Search results for "silica."

Widespread Increases in Iron Concentration in European and North American Freshwaters

2017

Recent reports of increasing iron (Fe) concentrations in freshwaters are of concern, given the fundamental role of Fe in biogeochemical processes. Still, little is known about the frequency and geographical distribution of Fe trends or about the underlying drivers. We analyzed temporal trends of Fe concentrations across 340 water bodies distributed over 10 countries in northern Europe and North America in order to gain a clearer understanding of where, to what extent, and why Fe concentrations are on the rise. We found that Fe concentrations have significantly increased in 28% of sites, and decreased in 4%, with most positive trends located in northern Europe. Regions with rising Fe concent…

Trace-element partitioning between amphibole and silicate melt.

2007

Knowledge of the partitioning behavior of trace elements between solid and liquid is a prerequisite for modern igneous and mantle petrology. Most of the mathematical models simulating melt generation, migration and evolution within the mantle and/or the crust require the availability of reliable solid/liquid partition coefficients for the mineral phases involved in the process. Calcic amphiboles are extremely important for the understanding of lithospheric processes because of both their common occurrence in a variety of igneous and metamorphic rocks types and their capability of hosting a large number of geochemically important trace elements. A series of studies on the partitioning behavi…

2017

A hybrid bioinspired material with manganese(II) complexes grafted on the surface of a mesostructured porous silica is investigated. The Mn sites mimic the manganese-dependent dioxygenase (MndD), which is an enzyme that catalyses the oxidation of catechol derivatives. The metal complexes were introduced in the silica using a dinuclear complex [Mn2L2(Cl)2(μ-Cl)2] as a precursor with a clickable ligand N,N′-bis[(pyridin-2-yl)methyl]prop-2-yn-1-amine (L). Azide moieties covalently grafted on MCM-41 type mesoporous silica were utilised to anchor the manganese complex through Huisgen cycloaddition using CuBr(PPh3)3 as a catalyst. A second functional group – trimethylsilyl or pyridine—was grafted…

Neptunium(V) Sorption and Diffusion in Opalinus Clay

2009

The sorption and diffusion behavior of 8 x 10(-6) M Np(V) in Opalinus Clay (OPA) with synthetic pore water (pH 7.6) as mobile phase was studied under ambient conditions by batch and diffusion experiments, respectively. The Kd value determined by batch experiments with OPA suspensions is equal to 0.025 +/- 0.005 m3/kg. The diffusion-accessible porosity epsilon of intact OPA as determined by through- and out-diffusion experiments with tritiated water (HTO) is equal to 0.15 +/- 0.01. The diffusion coefficient De and the rock capacity factor alpha of 22Na+ in OPA were measured by through-, out-, and in-diffusion experiments and asserted the reliability of these diffusion techniques. For the dif…

Análisis de la citocompatibilidad, la bioactividad y la activación de vías de señalización celular inducida por nuevos biosilicatos hidráulicos de us…

2022

Introducción: Las células madre dentales son un subgrupo de células madre postnatales que presentan un fenotipo similar al de las células madre mesenquimales. Los biomateriales que se apliquen en tratamientos basados en células madre y enfoques de ingeniería tisular deben presentar ciertas propiedades biológicas, a saber, biocompatibilidad y bioactividad. Entre los biomateriales endodónticos, los materiales hidráulicos a base de silicato de calcio parecen ser candidatos prometedores para los procedimientos endodónticos de base biológica y la ingeniería tisular. Por lo tanto, estos materiales deben expresar propiedades biológicas adecuadas para no interferir o incluso potenciar los procesos …

Modulación de la mesoestructura y composición en sílices nanoparticuladas con porosidad jerárquica

2014

Dentro de la amplia variedad de materiales porosos, y más concretamente mesoporosos, las sílices mesoporosas bimodales nanopartículadas (NBS, en sus siglas en inglés) han despertado un gran interés en los últimos años. La síntesis de NBS fue por primera vez descrita por Zhang y col., quienes prepararon los materiales hexagonales de sílice (HMS, en sus siglas en inglés) empleando un único surfactante no iónico. Más tarde, ambos Ågre y col. y Haskouri y col. publicaron el uso de un surfactante catiónico (bromuro de cetiltrimetilamonio (C16TMABr)) para sintetizar materiales NBS tipo MCM-41 y tipo UVM-7. En estos trabajos se establecieron como claves diferentes variables procedimentales para la…

Emerging hierarchical porous silica-based nanomaterials as sorbents for the analytical determination of organic hazardous compounds

2022

Actualment, l'exposició humana a compostos orgànics perillosos s'ha convertit en una preocupació molt important. La presència de contaminants orgànics al medi ambient ha provocat l'aparició de noves normatives per tal de restringir o prohibir aquestes substàncies perilloses, i el desenvolupament de noves metodologies analítiques per a la seua determinació ha esdevingut un gran repte per a la química analítica actual. A més a més, a part del desenvolupament de noves tècniques instrumentals, l'anàlisi de matrius complexes requereix d’un pas de preconcentració i neteja, per al qual s’han proposat diversos materials nous com a alternatives als adsorbents clàssics. Entre ells, la sílice mesoporo…

A new efficient, highly dispersed, Pd nanoparticulate silica supported catalyst synthesized from an organometallic precursor. Study of the homogeneou…

2018

[EN] A new Pd(0) catalyst supported on silica UVM-7 has been synthesized from the organometallic [Pd-2(mu-(C6H4) Pp(2))(2)(CH3CN)(4)](BF4)(2) precursor, characterized by the high dispersion, activity, and small size of the palladium nanoclusters fixed on the silica surface. The catalyst was tested for the Suzuki-Miyaura (SM) reaction of different 4-substitutedphenyl halides with phenylboronic acid. The kinetic study concurs with most of the catalytic action was carried out by Pd species originated by the partial solubilization of Pd immobilized on mesoporous silica. The Schmidt's analysis of differential selectivity (SADS) in several competitive SM reactions, together the STEM-HAADF and HRT…

Near infrared spectroscopic study on the adsorption of methanol on silica gel

2013

Author's version of an article in the journal: Advanced Materials Research. Also available from the publisher at: http://dx.doi.org/10.4028/www.scientific.net/AMR.650.150 The silanol groups on Silica gel surface are sites for adsorption of polar molecules. Alcohols and other polar molecules are easily adsorbed by forming hydrogen bondings with OH groups on silica gel surface. A study on the adsorption of methanol on silica gel was carried out by using NIR spectroscopy in combination with ssecond derivative techniques. Four of the well characterised silica gel samples were used in this study. Each of the silica gel (0.25g) samples with different surface areas and silanol number was pressed i…

Chemical effect on the XPS spectra of the valence band and on O KLL and Pd MNN Auger spectra in pumice-supported catalysts

1992

X-ray photoelectron spectra of the valence band and X-ray-excited O KLL Auger transition of pumice-supported Pd and Pt catalysts have been obtained and compared to the corresponding spectra of pumice (a naturally occurring amorphous aluminosilicate). The changes observed indicate interaction between metal and support. The valence region of the catalysts consists of three large peaks: one due to the d band of the metals and the other to the O 2p non-bonding orbitals and bonding-type orbitals formed by a mixing of the atomic orbitals (O 2p, Si 3s and Si 3p) of oxygen and silicon from the support. The intensity decrease of the component due to the bonding orbitals, observed in the catalyst spe…