Study of the influence of the different synthesis parameter on the structure, morphology, bonding and properties of the graphene oxide (GO), reduced graphene oxide and graphene/alumina nanocomposites

Abstract

Graphene is an emerging material due to its unique properties such as electrical, mechanical, optical, chemical and thermal properties and hence it has a lot of potentials to use in several applications. The graphene oxide is generally defined as a single layer of graphene with oxygen functional groups present in basal planes and edges of the graphene structures. These functional groups are mostly hydroxyl, epoxide, ketone and carboxyl on the surface of graphene layer at basal plane and edges. Therefore, GO is easily dispersible in water and other organic solvents and hence, mostly applicable in different forms such as thin films, composites and hybrid materials. Composites are novel type materials and have unique properties than host matrix. Graphene can be used in the composite material as filler to develop novel composites which have novel and unique properties. Comparative other nanomaterial graphene is more suitable for making the nanocomposite because of easy synthesis process of graphene with large-scale production for industrial application. To prepare the graphene-based composite mostly used graphene derivatives, it has tunable electrical and optical properties, based on the composite properties the applicationsFrom the recent literature, we have concluded that graphene oxide can be synthesized by a chemical process which is a simple, cost- effective and more economical. Further, the obtained GO can be reduced by using suitable reducing agents to obtain reduced graphene oxide(RGO), which has a lot of potentials to be used in several applications. However, most of current studied mainly focus on the synthesis of the graphene oxide and the corresponding reduced graphene oxide by using one size graphite precursor material (~45μm). Therefore, the impacts of the different size graphite precursors ( very smaller to a larger size) as starting material for synthesis of GO and RGO and the details study of the oxidation process, structure, Morphology, bonding characteristics etc are not addressed to our best knowledge. Therefore, there is a lack of clear understanding of the influence of different sizes graphite precursor on the synthesis of GO and RGO by a chemical process. Thus, these issues and challenges need to be addressed. Further, the oxidation reaction temperature is a key factor for controlling the properties of the GO, and further, the quality of RGO obtain from the as-synthesized GO. Hence, the influence of the reaction temperature of the oxidation process need to be addressed and a more details investigation of its effects on the structure, morphology, bonding to be required. Moreover, the reduction of GO to RGO is generally carried out in a few solutions, so more work is still required to understanding the solution effects on the reduction of GO to RGO. In the second part of literature review part, we have thoroughly searched all the recent literature on the synthesis and characterization of the graphene/alumina nanocomposite for its potential to be utilized as potential materials for several applications such as energy, storage devices, capacitors, memory devices and so.on. Though, there are several existing syntheses processes has been reported by several groups and also mentioned that electrical and mechanical properties can be improved by 7 fabrication of the graphene alumina nanocomposite. It is observed that most of the reported work has chosen the α – phase alumina nanoparticles to synthesize the nanocomposites due to the stable phase of the alumina. Also, few reported work are existing, where they have prepared alumina by choosing the alumina precursor to synthesize the alumina by chemical processes such as sol-gel method, finally fabricating the graphene/alumina nanocomposites. Moreover, the most of the reported work mainly focuses on the fabrication of the bulk materials by SPS process and then to investigate the different properties of the nanocomposites. Therefore, to the best of our knowledge, still, there is a lacking of clearly understanding the graphene /alumina nanocomposite structure, morphology, and bonding characteristics, when γ – phase alumina is employed as matrix material insisted of α – phase alumina. Further, the as the obtained powder form of the graphene /alumina nanocomposite need to be studied in details, as these powder form can be used as starting material for thin films formation, for another hybrid material synthesis and also for utilizing as filler material for more complex hybrid material fabrication. Thus there are still more challenges are there to clearly understand the GO and RGO synthesis process by a chemical method and also for fabrication of graphene /alumina nanocomposites for effectively using these materials for mass production and also for several practical applications. In this thesis research work, the influence of the synthesis parameters such as oxidation reaction temperature (low and high) on the structure, morphology, bonding and properties of the graphene oxide(GO) and the corresponding chemically and thermally reduced graphene oxide(RGO) was studied by using the standard Modified Hummers synthesis method. In the second part of the thesis work, the influence of the different sizes source graphite on the synthesis of graphene oxide (GO) and corresponding reduced graphene oxide (RGO) was investigated by choosing the optimum synthesis parameters as obtained from the first part of the research work. The impacts of host graphite powder sizes on the structure, morphology, disorder, bonding and properties were also investigated by using the different analytical instruments. In the final part of the thesis work, a set of six GO/RGO-Al2O3 nanocomposite was synthesized by choosing -phase Al2O3 using the colloidal mixing process and the effects of the different additives such as HCl, Hydrazine hydrate and without any additives were investigated. The corresponding nanocomposites structure, morphology, bonding, interface and thermal stability were investigated by using different analytical instruments such as XRD, FESEM, TEM, FT IR, Raman spectroscopy and TGA/DTA for understanding the nanocomposite formation. Graphene oxide was synthesized by varying the reaction temperature (low and high) by using the equal ratios of graphite, H2SO4, NaNO3 and KMnO4. All the samples were analyzed by using the XRD, FT IR, Raman, TEM, FESEM, UV and TGA/DTA for structural, molecular & bonding characteristics, morphological and thermal analysis. Experimental results indicated that oxidation reaction temperature has an effective role in the synthesis of GO. It was observed that low- temperature reaction showed the good quality of graphene oxide(GO) with better structural, less disorder and 2-3 layers of GO as compared to the higher reaction temperature. Further, the 8 corresponding reduced graphene oxide (RGO) was obtained by using hydrazine hydrate and thermal reduction process, and experimental results confirmed that the RGO which was obtained by using the lower reaction temperature GO showed less disorder, more graphical structure, flat type and 2-3 layers as compared to the GO obtained at higher temperature. Three different sizes graphite precursor (2-15 μm, <45 μm, and 170-840μm,) were oxidized by MHM method and then corresponding RGO were synthesized by the hydrazine hydrate reduction process. The experimental results indicated that the smaller size precursor graphite was fully oxidized in comparison to the large size graphite as source material. Hence, oxidation of graphite to graphene oxide is size depended on the source graphite and also showed better quality of reduced graphene oxide than other sizes. Further, from the TGA and DTA analysis, it is observed that different weight loss and different exothermic peak position in the graphite oxide which suggest that weight loss also depends on the size graphite due to the oxidation rate. UV spectroscopy analysis shows different abortion peaks which indicated that all the sizes graphite oxidized differently. Hence, the precursor graphite size has a key role in the synthesis of GO and corresponding RGO. A set of six GO/RGO-Alumina nanocomposites were prepared by colloidal mixing process by varying the reaction temperature (at RT and 800c) and different additives such as HCL and hydrazine hydrate. From all the analytical analysis results such as XRD, FESEM, FTIR, Raman, TEM is TGA and DTA, it was concluded that only when hydrazine hydrate was used as an additive GO was reduced during the synthesis process and RGO – Al2O3 nanocomposite was formed. All other cases GO – Al2O3 nanocomposites formed. Hence, RGO-Alumina nanocomposite can be synthesized by using hydrazine hydrate as an additive during fabrication process by using a smaller size -phase alumina nanoparticles. Different GO/RGO- Al2O3 nanocomposites were synthesized by using the optimum process parameters as obtained by varying the wt% GO (0.5, 1, 3, 5, 10 and 20 wt %) and all the samples were analyzed by using XRD, FT IR, Raman and TEM. Experimental results indicated that as the GO content increases more disorder and less agglomeration of the alumina nanoparticles are observed. Further, it was seen that as the GO content increases the oxygen-related function groups are removed because of more interaction between the GO and alumina nanoparticles. In this thesis work, GO/RGO- alumina nanocomposites were synthesized and formation of the graphene-alumina nanocomposite was confirmed based on the structural, bonding, morphological and TGA/DTA analysis, however still to use such nanocomposites in practical application such as energy storage, memory devices and other applications, properties such as mechanical, catalytic and electrical are needed to be addressed. Therefore, the future scope of this thesis works to investigate the electrical, mechanical properties and the percolation threshold in order to utilize this nanocomposite for practical memory devices and energy applications.