Search results for "SILICA"

Encapsulation of folic acid in different silica porous supports: A comparative study.

2016

Although folic acid is essential to numerous bodily functions, recent research indicates that a massive exposition to the vitamin could be a double-edged sword. In this study, the capacity of different caped mesoporous silica particles (i.e. Hollow Silica Shells, MCM-41, SBA-15 and UVM-7) to dose FA during its passage through the gastrointestinal tract has been evaluated. Results confirmed that the four capped materials were capable to hinder the delivery of FA at low pH (i.e. stomach) as well as able to deliver great amounts of the vitamin at neutral pH (i.e. intestine). Nevertheless, the encapsulation efficiency and the deliver kinetics differed among supports. While supports with large p…

Effect of heating of organo-montmorillonites under different atmospheres

2009

Abstract We studied the influence of heating on the behaviour of two organo-montmorillonites paying particular attention to the possible degradation effects of the organic modifier under different atmospheres. Hoffmann elimination and anucleophilic substitution on the nitrogen led to rapid degradation of the modifier. As confirmed by deconvoluted FTIR spectra, the presence of oxygen accelerated the degradation rate. The degradation products of the modifier (α-olefins transforming into various carboxyl compounds if oxygen is present) initially increased the basal spacing, followed by a collapse of the particle layers when the decomposition products migrated toward the surface and eventually …

Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions

2018

Iron oxides are among the major constituents of the deep Earth’s interior. Among them, the epsilon phase of Fe2O3 is one of the less studied polymorphs and there is a lack of information about its structural, electronic and magnetic transformations at extreme conditions. Here we report the precise determination of its equation of state and a deep analysis of the evolution of the polyhedral units under compression, thanks to the agreement between our experiments and ab-initio simulations. Our results indicate that this material, with remarkable magnetic properties, is stable at pressures up to 27 GPa. Above 27 GPa, a volume collapse has been observed and ascribed to a change of the local env…

Radiation hardening of FBG in harsh environments

2014

International audience; The difficulties encountered in the implementation of a temperature or strain sensor based on Fiber Bragg Grating in a harsh radiative environment are introduced. We present the choices made to select both a radiation-resistant fiber in terms of transmission and also the grating inscription conditions necessary to write radiation tolerant FBGs in such fibers with a femto-second laser. The response of different classes of gratings was also studied under radiation at high doses (>1MGy). The comparison between F- and Ge-doped fibers was highlighted.

Radiation Vulnerability of Fiber Bragg Gratings in Harsh Environments

2015

International audience; The difficulties encountered in the implementation of a temperature or strain sensor based on fiber Bragg grating (FBG) in a harsh radiative environment are introduced. We present the choices made to select both a radiation-resistant fiber in terms of transmission and also the grating inscription conditions necessary to write radiation tolerant FBGs in such fibers with a femtosecond laser. The radiation response of these gratings was also studied under radiation at dose up to 1 MGy. The comparison between Ge-free and Ge-doped fibers was highlighted.

Corrigendum to “The effect of silica nanoparticles on the morphology, mechanical properties and thermal degradation kinetics of PMMA [Pol. Degrad. St…

2012

Full inhibition of enzymatic browning in the presence of thiol-functionalised silica nanomaterial

2018

[EN] Darkening processed fruits and vegetables is caused mainly by enzymatic browning through polyphenol oxidase (PPO) action. Accordingly, we explored the potential of four silica-based materials (MCM-41 nanometric size, MCM-41 micrometric size, UVM-7 and aerosil), non-functionalised and functionalised with thiol groups, to inhibit PPO activity in the model system and apple juice. All materials showed relevant performance when immobilising and inhibiting PPO in model systems, and support topology is a main factor for enzyme immobilisation and inhibition. Thiol-containing silica UVM7-SH showed the greatest inactivation, and similar browning values to those obtained by acidification. The enz…

Influence of the functionalisation of mesoporous silica material UVM-7 on polyphenol oxidase enzyme capture and enzymatic browning

2020

Polyphenol oxidase (PPO), also known as tyrosinase and catechol oxidase, is the enzyme responsible for enzymatic browning in foods. It causes undesirable organoleptic, nutritional and colour changes. Here, we report the preparation of five nanomaterials and a study of their ability to modulate PPO enzyme activity. The materials consist of UVM-7 supports (a mesoporous silica material) modified with diverse functional groups (i.e. amine, carboxylic acid, isocyanate, alkane and pyridine). We also studied the PPO immobilisation capability of the materials. All the materials, except the carboxylic acid functionalised one, offer high PPO loading capabilities and the immobilisation speed increases…

A molecular approach to remove lead from drinking water

2005

Abstract Corrosion of lead-containing plumbings is responsible for significant contamination of tap water, which can reach several hundreds of micrograms per liter. According to a decision of the European Council applicable in 2013, the maximal lead level in tap water should not exceed 10 μg l −1 . A new concept has been explored that relies on solid-phase extraction by covalent attachment of a lead-selective macrocyclic sequestering agent onto the surface of silica gel. An N -carbamoylmethyl substituted 1,4,8,11-tetraazacyclotetradecane (cyclam) derivative was shown to exhibit favorable protonation properties together with an almost 10 6 -fold selectivity for lead over calcium. Structural …

Performance of porous silica layers in open-tubular columns for liquid chromatography

1989

Abstract Progress has been made in the preparation of porous silica layers in fused-silica capillaries for open-tubular liquid chromatography. The porous silica layer is prepared by (i) static coating of the silica precursor, polyethoxysiloxane (PES), followed by (ii) converting the PES film into a porous silica layer with ammonia solution. The porous silica layer can be easily modified by silane reagents commonly used in packed column high-performance liquid chromatography. The performance of the silica layer with the different phase systems was tested with polyaromatic hydrocarbons and derivatized amino acids as samples.