Eco-friendly green synthesis, structural and photoluminescent studies of CeO2:Eu3+ nanophosphors using E. tirucalli plant latex

The investigation involves preparation and photoluminescence properties of CeO2:Eu3+ (1-11 mol%) nano phosphors by eco-friendly green combustion route using Euphorbia tirucalli plant latex as fuel. The final product was characterized by powder X-ray diffraction (PXRD), Scanning electron microcopy (SEM) and Transmission electron microscopy (TEM). The PXRD and SEM results reveals cubic fluorite phase with flaky structure. The crystallite size obtained from TEM was found to be similar to 20-25 nm, which was comparable to W-H plots and Scherrer's method. Photoluminescence (PL) emission of all the Eu3+ doped samples shows characteristic bands arising from the transitions of D-5(0) -> F-5(J) (J = 0, 1, 2, 3, 4) manifolds under excitation at 373 and 467 nm excitation. The D-5(0) -> F-7(2) (613 nm) transition often dominate the emission spectra, indicating that the Eu3+ cations occupy a site without inversion center. The highest PL intensity was recorded for 9 mol% Eu3+ ions with 5 ml latex. PL quenching was observed upon further increase in Eu3+ concentration. The international commission on illumination (CIE) chromaticity co-ordinates were calculated from emission spectra, the values (x, y) were very close to national television system committee (NTSC) standard values of pure red emission. The results demonstrate that the synthesized phosphor material could be very useful for display applications. Further, the phosphor material prepared by this method was found to be non toxic, environmental friendly and could be a potential alternative to economical routes. (C) 2014 Elsevier B.V. All rights reserved.

Noble metal ion substituted CeO2 catalysts: Electronic interaction between noble metal ions and CeO2 lattice

In last 40 years, CeO2 has been found to play a major role in the area of auto exhaust catalysis due to its unique redox properties. Catalytic activity is enhanced when CeO2 is added to the noble metals supported Al2O3 catalysts. Reason for increase in catalytic activity is due to higher dispersion of noble metals in the form of ions in CeO2. This has led to the idea of substitution of noble metal ions in CeO2 lattice acting as adsorption sites instead of nanocrystalline noble metal particles on CeO2. In this article, a brief review of synthesis, structure and catalytic properties of noble metal ions dispersed on CeO2 resulting in noble metal ionic catalysts (NMIC) like Ce1-xMxO2-delta, Ce1-x-yTixMyO2-delta, Ce1-x-yZrxMyO2-delta, Ce1-x-ySnxMyO2-delta and Ce1-x-yFexMyO2-delta (M = Pt, Pd, Rh and Ru) are presented. Substitution of Ti, Zr, Sn and Fe in CeO2 increases oxygen storage capacities (OSC) due to structural distortion, whereas dispersion of noble metal ions in Ti, Zr, Sn and Fe substituted CeO2 supports increase both OSC and catalytic activities. Electronic interaction between noble metal ions and CeO2 in NMICs responsible for higher OSC and higher catalytic activities is discussed. (C) 2015 Published by Elsevier B.V.

Noble metal ions in CeO2 and TiO2: synthesis, structure and catalytic properties

In the past four decades, CeO2 has been recognized as an attractive material in the area of auto exhaust catalysis because of its unique redox properties. In the presence of CeO2, the catalytic activity of noble metals supported on Al2O3 is enhanced due to higher dispersion of noble metals in their ionic form. In the last few years, we have been exploring an entirely new approach of dispersing noble metal ions on CeO2 and TiO2 matrices for redox catalysis. In this study, the dispersion of noble metal ions by solution combustion as well as other methods over CeO2 and TiO2 resulting mainly in Ce1-xMxO2-delta, Ce1-x-yTixMyO2-delta, Ce1-x-ySnxMyO2-delta, Ce1-x-yFexMyO2-delta, Ce1-x-yZrxMyO2-delta and Ti1-xMxO2-delta (M = Pd, Pt, Rh and Ru) catalysts, the structure of these materials, their catalytic properties toward different types of catalysis, structure-property relationships and mechanisms of catalytic reactions are reviewed. In these catalysts, noble metal ions are incorporated into a substrate matrix to a certain limit in a solid solution form. Lower valent noble metal-ion substitution in CeO2 and TiO2 creates noble metal ionic sites and oxide ion vacancies that act as adsorption sites for redox catalysis. It has been demonstrated that these new generation noble metal ionic catalysts (NMIC) have been found to be catalytically more active than conventional nanocrystalline noble metal catalysts dispersed on oxide supports.

Estudo de catalisadores modelo à base de CeO2-ZrO2 dopado com cobre para controle de emissões de NOx

Convencionalmente, metais nobres são empregados como metais ativos em catalisadores automotivos, mas o uso de cobre vem sendo estudado pelo fato de promover sítios ativos para adsorção química e redução de NOx. Diante deste contexto, esta dissertação visa testar novas formulações de catalisadores, com foco em seu desempenho na reação de redução do NO pelo CO e sua seletividade a N2. Foram avaliados o método de adição de cobre no preparo e os teores de cobre utilizados na preparação. Os métodos de adição utilizados foram impregnação a seco (IS), reação em estado sólido (RS) e coprecipitação (CO). Os teores de cobre estudados ficaram entre 0,36 e 6,9% (m/m). Além disso, foi estudado o impacto no desempenho do catalisador após envelhecimento térmico a 950C por 12h. Foram empregadas as seguintes técnicas de caracterização textural e físico-química como espectrometria de absorção atômica, fisissorção de N2, difração de raios X, espectroscopia Raman e redução a temperatura programada. Os catalisadores também foram avaliados na reação de redução do NO pelo CO. A análise textural indicou que o método de coprecipitação levou a características texturais diferentes dos outros catalisadores. Análises de DRX mostraram a formação de CuO cristalino para teores iguais ou superiores a 3,3% (m/m) de cobre. As análises de Redução a Temperatura Programada (RTP) indicaram que ocorreu uma forte interação na interface entre o suporte e as espécies de cobre dispersas, acompanhada da diminuição da temperatura de redução do CuO e da redução parcial da céria em temperaturas mais baixas. Os testes catalíticos mostraram um melhor desempenho dos catalisadores (IS) que apresentaram conversões mais elevadas em menores temperaturas. Com relação ao envelhecimento, observou-se uma diminuição significativa da eficiência dos catalisadores. Uma comparação com catalisadores à base de metal nobre mostrou um bom desempenho dos catalisadores à base de cobre, com a vantagem destes apresentarem emissão de N2O restrita a baixas temperaturas

Growth of CeO2 : Bi12SiO20 crystals in multi-position furnace(II) - Space growth experiment

Ce-doped Bi12SiO20 single crystal with size of phi10mm x 40mm was successfully grown in space on board of the spacecraft Shenzhou No.3. The surface morphology of space-grown crystal is different from that of ground-grown crystal The space- and ground-grown crystals were measured by X-ray rocking curves, absorption spectra and micro-Raman spectra. The results show that the quality of Ce-deped crystal grown in space is better than that of the ground-grown one. The effect of doping on optical properties of BSO grown in space is evident in comparison with the ground-grown crystal.

Violet/blue photoluminescence from CeO2 thin film

CeO2 thin film was fabricated by dual ion beam epitaxial technique. The violet/blue PL at room temperature and lower temperature was observed from the CeO2 thin film. After the analysis of crystal structure and valence in the compound was carried out by the XRD and XPS technique, it was inferred that the origin of CeO2 PL was due to the electrons transition from Ce4f band to O2p band and the defect level to O2p band. And these defects levels were located in the range of 1 eV around Ce4f band.

Growth and photoluminescence of epitaxial CeO2 film on Si (111) substrate

A CeO2 film with a thickness of about 80nm was deposited by a mass-analysed low-energy dual ion beam deposition technique on an Si(111) substrate. Reflection high-energy electron diffraction and x-ray diffraction measurements showed that the film is a single crystal. The tetravalent state of Ce in the film was confirmed by x-ray photoelectron spectroscopy measurements, indicating that stoichiometric CeO2 was formed. Violet/blue light emission (379.5 nm) was observed at room temperature, which may be tentatively explained by charge transitions from the 4f band to the valence band of CeO2.

A study of the interface of CeO2/Si heterostructure grown by ion beam deposition

Epitaxial cerium dioxide films on single-crystal silicon substrates (CeO2/Si) have been grown by a dual mass-analyzed low-energy ion beam deposition (IBD) system. By double-crystal X-ray diffraction (XRD), Full Width at Half Maximum (FWHM) are 23' and 33' in the rocking curves for (222) and (111) faces of the CeO2 film, respectively, and the lattice-mismatch Delta a/a with the substrate is about - 0.123%. The results show that the CeO2/Si grown by IBD is of high crystalline quality. In this work, the CeO2/Si heterostructure were investigated by X-ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES) measurements. Especially, XPS and AES depth profiling was used to analyze the compositions and structures in the interface regions of the as-grown and post-annealed CeO2/Si. It was found that there was no silicon oxide in the interface region of the as-grown sample but silicon oxide in the post-annealed sample. The reason for obtaining such high quality heterostructure mainly depends on the absence of silicon oxide in the surface at the beginning of the deposition. (C) 1998 Elsevier Science Ltd. All rights reserved.

Identification of induced reaction during XPS depth profile measurements of CeO2/Si films grown by ion beam epitaxy

An anomalous behavior was observed in X-ray photoelectron Spectroscopy (XPS) depth profile measurements conducted on CeO2/Si epilayers grown by ion beam epitaxy (IBE): the signals of Ce3+ and Ce4+ co-exist, and the ratio between them increases during the etching time and then tends to maintain a constant level before increasing again. The results of X-ray Diffraction (XRD), Auger Electron Spectroscopy (AES), and Rutherford Back-Scattering (RES) measurements proved that the reduction chemical reaction of CeO2 is induced by ion-etching. (C) 1998 Elsevier Science Ltd. All rights reserved.

Mechanism of induced reaction during XPS depth profile measurements of CeO2/Si films grown by ion beam epitaxy

In a search for the mechanism of the induced reduction reaction that occurred in X-ray photoelectron Spectroscopy (XPS) depth profiles measured experimentally on CeO2/Si epilayers grown by ion beam epitaxy (IBE), several possibilities have been checked. The first possibility, that the X-ray induces the reaction, has been ruled out by experimentation. Other possible models for the incident-ion induced reaction, one based on short-range interaction (direct collision) and the other based on long-range potential accompanied with the incident-ions, have been tested by simulation on computer. The results proved that the main mechanism is the former, not the latter. (C) 1998 Elsevier Science Ltd. All rights reserved.

The role of CeO2-ZrO2 as support in the ZnO-ZnCr2O4 catalysts for autothermal reforming of methanol

Autothermal reforming of methanol for hydrogen production was investigated over ZnO-ZnCr2O4 supported on a series of metal oxides (Al2O3, CeO2, ZrO2 and CeO2-ZrO2)CeO2-ZrO2 mixed oxides with Ce /Zr molar ratio of 4/1 was found to be the optimal support which showed significant effect on the catalytic activity and selectivity. The ZnO-ZnCr2O4/CeO2-ZrO2 and ZnO-ZnCr2O4 catalysts were characterized by XRD, TEM, H-2-TPR and XPS. The results show that CeO2-ZrO2 mixed oxides have significant effect on the catalytic performance and the supported catalyst shows more uniform temperature distribution in the catalyst bed which was mainly due to its reasonable redox properties.

High quality CeO2 film grown on Si(111) substrate by using low energy dual ion beam deposition technology

By using the mass-analyzed low energy dual ion beam deposition technique, a high quality epitaxial, insulating cerium dioxide thin film with a thickness of about 2000 Angstrom, has been grown on a silicon (111) substrate. The component species, cerium and oxygen, are homogeneous in depth, and have the correct stoichiometry for CeO2. X-ray double-crystal diffraction shows that the full width at half maximum of the (222) and (111) peaks of the film are less than 23 and 32 s, respectively, confirming that the film is a perfect single crystal. (C) 1995 American Institute of Physics.

CeO2/Si薄膜的紫／蓝光跃迁

利用双离子束外延技术制备了CeO2/Si薄膜，观察到了CeO2室温蓝光发光以及低温紫光致发光(PL)现象．利用XRD和XPS对薄膜结构及价态进行分析后表明，Ce02的发光机制是由于电子的Ce4f→O2p跃迁和缺陷能级→O2p能级跃迁共同作用的结果，并且这些缺陷能级位于Ce4f能级上下1eV的范围内．