The surface science of titanium dioxide

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Sustainable hydrogen production is an essential prerequisite of a future hydrogen economy. Water electrolysis driven by renewable resource-derived electricity and direct solar-to-hydrogen conversion based on photochemical and photoelectrochemical water splitting are promising pathways for sustainable hydrogen production. All these techniques require, among many things, highly active noble metal-free hydrogen evolution catalysts to make the water splitting process more energy-efficient and economical. In this review, we highlight the recent research efforts toward the synthesis of noble metal-free electrocatalysts, especially at the nanoscale, and their catalytic properties for the hydrogen evolution reaction (HER). We review several important kinds of heterogeneous non-precious metal electrocatalysts, including metal sulfides, metal selenides, metal carbides, metal nitrides, metal phosphides, and heteroatom-doped nanocarbons. In the discussion, emphasis is given to the synthetic methods of these HER electrocatalysts, the strategies of performance improvement, and the structure/composition-catalytic activity relationship. We also summarize some important examples showing that non-Pt HER electrocatalysts could serve as efficient cocatalysts for promoting direct solar-to-hydrogen conversion in both photochemical and photoelectrochemical water splitting systems, when combined with suitable semiconductor photocatalysts.

Noble metal-free hydrogen evolution catalysts for water splitting

Mechanical properties of nanocrystalline materials

The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

We have produced nanocomposite films of Ni:SiO2 by an alternative polymeric precursor route. Films, with thickness of ~ 1000 nm, were characterized by several techniques including X-ray diffraction, scanning electron microscopy, atomic force microscopy, flame absorption atomic spectrometry, and dc magnetization. Results from the microstructural characterizations indicated that metallic Ni-nanoparticles with average diameter of ~ 3 nm are homogeneously distributed in an amorphous SiO2 matrix. Magnetization measurements revealed a blocking temperature TB ~ 7 K for the most diluted sample and the absence of an exchange bias suggesting that Ni nanoparticles are free from an oxide layer.

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Síntese e Caracterização de Nanocompósitos Ni:SiO 2 Processados na Forma de Filmes Finos

A degradacao eletrica de varistores a base de SnO2 foi estudada e verificou-se que na temperatura de 220 oC ocorreu a degradacao do material. Suas caracteristicas foram recuperadas quando tratadas em atmosfera de O2, o que mostra que esta atmosfera e fundamental para a caracteristica do varistor.

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Influência de dopantes doadores na degradação do varistor à base de SnO2 e o efeito do oxigênio pós-degradação

: A modified sol-gel technique was used to synthesize nanocomposites of Ni:SiO2 which resulted in Ni nanoparticles embedded in a SiO2 amorphous matrix. Transmission electron microscopy TEM analysis were performed to study the structure and morphology of the magnetic powders. The Ni particles were found to have a good dispersion and a controlled particle size distribution, with average particle radius of approximately 3 nm. A detailed characterization of the magnetic properties was done through magnetization measurements M(T,H) in applied magnetic fields up to plus/minus 7 T and for temperatures ranging from 2 to 300 K. The superparamagnetic (SPM) behavior of these metallic nanoparticles was inferred from the temperature dependence of the magnetization. The blocking temperature T(B), as low as 20 K, was found to be dependent on Ni concentration, increasing with increasing Ni content. The SPM behavior above the blocking temperature T(B) was confirmed by the collapse of M/M(S) vs. H/T data in universal curves. These curves were fitted to a log-normal weighted Langevin function allowing us to determine the distribution of magnetic moments. Using the fitted magnetic moments and the Ni saturation magnetization, the radii of spherical particles were determined to be close to 3 nm, in excellent agreement with TEM analysis. Also, magnetic hysteresis loops were found to be symmetric along the field axis with no shift via exchange bias, suggesting that Ni particles are free from an oxide layer. In addition, for the most diluted samples, the magnetic behavior of these Ni nanoparticles is in excellent agreement with the predictions of randomly oriented and noninteracting magnetic particles. This was confirmed by the temperature dependence of the coercivity field that obeys the relation H(C(T))=H(C01-(T/T(B))(sup 1/2) below T(B) with H(C0) difference 780 Oe.

Magnetic Properties of Ni Nanoparticles Embedded in Amorphous SiO2

Hydrothermal microwave method was used as a new route to synthesize pure BaTiO3 (BT) nanoparticles at 140°C for 10 min under rapid reacting with stoichiometric Ba/Ti ratio. The crystalline products were characterized by X-ray powder diffraction (XRD) and the structure was refined by the Rietveld method from the tetragonal structure, which was supported by the Ti K-edge X-ray absorption near-edge structure (XANES). The pre-edge of Ti in the XANES spectra indicated that titanium ions are localized in a nonregular octahedron. Typical FT-Raman spectra for tetragonal BaTiO3 nanoparticles presented well-defined peaks, indicating a substantial short-range order in the system. However, a scattering peak at 810 cm−1 was attributed to the presence of lattice OH− groups, commonly found in materials obtained by hydrothermal process. Besides, the peak at 716 cm−1 can be related to eventual Ba2+ defects in the BaTiO3 lattice. BaTiO3 (BT) nanoparticles presented spherical morphology with a non-uniform distribution of pa...

Hydrothermal Microwave: A New Route to Obtain Photoluminescent Crystalline BaTiO3 Nanoparticles.

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Edson R. Leite

Papers

Síntese e Caracterização de Nanocompósitos Ni:SiO 2 Processados na Forma de Filmes Finos

Influência de dopantes doadores na degradação do varistor à base de SnO2 e o efeito do oxigênio pós-degradação

Magnetic Properties of Ni Nanoparticles Embedded in Amorphous SiO2

Hydrothermal Microwave: A New Route to Obtain Photoluminescent Crystalline BaTiO3 Nanoparticles.

Synthesis of Ba1-xCaxTiO3 by Complex Polymerization Method (CPM)