Graphene Nanosheets Film Research Articles

Surface functionalization of GO, preparation and characterization of PVA/TRIS-GO nanocomposites

In this work, poly(vinyl alcohol) (PVA) nanocomposite films were prepared using different concentrations of functionalized graphene (0, 1, 3 and 5 wt%) to study the permeability of oxygen gas in the PVA nanocomposites. For this aim, graphene layers were covalently functionalized with tris(hydroxymethyl)aminomethane (TRIS) and used as a nanofiller in the PVA matrix. The obtained PVA/TRIS-functionalized graphene nanosheets (TRIS-GO) films which have highly water absorbent ability were completely smooth, uniform, and flexible. Fourier transform infrared, Raman and X-ray photoelectron spectroscopies, atomic force microscopy, thermogravimetric analysis, elemental analysis, field emission scanning electron microscopy and transmission electron microscopy were used to investigate the nanostructures and properties of prepared materials. Following, effects of modified graphene on the certain properties of resulting nanocomposites were studied. The oxygen permeability of the nanocomposites was increased remarkably by the presence of TRIS-GO due to an increase in hydrophilic volume.

Fully Converting Graphite into Graphene Oxide Hydrogels by Preoxidation with Impure Manganese Dioxide.

Potassium permanganate (KMnO4) has been proved to be an efficient oxidant for converting graphite into graphite oxide, but its slow diffusion in the interlayer of graphite seriously restricts the production of graphene oxide (GO). Here, we demonstrate that the preoxidation of graphite by impure manganese dioxide (MnO2) in a mixture of concentrated sulfuric acid (H2SO4) and phosphorus pentoxide (P2O5) can efficiently improve the synthesis of GO when KMnO4 is employed as the oxidant. The prepared honey-like GO hydrogels possess a high yield of single-layer sheets, large sizes (average lateral size up to 20 μm), wide ranges of stable dispersion concentrations (from dilute solutions, viscous hydrogels, to dry films), and good conductivity after reduction (~2.9 × 10(4) S/m). The mechanism for the improved synthesis of GO by impure MnO2 was explored. The enhanced exfoliation and oxidation of graphite by oxidative Mn ions (mainly Mn(3+)), which are synergistically produced by the reaction of impure MnO2 with H2SO4 and P2O5, are found to be responsible for the improved synthesis of such GO hydrogels. Particularly, preoxidized graphite (POG) can be partially dispersed in water with sonication, which allows the facile construction of flexible and highly conductive graphene nanosheet film electrodes with excellent electrochemical sensing properties.

Graphene Induces Formation of Pores That Kill Spherical and Rod-Shaped Bacteria.

Pristine graphene, its derivatives, and composites have been widely reported to possess antibacterial properties. Most of the studies simulating the interaction between bacterial cell membranes and the surface of graphene have proposed that the graphene-induced bacterial cell death is caused either by (1) the insertion of blade-like graphene-based nanosheets or (2) the destructive extraction of lipid molecules by the presence of the lipophilic graphene. These simulation studies have, however, only take into account graphene-cell membrane interactions where the graphene is in a dispersed form. In this paper, we report the antimicrobial behavior of graphene sheet surfaces in an attempt to further advance the current knowledge pertaining to graphene cytotoxicity using both experimental and computer simulation approaches. Graphene nanofilms were fabricated to exhibit different edge lengths and different angles of orientation in the graphene sheets. These substrates were placed in contact with Pseudomonas aeruginosa and Staphylococcus aureus bacteria, where it was seen that these substrates exhibited variable bactericidal efficiency toward these two pathogenic bacteria. It was demonstrated that the density of the edges of the graphene was one of the principal parameters that contributed to the antibacterial behavior of the graphene nanosheet films. The study provides both experimental and theoretical evidence that the antibacterial behavior of graphene nanosheets arises from the formation of pores in the bacterial cell wall, causing a subsequent osmotic imbalance and cell death.

Graphene Nanosheets as the Counter Electrode in p-Type Dye-sensitized Solar Cells

Abstract Graphene nanosheet (GN) films on fluorinated tin oxide (FTO) are used as the counter electrode in p-type dye-sensitized solar cells. These films show unique 3D networks with enlarged effective reaction area, good adhesion to FTO, and high catalytic activity. By using the developed GN films on FTO as the counter electrode, a p-type dye-sensitized device with an open-circuit voltage of 134 mV, a short circuit of 1.90 mA cm−2, and a fill factor of 36.37% is obtained, which is comparable to the performance of a device with a Pt counter electrode.

Determination of 4-nitrophenol at Iron Phthalocyanine Decorated Graphene Nanosheets Film Modified Electrode

Determination of 4-nitrophenol at Iron Phthalocyanine Decorated Graphene Nanosheets Film Modified Electrode

Nerve cell differentiation using constant and programmed electrical stimulation through conductive non-functional graphene nanosheets film

Electrical signal is one of the most important elctrophysiological phenomena and is widely used in electrogensis and electrodiagnosis. The use of appropriate external electrical stimulation (ES) to in situ modify cellular behavior can desirably promote tissue regeneration. Considering its high electron mobility and surface area, graphene could become a promising conductive scaffold in biomedical applications. In this study, a programmed ES, comprehensively concerning the ES factors, such as ES period, intensity, frequency, electrical pulse and interval change, was used to modify Rat pheochromocytoma PC-12 cells behaviours through a large size non-functional graphene nano-film (NGNF) which was prepared by spray coating the high conducting graphene sheets onto polyurethane film. The constant ES was used to select the optimized ES intensity and as well as control. The optimized ES condition with intensity of 100 mV/mm was shown to significantly enhance PC-12 cell differentiation, neurite extension and growth. Comparing the results by different ES, i.e. the constant 100 mV/mm and the programmed ES 100 mV/mm at 1 Hz and 10 Hz, the programmed ES increased longer neuritis length. The positive enhancement to nerve behaviour by programmed ES was still significant maintained at long periods of ES (48 h).

Layer-by-Layer Self-Assembly of CdS Quantum Dots/Graphene Nanosheets Hybrid Films for Photoelectrochemical and Photocatalytic Applications

In recent years, increasing interest has been devoted to synthesizing graphene-semiconductor nanocomposites as efficient photocatalysts for extensive applications. Unfortunately, it is still challenging to make uniform graphene-semiconductor composite films with controllable film thickness and architecture, which are of paramount importance to meet the application requirements. In this work, stable aqueous dispersion of polymer-modified graphene nanosheets (GNs) was prepared via in situ reduction of exfoliated graphite oxide in the presence of cationic poly(allylamine hydrochloride) (PAH). The resultant water-soluble PAH-modified GNs (GNs-PAH) in conjunction with tailor-made negatively charged CdS quantum dots (QDs) were utilized as nanobuilding blocks for sequential layer-by-layer (LbL) self-assembly of well-defined GNs-CdS QDs hybrid films, in which CdS QDs overspread evenly on the two-dimensional (2D) GNs. It was found that the alternating GNs-CdS QDs multilayered films showed significantly enhanced photoelectrochemical and photocatalytic activities under visible light irradiation as compared to pure CdS QDs and GNs films. The enhancement was attributed to the judicious integration of CdS QDs with GNs in an alternating manner, which maximizes the 2D structural advantage of GNs in GNs-CdS QDs composite films. In addition, photocatalytic and photoelectrochemical mechanisms of the GNs-CdS QDs multilayered films were also discussed. It is anticipated that our work may open new directions for the fabrication of uniform semiconductor/GNs hybrid films for a wide range of applications.

Facile room temperature methods for growing ultra thin films of graphene nanosheets, nanoparticulate tin oxide and preliminary assessment of graphene–tin oxide stacked layered composite structure for supercapacitor application

We report a novel, facile, single step process for growing highly uniform few layer graphene nanosheet (FLGNS) thin films over a micrometer scale, formed at the liquid–air interface. The process is further extended to form monolayer graphene nanosheets (GNS). The films are characterized by Raman spectroscopy, Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The results indicate that very few chemical and/or physical defects are introduced during formation of films. Further, an innovative single step method to form tin oxide (SnO2) films at the liquid–air interface is presented. A special feature of the method is that entire process is completed at room temperature. The film can be suitably transferred to the desired substrates by Blodgett technique. Characterization by various techniques such as XPS, TEM and energy dispersive spectroscopy (EDS) shows that the films are made up of uniform spherical, crystalline SnO2 particles with the size in the range of 3–5 nm. Layer-by-layer (LbL) techniques can be exploited to stack graphene and SnO2 films alternately, in a desired sequence, forming a stacked composite structure. The composite structure is subjected to characterization by XPS, FE-SEM, TEM and EDS. The results show that the structure consists of a stack of predetermined thickness consisting of alternate layers of both the components. Such a structure is subjected to cyclic voltammetry (CV) studies. The results suggest LbL grown SnO2–GNS stacked composites exhibit better electrochemical performance in terms of specific capacitance and cycling ability which are primary requirements for the supercapacitor application. The coating techniques of few layer graphene nanosheets, SnO2 film and their stacked composite film are simple and inexpensive. A suitable explanation of the formation of both GNS and SnO2 films is discussed. The proposed methods extend the scope for production of high quality and defect free graphene nanosheets (GNS) and other components for forming LbL stacking of composite films.

Study and Electrochemical Determination of Tyrosine at Graphene Nanosheets Composite Film Modified Glassy Carbon Electrode

A graphene nanosheets (GNS) film coated glassy carbon electrode (GCE) was fabricated for sensitive determination of tyrosine (Tyr). The GNS-based sensor was characterized by scanning electron microscope and electrochemical impedance spectroscopy. The voltammetric techniques were employed to study electro-oxidation of Tyr. The results revealed that the modified electrode showed an electrocatalytic activity toward the anodic oxidation of Tyr by a marked enhancement in the current intensity and the shift in the oxidation potential to lower values (50 mV) in comparison with the bare GCE. Some kinetic parameters such as the electron transfer coefficient (α) were also determined for the Tyr oxidation. The detection limit for Tyr was found to be 2.0×10-8 M (n=9), and the peak current increases linearly with the Tyr concentration within the molar concentration ranges of 5.0 ×10-6 to 1.2 ×10-4 M. The modified electrode shows good sensitivity, selectivity and stability. The prepared electrode was applied for the determination of Tyr in real sample.

High-quality production of graphene by liquid-phase exfoliation of expanded graphite

As one of the most promising candidates, graphene exhibits a potential application in post-silicon nanoelectronics. However, it is a key issue to produce high-quality graphene in large scale. Here, a facile method is demonstrated to produce graphene dispersions by exfoliation of expanded graphite in the co-solvent with N,N-dimethylformamide (DMF) and water. We confirm that the optimal ratio of DMF to water for graphene exfoliation is 9:1 (v:v) by means of UV–Vis absorption spectra. This exfoliation results in large flakes ∼2 μm in diameter, which can potentially be improved by adjusting the sonication power. The relatively perfect hexagonal structure of graphene is confirmed by Raman spectroscopy and the as-prepared graphene nanosheet film the as-prepared graphene nanosheet film possesses good electrical conductivity (∼8.3 × 103 S m−1). DC electrical transport phenomena for the deposited film of graphene nanosheets are well described in terms of conduction models for non-crystal semiconductor. This convenient approach provides an extensive route to prepare high-quality graphene nanosheets.

Electrodynamically Sprayed Thin Films of Aqueous Dispersible Graphene Nanosheets: Highly Efficient Cathodes for Dye-Sensitized Solar Cells

Highly efficient cathodes for dye-sensitized solar cells (DSSCs) were developed using thin films of graphene nanosheets (GNS), which were fabricated by the electrospray method (e-spray) using aqueous dispersions of chemically driven GNS. The e-sprayed GNS films had the appropriate properties to be an efficient counter electrode (CE) for DSSCs; sufficient electrocatalytic activity for I(-)/I3(-) redox couples and low charge transfer resistance (RCT) at the CE/electrolyte interface as characterized by cyclic voltammetry and electrochemical impedance analysis. The performance of the GNS film based CEs was optimized by manipulating the density of surface chemical functional groups and plane conjugation of GNS via post thermal annealing (TA). Upon TA, the oxygen-containing surface functional groups, which have been shown to improve electrocatalytic activity of carbon based materials, were significantly reduced, while the electrical conductivity was enhanced by ∼40 times. The improvement of electrocatalytic activity and fill factor (FF) with reduced RCT of DSSCs after TA was primarily attributed to the increased charge transport within the GNS films, while the chemically prepared GNS typically contained sufficient defects, edges and surface functional groups for electrocatalysis. The performance of the DSSCs using our GNS-CEs was nearly identical (>95%) to the DSSCs using the state-of-the-art CE, thermolytically prepared Pt crystals. Our e-sprayed GNS-CE based DSSCs had a higher FF (69.7%) and cell efficiency (6.93%) when compared previously reported graphene based CEs for DSSCs, demonstrating the outstanding properties of graphene as the electrodes in electrochemical devices.

Edge-carboxylated graphene nanosheets via ball milling

Low-cost, high-yield production of graphene nanosheets (GNs) is essential for practical applications. We have achieved high yield of edge-selectively carboxylated graphite (ECG) by a simple ball milling of pristine graphite in the presence of dry ice. The resultant ECG is highly dispersable in various solvents to self-exfoliate into single- and few-layer (≤5 layers) GNs. These stable ECG (or GN) dispersions have been used for solution processing, coupled with thermal decarboxylation, to produce large-area GN films for many potential applications ranging from electronic materials to chemical catalysts. The electrical conductivity of a thermally decarboxylated ECG film was found to be as high as 1214S/cm, which is superior to its GO counterparts. Ball milling can thus provide simple, but efficient and versatile, and eco-friendly (CO(2)-capturing) approaches to low-cost mass production of high-quality GNs for applications where GOs have been exploited and beyond.

Comparison between metal ion and polyelectrolyte functionalization for electrophoretic deposition of graphene nanosheet films

Graphene nanosheets (GNSs) were modified either by metal magnesium (Mg) ions or a polyelectrolyte, polydiallyldimethylammonium chloride (PDDA), to produce positive charges on them. The two materials were used to produce GNS films with different surface morphologies. They were deposited on single-crystal silicon substrates using simple direct current electrophoretic deposition method. The Mg ion-modified GNS film has a relatively rough surface with some GNSs almost perpendicular to the surface, whereas the PDDA-modified GNS film has a relatively smooth surface with most GNSs parallel to the substrate. This difference is attributed to the different interactions of Mg ions and PDDA molecules with GNSs. Because of the favorable surface morphology, the Mg ion-modified GNS film displays better field emission compared with the PDDA-modified GNS film. Biocompatibility tests indicate that the rougher Mg ion-modified GNS film is more beneficial to cell adhesion and growth.

Influence of pH condition on colloidal suspension of exfoliated graphene oxide by electrostatic repulsion

A facile chemical process is described to produce graphene oxide utilizing a zwitterions amino acid intermediate from graphite oxide sheets. 11-aminoundecanoic acid molecules were protonated to intercalate molecules into the graphite oxide sheets to achieve ion exchange, and the carboxyl groups were then ionized in a NaOH solution to exfoliate the graphite oxide sheets. In this way, the produced graphene oxide nanosheets were stably dispersed in water. The delaminated graphene nanosheets were confirmed by XRD, AFM, and TEM. XRD patterns indicated the d002-spacing of the graphite greatly increased from 0.380nm and 0.870nm. AFM and TEM images showed that the ordered graphite crystal structure of graphene nanosheets was effectively exfoliated by this method. The prepared graphene nanosheets films showed 87.1% transmittance and a sheet resistance of 2.1×103Ω/square.

Graphene-based counter electrode for dye-sensitized solar cells

Graphene nanosheets (GNs) were synthesized and used as a substitute for platinum as counter-electrode materials for dye-sensitized solar cells (DSSCs). The as-synthesized GNs were dispersed in a mixture of terpineol and ethyl cellulose. GN films were screen-printed on fluorine-doped tin oxide (FTO) slides using the formed GN dispersions. GN counter-electrodes were produced by annealing the GN films at different temperatures. The annealed GN films revealed an unusual 3D network structure. Structural and electrochemical properties of the formed GN counter-electrodes were examined by field emission scanning electron microscopy, Raman spectroscopy and electrochemical impedance spectroscopy. It was found that the annealing temperature of GN materials played an important role in the quality of the GN counter-electrode and the photovoltaic performance of the resultant DSSC. The grown DSSCs with graphene-based counter-electrodes exhibited a conversion efficiency high up to 6.81%.

Effect of extended polymer chains on properties of transparent graphene nanosheets conductive film

This study examined the intercalation reaction of graphite oxide (GO) with poly(acryl amide)/poly(acrylic acid) (PMA) as a method to control the spacing between GOs. The interlayer spacing of GO was increased from 0.80 to 1.21 nm by grafting PMA on the GO surface. To fabricate transparent conductive films (TCFs), GOs must be reduced to graphene nanosheets (GNS) by a two-step chemical reduction with increased conductivity. The intercalated polymer chains of poly(acrylic acid) between GNS were extended as the carboxylic acid groups were deprotonated by the Na+ ions of NaBH4 on reduction, which efficiently inhibits GNS aggregation and restacking. The Na+ bonding on the polymer chains also facilitates electron transfer between the layers, yielding lower surface electrical resistance at the same GNS film thickness. The PMA grafted GNS (NE-PMA-GNS) composite films show the lowest sheet resistance of 2.11 × 102 Ω □−1, which is one order of magnitude less than that without grafting polymer (NE-GNS, 1.86 × 103 Ω □−1); moreover, instead of 0.22, the ratio of DC conductivity to optical conductivity (σDC/σOP) was 2.60. The higher σDC/σOP ratio indicates a higher TCFs performance.

Controllable Adsorption of Reduced Graphene Oxide onto Self-Assembled Alkanethiol Monolayers on Gold Electrodes: Tunable Electrode Dimension and Potential Electrochemical Applications

This paper describes a facile and effective method to construct graphene nanosheet film (GNF) by controllable adsorption of reduced graphene oxide (rGO) onto the self-assembled monolayer (SAM) of n-octadecyl mercaptan (C18H37SH) at Au electrodes. Nyquist plots show a gradual decrease of the charge transfer resistance (Rct) of the [Fe(CN)6]3−/4− redox couple at the GNF/SAM electrode with prolonging the self-assembly time, suggesting the controllable adsorption of rGO onto the SAM. Cyclic voltammetry (CV) studies reveal that the GNF/SAM electrodes have tunable dimensions ranging from a nanoelectrode ensemble to a conventional electrode, depending on the self-assembly time of rGO. The excellent electrocatalytic activity of the GNF/SAM electrode toward ascorbic acid, dopamine, and uric acid further indicates that our approach is successful for the fabrication of stable GNF with excellent electrochemical properties, which is very attractive for electrochemical studies and electroanalytical applications. At the...