Elsevier

Current Applied Physics

Volume 40, August 2022, Pages 1-11
Current Applied Physics

Synthesis and characterization of graphene oxide, reduced graphene oxide and their nanocomposites with polyethylene oxide

https://doi.org/10.1016/j.cap.2020.03.002Get rights and content

Highlights

  • Synthesis of GO, rGO and their nanocomposites with PEO employing solution casting protocol.

  • Preparation of GO by modified Hummers method.

  • RGO prepared by in-situ reduction of GO with in the PEO matrix utilizing green reductant i.e., L (+) Ascorbic acid.

  • Better thermal stability for rGO/PEO nanocomposites as compare to the GO/PEO nanocomposites.

  • Enhanced mechanical properties for GO/PEO as compare to rGO/PEO nanocomposites.

Abstract

This work describes the synthesis of GO, rGO and their nanocomposites with PEO. GO and rGO were prepared by the modified Hummers method and in-situ reduction of GO utilizing green reductant L (+) Ascorbic acid. The nanocomposites were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Thermogravimetric Analysis (TGA), and Universal Testing Machine (UTM). FT-IR and XRD confirmed the synthesis of GO and rGO. FE-SEM confirmed the uniformly exfoliated GO and rGO nanosheets in the polymer matrix. Hydrogen bonding was the main interaction mechanism for GO with PEO while no interaction was detected by FT-IR for rGO. Enhanced thermal stability was observed for both GO/PEO and rGO/PEO nanocomposites. The mechanical analysis showed an increase in Young's modulus, tensile strength, and elongation at break for GO/PEO nanocomposites, which is attributed to the homogeneous dispersion and hydrophilic hydrogen bonding interaction of GO with PEO.

Introduction

Carbonaceous nanoparticles based polymer nanocomposites have attended great interest in the scientific community, in the last few decades, due to their exceptional structures and physical properties [1,2]. Nanoparticles on the basis of their dimensions are categorized into; one dimensional (ID), which includes nanotubes and nanowires; two dimensional (2D), which include nanoclays and graphene, and three dimensional (3D), which include spherical and cubical nanoparticles. Among the various nanoparticles, carbonaceous nanoparticles such as nanotubes (ID) and graphene (2D) [3] have displayed excellent properties due to their excellent mechanical strength and high aspect ratio. Between the two graphene is favored due to its young's modulus of 1 TPa, tensile strength in the range of 50–150 GPa and a failure strain in excess of 5%. A graphene nanosheet with Young's modulus of 1 TPa and strength of 130 GPa, a specific area of 2600 m2/g, the electric conductivity of 6000 S/cm, and thermal conductivity of ~5000 W/mK is one of the strongest known materials [[4], [5], [6]]. Although, graphene has attained immense interest in its exceptional electrical, mechanical (strongest material known to man), optical and thermal properties. However, the production cost of graphene is still higher, hence tremendous efforts are required to find new, efficient, facile, and economical ways of producing graphene and its derivative materials like graphene oxide (GO) and reduced graphene oxide (rGO). GO, an oxidized form of graphene is a single-atomic layered material. It consists of oxygen-containing groups and is produced by the oxidation of cheaply available graphite. As it readily disperses in water and other solvents, hence it is considered to be a good alternative for producing graphene [7]. Structure of GO has been a hot topic among researchers for many years [8]. Generally, GO is believed to have a graphene backbone where hydroxyl and epoxide groups are on the basal plane, and predominantly carboxyl and hydroxyl groups are on the edges. Also, there exists an inter platelet hydrogen bonding through the alcohol and epoxide functional groups which helps to maintain the stacked structure of GO. GO is synthesized by treating graphite with a strong oxidizing agent such as potassium permanganate in the presence of sulfuric acid.

The most appealing feature of GO is that it can be reduced to graphene-like sheets (rGO). During the synthesis of rGO much of the surface functional groups are removed resulting in the restoration of the structure similar to that of pristine graphene. Perfect graphene sheets with no functional groups show high electrical conductivity, but they are difficult to produce in large amounts by mechanical exfoliation. Therefore, its compounds including GO, thermally rGO (T rGO) or chemically rGO (C rGO), etc. are widely used. The presence of an oxygen functional group in GO results in disruption of the sp2 network, and hence it is electrically insulating. The reduction of GO produces TrGO or CrGO where sp2 network is partially restored which then enhances the conductivity of graphene [[9], [10], [11]].

Graphene nanocomposites consist of the combination of graphene, which is also known as the reinforcing agent, and a polymer material that acts as a matrix. It has been observed that the properties of nanocomposite are more effective than that of micro composites. Therefore, it will be extremely interesting to fabricate composites with GO and rGO (due to their low cost and high yield) and observe their impact on improving the mechanical and thermal properties of the pristine polymer [12]. Polyethylene oxide (PEO), an elastomer, was selected as a matrix polymer. PEO is a neutral, non-toxic, water/organic soluble polymer and a potential material for solid polymer electrolytes, sensors, biomaterials, drug delivery devices and cosmetology (skin creams, emulsions, personal lubricants) [13]. Furthermore, PEO is a hygroscopic insulating polymer and has the ability to retain high crystallinity in the binary hybrid materials, resulting in reliable and accurate detection of humidity [14]. PEO has been blend with a number of nanomaterials and characterized for conductivities with the aim of application in batteries, however, its structure relationship with the mechanical properties has not been focused on lately.

In this work, we have synthesized GO/PEO and rGO/PEO nanocomposite employing solution casting protocol. GO was prepared by the Hummers method, where rGO was synthesized by in-situ reduction of GO in the PEO matrix. The composites were investigated not only physically but also chemically to find a relationship between structural changes and improved physical properties. Various spectroscopic and analytical techniques were used to study the above-mentioned relationship. These include Fourier transform infrared spectroscopy (FITR) X-ray powder diffraction (XRD), Scanning electron microscopy (SEM), surface profilometry, thermogravimetric analysis (TGA) and universal testing machine (UTM).

Section snippets

Materials

Graphite (99%), Potassium Nitrate (KNO3, 98–100%), Hydrogen peroxide (30% w/w) and L (+)-Ascorbic acid were obtained from Scharlau Spain. Polyethylene oxide (PEO) (98%, MW 600,000 g/mol) and Ammonia solution (NH4OH, (25%) were purchased from BDH Chemicals Ltd Poole, England. Potassium permanganate (KMnO4,99–100%) was purchased from Merck, Germany and Sulfuric acid (H2SO4) from Delta chemicals. Deionized water, with 7 pH and 3 μ cm conductivity, was used in the experiments.

Synthesis of graphene oxide

Graphene oxide (GO)

FT-IR study

Fig. 4 shows the FT-IR spectra of GO, rGO powders, pristine PEO film, and rGO/PEO and GO/PEO nanocomposites. The FT-IR spectrum of GO showed the characteristic absorption bands of hydroxyl, carboxyl, and epoxide groups. The band around 1733 cm−1 is assigned to the stretching vibration of carbonyl groups (C=O). Whereas the bands around 3400 cm−1 and 1404 cm−1 were attributed to the deformation of hydroxyl groups (–OH). The bands around 1049 cm−1(alkoxy), and 1200 cm−1 (epoxy) were attributed to

Conclusion

Various GO/PEO and RGO/PEO composites were successfully synthesized by using a solution casting technique. The GO for composites was prepared by the modified Hummers method and RGO was prepared by in-situ reduction of GO within the PEO matrix utilizing green reductant i.e., L (+) Ascorbic acid. The obtained composites were characterized by using XRD, SEM, TGA, and UTM. XRD results showed uniform dispersion of GO at the molecular level. The degree of crystallinity of the GO/PEO composites first

Declaration of competing interest

No conflict of interest has been declared. All authors equally contributed in this article.

Acknowledgment

The authors would like to extend their sincere appreciation to the Deanship of Scientific Research (DSR) at King Saud University, Saudi Arabia, for its funding of this research through the Research Group no RG-1440-060.

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