M.Sc. / This study focused on the synthesis and evaluation of phosphine ligands with multiple functional ities. Polar ligands suitable for use in homogeneous catalysis in aqueous/organic systems were synthesised, as were ligands incorporating a boron atom in an intramolecular Lewis acid-Lewis base interaction with the phosphorus atom. A malonate moiety was readily incorporated into a phosphorus starting material, and derivatives were obtained by reduction of the ester groups. The polar diol products were reacted with 1,4-butanesultone which made them water soluble and thus ideal for biphasic catalysis. Wittig chemistry was employed to introduce alkenes of varying electronic nature into a phosphorus-containing aldehyde starting material. The catalysed hydroboration reaction making use of diboron reagents was used to introduce a boron functionality into the resulting a, n-unsaturated ester phosphine I igands. All of the ligands produced were tested in transition metal-catalysed reactions, namely the Heck reaction, the Suzuki reaction, the Stille reaction, the carboxymethylation reaction and the hydroformylation reaction. The polar and water soluble ligands all showed comparable or improved yields to the standard benchmark triphenylphosphine ligand in organic, biphasic and ionic liquid media. The electronic nature of the alkene ligands largely dictated the activities observed in the Heck, Suzuki and Stille reactions. The electron rich ligands showed improved activities in the Heck reaction, while the electron poor ligands showed improved activities in the Suzuki reaction. In contrast, the Stille reaction seemed to be more affected by the steric demands of the ligands rather than by electronic considerations. It was also found that the boron containing ligands showed an enhanced activity in comparison to the boron free unsaturated and saturated ester ligands. This enhancement was directly ascribable to the Lewis acidic boron atom. This study allowed the synthesis of a range of functionally varying phosphine ligands which where shown to influence transition metal-catalysed reactions based specifically on the functionality present.

Two dimensional (2D) materials are poised to revolutionize the future of optics and electronics. The past decade saw intense research centered around graphene. More recently, the tide has shifted to a bigger class of two-dimensional materials including graphene but more expansive in their capabilities. The so called ‘2D material zoo’ includes metals, semi-metals, semiconductors, superconductors and insulators. The possibility of mixing and matching 2D materials to fabricate heterostructures with desirable properties is very exciting. To make devices with superior electronic, optical and thermal properties, we need to understand how the electrons, phonons and other quasi particles interact with each other and exchange energy in the femtosecond and nanosecond timescales. To measure the timescales of energy distribution and dissipation, I used ultrafast pump-probe spectroscopy to perform time-domain measurements of optical absorption. This approach allows us to understand the impact of manybody interactions on the bandstructure and carrier dynamics of 2D materials. After a brief introduction to femtosecond laser spectroscopy, I will explore the transient absorption dynamics of three classes of 2D materials: intrinsic graphene, graphene-hBN heterostructures and Transition Metal Dichalcogenides (TMDs). We will see that using pumpprobe measurements around the high energy M-point of intrinsicgraphene, we can extract the value of the acoustic deformation potential which is vital in characterizing the electron-acoustic phonon interactions. In the next part of the thesis, I will delineate the role of the substrate in the cooling dynamics in graphene devices. We will see that excited carriers in graphene on hBN substrates cool much faster that on SiO2 substrates due to faster decay of the optical phonons in graphenehBN heterostructures. These results show that graphene-hBN heterostructures can solve the hot phonon bottleneck that plagues graphene devices at high power densities. In the last part, I will demonstrate the role of phonon induced bandgap renormalization in the carrier dynamics of TMD materials and measure the timescale of phonon decay through the generation of low-energy phonons and transfer to the substrate. This study will help us understand carrier recombination in TMD devices under high-bias conditions which show great potential in opto-electronic applications such as photovoltaics, LEDs etc.

Anatase TiO2 has attracted a lot of attention due to its applications as a photocatalyst in water and air treatment technologies. However, its large band gap energy (⁓3.2 eV) limits its application only to UV light. Also, anatase TiO2 suffers from high electron/hole recombination, which diminishes its photocatalytic activity. Therefore, different methods have been employed to decrease its band gap energy and reduce the recombination of the charge carriers. One of the methods is to incorporate impurities as dopants in its crystal lattice. Different metal and non-metal dopants have been studied for this aim. Among the different choices, Fe3+ has showed a great potential to improve the photocatalytic activity of TiO2 under visible light irradiation. Firstly, the d orbitals of Fe3+ interact with the 3d orbitals of Ti4+ generating intermediate band gap energy levels to facilitate excitation of electrons under visible light by a red shift in the absorption of light. Secondly, Fe3+ can interact with both electrons and holes to produce Fe2+ and Fe4+ trapping the charge carriers and reducing their recombination rate. Fe2+ and Fe4+ can release the electron and hole and revert back to the Fe3+. The released charge carriers migrate to the surface of the nanoparticles to initiate the photocatalytic reactions. However, it was found that the photocatalytic activity of Fe-TiO2 is not as high as expected. Therefore, in this research study I investigated the cause for its low photocatalytic activity and found methods to improve it. The Fe-TiO2 was synthesized using a facile sol-gel method and its structure and properties were characterized by different instrumental techniques. Using TEM and HRTEM an amorphous layer was seen on the surface of the nanoparticles. This layer characterized using XPS and EDX was composed of iron oxide layers. This layer was contaminating the surface of the nanoparticles where the photocatalytic reactions take place. Moreover, the contamination layer was acting as a recombination center for the electrons and holes. To the best of our knowledge, no previous study was conducted to investigate the effect of an iron oxide contamination layer on the photocatalytic activity of Fe-TiO2 nanoparticles. This layer was removed using a concentrated HCl solution confirmed using HRTEM and XPS. Also, using DRS it was shown that its removal does not effect the optical properties of the Fe-TiO2 confirming that the acid treatment process did not influence the doped Fe3+ in the TiO2 crystal lattice. The degradation of methelyne orange (MO), a representative pollutant, was increased from 25% to 98% under visible light irradiation. Also, in order to achieve the highest performance of the photocatalyst, it was necessary to study the parameters of the photocatalytic activity and the degradation efficiency. Therefore, experiments using a phenol solution, another representative pollutant, were conducted to investigate and optimize the effects of the catalyst load, reaction time, initial concentrating of the pollutant and pH. The degradation efficiency of the phenol solution was found to increase from 31% to 57% by the removal of the contamination layer and by controlling the pH of the solution. / Graduate

Transition Metal Silicides (TMS) are well known refractory materials because of their high thermal and structural stability at elevated temperature. In addition TMS materials are known for their moderate thermoelectric applications at high temperature since they exhibit superior semiconducting behavior. But TMS materials have relatively higher thermal conductivity which limits their applications in the field of thermoelectrics. So it is important to reduce their thermal conductivity to enhance conversion efficiency. In this regard, the work is performed to reduce the thermal conductivity of selected silicides such as CrSi2, MnSi2, and β-FeSi2 through alloys scattering and nano-structuring by mechanical alloying. A brief introduction about basic principles of thermoelectricity and related parameters are described in the chapter 1. Thermoelectric material’s figure of merit (zT) depends on the ratio of carrier charge transport and thermal energy transport. The conversion efficiency can be significantly enhanced by increasing the zT value. This chapter discusses the methods to increase the zT and list out some of the state-of-art of thermoelectric materials which possesses high zT value. Chapter 2 covers the preparation of selected silicides, such as CrSi2, MnSi2 and β-FeSi2, and the characterization techniques used to define the thermoelectric performance. In this chapter the suitability and the performance of transition metal silicides for high temperature thermoelectric application are discussed. In summary, the objective of the thesis has been framed. Chapter 3 deals with thermoelectric properties of pure and Mn, Al doped chromium disilicide (CrSi2). This chapter has been divided into three parts and discussed the effect of composition variation (CrSi1.90-2.10), point defects (by introducing Al at Si site), and mass-fluctuation scattering (by co-substitution of Mn and Al) on thermoelectric properties of polycrystalline CrSi2 in the temperature range of 300K-800K. In the first part, it is observed that CrSi2 has a homogeneity range of CrSi1.95-CrSi2.02. The secondary phases evolve above and below this homogeneity range. These secondary phases significantly scatter phonons and reduce the thermal conductivity. In the second part, Al has been introduced at Si site in CrSi2 and creates the point defects which is also scatter the short wavelength phonons and lead to low thermal conductivity. The third part explores the influence of co-substitution of Mn at Cr site and Al at Si site on lattice thermal conductivity. Here, substitution of Al creates point defects and addition of Mn leads to mass fluctuation scattering. These combined effects result in huge reduction in lattice thermal conductivity and thereby enhanced the zT. Chapter 4 deals with efforts of nano-structuring the CrSi2 through Mechanical Alloying (MA) using SS (stainless steel) and WC (Tungsten Carbide) milling media. The effects of two milling media on crystallite size reduction are discussed. It is seen that as milling time increases the rate of crystallite size reduction also increases. The X-ray diffraction studies of hot pressed pellets show the formation of secondary metallic phase like Cr1-xFexSi from SS milled samples and CrSi from WC milled samples. It indicates that CrSi2 gains metallic Fe atoms during mechanical alloying and the secondary phases are formed. As milling time increases it is observed that weight loss from the milling balls also increases. The Fe content coming from SS ball forms a solid solution with CrSi phase. The transport properties like resistivity, Seebeck coefficient and thermal conductivity were measured for milled samples from 300K-800K. It is observed that formation of the secondary metallic phase reduces resistivity and Seebeck coefficient of overall ceramics. Very large reduction in thermal conductivity was found for samples which were 15hrs-WC-milled (7.4 W/m.K at 375K) due to increased phonon scattering by grain boundaries. The 15hrs-SS-milled samples show thermal conductivity ~10 W/m.K which is considerably low as compared to the as-cast CrSi2 (13.5 W/m.K). This chapter explores the structural studies and mechano-chemical decomposition of CrSi2. In addition, the influences of mechanical milling media and micron size secondary phase on transport properties of CrSi2 are also discussed. Chapter 5 deals with the influence of microstructures of MnSi2 densified by hot uni-axial pressing (HP) and spark plasma sintering (SPS) on thermoelectric properties. The effects of these densification processes on arresting the grain growth during sintering are explored. The powder X-ray diffraction studies show higher manganese silicide (HMS) with secondary Si phase. The SEM and EPMA results confirmed the presence of Si phase. The TEM micrographs are shown the particle size distribution of HMS to be <200nm with fine precipitates of Si, of 5-10nm size, in the HMS matrix. The ball milled samples of MnSi2 showed increase in resistivity and Seebeck coefficient with large reduction in total thermal conductivity as compared to that seen in as-cast sample. The SPS densified samples show lower thermal conductivity, with reduction by about 52%, as compared to HP sample’s (45%) reduction for same conditions. An enhancement in zT by 73% could be achieved for the SPS densified for 2 min at 1060˚C. Chapter 6 examines (i) the decomposition of α–FeSi2, generally known as α-Fe2Si5, (eutectoid reaction) into β-FeSi2 with Si dispersoids (ii) formation of β-FeSi2 from ε-FeSi and α-Fe2Si5 (peritectoid reaction). This is accompanied by a discussion of the microstructural effect on thermoelectric properties. Prolonged annealing of peritectoid composition decomposes the α– FeSi2 phase, replaces the ε–FeSi phase, and forms pure β-FeSi2 whereas eutectoid composition of α–FeSi2 decomposes into lamellar structure of β-FeSi2 and Si dispersions. The aging heat treatment carried out for composition prepared from eutectoid reaction at various temperatures (600°C, 700°C, 800°C and 850°C for duration of 100hrs, 10hrs, 4hrs and 10hrs, respectively) below the equilibrium eutectoid temperature were found to have fine and homogenous dispersions of Si particles. The XRD and SEM studies confirmed the presence of a secondary Si phase on the matrix of β-FeSi2 for the heat treated eutectoid composition. The excess Si phase in β-FeSi2 increases the resistivity and Seebeck coefficient by the reducing carrier concentration of system as compared to those that of pure β-FeSi2, which is prepared from peritectoid composition. The samples heat treated at 600°C showed relatively low thermal conductivity as compared to that of β-FeSi2. This chapter gives a route map for reducing the thermal conductivity by micro structural engineering through Si dispersions on β-FeSi2. In addition, this comparison of two the decomposition processes and its influence on the microstructure and thermoelectric properties is made. Chapter 7 summarizes the key conclusions of the work performed in this thesis. The work reported in this thesis has been carried out by the candidate as a part of Ph.D training programme. He hopes that this would constitute a worthwhile contribution to the field of thermoelectrics for understanding the (i) effect of alloy scattering, (ii) mass fluctuation scattering, (iii) and nano-structuring of transition metal silicides for high temperature thermoelectric materials.

The development of energy storage and conversion techniques with high efficiency and power density is of great importance for the sustainable development of our green world. Li-O₂ batteries with high theoretical energy density has attracted extensive attention. However there are still many issues waiting to be solved, such as low stability of cathode catalyst, as well as the deactivation of cathode by H₂O and CO₂ from air. Reversible solid oxide fuel cells can be used for electricity production by SOFCs and fuel production (H₂ and O₂) by SOECs. Thus, oxygen storage materials can bridge Li-O₂ batteries and reversible SOFCs with the purpose of increasing the whole efficiency of the system. The discovery of oxygen storage materials with reversible oxygen release/storage behaviours and high oxygen storage capacities dependent on temperature or oxygen partial pressures (e.g., inert and oxidation gases) still needs further research. The work in this thesis mainly focuses on the preparation of transition-metal based oxides (such as perovskite oxides, brownmillerite-type oxides, layered-perovskite oxides, coated β-MnO₂ nanorods, transition-metal doped CeO₂ nanocrystals) as oxygen storage materials and their energy-related applications, seeking to discover the principles for oxygen storage/release properties and their performance in energy conversion and storage applications. The prepared materials included nanostructured and bulk materials via various synthesis methods, including citrate-modified evaporation-induced self-assembly method, hydrothermal method, pechini method, as well as solid state method. This work investigated the oxygen storage capacities of several crystal structure types oxides based on transition-metals. Nanostructured La₀.₆Ca₀.₄Fe₁₋ₓCoₓO[sub](3-δ) and La₀.₆Ca₀.₄Mn₁₋ₓFeₓO[sub](3-δ) exhibit high oxygen storage capacities and stability under reductive 5%H₂/Ar, but the oxygen-storage content under inert argon is low, just about 0.2 wt%. Brownmillerite-type Ca₂AlMnO₅ is demonstrated to possess a large amount of oxygen release/storage capacities depending on temperature even under flowing oxygen, as well as high oxygen storage/release properties and reversibility under alternating inert and oxygen gases at 500 °C. Substituting Ga on the Al-site would reduce the oxygen storage capacities, even though these substituted samples still posses good reversibility. The effect of A-site species (Mg, Ca, Sr) have been also investigated and demonstrated. It can't obtain pure brownmillerite-type crystal structure when Ca is partially or totally substituted by Mg or Sr, resulting in poor reversibility and low oxygen storage capacities. Nanostructured layered-perovskite La₁.₇Ca₀.₃M₁₋ₓCuₓO[sub](4-δ) (M = Fe, Co, Ni, Cu) have also been investigated for oxygen storage and as potential cathodes for IT-SOFCs. Even though the as-prepared layered-perovskite oxides have been demonstrated to be good candidates as cathode materials for IT-SOFCs with high performance, they do not possess high amount of oxygen storage/release ability under inert atmospheres because of the robust phase stability. β-MnO₂ nanorods can release large amount of oxygen (ca. 9.2 wt%) with increasing temperature at about 560 °C under various gases (air, N₂). Coating β-MnO₂ nanorods with CeO₂ nanocrystals could result in lower temperatures for oxygen mobility and removal under N₂ because of the enhanced oxygen mobility between CeO₂₋ₓ and β-MnO₂, while coating β-MnO₂ nanorods with SnO₂ nanocrystals have no enhanced oxygen mobility behaviours. The results demonstrate the positive and negative synergetic effect between other metal oxides and β-MnO₂ on the oxygen migration. Cr- and Cu-doped CeO₂ nanocrystals (i.e. nanorods, nanocubes and nanoparticles) were chosen to investigate the effect of transition-metal doping on CeO₂ and their valence changes with temperature and various atmospheres, as well as their oxygen storage capacities. The effect of Cr- or Cu- doping on CeO₂ nanocrystal morphology and oxygen storage capacities have been investigated and demonstrated. This provides some basic information for transition-metals doped CeO₂ nanocrystal evolution and stability, as well as further applications in energy-related fields, such as three-way catalysts, electrode materials in solid oxide fuel cells and Li-air batteries.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17162号 / 工博第3652号 / 新制||工||1555(附属図書館) / 29901 / 京都大学大学院工学研究科分子工学専攻 / (主査）教授 佐藤 啓文, 教授 横尾 俊信, 教授 梶 弘典 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17525号 / 工博第3684号 / 新制||工||1560(附属図書館) / 30291 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 佐藤 啓文, 教授 今堀 博, 教授 山本 量一 / 学位規則第4条第1項該当

M.Sc. / This study deals with the synthesis of nitrogen-donor imidazolyl- and pyrazolyl-salicylaldimine compounds, their reactions with selected transition metals and applications as catalysts for Heck coupling reactions of aryl halides with butyl acrylate, ethylene polymerization reactions and reactions of higher α-olefins. Imidazole-based salicylaldimine compounds 2,4-di-tert-butyl-6-{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1) and 4-tert-butyl-2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L2) were prepared by Schiff base condensation reaction of histamine dihydrochloride with 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 5-tert-butyl-2-hydroxybenzaldehyde respectively. The compounds were characterized by 1H, 13C{1H} NMR and IR spectroscopy; and high resolution mass spectrometry (HRMS). Compounds 2-{[2-(1H-imidazole-4-yl)-ethylimino]-methly}-phenol (L3), 2,4-di-tert-butyl-6-{[2-(3,5-dimethyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L4), 2,4-di-tert-butyl-6-[(2-pyrazol-1-yl-ethylimino)-methyl]-phenol (L5) and 2,4-di-tert-butyl-6-{[2-(3,5-diphenyl-pyrazol-1-yl)-ethylimino]-methyl}-phenol (L6) were synthesized according to literature procedure. Reactions of L1-L3 with [PdCl2(MeCN)2] yielded complexes 2.1-2.3 respectively. Ligand L1 was also complexed with [FeCl2] and [CoCl2] to give complexes 2.4 and 2.5 respectively, while complexes 2.6-2.15 were synthesized by reactions of L1, L2 and L4-L6 with [VCl3] and [CrCl3(THF)3]; all in a ratio of 1:1. The palladium(II) complexes (2.1-2.3) were characterized by 1H, 13C{1H} NMR and IR spectroscopy, mass spectrometry and elemental analysis, while complexes 2.4-2.15 were characterized by IR spectroscopy, mass spectrometry and elemental analysis due to their paramagnetic nature. The structures of complexes 2.1 and 2.4 were confirmed by single crystal X-ray diffraction analysis. All the complexes formed were mononuclear.

Luminescent transition metal complexes have arisen as viable alternatives to organic dyes for sensory applications due to their notable advantages. This thesis aimed to synthesize different kinds of iridium(III) complexes as chemosensors and G-quadruplex probes for the detection of metal ions, small molecules, proteins and DNA to demonstrate the versatility of iridium(III) complex in luminescence sensing. Iridium(III) complex chemosensors were synthesized and developed for the detection of Cu2+ and cysteine. The iridium(III) complex plays the role of the "signaling unit", which transduces the analyte binding event into an optical (luminescent) signal and the "receptor unit" attached to the metal complex selectively binds the analyte of interest. Meanwhile, a series of iridium(III) complexes incorporating a variety of C^N and N^N donor ligands were synthesized and were shown to exhibit G-quadruplex-selective binding properties via emission titration, fluorescence resonance energy transfer melting and G-quadruplex fluorescent intercalator displacement experiments. These G-quadruplex-selective Ir(III) complexes were utilized as signal transducers to monitor the conformational changes of oligonucleotides in label-free oligonucleotide-based luminescent detection platforms for metal ion (Ag+), small molecules (cocaine), protein (insulin and AGR2) and gene deletion.

Philosophiae Doctor - PhD / Transition metal oxides magneli phases present crystallographic shear structure which is of great interest in multiple applications because of their wide range of valence, which is exhibited by the transition metals. The latter affect chemical and physical properties of the oxides. Amongst them we have nanostructures VO2 system of V and O components which are studied including chemical and physical reactions based on non-equilibrium thermodynamics. Due to their structural classes of corundum, rocksalt, wurtzite, spinel, perovskite, rutile, and layer structure, these oxides are generally used as catalytic materials which are prepared by common methods under mild conditions presenting distortion or defects in the case of VO2. Existence of an intermediate phase is proved using an x-ray thermodiffraction experiment providing structural information as the nanoparticles are heated. Potential application as gas sensing device has been the first time obtained due to the high surface to volume ratio, and good crystallinity, purity of the material and presence of suitable nucleating defects sites due to its n-type semiconductor behavior. In addition, annealing effect on nanostructures VO2 nanobelts shows a preferential gas reductant of Ar comparing to the N2 gas. Also, the hysteresis loop shows that there is strong size dependence to annealing treatment on our samples. This is of great interest in the need of obtaining high stable and durable material for Mott insulator transistor and Gas sensor device at room temperature.