الفهرس 
Chapter 1: IntroductionOnly 14 pages are availabe for public view
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Abstract
This work reports on the synthesis and characterization of graphene obtained by oxidation of graphite using Hummer’s method and using different reduction methods of graphene oxide. The reduction techniques investigated include chemical reduction using sodium borohydride NaBH4 as a reducing agent, thermal reduction by thermal treatment of GO at 900°C in Ar-N2 atmosphere, and laser reduction using CO2 laser irradiation. In addition, two approaches have been developed for the synthesis of Hausmannite Manganese oxide Mn3O4/reduced Graphene Oxide rGO nanocomposite. In the first approach, Hausaminnite Mn3O4 nanoparticles are introduced in situ into the pores of the rGO during the auto-combustion synthesis of Mn3O4 to obtain the rGO/Mn3O4 nanocomposite. In the second approach, physical deposition of Mn3O4 prepared by auto-combustion on laser rGO film has been adopted to obtain the rGO/Mn3O4 nanocomposite.
The crystalline structure of the nanocomposite has been characterized by X-ray diffraction (XRD) and thermogravimetric analysis (TGA) has been used to determine the weight% of Mn3O4 in the composite. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) confirm the decrease of oxygen-containing functional groups and the reduction of GO to rGO. Also, Scanning Electron Microscopy (SEM) shows the morphology of rGO nanosheets and Mn3O4-rGO composites.
Electrochemical characterizations including Cyclic Voltammetry (CV), Galvanostatic charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) measurements have been utilized to analyze the supercapacitor performance and evaluate the electrochemical properties of rGO and Mn3O4-rGO nanocomposites as electrode materials for supercapacitors. The developed nanocomposite displays excellent electrochemical capacitive behavior and shows a good potential as candidate materials for electrodes of supercapacitors.
In conclusion, this work focused on synthesis of reduced graphene oxide rGO using three reduction methods of graphene oxide GO: chemical, thermal treatment, and photoreduction using laser. The salient findings of the present work can be summarized as follows:
-The chemical reduction using sodium borohydride NaBH4 is an available route to obtain rGO but exhibits incomplete reduction of GO and inefficient removal of hydroxyl groups.
-However thermal treatment of GO at 900 °C exhibits an efficient and relative complete reduction more than chemical reduction, the GO is decomposed into stacked multi-layers of rGO.
-The laser reduction of GO shows advantages over chemical and thermal reduction methods as a clean, cost effective, and fast processing method to reduce GO simultaneously.
-from the study of laser scribing process, it is concluded that by controlling the laser parameters such as laser power and scanning speed (exposure time), we can tune the properties of rGO with different degrees of reduction and few-layers of graphene sheets with different properties have been successfully grown. This study demonstrates that CO2 laser scribing is a promising technique for fabrication of graphene as the electrode material for supercapacitors.
-The laser scribing is considered as an efficient and heat localized process for simultaneous reduction and patterning of GO film by CO2 laser, which is suitable for scalable production of reduced graphene oxide rGO films on flexible substrates for future development of graphene-based micro-scale devices.
-In-situ auto-combustion is an efficient method to synthesize Mn3O4/rGO nanocomposites for hybrid electrodes of supercapacitor. It provides good dispersion of manganese oxide in the composite with different crystal size. However, the disadvantage is the difficult control of the manganese oxide weight in the composite because of the difficulty to determine the optimum fuel (glycine) and the oxidizer (manganese II nitrate) contents during the synthesis processing, leading to difficult prediction of the Mn3O4 weight in the composite.
-In another approach, synthesis of Mn3O4/rGO nanocomposites using physical deposition by DROP casting results in non-uniform distribution of the Mn3O4 nanoparticles on the laser rGO film forming agglomerated film that leads to unsatisfactory increase in capacitance.
-Based on the results, it can be concluded that the increase capacitance of Mn3O4/rGO nanocomposites is attributed to the contribution of the redox pseudo-capacitance of Mn3O4. Good charge/discharge cyclic stability is attributed to electrochemical stability of rGO which improved the cycle life of Mn3O4.
-The hybrid electrode material of Mn3O4-Chem.rGO achieve high specific capacitance of 309 F/g, and can be considered one of the high values achieved of hybrid electrodes.
-In addition, the auto-combustion synthesis method can be readily used for large-scale production of graphene and any other transition metal oxide composite for supercapacitor applications.