Exfoliated Graphene Oxide Research Articles

Thermally exfoliated graphene oxide reinforced polycaprolactone-based bactericidal nanocomposites for food packaging applications

ABSTRACT The inherent biodegradable of PCL is a major challenge for its use in various commercial applications. Thermally exfoliated graphene oxide (TEGO) reinforced polycaprolactone (PCL) based bio-composite films were prepared by solution casting method. Extended probe ultrasonication was employed to ensure efficient dispersion of TEGO. The microstructure and properties of the obtained PCL/TEGO bio nanocomposite films were investigated by FTIR, SEM, XRD, TGA and antimicrobial activity. The effect on water absorption properties and antimicrobial activity of the biopolymer in presence of TEGO were also investigated. The SEM results showed that TEGO was successfully dispersed in PCL matrix generating a porous microstructure. Moreover, incorporation of TEGO particles lead to enhancement of water absorption capacity while decrease in the density. The out-turn (effect) of the functionalized TEGO reinforcement on the thermal and water absorption properties of PCL/TEGO samples were also studied and compared with PCL films.

Rheology of graphene oxide suspended in yield stress fluid

• Suspensions of graphene oxide (GO) in Carbopol are also elastic yield stress fluids. • Addition of GO nanosheets in Carbopol decreases viscosity and elasticity. • Oxidation level of GO affects the rheological behavior. • Higher level of interaction of the GO/water system oxidized for 96 h. This work investigates the rheology of graphene oxide (GO) suspension on a yield stress model fluid. The effects caused by the variation of the GO concentration in the suspension and by the amount of oxygenated groups pendant present on the nanosheets surface, on the rheology of the suspensions were evaluated. The dispersant used was an aqueous solution of Carbopol® Ultrez 10. This is a transparent, nontoxic elastic yield stress fluid. GO nanosheets were produced from synthesis of graphite oxide (GrO) by modified Hummers method, and the nanosheets were characterized by XRD, Raman, FTIR, TEM and AFM techniques. The rheological behavior of these suspensions was characterized by oscillatory and steady-state flow experiments. The GO structure characterization shows that oxygenated functional groups were incorporated in its graphite surface in different levels after using two distinct times of oxidation. GO oxidized for 96 h (GO 96 h) showed greater interplanar distance and also presented few layers when compared with GO oxidized for 2 h (GO 2 h). The GO exfoliation process directly into the aqueous dispersion of Carbopol® showed to be an effective method. As for the pure Carbopol solutions, the GO suspensions were well modeled by the Hershel-Bulkley equation. The increase of GO concentration in the suspensions impairs the level of fluid structure and leads to a decrease in viscosity, yield stress, and elasticity. When compared, the GO 96 h promoted a lower decrease in viscosity, yield stress and elasticity than the GO 2 h suspension. For the suspension with a higher concentration of GO 96 h, it was observed the appearance of hysteresis at low shear rates. These results show that small changes in the GO nanosheets surface can significantly influence the rheological responses of a non-Newtonian fluid.

Scalable fabrication of high‐performance graphene/polyamide 66 nanocomposites with controllable surface chemistry by melt compounding

AbstractScalable and ease fabrication of high‐performance graphene reinforced polyamide 66 (PA66) nanocomposites by melt‐mixing were achieved by selecting ideal graphene reinforcement having high C/O ratio. In this study, single‐layer amine functionalized reduced graphene oxide and multi‐layer thermally exfoliated graphene oxide (TEGO) were used to investigate the influence of surface chemistry and dispersion state on crystallization behaviors, mechanical, and thermal properties of graphene reinforced PA66 nanocomposites. Both types of graphenes acted as nucleating agent but TEGO showed the better performance due to its intercalated structure formation mechanism and efficient viscous flow during melting. Mechanical results indicated that 0.5 wt% TEGO based PA66 nanocomposite showed the highest tensile properties by increasing tensile modulus and tensile strength up to 45% and 16.1%, respectively. In addition, TEGO reinforced nanocomposites showed more stable viscoelastic behavior by reaching a plateau at high temperatures and restraining long‐range motion of polymer chains.

Mixed Dye Removal Efficiency of Electrospun Polyacrylonitrile-Graphene Oxide Composite Membranes.

Exfoliated graphene oxide (GO) was reliably modified with a cetyltrimethylammonium chloride (CTAC) surfactant to greatly improve the dispersity of the GO in a polyacrylonitrile (PAN) polymer precursor solution. Subsequent electrospinning of the mixture readily resulted in the formation of GO–PAN composite nanofibers containing up to 30 wt % of GO as a filler without notable defects. The absence of common electrospinning problems associated with clogging and phase separation indicated the systematic and uniform integration of the GO within the PAN nanofibers beyond the typical limits. After thoroughly examining the formation and maximum loading efficiency of the modified GO in the PAN nanofibers, the resulting composite nanofibers were thermally treated to form membrane-type sheets. The wettability and pore properties of the composite membranes were notably improved with respect to the pristine PAN nanofiber membrane, possibly due to the reinforcing filler effect. In addition, the more GO loaded into the PAN nanofiber membranes, the higher the removal ability of the methylene blue (MB) and methyl red (MR) dyes in the aqueous system. The adsorption kinetics of a mixed dye solution were also monitored to understand how these MB and MR dyes interact differently with the composite nanofiber membranes. The simple surface modification of the fillers greatly facilitated the integration efficiency and improved the ability to control the overall physical properties of the nanofiber-based membranes, which highly impacted the removal performance of various dyes from water.

Thermally reduced graphene oxide as an electrode for CDI processes: A compromise between performance and scalability?

Capacitive deionization (CDI) is an alternative water desalination technology, which was investigated extensively in the last decade. The choice of electrodes' materials plays a major role in the electrosorption performance, affecting the whole desalination process. Graphene-based nanostructures in various types were extensively studied owing to their superior inherent physico-chemical properties. Whereas excellent electrosorption performance was reported – expressed in terms of salt adsorption capacity (SAC) or average salt adsorption rate (ASAR) – the cost-benefit of graphene-based electrodes, considering total production cost and much lower price of commercial activated carbon, is still controversial.Here, we explore partially exfoliated thermally reduced graphene oxide (GO) – denoted as PE-rGO – prepared by scalable low-temperature thermal exfoliation of GO under air atmosphere. PE-rGO displays a “paper-like” structure with nanoscale pores. By the construction of a lab-scale system, a few grams of product were produced in one batch. A PE-rGO electrode assembled in membrane-CDI three-electrode configuration showed moderate to high SAC of around 13 mg/g under potential window of 0–550 mV versus Ref. electrode in 2000 ppm NaCl solution. However, the energy consumption was shown to be nearly constant with increasing ASAR. This has significant implications for the energy consumption and the projected capital costs.

Industrial manufacturing and characterization of multiscale CFRP laminates made from prepregs containing graphene-related materials

The introduction of graphene-related materials (GRMs) in carbon fibre-reinforced polymers (CFRP) has been proved to enhance their mechanical and electrical properties. However, methodologies to produce the 3-phase materials (multiscale composites) at an industrial scale and in an efficient manner are still lacking. In this paper, multiscale CFRP composites containing different GRMs have been manufactured following standard procedures currently used in the aerospace industry with the aim to evaluate its potential application. Graphite nanoplateletelets (GNPs), in situ exfoliated graphene oxide (GO) and reduced graphene oxide (rGO) have been dispersed into an epoxy resin to subsequently impregnate aeronautical grade carbon fibre tape. The resulting prepregs have been used for manufacturing laminates by hand lay-up and autoclave curing at 180 °C. A broad characterization campaign has been carried out to understand the behaviour of the different multiscale laminates manufactured. The degree of cure, glass transition temperature and degradation temperature have been evaluated by thermal evolution techniques. Similarly, their mechanical properties (tensile, flexural, in-plane shear, interlaminar shear and mode I interlaminar fracture toughness) have been analysed together with their electrical conductivity. The manufacturing process resulted appropriated for producing three-phase laminates and their quality was as good as in conventional CFRPs. The addition of GO and rGO resulted in an enhancement of the in-plane shear properties and delamination resistance while the addition of GNP improved the electrical conductivity.

Highly Exfoliated Graphene Oxide with Enhanced Carbonyl Content and Facile Amine Functionalization for Biomedical Applications

A reroute process of Hummers’ method was carried out to reduce some steps in the synthesis of highly exfoliated graphene oxide (HEGO). Using pure KMnO4 and NaNO3 in concentrated H2SO4, HEGO was suc...

Fabrication of Few-Layer Graphene-Supported Copper Catalysts Using a Lithium-Promoted Thermal Exfoliation Method for Methanol Oxidative Carbonylation.

Exfoliation of graphene oxide (GO) via thermal expansion is regarded as the most promising approach to obtain few-layer graphene (FLG) in bulk. Herein, we introduce an efficient strategy for improving the exfoliation process by adding a tiny amount of lithium nitrate in the precursors, which significantly enhances the removal of oxygen-containing functional groups and produces 1-2 layer graphene. FLG-supported highly dispersed Cu nanoparticles (NPs, ≈4.2 nm) can be further synthesized through exfoliating the mixture of GO, lithium nitrate, and copper(II) nitrate, which displayed superior catalytic activity and stability in the synthesis of dimethyl carbonate (DMC) using liquid methanol oxidative carbonylation. The characterization results demonstrate that during the thermal expansion process, lithium nitrate was decomposed to Li2O and immediately reacted with CO2 released by the decomposition of GO to form stable Li2CO3, which promotes efficient charge transfer and produces Cuδ+ (0 < δ < 1) species in the Cu/Li-PGO catalyst. Density functional theory calculations prove that the presence of Cuδ+ markedly facilitates CO adsorption over the resulting catalyst and causes a decrease of the energy barrier of the rate-limiting step for DMC formation (CO insertion). These findings give a theoretical explanation of the enhanced catalytic performance of the Cu/Li-PGO catalyst. The present work provides a simple and practical avenue to the exfoliation of graphene and the dispersions of metal NPs on graphene sheets.

Covalent functionalization of reduced graphene oxide using azido-terminated poly(2-isopropyl-2-oxazoline)

Azido-Terminated Poly(2-isopropyl-2-oxazoline)(N3-PIPOZ) was prepared and it was then functionalized onto reduced graphene oxide (rGO). rGO was prepared from the reduction of graphene oxide (GO) by using hydrazine. The exfoliation of GO was measured using UV-Vis Spectroscopy. As a result, covalent functionalized reduced graphene (rGO-PIPOZ) with good solubility was successfully produced using grafting-on technique. Fourier transform infrared (FTIR) and thermogavimetric analysis(TGA) results proved the attachment of PIPOZ macromolecules onto rGO. rGO-PIPOZ showed best solubility in methanol (MeOH). The production of rGO- PIPOZ can be facilitated to a broad range application of graphene such as in polymer nanocomposites and lithium ion batteries.

Solar Exfoliated Graphene Oxide: A Platform for Electrochemical Sensing of Epinephrine

Introduction:In this study, solar exfoliated graphite oxide modified glassy carbon electrode was used for the anodic oxidation of epinephrine in a phosphate buffer medium at pH7. The modified electrode showed fast response and sensitivity towards Epinephrine Molecule (EP). The electrode was characterized electrochemically through Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV). Area of the electrode enhanced three times during modification and studies reveal that the oxidation process of EP occurs by an adsorption controlled process involving two electrons. The results showed a detection limit of 0.50 ± 0.01μM with a linear range up to 100 μM. The rate constant calculated for the electron transfer reaction is 1.35 s-1. The electrode was effective for simultaneous detection of EP in the presence of Ascorbic Acid (AA) and Uric Acid (UA) with well-resolved signals. The sensitivity, selectivity and stability of the sensor were also confirmed.Methods:Glassy carbon electrode modified by reduced graphene oxide was used for the detection and quantification of epinephrine using cyclic voltammetry and differential pulse voltammetry.Results:The results showed an enhancement in the electrocatalytic oxidation of epinephrine due to the increase in the effective surface area of the modified electrode. The anodic transfer coefficient, detection limit and electron transfer rate constant of the reaction were also calculated.Conclusion:The paper reports the determination of epinephrine using reduced graphene oxide modified glassy carbon electrode through CV and DPV. The sensor exhibited excellent reproducibility and repeatability for the detection of epinephrine and also its simultaneous detection of ascorbic acid and uric acid, which coexist in the biological system.

Improvement in Barrier Properties Using a Large Lateral Size of Exfoliated Graphene Oxide

The gas barrier properties of polymers can be improved by reducing gas diffusivity and solubility by using graphene oxide (GO) of various lateral sizes (~3, ~25, ~45 µm). By using GO, the gas diffusion path of the polymer was effectively increased. To reduce the solubility, alkylated GO (AGO) was synthesized by an SN2 reaction between octyl amine and GO. The hydrophobicity of AGO was confirmed through contact angle measurements, and octylamine on the AGO surface was identified by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. When GO and AGO with comparatively large lateral size (~45 µm) were homogeneously dispersed in polyvinyl alcohol (PVA) and polyvinylidene chloride (PVDC), respectively, the oxygen transmission rates (OTR) of resulting PVA/GO and PVDC/AGO composite films were significantly reduced. The OTR of PVA/GO composite film reduced from 1.9 × 100 to 5.0 × 10−2 cm3/m2·day as compared to neat PVA; whereas, the OTR of PVDC/AGO composite film reduced from 1.2 × 100 to 6.8 × 10−1 cm3/m2·day. In addition, the water vapor transmission rate (WVTR) of the PVDC/AGO composite film remarkably decreased from 1.4 g/m2·day (neat PVDC) to ∼5.5·10−1 g/m2·day, where the lateral size of AGO was insignificant. The WVTR results of PVDC/AGO composite films are in contrast to those for PVA/GO composite films, which did not demonstrate any improvement in WVTR with the addition of GO. Based on the experimental results, it was determined that oxygen permeability and water vapor permeability are more affected by diffusivity and solubility, respectively.

Incorporation of Graphene and Graphene-Based Materials into Membranes As an Alternative Electrolyte Configuration for Low and High Temperature Polymeric Electrolyte Membranes Fuel Cells

The electrolyte plays an important role in the Membrane Electrode Assembly (MEA) of Polymeric Electrolyte Membranes Fuel Cells, (PEMFCs), having three main functions, to act as ion conductor, electronic insulator and a separator for the reactant gases [1]. The electrolyte is a Proton Exchange Membrane and Nafion is the most widely used polymeric membrane in this technology. However, because its particular structure it requires a good hydration to lead a high proton conductivity, which limit the operating temperature to lower than 100 oC. Poly[2,2′-m-(phenylene)-5,5′-benzimidazole (PBI) membrane doped with Phosphoric Acid, has been presented as an alternative to Nafion membranes allowing higher operating temperatures, 200oC, which enhance the kinetics of the reactions. However, during the operation of High Temperature Fuel Cells (HT-PEMFCs) these membranes suffer Phosphoric Acid leaching leading to a low proton conductivity and degradation of the fuel cell [2].The 2D honeycomb lattice of Graphene provides this material particular properties such as high surface area, exceptionally high electrical conductivity, good chemical and thermal stability and excellent barrier properties, which make it a potential material for a large number of applications. In addition to this [1], Hu. et al. [3] have demonstrated that Single Layer Graphene present a high proton conductivity being at the same time a barrier for other elements, which makes this material a potential electrolyte for PEMFC. However, SLG has some drawbacks notably due to the complex process to produce it and its high cost. These limitations leave an open window to Graphene based materials such as Graphene Oxide, which shows very attractive properties to act as filler in Nafion and PBI membranes due to its chemical functionalization and its non-porous structure, which provides additional resistance for mass transport and increases the tortuosity of the permeation pathways leading to higher selectivity [1].Here we will describe the work carried out at University of Mancheschester incorporating SLG and GO composite membranes into the MEA of both PEM Fuel Cells, Low Temperature (LT-PEMFC) and HT-PEMFC. The addition of the SLG produced by CVD into the MEA of LT-PEMFC has demonstrated no change in the proton conductivity, supporting the hypothesis that SLG is a good proton conductor. In addition, for a particular LT-PEMFC, Direct Methanol Fuel Cells (DMFC), a decreasing of the methanol crossover has found leading a significant enhancement of the power density [4]. SLG has been also incorporated into the MEA of HT-PEMFC, which use PBI membrane instead of Nafion, to evaluate its proton conductivity and barrier properties, this time to stop the Phosphoric Acid leaching.Although positive results have been reported by adding SLG into the MEAs, a different approach has been conducted by the development of GO-composite membranes also for both type of PEMFC. Exfoliated Graphene Oxide has been synthesized by electrochemical exfoliation of graphite and has been incorporated as a filler into two different of matrix polymer, Nafion and PBI, to evaluate their performance in both PEMFC, high and low temperature.

Synthesis and Applications of High Quality Graphene Made By a Novel Electrochemical Exfoliation of Natural Graphite Flakes

Since its discovery in 2004, Graphene has been widely study for different applications, noticeable for electrochemical energy devices, due to its excellent properties as a barrier material, electrical conductivity or high surface area. However, it is still an expensive material since it cannot be produced in a large scale. Graphene based materials such as Graphene oxide (GO) or Reduced Graphene Oxide (rGO) also present similar properties than Graphene and can be produce in a more economical way [1]. However, traditional method to produce GO, Hummer’s method, which base on chemical exfoliation of graphite, is a long and tedious process which requires the use of strong oxidants and hazardous chemicals leading environmental pollution that cannot be repaired [2,3]. Recently, electrochemical exfoliation of graphite to produce GO has attracted more and more attention due its environmental protection, low price, easy process and high efficiency [4-7]. Since natural graphite is mostly in the form of flakes and its tiny size is not conducive to its direct use in electrochemical exfoliation, currently, electrochemical exfoliation is mostly made of graphite foil, graphite rod and other graphite processed products. These materials are obtained by using processes such as chemical, thermodynamic, and mechanical compression, leading in physical or chemical changes that alter their original properties or structure. There are also some attempts to use natural graphite flakes for electrochemical exfoliation [8,9]. However, this makes electrochemical exfoliation require more voltage, longer time and less yield. In this work, we present novel design reactor to perform electrochemical exfoliation using natural graphite flakes as raw materials. By using ammonium sulphate as electrolyte, electrochemical exfoliation of natural graphite flakes can be done at low voltage with short time. This achievement also enables the comparison of electrochemical exfoliation products with different raw materials (graphite foil and natural graphite flakes) at the same exfoliation voltage and the same exfoliation time. We explored the properties of the product by raman spectroscopy, ultraviolet–visible spectroscopy (UV-VIS), fourier-transform Infrared Spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Thermogravimetric analysis (TGA), four-probe method and contact angle measurement. We have found that by combining natural graphite flakes with the reactor, the product obtained is significantly different from the exfoliated product based on graphite foil, achieving better oxidation, better dispersion in deionized water, more defects and greater yield. In addition, the special structure of the reactor allows the exfoliation time to be controlled, and we also compare the products obtained at different exfoliation times. The Exfoliated Graphene Oxide (EGO) obtained it has been used as a filler material in proton exchange membranes for hydrogen fuel cells as well as a support material for electrocalyst to enhance the kinetics for the reactions which take place in these fuel cells.

Electrochemical Characterization of Graphene-like Materials Obtained By Electrochemical Exfoliation of Graphite

Graphene and its derivatives have been widely used in electrochemical sensors due to their unique properties, including high electron conductivity and large surface area [ 1 ], which are expected to significantly improve the sensitivity of sensors. With oxygen functional groups located at the edge and at the surface of the graphene sheets, graphene oxides exhibit better dispersion in water, biocompatibility, and higher affinity for specific molecules than graphene. [ 2 - 3 ] The electrochemical exfoliation of graphite in aqueous solution is a fast and easy method to obtain large amounts (1-2 g) of graphene oxide materials with tunable composition[ 4 ]. In this respect, it is necessary to investigate the physicochemical and electrochemical properties of electrochemically exfoliated graphene oxide (EGO) in order to choose the most suitable material to be used in electrochemical sensors.Here, we report a simple and facile method for the electrochemical characterization of a series of EGOs produced by electrochemical exfoliation of graphite [ 4 ] under different experimental conditions (electrolyte, applied potential difference, and thermal treatment). First, the EGOs were sonicated in water for three hours to obtain a uniform dispersion. Then, the EGO sheets were successfully assembled on a glassy carbon electrode (GCE) through an aminophenyl-film linker (AP) by the electrostatic attraction between positively charged amine groups and the negatively charged EGO sheets, and through the pi-pi stacking as well, Figure 1. [ 5 ] The electrodes modified with the EGOs (EGO/AP/GCE) were electrochemically characterized by cyclic voltammetry with 1 mM [Fe(CN)6]3-/4- redox couple, Figure 1, to determine the electrochemical surface area (ESA) through the Randles-Sevcik equation and to calculate the standard rate constant of electron transfer (k°) by the Nicolson method [ 6 ]. As a result, the synthesis conditions leading to the EGO with the highest electrochemical surface area and the highest standard rate constant were identified. Finally, the electrochemical response of the EGO materials was correlated to their chemical composition and structural defects determined by X-ray photoelectron (at%Oxygenated-C/at%C) and Raman (ID/IG) spectroscopies, respectively. Both of the ESA and k° show a Vulcano dependence with the potential difference applied during the electrochemical exfoliation of graphite. The origin behind these trends will be presented and discussed.References(1) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Science 2004, 306, 666-669.(2) Deng, X.; Tang, H.; Jiang, J. Analytical and Bioanalytical Chemistry 2014, 406, 6903-6916.(3) Lee, J.; Kim, J.; Kim, S.; Min, D.-H. Advanced Drug Delivery Reviews 2016, 105, 275-287.(4) Ossonon, B. D.; Bélanger, D. Carbon 2017, 111, 83-93.(5) Elshafey, R.; Siaj, M.; Tavares, A. C. Analyst 2016, 141, 2733-2740.(6) Nicholson, R. S. Analytical chemistry 1965, 37, 1351-1355. Figure 1

Graphene Oxide Carboxymethylcellulose Nanocomposite for Dressing Materials.

Sore, infected wounds are a major clinical issue, and there is thus an urgent need for novel biomaterials as multifunctional constituents for dressings. A set of biocomposites was prepared by solvent casting using different concentrations of carboxymethylcellulose (CMC) and exfoliated graphene oxide (Exf-GO) as a filler. Exf-GO was first obtained by the strong oxidation and exfoliation of graphite. The structural, morphological and mechanical properties of the composites (CMCx/Exf-GO) were evaluated, and the obtained composites were homogenous, transparent and brownish in color. The results confirmed that Exf-GO may be homogeneously dispersed in CMC. It was found that the composite has an inhibitory activity against the Gram-positive Staphylococcus aureus, but not against Gram-negative Pseudomonas aeruginosa. At the same time, it does not exhibit any cytotoxic effect on normal fibroblasts.

Comparing Graphene Oxide and Reduced Graphene Oxide as Blending Materials for Polysulfone and Polyvinylidene Difluoride Membranes

Graphene is a single atomic plane of graphite, and it exhibits unique electronic, thermal, and mechanical properties. Exfoliated graphene oxide (GO) contains various hydrophilic functional groups, such as hydroxyl, epoxide, and carboxyl groups, that can modify the hydrophobic characteristics of a membrane surface. Though reduced graphene oxide (rGO) has fewer functional groups than GO, its associated sp2 structures and physical properties can be recovered. A considerable amount of research has focused on the use of GO to obtain a pristine graphene material via reduction processes. In this study, polysulfone (PSf) and polyvinylidene fluoride (PVDF) membranes that were blended with GO and rGO, respectively, were fabricated by using the immersion phase inversion method and an n-methylpyrrolidone (NMP) solvent. Results showed that the graphene nanomaterials, GO and rGO, can change the pore morphology (size and structure) of both PSf and PVDF membranes. The optimum content of both was then investigated, and the highest flux enhancement was observed with the 0.10 wt% GO-blended PSf membrane. The presence of functional groups in GO within prepared PSf and PVDF membranes alters the membrane characteristics to hydrophilic. An antifouling test and rejection efficiency evaluation also showed that the 0.10 wt% membrane provided the best performance.

Dopamine-functionalized graphene oxide as a high-performance material for biosensing

We describe a nanocomposite material for the electrochemical detection of β-nicotinamide adenine dinucleotide (NADH), a coenzyme involved in redox reactions of all living cells and in the detection of many organic species by electrochemical biosensors. The composite is made of nanosheets of electrochemically exfoliated graphene oxide (EGO) covalently functionalized with dopamine (DP) molecules. The EGODP material finally obtained is rich of 1,2-dihydroxyphenyl moieties and is able to detect NADH at a particular low potential value with higher sensitivity with respect to pristine EGO.To study the effectiveness of 1,2-dihydroxyphenyl moieties in inducing electrocatalytic oxidation of NADH, we combined standard voltammetric techniques with UV–Vis absorption spectroelectrochemistry, which allowed us to measure the variations in composition occurring at the electrode|solution interface, i.e. to measure the consumption rate of NADH.Spectroelectrochemical tests performed by polarising the electrode at a fixed potential value were finally used to compare the performance of EGODP with both EGO and EGO-DP blend (MIX) for the detection of NADH. The covalently functionalized EGO (EGODP) shows sensitivity to NADH up to 300 M−1, around 180 % and 140 % better than either pristine EGO or MIX, respectively.

Experimental and molecular dynamics study on dye removal from water by a graphene oxide-copper-metal organic framework nanocomposite

In this study, a novel copper-based metal-organic framework (Cu-MOF), immobilized on graphene oxide (GO), was fabricated via ultrasonication method. The synthesized GO-Cu-MOF was used as an adsorbent, and the kinetics data for the removal of dye molecules investigated along with the molecular dynamics simulations. Various parameters such as solution temperatures and pH, dye, and adsorbent concentrations were studied to evaluate the performance of the adsorbent in removing a model contaminant based on the real-world water treatment conditions. The synthesized adsorbent was characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Ultraviolet-visible spectroscopy (UV–vis), Brunauer–Emmett–Teller (BET) analysis, and Zeta Potential. The characterization results showed full exfoliation of GO in Cu-MOF. The adsorption kinetic results followed the rapid adsorption process with a pseudo-second-order characteristic. The GO-Cu-MOF exhibited higher adsorption capacity of 173, 251, and 262 mg/g at 25 °C, 45 °C and 65 °C compared to 106, 117 and 142 mg/g adsorption capacity of Cu-MOF at the same temperature. The dye removal experiments suggest that the acidic condition and the higher temperature (65 °C) favors the adsorption of Methylene blue (MB) on GO-Cu-MOF compound. The molecular dynamics simulation performed to calculate the adsorption energy for Cu-MOF and GO-Cu-MOF. The calculated adsorption energy of -323 (kCal/mol), and -119 (kCal/mol) for GO-Cu-MOF and Cu-MOF was in agreement with the experimental data.

Preparation of graphene oxide/natural rubber composites by latex co-coagulation: Relationship between microstructure and reinforcement

Abstract Graphene oxide (GO) has recently attracted substantial interest as a possible reinforcing agent for next generation rubber composite materials. In this research, GO was incorporated in natural rubber (NR) composites through latex co-coagulation technique. The microstructures of GO/NR composites were characterized through a combination of transmission electron microscope, scanning electron microscope, X-ray diffraction, Fourier transform infrared spectroscopy, and Differential scanning calorimeter. The results showed that highly exfoliated GO sheets were finely dispersed into NR rubber matrix with strong interface interaction between GO and NR. The mechanical properties of the GO/NR composites were further evaluated. The results showed that the tensile strength, tear strength and modulus can be significantly improved at a content of less than 2 phr. Especially, GO exhibited specific reinforce mechanism in NR due to the stress-induced crystallization effects of NR. The stress transfer from the NR to the GO sheets and the hindrance of GO sheets to the stress-induced crystallization of NR were further displayed in stress–strain behavior of GO/NR composites. These enhanced properties were attributed to the high surface area of GO sheets and highly exfoliated microstructures of GO sheets in NR.

Performance improvement of organic resistive memories by exploiting synergistic layered nanohybrid dispersed polymer composites

Functionalized layered nanohybrid materials have been thoroughly explored in numerous practical applications including photocatalysis, supercapacitors, and sensors, and have inherent potential to excel in the field of organic resistive random access memory devices as well. Herein, we report an efficient, facile, and cost-effective in situ synthesis route to prepare a layered nanohybrid by grafting cadmium sulfide (CdS) nanorods with exfoliated graphene oxide (GOs) sheets via the one-step hydrothermal functionalization technique. Such a nanohybrid material displays advantageous characteristics possessed by them due to the formation of organic–inorganic heterojunctions at their interface. Sandwiched devices, with a configuration of ITO/reduced graphene oxide–CdS/poly-methyl methacrylate (PMMA)/Al, are fabricated by dispersing different wt. % of the layered nanohybrid in a poly-methyl methacrylate (PMMA) matrix. Detailed current density vs voltage (J–V) studies exhibit excellent bipolar resistive switching characteristics reaching a very low set voltage of ∼−0.48V, high current ION/IOFF ratios of ∼106, and ultralow set/reset power densities of ∼10−8/10−6W/cm2 for devices containing 0.4 wt. % nanohybrid nanofillers. Partial reduction of GOs and the formation of heterojunctions during the synthesis process undoubtedly boost the resistive memory performances resulting from the synergistic effect in layered nanohybrid materials. The fabricated devices have been subjected to various analyses in order to test their stability, repeatability, and reliability, all of which have been found to display encouraging results.