Thick Graphene Oxide Research Articles

Preparation of Graphene Oxide Coatings onto Carbon Fibers by Electrophoretic Deposition for Enhancing Interfacial Strength in Carbon Fiber Composites

Graphene oxide (GO) were utilized to improve the interfacial performance of carbon fiber (CF) and epoxy resin. An effective way to prepare graphene oxide/carbon fiber hybrid fiber was proposed by the treatment with hydrogen peroxide and concentrated nitric acid combined with electrophoretic deposition process. A characterization of the fiber surface properties was done before and after coating (surface morphologies, surface chemistry, and surface energy). Results showed that a uniform and thick graphene oxide films were tightly attached on the surface of carbon fiber. Moreover, surface wettability of carbon fibers to epoxy resin is significant improved by enhanced surface free energy due to the deposition of GO. Meanwhile, the introduction of GO in the carbon fiber/epoxy resin composites results in a 55.6% enhancement in the interlaminar shear strength, measured by short beam shear tests. Such a fabrication process is simple and effective, without complex chemical reactions and long processing time, and can be a continuous one for industrial scale.

Reliable determination of the few‐layer graphene oxide thickness using Raman spectroscopy

We report on a reference‐free Raman spectroscopy method for a precise thickness determination of the multilayered graphene oxide flakes. The method is based on the normalization of the total integral intensity of D and G Raman bands to the integral intensity of the second‐order optical phonon peak of the silicon substrate in the Raman spectrum. The normalization provides discrete ratio values corresponding to the number of graphene oxide layers in the respective flakes with the intensity linearly increasing with the number of layers. This provides a fast and robust determination of the thickness of graphene oxide flakes in terms of the layer number up to high values. A comparison with conventional spectrally resolved reflectivity mapping shows similar sensitivity, while selectivity to particular functional chemical groups is a bonus of the Raman‐based method. Copyright © 2015 John Wiley & Sons, Ltd.

Fracture Mechanism and Toughness Optimization of Macroscopic Thick Graphene Oxide Film.

Combined high strength and toughness of film materials are rather important for their industrial applications. As a new class of films, graphene oxide films (GOFs) attract intense attention in many applications but are frequently divergent, inconsistent, and poorly reproducible in their mechanical properties. In this study, we first demonstrate that different chemical compositions and assembly structures probably are responsible for the difference in elongations between cast GOFs and filtration GOFs. Comprehensive analysis of the morphologies and mechanical properties indicates that the enhanced elongation of the thick cast GOFs is mainly attributed to the presence of a unique skin-wrinkles-skin structure, which more easily forms in cast GOFs than in filtration counterparts. On the basis of this finding, we attempt to optimize the strength-toughness performance of the cast GOFs by adjusting their structures. With an appropriate thickness of 12.5 μm, the GOFs can achieve an ultrahigh toughness up to 4.37 MJ m−3, which is even comparable to the polymer-toughening graphene/GO-based paper-like materials. Such an optimization of the mechanical properties from the perspective of skin-wrinkles-skin structure appears to be a universal approach that could be extended to a variety of other film materials.

Thickness Dependence of the Mechanical Properties of Free‐Standing Graphene Oxide Papers

Graphene oxide (GO) papers are candidates for structural materials in modern technology due to their high specific strength and stiffness. The relationship between their mechanical properties and structure needs to be systematically investigated before they can be applied to the broad range fields where they have potential. Herein, the mechanical properties of GO papers with various thicknesses (0.5–100 μm) are investigated using bulge and tensile test methods; this includes the Young's modulus, fracture strength, fracture strain, and toughness. The Young's modulus, fracture strength, and toughness are found to decrease with increasing thickness, with the first two exhibiting differences by a factor of four. In contrast, the fracture strain slightly increases with thickness. Transmission electron, scanning electron, and atomic force microscopy indicate that the mechanical properties vary with thickness due to variations in the inner structure and surface morphology, such as crack formation and surface roughness. Thicker GO papers are weaker because they contain more voids that are produced during the fabrication process. Surface wrinkles and residual stress are found to result in increased fracture strain. Determination of this structure–property relationship provide improved guidelines for the use of GO‐based thin‐film materials in mechanical structures.

Effects of reduction process and carbon nanotube content on the supercapacitive performance of flexible graphene oxide papers

The effects of the reduction process and carbon nanotube (CNT) content on the supercapacitive behavior of electrodes made from flexible, binder-free thick graphene oxide (GO) papers are studied. It is found that the supercapacitive performance depends on several factors, including the presence of oxygenated functional groups after reduction, the interlayer spacing of the GO papers and their wettability with electrolyte. A moderate reduction of GO papers using hydrazine or annealing at a low temperature of 220°C in air is proven to be more beneficial to achieve a high capacitance than the heavy reduction using a hydrazine vapor or a high temperature thermal treatment. The addition of a small amount of CNT, typically 12.5wt.%, to form thick GO/CNT sandwich papers gives rise to an excellent specific capacitance of 151Fg−1 at a current density of 0.5Ag−1, as well as a retention ratio of 86% of the initial value after 6000 charge/discharge cycles at 5Ag−1. These improvements arise from the synergistic effects of the increased electronic conductivity and effective surface area associated with large electrochemical active sites due to the presence of intercalated CNT.

In situ synthesis of graphene oxide and its composites with iron oxide

A single step method was developed for the preparation of graphene oxide/Fe 2O 3 composites by exfoliation of graphite oxide with an oxygen-rich ferric acetyl acetonate complex. The synthesized materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometry, atomic force microscopy, and low temperature dc conductivity measurements. After exfoliation, the Fourier transform infrared studies reveal the decomposition of epoxy groups and the simultaneous formation of composites of iron oxide particles within the graphene oxide. Atomic force microscopy reveals the formation of an ∼5nm thick graphene oxide stack with layered morphology. The layered morphology of graphene oxide degrades at higher concentrations of iron oxide. The vibrating sample magnetometer studies show ferromagnetic behavior of all composites in the range of 0.13–5.5 emu/g at room temperature. The conductivity of these composites is found to be governed by a quasi 1D hopping mechanism.