitance (2074 Fg^?1) due to the highly conductive network, synergistic link between GO and carbon nanotubes and achieving high surface area monodispersed NiO decorated rGO/CNTs composite employing the liquid crystallinity of GO dispersions. To further assess the practicality of this material for supercapacitor manufacture, we assembled an asymmetric supercapacitor device incorporating activated carbon as the anode. The asymmetric supercapacitor device showed remarkable capacity retention (>96%), high energy density (23 Wh kg^?1), and a coulombic efficiency of 99.5%.     

Synthesis of RGO/Cu8S5/PPy Composite Nanosheets with Enhanced Peroxidase‐Like Activity for Sensitive Colorimetric Detection of H2O2 and Phenol

In this paper, a novel strategy for the fabrication of reduced graphene oxide (rGO)/Cu₈S₅/polypyrrole (PPy) composite nanosheets with Cu₈S₅ nanoparticles and PPy layer anchored on the surface of rGO as peroxidase‐like nanocatalyst is reported. During the synthesis, graphene oxide (GO)/CuO composite nanosheets are prepared first and used as templates, then the sulfuration of CuO and polymerization of pyrrole are accompanied with the reduction of GO, resulting in ternary rGO/Cu₈S₅/PPy composite nanosheets. The synthesized Cu₈S₅ nanoparticles with a diameter in the range from tens to hundreds of nanometers are dispersed within PPy decorated rGO nanosheets. The resultant ternary rGO/Cu₈S₅/PPy composite nanosheets exhibit a higher peroxidase‐like catalytic activity toward the oxidation of 3,3′,5,5′‐tetramethylbenzidine in the presence of H₂O₂ than GO/CuO and rGO/CuS composite nanosheets, revealing a synergistic effect on their activity. The as‐prepared rGO/Cu₈S₅/PPy platform provides a simple colorimetric approach for the detection of H₂O₂ and phenol with a high sensitivity. This work offers a new way for the fabrication of rGO‐based nanocomposite with superior enzyme‐like activity, which displays great potential applications in biocatalysis and environmental monitoring.     

Enhanced Fluorescence of Graphene Oxide by Well-Controlled Au@SiO2 Core-Shell Nanoparticles

Graphene and graphene derivatives, including graphene oxide (GO) and reduced GO (rGO), have attracted remarkable attention in different fields due to their unique electronic, thermal, and mechanical properties, whereas the fluorescence property is rarely been studied. This paper reports on metal-enhanced fluorescence Au@SiO₂ composite nanoparticles adsorbed graphene oxide nanosheets, where the silica-shell is used to control the distance between gold-core and fluorophore GO, and a positively charged polyelectrolyte poly(allylamine hydrochloride) (PAH) is used to adsorb the negatively charged silica-shell and GO by layer-by-layer assembly (LbL) approach. The silica-shell around the 80 nm gold-core can be well-controlled by ending the reaction at different times. Various analytical techniques were applied to characterize the morphology and optical characters of the as-prepared particles. A more than three-fold increase of the fluorescence intensity of GO was obtained.     

Ultrasound assisted reduction of graphene oxide to graphene in l-ascorbic acid aqueous solutions: Kinetics and effects of various factors on the rate of graphene formation

The reduction of graphene oxide (GO) to graphene (rGO) was achieved by using 20 kHz ultrasound in l-ascorbic acid (l-AA, reducing agent) aqueous solutions under various experimental conditions. The effects of ultrasound power, ultrasound pulse mode, reaction temperature, pH value and l-AA amount on the rates of rGO formation from GO reduction were investigated. The rates of rGO formation were found to be enhanced under the following conditions: high ultrasound power, long pulse mode, high temperature, high pH value and large amount of l-AA. It was also found that the rGO formation under ultrasound treatment was accelerated in comparison with a conventional mechanical mixing treatment. The pseudo rate and pseudo activation energy (E_a) of rGO formation were determined to discuss the reaction kinetics under both treatment. The E_a value of rGO formation under ultrasound treatment was clearly lower than that obtained under mechanical mixing treatment at the same condition. We proposed that physical effects such as shear forces, microjets and shock waves during acoustic cavitation enhanced the mass transfer and reaction of l-AA with GO to form rGO as well as the change in the surface morphology of GO. In addition, the rates of rGO formation were suggested to be affected by local high temperatures of cavitation bubbles.     

Sono-synthesis approach of reduced graphene oxide for ammonia vapour detection at room temperature

In this paper, we report the sono-synthesis of reduced graphene oxide (rGO) using polyethyleneimine (PEI), and its performance for ammonia vapour detection at room temperature. Graphene oxide (GO) and reduced graphene oxide (rGO) were prepared by sonication method by using low-frequency ultrasound under ambient condition and films were deposited by Doctor Blade method. The rGO, which has vapour accessible structure showed a good sensing response with a minimum detection limit of 1 ppm and the detection range from 1 ppm to 100 ppm. The sensing response was found to be 2% at 1 ppm and 34% at 100 ppm of ammonia and the developed sensor operated at room temperature. The sensor displays a response time of 6 s and a recovery time of 45 s towards 100 ppm of ammonia vapour. The source for the highly sensitive, selective and stable detection of ammonia with negligible interference from other vapours is discussed and reported. We believe reduced graphene oxide (rGO) could potentially be used to manufacture a new generation of low-power portable ammonia sensors.     

Synthesis of PANI/rGO composite as a cathode material for rechargeable lithium-polymer cells

Graphene oxide (GO) was synthesized by an improved Hummers method and then reduced with NaBH₄; GO became rGO with regular layered structure. Polyaniline (PANI)/rGO composite was prepared by a adsorption double oxidant method with rGO as a template. Some physical characterization methods (Fourier transform infrared spectroscopy analysis, X-ray diffraction, scanning electron microscope, and transmission electron microscope) were used to analyze the morphology and crystallinity of the composite. The electrochemical properties were characterized by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge, and rate capability. The first discharge specific capacity of the rPANI/rGO and PANI/rGO was 181.2 and 147.8 mAh/g. After 100 cycles, the capacity retention rate was still 90.2 and 88.9% separately, and the coulombic efficiency of batteries is close to 100%. These results demonstrate the composite has exciting potentials for the cathode material of lithium-ion battery.     

Density functional theory prediction for oxidation and exfoliation of graphite to graphene

A density functional theory (DFT) study of graphene synthesis from graphite oxidation and exfoliation is presented. The calculated DFT results for O adsorption predict CO as a most stable bond on the graphene oxide (GO) sheet. The obtained exfoliation energy for the graphene and the GO are 143 and ∼70 mJ/m² that verify easier exfoliation of the graphite oxide compared with the graphite. Furthermore, the DFT results show that for decreasing the exfoliation energy of the GO at least two layers of the graphite should be oxidized during the oxidation process.     

Enhanced catalytic hydrogenation activity of Ni/reduced graphene oxide nanocomposite prepared by a solid-state method

A simple solid-state method has been applied to synthesize Ni/reduced graphene oxide (Ni/rGO) nanocomposite under ambient condition. Ni nanoparticles with size of 10–30 nm supported on reduced graphene oxide (rGO) nanosheets are obtained through one-pot solid-state co-reduction among nickel chloride, graphene oxide, and sodium borohydride. The Ni/rGO nanohybrid shows enhanced catalytic activity toward the reduction of p-nitrophenol (PNP) into p-aminophenol compared with Ni nanoparticles. The results of kinetic research display that the pseudo-first-order rate constant for hydrogenation reaction of PNP with Ni/rGO nanocomposite is 7.66 × 10^?3 s^?1, which is higher than that of Ni nanoparticles (4.48 × 10^?3 s^?1). It also presents superior turnover frequency (TOF, 5.36 h^?1) and lower activation energy (E_a, 29.65 kJ mol^?1) in the hydrogenation of PNP with Ni/rGO nanocomposite. Furthermore, composite catalyst can be magnetically separated and reused for five cycles. The large surface area and high electron transfer property of rGO support are beneficial for good catalytic performance of Ni/rGO nanocomposite. Our study demonstrates a simple approach to fabricate metal-rGO heterogeneous nanostructures with advanced functions.

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Graphene nanosheets: Ultrasound assisted synthesis and characterization

A facile sonochemical route for the synthesis of graphene nanosheets via reduction of graphene oxide (GO) has been reported. The synthesized graphene sheets are characterized using UV–vis spectra, Fourier transform infra-red (FT-IR) spectra, transmission electron microscope, X-ray photoelectron spectra (XPS) and Raman spectroscopic techniques. The UV–vis spectroscopy results showed that the absorption peak was red shifted due to the reduction of GO into graphene. FT-IR and XPS spectra revealed the removal of oxygenated functional groups in graphene after the reduction process. Raman spectra confirmed the restoration of new sp² carbon domains in graphene sheets after the reduction. The sonochemical approach for the synthesis of graphene nanosheets is relatively fast, cost-effective and efficient as compared to other methods.     

Ecofriendly Route for the Synthesis of Highly Conductive Graphene Using Extremophiles for Green Electronics and Bioscience

Highly conductive biocompatible graphene is synthesized using ecofriendly reduction of graphene oxide (GO). Two strains of non‐pathogenic extremophilic bacteria are used for reducing GO under both aerobic and anaerobic conditions. Degree of reduction and quality of bacterially reduced graphene oxide (BRGO) are monitored using UV–vis spectroscopy, X‐ray photoelectron spectroscopy, and Raman spectroscopy. Structural morphology and variation in thickness are characterized using electron microscopy and atomic force microscopy, respectively. Electrical measurements by three‐probe method reveal that the conductivity has increased by 10⁴–10⁵ fold from GO to BRGO. Biocompatibility assay using mouse fibroblast cell line shows that BRGO is non‐cytotoxic and has a tendency to support as well as enhance the cell growth under laboratory conditions. Hereby, a cost effective, non‐toxic bulk reduction of GO to biocompatible graphene for green electronics and bioscience application is achieved using halophilic extremophiles for the first time.     

Mechanical properties of thin films of graphene materials: A study on their structural quality and functionalities

Several studies have been done on physiochemical properties of thin films of graphene materials, but less on their mechanical properties. The mechanical properties such as tensile and storage modulus of films of graphene oxide (GO), different reduced graphene oxides (rGO), functionalised reduced graphene oxide (frGO) and a few layers graphene (graphene) were analysed in this study. During syntheses processes, a range of variations occurs due to different reducing agents and functionalising components used; this affects or changes the mechanical properties of the materials. In addition, it has become vital to comprehend the mechanical properties of these films as the potential applications such as sensor and electrodes demand extended life cycles or lifetime. It has been found that the ultimate tensile strength (UTS), tensile modulus, and storage modulus vary across all the samples that highly depend on nature/efficiency of reducing agent used, amount of impurities such as oxygen functional groups and defect density such as discrepancies/holes in the aromatic structure. The highest UTS and modulus have been identified with a few layers graphene and with hydroiodic acid reduced GO among the rGOs. The frGO shows almost similar properties to that of graphene.