Novel Wet Chemical Syntheses of Graphene Oxide and Vanadium Oxide for Energy Storage Applications

Graphene has inspired the intrigue of researchers and industry for its potential to improve the performance of existing materials and create entirely new materials and devices. Although graphene has numerous proposed applications, it has not seen widespread adoption in the marketplace. This is partly due to the limitations of existing graphene synthesis routes, which can be costly, hazardous, low yield, or difficult to scale. Electrochemical approaches to graphene synthesis, however, may allow us to address these challenges. In this thesis, an electrochemical route to graphene is developed and its applications explored. Specifically, a packed bed electrochemical reactor capable of producing electrochemically-derived graphene oxide (EGO) from graphite is introduced. The developed method has several distinguishing features which make it promising for certain applications and larger-scale implementation. In contrast to most existing electrochemical approaches, the current method can use as its input natural flake graphite with no binder, compression, or extensive preprocessing. Low, constant current anodic charging in a dilute sulfuric acid electrolyte produces graphite oxide which can be readily dispersed in polar solvents to predominantly single- to few-layer EGO. The graphite electrode making up the packed bed can be scaled along all of its dimensions for larger scale implementations. The product can be thermally treated in air at 200 °C to increase its conductivity beyond what is possible with conventional, chemically-derived graphene oxide. Throughout the thesis, several key synthesis parameters are explored to improve our fundamental understanding of graphite oxidation and produce a variety of EGO products. It was found that using boron-doped diamond as the conductive interface between the graphite and power source dramatically improved the yield. The dispersibility and degree of oxidation could be increased by using expanded graphite as precursor. Poor electrolyte diffusion throughout the packed bed was overcome by implementing bulk solution diffusion channels inside the bed itself. A systematic study found several relationships between the electrolyte acid concentration and the product. Dilute sulfuric acids (less than or equal to 7.1 M) produced EGO with a less crystalline and less oxidised structure, relative to the more concentrated acid. It was found that 11.6 M sulfuric acid produced optimally oxidised graphene, while 7.1 M acid produced less oxidised, but more conductive material. Two different graphene applications were considered. The utility of EGO as a conductive nanofiller in lithium ion battery cathodes was demonstrated. A thorough investigation also explored EGO as a conductive nanofiller in flexible, wearable tactile sensors. Here, EGO can be readily mixed with aqueous surfactantwrapped polydimethylsiloxane (PDMS), 3D printed, then thermally deoxygenated in situ. The 3D printed sensors have exceptional feature resolution and performance. Ultimately, the current thesis represents a significant step forward for EGO synthesis and application. The experiments demonstrate the utility of electrochemical reactor engineering for producing new processes and unique types of graphene. This type of work will be critical for the eventual larger-scale production of electrochemically-derived graphene.

The chemically modified graphite oxide was characterized using FTIR and XRD method. Both results indicate that the presence of oxidation functional groups on the surface of graphite oxide might enlarge the interlayer spacing of graphite. The ratio of ID/IG for graphite oxide determined using Raman spectrometer was increased, which could be well dispersed into graphene oxide through ultrasonication process. Therefore, polyamide 46 (PA46)/graphene oxide (GO) and polyamide 612 (PA612)/graphene oxide nanocomposits were successfully fabricated in this study by solution mixing PA46 and PA612 into chemically modified graphite oxide through ultrasonication process. The effect of GO on the microstructure, crystallization behavior and physical properties were investigated. Both TEM and XRD results show the graphene oxide was well distributed into polyamide matrix. The crystallize structure of polyamide did not change with the incorporation of GO. The crystallization behavior of PA46/GO nanocomposite were investigated using DSC. The addition of 5wt% GO into PA46 matrix could induce hetergeneous nucleation and enhance the crystalline growth rate of PA46 crystalline. The incorporation of 5wt% GO into PA46 matrix could reduce the activation energy from 742.8 kJ/mol for PA46 into 588.0 kJ/mol. The equilibrium melting temperature of 5wt% PA46/GO nanocomposite is reduced from 335.7℃ for neat PA46 matrix into 323.9℃, suggesting that the crystalline structures of PA46/GO nanocomposites was less perfect than that of the PA46 matrix. The POM data of nanocomposite revealed that the addition of GO into PA46 matrix could increase the nucleation density and reduce the spherulitic size. The folding energy of PA46/GO nanocomposites decreased from 3.71×103 erg2/cm4 for PA46 into 2.08×102 erg2/cm4 for 5wt% PA46/GO nanocomposites. The storage modulus of nanocomposites obtained using DMA increased from 8.9×108 Pa for PA46 into 1.8×109 Pa for 5wt% PA46/GO nanocomposite. The result suggests that the incorporation of GO into polymr matrix could reduce the polymr chain movement within the gallery of GO sheets. The crystallinity of PA46/GO nanocomposite is increased from 46.7% for neat PA46 matrix into 54.1% for 5wt% nanocomposite, suggesting that the addition of GO into PA46 matrix could induce hetergeneous nucleation and thus increased the crystallinity. DSC isothermal results of PA612/GO nanocomposites revealed that the addition of 3wt% GO into PA612 matrix could induce hetergeneous nucleation and enhance the crystalline growth rate of PA612 crystalline. Addition of 5wt% GO into PA612 matrix causes more steric hindrance, thus reduce the transportation ability of polymer chains during crystallization process. The incorporation of 3wt% GO into PA612 matrix could reduce the activation energy from 391.6 kJ/mol for PA612 into 308.3 kJ/mol, and then increase to 331.2 kJ/mol as the loading of 5wt% GO. This result indicates that the addition of 5wt% GO into PA612 matrix reduced the transportation ability of polymer chains during crystallization. The equilibrium melting temperature of 5wt% PA612/GO nanocomposite are reduced from 222.6℃ for neat PA612 matrix into 214.7℃, suggesting that the crystalline structures of PA612/GO nanocomposites was less perfect than that of the PA612 matrix. The POM data of nanocomposite revealed that the addition of GO into PA612 matrix could increase the nucleation density and reduce the spherulitic size. The folding energy of PA612/GO nanocomposites decreased from 1.71×102 erg2/cm4 for PA612 into 7.32×101 erg2/cm4 for 3wt% PA612/GO nanocomposites, and then increase to 9.24×101 erg2/cm4 as the loading of 5wt% GO, thus a reduces the transportation ability of polymer chains. The storage modulus of nanocomposites obtained using DMA increased from 1.03×109 Pa for PA612 into 1.57×109 Pa for 5wt% PA612/GO nanocomposite. The result suggests that the incorporation of GO into polymr matrix could reduce the polymr chain movement within the gallery of GO sheets. The crystallinity of PA612/GO nanocomposite is increased from 30.4% for neat PA612 matrix into 32.0% for 3wt% nanocomposite, suggesting that addition of GO into PA612 matrix could induce hetergeneous nucleation and thus increased the crystallinity. As the loading of 5wt% GO into PA612 matrix could decrease the crystallinity to 30.8%, which might due to the limitation of polymer chain movement for crystallization.

Development and Application of Operando Spectroscopy for Vanadium Oxide Catalysts in ODH Reactions: A Comparison of O2 and CO2 as Oxidising Agents

Bulk amount of graphite oxide was prepared by oxidation of graphite using the modified Hummers method and its ultrasonication in organic solvents yielded graphene oxide (GO). X-ray diffraction (XRD) pattern, X-ray photoelectron (XPS), Raman and Fourier transform infrared (FTIR) spectroscopy indicated the successful preparation of GO. XPS survey spectrum of GO revealed the presence of 66.6 at% C and 30.4 at% O. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) images of the graphene oxide showed that they consist of a large amount of graphene oxide platelets with a curled morphology containing of a thin wrinkled sheet like structure. AFM image of the exfoliated GO signified that the average thickness of GO sheets is ~1.0 nm which is very similar to GO monolayer. GO/epoxy nanocomposites were prepared by typical solution mixing technique and influence of GO on mechanical and thermal properties of nanocomposites were investigated. As for the mechanical behaviour of GO/epoxy nanocomposites, 0.5 wt% GO in the nanocomposite achieved the maximum increase in the elastic modulus (~35%) and tensile strength (~7%). The TEM analysis provided clear image of microstructure with homogeneous dispersion of GO in the polymer matrix. The improved strength properties of GO/epoxy nanocomposites can be attributed to inherent strength of GO, the good dispersion and the strong interfacial interactions between the GO sheets and the polymer matrix. However, incorporation of GO showed significant negative effect on composite glass transition temperature (Tg). This may arise due to the interference of GO on curing reaction of epoxy.

Graphene oxide(GO) was prepared by chemical oxidation- sonicated crushing method with flake graphite, sulfuric acid and potassium permanganate as raw materials. The prepared GO was characterized by means of spectroscopy SEM, laser granulometer, FT-IR, UV-vis and AFM. The results show that the few-layered GO could be differentiated from the multi-layered graphite oxide in a solution of the mixture of the two by observing the variation of the intensity and the profile of absorption peaks around 230 nm in the UV- vis spectroscopy. Based on this phenomenon, the qualitative and quantitative analysis of graphene oxides in the solution can be realized. Thereby the optimal conditions for the preparation of graphene oxide can be obtained. It is proposed that the appearence of multi absorption peaks nearby 230 nm in the UV spectra of GO may be attributed to the existence of a peculiar structure of discontinues p-p* conjugated system in the graphene oxide.

Graphene's superlative electrical and mechanical properties, combined with its compatibility with existing planar silicon-based technology, make it an attractive platform for novel nanoelectronic devices. The development of two such devices is reported—a nonvolatile memory element exploiting the nanoscale graphene edge and a field-effect transistor using graphene for both the conducting channel and, in oxidized form, the gate dielectric. These experiments were enabled by custom software written to fully utilize both instrument-based and computer-based data acquisition hardware and provide a simple measurement automation system. Graphene break junctions were studied and found to exhibit switching behavior in response to an electric field. This switching allows the devices to act as nonvolatile memory elements which have demonstrated thousands of writing cycles and long retention times. A model for device operation is proposed based on the formation and breaking of carbon-atom chains that bridge the junctions. Information storage was demonstrated using the concept of rank coding, in which information is stored in the relative conductance of multiple graphene switches in a memory cell. The high mobility and two dimensional nature of graphene make it an attractive material for field-effect transistors. Another ultrathin layered material—graphene's insulating analogue, graphite oxide—was studied as an alternative to bulk gate dielectric materials such as Al2O3 or HfO2. Transistors were fabricated comprising single or bilayer graphene channels, graphite oxide gate insulators, and metal top-gates. Electron transport measurements reveal minimal leakage through the graphite oxide at room temperature. Its breakdown electric field was found to be comparable to SiO2, typically 1–3 × 108 V/m, while its dielectric constant is slightly higher, κ ≈ 4.3. As nanoelectronics experiments and their associated instrumentation continue to grow in complexity the need for powerful data acquisition software has only increased. This role has traditionally been filled by semiconductor parameter analyzers or desktop computers running LabVIEW. Mezurit 2 represents a hybrid approach, providing basic virtual instruments which can be controlled in concert through a comprehensive scripting interface. Each virtual instrument's model of operation is described and an architectural overview is provided.

The partial catalytic oxidation of toluene on pure and mixed vanadium and molybdenum oxides was studied over the temperature range 300–500°C. The main reaction products were maleic anhydride (MA), benzaldehyde (BA), and carbon oxides (CO x ) depending on the catalyst composition and reactor temperature. The samples containing more than 50% vanadium were characterized by conversion and selectivity close to those of pure vanadium oxide V2O5. Reaction temperature was found to influence the amount of products formed, primarily the amounts of MA and BA. The role played by the generation of the singlet molecular oxygen form in the samples and its influence on the selectivity of the reaction is considered.

Selective oxidation is one of the simplest functionalization methods and essentially all monomers used in manufacturing artificial fibers and plastics are obtained by catalytic oxidation processes. Formally, oxidation is considered as an increase in the oxidation number of the carbon atoms, then reactions such as dehydrogenation, ammoxidation, cyclization or chlorination are all oxidation reactions. In this field, most of processes for the synthesis of important chemicals used vanadium oxide-based catalysts. These catalytic systems are used either in the form of multicomponent mixed oxides and oxysalts, e.g., in the oxidation of n-butane (V/P/O) and of benzene (supported V/Mo/O) to maleic anhydride, or in the form of supported metal oxide, e.g., in the manufacture of phthalic anhydride by o-xylene oxidation, of sulphuric acid by oxidation of SO2, in the reduction of NOx with ammonia and in the ammoxidation of alkyl aromatics. In addition, supported vanadia catalysts have also been investigated for the oxidative dehydrogenation of alkanes to olefins , oxidation of pentane to maleic anhydride and the selective oxidation of methanol to formaldehyde or methyl formate [1]. During my PhD I focused my work on two gas phase selective oxidation reactions. The work was done at the Department of Industrial Chemistry and Materials (University of Bologna) in collaboration with Polynt SpA. Polynt is a leader company in the development, production and marketing of catalysts for gas-phase oxidation. In particular, I studied the catalytic system for n-butane oxidation to maleic anhydride (fluid bed technology) and for o-xylene oxidation to phthalic anhydride. Both reactions are catalyzed by systems based on vanadium, but catalysts are completely different. Part A is dedicated to the study of V/P/O catalyst for n-butane selective oxidation, while in the Part B the results of an investigation on TiO2-supported V2O5, catalyst for o-xylene oxidation are showed. In Part A, a general introduction about the importance of maleic anhydride, its uses, the industrial processes and the catalytic system are reported. The reaction is the only industrial direct oxidation of paraffins to a chemical intermediate. It is produced by n-butane oxidation either using fixed bed and fluid bed technology; in both cases the catalyst is the vanadyl pyrophosphate (VPP). Notwithstanding the good performances, the yield value didn’t exceed 60% and the system is continuously studied to improve activity and selectivity. The main open problem is the understanding of the real active phase working under reaction conditions. Several articles deal with the role of different crystalline and/or amorphous vanadium/phosphorous (VPO) compounds. In all cases, bulk VPP is assumed to constitute the core of the active phase, while two different hypotheses have been formulated concerning the catalytic surface. In one case the development of surface amorphous layers that play a direct role in the reaction is described, in the second case specific planes of crystalline VPP are assumed to contribute to the reaction pattern, and the redox process occurs reversibly between VPP and VOPO4. Both hypotheses are supported also by in-situ characterization techniques, but the experiments were performed with different catalysts and probably under slightly different working conditions. Due to complexity of the system, these differences could be the cause of the contradictions present in literature. Supposing that a key role could be played by P/V ratio, I prepared, characterized and tested two samples with different P/V ratio. Transformation occurring on catalytic surfaces under different conditions of temperature and gas-phase composition were studied by means of in-situ Raman spectroscopy, trying to investigate the changes that VPP undergoes during reaction. The goal is to understand which kind of compound constituting the catalyst surface is the most active and selective for butane oxidation reaction, and also which features the catalyst should possess to ensure the development of this surface (e.g. catalyst composition). On the basis of results from this study, it could be possible to project a new catalyst more active and selective with respect to the present ones. In fact, the second topic investigated is the possibility to reproduce the surface active layer of VPP onto a support. In general, supportation is a way to improve mechanical features of the catalysts and to overcome problems such as possible development of local hot spot temperatures, which could cause a decrease of selectivity at high conversion, and high costs of catalyst. In literature it is possible to find different works dealing with the development of supported catalysts, but in general intrinsic characteristics of VPP are worsened due to the chemical interaction between active phase and support. Moreover all these works deal with the supportation of VPP; on the contrary, my work is an attempt to build-up a V/P/O active layer on the surface of a zirconia support by thermal treatment of a precursor obtained by impregnation of a V5+ salt and of H3PO4. In-situ Raman analysis during the thermal treatment, as well as reactivity tests are used to investigate the parameters that may influence the generation of the active phase. Part B is devoted to the study of o-xylene oxidation of phthalic anhydride; industrially, the reaction is carried out in gas-phase using as catalysts a supported system formed by V2O5 on TiO2. The V/Ti/O system is quite complex; different vanadium species could be present on the titania surface, as a function of the vanadium content and of the titania surface area: (i) V species which is chemically bound to the support via oxo bridges (isolated V in octahedral or tetrahedral coordination, depending on the hydration degree), (ii) a polymeric species spread over titania, and (iii) bulk vanadium oxide, either amorphous or crystalline. The different species could have different catalytic properties therefore changing the relative amount of V species can be a way to optimize the catalytic performances of the system. For this reason, samples containing increasing amount of vanadium were prepared and tested in the oxidation of o-xylene, with the aim of find a correlations between V/Ti/O catalytic activity and the amount of the different vanadium species. The second part deals with the role of a gas-phase promoter. Catalytic surface can change under working conditions; the high temperatures and a different gas-phase composition could have an effect also on the formation of different V species. Furthermore, in the industrial practice, the vanadium oxide-based catalysts need the addition of gas-phase promoters in the feed stream, that although do not have a direct role in the reaction stoichiometry, when present leads to considerable improvement of catalytic performance. Starting point of my investigation is the possibility that steam, a component always present in oxidation reactions environment, could cause changes in the nature of catalytic surface under reaction conditions. For this reason, the dynamic phenomena occurring at the surface of a 7wt% V2O5 on TiO2 catalyst in the presence of steam is investigated by means of Raman spectroscopy. Moreover a correlation between the amount of the different vanadium species and catalytic performances have been searched. Finally, the role of dopants has been studied. The industrial V/Ti/O system contains several dopants; the nature and the relative amount of promoters may vary depending on catalyst supplier and on the technology employed for the process, either a single-bed or a multi-layer catalytic fixed-bed. Promoters have a quite remarkable effect on both activity and selectivity to phthalic anhydride. Their role is crucial, and the proper control of the relative amount of each component is fundamental for the process performance. Furthermore, it can not be excluded that the same promoter may play different role depending on reaction conditions (T, composition of gas phase..). The reaction network of phthalic anhydride formation is very complex and includes several parallel and consecutive reactions; for this reason a proper understanding of the role of each dopant cannot be separated from the analysis of the reaction scheme. One of the most important promoters at industrial level, which is always present in the catalytic formulations is Cs. It is known that Cs plays an important role on selectivity to phthalic anhydride, but the reasons of this phenomenon are not really clear. Therefore the effect of Cs on the reaction scheme has been investigated at two different temperature with the aim of evidencing in which step of the reaction network this promoter plays its role.

The thesis conceives few important contemporary problems that are faced by graphene researchers, through its title, “Stabilized Graphene Nanohybrids: Magnetism and Cancer Therapy”. Even though, the experimental realization of graphene challenged the Mermin-Wagner theorem, graphene continues to be at the centre of research world by surprising the research community with its established astonishing attributes and mesmerising with scientific developments from time to time. The thesis revolves about the understanding of the intriguing magnetism of graphene and designing a suitable nanohybrid for cancer treatment applications. This is achieved through synthesizing graphene and its derivatives by novel techniques. Further, the origin of magnetism is explored. Finally, we demonstrate ways to tackle few generic issues of this wonder material for potential applications. There are seven chapters in the thesis. The first chapter clearly expresses the aim, motivation and the highlights of the project undertaken. The second chapter gives a brief review of the literature in concerned areas that is necessary to comprehend the mid-chapters, thereby contributing to the growth of it. However, specific literature survey could also be found in the introduction of every chapter. The third chapter gives a novel method to synthesize luminescent graphitic quantum dots by exposing the size reduced graphene oxide to UV radiation. These quantum dots showed defect mediated ferromagnetic behavior. The chapter four reports the production of bi- and tri-layered graphene solution by liquid phase exfoliation of graphite at high temperature and pressure. The bi- and tri-layered graphene were found to be twisted and with lesser defects due to the oxidation or reduction free synthesis. These types of twisted graphene are potential candidates for spintronics applications. Further, the origin of magnetism and deconvolution of the mixed magnetism in exfoliated graphite is discussed. The mixed magnetism in exfoliated graphite is deconvoluted using low field-high field hysteresis loops at different temperatures. The strength of the interactions among the edge states (intra- and inter-zigzag), the external field and the temperature play important roles in deciding the final magnetic state of the system. The chapter five solves a serious problem of reduced graphene oxide pertaining to its dispersion stability that has impaired its use in several commercial applications. The reduced graphene oxide is stabilized using cross-linking polymers, thereby improving its bio-compatibility. The dispersion follows an electrosteric stabilization mechanism. Also, various theoretical models were adopted to understand this enhanced stability by estimating the potential barrier for agglomeration, surface free energy and Hansen solubility parameters of the dispersion. The chapter six combines few of the above synthesis techniques to produce a polymer stabilized iron oxide-graphene nanohybrid that has good response to the thermo-chemotherapy of cancer. The synthesis procedure is simple and easy to commercialize for large scale production due to its one-pot approach. The nanohybrid is found to have a good colloidal stability and is also biocompatible even at higher concentrations (2.5 mg/ml) by virtue of cross-linking polymers. The bio-compatibility of the composite is tested using HeLa cell lines by computing the percentage of the reactive oxygen species. The composite has the ability to load and release both hydrophobic and hydrophilic drugs with a good loading efficiency and capacity. Under an AC magnetic field, it takes less than 16 min to reach the stable hyperthermia temperature, suggesting it as a good anticancer material. A time-dependent cellular uptake of doxorubicin-conjugated composite has been studied to optimize the parameters for thermo-chemotherapy of cancer. The synergetic effect of both, the drug and hyperthermia is observed in the killing of the cancerous cells-verified by computing the cell apoptotic population using a flow cytometer. However, it has been noticed that, even in the absence of chemotherapy, the composite shows good antiproliferative activity with thermotherapy alone. Finally, the chapter seven summarises the thesis and outlines any future prospects. The thesis have produced five international journal articles (Carbon, RSC Advances, Applied Physics Letters, Journal of Physical Chemistry C, and ACS Applied Materials & Interfaces). The thesis winds up with a gratefulness to the persons who have directly or indirectly contributed for its existence. Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the Indian Institute of Technology Bombay, India and Monash University, Australia.

Graphite intercalation compounds (GIC), i.e., graphite flakes embedding small molecules or ions, have been described in the literature since 1851 by Schafheutl. These extraordinary materials can be exploited for a number of technological applications, in different industrial �elds (for example, they have been used for the industrial preparation of expanded graphite, novel superconductors, catalysts, anode materials, etc.). Some GICs (e.g., graphite nitrate and graphite bisulfate) are able to expand remarkably by thermal heating, and the achieved expanded graphite can be used to prepare graphite nanoplatelets (GNP), Few Layer Graphene (FLG), and graphene monolayer. Here an expandable graphite (graphite bisulfate) is prepared by intercalation of graphite with sulfuric acid, in presence of an oxidizing agent. In this study, different chemical formulations for the synthesis of highly intercalated graphite bisulfate have been tested. In particular, nitric acid, potassium nitrate, potassium dichromate, potassium permanganate, sodium periodate, sodium chlorate, and hydrogen peroxide have been used in this synthesis scheme as the auxiliary reagent (oxidizing agent). The intercalation reaction was performed in a glass-flask reactor (placed in a thermostatic bath), using air bubbling as homogenizing approach. The reaction time always was 1h and the H2SO4: oxidizing agent ratio was 9 : 1 by volume for all reactive mixtures. Graphite flakes were placed in the glass reactor and then the oxidizing compound, dissolved in absolute H2SO4, was added. The reactions were stopped by adding deionized water to the systems. In order to evaluate the presence of delamination, and pre-expansion phenomena, and the achieved intercalation degree in the prepared samples, the obtained graphite intercalation compounds have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), infrared spectroscopy (FT-IR), micro-Raman spectroscopy (µ=RS) and thermal analysis (TGA). Delamination and pre-expansion phenomena were observed only for nitric acid, potassium dichromate and hydrogen peroxide, while the presence of strong oxidizers (KMnO4; NaIO4) led to stable graphite intercalation compounds. The largest content of intercalated bisulfate is achieved in the GICs obtained from NaIO4 and NaClO3.

Although ordinary Portland cement (OPC) is one of the most widely used construction materials in the world, its relatively weak tensile strength and proneness to cracks limit wider structural applications. Graphene oxide (GO) offers an interesting prospect of two-dimensional nanosheets in reinforcing OPC. Investigation of GO-reinforced cement composites is at a relatively early stage and very limited research into the effectiveness of GO in enhancing the tensile or flexural strengths of OPC is available. Thus there is a significant need for further studies in this area to understand the reinforcing behaviour of GO in cement matrix, including the dispersion of GO and the effect of GO on OPC paste in terms of mechanical properties, workability and microstructure. This study develops a fabrication protocol for the production of GO-paste and subsequently characterises the mechanical properties of the composite. Specifically, the objectives of this study are (1) to understand the procedure of preparing GO nanomaterial, (2) to study the dispersion behaviour of GO and (3) to investigate the role of GO in reinforcing cement matrix via mechanical properties and microstructural observations. As an emerging field of study, the procedure of incorporating GO nanomaterial into cement composites is yet to be established. During the production of GO, a two-step oxidation is applied to attach oxygen functional groups into the GO nanosheets. To ensure that GO is well dispersed in water as single-layered nanosheets, mild ultrasonication is supplied. The size distribution and dispersion quality of the GO produced is studied using zeta potential. This step is necessary to determine the optimal ultrasonication input, which is established as 15 J/mL. To develop high-performance GO-reinforced OPC paste, the dispersion of GO in water, alkali and aqueous solutions is studied. UV-vis confirms that only a mild sonication input is required for GO to be well dispersed in water. However, GO undergoes agglomeration when exposed to very alkaline solutions exceeding pH 13, highly concentrated ionic solutions, or in the presence of calcium ions. Therefore, the use of surfactants in the form of cement admixtures is crucial to protect GO against agglomeration. The incorporation of GO (of 0.02 wt.% of cement) substantially enhances the mechanical properties of plain cement. For example, the tensile strength is improved by 68.3% and flexural strength by 53.5%. These enhancements in the tensile and bending strengths may be attributed to the filling of GO in nano-sized colloidal pores and bridging over cracks. Moreover, a pore solution rich in calcium ions converts GO nanosheets into GO paper, producing stronger reinforcement. This project lays the foundation for other researchers and practitioners to better understand and apply the novel GO-cement composite with improved mechanical properties in the design of structures.

In this work, properties of Calcium alginate-reduced graphene oxide and Barium alginate‐reduced graphene oxide composite films are explored. In addition, the properties of the divalent metal ion-cross-linked alginate composite films are compared to the analogous properties of uncross‐linked Sodium alginate-graphene oxide composite films of the corresponding compositions. As the filler, used in the preparation of the composite films, is obtained by chemical oxidation of graphite, the prevailing knowledge of the process coupled with in situ X-ray diffraction investigation of the samples prepared by such a method is presented as well.

In this thesis, shape memory nanocomposites were prepared and characterized. The polymer matrix consisted in an epoxy-based liquid crystalline elastomer (LCE). Multi-walled carbon nanotubes (MWCNT) and graphite nanoplatelets (GNP) were selected as fillers. The influence of different contents of nanofillers on mechanical, thermal and shape memory properties was evaluated. In order to disperse and homogeneously distribute the nanofillers within the polymer matrix an in-depth evaluation on the optimal conditions to synthesize the materials was carried out. These conditions had a substantial influence on the final distribution of the nanofillers within the epoxy-based matrix, which was analyzed from a macroscopic and microscopic point of view. The best results were obtained through a chemical surface modification of the nanoparticles. The chemical modification of MWCNTs consisted in grafting the selected epoxy monomers on the surface. The obtained adducts were characterized in terms of chemical, thermal and morphological features. Concerning GNP, a similar protocol based on surface modification was carried out. In this case, a preliminary oxidation process was performed in order to promote the exfoliation of graphene sheets, in form of graphene oxide (GO), and to favour their dispersion within the polymer matrix. Different degrees of oxidation were attempted. GO nanoparticles were successively modified with epoxy monomers. Also in this case, chemical, morphological, structural and thermal characterization was carried out. Surface modified carbonaceous nanoparticles were then dispersed in varying amounts in the organic matrix. The obtained nanocomposite systems were characterized in their chemical-physical and morphological properties. The adopted compatibilization strategies used for both MWCNTs and GNP were found to be extremely effective to get homogeneous samples and to enable a dramatic enhancement of the actuation extent at low nanofiller content. Moreover, the stress threshold required to trigger the reversible thermomechanical actuation was significantly decreased. The effect of nanoparticles on thermomechanical properties of the materials was correlated to the microstructure and the phase behavior of the host system. Results demonstrated that the incorporation of carbon nanofillers amplified the soft-elastic response of the liquid crystalline phase to external stimuli. Tunable thermomechanical properties of these systems make them suitable for a variety of potential advanced applications ranging to robotics, sensing and actuation, and artificial muscles.

Alkanes are the major components of natural gas and petroleum; however, there are only few practical processes that can functionalize them into more valuable products such as alkene or alcohols. The reason for this difficulty is because alkanes possess strong and inert C-H bonds. The development of such a process that can convert alkanes to other more valuable functionalized hydrocarbons in a catalytic fashion would produce enormous economic benefits. The key to achieve this goal is to develop a proper catalyst. The catalysts can be organometallic complexes or metal oxide surfaces that catalyze alkane C-H activation and functionalization in homogeneous or heterogeneous conditions. In this thesis, we apply quantum mechanics to study the known alkane functionalization reactions to provide more insight into those catalytic processes, and we further utilize our computational results to design new reaction pathways for alkane functionalization. Each chapter presented herein constitutes an independent publication focusing on different aspects of the problem. Chapter 1: Single-Site Vanadyl Activation, Functionalization, and Reoxidation Reaction Mechanism for Propane Oxidative Dehydrogenation on the Cubic V4O10 Cluster: Vanadium oxide is a powerful heterogeneous catalyst that can convert oxidative dehydrogenation (ODH) of propane. Despite numerous studies, either computational or experimental, on this topic, no complete catalytic cycle is provided. In this paper, we examined the detailed mechanism for propane reacting with a V4O10 cluster to model the catalytic oxidative dehydrogenation (ODH) of propane on the V2O5(001) surface. We reported the mechanism of the complete catalytic cycle, including the regeneration of the reduced catalyst using gaseous O2, in which only a single vanadyl site is involved. This mechanism is applicable to propane ODH on the supported vanadium oxide catalysts where only monovanadate (O=V-(O)4-) species is present. Chapter 2: The Magnetic and Electronic Structure of Vanadyl Pyrophosphate from Density Functional Theory: We have studied the magnetic structure of the high-symmetry vanadyl pyrophosphate, focusing on the spin exchange couplings, applying density functional theory with exact exchange and the full three-dimensional periodicity to this system for the first time. Based on the local density of states and the response of spin couplings to varying the cell parameter a, we found that two major types of spin exchange couplings originate from different mechanisms: one from a super-exchange interaction and the other from a direct exchange interaction. Based on the variations in V–O bond length as a function of strain along a, we found that the V–O bonds of V–(OPO)2–V are covalent and rigid, whereas the bonds of V–(O)2–V are fragile and dative. Chapter 3: The Para-Substituent Effect and pH-Dependence of the Organometallic Baeyer-Villiger Oxidation of Rhenium-Carbon Bonds: Organometallic Baeyer-Villiger represents another means of oxidizing M-R to M-OR. In this work, we conducted a series of calculations with the goal of providing more insights into the reaction. We find that during this organometallic BV oxidation, the migrating phenyl plays the role of a nucleophile and the leaving group OH is nucleophile. Moreover, we also find that for R = Ph the reaction rate is much faster than that for R = Me, which is later confirmed by experiments. Chapter 4: Carbon-Oxygen Bond-Forming Mechanisms in Rhenium Oxo-Alkyl Complexes: Intramolecular 1,2-migration of hydrocarbyl across metal-oxo bonds is one of the few means of oxy-functionalizing M-R to M-OR bonds. This strategy works for R = Ph, but fails for R = Me and Et. In this work, we study these systems with the goal of understanding the reason. We find that when R = Me and Et the α-hydrogen is very acidic and easy to abstract even with weak base, such as the counter ion of the complex, leading to unwanted by-products. We find that these side reactions can be avoided by two means: (1) use counter ions with weaker basicity to increase proton abstraction barriers, and (2) use R = iPr, which has a higher migratory aptitude, to accelerate the 1,2-migration rate. Chapter 5: A Homolytic Oxy-Functionalization Mechanism: Intermolecular Hydrocarbyl Migration from M-R to Vanadyl Oxo: Oxy-functionalization Mδ+-Rδ- to M-OR bonds is one of the key challenges in the development of hydrocarbon hydroxylation catalysts. This can be achieved by limited means: (1) organometallic Baeyer-Villiger oxidation, and (2) intramolecular 1,2-migration of hydrocarbyl across metal-oxo bonds. In this work, we have examined C-O bond formation in the reaction of OVCl3 with Ph2Hg to generate phenol using quantum mechanics. Surprisingly, we find this reaction is through an unprecedented bimolecular, one-electron oxidation of the V-Ph bond by a second V=O moiety, not through the experimentally proposed intramolecular phenyl 1,2-migration across V=O bonds. Our calculations on the oxidation of Rh-CH3 and Ir-CH3 complexes by OVCl3 further suggest that the possibility of integrating this new oxidation mechanism into alkane oxidation catalytic cycles. We also give guidelines to choose the systems in which this oxidation mechanism may play an important role.

Pyrenebutyric acid-assisted room-temperature synthesis of large-size monolayer graphene oxide with high mechanical strength