A glycerol–water-based nanofluid containing graphene oxide nanosheets

Nanofluids are simply the dispersion of nanometer-sized particles in different fluids. Graphene oxide nanosheets (GONs) were prepared by exfoliating the graphite oxide. The GONs were investigated using Fourier transform-infrared spectroscopy, Raman spectroscopy, XRD analysis, high-resolution emission electron microscopy, transmission electron microscopy, and UV–visible spectroscopy. GONs/glycerol–water-based nanofluid was prepared by the two-step method. The stability of the nanofluid was investigated with respect to time. Thermal and electrical conductivity of the prepared nanofluid was examined with different temperatures (25–45 °C) and weight fractions (0.02–0.1 wt%). The nanofluid is found to be stable for more than 5 months. The results showed an enhancement in thermal conductivity of about 4.5 % at 25 °C with a weight fraction of 0.02 %. The improvement was up to 11.7 % with a weight fraction of 0.1 wt% at 45 °C. The electrical conductivity was increased with increasing the weight fraction and temperature. The improvement in electrical conductivity was about 5890 % at 25 °C and 0.1 wt%.     

One-step synthesis of mesoporous silica–graphene composites by simultaneous hydrothermal coupling and reduction of graphene oxide

Silica–graphene oxide composites were synthesized by hydrothermal method with simultaneous functionalization and reduction of graphene oxide (GO) in the presence of mesoporous silica. Two types of silica were used in the study, mesoporous synthetic silica (MSU-F) synthesized by sol-gel method and mesoporous mineral silica (meso-celite) from pseudomorphic synthesis. The infrared spectra of the composites showed the disappearance of the carboxyl peak at 1735 cm^-1 which could be due to the reduction of the –COOH group. The enhancement of the band at 1385 cm^–1 is attributed to the vibration of the Si–O–C=O moiety formed by reaction of the –COOH group of GO and the silanol (Si–OH) of silica. The Raman spectra of the composites show a diminished intensity ratio of D to G band indicating that GO was reduced to graphene sheets. The TEM images demonstrate the coupling of silica to GO surface revealing dense loading of silica on GO in planar structure.     

Hysteresis I–V nature of mechanically exfoliated graphene FET

Graphene is an attractive material for device applications due to its excellent electrical and mechanical properties. The mechanical exfoliation is an attractive method to fabricate graphene devices using mono and multilayer graphene flakes. As the graphene is very sensitive to atmosphere the occurrence of hysteresis and p-doping is common. This paper reports electrical characterization and hysteresis effect of graphene field effect transistor (FET) fabricated using mechanically exfoliated graphene flakes. Raman spectra and atomic force microscopy techniques have been used to examine the quality and thickness of the exfoliated graphene. This fabricated graphene FET has shown hysteresis nature with p-type doping. The possible reason for the observed hysteresis and p-doping has been explained.     

3D-assembled graphene–LiFePO4 frameworks with enhanced electrochemical performance

In the on-going development of power sources and energy-storage devices, achieving both high power and large energy capacity with a high discharge rate is still a great challenge. In this paper, three dimension assembled graphene–LiFePO₄ (G–LFP) composites were prepared by one-step hydrothermal method. LiFePO₄ (LFP) particles became smaller and were dispersed uniformly on the graphene sheets after compositing with graphene. Compared to the pristine LFP, the electrochemical properties of the G–LFP are greatly improved, especially the rate capability and the cyclic performance. At 10 C, the G–LFP holds nearly 80 % of the initial capacity and has a flat voltage platform, while for the LFP, its capacity drops down to 65 % and its voltage platform is not noticeable. After 600 cycles at 10 C, the specific capacity of the G–LFP decreases from 135 to 125 mA hg^?1 with a capacity loss of 5.1 %, while it drops from 105  to 86  mA hg^?1 with a capacity loss of 30 % for the LFP. The reason for the improvement of the electrochemical performances could be ascribed to the introduction of graphene which enhances the conductivity and diminishes the LFP size which improves the diffusion of lithium ions.     

Gold nanoparticles–graphene hybrids as active catalysts for Suzuki reaction

Graphene was successfully modified with gold nanoparticles in a facile route by reducing chloroauric acid in the presence of sodium dodecyl sulfate, which is used as both a surfactant and reducing agent. The gold nanoparticles–graphene hybrids were characterized by high-resolution transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction and energy X-ray spectroscopy. We demonstrate for the first time that the gold nanoparticles–graphene hybrids can act as efficient catalysts for the Suzuki reaction in water under aerobic conditions. The catalytic activity of gold nanoparticles–graphene hybrids was influenced by the size of the gold nanoparticles.     

Tunable unidirectional light transmission in a graphene–metal hybrid metamaterial

Graphene’s unique properties, such as strong plasmonic response and electrostatic doping, enable control over the properties of light in an active way. In this paper, we propose a graphene–metal hybrid metamaterial, which exhibits tunable wideband unidirectional light transmission. The hybrid metamaterial consists of a complementary split-ring graphene and a metallic grating. Unidirectional optical transmission with a wide bandwidth of 14.8% of the central frequency at 29.3?THz and a large tuning range of 6.6?THz is found to be achievable in simulations. The light reflection and graphene absorption are shown to be the major factors limiting the efficiency of unidirectional transmission. A large electron scattering time of graphene is beneficial for improving the transmission efficiency. The graphene–metal hybrid metamaterial enables active control over the propagation of light, which could be of interest for infrared isolation, polarization transformation, etc.     

The photo-electrochemical studies of Eu doped yttrium orthovanadate–zinc oxide–reduced graphene oxide nanohybrid

A new class of nanostructured photo-electrocatalyst Eu³⁺ doped yttrium orthovanadate–zinc oxide–reduced graphene oxide (YVO₄:Eu³⁺–ZnO–RGO) nanohybrid was developed by a simple electrostatic self-assembly at room temperature, using ZnO, YVO₄:Eu³⁺ and RGO as building blocks. Interaction among YVO₄:Eu³⁺, ZnO and RGO is indicated by variation in hydrodynamic diameter (H_D) and zeta potentials of the products as compared to their individual components, thus suggesting that YVO₄:Eu³⁺–ZnO–RGO is a nanohybrid and not a physical mixture. Electrochemical response of this nanohybrid towards the redox couple of Fe(CN)₆^3−/4− was investigated before and after UV irradiation. Apart from quenching of the green emission of ZnO in photoluminescence spectrum, which serves as a probe to monitor the interfacial electron transfer from excited ZnO to RGO, degradation in electrochemical redox process provides an additional path to monitor interfacial electron transfer.     

Tribological performance of carbon nanotube–graphene oxide hybrid/epoxy composites

An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr.     

Molecular dynamics simulations of the rheological properties of graphene–PAO nanofluids

Graphene is a promising additive for lubricants. The rheological properties of graphene nanofluids have a significant impact on the tribological performance of base oil. In this case, rheological properties including viscosity, density, mean square displacement and diffusion coefficient of graphene–PAO nanofluids were investigated by using the nonequilibrium molecular dynamics simulations in order to understand the effects of graphene on the rheological properties of base oil under extreme conditions. The molecular dynamics model was validated according to the experimental and numerical statistics reported by other researchers. The simulation results reflected that the viscosity of base oil was effectively improved by adding graphene nanoparticles. As the concentration of graphene increased, the viscosity of nanofluids becomes higher. However, the diffusion coefficient reached its highest value (3.73?×?10^?9 m²/s) with nanofluids containing two pieces of graphene in the system. Furthermore, we found that the graphene played a more significant role in enhancing the viscosity of base oil at high temperature and pressure. The viscosity was especially improved by 290.2% at 0.1 MPa, 500 K. The boiling point of the base oil became higher than 800 K after adding graphene. To our best knowledge, this work is the first study of the rheological properties of graphene–PAO nanofluids using molecular dynamic simulations.     

Reduced graphene oxide–nickel oxide composites with high electrochemical capacitive performance

Reduced graphene oxide (RGO)–NiO composites have been fabricated by a simple solvothermal route starting with graphite oxide (GO). The morphology, composition and microstructure of the as-obtained samples are systematically characterized by thermogravimetric (TG) analysis, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Moreover, the electrochemical performances of composites were evaluated by cyclic voltammogram (CV) and galvanostatic charge–discharge. Interestingly, it was found that the electrochemical performance of the composites could be affected by the mass ratio between RGO and NiO. The composite with the mass ratio up to 79:21 (NiO:RGO) exhibits the highest specific capacitance of 576 F g⁻¹ at 1 A g⁻¹, which is much higher than that of pure NiO (240 F g⁻¹) and pure RGO (98 F g⁻¹). In addition, the cycling measurements showed that RGO–NiO composite exhibited excellent cycling stability with no decay in the available capacity over 1100 cycles. The enhancement in specific capacitance and cycling stability may be attributed to the increased electrode conductivity owing to RGO network, the increased effective interfacial area between NiO and the electrolyte, as well as the contact area between NiO and RGO.     

Highly efficient photocatalytic performance of graphene–Ag3VO4 composites

In the present paper, graphene–Ag₃VO₄ composites with broad-spectrum response were prepared by hydrothermal method, which performed high photocatalytic activity in decomposing Rhodamine B under visible light irradiation. The graphene content exhibited an obvious influence on the photocatalytic activity. Composite with 5 wt% graphene possessed the highest activity: the degradation rate reached about 92.3 %, which was nearly 1.5 times higher than that of the pure Ag₃VO₄. The enhancement of the photocatalytic activity was attributed to the synergetic effect between graphene and Ag₃VO₄ particles. Here, graphene was served as an excellent electron acceptor and transporter, which markedly decreased the recombination efficiency of electron–hole pairs and accelerated the degradation process.     

Preparation and corrosion behavior of Ni and Ni–graphene composite coatings

The graphite oxide was synthesized using the Hummers method, and then it was reduced by hydrazine hydrate to obtain graphene. It was characterized with UV (ultra violet), IR (infra red), XRD (X-ray diffraction) spectra and SEM (scanning electron microscope) images. The composite coating of Ni–graphene on mild steel specimens was obtained by the electrodeposition technique. The composite coating was subjected to various electrochemical tests to know its corrosion behavior and compared with pure Ni coating. The EIS (electrochemical impedance spectroscopy) was performed to confirm the corrosion resistance property. The composite film was studied by recording its XRD and SEM. The crystallite size, texture coefficients and hardness of coating was measured.     

Effect of strain rate on the fracture behaviour of epoxy–graphene nanocomposite

In this study, epoxy-based nanocomposite was fabricated by the addition of graphene nanosheet via a solution casting method. To investigate the effect of strain rate on tensile properties of epoxy, tensile tests were done on standard samples at different strain rates (0.05–1 min^?1). The role of strain rate and presence of graphene on fracture behaviour of epoxy were also studied by investigation of the fracture surfaces of some samples by scanning electron microscopy (SEM). Finally, Eyring’s model was performed to clarify the role of strain rate on activation volume and activation enthalpy of epoxy. The results of tensile tests showed a maximum strength of epoxy–graphene nanocomposite at the graphene wt% of 0.1%. Tensile strength of epoxy obviously improved with increasing strain rate, but tensile strength of epoxy/graphene nanocomposite sample was less sensitive. Fracture micrographs showed that the mirror zone of the fracture surface of epoxy diminished by increasing strain rate or addition of graphene; and final fracture zone also became rougher. Finally, by investigation of the activation enthalpies, it was showed that much higher enthalpy was needed to fracture the nanocomposite sample, as the activation enthalpy changed from 41.54 for neat epoxy to 67.34 kJ mol^?1 for EP–0.1% GNS sample.     

Adsorption and photocatalysis removal of fulvic acid by TiO2–graphene composites

The adsorption and photocatalysis of natural organic matter, fulvic acid (FA), by TiO₂–graphene (T–G) composites under UV₂₅₄ was investigated in this study. A one-step solvothermal reaction of graphene oxide (GO) and titanium(IV) butoxide (Ti(OBu)₄) in an ethanol solvent was used to prepare T–G composites. During the solvothermal process, both of the reduction of GO and depositing of T nanoparticles were achieved. Field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were applied to investigate the morphologies and structures of the as-prepared samples. Results from this study indicated that the as-prepared T–G composites exhibited great adsorptivity and photocatalytic activity of FA. Two removal mechanisms have been identified as significant for FA aqueous interacting with T–G composites: surface adsorption and photocatalytic degradation. It is revealed that the photocatalytic degradation of FA is correlated to surface adsorption, an effective surface adsorption resulting in a quick degradation.     

Is graphene aromatic?

We analyze the chemical bonding in graphene using a fragmental approach, the adaptive natural density partitioning method, electron sharing indices, and nucleus-independent chemical shift indices. We prove that graphene is aromatic, but its aromaticity is different from the aromaticity in benzene, coronene, or circumcoronene. Aromaticity in graphene is local with two π-electrons delocalized over every hexagon ring. We believe that the chemical bonding picture developed for graphene will be helpful for understanding chemical bonding in defects such as point defects, single-, double-, and multiple vacancies, carbon adatoms, foreign adatoms, substitutional impurities, and new materials that are derivatives of graphene.      

Mesoporous titanium dioxide@ zinc oxide–graphene oxide nanocarriers for colon-specific drug delivery

In this project, TiO₂@ZnO nanoparticles core–shell nanostructured and titanium dioxide@ mesoporous zinc oxide–graphene oxide (TiO₂@ZnO–GO) hybrid nanocomposites as controlled targeted drug delivery systems were synthesized by a facile sono-chemical method. We prepared a novel mesoporous and core–shell structure as a drug nanocarrier (NCs) for the loading and pH-responsive characteristics of the chemotherapeutic curcumin. The structure, surface charge, and surface morphology of NCs were studied using with X-ray diffraction, Fourier transform infrared spectroscopy, dynamic light scattering, brunauer–emmett–teller, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SEM and TEM images of NCs show the uniform hexagonal mesoporous morphology with average grain size of about ～ 190 nm. The drug loading was very high about 16 and 19 for TiO₂@ZnO and TiO₂@ZnO–GO, respectively. The NCs showed pH-dependent drug release behavior. Drug release from TiO₂@ZnO–GO in neutral pH were higher than in acidic medium, due to anionic charge of GO nanosheet. MTT assay results showed that the curcumin-loaded NCs showed significant toxicity due to which cell viability reduced to below 50% at 140 μg/mL concentration, thereby confirming its anticancer effects. The goal of this study is the application of water-dispersed TiO₂@ZnO–GO with pH-dependent release properties for design a new drug delivery carrier.