Croissance catalytique et étude de nanotubes de carbone multi-feuillets produits en masse et de nanotubes de carbone ultra-long individuels à quelques feuillets Résumé: Ce travail expérimental traite de la croissance catalytique à partir d'une phase vapeur (CCVD) de nanotubes de carbone multi-feuillets (MWCNT) et de nanotubes de carbone (CNT) ultralongs ainsi que de l'étude de leurs propriétés physiques. Dans la première partie du manuscrit est décrite l'optimisation des paramètres pour la croissance CCVD de MWNT en masse et à faible coût. Avec l'acétylène comme source de carbone, Fe(NO3)3.9H2O comme précurseur de catalyseur et CaCO3 comme support, nous rapportons les conditions optimales pour la production de 525 g de MWCNT par jour à un coût estimé de 0.6$/g. La purification des MWCNT ainsi produits par un traitement à l'oxygène ou au dioxyde de carbone est également présentée. La seconde partie est consacrée à la synthèse de CNT ultralongs. L'influence des paramètres de synthèse est étudiée et, à partir de ces observations, les mécanismes de croissance possibles sont discutés. La dernière partie de la thèse est dédiée à la fabrication et à l'étude des propriétés physiques de nanotubes individuels ultralongs. Sur la base du savoir-faire développé précédemment, nous avons réalisé des CNT ultralongs alignés, des jonctions de CNT (suspendus ou supportés) ainsi que des CNT suspendus au-dessus de différents supports. Les propriétés électroniques et de transport des CNT individuels ultralongs sur substrat de silicium ont été étudiées par microscopie à force atomique, spectroscopie Raman et mesures de transport. Enfin, les modes de phonons actifs en Raman sont étudiés par des expériences combinant microscopie électronique à transmission, diffraction électronique et spectroscopie Raman.Mots clés: Nanotubes de carbone multi-feuillets, nanotubes de carbone ultralongs, croissance catalytique à partir d'une phase vapeur, mécanisme de croissance, lithographie, spectroscopie Raman de résonance, transport électronique. / Catalytic growth and study of mass-produced multi-walled carbon nanotubes and ultralong individual few-walled carbon nanotubesAbstract: This experimental work deals with the growth of multi-walled carbon nanotubes (MWCNTs) and ultralong carbon nanotubes (CNTs) by catalytic chemical vapor deposition (CCVD), and the study of their physical properties. In the first part of the manuscript is described the parameter optimization of the CCVD growth of MWCNTs for a large-scale production at low cost. By using acetylene as a carbon source, Fe(NO3)3.9H2O as a precursor catalyst and CaCO3 as a catalyst support, we report on optimized growth conditions allowing the production of 525 g of MWCNTs per day at an estimated cost of 0.6 $ per gramme. The purification of the as-grown MWCNTs by oxygen or carbon dioxide treatments is also presented. In the second part is presented the synthesis of ultralong individual CNTs. The influence of the growth parameters is investigated and based on the experimental observations, the possible growth mechanisms are discussed. Finally, the last part of the thesis is dedicated to the preparation and to the study of the physical properties of ultralong individual carbon nanotubes. From the know-how developed in the previous part, we prepared well-aligned ultralong CNTs, cross junction of CNTs (on a substrate or suspended) and suspended CNTs over different supports. Electronic and electron transport properties of the individual ultralong CNTs on silicon substrate are then studied by atomic force microscopy, Raman spectroscopy and transport measurements. Finally, the Raman-active phonons of suspended individual CNTs were investigated in combined experiments by transmission electron microscopy, electron diffraction and Raman spectroscopy. Keywords: Multi-walled carbon nanotubes, ultralong carbon nanotubes, catalytic chemical vapor deposition, growth mechanism, lithography, resonant Raman spectroscopy, electronic transport.

Der elektrochemische Nachweis von polycyclischen aromatischen Kohlenwasserstoffen (PAK), zu denen Anthracen und Pyren gehören, bietet eine kostengünstigere, einfachere und schnellere alternative Analysemethode als herkömmliche Methoden wie GC und HPLC. Im Vergleich zu diesen Methoden weist er jedoch nach wie vor eine geringere Empfindlichkeit auf. Einige neuere Bemühungen haben an einem Mangel an Selektivität gelitten, entweder aufgrund der elektrodenmodifizierende Schicht mit hohem Hintergrundstrom oder der Wahl eines Leitelektrolyten, der die Detektion stört. Bei dem vorliegenden Versuch wurden Pt-Pd-Nanopartikel (NPs) und MWCNTs verwendet, um eine Glaskohlenstoffelektrode (GCE) zum empfindlichen Nachweis von Anthracen und Pyren zu modifizieren. Die verwendeten NPs wurden unter Verwendung eines wässrigen Extrakts aus Blättern von E. grandis synthetisiert, einem nachhaltigen und umweltfreundlichen Syntheseweg. Durch einer Optimierung der Mengen an Pt- und Pd-Ionen im Vorläufer wurden NPs mit einer durchschnittlichen Größe von 10 nm erhalten, wobei ein Verhältnis von 1 Pt-Ion zu 3 Pd-Ionen die kleinste Größe ergab. Durch XPS wurde festgestellt, dass die Zusammensetzung der NPs von Pt2+ und Pd0 dominiert wird. Die XRD-Analyse ergab eine kristalline Natur mit einer flächenzentriert-kubischen Struktur. Die Pt-Pd-NPs bewirkten eine Erhöhung des Spitzenstroms um 94 % für Pyren, führten jedoch zu niedrigeren Spitzenströmen für Anthracen. Wenn die NPs weiter mit MWCNTs zum Nachweis von Pyren verwendet wurden, wurde eine Spitzenstromsteigerung von etwa 200 % mit einem Dynamikbereich von 66–130 μM und einer LOD von 23 μM beobachtet. Es wurde auch festgestellt, dass der elektrochemische Prozess gemischt diffusions- und adsorptionskontrolliert ist. Aufgrund des Einflusses der Adsorption musste die Akkumulationszeit im Analyseverfahren berücksichtigt werden. MWCNTs wurden beim Nachweis von Anthracen angewendet, wobei eine Erhöhung des Spitzenstroms um 74 % und eine Verringerung des Überpotentials um 53 mV beobachtet wurde. Ein dynamischer Bereich von 50–146 µM und eine LOD von 42 µM wurden bestimmt. Niedrigere Konzentrationen wurden mit einer Leitungswasserprobe gemessen, die mit Anthracen versetzt war, hauptsächlich wegen der geringen Löslichkeit von PAK in Wasser. Der Einfluss der Säurebehandlung von MWCNTs auf den Nachweis von Anthracen und Pyren wurde ebenfalls untersucht. Die Säurebehandlung ermöglichte das Laden von mehr Material ohne Ablösen der modifizierten Schicht, was zu höheren Spitzenstromverbesserungen für Anthracen (533 %) und Pyren (448 %) führte. Für Anthracen und Pyren wurden LODs von 40 µM bzw. 14 µM bestimmt, die nur geringfügig niedriger sind als die bei MWCNTs/GCE und Pt-PdNPs/MWCNTs/GCE beobachteten Werte. Der Nachweis von Anthracen wurde durch die Anwesenheit von Pyren und gewöhnlichen Ionen gestört, während die LOD für Pyren in Gegenwart von Anthracen 18 µM betrug. Es wurde festgestellt, dass die auf MWCNTs basierende elektrochemische Nachweisplattform eine bessere Reaktion auf Pyren aufweist.:Bibliographische Beschreibung i Referat i Abstract iii Zeitraum, Ort der Durchführung v Acknowledgements vi Dedication vii Table of Contents viii List of Abbreviations and Symbols xii Chapter 1 1 Introduction 1 1.1 Overview 1 1.2 Polycyclic Aromatic Hydrocarbons 2 1.3 Electrochemical Sensors 7 1.3.1 General Response Curve for Chemical Sensors 10 1.4 Carbon Nanotubes 13 1.5 Use of Nanoparticles in Electrochemical Detection 18 1.6 Green Synthesis of Nanoparticles and The Rationale Behind It 21 1.7 Previous Efforts in the Electrochemical Detection of Polycyclic Aromatic Hydrocarbons 24 1.8 Objectives of the Study 26 Chapter 2 28 Experimental 28 2.1 Chemicals 28 2.1.1 Preparation of Anthracene and Pyrene Solutions 28 2.2 Collection and Preparation of Plant Material 29 2.3 Synthesis and Preparation of Materials 29 2.3.1 Synthesis of Metallic Nanoparticles 29 2.3.2 Acid Treatment of Multi-walled Carbon Nanotubes 30 2.4 Characterization of the Nanomaterials 30 2.4.1 UV-Vis Spectrophotometry 30 2.4.2 SEM/EDX and TEM Analysis 30 2.4.3 Powder X-ray Diffractometry 31 2.4.4 XPS Analysis 31 2.5 Electrochemical Measurements 31 2.5.1 Preparation of the Bare and Modified Glassy Carbon Electrode 32 2.5.2 Characterization of the Bare and the Modified Glassy Carbon Electrode 33 2.5.3 Electrocatalytic Oxidation of Anthracene on the Bare and Modified GCEs 33 2.5.4 Electrocatalytic Oxidation of Pyrene on the Bare and Modified GCEs 34 Chapter 3 35 Synthesis, Characterization, and Application of Pt-Pd Nanoparticles in the Electrochemical Detection of Anthracene and Pyrene 35 3.1 Test for Flavonoids and Polyphenols in the E. grandis Leaves’ Extract 35 3.2 Synthesis of Nanoparticles 35 3.3 Characterization of Nanoparticles 37 3.3.1 TEM Analysis 37 3.3.2 SEM Analysis 40 3.3.3 EDX Analysis 41 3.3.4 Powder X-Ray Diffraction Analysis 45 3.3.5 XPS Analysis of Pt-Pd Particles 46 3.4 Impedance Measurements of the Bare and Nanoparticle-modified Glassy Carbon Electrode 49 3.5 Electrochemical Oxidation of Anthracene and Pyrene at the Bare and Nanoparticles-modified Glassy Carbon Electrode 51 3.6 Conclusions 53 Chapter 4 55 Pt-PdNPs/MWCNTs-Modified GCE for the Detection of Pyrene 55 4.1 Impedance Measurement with Pt-PdNPs/MWCNTs/GCE 55 4.2 Electrochemical Oxidation of Pyrene on Pt-PdNPs/MWCNTs/GCE 56 4.3 Analysis of Varying Concentrations of Pyrene on Pt-PdNPs/MWCNTs/GCE 59 4.4 Selectivity 61 4.5 Conclusions 62 Chapter 5 64 Exploring Multi-walled Carbon Nanotubes for the Detection of Anthracene 64 5.1 Impedance Measurement of MWCNT-Modified Glassy Carbon Electrode 64 5.2 Electrochemical Oxidation of Anthracene on MWCNT/GCE 65 5.3 Analysis of Varying Concentrations of Anthracene Using MWCNTs/GCE 68 5.4 Detection of Anthracene in Tap Water 71 5.5 Conclusions 72 Chapter 6 73 Effect of Acid Treatment of Multi-walled Carbon Nanotubes on the Detection of Anthracene and Pyrene 73 6.1 Characterization of fMWCNTs 74 6.2 Electrochemical Oxidation of Anthracene on fMWCNTs/GCE 75 6.2.1 Effect of Change in Scan Rate 76 6.2.2 Effect of Accumulation Time 77 6.2.3 Application of fMWCNTs/GCE in the Analysis of Varying Concentrations of Anthracene 77 6.3 Electrochemical Oxidation of Pyrene on fMWCNTs/GCE 79 6.4 Selectivity 82 6.4.1 Co-detection of Anthracene and Pyrene at fMWCNTs/GCE 83 6.4.2 Interference of Some Common Ions 85 6.5 Detection of Pyrene in Tapwater using fMWCNTs/GCE 86 6.6 Conclusions 87 Chapter 7 88 Summary and Outlook 88 7.1 Summary 88 7.2 Outlook 90 References 92 Selbständigkeitserklärung 101 Curriculum Vitae 102 / Electrochemical detection of polycyclic aromatic hydrocarbons (PAHs), which include anthracene and pyrene, offers a cheaper, simpler, and faster alternative method of analysis than conventional methods like GC and HPLC. However, it still is not as sensitive as these methods. Some recent efforts have suffered from lack of selectivity, either from the electrode modifying layer having high background current or from the choice of supporting electrolyte interfering with the detection. In this work, Pt-Pd nanoparticles (NPs) and MWCNTs were used to modify a glassy carbon electrode (GCE) for sensitive detection of anthracene and pyrene. The NPs used were synthesized using an aqueous extract from E. grandis leaves, a sustainable and environmentally friendly synthetic route. NPs with an average size of 10 nm were obtained by optimizing the amounts of Pt- and Pd-ions in the precursor, with a ratio of 1:3 Pt to Pd-ions producing the smallest size. Through XPS, the composition of the NPs was established to be dominated by Pt2+ and Pd0. XRD analysis revealed a crystalline nature with a face-centered cubic structure. The Pt-Pd NPs produced 94 % enhancement in the peak current for pyrene but resulted in lower peak currents for anthracene. When the NPs were further used with MWCNTs for the detection of pyrene, about 200% peak current enhancement was observed with a dynamic range of 66–130 µM and LOD of 23 µM. The electrochemical process was also established to be mixed diffusion- and adsorption-controlled. The influence of adsorption necessitated the employment of accumulation time in the analysis procedure. MWCNTs were applied in the detection of anthracene and a 74 % peak current enhancement and a reduction in the overpotential by 53 mV were observed. A dynamic range of 50–146 µM and LOD of 42 µM were determined. Lower concentrations were recovered from a tap water sample that was spiked with anthracene, mainly because of the low solubility of PAHs in water. Effect of acid treatment of MWCNTs on the detection of anthracene and pyrene was also investigated. Acid treatment allowed for loading of more material without peeling off of the modified layer which resulted in higher peak current enhancements for anthracene (533%) and pyrene (448%). LODs of 40 µM and 14 µM were determined for anthracene and pyrene respectively, which are only slightly lower than what was observed at MWCNTs/GCE and Pt-PdNPs/MWCNTs/GCE. Detection of anthracene was interfered by the presence of pyrene and common ions, while the LOD for pyrene in the presence of anthracene was 18 µM. The MWCNTs based electrochemical detection platform was found to have a better response towards pyrene.:Bibliographische Beschreibung i Referat i Abstract iii Zeitraum, Ort der Durchführung v Acknowledgements vi Dedication vii Table of Contents viii List of Abbreviations and Symbols xii Chapter 1 1 Introduction 1 1.1 Overview 1 1.2 Polycyclic Aromatic Hydrocarbons 2 1.3 Electrochemical Sensors 7 1.3.1 General Response Curve for Chemical Sensors 10 1.4 Carbon Nanotubes 13 1.5 Use of Nanoparticles in Electrochemical Detection 18 1.6 Green Synthesis of Nanoparticles and The Rationale Behind It 21 1.7 Previous Efforts in the Electrochemical Detection of Polycyclic Aromatic Hydrocarbons 24 1.8 Objectives of the Study 26 Chapter 2 28 Experimental 28 2.1 Chemicals 28 2.1.1 Preparation of Anthracene and Pyrene Solutions 28 2.2 Collection and Preparation of Plant Material 29 2.3 Synthesis and Preparation of Materials 29 2.3.1 Synthesis of Metallic Nanoparticles 29 2.3.2 Acid Treatment of Multi-walled Carbon Nanotubes 30 2.4 Characterization of the Nanomaterials 30 2.4.1 UV-Vis Spectrophotometry 30 2.4.2 SEM/EDX and TEM Analysis 30 2.4.3 Powder X-ray Diffractometry 31 2.4.4 XPS Analysis 31 2.5 Electrochemical Measurements 31 2.5.1 Preparation of the Bare and Modified Glassy Carbon Electrode 32 2.5.2 Characterization of the Bare and the Modified Glassy Carbon Electrode 33 2.5.3 Electrocatalytic Oxidation of Anthracene on the Bare and Modified GCEs 33 2.5.4 Electrocatalytic Oxidation of Pyrene on the Bare and Modified GCEs 34 Chapter 3 35 Synthesis, Characterization, and Application of Pt-Pd Nanoparticles in the Electrochemical Detection of Anthracene and Pyrene 35 3.1 Test for Flavonoids and Polyphenols in the E. grandis Leaves’ Extract 35 3.2 Synthesis of Nanoparticles 35 3.3 Characterization of Nanoparticles 37 3.3.1 TEM Analysis 37 3.3.2 SEM Analysis 40 3.3.3 EDX Analysis 41 3.3.4 Powder X-Ray Diffraction Analysis 45 3.3.5 XPS Analysis of Pt-Pd Particles 46 3.4 Impedance Measurements of the Bare and Nanoparticle-modified Glassy Carbon Electrode 49 3.5 Electrochemical Oxidation of Anthracene and Pyrene at the Bare and Nanoparticles-modified Glassy Carbon Electrode 51 3.6 Conclusions 53 Chapter 4 55 Pt-PdNPs/MWCNTs-Modified GCE for the Detection of Pyrene 55 4.1 Impedance Measurement with Pt-PdNPs/MWCNTs/GCE 55 4.2 Electrochemical Oxidation of Pyrene on Pt-PdNPs/MWCNTs/GCE 56 4.3 Analysis of Varying Concentrations of Pyrene on Pt-PdNPs/MWCNTs/GCE 59 4.4 Selectivity 61 4.5 Conclusions 62 Chapter 5 64 Exploring Multi-walled Carbon Nanotubes for the Detection of Anthracene 64 5.1 Impedance Measurement of MWCNT-Modified Glassy Carbon Electrode 64 5.2 Electrochemical Oxidation of Anthracene on MWCNT/GCE 65 5.3 Analysis of Varying Concentrations of Anthracene Using MWCNTs/GCE 68 5.4 Detection of Anthracene in Tap Water 71 5.5 Conclusions 72 Chapter 6 73 Effect of Acid Treatment of Multi-walled Carbon Nanotubes on the Detection of Anthracene and Pyrene 73 6.1 Characterization of fMWCNTs 74 6.2 Electrochemical Oxidation of Anthracene on fMWCNTs/GCE 75 6.2.1 Effect of Change in Scan Rate 76 6.2.2 Effect of Accumulation Time 77 6.2.3 Application of fMWCNTs/GCE in the Analysis of Varying Concentrations of Anthracene 77 6.3 Electrochemical Oxidation of Pyrene on fMWCNTs/GCE 79 6.4 Selectivity 82 6.4.1 Co-detection of Anthracene and Pyrene at fMWCNTs/GCE 83 6.4.2 Interference of Some Common Ions 85 6.5 Detection of Pyrene in Tapwater using fMWCNTs/GCE 86 6.6 Conclusions 87 Chapter 7 88 Summary and Outlook 88 7.1 Summary 88 7.2 Outlook 90 References 92 Selbständigkeitserklärung 101 Curriculum Vitae 102

Thesis (M.Sc.(Chemistry)) -- University of Limpopo, 2022 / Water contamination caused by toxic elements has serious human health and ecological implications. The increasing quantity of toxic elements in surface and groundwater is currently an area of greater concern, especially since many industries are discharging their metal containing effluents into freshwater without any adequate treatment. The mineral dissolution in mining regions is highly enhanced by mining and smelting activities. The mine waste and drainage in areas surrounding mines have high levels of toxic element contamination above the permissible limits. Contamination of groundwater by toxic elements such as As, Fe, Mn, Al, Cr, Zn and Co due to operational activities of surrounding mines in the Sekhukhune district was reported by several researchers. Removal of toxic elements from contaminated water is a big challenge. The affected communities need to attain a safe water supply source for daily usage, hence there is an urgent need of technologies for the treatment of water supplies contaminated with these toxic elements to ensure the safety of potable water. The study was undertaken by modifying nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) and investigating the removal of chromium, nickel and lead from anthropogenic contaminated groundwater in the Sekhukhune area, in Limpopo. The as-prepared N-MWCNTs functionalised with metal oxide, thiol and amino functional groups are expected to increase the surface area of the nanocomposite, which can facilitate high adsorption of contaminants from water samples. The adsorption capabilities for the removal of these toxic elements by modified N MWCNTs nanocomposites were investigated in batch studies as a function of different parameters. The parameters studied included pH, contact time, adsorbent dosage, initial concentration, temperature, competing ions and reusability. The optimum condition was then acquired for removal of selected toxic elements from real water studies. The removal efficiencies of the as-prepared nanocomposites were pH dependent and the optimal pH values for adsorption was 5.5, 1.5, 11 and 6 at optimum contact time of 10, 80, 60 and 120 min and dosage of 0.30, 0.35, 0.05 and 0.6 g/L for Cr(III), Cr(VI), Ni(II) and Pb(II), respectively. The prepared nanocomposites were characterised using various techniques such as Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmet-Teller (BET) and thermogravimetric analysis (TGA). The FTIR analysis confirmed the presence of Fe3O4, -SH and -NH2 groups on the functionalised MWCNTs. The PXRD analysis further supported that the synthesized nanocomposites consisted of hexagonal graphite structure of MWCNTs. Furthermore, SEM and TEM results showed that the introduced functional groups were uniformly attached on the surface of the MWCNTs. The BET analysis indicated that the surface area of the modified MWCNTs nanocomposites increased significantly as compared to the acid treated MWCNTs. In addition, TGA showed that the M-MWCNTs (M = modified) nanocomposites possess high thermal stability. Raw N-MWCNTs showed higher stability as compared to oxidised N-MWCNTs, which decomposes at lower temperatures of 200 °C. No weight loss was observed below 800 °C for the hydrazine functionalised nanocomposites as compared to the triethylenetetramine (TETA)- substituted nanocomposites, which showed weight loss at 300 °C. Toxic elements in solutions before and after treatment were quantified using flame atomic absorption spectrometry (F-AAS). The adsorption isotherms of the as-prepared nanocomposites for chromium, nickel and lead removal fitted both the Langmuir and Freundlich model depending on the adsorbent used, which suggest that the adsorption process met both monolayer and heterogeneous adsorption. Thermodynamic analysis showed that the adsorption of Cr(III), Cr(VI), Ni(II) and Pb(II) ions are spontaneous and endothermic. The as-prepared nanocomposites showed an outstanding regeneration performance retaining over 50% toxic elements removal. Thus, the as prepared nanocomposites are promising for practical application in toxic element treatment. Analysis of the collected river and borehole water in Sekhukhune indicated that the concentration of total chromium, nickel and lead before treatment varied from (0.207 to 0.286 mg/L), (0.226 to 0.380 mg/L) and (3.301 to 8.017 mg/L), respectively which were above acceptable levels recommended by the South African National Standards (SANS), United States Environmental Protection Agency (USEPA) and World Health Organisation (WHO), i.e., 0.05 mg/L, 0.07 mg/L and 0.01 mg/L. After treatment, the nanocomposites were able to remove 100% of the metal ions from the water. TETA-functionalised nanocomposites showed greater removal efficiencies in comparison to the hydrazine-functionalised nanocomposites for all the studies done. / Water Research Commission (WRC)

Le présent travail de thèse décrit le développement de systèmes actifs de polymérisation d’oléfines basés sur des métaux de fin de transition (nickel et fer) supportés sur des nanomatériaux. Le chapitre I décrit l’état de l’art des systèmes catalytiques supportés ou non pour la polymérisation d’oléfines. Dans le chapitre II, nous décrivons la polymérisation de l’éthylène en utilisant des catalyseurs de nickel contenant un groupement –NH2 pour leur immobilisation covalente sur nanotubes de carbone ; montrant l’influence positive de l’immobilisation : les catalyseurs ainsi supportés sont en effet à la fois plus actifs et conduisant à des polymères de plus haut poids moléculaire. Dans le chapitre III, des complexes de fer contenant un groupement pyrène sont décrits et immobilisés sur nanotubes de carbone par interaction non covalente π-π. Dans ce cas, à la fois les systèmes homogènes et leurs analogues supportés catalysent la réaction de polymérisation de l’éthylène avec des activités particulièrement élevées. Il a également pu être mis en évidence l’importante influence du support carboné sur les performances du système catalytique ainsi que sur la structure des polymères obtenus. Différents types de complexes de nickel contenant un ligand imino-pyridine et différents groupes polyaromatiques ont été synthétisés et leur utilisation en polymérisation de l’éthylène est décrite dans le chapitre IV. L’influence de l’addition de faibles quantités de matériaux nanocarbonés (nanotubes de carbone ou graphène) au milieu réactionnel a ainsi été étudiée. Le graphène s’est dans ce cas révélé particulièrement bénéfique sur les performances du catalyseur. Enfin, le chapitre V décrit la polymérisation de l’isoprène à l’aide de catalyseurs de fer contenant des groupements polyaromatiques permettant leur immobilisation à la surface de nanoparticules de fer. Ces systèmes ont ensuite pu être confinés dans des nanotubes de carbone. Les systèmes catalytiques décrits sont particulièrement actifs produisant des polyisoprènes à température de transition vitreuse élevée et avec une haute sélectivité trans-1,4-polyisoprène. / This present thesis deals with the development of active olefin polymerization catalysts based on late transition metal (nickel and iron) imino-pyridine complexes supported on nanomaterial. Chapter I gives a comprehensive literature review of unsupported and supported ethylene polymerization catalyst. In Chapter II we report the ethylene polymerization studies using nickel complexes containing an –NH2 group for covalent immobilization on multi-walled carbon nanotubes (MWCNTs) of the corresponding precatalysts. Comparison of the homogeneous catalysts with their supported counterparts evidenced higher catalytic activity and higher molecular weights for the polymers produced. In Chapter III, iron complexes containing a pyrene group have been synthesized and immobilized on MWCNTs through non-covalent π-π interactions between pyrene group and surface of MWCNTs. Activated by MMAO, both the iron complexes and immobilized catalysts show high activities for ethylene polymerization. It was possible to evidence that MWCNTs have a great influence on the catalytic activity and on the structure of the resulting polyethylenes. Imino-pyridine nickel complexes containing various kinds of aromatic groups have been synthesized in Chapter IV and polymerization conditions in the presence and in the absence of nanocarbon materials, such as MWCNTs or few layer graphene (FLG), are discussed. For those nickel catalysts bearing 1-aryliminoethylpyridine ligands, the presence of MWCNTs in the catalytic mixture allows the formation of waxes of lower molecular weight and polydispersity, whereas the presence of FLG proved to be beneficial for the catalytic activity. In Chapter V, isoprene polymerization catalyzed by iron complexes containing polyaromatic groups and non-covalently supported on nanoparticles and confined into the inner cavity of MWCNTs (Cat@NPs and Cat@NPs@MWCNTs) are investigated. Iron complexes show excellent activity for the isoprene polymerization and produced high glass temperature polyisoprene with a high trans-1,4-polyisoprene selectivity. Polymer nanocomposites are produced by supported catalysts and, transmission electron microscopy (TEM) evidenced efficient coating of the resulting polyisoprene around the oxygen sensitive iron nanoparticles.

The objective of my work was to develop HDPE clay nanocomposites for packaging with superior barrier (gas and water) properties by economical processing technique. This work also represents a comparative study of thermoplastic nanocomposites for packaging based on linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon12. In this study properties and processing of a series of linear low density polyethylene (LLDPE), high density polyethylene (HDPE) and Nylon 12 nanocomposites based on Na-MMT clay and two different aspect ratio grades of kaolinite clay are discussed.

In recent years, increased use of electronic devices and wireless operations resulted in unavoidable electromagnetic (EM) pollution which has a significant impact on civil and military sectors. Considering the foremost requirement, huge efforts were invested in the development of electromagnetic interference (EMI) shielding materials. In this context, metals are usually preferred but design complexities like high density and susceptibility towards corrosion are limiting factors; additionally, the reflection of microwaves from the surface fails to serve as EM absorbers. The concern here is to minimize the reflection of the high frequency electromagnetic wave from the surface and to enhance the microwave absorption in GHz frequencies. In this thesis, we have made an attempt to design EMI shielding materials with exceptional absorption ability derived from Polycarbonate (PC)/ Poly styrene-co-acrylonitrile (SAN) based polymer blends. Herein, unique co-continuous micro-phase separated blend structures with selective localization of microwave active nanoparticles in one of the phases were realized to be most effective for microwave attenuation over just dispersing it in one polymer matrix (i.e. PC and SAN composites). The synergistic attenuation of electric and magnetic field associated with EM radiation was achieved through incorporation of various magnetic nanoparticles, however, dispersion of magnetic nanoparticles was a challenging task. Therefore, in order to localize magnetic nanoparticles in PC phase of the blends and to enhance the dispersion state, various modification strategies have been designed. In summary, we have developed a library of engineered nanoparticles to achieve synergistic attenuation of EM radiation mostly through absorption. For instance, the PC/SAN blends containing MWNTs and rGO-Fe3O4 nanoparticles manifested in exceptional EMI shielding, well above required shielding effectiveness value for most of the commercial applications, essentially through absorption. Taken together, the finding suggests that immiscible blends containing MWNTs and the decoration of magnetic nanoparticles (rGO-Fe3O4) on the surface of reduced graphene oxide sheets can be utilized to engineer high-performance EMI shielding materials with exceptional absorption ability.

Récemment, les liquides ioniques ont attiré l'attention de la communauté scientifique de la catalyse homogène en tant que solvants répondant aux principes de la chimie verte. De par leur nature chargée, ces phases ioniques sont idéales pour des réactions biphasiques avec des substrats organiques et permettent une récupération facile du catalyseur. Leur caractère ionique leur confère une organisation spatiale à l'échelle nanométrique permettant des phénomènes de solvatations particuliers et une réactivité spécifique. Néanmoins, ces solvants continuent à être onéreux et les supporter peut permettre à la fois de réduire de façon significative les quantités utilisées et de récupérer facilement le catalyseur immobilisé dans la phase liquide ionique. Jusqu'à présent, la catalyse supportée sur liquides ioniques a mis en jeu des supports oxydes mésoporeux classiques comme la silice. Au cours de cette thèse, une étude comparative entre ces types de supports et des nanotubes de carbone multiparois a été réalisée pour différentes réactions catalytiques. Les nanotubes de carbone présentent une macrostructure très ouverte avec une mésoporosité importante. Ainsi, la limitation par transfert de masse dans la porosité du support est diminuée et la cinétique de la réaction, augmentée. Une première étape de fonctionnalisation des nanotubes de carbone a permis d'améliorer la compatibilité avec la phase liquide ionique. L'immobilisation stabilise le catalyseur (complexe métallique [Rh(nbd)(PPh3)2][PF6] ou nanoparticules de palladium) dans la phase liquide ionique après formation d'un film autour des nanotubes. Les systèmes catalytiques supportés ont été utilisés pour différentes réactions tests : l'hydrogénation, le couplage C-C de Heck et la réaction séquentielle Heck/hydrogénation. Des composites supports oxydes (SiO2 ou Al2O3)/liquide ionique ont été préparés afin d'étudier les interactions spécifiques liquide ionique-surface et les comparer avec le liquide ionique pur. / As catalytic support, carbon nanotubes present an open macrostructure with large mesoporosity which avoids mass transfer limitations. Ionic Liquids (ILs) have received much attention in the past years due to their importance in a broad range of applications. In catalysis, they are used to immobilize the catalyst in biphasic reactions and enable an easy separation. Their ionic character confers to these media a special organization of several nanometers that induces solvation phenomena and specific reactivity that can be linked either to confinement effects in the organized structure or to molecular interactions. However, these solvents remain expensive and the fact to support them onto carbon nanotubes as a thin film should permit to reduce significantly the volumes used. In this PhD thesis in order to prepare carbon nanotubes-IL hybrid materials, multi-walled carbon nanotubes were covalently modified with imidazolium salt-based moieties. This functionalization allowed specific interactions between the IL thin film and the chemical moieties on the MWCNTs surface. Then, the catalyst (rhodium complex or palladium nanoparticles) was immobilized into the IL thin film. The catalytic performances have been evaluated in bench reactions: hydrogenation of 1-hexene for rhodium, and selective hydrogenation, Heck, and sequential Heck/hydrogentation process for palladium. Finally, a comparative study has been performed between carbon nanotubes and other classical mesoporous oxide supports, including silica. The carbon nanotubes based catalyst present better performances than their counterparts prepared on conventional supports. Additionally, composites based on SiO2/IL or Al2O3/IL were prepared to carry out a structural study with the aim of understanding their specific surface interactions and compare them to pure ionic liquid.

Materials with appropriate combinations of multifunctional properties (strength, toughness, electrical conductivity and piezoelectricity) together with desired biocompatibility are promising candidates for biomedical applications. Apart from these material properties, recent studies have shown the efficacy of electric field in altering cell functionality in order to elicit various cell responses, like proliferation, differentiation, apoptosis (programmed cell death) on conducting substrates in vitro. In the above perspective, the current work demonstrates how CaTiO3 (CT) addition to Hydroxyapatite (HA) can be utilised to obtain an attractive combination of long crack fracture toughness (up to 1.7 MPa.m1/2 measured using single edge V-notch beam technique) and a flexural strength of 155 MPa in addition to moderate electrical conductivity. The enhancement of fracture toughness in HA-CT composites has been explained based on the extensive characterization of twinned microstructure in CT along with the use of theoretical models for predicting the enhancement of toughening through crack tip tilt and twist mechanisms. Subsequent in vitro studies on HA-CT composites with human Mesenchymal Stem cells (hMSCs) in the presence of electric field has shown enhanced differentiation towards bone like cells (osteogenic lineage) as evaluated by ALP activity, Collagen content and gene expression analyses through Polymerase Chain Reaction (PCR) at the end of two weeks. he extracellular matrix mineralization analysis at the end of 4 weeks of hMSC culture further substantiated the efficacy of electric field as a biochemical cue that can influence the stem cell fate processes on conducting substrates. The electric field stimulation strategy was also implemented in in vitro studies with C2C12 mouse myoblast (muscle) cells on elastically compliant poly(vinylidene difluoride) (PVDF)-multiwall carbon nanotube (MWNT) composite substrates. PVDF is a piezoelectric polymer and the addition of MWNTs makes the composite electrically conducting. Upon, electric field stimulation of C2C12 mouse myoblast cells on these composites, has been observed that in a narrow window of electric field parameters, the cell viability was enhanced along with excellent cell alignment and cell-cell contact indicating a potential application of PVDF-based materials in the muscle cell regeneration. In an effort to rationalise such experimental observations, a theoretical model is proposed to explain the development of bioelectric stress field induced cell shape stability and deformation. A single cell is modelled as a double layered membrane separating the culture medium and the cytoplasm with different dielectric properties. This system is linearized by invoking Debye-Huckel approximation of the Poisson-Boltzmann equation. With appropriate boundary conditions, the system is solved to obtain intracellular and extracellular Maxwell stress as a function of multiple parameters like cell size, intracellular and extracellular permittivity and electric field strength. Based on the stresses, we predict shape changes of cell membrane by approximating the deformation amplitude under the influence of electric field. Apart from this, the shear stress on the membrane has been used to determine the critical electric field required to induce membrane breakdown. The analysis is conducted for a cell in suspension/on a conducting substrate and on an insulating substrate to illustrate the effect of substrate properties on cell response under the influence of external electric field.

Différents effets de nanotubes de carbone (NTC) sur des diatomées benthiques ont été évalués via des approches microscopiques et biochimiques. Il a été montré que la structure du frustule, paroi silicifiée propre aux diatomées, est déterminante sur l'entrée ou non des NTC dans les cellules. Une internalisation des NTC dans la cellule a conduit à des effets génotoxiques et tératogènes. L'interaction des NTC avec les substances polymériques extracellulaires (SPE) produites par les diatomées a aussi été évaluée. Les SPE ont favorisé l'agglomération des NTC entre eux, ainsi que leur isolement physico-chimique vis-à-vis des diatomées. Une réponse des diatomées à la présence des NTC par la surproduction de SPE explique partiellement le retard de croissance observé. De plus, Des interactions entre SPE et NTC, majoritairement hydrophobes, ont été révélées. Ces interactions ont permis de réduire considérablement les effets des NTC sur les diatomées au cours du temps. / Various effects of carbon nanotubes (CNTs) on benthic diatoms were assessed via microscopic and biochemical approaches. It has been shown that the structure of the specific to diatoms silicified frustule has a key role in the entry or not of CNTs into the cells. Moreover, Internalization of CNTs in the cell led to genotoxic and teratogenic effects. The interaction of the CNTs with the extracellular polymeric substances (EPS) produced by diatoms was also evaluated. EPS favored agglomeration of CNTs between them as well as their physico-chemical isolation for diatoms. A response of diatoms in the presence of CNTs by the overproduction of EPS partially explains the observed growth retardation. In addition, interactions between the EPS and CNTs, mainly hydrophobic, have been revealed. These interactions significantly reduced the effects of CNTs in diatoms over time.

In this study, we propose a multi-walled carbon nanotube epoxy composite sensor for force and pressure sensing in the range of 50 N–2 kN. A manufacturing procedure, including material preparation and deposition techniques, is proposed. The electrode dimensions and the layer thickness were optimized by the finite element method. Temperature compensation is realized by four nanocomposites elements, where only two elements are exposed to the measurand. In order to investigate the influence of the filler contents, samples with different compositions were prepared and investigated. Additionally, the specimens are characterized by cyclical and stepped force/pressure loads or at defined temperatures. The results show that the choice of the filler content should meet a compromise between sensitivity, temperature influence and noise behavior. At constant temperature, a force of at least 50N can be resolved. The measurement error due to the temperature influence is 150N in a temperature range of –20°C–50°C.