Surface Of Graphene Oxide Nanosheets Research Articles

Morphology Tunable Hybrid Carbon Nanosheets with Solvatochromism.

The tunable photoluminescence of carbon-based nanomaterials has received much attention for a wide range of applications. Herein, a unique, broad-solvatochromic hybrid carbon nanosheet (CNS) synthesized through the hydrothermal carbonization of molecular precursors exploiting graphene oxide as a template is reported, resulting in the formation of clusters of carbon nanorings on the surface of graphene-oxide nanosheets. Under UV and visible-light excitation, the hybrid CNS exhibits tunable emission spanning the wide range of colors in a series of solvents with different polarities. This interesting spectroscopic behavior is found to originate from hydrogen-bonding interactions between CNS and solvents, which eventually induce the morphological transition of CNS from 2D sheets to 3D crumpled morphologies, affecting the lifetimes of emissive states. This novel soft carbon nanostructure may open up a new possibility in tailoring the photophysical properties of carbon nanomaterials.

Structural, mechanical and thermal behaviors of novolac/graphene oxide nanocomposite aerogels

Main microstructural properties of organic aerogels dictate the thermal degradation of these materials. Incorporating of nanomaterials into the structure of organic aerogels can result in controlling and engineering the microstructural characteristics and as a result, the thermal degradation of organic aerogels. Here, the role of graphene oxide (GO) presence on the microstructure and morphology of novolac/GO nanocomposite aerogels is investigated. Although, the presence of GO nanosheets results in an enhancement of the density, but the specific surface area of aerogels increased with the contents of loaded-nanosheets, due to the high available surface area of GO nanosheets. The sol-gel polymerization of novolac resin in the presence of GO nanosheets results in formation of colloidal nanoparticles on the surface of GO nanosheets. Chemical characterizations confirm that the reason behind this phenomenon is the formation of covalent interactions between polymer chains and GO surface. Moreover, the thermal degradation and thermal conductivity behaviors of novolac/GO nanocomposite aerogels are studied here, to investigate the influences of GO presence on the heat-transfer mechanism through the aerogel. Thermal studies approve that the heat transfer depends strongly on the reduction of GO nanosheets, as well as on the contents of loaded-GO. As the contents of loaded-GO reach a percolation threshold, the structural characteristics, and consequently, the mechanism of thermal degradation throughout aerogel structure, change.

Facile One-Pot Green Synthesis and Antibacterial Activities of GO/Ag Nanocomposites

New materials with good antibacterial activity synthesized by simple, environmentally friendly method have attracted numerous research interests. Taking advantage of Ag and graphene oxide (GO), the GO/Ag nanocomposites were prepared by a facile, green “one-pot” reaction to achieve superior antibacterial properties. AgNO3 is as a precursor of Ag nanoparticles (Ag NPs), and the grape seeds extract as an environmentally friendly reducing and stabilizing agent. The as-prepared GO/Ag nanocomposites were characterized by various technologies. The results indicated that the silver ion was reduced by the grade seeds extract and Ag NPs were decorated on the surface of GO nanosheets successfully. The average size of the Ag NPs anchored on the GO surface was 40–50 nm. In this study, we prepared GO/Ag nanocomposites with different Ag NPs to GO ratios and carefully investigated their antibacterial activities. We found that the GO/Ag nanocomposites show better antibacterial activity when the concentration of AgNO3 is 2 mM. GO/Ag nanocomposites have a minimum inhibitory concentration 23.8 μg/mL, lower than bare Ag NPs 25.5 μg/mL. We try to explain the antibacterial mechanism based on optical microscopy observation.

Poly (vinylidene fluoride) dielectric composites with both ionic nanoclusters and well dispersed graphene oxide

Nanostructured polymeric dielectric composites, based on poly (vinylidene fluoride) (PVDF), graphene oxide (GO), and an ionic liquid (IL), 1-vinyl-3-ethylimidazolium tetrafluoroborate ([VEIM] [BF4]), denoted as Nano-PVDF/IL/GO, were fabricated through casting method, electron beam (EB) irradiation and microphase separation processes. Through the strategy, GO nanosheets were dispersed homogeneously in PVDF matrix and the organic nanoclusters formed by microphase separation of IL grafted PVDF (PVDF-g-IL) chain segments tended to adhere onto the surface of GO nanosheets. The Nano-PVDF/IL/GO composites displayed a drastic reduction in dc conductivity compared with PVDF/GO and PVDF/IL/GO composites because of impeding the direct contact between GO nanosheets by the nanoclusters. Furthermore, the mircocapacitors between the adjacent GO nanosheets and nanoclusters contributed the increase of dielectric constant. At the same time, the dielectric loss from the current leakage of GO nanosheets was almost fully eliminated due to the strong interfacial bonding between polymer matrix and fillers which restrained the formation of conductive network. Therefore, we proposed an effective strategy for using the organic nanoclusters to modify the inorganic conductive fillers and impeding the formation of conductive network in the dielectric materials, which paves new possibility to prepare polymer nanocomposites with both high dielectric constant and low dielectric loss.

Molecular Functionalization of Graphene Oxide for Next-Generation Wearable Electronics.

Acquiring reliable and efficient wearable electronics requires the development of flexible electrolyte membranes (EMs) for energy storage systems with high performance and minimum dependency on the operating conditions. Herein, a freestanding graphene oxide (GO) EM is functionalized with 1-hexyl-3-methylimidazolium chloride (HMIM) molecules via both covalent and noncovalent bonds induced by esterification reactions and electrostatic πcation-π stacking, respectively. Compared to the commercial polymeric membrane, the thin HMIM/GO membrane demonstrates not only slightest performance sensitivity to the operating conditions but also a superior hydroxide conductivity of 0.064 ± 0.0021 S cm(-1) at 30% RH and room temperature, which was 3.8 times higher than that of the commercial membrane at the same conditions. To study the practical application of the HMIM/GO membranes in wearable electronics, a fully solid-state, thin, flexible zinc-air battery and supercapacitor are made exhibiting high battery performance and capacitance at low humidified and room temperature environment, respectively, favored by the bonded HMIM molecules on the surface of GO nanosheets. The results of this study disclose the strong potential of manipulating the chemical structure of GO to work as a lightweight membrane in wearable energy storage devices, possessing highly stable performance at different operating conditions, especially at low relative humidity and room temperature.

Cetyltrimethylammonium bromide assisted self-assembly of phosphotungstic acid on graphene oxide nanosheets for selective determination of tryptophan

A one-step method was developed to prepare cetyltrimethylammonium bromide (CTAB) and phosphotungstic acid (PTA)-modified graphene oxide (GO) (PTA/CTAB/GO). In a system containing CTAB, GO, and PTA, negatively charged GO forms stable complex with positively charged CTAB, which assembled on the GO nanosheet surface. And then, with CTAB molecules as the molecular linker, PTA was loaded on CTAB/GO hybrid by electrostatic interaction. The PTA/CTAB/GO was characterized with Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and subsequently used in the construction of tryptophan (Trp) sensor. Compared with the CTAB/GO, PTA/CTAB/GO exhibits better electrocatalytic activity towards the oxidation of Trp, which is attributed to the synergistic effect of PTA and GO. The differential pulse voltammetry (DPV) curve of Trp at PTA/CTAB/GO/glassy carbon electrode (GCE) exhibited two linear dynamic ranges with a detection limit of 0.02 μM (S/N = 3). In addition, the proposed sensor is successfully employed to detect Trp in the real samples with satisfactory results.

Covalently-grafted graphene oxide nanosheets to improve barrier and corrosion protection properties of polyurethane coatings

Surface modification of graphene oxide (GO) has been performed by grafting of polyisocyanate (PI) resin. Results obtained from X-ray photo electron spectroscopy, thermal gravimetric analysis and X-ray diffraction analysis revealed that the PI resin chains were successfully attached onto the surface of GO nanosheets through covalent bonding with hydroxyl and carboxylic groups leading to amides and carbamate esters bonds formation. Subsequently, the PI functionalized GO sheets were incorporated into the polyurethane (PU) matrix. The X-ray diffraction analysis showed that surface modification of GO nanosheets with PI enhanced the level of exfoliation of PI–GO in the PU matrix. Scanning electron microscope analysis showed the enhanced interaction between GO and PU matrix after functionalization by PI resin. The electrochemical impedance spectroscopy and salt spray tests were performed to reveal the effects of addition of 0.1wt.% GO and PI–GO nanosheets on the corrosion protection properties of the PU coating. Also, the adhesion loss of the coatings was obtained by pull-off adhesion test after 30days immersion in 3.5wt.% NaCl solution. It was found that incorporation of 0.1wt.% surface modified GO nanosheets into the PU matrix resulted in significant improvement of the coating corrosion protection properties and ionic resistance.

Toxicology of Graphene Oxide Nanosheets Against Paecilomyces catenlannulatus.

Graphene oxide (GO) nanosheets have been extensively investigated to fabricate the graphene in recent years. The migration of GO nanosheets into the environment could lead to the instability of biological system. In this study, the GO nanosheets were synthesized and were characterized by SEM, high resolution TEM, XRD, Raman, FTIR and XPS techniques. Toxicology testing of GO nanosheets against Paecilomyces catenlannulatus (P. catenlannulatus) was performed by measuring the efflux of cytoplasmic materials of P. catenlannulatus. Approximate 35 % of the bacteria could survive on the surface of GO nanosheets compared to the control sample (~92 %) within 3 h, indicating that GO nanosheets presented significantly antibacterial activities. It was observed that the concentration of RNA in the solution was obviously higher than that of control sample, which could be due to direct contact of the bacterial cell. The results showed that the damage of cell membrane of P. catenlannulatus was attributed to the direct contact of the P. catenlannulatus with the extremely sharp edges of GO nanosheets, which resulted in the P. catenlannulatus inactivation. The less resistant to the damage of cell membrane was observed with increasing of GO concentration and contact time.

ZnS–CdS/Graphene oxide heterostructures prepared by a light irradiation-assisted method for effective photocatalytic hydrogen generation

Graphene oxide (GO) nanosheets are introduced to ZnS–CdS heterostructures to improve photocatalytic hydrogen generation. ZnS and CdS nanoparticles are formed on the surface of GO nanosheets via a light irradiation-assisted method. Here, GO construct a carrier transport channel between ZnS and CdS to enhance cooperative effects. The ZnS–CdS/GO heterostructures exhibit high photocatalytic hydrogen generation rates under either UV–visible or visible light irradiation. After loading of Pt nanoparticles as co-catalysts, the photocatalytic hydrogen generation rate of the proposed heterostructures is significantly improved to as high as 1.68mmolh−1 under UV–visible light irradiation.

Facile solid-state synthesis of Ag/graphene oxide nanocomposites as highly active and stable catalyst for the reduction of 4-nitrophenol

A facile solid-state synthetic route was used to fabricate graphene oxide (GO) decorated with Ag nanoparticles. Ag/GO nanocomposites were prepared by reducing silver acetate with ascorbic acid in the presence of GO at ambient conditions. The characterization results showed that Ag nanoparticles with an average diameter of ~50nm were well dispersed on the surface of GO nanosheets. Moreover, an application of the obtained Ag/GO nanocomposites as a catalyst in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol by NaBH4 was demonstrated. The Ag/GO nanocomposites exhibited high activity and stability for the catalytic reduction of 4-NP.

Adsorption of Clofibric Acid from Aqueous Solution by Graphene Oxide and the Effect of Environmental Factors

Graphene oxide (GO) nanosheets were used as adsorbent material for the removal of clofibric acid (CA) which was difficult to be removed from wastewater by traditional wastewater treatment technique. Adsorption kinetics, adsorption equilibrium, and effect of pH, ionic strength, and humic acid (HA) of the adsorption of CA onto the GO nanosheets in aqueous solution were investigated in detail. Adsorption isotherm studies indicated that the Langmuir isotherm equation fitted the sorption isotherm data better than Freundlich model and the maximum adsorption capacity of GO nanosheets for CA was 994 mg g−1. In addition, adsorption kinetics data showed that the sorption of CA on GO nanosheets reached equilibration within a few minutes and were well fitted by pseudo second-order model. The results of the effects of environment factors indicated that CA sorption on GO nanosheets was weakly affected by ionic strength and strongly depended on pH and HA because of the structure of CA and the large number of oxygen-containing function groups presented on the surface of GO nanosheets. Besides, the removal efficiency of GO nanosheets for CA was reduced at pH >4 and enhanced at pH <4 in the presence of HA.

One step synthesis of β-FeOOH nanowire bundles/graphene oxide nanocomposites

A nanocomposite of graphene oxide (GO) and β-ferric oxyhydroxide (β-FeOOH) nanowire bundles is synthesized by in situ hydrolysis of the precursor ferric chloride and GO nanosheets. Characterization by X-ray diffraction, transmission electron microscopy, and thermogravimetric analysis established the composite structure of the synthesized sample. The results revealed that the surface of GO nanosheets was uniformly assembled by numerous nanowire bundles with diameters in the range of 30–50 nm and lengths of 100–150 nm. Furthermore, β-FeOOH/GO nanocomposites showed a very high adsorption capacity of Congo red and thus these nanocomposites can be used as good adsorbents and can be used for the removal of organic dye from the waste water system.

NiAl-layered Double Hydroxide/Reduced Graphene Oxide Composite: Microwave-assisted Synthesis and Supercapacitive Properties

Pure NiAl-layered double hydroxides (LDHs) and graphene oxide (GO)/NiAl-LDHs composites are both fabricated by refluxing solution with the assistance of microwave irradiation within 2hours. The structural characterization and morphological observation of the composites suggest that small NiAl-LDHs crystals are in situ grown on the surface of GO nanosheets, preventing the compact stacking of GO as an intercalated spacer. The electrochemical performances of pure LDHs and GO/NiAl-LDHs composites with different content of GO are investigated and compared. The GO/NiAl-LDHs composite containing 23 wt% GO exhibits a higher specific capacitance of 1630 F g−1 at 1 A g−1 in 6M KOH solution and more stable rate capability than others. When GO is substituted by microwave reduced graphene oxide (rGO) or the GO in the GO/NiAl-LDHs composite is thermally reduced at a rational temperature, rGO/NiAl-LDHs composites are obtained with enhanced electrochemical behavior in rate capability and cycle life. Critical comparisons indicate that rGO/NiAl-LDHs composite prepared by thermal reducing GO/NiAl-LDHs has better cycling performance and rate capability than the counterpart directly prepared with rGO.

Fabrication of highly dispersed palladium/graphene oxide nanocomposites and their catalytic properties for efficient hydrogenation of p-nitrophenol and hydrogen generation

In this report, graphene oxide (GO) nanosheets decorated with ultrafine Pd nanoparticles (Pd NPs) have been successfully fabricated through a reaction between [Pd2(μ-CO)2Cl4]2− and water in the presence of GO nanosheets without any surfactant or other reductant. The as-synthesized small Pd NPs with average diameter of about 4.4 nm were well-dispersed on the surface of GO nanosheets. The Pd/GO nanocomposites show remarkable catalytic activity toward the hydrogenation of p-nitrophenol at room temperature. The kinetic apparent rate constant (kapp) could reach about 34.3 × 10−3 s−1. Furthermore, the as-prepared Pd/GO nanocomposites could also be used as an efficient and stable catalyst for hydrogen production from hydrolytic dehydrogenation of ammonia borane (AB). The catalytic activity is much higher than the conventional Pd/C catalysts.

Preparation and properties of novel epoxy/graphene oxide nanosheets (GON) composites functionalized with flame retardant containing phosphorus and silicon

2-(Diphenylphosphino)ethyltriethoxy silane (DPPES) was grafted onto the surface of graphene oxide nanosheets (GON) via a condensation reaction. X-ray photoelectron spectroscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and Raman spectroscopy verify that DPPES did not only covalently bond to GON as a functionalization moiety, but partly restored its conjugated structure as a reducing agent. DPPES on graphene sheets oxide was observed by transmission electron microscopy, and contributed to the favorable dispersion of DPPES-GON in nonpolar toluene. Additionally, the flame retardancy and thermal stability of epoxy/DPPES-GON nanocomposites that contain various weight fractions of DPPES-GON were studied using the limiting oxygen index test, UL-94 test and by thermogravimetric analysis in nitrogen. The composites containing 10 wt% DPPES-GON can pass V-0 rating in UL-94 test. Adding 10 wt% DPPES-GON in epoxy greatly increased the char yield and LOI by 42% and 80%, respectively. Epoxy/DPPES-GON nanocomposites with phosphorus, silicon and graphene layer structures were found to exhibit much greater flame retardancy than neat epoxy. The synergistic effects among silicon, phosphorus and GON can improve the flame retardancy of epoxy resin.

Preparation and electrochemical performance of graphene–Pt black nanocomposite for electrochemical methanol oxidation

This work reports the preparation, characterization, and electrocatalytic characteristics of a new metallic nanocatalyst. The catalyst, Pt black–graphene oxide (Pt-GO), was prepared by deposition of Pt black on the surface of graphene oxide nanosheet and characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and voltammetry. The Pt-graphene (Pt-GR) composite modified glassy carbon electrode (Pt-GR/GCE) was prepared with cyclic voltammetric scanning of Pt-GO/GCE in the potential range from −1.5 to 0.2 in 0.1 M phosphate buffer solution at 50 mV·s−1 for 5 cycles. The electrocatalytic properties of the Pt-GR/GCE for methanol (CH3OH) oxidation have been investigated by cyclic voltammetry (CV); high electrocatalytic activity of the Pt-GR/GCE can be observed. This may be attributed to the high dispersion of Pt catalyst and the particular properties of GR support. The long-term stability of Pt-GR composite was investigated in 0.05 M CH3OH in 0.1 M H2SO4 solution. It can be observed that the peak current decreases gradually with the successive scans. The loss may result from the consumption of methanol during the CV scan. It also may be due to the poisoning organic compounds. The results imply that the Pt-GR composite has good potential applications in fuel cells.

Spectra investigation on surface characteristics of graphene oxide nanosheets treated with tartaric, malic and oxalic acids

The surface characteristics of graphene oxide nanosheets (GO) treated respectively with tartaric acid, malic acid and oxalic acid, have been investigated by mainly using optical spectroscopic methods including Fourier transform infrared spectroscopy (FT-IR), Ultraviolet–visible (UV–Vis) absorption and Raman spectroscopy. Additionally, the electrochemical property of the products has also been studied. The data revealed that oxygen-containing groups such as OH, COOH and CO on the GO surface have been almost removed and thus reduced graphene oxide nanosheets (RGN) were obtained. Interestingly, the number of sp2 domains of RGN increases as treated by tartaric acid<malic acid<oxalic acid whereas the steric hindrance (SH) decreases and the ionization constant (IC) differs among these three acids. Furthermore, the specific capacitances (Cs) of GO have been greatly promoted from 2.4Fg−1 to 100.8, 112.4, and 147Fg−1 after treated with tartaric, malic and oxalic acids, respectively. This finding agrees well with the spectra result of the tendency of surface conjugated degree alteration. We claim that the difference in both SH and IC among these acids is the main reason for the diverse surface characteristics as well as the improved Cs of the RGN.

Hydrothermal synthesis of flower-like TiO2 nanocrystals/graphene oxide nanocomposites

A facile hydrothermal method has been developed to be capable of decorating graphene oxide (GO) with flower-like TiO2 nanocrystals without using any bridging species. The flower-like TiO2 nanocrystals were uniformly self-assembled on the surface of GO nanosheets. The photocatalytic activity experiment indicated that the prepared TiO2/GO nanocomposites exhibited a higher photocatalytic activity for the photocatalytic degradation of rhodamine B (RB) aqueous solution under the UV illumination, this methodology made the synthesis of TiO2/GO nanocomposites possible and may be further extended to prepare more complicated nanocomposites based on GO for technological applications.

Mussel-inspired green synthesis of silver nanoparticles on graphene oxide nanosheets for enhanced catalytic applications

We report a facile green approach to the synthesis of silver nanoparticles (Ag NPs) on the surface of graphene oxide nanosheets functionalized with mussel-inspired dopamine (GO-Dopa) without additional reductants or stabilizers at room temperature. The resulting hybrid Ag/GO-Dopa exhibits good dispersity and excellent catalytic activity in the reduction of nitroarenes.

Graphene oxide nanosheets/polymer binders as superior electrocatalytic materials for vanadium bromide redox flow batteries

Few layered graphene oxide (GO) nanosheets with large specific surface area (42.1m2g−1) are successfully prepared by a modified Hummers method for use as electrodes in the vanadium bromide redox battery. The structure and physicochemical properties of GO are investigated by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. Cyclic voltammetry results indicate that GO nanosheets with polymer binder (i.e., polyvinylidiene fluoride (PVDF) or sulfonated poly(ether ether ketone) (SPEEK)) hybrids demonstrate more favorable electrocatalytic activity towards the Br−/Br3− and V3+/V2+ redox couples than the pure graphite. This is attributed to the large numbers of oxygen-containing functional groups on the GO nanosheet surface which can generate more active sites to catalyze the redox reactions. For the binder-based electrodes, the SPEEK based electrode gives the best electrochemical performance (e.g., lower overvoltage for both Br−/Br3− and V3+/V2+ redox couple reactions and higher peak currents for the V3+/V2+ redox couple).