This work contains a study of CeRuSn, which undergoes two structural transitions at 290 K and 256 K both connected with large temperature hysteresis. During the transitions the lattice shrinks along the c axis. At low temperatures the compound orders antiferromagnetically below 2.8(1) K. A strong magnetocrystalline anisotropy is caused by very shortened Ce-Ru separations pointing approximately along the c axis. Due to a strong hybridization, two thirds of Cerium atoms are in a non integer valence state. For the first time synthesized single-crystals of YbPt2Si2 a Yb2Pt3Si5 show no magnetic ordering. A maximum, which is visible in the temperature dependences of magnetic susceptibility originate in thermal population of the magnetic Yb3+ state. Powered by TCPDF (www.tcpdf.org)

This work is concerning the study of model ceria based calalysts structure by methods of electron diffraction RHEED and photoelectron spectroscopy XPS. The influence of deposition conditions and substrate on the growth of epitaxial cerium oxide films on copper single crystals is described in detail. The work then describes the interaction of cerium and tin in model systems and the creation of SnCeOx mixed oxide and its structure. In the last chapter, the interaction of palladium with cerium and tin oxide layers is examined, and the creation of paladium bimetallic alloys is described. Powered by TCPDF (www.tcpdf.org)

The thesis is focused on the investigation of fundamental catalytic properties of two model catalysts-CeOx/Cu(111) and CuOx/Cu(111)-by means of advanced surface science techniques. The investigations performed on CeOx are devoted to the study of the relationship between the surface structure and the surface activity of ceria. We develop the preparation method leading to growth of epitaxial CeOx(111) thin films with the adjustable morphological parameters-the step density and the ordering of surface oxygen vacancies. By using the CeOx(111) films with precisely controlled structure we identify the role of the step edges and of the oxygen vacancies in the interaction of water with ceria. The investigation performed on CuOx is focused on the microscopic characterization of the reduction process of Cu2O(111) on the molecular level directly under a near ambient pressure of CO. In direct microscopic study we identify the active initiation centers, the intermediate oxide phases, and the kinetics of the reduction reaction of Cu2O(111).

Catalysts based on cerium oxide are ubiquitous in industrial-scale chemical conversion. Here, a thorough study of their fundamental properties is undertaken via a model system ap- proach with the goal of furthering rational design in heterogeneous catalysis. A focus is put on understanding the behavior of oxygen vacancies in cerium oxide with respect to atomic co-ordination and electronic structure perturbations. Utilizing state-of-the-art probing tech- niques, a scalable model system framework is developed that allows for control over both the oxygen vacancy concentration and local co-ordination. High precision of the innova- tive approach facilitated observation of new phases of substoichiometric cerium oxide and lead to a first-of-a-kind investigation of the electronic structure of cerium oxide throughout isostructural transition from CeO2 to Ce2O3. The acquired results advance fundamental understanding of essential properties of cerium oxide that are relevant to its utilization in heterogeneous catalysis and open new pathways for functionalization of cerium oxide-based materials. Furthermore, the methodology developed in the thesis is transferable to other important reducible oxides. 1

Cerium oxide nanoparticles (nanoceria) have shown great potential as antioxidant and radioprotective agents for applications in cancer therapy. Recently, various polymer-coated nanoceria preparations have been developed to improve their aqueous solubility and allow for surface functionalization of these nanoparticles. However, the interaction of polymer-coated nanoceria with cells, their uptake mechanism, and subcellular localization are poorly understood. Herein, we engineered polymer-coated cerium oxide nanoparticles with different surface charges (positive, negative, and neutral) and studied their internalization and toxicity in normal and cancer cell lines. The results showed that nanoceria with a positive or neutral charge enters most of the cell lines studied, while nanoceria with a negative charge internalizes mostly in the cancer cell lines. Moreover, upon entry into the cells, nanoceria is localized to different cell compartments (e.g., cytoplasm and lysosomes) depending on the nanoparticles surface charge. The internalization and subcellular localization of nanoceria plays a key role in the nanoparticles cytotoxicity profile, exhibiting significant toxicity when they localize in the lysosomes of the cancer cells. In contrast, minimal toxicity is observed when they localize into the cytoplasm or do not enter the cells. Taken together, these results indicate that the differential surface-charge-dependent localization of nanoceria in normal and cancer cells plays a critical role in the nanoparticles toxicity profile.

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Orientador: Devaney Ribeiro do Carmo / Resumo: Neste trabalho esta descrito a preparação de nanopartículas de Hexacianoferrato (II) de Cério (III) (NpsCe), em quatro proporções diferentes de solventes a saber: Água/Formamida (100:0; 80:20; 40:60; 0:100), afim de se investigar a influência dos solventes no tamanho, morfologia, nas propriedades físico-químicas, voltamétrica e eletrocatalíticas da NpsCe. As Nps foram caracterizadas pelas técnicas de Espectroscopia na Região do Infravermelho (FTIR), Difração de Raios-X (DRX), Microscopia Eletrônica de Varredura (MEV), Potencial Zeta, Voltametria Cíclica (VC) e Voltametria de Pulso Diferencial (VPD). Dos quatro sistemas estudados apenas o CeHCF-1 (100/0) e o CeHCF - 3 (40/60) se apresentaram sensíveis a concentrações do neurotransmissor L-dopamina permitindo a confecção de uma curva de calibração. O sistema CeHCF-1 apresentou duas regiões linerares de sinal em função da concentração de L-dopamina, com limite de detecção (LD) de 0,125 mmol L-1 e 0,023 mmol L-1 obtido pelas técnicas de VC e VPD, respectivamente. Para o sistema CeHCF-3 observou-se por VC uma região linear de intensidade de corrente anódica e a concentração de L-dopamina com LD de 0,0317 mmol L-1, já por VPD apresentou duas regiões lineares de sinal em função da concentração de L-dopamina, com LD de 1,98 x 10-4 e 0,0104 mmol L-1. O sistema CeHCF – 3 apresentou promissor a detecção e quantificação de DA em amostras reais. Assim realizou-se o estudo para avaliar a seletividade deste frente a substâncias comumente en... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work is rearmed to nanoparticles of Cerium (III) Hexacyanoferrate (II) (NpsCe) analog of PB in four different proportions of Water / Formamide solvents (100: 0, 80:20, 40:60, 0: 100 ), to investigate the influence of solvents on the size, morphology, physicochemical, electrochemical and electrocatalytic properties of NpsCe. The Nps were characterized by the techniques of Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Zeta Potential, Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV). Of the four systems studied, only CeHCF-1 (100/0) and CeHCF-3 (40/60) are formed in small concentrations of the neurotransmitter L-dopamine. The CeHCF-1 system showed two signal regions as a function of L-dopamine concentration, with detection limit (LD) of 0.125 mmol L-1 and 0.023 mmol L-1 given by the CV and DPV techniques, respectively. For the CeHCF-3 system it can be seen as a linear signal region as a function of the L-dopamine concentration by the CV technique with LD of 0.0317 mmol L-1, or by DPV through two linear signal regions in the function of the concentration of L-dopamine, with LD of 1.98 x 10-4 and 0.0104 mmol L-1. The launched CeHCF – 3 system promises to detect and quantify DA in real cases. Thus, a study was carried out to reduce the resistance of a substance found in the physiological industries that have the potential of oxidation and reduction of the DA. Substantial subtranslators studied here were Urea and Asco... (Complete abstract click electronic access below) / Mestre

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Cerium oxide (Ceria) at nano scale has gained significant attention due to its numerous technological applications. Ceria in both doped and undoped forms are being explored as oxygen sensor, catalysis, protective coating against UV and corrosion, solid oxide fuel cell (SOFC) electrolyte and newly discovered antioxidant for biomedical applications. Therefore, there is an imminent need of a technology which can provide a cost effective, large scale manufacturing of nanoceria and its subsequent consolidation, specially using thermal spray. This dissertation aims to develop a scientific understanding towards the development of pure and doped ceria- based coating for a variety of technological applications, from SOFC applications to corrosion resistant coating. Atmospheric plasma spray (APS) and solution precursor plasma spray (SPPS) techniques for the fabrication of nano ceria coating were investigated. For feedstock powder preparation, a spray drying technique was used for the agglomeration of cerium oxide nano particles to achieve high density coating. Deposition efficiencies and coating porosity as a function of processing parameters were analyzed and optimized using a statistical design of experiment model. The coating deposition efficiency was dependent on the plasma temperature and vaporization pressure of the ceria nanoparticles. However, low standoff distance and high carrier gas flow rate were responsible for the improved density upto 86 [plus or minus] 3%.An alternative novel SPPS technique was studied for a thin film of cerium oxide deposition from various cerium salt precursors in doped and undoped conditions. The SPPS process allows controlling the chemistry of coating at a molecular level. The deposition mechanism by single scan experiments and the effect of various factors on coating microstructure evolution were studied in terms of splats formation. It was found that the precursor salt (nitrate of cerium) with lower thermal decomposition temperatures was suitable for a high density coating. The high concentration and low spray distance significantly improve the splat morphology and reduced porosity (upto 20%). The feasibility of the trivalent cations (Sm 3+ and Gd 3+) doping into cerium oxide lattice in high temperature plasma was discussed and experimentally studied. XRD analysis revealed the nano crystalline characteristic of the coating and lattice expansion due to doping. The extensive transmission electron microscopy, Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and thermo gravimetric were conducted to evaluate the precursors, and coating microstructure. Due to facial switching between Ce4+ and Ce3+ oxidation state, the cerium oxide surface becomes catalytically active. Thus, the APS ceria coatings were investigated for their applicability under extreme environmental conditions (high pressure and temperature). The air plasma sprayed coated 17-4PH steel was subjected to high pressure (10 Kpsi) and temperature (300 oF) corrosive environment. The coated steel showed continuous improvement in the corrosion resistance at 3.5 wt% NaCl at ambient temperature for three months study whereas, high pressure did not reveal a significant role in the corrosion process, and however, one needs to do further research. The ceria coated steel also revealed the improvement in corrosion protection (by 4 times) compared to the bare steel at low pH, 300 oF and 4000 Psi environment. This study projects the importance of cerium oxide coatings, their fabrication, optimization and applications.