Large-scale Graphene Oxide Research Articles

Separation of graphene oxides of different sizes by multi-layer dialysis and anti-friction and lubrication performance

Abstract As a 2D carbon material, graphene exhibits a unique structure and outstanding properties and has been widely applied in various fields. Because the properties of graphene are closely related to their structural parameters, graphene with different size distributions is suitable for different applications. However, current methods of fine-scale separation of graphene and its derivatives have certain limitations. In this study, graphene oxide (GO) size separation using multilayer dialysis was proposed. Multiple size separation in one step was achieved by customizing the dialysis size of each layer according to the actual requirements. In this way, GOs of different sizes were separated and large-scale synthesis can be achieved using this method. Meanwhile, the anti-friction and lubrication properties of aqueous dispersion solutions of GOs of different sizes were investigated. The results indicated significant improvements of the anti-friction and lubrication properties of GO samples prepared by the proposed method, as large-scale GOs can act as lubricants by relieving, if not preventing, friction between the two friction surfaces.

An Injection Method for the Fast Preparation of Graphene Oxide Membranes with Tunable Microstructures and Controllable Mechanical Properties

Objectives Graphene oxide (GO) membranes are promising materials in many fields such as supercapacitors1, gas and liquid separation2, sensing3, and acoustic transduction4. For these applications, a high efficiency, scalable method for preparing GO membranes without compromising mechanical properties are required.To date, the most commonly used technique to manufacture GO membranes is vacuum filtration. By filtering the GO suspension, GO sheets are stacked and assembled into membranes. However, this technique has several shortcomings. Firstly, this method cannot be used to control the ordering of GO sheets – a property that determines the microstructures and directly influences interactions between sheets. Secondly, this technique is time- and energy-consuming, and the size of the GO membranes produced is limited by the size of the filter5. New Results We report a new method for preparing large scale GO membranes with tunable microstructures and controllable mechanical properties. This method involves injecting the GO suspension through a thin nozzle into a coagulation bath for promoting the gelation of the GO into a membrane. The nozzle moves at a speed coordinated with the injection flow rate to prepare uniformly thick membranes (Fig. 1(a)). The flow rate in the nozzle induces shear stress, which in turn induces the alignment of GO sheets. Therefore, by adjusting the flow rate, the alignment of GO sheets is tunable, and the mechanical property is controllable. By using this technique, we achieved a long continuous GO membrane with high ultimate tensile strength (UTS) of 67-160 MPa at preparation speeds of up to 160 cm/min. As a comparison, the vacuum filtration method takes a day to prepare a single 47 mm diameter GO membrane with a UTS of 70-125 MPa6. Conclusions In this study, we designed a highly efficient flow injection method that allows us to prepare large-scale GO membranes with tunable microstructures rapidly. This in turn allows us to influence interactions between sheets and, most importantly, manipulate the mechanical properties. In this paper, we show the vast improvement in UTS measurements for GO membranes prepared using the flow injection method as opposed to the vacuum-filtration. This technique will enable fast and controllable production of GO membranes for various fields which call for membranes with good mechanical performance.Fig. 1. (a) Schematically drawing of the process of the injection method for GO membranes preparation; (b) UTS of GO membranes prepared under different flow rates Acknowledgments This research is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the McGill Engineering Doctoral Awards (MEDA).

Self-assembly of defect-rich graphene oxide nanosheets with Na2Ti3O7 nanowires and their superior absorptive capacity to toxic dyes

Graphene sheets, a flexible 2D material with excellent absorptive capacity, have great potential as absorbing materials. However, this material has always suffered from irreversible aggregation and thus loses the abundant active sites and large surface area. In this paper, large-scale graphene oxide (GO) sheets were cut and reduced to tiny reduced graphene oxide (RGO) sheets by a cell-break sonicator, for producing numerous defects, which are the center of chemisorption. Furthermore, sodium titanate nanowires functioned as a framework to help to disperse the tiny RGO sheets uniformly. And, in turn, the flexible tiny RGO sheets glued robust nanowires into a free-standing membrane. This novel composite membrane exhibited an ultra-high decoloration efficiency of 99.8% of rhodamine B in a continuous flow mode, and an outstanding absorptive capability of 1.30 × 10−2 mol g−1 correlated to RGO content in batch reaction, which is about two orders of magnitude higher than other reported graphene-based absorbents. In addition, an efficient and feasible method without any heat treatment for regenerating the membrane is illustrated, and the recycled membrane retains superior decoloration efficiency. The excellent absorptive performance indicates the framework-based disperse strategy has great potential for the construction and application of defect-rich graphene.

The phosphorescence and excitation-wavelength dependent fluorescence kinetics of large-scale graphene oxide nanosheets

In this study, phosphorescence emission and a strong excitation-wavelength dependent fluorescence has been found in large-scale graphene oxide (GO) nanosheets.

Synthesis of large scale graphene oxide using plasma enhanced chemical vapor deposition method and its application in humidity sensing

Large scale graphene oxide (GO) is directly synthesized on copper (Cu) foil by plasma enhanced chemical vapor deposition method under 500 °C and even lower temperature. Compared to the modified Hummer's method, the obtained GO sheet in this article is large, and it is scalable according to the Cu foil size. The oxygen-contained groups in the GO are introduced through the residual gas of methane (99.9% purity). To prevent the Cu surface from the bombardment of the ions in the plasma, we use low intensity discharge. Our experiment reveals that growth temperature has important influence on the carbon to oxygen ratio (C/O ratio) in the GO; and it also affects the amount of π-π* bonds between carbon atoms. Preliminary experiments on a 6 mm × 12 mm GO based humidity sensor prove that the synthesized GO reacts well to the humidity change. Our GO synthesis method may provide another channel for obtaining large scale GO in gas sensing or other applications.

Ultra-low-damage radical treatment for the highly controllable oxidation of large-scale graphene sheets

We have used low-damage oxygen radical treatment (O-LDRT)—with chemically reactive radicals generated in a plasma system equipped with a complementary filter—to prepare large-scale graphene oxide sheets with highly controllable levels of oxidation. Raman spectroscopy and X-ray photoelectron spectroscopy revealed that oxidative functionalities were formed on the graphene surfaces in a highly controllable manner and with a wide process window. Contact angle measurements revealed the high hydrophilicity of the large-scale graphene after O-LDRT. We measured the current–voltage characteristics of oxidized double-layer graphene (DLG) sheets to confirm the low degree of damage after using O-LDRT for the oxidation process. For treatment times of up to 5min, the current passing through the DLG sheets remained almost identical to that passing through the corresponding sample that had not been subjected to O-LDRT, indicating that the bottom layer of the graphene sheet remained almost unmodified, whereas a massive number of oxidative functionalities had been formed on the top layer of the graphene sheet; in addition, the adhesion energy increased to approximately twice that of the untreated graphene sheet.

Electrical and mechanical properties of graphene oxide on flexible substrate

Graphene oxide (GO) was deposited via the electrophoretic deposition (EPD) method to lower the oxygen concentration of graphene sheets for large-scale production. In addition, the direct synthesis of large-scale GO films using transfer processes on a polydimethylsiloxane (PDMS) substrate was conducted. The thickness of the GO films was controlled to adjust the optical, electrical, and mechanical properties. The Young's modulus values of films with thicknesses of 100–200nm were 324–529GPa. Moreover, the GO films exhibited excellent conductivity, with a sheet resistance of 276–2024Ω/sq at 23–77% transparency. Experiments show that transfer processes for flexible substrates can produce high-quality cost-effective transparent conductive films.

Reduced graphene oxide micropatterns as an interface for adherent cells

In the present study, reduced graphene oxide (rGO) is used as a biointerface for the investigation of cell adhesion of human embryonic kidney (HEK 293) cells. A fast, straightforward, and substrate-independent soft lithography approach known as “Micromolding In Capillaries” (MIMIC) was utilized to pattern graphene oxide (GO) arrays. Large-scale GO patterns with widths and distances in the micrometer range were obtained and were subsequently reduced to rGO via an environmentally-friendly procedure using L-ascorbic acid. Physical characterization of rGO patterns and cells was performed by optical microscopy, atomic force microscopy, and scanning electron microscopy. Impedance spectroscopy was used for the electrochemical characterization of GO before and after reduction. Cell adhesion and alignment was strong on the rGO micropatterns. In future assays, the rGO could combine two functions: cellular patterning and electrical interfacing of cells. HEK 293 cells aligning on rGO micro patterns (SEM image)

Bottom-up synthesis of large-scale graphene oxide nanosheets

Graphene oxide nanosheets (GONs) have attracted considerable interest due to their potential applications in electronic and optoelectronic devices. Graphene oxide (GO) is usually prepared by using Hummers' method or modified Hummers' methods, which require graphite and strong oxidizers, followed by exfoliation to obtain GONs. The main drawbacks of this top-down approach are the use of strong oxidizing agents and small lateral size of GONs. Here, we present a self-assembly method to synthesize GONs with tunable thickness ranging from ∼1 nm (monolayer) to ∼1500 nm. The lateral sizes of the monolayer and few-layer (<5) GONs are about 20 μm and 100 μm respectively. The GONs are prepared by a hydrothermal method using glucose as a sole reagent. The method is environmentally friendly, facile, low-cost as well as capable of scaling up for mass production. The electrical, optical and structural properties of the as-grown and annealed GONs are comparable to GO and reduced GO prepared by the top-down method, respectively. The electrical resistivity of the GONs can be tuned by annealing for 8 orders of magnitude ranging from 106 Ω cm to 10−2 Ω cm. A GO-based photodetector has been fabricated, demonstrating the optoelectronic properties of the GONs.

An Electrochemical Route to Graphene Oxide

Large-scale graphene oxide (GO) with adjustable resistivity was synthesized from graphite via an electrochemical method using KCl solution as an effective electrolyte. During the exfoliation process, electrostatic force intercalates chloride ions between the expanded graphite layers on the anode. These chloride ions form small gas bubbles between the graphite layers in the electrochemical reaction. It is believed that the gas bubbles expand the gap between graphite sheets and produce a separating force between adjacent graphene layers. This separating force overcomes the Van der Waals force between adjacent sheets and exfoliates graphene layers from the starting graphite. Because the graphene is electrochemically oxidized by chorine during the exfoliation, the exfoliated GO sheets are hydrophilic and easily dispersed in the electrolyte solution. The GO solution prepared by the electrochemical exfoliation can be simply sprayed or spin-coated onto any substrate for device applications. The measured average thicknesses of a monolayer, bilayer, and trilayer exfoliated GO on SiO2 substrate were 1.9, 2.8, and 3.9 nm, respectively. It was observed that the measured resistance of the exfoliated GO sheets increases due to electrochemical oxidation in the solution. This electrochemical approach offers a low-cost and efficient route to the fabrication of graphene based devices.