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Lacovig, Paolo. "Electronic structure, morphology and chemical reactivity of nanoclusters and low-dimensional systems: fast photoemission spectroscopy studies." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3685.
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2008/2009L'obiettivo di questa tesi è l'applicazione della spettroscopia di fotoemissione allo studio di nanoparticelle supportate e di sistemi a bassa dimensionalità. Ad una primo periodo dedicato allo sviluppo del rivelatore e del software per un nuovo analizzatore d'energia per elettroni installato presso la linea di luce SuperESCA ad Elettra, è seguita una fase durante la quale ho eseguito una serie di esperimenti mirati ad esplorare le potenzialità del nuovo apparato sperimentale. Il primo risultato ottenuto riguarda la comprensione della relazione che intercorre tra le variazioni della reattività chimica del sistema Pd/Ru(0001) e il numero degli strati di Pd cresciuti in modo pseudomorfico sul substrato di rutenio. La risoluzione temporale raggiunta con la nuova strumentazione ci ha permesso di studiare processi dinamici su una scala temporale fino ad ora inaccessibile per la spettroscopia di fotoemissione dai livelli di core: in particolare abbiamo studiato la crescita del grafene ad alta temperatura sulla superficie (111) dell'iridio e la reattività chimica di nanocluster di Pt supportati su MgO. Nel primo caso abbiamo messo in evidenza come la formazione del grafene proceda attraverso la nucleazione di nano-isole di carbonio che assumono una peculiare forma di cupola. Nel secondo caso siamo riusciti a seguire sia la dinamica del processo di adsorbimento di CO, sia la reazione CO + 1/2 O2 -> CO2 sulle nanoparticelle di Pt depositate su un film ultra-sottile di ossido di magnesio. Infine, abbiamo caratterizzato la morfologia di nanoparticelle di Pd, Pt, Rh e Au cresciute su diversi substrati a base di carbonio, in particolare grafite, nanotubi a parete singola e grafene. Tra i vari risultati abbiamo compreso come l'interazione metallo-substrato dipenda dalla dimensione delle nano-particelle e abbiamo evidenziato il ruolo centrale dei difetti del substrato nei processi di nucleazione e intercalazione.
The objective of this thesis is the application of photoelectron spectroscopy for the investigation of supported nanoclusters and low-dimensional systems. After a first stage devoted to the development of the detector and the software for the electron energy analyser installed on the SuperESCA beamline at Elettra, during the PhD project I've performed a series of experiments aimed to explore the capabilities of the new experimental apparatus. One of the first results concerns the understanding of the relation between the modifications in the chemical reactivity of the Pd/Ru(0001) system and the thickness of the pseudomorphically grown Pd overlayer. The temporal resolution achieved with the new experimental set-up allowed us to study dynamical processes on a new time scale, in particular the graphene growth process at high temperature on the Ir(111) surface and the chemical reactivity of Pt nanoclusters supported on MgO. In the former case, we discovered that graphene formation proceeds via preliminary nucleation of dome-shaped C nano-islands. In the second case, we succeded in following both the dynamics of CO adsorption process and the CO + 1/2 O2 -> CO2 reaction on Pt nanoclusters grown on a ultra-thin film of magnesium oxide. Finally, the morphology of Pd, Pt, Rh and Au nanoclusers grown on different carbon-based substrates (namely graphite, single-walled carbon nanotubes and graphene) has been characterized. Among the results we report the understanding of the dependence of the metal-substrate interaction on the cluster size and the role of defects in the nucleation and intercalation processes.
XXII Ciclo
1972
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Thomas, Helen R. "The structure and reactivity of graphene oxide." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/74090/.
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Graphene oxide (GO) can provide a cost-effective route to a graphene-like material on an industrial scale, but produces an imperfect product. In order to improve the quality of the resultant graphene, unanswered questions regarding the structure and chemical reactivity of GO need to be addressed. In this thesis, chapters 1 and 2 serve to introduce the field of graphene and graphene oxide research, as well as standard characterisation techniques. Chapter 3 is concerned with investigating the validity and general applicability of a recently proposed two-component model of GO – the formation of the two components was shown to be largely independent of the oxidation protocol used in the synthesis, and additional characterisation data was presented for both base-washed graphene oxide (bwGO) and oxidation debris (OD). The removal of the OD cleans the GO, revealing its true mono-layer nature and in the process increases the C:O ratio, i.e. a deoxygenation. By contrast, treating GO with hydrazine was found to both remove the debris and reduce (cleaning and deoxygenation) the graphene-like sheets. In chapter 4, different nucleophiles were used to explore bwGO functionalisation via epoxy ring-opening reactions. Treatment of bwGO with potassium thioacetate, followed by an aqueous work-up, was shown to yield a new thiol functionalised material (GO-SH). As far as is known, this was the first reported example of using a sulfur nucleophile to ring open epoxy groups on GO. The incorporation of malononitrile groups, and the direct grafting of polymer chains to the graphene-like sheets was also demonstrated. The thiol groups on GO-SH are amendable to further chemistry and in chapter 5 this reactivity is exploited with alkylation, thiol-ene click and sultone ring-opening reactions. Au(I) and Pd(II) metallo-organic complexes were also prepared, and gold deposition experiments were carried out, demonstrating that GO-SH has a strong affinity for AuNPs. These CMGs have varying solubility and improved thermal stability. Chapter 6 concludes the work covered in this thesis, and full experimental details can be found in chapter 7.
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CARRARO, GIOVANNI. "Chemical reactivity of supported Graphene single layers." Doctoral thesis, Università degli studi di Genova, 2018. http://hdl.handle.net/11567/930002.
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Vacchi, Isabella Anna. "Controlled chemical functionalization of graphene oxide." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAF053.
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L’oxyde de graphène est un nanomatériau prometteur grâce à ses caractéristiques physicochimiques. Cependant, jusqu’à aujourd’hui, sa composition exacte reste encore inconnue. Ceci est dû à la complexité et au caractère non-stoechiométrique de ce matériau. Nous avons commencé par étudier sa composition de surface et sa réactivité. Nous avons utilisé des échantillons synthétisés de manière différente pour explorer la relation entre la méthode de synthèse et la composition de surface. En outre, nous avons préparé un dérivé fonctionnalisé avec un agent chélatant de radionucléides pour étudier sa biodistribution et l’impact de la taille latérale.Par la suite, nous avons essayé plusieurs stratégies de multi-fonctionnalisation. L’avantage est de pouvoir combiner différentes propriétés. Nous avons observé que, souvent après la fonctionnalisation, la dispersabilité de l’oxyde de graphène diminue. Ainsi, nous avons développé un échantillon fonctionnalisé par un polymère soluble dans l’eau. Enfin, nous avons exploré et amélioré les méthodes de caractérisation de l’oxyde de graphène. Une caractérisation approfondie par différentes techniques est fondamentale pour comprendre les modifications que le matériau a subiesGraphene oxide is a promising nanomaterial thanks to its physicochemical characteristics. However, until today its exact composition remains still unknown. This is due to the complexity and non-stoichiometric character of this material.We started by investigating the surface composition of graphene oxide and its reactivity. We used differently synthesized samples to explore the relationship between the synthesis method and the surface composition. Furthermore, we functionalized graphene oxide with a chelating agent of radionuclides to study its biodistribution, and the impact of the lateral size. Afterwards, we tried different strategies for multifunctionalization with the aim to combine different properties. We observed that the dispersibility of graphene oxide often decreased after functionalization. Thus, we developed a highly water-stable graphene oxide sample by grafting awater-soluble polymer on its surface. Finally, we explored and improved the characterization methods for graphene oxide. Athorough investigation using different characterization techniques is fundamental to understand the modifications that the material underwent
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Abedi, Khaledi Navid. "Chemical recognition and reactivity of zinc-oxide surfaces." Doctoral thesis, Humboldt-Universität zu Berlin, 2021. http://dx.doi.org/10.18452/21516.
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ZnO hat wegen seiner potenziellen Anwendung in elektronischen Geräten und als Katalysator viel Aufmerksamkeit erhalten. Die Struktur und Reaktivität von ZnO-Oberflächen haben eine direkte Bedeutung für die Leistung und Funktionalität dieser Geräte. Daher ist die Definition und das Verständnis der atomistischen Details von ZnO-Oberflächenstrukturen von besonderer Bedeutung.
Die atomistischen Details von ZnO-Oberflächen hängen von den Präparationsverfahren ab. Nach der Kristallpräparation ist es notwendig, eine Oberflächencharakterisierung durchzuführen, um eine Verbesserung der Funktionalität und Effizienz von ZnO-basierten opto-elektronischen Bauelementen und Katalysatoren zu erreichen.
Die atomistische Wahrnehmung der Reaktion zwischen einem organischen Molekül und ZnO-Oberflächen spielt eine entscheidende Rolle bei der Optimierung der Wasserstoff-on-demand-Lieferung in Brennstoffzellen. Das Verständnis der atomistischen Details von Adsorption, Diffusion und Dissoziation eines organischen Moleküls ebnet den Weg, um die Vorgänge bei der Wasserstofffreisetzung für Brennstoffzellen zu enträtseln.
Mit dem Ziel, die Struktur- und Stöchiometriebestimmung mit Hilfe der XPS zu ermöglichen, präsentiere ich in dieser Arbeit die Ergebnisse einer umfassenden theoretischen Studie über die Kernniveauverschiebungen von ZnO-Oberflächenrekonstruktionen. Darüber hinaus biete ich eine gründliche Untersuchung der gemischt-terminierten Oberfläche, indem ich zunächst die Bedingungen untersuche, unter denen sich Methanol-Monolagen auf dieser Kristallfläche bilden können, und dann alle möglichen Wege für deren Reaktion erforsche. Diese Studie liefert ein umfassendes Bild, um die wahrscheinlichsten Reaktionsschritte zu identifizieren, die zur Interpretation der experimentellen Ergebnisse herangezogen werden können. Sie wird zukünftigen theoretischen Studien für ähnliche Reaktionen wie die Dehydrierung und die Kinetik der Monolagenbildung, die hier untersucht wurden, helfen.Zinc-Oxide (ZnO) has been getting much attention over the past decades because of its potential application in electronic devices and as a catalyst. The structure and reactivity of ZnO surfaces have direct relevance for the performance and functionality of these devices. Therefore, defining and understanding the atomistic details of ZnO surface structures is of particular importance. The atomistic details of ZnO surfaces depend on the preparation procedures. After the crystal preparation, it is necessary to perform a surface characterization, to achieve an improvement in the functionality and efficiency of ZnO-based opto-electronic devices and catalysts. The atomistic perception of the reaction between an organic molecule and ZnO surfaces plays a crucial role in optimizing hydrogen-on-demand delivery in fuel cells, and understanding the atomistic details of adsorption, diffusion, and dissociation of a simple organic molecule paves the way towards unraveling the procedures involved in the hydrogen liberation for fuel cells. In this work, with the aim of enabling structure and stoichiometry determination by using X-ray photoelectron spectroscopy, I present the results of a comprehensive theoretical study on the core-level shifts of ZnO surface reconstructions. Moreover, I provide a thorough investigation of the mixed-terminated (10-10) surface by first examining the conditions under which methanol monolayers can form on this crystal face and by then exploring all possible pathways for its adsorption, diffusion, and initial dehydrogenation. This study provides a comprehensive picture to identify the most probable reaction steps that can be used to interpret experimental findings and will help future theoretical studies for reactions similar to dehydrogenation of organic molecules and monolayer-formation kinetics that were studied here.
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Nyangiwe, Nangamso Nathaniel. "Graphene based nano-coatings: synthesis and physical-chemical investigations." Thesis, UWC, 2012. http://hdl.handle.net/11394/3237.
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Magister Scientiae - MScIt is well known that a lead pencil is made of graphite, a naturally form of carbon, this is important but not very exciting. The exciting part is that graphite contains stacked layers of graphene and each and every layer is one atom thick. Scientists believed that these graphene layers could not be isolated from graphite because they were thought to be thermodynamically unstable on their own and taking them out from the parent graphite crystal will lead them to collapse and not forming a layer. The question arose, how thin one could make graphite. Two scientists from University of Manchester answered this question by peeling layers from a graphite crystal by using sticky tape and then rubbing them onto a silicon dioxide surface. They managed to isolate just one atom thick layer from graphite for the first time using a method called micromechanical cleavage or scotch tape. In this thesis chemical method also known as Hummers method has been used to fabricate graphene oxide (GO) and reduced graphene oxide. GO was synthesized through the oxidation of graphite to graphene oxide in the presence of concentrated sulphuric acid, hydrochloric acid and potassium permanganate. A strong reducing agent known as hydrazine hydrate has also been used to reduce GO to rGO by removing oxygen functional groups, but unfortunately not all oxygen functional groups have been removed, that is why the final product is named rGO. GO and rGO solutions were then deposited on silicon substrates separately. Several characterization techniques in this work have been used to investigate the optical properties, the morphology, crystallography and vibrational properties of GO and rGO.
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Qin, Jiadong. "Novel Wet Chemical Syntheses of Graphene Oxide and Vanadium Oxide for Energy Storage Applications." Thesis, Griffith University, 2020. http://hdl.handle.net/10072/393192.
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The ever-growing demand for high performance energy storage systems has become a driving force for seeking the ideal materials to deliver superior efficacy, and graphene oxide (GO) and vanadium oxide are such two promising nanostructured materials. However, neither of them has been widely adopted in the marketplace at the current stage, mainly limited by their costeffectiveness.
While GO and vanadium oxide have been proved to outperform existing materials in the lab-scale studies, the more expensive and less scalable synthesis methods discourage industrial manufacturers from adopting the two materials. The research herein focuses on the novel low cost and scalable wet chemical synthesis methods, which may lead GO and vanadium oxide to greater commercial success.
The PhD thesis generally is unfolded into two parts. In the first part, a simple hydrothermal method to synthesize tungsten-doped V6O13 is reported. The introduction of tungsten dopant can have a significant impact on the nanostructure evolution of vanadium oxide during hydrothermal reaction, which results in the formation of nanocrystalline structure. A realtime characterization of the hydrothermal reaction process was employed to reveal the complex phase changes of vanadium oxide in the course, which can be important guidance for controlling the product quality in larger-scale production. Moreover, when applied to lithium ion batteries (LIBs), the doped nanocrystalline V6O13-based electrode can provide better battery performance than the undoped V6O13.
In the second part, graphite oxide route to synthesize graphene oxide is investigated in terms of the choices of graphite sources (expanded graphite, graphite intercalation compound and natural graphite), pre-treatment of expanded graphite (microwave-induced expansion of graphite in different atmospheres), reaction temperature, and post-processing of GO. It was found that the expanded graphite prepared in ambient air had higher dispersibility in organic solvent and finally led to higher GO yield, through the modified Hummers oxidation, than those prepared in pure carbon dioxide or argon. This is possibly due to the introduction of extra oxygen-containing functionalities accompanied by the rapid heating of graphite. We also found that graphite intercalation compound was a more suitable starting material for making large-sized GO at room temperature. One distinguishing feature of the GO produced at room temperature is that it has more thermal labile oxygen functional groups which allows the facile restoration of electrical conductivity via a mild thermal annealing. This characteristic will be very helpful to better combine GO with the electroactive particles in LIBs and thus benefit the overall battery performance. Finally, we further compared the cost-effectiveness between the room temperature synthesis method and the lower temperature method, using commercial expanded graphite powder as the graphite source. It revealed that the GO synthesized at room temperature could regain more conductive sp2 carbon and reached the same level of electrical conductivity through thermal or chemical reduction. Therefore, the room temperature method can produce conductive graphene for energy storage applications in a more cost-effective manner.
On balance, this PhD thesis further develops the scalable wet chemical production of GO and vanadium oxide for energy storage by systematically investigating the key synthesis parameters and establishing the improved protocols. Ultimately, this work is anticipated to push forward the commercialization of GO and vanadium oxide in the field of energy storage in the near future.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Pan, Li. "First-Principles Studies of the Reactivity of Transition Metal Oxide Surfaces." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448910602.
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Lin, Han. "GRAPHENE OXIDE-BASED MEMBRANE FOR LIQUID AND GAS SEPARATION." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1595260029225206.
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Watson, Venroy George. "Decoration of Graphene Oxide with Silver Nanoparticles and Controlling the Silver Nanoparticle Loading on Graphene Oxide." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1396879714.
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Deshpande, Niranjani. "Calcium and Iron Oxide Reactivity Studies for Chemical Looping Applications of Clean Energy Conversion." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1429632077.
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Arbuzov, A. A., V. E. Muradyan, and B. P. Tarasov. "Synthesis of Few-layer Graphene Sheets via Chemical and Thermal Reduction of Graphite Oxide." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35063.
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Few-layer graphene sheets were produced from graphite oxide (GO) chemical and thermal reduction.
For the chemical reduction of GO as reducing agents were used hydrazine hydrate, hydroxylammonium
chloride, sodium borohydride and sodium sulfite. The reduced material was characterized by elemental
analysis, thermo-gravimetric analysis, scanning electron microscopy, X-ray diffraction, Fourier transform
infrared and Raman spectroscopy. A comparison of the deoxygenation efficiency of graphene oxide suspension by different method or reductants has been made, revealing that the highest degree of reduction was
achieved by thermal reduction and using hydrazine hydrate and hydroxylammonium chloride as a reducing agents.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35063
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Gildea, Arthur N. "Self-Supporting Tin Oxide/ Graphene Electrode for Lithium Ion Batteries." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1385484532.
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Rodriguez-Silva, Allen A. "Graphene Oxide-based Novel Supercapacitor Immunosensors for Physiological Biomarkers Detection." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1458922749.
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Blake, Aaron Joseph. "Synthesis and Characterization of Graphene Oxide/Sulfur Nanocomposite for Lithium-Ion Batteries." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1382173213.
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Bienati, Massimiliano. "Ab initio study of the chemical reactivity of metal clusters and metal oxide clusters." Doctoral thesis, [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=96444237X.
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Kumar, Priyank Vijaya. "Enhanced electrical, optical and chemical properties of graphene oxide through a novel phase transformation." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98736.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 86-98).
Graphene oxide (GO) is a versatile, solution-processable candidate material for next-generation, large-area, ultrathin electronics, optoelectronics, energy conversion and storage technologies. GO is an atom-thick sheet of carbon functionalized with several oxygen-containing groups dominated by the epoxy and hydroxyl functional groups on the basal plane, with carboxyls and lactols at the sheet edges. It is well known that reduction of GO at temperatures > 150°C leads to the removal of oxygen atoms from the carbon plane, leading to the formation of reduced GO (rGO) structures. Although GO has been utilized for multiple applications in the last decade, our understanding of the structure-property relationships at the atomic-level has still been lacking owing to the amorphous nature and chemical inhomogeneity of GO, which has in turn limited our ability to design and tailor GO nanostructures for high-performance applications. In particular, the material's structure and its structural evolution at mild annealing temperatures (< 1000°C) has been largely unexplored. In this thesis, we use a combination of first-principles computations, classical molecular dynamics simulations based on reactive force fields and experiments to model realistic GO structures and develop a detailed understanding of the relationship between the carbon-oxygen framework and the sheet properties, at the atomic level. Based on our understanding, we demonstrate a new phase transformation in GO sheets at mild annealing temperatures (50-80°C), where the oxygen content is preserved and as-synthesized GO structures undergo a phase separation into prominent oxidized and graphitic domains facilitated by oxygen diffusion. Consequently, as-synthesized GO that absorbs mainly in the ultraviolet region becomes strongly absorbing in the visible region, photoluminescence is blue shifted and electronic conductivity increases by up to four orders of magnitude. We then use this novel phase transformation to improve two sets of applications. 1) We demonstrate that cell capture devices making use of phase transformed-GO substrates have higher capture efficiencies compared to devices making use of as-synthesized GO substrates. 2) We show that the reduction of phase transformed-GO leads to better electrical properties of rGO thin films. Our results fill an important gap and establish a complete theory for structural evolution of GO over the entire range of temperatures, i.e. from room temperature to ~1000°C. Taken together, this structural transition in GO enables us to predict and control the sheet properties in new ways, as opposed to reduction, which is till date the only handle to control the structure of GO. This could potentially open the door for completely new applications or for enhancing the performance of existing applications based on GO.
by Priyank Vijaya Kumar.
Ph. D.
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Gordon, Wesley Odell. "Metal Oxide Nanoparticles: Optical Properties and Interaction with Chemical Warfare Agent Simulants." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/29634.
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Materials with length scales in the nanometer regime demonstrate properties that are remarkably different from analogous bulk matter. As a result, researchers are striving to catalog the changes in properties that occur with decreasing size, and more importantly, understand the reason behind novel nanomaterial properties. By learning the true nature of nanomaterials, scientists and engineers can design better materials for a variety of applications. Inert gas-phase condensation synthesis of metal oxide nanoparticles was used to develop materials to explore the optical and chemical properties of metal oxide nanoparticles.
One potential application for nanomaterials is use in optical applications. The possibility of interparticle energy transfer was investigated for lanthanide-doped yttrium oxide nanoparticles using laser spectroscopy. Experimental evidence collected with this study indicates that interparticle, lanthanide-mediated energy transfer may have been observed. In addition, lanthanide-doped gadolinium oxide nanoparticles were synthesized and investigated with optical spectroscopy to identify the best potential candidates for bioanalytical applications of this material. The influence of particle annealing and dopant concentration were also studied.
Nanoparticle film structure was investigated with scanning electron microscopy. Two different film structures composed of oxide nanoparticles were found to grow under different synthesis conditions. The film structure was found to be determined by the degree of particle aggregation in the gas phase during synthesis. Aggregation of the particles was found to be controlled by a combination of gas pressure and properties.
Chemical properties of metal oxide nanoparticles also are very important. Reflection-absorption Infrared Spectroscopy and vacuum surface analytical techniques were used to explore the chemistry of the chemical warfare agent dimethyl methylphosphonate (DMMP) on yttrium oxide as well as other metal oxide nanoparticles. DMMP was found to dissociate at room temperature on several types of metal oxide nanoparticles. Hydroxyl groups were found to be critical for the adsorption of DMMP onto the particles. Finally, the reactivity of the nanoparticles was found to increase with decreasing particle size. This was attributed to a relative increase in the number of high-energy surface defects for the smaller particles.Ph. D.
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PARGOLETTI, ELEONORA. "THREE-DIMENSIONAL NANO-HETEROJUNCTIONS FOR PHOTO- AND CHEMICAL SENSING." Doctoral thesis, Università degli Studi di Milano, 2020. http://hdl.handle.net/2434/703276.
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La percezione sensoriale dell'ambiente circostante è strettamente correlata allo sviluppo della vita animale e umana; in particolare, il rilevamento di gas è un'esperienza sensoriale complessa che influenza le nostre decisioni e azioni. Tuttavia, il sistema olfattivo umano è limitato ad una rilevazione qualitativa di pochi gas. Inoltre, lo sviluppo industriale negli ultimi decenni, insieme al drastico miglioramento della qualità della vita e della mobilità, ha aumentato le esigenze di rilevazione quantitativa di diversi analiti. L'analisi di miscele di gas online è fondamentale in molti campi di ricerca e, al giorno d'oggi, l'attenzione è rivolta al rilevamento analitico a fini diagnostici. In particolare, il crescente sviluppo di dispositivi innovativi ha portato all’ottenimento di nuovi sensori miniaturizzati, capaci di sentire basse concentrazioni di differenti biomarker, con veloci tempi di risposta a temperatura ambiente. Nello specifico, i principali parametri da considerare per la fabbricazione di dispositivi ottimali sono i seguenti: sensibilità, basse temperature di lavoro, tempi di risposta/recupero e selettività. A tal proposito, i nanomateriali a base di carbonio, nonostante mostrino numerose proprietà come una bassa resistività e buona resistenza meccanica, non possiedono buone capacità di rilevazione e trasduzione nei confronti di molecole o fotoni. D'altra parte, i chemoresistori a base di Semiconduttori di Ossidi Metallici (MOS) nonostante siano ampiamente utilizzati, presentano ancora numerosi inconvenienti, in particolare legati alle alte temperature operative e alla scarsa selettività. Lo scopo del presente progetto di dottorato è, quindi, la sintesi di nanostrutture tridimensionali, caratterizzate da eterogiunzioni perfettamente integrate di Ossido di Grafene (GO) e MOS (di tipo n) per il rilevamento a bassa temperatura e sotto irraggiamento UV di Composti Organici Volatili (VOC come ad esempio etanolo, acetone, toluene ed etilbenzene). Nello specifico, sono stati investigati diversi ossidi di metalli di transizione (ZnO, SnO2, WO3, TiO2 o una soluzione solida di SnO2-TiO2) al fine di preparare film porosi e micrometrici (alcuni micron) aventi promettenti proprietà chemoresistive. Inoltre, mentre il semiconduttore a base ossidica è di solito responsabile del rilevamento di gas ad alte temperature, l’ossido di grafene svolge il ruolo fondamentale di migliorare la sensibilità e soprattutto la detection a bassa temperatura, anche grazie alla presenza della luce UV. I materiali così ottenuti, avendo un'eccellente risposta alle radiazioni ultraviolette, risultano essere anche ottimi fotorilevatori. Successivamente, è stato studiato l'effetto della quantità di GO sulle performance dei semiconduttori, specialmente in presenza di una matrice di ZnO o di SnO2. Nel caso del biossido di stagno, infatti, un alto contenuto di GO consente di ottenere sia una risposta a temperatura ambiente, che una maggiore selettività verso molecole più grandi e non polari, come l'etilbenzene. Al contrario, basse quantità di GO aumentano la selettività verso molecole polari come l’etanolo, aprendo di fatto nuovi orizzonti alla sintesi e all’ingegnerizzazione di nuovi materiali, in grado di rilevare concentrazioni di VOC dell’ordine dei ppb. In aggiunta, la matrice di SnO2 porta a performance migliori rispetto a quelle ottenute con l’ossido di zinco, sia in termini di intensità del segnale che di sensibilità. Quindi, studi preliminari, volti a migliorare ulteriormente la selettività, sono stati condotti preparando composti ternari formati da una soluzione solida SnO2-TiO2 e GO: in questo caso è stata osservata una maggiore selettività per le molecole grandi e non polari, come il toluene. Inoltre, è noto che le proprietà chimico-fisiche dei chemoresistori influenzano fortemente le loro caratteristiche di detection. Quindi, parallelamente al precedente studio, l’attenzione è stata focalizzata sulla sintesi ad hoc di ossido di tungsteno adottando diversi precursori e agenti strutturanti. In particolare, si è osservato che il diametro dei cristalliti, l’area superficiale e il volume/forma dei pori sono i principali parametri alla base delle performance sensoristiche in termini di intensità del segnale e tempi di risposta/recupero. Allo stesso tempo, calcoli computazionali e misurazioni XANES in situ presso il sincrotrone (ESRF) di Grenoble sono stati effettuati al fine di confermare/ipotizzare il meccanismo di sensing. Particolare attenzione è stata, poi, rivolta ai sistemi misti MOS-GO, dove la formazione di giunzioni p (GO) – n (MOS) amplifica e migliora il segnale. In conclusione, i risultati ottenuti con questo progetto di dottorato possono essere considerati delle linee guida per l’ingegnerizzazione di nuovi dispositivi ibridi a base di materiali carboniosi e ossidi di metallo, per applicazioni che vanno dall'optoelettronica al campo sensoristico e a quello dell'elettrocatalisi.The sensorial perception of the surroundings is critically related to the development of animal and human life. Human smell, or more generally, gas detection is a complex experience that subtly influences our decisions and actions. However, the human olfactory system is limited to a qualitative detection of few gases. Besides, the industrial development in the last decades, together with the drastic improvement of life quality and mobility, has increased the needs for quantitative detection of different analytes. Online analysis of gas mixtures is fundamental in many research fields and, nowadays, the attention has been particularly focused on their analytical detection for diagnostic purposes. Specifically, the rapid development of smart wearable electronic devices is driving the engineering of novel miniaturized sensing materials that can rapidly respond to very small changes in the concentration of biomarkers at room temperature. In particular, sensitivity, low operating temperature, response/recovery times and selectivity are the main parameters to consider in order to prepare optimal sensing devices. Hence, carbon-based nanomaterials offer numerous attractive properties such as low resistivity, good mechanical robustness and integration potential, but lack a strong detection for the measurement of chemical molecules or photons. On the other hand, chemiresistors based on Metal Oxide Semiconductors (MOS) have been widely exploited, even if they still show several drawbacks especially connected to the high operating temperatures and scarce selectivity. Thus, the focus of the present PhD research project was the synthesis of three-dimensional nanostructured architectures comprising of optimally integrated Graphene Oxide (GO) – n-type MOS heterojunctions for the photo-assisted low temperature sensing of Volatile Organic Compounds (VOCs, i.e. ethanol, acetone, toluene and ethylbenzene). Specifically, different transition metal oxides (ZnO, SnO2, WO3, TiO2 or a solid solution of SnO2-TiO2) have been deeply investigated in order to prepare few micrometers porous films with promising chemoresistive properties. Moreover, while MOS is usually responsible for the gas detection at high operating temperatures, the addition of graphene oxide plays the pivotal role of enhancing the sensitivity, especially at room temperature, by exploiting the UV light. These layouts have been also demonstrated to provide excellent response to UV irradiations showcasing their applicability as visible-blind photodetectors. Furthermore, the effect of low and high GO content has been evidenced, emphasizing the different result when combined to ZnO or SnO2 matrix. Notably, in the case of tin dioxide, great GO content allows to obtain both a response at RT and an increased selectivity towards bigger and non-polar molecules, as ethylbenzene. Whereas, small amounts of GO lead to a higher selectivity to polar molecules as ethanol, opening up new horizons for the preparation of well-performing low ppb sensing materials. In addition, SnO2 matrix seems to have higher sensing features than zin oxide material, in terms of either signal intensity or sensitivity. Therefore, preliminary studies, aimed at further improving the selectivity, were carried out by fabricating ternary compounds composed by SnO2-TiO2 solid solution and GO: a smooth selectivity towards large and non-polar molecules (such as toluene) was noticed. Parallelly, the physico-chemical properties of chemoresistors strongly influence their sensing behavior: adopting WO3 as a case study, the synthetic strategy was modified by finely tuning the tungsten precursors and the structure directing agents. Notably, it was noticed that the crystallite diameters, the surface area and the pores volume/shape drastically affect the sensing performances, in terms of either the signal intensity or the response/recovery times. Concurrently, a computational study and in situ XANES measurements (at the European Synchrotron Radiation Facility, ESRF in Grenoble) on acetone detection by tungsten trioxide were conducted to further corroborate the sensing mechanism. Finally, an extension of this mechanism to MOS-GO composites was hypothesized in which the formation of p(GO) – n(MOS) junctions clearly enhances the sensing behavior. In conclusion, we believe that the findings obtained with this doctoral project can provide guidelines for the future engineering of hybrid carbon-metal oxide devices for application extending from optoelectronics to chemical sensing and electrocatalysis.
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AL-SAEEDI, JAMAL N. "MOLECULAR STRUCTURE-REACTIVITY RELATIONSHIPS FOR PROPANE OXIDATION OVER MODEL MIXED OXIDE CATALYSTS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1053698262.
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Nilsson, Kristina. "Oxidative dissolution of doped UO2 and H2O2 reactivity towards oxide surfaces : A kinetic and mechanistic study." Licentiate thesis, KTH, Tillämpad fysikalisk kemi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145691.
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Oxidative dissolution of std. UO2 and UO2 doped with Cr2O3 and Al2O3, i.e. ADOPT, induced by H2O2 and γ radiation has been the main focus in this licentiate thesis. The catalytic decomposition of H2O2 on oxides like Gd2O3, HfO2, CeO2, Fe2O3 and CuO were also investigated. A kinetic study was performed by determining first and second order rate constants together with Arrhenius parameters for the decomposition of H2O2. The reactivity of H2O2 towards the oxides mentioned was observed to differ significantly despite their similarities. In the mechanistic study, the yields and dynamics of the formation of the intermediate hydroxyl radical from the decomposition of H2O2 was determined for the oxides and found to differ considerably. A turnover point could be found for most of oxides studied, i.e. an increase in the rate of hydroxyl radical scavenging after a specific amount of consumed H2O2. The reactivity of the std. UO2 and ADOPT towards H2O2 was similar to what was observed for other UO2-based materials in previous studies. The oxidative dissolution in radiation experiments showed a slight but significant difference. This was attributed to a difference in exposed surface area instead of an effect of doping. The difference in oxidative dissolution yield was too small to be significant which supports the previous conclusion. Leaching experiments using spent nuclear fuel were also performed on the two types of fuel showing the same behavior as the unirradiated pellets, i.e., a slightly lower 238U release from ADOPT. The difference was attributed to difference in exposed surface area. The release of fission products with low UO2 solubility displayed a higher release from ADOPT which was attributed to a difference in matrix solubility. Cs was released to a larger extent from std. UO2. This is attributed to the larger grain size of ADOPT, extending the diffusion distance. The release of lanthanides and actinides was slightly higher for the conventional UO2, nevertheless the difference was relatively small.QC 20140527
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Liu, Fang. "CERIUM OXIDE (CeO2) PROMOTED OXYGEN CARRIER DEVELOPMENT AND SCALE MODELING STUDY FOR CHEMICAL LOOPING COMBUSTION." UKnowledge, 2013. http://uknowledge.uky.edu/me_etds/31.
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According to IPCC reports, the greenhouse gas CO2 is responsible for global climate change. Studies show that CO2 concentration reached a level of 400 ppm in 2013, or 40 % above pre-industrial levels. The contribution of CO2 from industrial activity to increasing global CO2 concentrations is widely accepted and points to the need to reduce the emission of this greenhouse gas.One possible combustion technology that shows promise for reducing CO2 emissions is chemical looping combustion (CLC). It is an oxy-fuel technology, but has the advantages of in situ oxygen separation, low NOx emissions and low cost of CO2 emission abatement; it entails the use of an oxygen carrier (OC) to provide oxygen for combusting fuels.
OC development is an important task in CLC. Iron based OCs have attracted most research attention in recent years, mainly due to their inexpensive and non-toxic nature. Bi-metal oxide OCs usually impart better CLC performance than mono-metal oxide OCs, one example of which is the introduction of CeO2 as a partially reducible material capable of generating oxygen vacancies that lead to oxygen storage and transfer. In this study, CeO2 was used as an additive to a Fe2O3-based OC and its effect on physical properties, such as morphology, surface area and mechanical strength, was analyzed in detail. The reactivity of OCs is studied using TGA-MS and a bench scale CLC setup. The results show that the reduction reaction at the surface is independent of whether CeO2 is present or not, but after the surface oxygen had been consumed, the OC with CeO2 provided faster oxygen transfer rates from the bulk to the surface to produce better average reaction rates. The OCs after reduction and oxidation were analyzed using XRD and Raman spectroscopy; based on these analytical data, a model for the promoting role of CeO2 is discussed. Furthermore, the reaction kinetics of the OCs were also studied using shrinking core model, the kinetics parameters were obtained and compared.
Scale-up of laboratory-scale CLC reactors is another important task necessary to develop an understanding of the potential and efficiencies of CLC. In this study, scaling laws were used as a guide to design and then build two different-sized CLC reactors. Testing of the reactors involved a focus on chemical similarities. Comparisons of the performance of both reactors showed good consistency, thereby validating the scale modeling method and the scale laws for CLC reactors.
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Benchirouf, Abderrahmane, Christian Müller, and Olfa Kanoun. "Electromechanical Behavior of Chemically Reduced Graphene Oxide and Multi-walled Carbon Nanotube Hybrid Material." Universitätsbibliothek Chemnitz, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-203092.
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In this paper, we propose strain-sensitive thin films based on chemically reduced graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) without adding any further surfactants. In spite of the insulating properties of the thin-film-based GO due to the presence functional groups such as hydroxyl, epoxy, and carbonyl groups in its atomic structure, a significant enhancement of the film conductivity was reached by chemical reduction with hydro-iodic acid. By optimizing the MWCNT content, a significant improvement of electrical and mechanical thin film sensitivity is realized. The optical properties and the morphology of the prepared thin films were studied using ultraviolet-visible spectroscopy (UV-Vis) and scanning electron microscope (SEM). The UV-Vis spectra showed the ability to tune the band gap of the GO by changing the MWCNT content, whereas the SEM indicated that the MWCNTs were well dissolved and coated by the GO. Investigations of the piezoresistive properties of the hybrid nanocomposite material under mechanical load show a linear trend between the electrical resistance and the applied strain. A relatively high gauge factor of 8.5 is reached compared to the commercial metallic strain gauges. The self-assembled hybrid films exhibit outstanding properties in electric conductivity, mechanical strength, and strain sensitivity, which provide a high potential for use in strain-sensing applications.
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Brumbach, Michael T. "Near Surface Composition and Reactivity of Indium Tin Oxide: An Evaluation Towards Surface Chemical Concepts and Relevance in Titanyl Phthalocyanine Photovoltaic Devices." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/195338.
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Photovoltaics manufactured using organic materials as a substitute for inorganic materials may provide for cheaper production of solar cells if their efficiencies can be made comparable to existing technologies. Photovoltaic devices are comprised of layered structures where the electrical, chemical, and physical properties at the multiple interfaces play a significant role in the operation of the completed device. This thesis attempts to establish a relationship between interfacial properties and overall device performance by investigation of both the organic/organic heterojunction interface, as well as the interface between the inorganic substrate and the first organic layer with useful insights towards enhancing the efficiency of organic solar cells.It has been proposed that residual chemical species may act as barriers to charge transfer at the interface between the transparent conductor (TCO) and the first organic layer, possibly causing a large contact resistance and leading to reduced device performance. Previous work has investigated the surface of the TCO but no baseline characterization of carbon-free surfaces has previously been given. In this work clean surfaces are investigated to develop a fundamental understanding of the intrinsic spectra such that further analyses of contaminated surfaces can be presented systematically and reproducibly to develop a chemical model of the TCO surface.The energy level offset at the organic/organic heterojunction has been proposed to relate to the maximum potential achievable for a solar cell under illumination, however, few experimental observations have been made where both the interface characterization and device performance are presented. Photovoltaic properties are examined in this work with titanyl phthalocyanine used as a novel donor material for enhancement of spectral absorption and optimization of the open-circuit potential. Characterization of the interface between TiOPc and C60 coupled with characterization of the interface between copper phthalocyanine and C60 shows that the higher ionization potential of TiOPc does correlate to greater open circuit potentials.Examination of photovoltaic behavior using equivalent circuit modeling relates the importance of series resistance and recombination to the homogeneity of the solar cell structure.
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Martin, Tayla. "Determination of Thallium and Indium with an Electrochemically-reduced Graphene Oxide-Carbon Paste Electrode by Anodic Stripping Voltammetry." University of the Western Cape, 2018. http://hdl.handle.net/11394/6433.
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Magister Scientiae - MSc (Chemistry)In this study, graphene oxide was synthesized by oxidizing graphite using the modified Hummer's method. The graphene oxide was characterized by Raman Spectroscopy, Fourier Transform Infrared Spectroscopy, High Resolution Transmission Electron Microscopy, Scanning Electron Microscopy and X-Ray Diffraction for structural and morphological properties. The graphene oxide was electrochemically reduced on a carbon paste electrode followed by the in situ deposition of mercury thin films to achieve electrochemically reduced graphene oxide modified carbon paste metal film electrodes (ERGO-CP-MEs). The experimental parameters (amplitude, deposition time, deposition potential, frequency and rotation speed) were optimized, and the applicability of the modified electrode was investigated towards the simultaneous and individual determination of TI1+ and In3+ at the low concentration levels (?g L-1) in 0.1 M acetate buffer (pH 4.6) using square wave anodic stripping voltammetry (SWASV). The detection limit values for individual analysis at electrochemically reduced graphene oxide modified carbon paste mercury film electrode (ERGO-CP-HgE ) was 2.4 and 1.1 ?g L-1 for TI1+ and In3+, respectively. The detection limit values for simultaneous analysis at ERGO-CPE was 1.32 and 1.33 ?g L-1 and individual analysis was 0.975 and 1.04 ?g L-1 for TI1+ and In3+, respectively.
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Alhassan, Saeed M. "COLLOIDAL INTERACTIONS AND STABILITY IN PROCESSING, FORMATION AND PROPERTIES OF INORGANIC-ORGANIC NANOCOMPOSITES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1301326975.
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Santos, Fabrício Aparecido dos. "Processamento de grafeno oxidado na forma de filmes ultrafinos e aplicações em sensores." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-14042015-090739/.
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Dentre as formas alotrópicas do carbono, o grafeno merece destaque. Este material consiste de uma monocamada atômica de carbono sp2 disposta em uma rede bidimensional cristalina hexagonal tipo favo de mel. Uma das formas de se obter o grafeno é pela esfoliação química, que consiste da oxigenação do grafite policristalino em um ambiente altamente oxigenado, formando um produto intermediário chamado de grafeno oxidado (GO). Por este método, gera-se um produto altamente estável e solúvel em água, podendo ser utilizado na construção de filmes ultrafinos. Uma das aplicações possíveis do grafeno oxidado é em sensores e biossensores, área de aplicações de novos materiais que viabilizem o diagnostico rápido, preciso, seletivo e de baixo custo, principalmente os do tipo, point-of-care. O grafeno é um forte candidato, nessa área, devido a sua alta performace e seu baixo custo de processamento. Neste trabalho, a técnica de automontagem eletrostatic layer-by-layer (ELBL) foi utilizada na construção de filmes de grafeno oxidado, juntamente com o policátion dendritico poli(amido amina) geração 4 (PAMAM-G4) em uma plataforma potenciométrica, utilizando um amplificador de instrumentação comercial AD620 como transdutor em um sensor de pH para caracterização da sensibilidade do dispositivo. Diversas técnicas espectroscópicas, óticas e morfológicas foram utilizadas para caracterizar a esfoliação química do grafite e dos filmes automontados. Através destas caracterizações mostrou-se que a esfoliação ocorreu satisfatoriamente concordando com resultados já existentes na literatura. A construção dos filmes ultrafinos ocorreu pela rápida adsorção do GO em camadas alternadas de PAMAM-G4, e o monitoramento do crescimento dos filmes foi realizado utilizando espectroscopia no UV-Vis, onde o crescimento é linear a partir da décima camada. Por microscopia de força atômica, mostrou-se que a adsorção das folhas de grafeno se dá primeiramente pelas folhas de menor número de camada (1 e 2 camadas) de GO e para camadas de número superior tem-se uma morfologia totalmente diferente da primeira. Por espectroscopia no infravermelho, mostrou-se a interação entre os dois polieletrólitos, onde há formação de ligações do tipo cross-linking entre as camadas. Medidas de potenciometria indicam a sensibilidade máxima em torno de 57 mV/pH em um substrato de ouro( sensibilidade Nerstiana), o que evidencia a sua aplicabilidade em sensoriamento e também a sua aplicação em biossensores.Among the allotropic forms of carbon, graphene deserves special attention. This material consists of one atomic monolayer of sp2 carbon arranged in a two-dimensional hexagonal lattice type, namely \"honeycomb\". One common method to obtain graphene is -=by chemical exfoliation, which consists of oxygenation of polycrystalline graphite in a highly oxygenated medium, forming an intermediate product namely graphene oxide (GO). This method generates a highly stable and water soluble GO that can be used in the fabrication of ultrathin films. Graphene is a strong candidate for sensing, due to its high performance and low cost processing. In this dissertation, GO was obtained via chemical routs and processed in the form of ultrathin films in conjunction with polyamidoamine dendrimer (PAMAM G4) in a layered fashion using the Electrostatic Layer-by-Layer (ELBL). The GO/PAMAM films were deposited on potentiometric platforms and used as pH sensors using a commercial amplifier AD620 instrumentation as the detection technique. GO and the LbL films were characterized via spectroscopic, optical and morphological techniques. Film growth was monitored via UV-Vis spectroscopy and revealed a linear adsorption up to the tenth GO/PAMAM bilayer. AFM analyses revealed that graphene sheets containing 1 or 2 layers occurred adsorbed first on the substrates. Potentiometric measurements indicated a maximum sensitivity of ca. 57 mV/pH for GO/PAMAM films deposited on gold substrates (Nernstian Sensitivity), which demonstrates the applicability of the films in sensing and biosensing.
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Muthoosamy, Kasturi. "Exceedingly biocompatible and thin-layered reduced graphene oxide nanosheets and its application in co-delivery of curcumin and paclitaxel shows highly potent synergistic anticancer effects in A549 and MDA-MB-231 cells." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/34368/.
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Delivery of anti-cancer drugs using graphene and its derivatives: graphene oxide (GO) and reduced graphene oxide (RGO) has sparked major interest in this emerging field. The anti-cancer therapies often pose a limitation of insolubility, administration problems and cell-penetration ability. In addition, systemic toxicity caused by lack of selective targeting towards cancer cells and inefficient distribution limits its clinical applications. Graphene nanocomposite is a promising tool to address these drawbacks. Graphene is a flat monolayer of carbon atoms that holds many promising properties such as unparalleled thermal conductivity, remarkable electronic properties, and most intriguingly high planar surface and superlative mechanical strength, which are attractive in biotechnology applications. However the synthesis route for the production of GO or RGO often involves the use of harsh chemicals which jeopardize its further application as a drug delivery cargo. To overcome these limitations, a simple one-pot strategy was used to synthesize RGO nanosheets by utilizing an easily available over-the-counter medicinal and edible mushroom, Ganoderma lucidum. The produced RGO was readily dispersible in water and various solvents. The RGO was highly biocompatible towards colon (HT-29), brain (U87MG) and normal cells (MRC-5). By functionalization of RGO with an amphiphilic polymer, PF-127, a more stable RGO was produced, called GP. Curcumin (Cur) and Paclitaxel (Ptx) was then loaded onto the GP cargo, resulting in a nano-sized GP-Cur-Ptx sytem with the particle size of 140 nm. A remarkably high drug loading was also achieved with 678 wt.%, highest thus far, compared to any other Cur nanoformulations. Based on cell proliferation assay, the GP-Cur-Ptx is a synergistic treatment and is highly potent towards A549 (lung) and MDA-MB-231 (breast) cancer cells. These positive findings are further confirmed by increased reactive oxygen species (ROS); mitochondrial membrane potential (MMP) depletion; and cell apoptosis. The same treated with normal cells (MRC-5) shows that the system is biocompatible and cell-specific.
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Alhwaige, Almahdi A. "NOVEL BIOBASED CHITOSAN/POLYBENZOXAZINE CROSS-LINKED POLYMERS AND ADVANCED CARBON AEROGELS FOR CO2 ADSORPTION." Case Western Reserve University School of Graduate Studies / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=case1396437860.
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McNamara, Nicholas D. "Sonochemical Synthesis and Characterization of Metal Nanoparticle-Decorated Carbon Supports." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1311690542.
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Anouar, Aicha. "Préparation de matériaux à base de graphène et leur application en catalyse." Doctoral thesis, Universitat Politècnica de València, 2021. http://hdl.handle.net/10251/164030.
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[ES] Para abordar los desafíos ambientales, la química y los procesos químicos deben ser más sostenibles. Para ello, el desarrollo de nuevos catalizadores especialmente activos es de suma importancia. En catálisis heterogénea, el grafeno ha surgido recientemente como un excelente candidato desde que fue posible aislarlo a partir del grafito. Sus propiedades únicas han despertado un gran interés para aplicarlo en varios campos, desde el refuerzo de matrices poliméricas hasta el desarrollo de materiales para catálisis. En catálisis, su uso como soporte catalítico o como carbocatalizador es todavía objeto de varios estudios.
Con el objetivo de preparar catalizadores extremadamente activos en varias reacciones de química fina o de producción de hidrógeno, nuestro trabajo de investigación se ha centrado en el uso de materiales a base de grafeno como soportes catalíticos.
Se consideraron diferentes aspectos:
La funcionalización del grafeno; al ser un material de baja dimensionalidad, las propiedades del grafeno están estrechamente relacionadas con la química de su superficie. Mediante la fosforilación del óxido de grafeno, hemos demostrado que la estabilidad térmica y la estabilización de las nanopartículas metálicas mejoran significativamente.
La combinación de grafeno con otros materiales; Pequeñas nanopartículas de paladio estabilizadas sobre materiales porosos a base de óxido de grafeno y quitosano han demostrado una excelente actividad para la deshidrogenación del formiato de amonio.
La estrategia de síntesis adoptada para preparar el grafeno; La pirólisis de películas de alginato de amonio y un precursor de rutenio (Ru) en diferentes atmósferas permitió la preparación de nanopartículas de Ru soportadas en grafeno cuya orientación depende de la atmósfera de pirólisis. Por lo tanto, fue posible una comparación de la actividad catalítica de diferentes facetas cristalográficas.
Dopaje de grafeno; la presencia de diferentes heteroátomos en su estructura ha permitido una mejor estabilización de nanopartículas y clusters metálicos. Los materiales basados en nanopartículas de óxido de cobre y grafenos dopados han demostrado poseer una excelente actividad catalítica en la síntesis de nuevas moléculas de interés farmacéutico.[CA] Per a abordar els desafiaments ambientals, la química i els processos químics han de ser més sostenibles. Per a això, el desenvolupament de nous catalitzadors especialment actius és de summa importància. En catàlisi heterogènia, el grafé ha sorgit recentment com un excel·lent candidat des que va ser possible aïllar-lo a partir del grafit. Les seues propietats úniques han despertat un gran interés per a aplicar-lo en diversos camps,des del reforç de matrius polimèriques fins al desenvolupament de materials per a catàlisis. En catàlisi, el seu ús com a suport catalític o com carbocatalitzador és encara objecte de diversos estudis. Amb l'objectiu de preparar catalitzadors extremadament actius en diverses reaccions de química fina o de producció d'hidrogen, el nostre treball de recerca s'ha centrat en l'ús de materials a base de grafé com a suports catalítics. Es van considerar diferents aspectes: La funcionalització del grafé; a l'ésser un material de baixa dimensionalitat, les propietats del grafé estan estretament relacionades amb la química de la seua superfície. Mitjançant la fosforilació de l'òxid de grafé, hem demostrat que l'estabilitat tèrmica i l'estabilització de les nanopartícules metàl·liques milloren significativament. La combinació de grafé amb altres materials; Xicotetes nanopartícules de pal·ladi estabilitzades sobre materials porosos a base d'òxid de grafé i quitosà han demostrat una excel·lent activitat per a la deshidrogenació del formiat d'amoni. L'estratègia de síntesi adoptada per a preparar el grafé; La piròlisi de pel·lícules de alginat d'amoni i un precursor de ruteni (Ru) en diferents atmosferes va permetre la preparació de nanopartícules de Ru suportades en grafé, l'orientació del qual depén de l'atmosfera de piròlisi. Per tant, va ser possible una comparació de l'activitat catalítica de diferents facetes cristal¿logràfiques. Dopatge de grafé; la presència de diferents heteroàtoms en la seua estructura ha permés una millor estabilització de nanopartícules i clústers metàl·lics. Els materials basats en nanopartícules d'òxid de coure i grafens dopats han demostrat posseir una excel·lent activitat catalítica en la síntesi de noves molècules d'interés farmacèutic.
[EN] To address environmental challenges, chemistry and chemical processes need to be more sustainable. For this, developing new particularly active catalysts is of paramount importance. In heterogeneous catalysis, graphene has emerged as an excellent candidate since it was possible to isolate it from graphite. Its properties have aroused substantial interest, earning it applications in various fields spanning from the reinforcement of polymer matrices to the development of materials for catalysis. In catalysis, its use both as a catalytic support or as a carbocatalyst is still the subject of several studies. Aiming to prepare extremely active catalysts in various fine chemical reactions or hydrogen production, our research work has focused on the use of graphene-based materials as catalytic supports. Different aspects were considered: The functionalization of graphene; being a material of low dimensionality, the properties of graphene are intimately related to the chemistry of its surface. Through phosphorylation of graphene oxide, we have shown that the thermal stability and stabilization of metal nanoparticles are significantly improved. Combination of graphene with other materials; small palladium nanoparticles stabilized on porous materials based on graphene oxide and chitosan have demonstrated excellent activity for the dehydrogenation of ammonium formate. The synthetic strategy adopted to prepare graphene; pyrolysis of films of ammonium alginate and ruthenium precursor (Ru) in different atmospheres enabled the preparation of Ru nanoparticles supported on graphene whose orientation depends on the atmosphere of pyrolysis. Thus, a comparison of the catalytic activity of different crystallographic facets was possible. Doping of graphene; the presence of different heteroatoms in its structure has allowed a better stabilization of metal nanoparticles and clusters. Materials based on copper oxide nanoparticles and tridoped graphene have demonstrated an excellent catalytic activity in the synthesis of new molecules of pharmaceutical interest.
Anouar, A. (2021). Préparation de matériaux à base de graphène et leur application en catalyse [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164030
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Xie, Fangyou. "Pressure Driven Desalination Utilizing Nanomaterials." DigitalCommons@CalPoly, 2020. https://digitalcommons.calpoly.edu/theses/2204.
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Nanomaterials such as graphene oxide and carbon nanotubes, have demonstrated excellent properties for membrane desalination, including decrease of maintenance, increase of flux rate, simple solution casting, and impressive chemical inertness. Here, two projects are studied to investigate nanocarbon based membrane desalination. The first project is to prepare hybrid membranes with amyloid fibrils intercalated with graphene oxide sheets. The addition of protein amyloid fibrils expands the interlayer spacing between graphene oxide nanosheets and introduces additional functional groups in the diffusion pathways, resulting in increase of flux rate and rejection rate for the organic dyes. Amyloid fibrils also provide structural assistance to the hybrid membrane, which supresses cracking and instability of graphene oxide sheets. The second project is to fabricate polymer nanocomposite membranes with carbon nanotubes encapsulated by polymerized surfactants. The designed polymerizable surfactant forms lyotropic liquid crystalline mesophases in an aqueous medium with hexagonal packing of cylindrical micelles. The adsorption of surfactants on the surface of carbon nanotubes allows a stable dispersion of carbon nanotubes encapsulated in the cylindrical micelles, resulting in the ordered structure. After photo-polymerization, the composite membranes display enhanced dye rejection. Both projects have shown promising ways to improve membrane filtration by using nanomaterials.
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Najjar, Samar. "Couplage AFM/Raman et spectroscopie Raman exaltée par effet de pointe de nanostructures." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00869044.
Full textAbstract:
Pour mieux comprendre leurs propriétés, diverses nanostructures individuelles ont été étudiées à l'aide d'une technique couplant microscopie à force atomique et spectroscopie Raman confocale. Sous excitation lumineuse polarisée, la composition chimique, la structure et la présence de défauts a pu être précisée dans des nanobâtonnets d'oxydes métalliques (ZnO et α-Fe2O3). Sous irradiation laser résonnante, les spectres de nanotubes de carbone monoparoi enrobés de polymères ont révélé notamment l'absence de transfert de charge polymère-nanotube et un effet de désolvatation. Finalement, des feuillets de graphène oxydé et des ADNs double-brin peignés ont pu être préparés et caractérisés par spectroscopie Raman exaltée par effet de pointe en atteignant une résolution spatiale latérale voisine du rayon de courbure de l'apex de la pointe utilisée (12 nm), bien plus faible que la limite de diffraction, ce qui ouvre la voie à de nouveaux travaux spectroscopiques à l'échelle nanométrique.
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"Chemical recognition and reactivity of zinc-oxide surfaces." Berlin : Humboldt-Universität zu Berlin, 2021. http://d-nb.info/1228333483/34.
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Lee, Edward L. "Molecular structure and reactivity of silica-supported metal oxide catalysts." 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3285745.
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Gao, Xiguang. "Synthesis, Characterization, Chemical Reduction and Biological Application of Graphene Oxide." Thesis, 2013. http://hdl.handle.net/10012/7823.
Full textAbstract:
As an atomic layer of sp2-hybridized carbon atoms closely packed in a honeycomb lattice, graphene has been attracting increasing attention since its discovery in 2004 due to its extraordinary physicochemical properties. Graphene oxide (GO), a non-stoichiometric graphene derivative with the carbon plane abundantly decorated with hydroxyl, epoxide and carboxylic groups, can be massively and cost-effectively produced from natural graphite following Hummers method. GO has greater aqueous solubility than pristine graphene due to its oxygen-functionalities. Various solution-based chemical methods can be applied to GO, which has stimulated a new research area called ???wet chemistry of grahene???. Among them, chemical reduction of GO provides a facile route for large-scale synthesis of graphene.
With abundant oxygen-functionalities in its structure, GO can potentially act as a suitable precursor for chemical modifications of graphene through methods used in organic chemistry. Special attention should be paid to that the hydroxyl groups in GO belong to tertiary alcohols, and steric hindrance should be considered when performing chemical modifications. Diethylaminosulfur trifluoride (DAST), a fluorinating reagent, is ineffective in fluorinating GO due to the steric hindrance of tertiary hydroxyls. However, DAST is effective in reducing GO. The capability of DAST for GO reduction is close to hydrazine, but the reduction reaction can be performed at lower temperature for DAST.
As a two-dimensional (2D) nanomaterial with good aqueous solubility, biocompatibility and excellent intrinsic mechanical properties, GO is particularly useful in preparing 3D hybrid hydrogel scaffolds for tissue engineering applications.
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"Synthesis and Gas Transport Properties of Graphene Oxide Membranes." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.48999.
Full textAbstract:
abstract: Graphene oxide membranes have shown promising gas separation characteristics specially for hydrogen that make them of interest for industrial applications. However, the gas transport mechanism for these membranes is unclear due to inconsistent permeation and separation results reported in literature. Graphene oxide membranes made by filtration, the most common synthesis method, contain wrinkles affecting their gas separation characteristics and the method itself is difficult to scale up. Moreover, the production of graphene oxide membranes with fine-tuned interlayer spacing for improved molecular separation is still a challenge. These unsolved issues will affect their potential impact on industrial gas separation applications.
In this study, high quality graphene oxide membranes are synthesized on polyester track etch substrates by different deposition methods and characterized by XRD, SEM, AFM as well as single gas permeation and binary (H2/CO2) separation experiments. Membranes are made from large graphene oxide sheets of different sizes (33 and 17 micron) using vacuum filtration to shed more light on their transport mechanism. Membranes are made from dilute graphene oxide suspension by easily scalable spray coating technique to minimize extrinsic wrinkle formation. Finally, Brodie’s derived graphene oxide sheets were used to prepare membranes with narrow interlayer spacing to improve their (H2/CO2) separation performance.
An inter-sheet and inner-sheet two-pathway model is proposed to explain the permeation and separation results of graphene oxide membranes obtained in this study. At room temperature, large gas molecules (CH4, N2, and CO2) permeate through inter-sheet pathway of the membranes, exhibiting Knudsen like diffusion characteristics, with the permeance for the small sheet membrane about twice that for the large sheet membrane. The small gases (H2 and He) exhibit much higher permeance, showing significant flow through an inner-sheet pathway, in addition to the flow through the inter-sheet pathway. Membranes prepared by spray coating offer gas characteristics similar to those made by filtration, however using dilute graphene oxide suspension in spray coating will help reduce the formation of extrinsic wrinkles which result in reduction in the porosity of the inter-sheet pathway where the transport of large gas molecules dominates. Brodie’s derived graphene oxide membranes showed overall low permeability and significant improvement in in H2/CO2 selectivity compared to membranes made using Hummers’ derived sheets due to smaller interlayer space height of Brodie’s sheets (~3 Å).Dissertation/Thesis
Doctoral Dissertation Chemical Engineering 2018
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Huang, Yu-Cheng, and 黃裕程. "Study on Graphene Oxide Hybrid Slurry in Chemical Mechanical Polishing of Monocrystalline Silicon Carbide Wafer." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/h3275y.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
105
Monocrystalline Silicon Carbide (SiC) substrate has high breakdown voltage and low resistivity electrical properties, which means a great potential for applying in high power devices. However, manufacturing process of SiC wafer take very long processing time and high cost due to its ultrahigh hardness and excellent chemical stability. This study aims to improve the process time in Chemical Mechanical Polishing (CMP) of 4H SiC wafer and maintain related wafer quality. A Hybrid-Slurry Chemical Mechanical Polishing (HSCMP) has been developed with an appropriate amount of Graphene Oxide (GO) in the slurry, to activate more OH and COOH bonding. That can react with SiC wafer to generate more passivation layer on SiC wafer surface. Research method includes the preparation of hybrid slurry, and then the formation of the reaction has been confirmed by Ellipsometer, Nano Indentation and XPS. It has been found that the substrates dipping in the hybrid slurry has more SiO2 bond and reaction layer thickness of SiC wafer surface about 30 nm or increasing 92.37% than that in original slurry. The hardness also reduces to 19.08 GPa or decresing 25.36%. In CMP process of two-inch SiC wafer, the material removal rate (MRR) is lower than that of conventional CMP, but the surface roughness has better performance on Sa < 1 nm and Ra < 0.1 nm. The HSCMP can be verified to reduce the process time of 30 ~ 50% relative to CMP effectively. Results of this study can be further applied on developing new slurry for smoothing SiC wafer.
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Lalsanati, Afsaneh. "Targeted modification of graphene quantum dots for design and fabrication of chemical sensors for some pharmaceutical compounds such as: serotonin and levodopa." Doctoral thesis, 2019. http://hdl.handle.net/10316/95090.
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Documentos apresentados no âmbito do reconhecimento de graus e diplomas estrangeirosIn this thesis, the design of electrochemical sensors based on electrodes modified with graphene quantum dot nanostructures and its nanocomposites have been considered for the analysis of pharmaceutical samples. This thesis includes four studyis for electrochemical analysis pharmaceutical compounds with proposed electrodes. In the first study, graphene quantum dot was synthesized by using thermal pyrolysis method and its morphology was investigated by electron-transfer microscopy. The results showed that 4-5 nm nanosheets were well synthesized. In the next step, carbon paste electrodes modified by ionic liquid and graphene quantum dot were used as a sensitive sensor for determination of Levodopa and Serotonin. By using the square wave voltammetry technique, the detection limit of the modified electrode for Levodopa was obtained 10/0 nM with linear range 0.05 to 250 μM. Also the linear range for Serotonin with the proposed electrode was 0.5 to 500 μM and the detection limit was 0.1 μM. In the second study, the possibility of Methyldopa measurement was studied by using of carbon paste electrode modified by graphene quantum dot and 1-methyl-3-butylimidazolium hexafluoro phosphate. The proposed sensor showed a linear concentration range of 0.04-750 μM with a limit of detection 0.01 μM for the Methyldopa analysis. The proposed sensor was successfully used to determine methyldopa in tablet and serum products. In the third study, the synthesis of graphene quantum dot / perasidium oxide nanocomposite was carried out. The synthesis nanocomposite was characterized by nanomaterial identification techniques such as X-ray Diffraction (XRD), Energy Dispersive X-ray spectroscopy (EDX), and Transfer -Electron Microscopy (TEM). Then, this nanocomposite and ionic liquid were used as carbon paste electrode modifier to detect Tramadol. The linear range for Tramadol was determined 4 × 10-4 mM to 9.0 × 10 -9M and the detection limit was 3.0 nM. Finally, the proposed sensor was successfully used to determine Tramadol in real samples. In the fourth study, the possibility of simultaneous determination of Acetaminophen and Diclofenac by electrochemical methods was studied. For this purpose, the graphene quantum dot / iron oxide nanocomposite was initially synthesized and characterization. Then, by using of differential pulse voltammetry technique, the effect of pH was investigated and optimum pH=8 obtained. In the final stage, the linear range of the proposed sensor for electrochemical simultaneous determination of Acetaminophen and Diclofenac were calculated 0/1 to 300 and 0/15 to 330 μM and the detection limit were 0/04 and 0/053 μM respectively.
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Manokaran, Rajasekaran. "Exploring water dynamics and gas separations in graphene oxide surfaces and nanopores." Thesis, 2020. https://etd.iisc.ac.in/handle/2005/4516.
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Graphene oxide (GO) is a chemically functionalized graphene with various oxygen-containing functional groups, such as epoxy (-O-), hydroxyl (-OH), and carboxyl (-COOH) on the basal plane. As a consequence, GOs have hydrophilic and hydrophobic regions at the molecular level. GO membranes are found to be a promising potential material for water filtration and desalination, gas separations, and fuel cell applications. The GO structure is non-unique and complex in nature due to variations in the extent of the oxidized regions. In this thesis, we use molecular simulations to understand the structure and dynamics of water confined in GO nanopores and on GO surfaces, as well as the manner in which the extent of hydrophobicity modulates these properties.
In the first part of this thesis, we model the GO surface to represent various scenarios. Here we study the adsorption of water on a GO surface as a function of varying levels of hydrophobicity using grand canonical Monte Carlo (GCMC) simulations. GCMC simulations reveal interesting water film growth as the vapor pressure is increased. Water is found to adsorb at the hydrophilic - hydrophobic interface at low pressures. Subsequently, a water bridge spanning the hydrophilic region is observed, and large number fluctuations are observed due to the Janus nature of the interface. The extent of hydrophobicity determines water layering, organization, and the adsorption isotherms.
We investigate the influence of surface chemistry on the dynamical transitions of supercooled interfacial water on the GO surface. Using the TIP4P/2005 water model, molecular dynamics (MD) simulations reveal that the rotational relaxation of bound water can undergo either a strong-to-strong or a single Arrhenius behaviour as a function of the surface hydrophilicity. This is in contrast to bulk water, which exhibits a fragile-to-strong transition upon supercooling. Molecular dynamics simulations on surface water where the influence of bulk-like water is absent, revealed a single Arrhenius behaviour during supercooling. Our results provide novel insights into the strong role played by the presence of bulk water as well as the influence of surface chemistry on the dynamical transitions of interfacial water.
In order to understand the influence of surface oxidation and the inherent heterogeneity imposed by opposing surfaces formed in macroscopic membranes, MD simulations of water confined in nanopores (8 - 15 Angstrom) made up of different surface types are carried out . The greatest differences are observed at 8 Angstrom, which is the optimal separation distance for molecular sieving of ions. The dipole-dipole relaxation and HH rotational relaxation of confined water are the slowest between fully oxidized (OO) surfaces with a two-order decrease in the dipole-dipole relaxation time observed for the Janus confinement consisting of an oxidized surface adjacent to a graphene surface. Although the water diffusivity is an order of magnitude smaller than bulk diffusivities at the smaller surface separations, water between the Janus surfaces always had the highest diffusivities. Thus the Janus interface appears to provide the optimal environment for water transport, providing a design strategy while assembling GO-based membrane for water purification.
Molecular dynamics simulations have been carried out to explore the dynamical crossover phenomenon in strongly confined and layered water in GO nanopores. In contrast to studies where confinement is used to study the properties of bulk water, we are interested in the dynamical transitions for strongly confined water in the absence of any bulk-like water. Graphene oxide surfaces having different degrees of hydrophilicity are placed at interlayer separation of d = 10 Angstrom, to produce an in-registry pore (IR) and a fully hydrophilic (OO) nanopore. Water confined in the IR pores exhibits a strong-to-strong dynamical transition in the diffusion coefficient and rotational relaxation time at 237 K and shows a fragile-to-strong transition in the alpha-relaxation at 238 K. In contrast, water confined in the OO pores did not display a dynamical crossover in any of the dynamical quantities studied. Our results indicate that water under strong confinement can undergo a dynamic transition, which is a strong function of the physicochemical nature of the confining surface.
In the last part of this thesis, we have studied the adsorption of pure CH4, CO2, N2, and H2 gases in GO nanopores of d = 10 Angstrom using grand canonical Monte Carlo (GCMC) simulations and have also evaluated adsorption selectivity for equimolar gas mixtures of CH4/CO2, CO2/N2, CO2/H2, and CH4/H2 in GO nanopores of d = 10 Angstrom at 298 K. Adsorption isotherm and isosteric heats of adsorption reveal that CO2 adsorption is highest, and adsorption of H2 is lowest. Adsorption selectivity of CO2 in all gas mixtures for the GO pores is highest, specifically in the CO2/H2 mixture, and in the case of the CH4/H2 mixture, CH4 selectivity is higher. These findings suggest that GO nanopores have the potential to be used as adsorbents for the CO2 capture from flue gas and natural gas streams.
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Lan, Kuen-chih, and 藍坤志. "The effect on Polycrystalline Silicon Surface Roughness by Electrical Chemical Machining Grinding Using Graphene Oxide Suspension." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/56961985890911503960.
Full textAbstract:
碩士國立中央大學
機械工程學系在職專班
102
There are some conclusions gotten from the experiment. The surface roughness and average friction coefficient are 0.092μm and 0.33μ by traditional mechanical grinding process; the surface roughness and average friction coefficient are 0.051μm and 0.10μ by adding 0.5% graphene into solution. The latter surface roughness and friction coefficient is 1.8 times and 3.3 times compared to the former. The research shows that the tribological properties of graphene reduce the friction coefficient of solution and improve the surface roughness on workpiece. The research can be applied to grinding process of silicon wafer. The method can not only simplify the experiment steps but also enhance the process efficiency. The research is expected to be an application reference for industry and academic area.
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Li, Kai. "A Study on Nano-Si/Polyaniline/Reduced Graphene Oxide Composite Anode for Lithium-Ion Batteries." Thesis, 2013. http://hdl.handle.net/10012/7495.
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Because of its high theoretical specific capacity (4200mAh/g) and natural abundance (2nd most abundant element on earth), silicon is considered a promising anode candidate for high energy density lithium-ion batteries. However, the dramatic volume changes (up to 400%) that occur during lithiation/delithiation and the relative low electrical conductivity of silicon prevent the implementation of this material. In this work, a nano-silicon/polyaniline/reduced graphene oxide composite was synthesized via a two-step process: in-situ polymerization of polyaniline (PANi) in the presence of nano-silicon followed by combination of the prepared n-Si/PANi binary composite with reduced graphene oxide (RGO), to form a n-Si/PANi/RGO composite. Electron microscopy reveals the unique nano-architecture of the n-Si/PANi/RGO composite: silicon nanoparticles are well dispersed within a PANi matrix, which in turn is anchored to the surface of RGO sheets. The n-Si/PANi/RGO ternary composite delivered an initial capacity of 3259 mAh/g and 83.5% Coulombic efficiency. The new composite displayed better rate performance and capacity recovery than either nano-Si or n-Si/PANi. Structural and morphological studies combined with AC impedance analysis suggest that the n-Si/PANi/RGO composite has higher electrical conductivity than the other two component materials, yielding better performance at high current densities or C rates. The good rate performance, high initial specific capacity and stable Coulombic efficiency of n-Si/PANi/RGO make it a promising anode material for high energy density lithium-ion batteries.
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Bienati, Massimiliano [Verfasser]. "Ab initio study of the chemical reactivity of metal clusters and metal oxide clusters / von Massimiliano Bienati." 2001. http://d-nb.info/96444237X/34.
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LIOU, JIAN-MING, and 劉建明. "Effects of experimental parameters and silicon oxide particles on the growth of graphene by chemical vapor deposition." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/59053048747044483033.
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碩士國立聯合大學
材料科學工程學系碩士班
105
We used high-purity copper foil to grow graphene by chemical vapor deposition in this thesis. The parameters of substrate holder, gas flow rate, growth time, and temperature were adjusted to investigate the quality of graphene. SEM, OM, Raman, AFM and XRD were used to analysze the morphology and microstructure of the samples. The results show that the ratio of I2D/IG presented in Raman spectra can be up to 5.79, and most of the ID/IG were less than 0.4, showing that the single layer graphenes were synthesized successfully. On the other hand, according to the ratio of I2D/IG, few-layer graphen was obtained at 800 ℃. In addition, continuous layer of graphene with high coverage was observed in SEM as the growth temperature was high (1000 ℃), but films with crack was observed at lower temperature even the growth time was extended to more than 20 to 30 min. We found that the surface of copper foil was flattened at 900 ℃ and 1000 ℃, which is consist with the result of AFM, in which the Ra of copper foil can be reduced from 30.6 to 2.51 as the foil was annealed at 1000 ℃, which may reduce the nucleation sites to promote the growth of large-area graphene. Finally, we used XRD to investigate the effect of annealing on the orientation of copper foil, which is important to determine the shape and size of graphene layer. We found that the orientation of copper foil was transferred from (200) to (111), and then to (220) as the heating time was increased to 30 min. Triangle shape graphene with micrometer size was observed on the (111) surface, indicating that the substrate orientation affects the shape of graphene grain. More interesting, we found that SiO2 nanoparticles accompanied with the graphene, especially at high temperature. These nanoparticles may enhance the Raman scattering so that the I2D/IG can be larger than 5 for the graphene on copper. These nanoparticles may come from the etching of quartz tube or substrate holder by hydrogen gas, and we also assemble these nanoparticles via silicon nanostructure to create a novel nanoparticle foil in this thesis.
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Lin, Yu-Jing, and 林妤靜. "Analysis on Compound Slurry with Graphene Oxide for Chemical Mechanical Polishing of Single Crystalline Silicon Carbide Wafer." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/f2ym7b.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
107
Single Crystalline Silicon Carbide (SiC) Wafer has high and wide voltage, high breakdown voltage, and high thermal conductivity properties in high power devices. However, it has a very high Mohs hardness 9.2 and brittle substrate, which is a time-consuming process in the traditional chemical mechanical polishing (CMP). A 30 minutes dipping test was performed on 4H-SiC with different base slurry, and 0.1 wt% GO powder add in C -face produce COOH and C-O-OH bonds, while Si-face had no obvious reaction by Raman spectroscopy. This study aims to improve the process time by Compound-Slurry Chemical Mechanical Polishing (CSCMP) add 0.1 wt% graphene oxide (GO) and Gas Liquid Assisted Chemical Mechanical Polishing (GLA-CMP). The process contains OH and COOH bonding to form a soft passivation layer on 4H-SiC wafer surface in the slurry. Four kinds of polishing processes for C-face and Si-face of SiC wafer with the same parameters. It can achieve the best material removal rate (MRR) is 1289.91 nm/ h on C-face and the best MRR is 267.72 nm/h on Si-face by the HS+GLACMP process. Comparision of CMP and CS+GLACMP, it reduces 60.6% processing time on C-face and reduce 39.5 % processing time on Si-face after single side lapping and reduce processing time.
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Chuang, Min-Chiang, and 莊敏強. "Nucleation and growth kinetics of graphene growth on copper oxide substrate in a rapid thermal chemical vapor deposition process." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/99374618512074093606.
Full textAbstract:
博士國立中央大學
物理學系
104
Graphene is a two dimension thin film consisted with carbon atoms in honeycomb ordered. Due to its unique band structure, graphene as unique electronic and material properties. Therefore graphene is expected to have great application potential in the future. However, it is still challenging to produce large amount and perfect graphene which is suitable for the application. This shortage limited the ceiling of the potential of graphene. Among all possible solution to produce large amount and defect-free graphene, chemical vapor deposition seems like to be the possible way to fabricate industry scale graphene. Three of the key issues in chemical vapor deposition is the time, cost and quality of graphene. First, nowadays it is the guarantee way to form large and perfect graphene in lower pressure chemical vapor deposition system. However, such a grain needs long growth time which is impossible to meet the needs of industry scale. Also, the long heating and cooling time for furnace decrease the throughput of graphene. Second, hot wall furnace waste unwanted heat into the environment which is not helpful for the chemical vapor deposition process. Third, the quality of graphene of CVD is comparing poorly with mechanical exfoliation. In order to suit above issues, rapid thermal chemical vapor deposition is considered. Although rapid thermal chemical vapor deposition is a low cost and fast production way to grow graphene, the graphene grain is small due to the non-equilibrium heating process. Recently this issue is solved by growing graphene on copper oxide. By exposing the oxygen on the defect on copper, rapid thermal chemical vapor deposition is able to grow large single crystal graphene. However, the underlying mechanism is still the shortage. In this work, we investigate the role of oxygen in graphene chemical vapor deposition on copper oxide. We find out the mechanism of the nucleation and growth process with oxygen exposure by extending the JMAK model into a non-equilibrium region to explain the initial situation of CVD process. The extending JMAK model is able to explain the increasing in nucleation rate. In addition, a correlation function analysis in traditional condensed matter physic is workable to quantify the spatial distribution and uniformity of Graphene Island. This analysis also points out the transition from carbon forming new grain at local nucleation site to joining larger cluster and coalescence after oxygen exposure.
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Chau-ChungHou and 侯朝鐘. "SnO2 inserted graphene oxide nanocomposites prepared by a facile chemical treatment as negative electrode materials for lithium-ion batteries." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/44194907831552825492.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系
104
We successfully synthesize the SnO2/graphene oxide nanocomposites through a relatively low temperature and rapid process of chemical treatment (electroless plating). We not only overcome the problem of lower capacities but also satisfy the concept of environmental protection and low cost. We control the reductant amounts in the chemical treatment to observe the affect the combination performance between the SnO2 nanoparticles and graphene oxide, and the electrochemical performance of capacities and cyclic performance during the coin-cell test. We confirm SnO2 actually can incorporate with oxygen-containing functional groups of graphene oxide, achieve the effect that similar to reduction. We also prove SnO2 nanoparticles insert into the layer structure of graphene oxide and get trapped inside, hence, the volume expansion problem of SnO2 nanoparticles during charge/discharge will be greatly relieve. In optimization chemical treatment parameters, SnO2 nanoparticles have a great distribution in the structure of graphene oxide and doesn’t appear the apparent the agglomeration problem of SnO2 nanoparticles. We also use different charge/discharge rate to confirm SnO2/graphene oxide nanocomposite own a great structure stability as anode material. Above results support SnO2/graphene oxide nanocomposite will have a great performance on the capacities and cyclic performance as anode material for lithium ion batteries.
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Chitara, Basant. "Properties And Applications Of Semiconductor And Layered Nanomaterials." Thesis, 2012. https://etd.iisc.ac.in/handle/2005/2288.
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This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc.
Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2.
The summary of the thesis is given at the end of the thesis.
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Chitara, Basant. "Properties And Applications Of Semiconductor And Layered Nanomaterials." Thesis, 2012. http://hdl.handle.net/2005/2288.
Full textAbstract:
This thesis deals with the research work carried out on the properties and applications such as GaN nanoparticles, Graphene etc.
Chapter 1 of the thesis gives introduction to nanomaterials and various aspects of the thesis. Chapter 2 of the thesis describes the synthesis of GaN nanocrystals and their use as white light sources and as room temperature gas sensors. It also discusses negative differential resistance above room temperature exhibited by GaN. Electroluminescence from GaN-polymer heterojunction forms the last section of this chapter. Chapter 3 demonstrates the role of defect concentration on the photodetecting properties of ZnO nanorods with different defects prepared at different temperatures. Chapter 4 presents remarkable infrared and ultraviolet photodetector properties of reduced graphene oxide and graphene nanoribbons. Chapter 5 presents the infrared detecting properties of graphene-like few-layer MoS2.
The summary of the thesis is given at the end of the thesis.
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(5929820), Shourya Jain. "Burning Behaviors of Solid Propellants using Graphene-based Micro-structures: Experiments and Simulations." Thesis, 2018.
Find full textAbstract:
Enhancing the burn rates of solid propellants and energetics is a crucial step towards improving the performance of several solid propellant based micro-propulsion systems. In addition to increasing thrust, high burn rates also help simplify the propellant grain geometry and increase the volumetric loading of the rocket motor, which in turn reduces the overall size and weight. Thus, in this work, burn rate enhancement of solid propellants when coupled to highly conductive graphene-based micro-structures was studied using both experiments and molecular dynamic (MD) simulations.
The experiments were performed using three different types of graphene-structures i.e. graphite sheet (GS), graphene nano-pellets (GNPs) and graphene foam (GF), with nitrocellulose (NC) as the solid propellant.
For the NC-GS samples, propellant layers ranging from 25 µm to 170 µm were deposited on the top of a 20 µm thick graphite sheet. Self-propagating combustion waves were observed, with burn rate enhancements up to 3.3 times the bulk NC burn rate (0.7 cm/s). The burn rates were measured as a function of the ratio of fuel to graphite layer thickness and an optimum thickness ratio was found corresponding to the maximum enhancement. Moreover, the ratio of fuel to graphite layer thickness was also found to affect the period and amplitude of the combustion wave oscillations. Thus, to identify the important non-dimensional parameters that govern the burn rate enhancement and the oscillatory nature of the combustion waves, a numerical model using 1-D energy conservation equations along with simple first-order Arrhenius kinetics was also developed.
For the GNP-doped NC lms, propellant layers, 500 30 µm thick, were deposited on the top of a thermally insulating glass slide with the doping concentrations of GNPs being varied from 1-5% by mass. An optimum doping concentration of 3% was obtained for which the burn rate enhancement was 2.7 times. In addition, the effective thermal conductivities of GNP-doped NC lms were also measured experimentally using a steady state, controlled, heat flux method and a linear increase in the thermal conductivity value as a function of the doping concentration was obtained.
The third type of graphene structure used was the GF - synthesized using a chemical vapor deposition (CVD) technique. The effects of both the fuel loading ratio and GF density were studied. Similar to the GNPs, there existed an optimum fuel loading ratio that maximized the burn rates. However, as a function of the GF density, a monotonic decreasing trend in the burn rate was obtained. Overall, burn rate enhancement up to 7.6 times was observed, which was attributed to the GF's unique thermal properties resulting from its 3D interconnected network, high thermal conductivity, low thermal boundary resistance and low thermal mass. Moreover, the thermal conductivity of GF strut walls as a function of the GF density was also measured experimentally.
Then as a next step, the GF structures were functionalized with a transition metal oxide (MnO2). The use of GF-supported catalyst combined the physical eect of enhanced thermal transport due to the GF structure with the chemical effect of increased chemical reactivity (decomposition) due to the MnO2 catalyst, and thus, resulted in even further burn rate enhancements (up to 9 times). The burn rates as a function of both the NC-GF and MnO2-NC loadings were studied. An optimum MnO2-NC loading corresponding to the maximum burn rate was obtained for each NC-GF loading. In addition, thermogravimetric (TG) and differential scanning
calorimetry (DSC) analysis were also conducted to determine the effect of NC-GF and MnO2-NC loadings on the activation energy (E) and peak thermal decomposition (PTD) temperatures of the propellant NC.
In addition to the experimental work, molecular dynamics simulations were also conducted to investigate the thermal transport and the reactivity of these coupled solidpropellant/graphene-structures. A solid monopropellant, Pentaerythritol Tetranitrate (PETN), when coupled to highly conductive multi-walled carbon nanotubes (MWCNTs) was considered. The thickness of the PETN layer and the diameter of the MWCNTs were varied to determine the effect of PETN-MWCNT loading on the burn rates obtained. Burn rate enhancement up to 3 times was observed and an optimal PETN-MWCNT loading of 45% was obtained. The enhancement was attributed to the faster heat conduction in CNTs and to the layering of PETN molecules around the MWCNTs surface. Moreover, the CNTs remained unburned after the combustion process, conrming that these graphene-structures do not take part in the chemical reactions but act only as thermal conduits, transferring heat from the burned to the unburned portions of the fuel.
A long-pursued goal, which is also a grand challenge, in nanoscience and nanotechnology is to create nanoscale devices, machines and motors that can do useful work. However, loyal to the scaling law, combustion would be impossible at nanoscale because the heat loss would profoundly dominate the chemical reactions. Thus, in addition to the solid propellant work, a preliminary study was also conducted to understand as how does the heat transfer and combustion couple together at nano-scales.
First, an experimental study was performed to understand the feasibility of combustion at nano-scales for which a nano-scale combustion device called "nanobubbles" was designed. These nanobubbles were produced from short-time (< 2000 µs) water electrolysis by applying high-frequency alternating sign square voltage pulses (1-500 kHz), which resulted in H2 and O2 gas production above the same electrode. Moreover, a 10 nm thick Pt thermal sensor (based on resistance thermometry) was also fabricated underneath the combustion electrodes to measure the temperature changes obtained. A signicant amount of bubble production was seen up to 30 kHz but after that the bubble production decreased drastically, although the amount of faradaic current measured remained unchanged, signifying combustion. The temperature changes measured were also found to increase above this threshold frequency of 30 kHz.
Next, non-reactive molecular dynamic simulations were performed to determine as how does the surface tension of water surrounding the electrodes is affected by the presence of dissolved external gases, which would in turn help to predict the pressures inside nanobubbles. Knowing the bubble pressure is a perquisite towards understanding the combustion process. The surface tension of water was found to decrease with an increase in the supersaturation ratio (or an increase in the external gas concentration), thus, the internal pressure inside a nanobubble is much smaller than what would have been predicted using the planar-interface surface tension value of water. Once the pressure behavior as a function of external gas supersaturation was understood, then as a next step, reactive molecular dynamic simulations were performed to study the effects of surface-assisted dissociation of H2 and O2 gases and initial system pressure on the ignition and reaction kinetics of the H2/O2 system at nano-scales. A signicant amount of hydrogen peroxide (H2O2), 6-140 times water (H2O), was observed in the combustion products. This was attributed to the low temperature(~300 K) and high pressure (2-80 atm) conditions at which the chemical reactions were taking place. Moreover, the rate at which heat was being lost from the combustion chamber (nanobubble) was also compared to the rate at which heat was being released from the chemical reactions and only a slight rise in the reaction temperature was observed (~68 K), signifying that, at such small-scales, heat losses dominate.