Surface Of Graphene Sheets Research Articles

Hollow MoS2/rGO composites as high-performance anode materials for lithium-ion batteries

As a representative of transition metal sulfides, MoS2 has a graphene-like structure and has recently been widely used as an anode in lithium ion batteries. However, the disadvantages of poor electrical conductivity and cycle performance limit its application. Here, hollow MoS2/reduced graphene oxide (rGO) composites were successfully synthesized by a hydrothermal method using polystyrene microspheres as hard templates. The hollow MoS2 microspheres with a size of about 180 nm are distributed on the surface of graphene sheets. The hollow MoS2/rGO composites exhibit superior electrochemical properties as anode materials for lithium-ion batteries compared with the hollow MoS2 microspheres. They show a high reversible capacity of 752.4 mAh g−1 at 500 mA g−1 after 100 cycles with negligible decay as well as a high-rate performance (620.8 mA h g−1, 1 A g−1). The excellent lithium storage performance of the hollow MoS2/rGO composites can be attributed to the synergistic effect of the hollow MoS2 microspheres and graphene sheets. Graphene effectively suppresses the agglomeration of the MoS2 and maintain the structural stability of the material.

A novel approach to synthesize porous graphene by the transformation and deoxidation of oxygen-containing functional groups

In this study, impurity-free porous graphene (PG) with intrinsic pore structure was synthesized through a facile acid-alkali etching-assisted sonication approach. The pore structure appears on the surface of graphene sheets due to intrinsic defects of graphene. The PG possessed an extremely high specific surface area of 2184 m2/g, the size of ∼5 μm and layer numbers of 3–8. Additionally, PG contained micropores and mesopores simultaneously, with an average pore diameter of approximately 3 nm. The effects of acid, alkali, and ultrasound treatment on PG preparation were elucidated by transmission electron microscopy and fourier transform infrared spectroscopy. First, in an acidic solution, oxygen-containing functional groups (hydroxyls, carboxyl, and epoxides) were formed due to the hydrolysis of sulfate and continuous transformations of these functional groups on graphene oxide. Second, under the synergistic effects of alkali and ultrasound treatment, PG was obtained due to the loss of carboxyl and epoxide groups. A new route for preparing PG was provided by the proposed method.

A comparative investigation of aminosilane/ethylene diamine–functionalized graphene epoxy nanocomposites with commercial and chemically reduced graphene: static and dynamic mechanical properties

Incorporation of nanosized fillers into polymers has created new composites by expanding the functions and applications while retaining the excellent engineering and processing flexibility inherent to polymers. Compared with traditional nanofillers, more recently, graphene has been increasingly preferred as a candidate for strengthening and/or functionalizing polymer nanocomposites. The easy synthetic methods, low cost, and non-toxicity of graphene make this material attractive for many technological applications. Herein, we discuss the synthesis of different types of graphene from graphite via graphene oxide reduction. Commercial graphene (CG) as well as the synthesized chemically reduced graphene (CRG) and chemically reduced silane-modified graphene (SMG) were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and ultraviolet visible (UV-vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies. The results confirmed that the silane molecules were attached on the surface of graphene sheets. Simultaneously, most of residual oxygen-containing functional groups of GO were reduced and the sp2-hybridized structure of graphene was restored. The utilization of these graphene-based materials in the fabrication of epoxy nanocomposites with enhanced properties has been explored and compared with those of neat epoxy and CG/epoxy nanocomposites. Inclusion of 0.25 phr CRG and SMG in an epoxy resin showed 28% and 32% increases in tensile strength, and the corresponding fracture toughness displayed 67.6% and 66.3% increase respectively. The improved mechanical properties of SMG/epoxy nanocomposites might be due to the uniform dispersion of functionalized graphene and strong interfacial bonding between modified graphene and epoxy resin.

Amphiphobic graphene aerogels modified with fluorosilane via one-pot hydrothermal method

The development of amphiphobic graphene aerogels (AGAs) with simpler fabrication procedure is of great significance to its real-life applications. Herein, we demonstrate the preparation of AGAs via one-pot hydrothermal method and their amphiphobic performance. AGAs exhibited a 3D porous structure with a low density, high surface area and porosity. Upon modification with fluorosilane, fluorosilanol groups with low surface energy grafted to graphene and tiny wrinkles were formed on the surface of graphene sheets, which was beneficial for the amphiphobic performance of AGAs. The water and oil contact angles of AGAs were 146.1° and 92.2°, respectively. When AGAs immersed in water or oil by application of an external force, they float immediately on water or oil surface without absorption of any water or oil, exhibiting excellent water/oil-repellency. The amphiphobic performance of aerogels can be exploited in a variety of applications, such as self-cleaning, anti-fouling and anti-fingerprint.

Platinum supported on reduced graphene oxide as a catalyst for the electrochemical hydrogenation of soybean oils

Platinum nanoparticles anchored over graphene nanocomposites (Pt/Gr) were synthesized and used for the investigation of the electrochemical hydrogenation of soybean oils. By exploiting Pt/Gr nanocomposites as cathode catalysts of a membrane electrode assembly, a promising solid polymer electrolyte (SPE) reactor was fabricated. The obtained Pt/Gr nanocomposites were characterized by transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy, which can definitely show that Pt nanoparticles successfully formed on graphene and were well-distributed on the surface of graphene sheets. The further electrochemical characterizations demonstrated that Pt/Gr has undoubtedly higher electrocatalytic activity and stability compared to the commercial Vulcan XC-72 supported Pt nanoparticles; this outcome will lead to further application as a new electrode material in the SPE reactor. The trans fatty acid content of the obtained hydrogenated soybean oil (IV: 111.3 g I2/100 g oil) using Pt/Gr as the cathode catalyst in the SPE reactor was only 1.53%. To achieve a similar IV, the usage of Pt was much less when graphene was selected as a catalyst carrier compared to Vulcan XC-72. The changes in the fatty acid components and the hydrogenated selectivity of octadecenoic acids were also discussed.

Transition Metal Oxides on Reduced Graphene Oxide Nanocomposites: Evaluation of Physicochemical Properties

Transition metal oxides on reduced graphene oxide (TMO@rGO) nanocomposites were successfully prepared via a very simple one-step solvothermal process, involving the simultaneous (thermal) reduction of graphene oxide to graphene and the deposition of TMO nanoparticles over its surface. Texture and morphology, microstructure, and chemical and surface compositions of the nanocomposites were investigated via scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. The results prove that Fe2O3@rGO, CoFe2O4@rGO, and CoO@rGO are obtained by using Fe and/or Co acetates as oxide precursors, with the TMO nanoparticles uniformly anchored onto the surface of graphene sheets. The electrochemical performance of the most promising nanocomposite was evaluated as anode material for sodium ion batteries. The preliminary results of galvanostatic cycling prove that Fe2O3@rGO nanocomposite exhibits better rate capability and stability than both bare Fe2O3and Fe2O3+rGO physical mixture.

Ultrasonication assisted thermal exfoliation of graphene-tin oxide nanocomposite material for supercapacitor

In this work, Graphene-SnO2 nanocomposite is synthesized by hydrothermal method for supercapacitor electrode material. The characterizations revealed that SnO2 nanoparticles exhibited tetragonal structure with an average crystalline size of ∼33 nm from XRD and for the nanocomposite material it is observed that SnO2 nanoparticles are decorated to the surface of graphene sheet from FE-SEM. The graphene-SnO2 nanocomposite, SnO2 nanoparticles and graphene oxide (GO) has band gap values of 3.44 eV, 3.67 eV and 2.51 eV respectively calculated from UV–Visible Spectroscopy. The DLS indicates better stable suspension in water with a zeta potential of −7.6 mV for graphene-SnO2 Nanocomposite and −4.1 mV for SnO2 nanoparticles. The electrochemical analysis is performed with 1 M Na2SO4 aqueous electrolyte. The resulted nanocomposite showed enhanced cyclic voltammetry with a comparison to SnO2 nanoparticles. The Galvanostatic charge-discharge analysis confirmed the cyclic stability of the nanocomposite composite material. Overall, it is suggested that graphene-SnO2 nanocomposite has enhanced electrochemical properties.

High-performance microwave absorption epoxy composites filled with hollow nickel nanoparticles modified graphene via chemical etching method

High efficient microwave absorption materials are in emergent demand for civil and military application, especially these with light weight and broad absorption bandwidth. In this work, lightweight microwave absorbers consisting of hollow nickel nanoparticles modified reduced graphene oxide (GHN) and epoxy matrix have been successfully prepared via chemical etching method and solution blending process. SEM and TEM images showed that hollow Ni nanospheres are uniformly anchored on the surface of graphene sheets. The introduction of magnetic Ni nanoparticles into dielectric graphene improved integral properties, not only reducing the density but also enhancing microwave absorption capacity. Compared with single hollow Ni samples or graphene samples, GHN/epoxy samples exhibited extraordinary performance originating from the specific structure and multiple loss mechanism. A delta-function and microwave attenuation constant were adopted to quantitatively evaluating the impedance matching condition and microwave energy consumption ability. For GHN-10 samples, optimal reflection loss (RL) could reach up to −33.1 dB with a matching thickness of 4.9 mm. As the coating thickness decreased to 2 mm, the corresponding RL still remained an acceptable numerical value of −23.8 dB and the effective absorption bandwidth extended to about 6.5 GHz (11.5–18 GHz), covering the whole Ku band. The as-synthesized high-performance microwave absorbers would pave a new and promising way to obtain lightweight, broad-band and strong microwave absorption materials.

Electrochemical sensor based on Ni/reduced graphene oxide nanohybrids for selective detection of ascorbic acid

Nowadays, graphene is integrated with different nanomaterials to form unique composite materials. Decorating the surface of graphene sheets with Ni nanoparticles (Ni NPs) is one of the popular methods. In this paper, a newly advanced electrochemical sensor based on the nanohybrid of graphene oxide modified with Ni NPs was developed with a facile and effective one-pot solvothermal strategy, which was synthesized by using hydrothermal method and followed calcining under Ar flow. The as-prepared composites were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), infrared spectrometry, and voltammetric methods. The results reveal that Ni/reduced graphene oxide (rGO) composite exhibit remarkable electrocatalytic performance toward detecting ascorbic acid (AA). After calcination in the argon gas at 450 °C, as-synthesized Ni/rGO has uniform particle size distribution with the average particle size of 10 nm. The corresponding line arrange and detection limit are estimated to be from 0.01 mM to 1.15 mM (r = 0.99919) and 0.61μM at a signal-to-noise ratio of 3.

Synthesis, characterization and photocatalytic properties of graphene-CdO/SnO2 ternary nanocomposites in visible light

rGO/CdO/SnO2 ternary nanocomposite (GCS) were synthesized using a combination of graphene sheet and CdO/SnO2 nanostructures through the hydrothermal process. The resulting GCS nanocomposite was characterized using XRD, FE-SEM, HR-TEM, and EDS for structural, morphological and compositional studies. The optical characteristics such as UV–vis and PL spectroscopy were used to study the optical properties of the nanocomposite. The XRD analysis showed that CdO and SnO2 nanostructures were crystalline in nature with cubic and orthorhombic phases respectively with the existence of graphene. FESEM images revealed the existence of both cubic and orthorhombic phases of CdO and SnO2 nanostructures respectively. HRTEM study revealed the dispersion of 50–200 nm sized agglomerated nanostructures on the surface of graphene sheets. The analysis of UV–visible & PL spectroscopy shows a considerable decrease in band gap energy from 2.87 to 2.41 eV and improved electron-hole separation respectively. The photocatalytic activity of as-synthesized samples were measured against malachite green (MG) and congo red (CR) dyes. It was found that photocatalytic activity was significantly affected by the ratio of graphene and CdO/SnO2 in the composite. The higher percentage of CdO/SnO2 in the rGO/CdO/SnO2 shows maximum photocatalytic degradation. It occurs due to maximum production and transfer of charge carriers from metal oxide to graphene. It is also found that higher degradation efficiency of MG dye is observed in all the samples of GCS nanocomposite as compared to CR dye.

Enhanced photocatalytic degradation of methyl orange by porous graphene/ZnO nanocomposite

Degrading aquatic organic pollutants efficiently is very important but strongly relied on the design of photocatalysts. Porous graphene could increase photocatalytic performance of ZnO nanoparticles by promoting the effective charge separation of electron-hole pairs if they can be composited. Herein, porous graphene, ZnO nanoparticles and porous graphene/ZnO nanocomposite were prepared by fine tuning of partial combustion, which graphene oxide imperfectly covered by the layered Zn salt was combusted under muffle furnace within few minutes. Resulting ZnO nanoparticles (32–72 nm) are dispersed uniformly on the surface of graphene sheets, the pore sizes of porous graphene are in the range from ∼3 to ∼52 nm. The synthesized porous graphene/ZnO nanocomposite was confirmed to show enhanced efficiency under natural sunlight irradiation compared with pure ZnO nanoparticles. Using porous graphene/ZnO nanocomposite, 100% degradation of methyl orange can be achieved within 150 min. The synergetic effect of photocatalysis and adsorption is main reason for excellent MO degradation of PG/ZnO nanocomposite. This work may offer a new route to accurately prepare porous graphene-based nanocomposite and open a door of their applications.

Investigation of cyclic voltammetry and impedance spectroscopy of thermally exfoliated biomass synthesized nickel decorated graphene

The cyclic voltammetry and impedance spectroscopy of nickel decorated multilayered graphene (NiMGr) thin films were investigated by the thermal exfoliation of onion (Allium cepa) with different process temperature from 600 to 1000 °C. The AFM images reveal the size distribution of Ni particles varies from 50 to 100 nm on the surface of graphene sheets. The diffraction planes (002), (111) and (200) are observed at 24, 44.3 and 51.6° corresponding Ni particles embedded with NiMGr sheets. The Raman parameter, ID/IG and I2D/IG ratio varied from 0.94 to 0.8 and 2.52 to 1.38 respectively indicated the formation of NiMGr containing some defect states. The areal capacitance of NiMGr varied from 12.19 to 22.9 μF/cm2 respectively, with different process temperature from 600 to 1000 °C. The corrosion potential (Ecorr) and corrosion current density (Icorr)values are −0.18 V and −13.29 A/cm2 respectively, for the NiMGr processed at 1000 °C, showing the highest corrosion resistance against acidic solutions. These encouraging findings for NiMGr demonstrate its possibility in various fields like supercapacitors as well as anti corrosion coatings.

Graphene supported ultrafine tin oxide nanoparticles enable conversion reaction dominated mechanism for sodium-ion batteries

Na-ion batteries are considered as promising alternatives for Li-ion batteries in electrochemical energy-storage. However, the lack of high performance anode materials severely plagues their practical application. In this work, we synthesized the SnO2@graphene (SnO2@G) nanocomposites through one-pot hydrothermal method, in which the ultrafine SnO2 nanoparticles (∼4 nm) evenly distributed on the graphene sheets surface. The synthesized SnO2@G delivered a Na storage capacity of 343 mAh g−1 at 100 mA g−1 after 100 cycles, with excellent capacity retention. Even at a low temperature of −20 °C, SnO2@G still maintains a specific capacity of 97 mAh g−1 after 100 cycles, making it both available for ambient and low temperature environment. The detailed Na-storage mechanism for SnO2@G is revealed. It is found that both conversion and alloying reaction contribute to sodium storage. The dominating contribution from conversion reaction is attributed to the ultrafine nanoparticles, which triggers the activity of conversion reaction of SnO2 with sodium. The study provides new insights for using SnO2 as the anode materials for Na-ion batteries.

Polymer Nanocomposites of Surface‐Modified Graphene. I: Thermal and Electrical Properties of Poly(Vinyl Alcohol)/Aminoacid‐Functionalized Graphene

Extrinsic electrically conducting polymer composites are versatile materials for applications in sensors, electrical components, antistatic coatings, among others. The use of carbon‐based conducting loads, such as graphene, in polymer nanocomposites allows the manufacturing of suitable electrically conducting films for a variety of applications. In our work, graphene sheets are covalently modified with histidine, phenylalanine, or beta‐alanine aminoacids, in order to improve dispersion and impart extrinsic conductivity to poly(vinyl alcohol) (PVA) films. The presence of organic groups in the surface of graphene sheets improved their dispersion in polymer matrices. In addition, such benign surface modifiers are suitable to produce environmentally friendly, electrically conducting loads for polymer nanocomposites. Our findings showed that aminoacid‐functionalized graphenes have good dispersability, resulting in semiconducting nanocomposite films with preserved thermal stability, suggesting that these carbon‐based nanoloads are suitable additives for PVA in applications including antistatic paints and coatings.

Atomistic mechanism of the weakened wear resistance of few-layer graphene induced by point defects

Abstract Effect of various point defects on the wear properties of few-layer graphene was investigated by molecular dynamics simulations. Our results show that the presence of Stone-Wales defect, double vacancies and single vacancy reduces the critical normal load for onset of adhesive wear to 85, 15 and 11% of that of the intact graphene, respectively. The analysis of the potential energy surfaces of defective graphene sheets indicates that it is the highest chemical reactivity induced by point defects that determines the onset of adhesive wear. This study provides an atomic-level understanding for the weakening effects of point defects on the wear resistance of few-layer graphene.

Preparation and characterization of silver-doped graphene-reinforced silver matrix bulk composite as a novel electrical contact material

The incorporation of graphene into silver nanopowder to prepare their bulk composite with enhanced electrical and mechanical properties is investigated. The silver-doped graphene composite (GNs–Ag) is introduced as a reinforcing phase. Silver nanopowder and GNs–Ag composite are ultrasonically mixed and plasma-sintered to prepare GNs–Ag reinforced silver matrix bulk composite. The phase structure, micromorphology, chemical state of elements of the GNs–Ag nanoparticles was analyzed in detailed. Meanwhile, micromorphology and electrical properties of the sintered bulk composites are also measured. The results showed that graphene oxide (GO) and Ag ions are simultaneously reduced by hydrazine hydrate during the reaction. Ag nanoparticles (AgNP) presents the uniformly distribution on the surface of graphene sheets. The Raman spectrum is significantly enhanced compared with that of GO due to the presence of AgNP in the GNS–Ag nanoparticles. It is observed that C/O mass ratio demonstrates an increasing trend from 1.84 in graphene oxide to 6.29 in the composites materials. Compared to International Annealed Copper Standard, this composite material possesses an electrical conductivity of 92.6%, a density of 9.59 g cm−3, and a hardness of 46.12 HV. This phenomenon can be explained as that grain boundaries will be formed at the grain boundaries of silver due to the addition of graphene. In addition, it is found that the resistance of the GNs–Ag/n-Si (111) Schottky contact is lower than Ag/n-Si (111) Schottky contact.

Monolayer rubrene functionalized graphene-based eletrochemiluminescence biosensor for serum cystatin C detection with immunorecognition-induced 3D DNA machine

Only surficial molecules of eletrochemiluminescent (ECL) nanomaterials are the most reactive species in the typical ECL reaction. Herein, monolayer rubrene was assembled on the surface of graphene sheet to obtain monolayer rubrene functionalized graphene composite (G/mRub) with strong ECL emission by maximizing the surficial rubrene molecules. Based on G/mRub as the strong ECL emitter, an ultrasensitive “on-off” biosensor was developed to detect cystatin C (Cys C) in human serum with the help of a novel immunorecognition-induced enzyme-free 3D DNA machine. Benefiting from the strong ECL emission of G/mRub and the efficient signal amplification of 3D DNA machine, the established biosensor achieved high sensitivity for Cys C detection with linear range from 1.0 fg mL−1 to 10 ng mL−1 and limit of detection down to 0.38 fg mL−1. In addition, this enzyme-free biosensing method was adopted to successfully detect the concentration of Cys C in human serum. Therefore, the G/mRub based ECL biosensor might provide a potential tool for protein detection in clinical diagnosis and a new avenue to prepare high-performance luminescent nanomaterials.

Synthesis of carbon-coated VBO3 nanoparticles on graphene sheets as anode material for lithium-ion batteries by freeze-drying method

Carbon-coated VBO3 on graphene sheets (VBO3/C@G) composite synthesized by freeze-drying method is presented as anode material for lithium-ion batteries. In the final material, VBO3 nanoparticles, which are uniformly coated by amorphous carbon, are either adhered to the surface of graphene sheets or covered by graphene sheets. The amorphous carbon and graphene not only prevent the growth of VBO3 nanoparticles but also provide an excellent conductive 3D network, which is beneficial for the battery performance. The material delivers an initial charge capacity of 787 mAh g−1 at 0.1 C and maintains 697 mAh g−1 after 100 cycles at 0.1 C. It also exhibits an excellent rate performance with a charge capacity of 609 mAh g−1 at 10 C.

Facile sonochemical synthesis of artichoke-like Co3O4-graphene nanocomposites

Facile sonochemical technique was used for the first time to synthesize Co3O4-graphene nanocomposites at room temperature. The nanocomposites under investigation were prepared with different Co3O4 molar ratios of nanoparticles. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FT-IR) and UV-vis spectroscopy. The results show that Co3O4 nanoparticles were distributed uniformly on the surface of graphene sheet. This work reports a simple preparation approach and recommends the described methodology for the decoration of graphene sheet surface with miscellaneous metal oxide nanoparticles.

Fabrication of GNS/MoS2 composite with different morphology and its tribological performance as a lubricant additive

MoS2 was anchored on the surface of graphene sheets (GNS) with hydrothermal process and chemical vapor deposition to obtain GNS/MoS2 nanoflowers (GNS/MoS2-NFs) and GNS/MoS2 nanoplates (GNS/MoS2 NPs). The GNS/MoS2 composite prepared with different methods was observed with XRD, Raman, SEM, TEM and XPS respectively, and the characterization results confirmed the different morphology of GNS/MoS2-NFs and GNS/MoS2 NPs. For GNS/MoS2-NFs, the MoS2 nanoflowers were dotted on the graphene surface, while the MoS2 nanoplates were uniformly attached on the graphene surface in GNS/MoS2 NPs. The tribological properties of (dibutyl phthalate) DBP containing GNS/MoS2-NFs or GNS/MoS2 NPs was compared with four-ball tribotester at 1200 rpm under 392 N for 30 min. The GNS/MoS2-NFs additive presented better performance than GNS/MoS2 NPs additive even at different concentration. For example, the friction coefficient and wear scar diameter of base oil were reduced by 42.8% and 16.9% with the introduction of 0.02 wt% GNS/MoS2-NFs, while that can only be reduced by 37.6% and 11.9% with the addition of 0.02 wt% GNS/MoS2-NPs. The two additives after friction was further analyzed to explore the lubrication mechanism, and a possible mechanism of GNS/MoS2-NFs was tentatively proposed. In addition, the friction-reducing and anti-wear performance of GNS/MoS2-NFs dispersed DBP can be improved more effectively comparing to that of individual GNS, MoS2 nanoflowers, and the mixture of them. The lubrication mechanism of different additives was investigated with the observation of wear scar, and it indicated that the synergistic effect between GNS and MoS2 nanoflowers played an important role during the friction due to its microstructure.