porous silica

Top PDF porous silica:

Porous silica obtained from biodegradable and biocompatible inorganic-organic hybrid materials

Porous silica obtained from biodegradable and biocompatible inorganic-organic hybrid materials

Keywords: porous silica, inorganic-organic hybrid, pyrolysis, texture characterization 1. Introduction Porous materials, such as silica [1-3], are emerging as a new area of great technological and scientific interest One method to obtain porous silica is the template-based approach [2, 5], in which porosity is created by removing the incorporated template from the silica network. The porosity is therefore tailored by the design of the template Recently, we have reported on novel biodegradable and biocompatible inorganic-organic hybrid materials prepared by the sol-gel process [6-9], Poly(ε- caprolactone) (PCL), well-known for its biocompatibility, permeability and biodegradability, has been successfully incorporated into silica network. The organic (PCL) and inorganic (SiO 2 ) constitutive
En savoir plus

5 En savoir plus

Submicron gap reduction of micro-resonator based on porous silica ridge waveguides manufactured by standard photolithographic process

Submicron gap reduction of micro-resonator based on porous silica ridge waveguides manufactured by standard photolithographic process

The method demonstrated in this paper allows to use lower coupling distances and so to miniaturize further PS ridge waveguides MRs. To do so, the fabrication process takes advantage of the volume expansion of silicon that occurs during the full oxidation of PS ridge waveguides. The volume expansion is all the more marked when the porosity of the core is low. In this work, we demonstrated a gap reduction of about 40% that has been obtained due to the expansion phenomena with an initial porosity of 50%. The resulting porosity after oxidation (20 %) remains sufficient for sensor application for gases or small molecules as proteins which can be easily grafted on porous silica after an appropriate functionalization of its high specific surface.
En savoir plus

24 En savoir plus

Cu2+-labeled, SPION loaded porous silica nonparticles for cell labeling and multifunctional imaging probes

Cu2+-labeled, SPION loaded porous silica nonparticles for cell labeling and multifunctional imaging probes

porous silica shell to impart biocompatibility and modified the surface of these nanoparticles with a ligand capable of coordinating with metal ions of interest for PET imaging, namely 64 Cu and 111 In [11] . We have chosen to utilize a porous silica shell because the MRI contrast enhancement imparted by the nanoparticles requires that there should be intimate contact between water molecules and the iron oxide nanoparticle. The pores in the silica shell should provide such an opportunity. We have also tuned the synthesis of the nanoparticles such that we can controllably incorporate either single iron oxide nanoparticle into a silica shell or a cluster of the nanoparticles into the silica matrix. The latter is of particular interest because it has recently been reported that clustering of superparamagnetic magnetite nanocrystals results in higher saturation magnetization than that of the individual nanoparticles [12] . This can be attributed to the interaction between the assembled nanocrystals. Further, it was also proposed that clustering of monodisperse SPIO particles inside the micelles resulted in high local concentrations or loadings of SPIOs in each nanoparticle that can consequently increase the relaxivity r 2 values
En savoir plus

16 En savoir plus

Phase transitions of adsorbates. V. Aqueous sodium chloride solutions adsorbed of porous silica glass

Phase transitions of adsorbates. V. Aqueous sodium chloride solutions adsorbed of porous silica glass

.\clsorption isotherms for \vater on porous silica glass containing various anno~unls of NaCI, determined a t room temperature, can be superimposed if salt evclusion in the fi[r]

19 En savoir plus

Carbon dioxide gas hydrate crystallization in porous silica gel particles partially saturated with a surfactant solution

Carbon dioxide gas hydrate crystallization in porous silica gel particles partially saturated with a surfactant solution

This paper reports on investigations into the way carbon dioxide (CO 2 ) hydrate forms in porous silica gel partially saturated with pure water or with a surfactant solution. The experiments, conducted at two different temperatures (278.2 and 279.2 K) and under a loading pressure of 3.8 MPa, used silica particles of different nominal pore diameters (30 and 100 nm), saturated at 80% pore volume with pure water or with a 100 ppm solution of either sodium dodecyl sulfate (SDS) or polyoxyethylenesorbitan monoleate (Tween 80). They were run following the “hydrate precursor method” developed in previous works ( Duchateau et al., 2009 , 2010 ) to form bulk hydrate under controlled subcooling conditions, and adapted for studying hydrate formation behavior in porous media.
En savoir plus

11 En savoir plus

Racetrack micro-resonators based on ridge waveguides made of porous silica

Racetrack micro-resonators based on ridge waveguides made of porous silica

For this case, the range of gap studied here allows us to reach a wide scale of coupling ratios that should be sufficient to obtain good MR transmission spectra. In Fig. 5, the top view (a) and the cross section (b) of the porous silica racetrack MR design are reported with the chosen waveguide dimensions and the MR geometry that provide a

29 En savoir plus

In situ loading of basic fibroblast growth factor within porous silica nanoparticles for a prolonged release

In situ loading of basic fibroblast growth factor within porous silica nanoparticles for a prolonged release

water droplets in oil phase can be controlled by adjusting the ratio of water and cyclohexane. Moreover, the bound- ary between the water droplets and the oil phase is tailored by adjusting the concentrations of surfactant, Triton X-100, and co-surfactant, hexanol [ 18 ]. In this acidic water-in-oil microemulsion, the hydrolysis of TEOS was promoted under the acidic condition at the initial stage, which leads to the formation of fuzzy active seeds to eventually build the porous structure at nano-scale. The addition of ammonium hydroxide then reacted with the active sites of TEOS in the microemulsion to perform the hydrolysis and condensation reactions. Basic FGF is a protein with a length of 155 amino acids and an isoelectric point of 9.6, which makes it stable in a weak basic solution. Therefore, NH4OH as a base catalyst for the hydrolysis and conden- sation reactions could trap the dissolved bFGF in the negative charge of nanoparticles with the form of Si–O - on the surface while still retaining protein integrity. Figure 2 a shows the SEM micrograph of the bFGF-loaded MSNs that are spherical. The average particle size (d) of the SiO2 NPs was 57 ± 8 nm, which is smaller than most of polymer nano-containers. It is also noted that there was a lightly broad size distribution. In addition, the high resolution TEM indicates the porous structure clearly. The pore size of silica NP is around 7–10 nm in diameter as shown in Fig. 2 b.
En savoir plus

7 En savoir plus

Study of CuO–CeO2 catalysts supported on ordered porous silica with different mesostructure and morphology. Influence on CO preferential oxidation

Study of CuO–CeO2 catalysts supported on ordered porous silica with different mesostructure and morphology. Influence on CO preferential oxidation

CO preferential oxidation reaction (COPrOx). By means of SAXS, XRD, SEM and TEM microscopies, the mesostructures and morphologies were characterized, as well as the preservation of the porous structure and the presence of oxides nanoparticles. In addition, XPS spectroscopy was used to analyze the chemical state and relative surface abundance of the elements present in the catalysts. From the catalytic results, it could be seen that the incipient wetness impregnation method was the most favorable. The unidirectional porous structure SBA-15 with fiber shape and incipient wetness impregnation achieved the highest conversion of CO and selectivity to CO 2 (CO conversion 98 % at 175 °C). SBA-16 based catalysts were found less active. However, it is noteworthy that the best material was prepared by using an irregular shaped SBA-16 impregnated by incipient wetness procedure. This catalyst exhibited a maximum CO conversion of 80 % at 175 °C. Finally, the SBA-15 mesoporous structure and the incipient wetness impregnation method had a greater influence on the better catalytic performance.
En savoir plus

51 En savoir plus

Ion-specific adsorption and electroosmosis in charged amorphous porous silica

Ion-specific adsorption and electroosmosis in charged amorphous porous silica

KCl 4 CsCl. This ordering is explained on the basis of the sizes and valencies of the cations. A larger ion charge density and localization of charges give rise to stronger correlations, which can lead to overscreening. Particular attention has been devoted to discussing the implications of large interaction energies between ions and surface charge sites. Strong ion binding can cause an ergodic hindrance when the energy barrier associated with unbinding is much larger than the thermal energy of an ion. It has been shown that the mono- valent ions in our system do not suffer from such ergodic hindrances, while additional measures are needed to study the adsorption of Sr 2+ at the charged silica surface. One of the possible measures is to perform multiple simulations which probe different sections of phase space. Averaging between these simulations gives a more reliable sampling of the true density of states. Another possibility is to use Monte Carlo simulations to equilibrate the system and validate our molecular dynamics results. However, equilibrating with MC suffers from some limitations; for instance, specific MC steps have to be developed in order to allow for collective redistribu- tions which are crucial to equilibrate strongly correlated sys- tems such as electrolyte solutions. Moreover, we note that the use of molecular dynamics in the present work would remain required for the study of transport properties.
En savoir plus

14 En savoir plus

Rhodium colloidal suspension deposition on porous silica particles by dry impregnation: Study of the influence of the reaction conditions on nanoparticles location and dispersion and catalytic reactivity

Rhodium colloidal suspension deposition on porous silica particles by dry impregnation: Study of the influence of the reaction conditions on nanoparticles location and dispersion and catalytic reactivity

catalysts for hydrogenation of various aromatic compounds [9] . Nevertheless, colloidal suspensions display some disadvantages as their lack of stability at elevated temperatures (agglomeration is often observed at temperature higher than 100 ◦ C) or their recycling with soluble products. It appears then clearly that the deposition of metal nanoparticles onto a support would circumvent these draw- backs and afford the advantages of traditional supported catalysts. The way followed to prepare supported nanocatalysts is generally the wet impregnation method [10] . It consists in the immersion of the chosen support in a colloidal suspension under stirring to favour the diffusion of the nanoparticles inside the support grains. This technique is easy to carry out but can present some weak points such as: loss of precursor, reduction of the support particle size (most of the porous supports, prepared by sol–gel process, disag- gregate in solution under stirring) and dependence of the deposit location on the physico-chemical properties of the solution-support couple.
En savoir plus

9 En savoir plus

Volume instability of porous solids: part 2: dissolution of porous silica glass in sodium hydroxide

Volume instability of porous solids: part 2: dissolution of porous silica glass in sodium hydroxide

Length changes of 1 mm thick specimens in NaOH solutions of various concentrations are shown in Fig. In general, the overall expansions of speci- mens compared at equ[r]

12 En savoir plus

From diatoms to silica-based biohybrids

From diatoms to silica-based biohybrids

Whole cell encapsulation also finds applications for medicine. Blood tests for the detection of antibodies have been performed using sol–gel immobilized parasite cells. First experiments have been performed via the so-called ELISA (Enzyme Linked Immuno-Sorbent Assay) method, using Leishmania cells as antigens. This parasite, transmitted by the sand fly, is responsible for the leishmaniasis disease that affects mammals. Whole cells are immobilized in a porous silica matrix within the micro-wells of a usual titration plate. They are then incubated in the presence of sera from infected patients. Antibodies bind specifically to the trapped cells and are detected via a usual colored reaction. 46 Immuno- fluorescence and immunoperoxidase assays have been performed recently with Trypanosoma cruzi epimastigotes and Leishmania guyanensis promastigotes trapped within a silica film. Homogeneous, ready to use, long lasting coated slides were then obtained, which are appropriate for making tests in field conditions. 47
En savoir plus

13 En savoir plus

Drying of Porous Media

Drying of Porous Media

Drying of porous media is part of our daily experience, yet this common process is central to many environmental and engineering applications ranging from soil evaporation affecting hydrological water balance and climatic processes, to the drying of food and building materi- als, and driving plant life through transpiration. Drying rates from porous media may exhibit complex dynamics reflecting internal transport mechanisms and motion of phase change fronts that determine rates of drying and critically affect surface energy partitioning. These interactions and resulting drying dynamics present a challenge to the prediction of drying rates and interplay among mass and energy exchange even for fixed boundary conditions.
En savoir plus

4 En savoir plus

Photophysical properties of dye-doped silica nanoparticles bearing different types of dye-silica interactions

Photophysical properties of dye-doped silica nanoparticles bearing different types of dye-silica interactions

Dye-doped silica particles of different sizes, colors, and architectures have previously been synthesized through either an aqueous Sto¨ber method or a reverse microemulsion method. 17-19 The Sto¨ber method is simple, but often leads to formation of large, polydisperse NPs. In one example, large particles have been observed just 10 s after the reaction start and the authors have attributed the faster than expected growth to the change of the surface charge density due to the incorporation of positively charged dye molecules. 18 Uniform dye-doped particles with a diameter smaller than 100 nm have been prepared with the reverse microemulsion method. How- ever, this method requires large amounts of surfactants and organic solvents and thus does not easily scale up. 23 Tradition- ally, it has been difficult to synthesize particles smaller than 30 nm by using either of these methods, though significant progress has been made very recently. Prasad’s group has synthesized ultrasmall dye-doped NPs (∼20 nm in diameter) using the Sto¨ber method. 24 Similarly, Webb’s group reported the synthesis of dye-doped silica particles with diameters of about 30 nm 25 and Wiesner’s group created fluorescent silica-based nanoparticles with hydrodynamic diameters as small as 3.3 and 6.0 nm. 13 Both methods employ TEOS as the main construction material for silica nanoparticle framework. More recently, a one-pot syn- thesis of organosilica NPs using a single organosilicate with only three silanization groups was reported. The synthesis leads to formation of dye-doped silica NPs with inherently function- alized surface, in contrast to the silanol terminated NPs typically produced. 26
En savoir plus

9 En savoir plus

Transport in Porous Media

Transport in Porous Media

to the repository administrator: tech-oatao@listes-diff.inp-toulouse.fr This presentation is published in : http://oatao.univ-toulouse.fr/20693 To cite this version: Quintard, Michel. Transport in Porous Media. (2018) In: École de recherche en mathématiques pour l'énergie nucléaire, 2-6 July 2018 (Roscoff, France). (Unpublished)

133 En savoir plus

Transfers in Porous Media

Transfers in Porous Media

[27] Davit, Y., Quintard, M., and Debenest, G., “Equivalence between volume averaging and moments matching techniques for mass transport models in porous media,” International Journal of[r]

21 En savoir plus

Dependence of the durability of mortars on sand/cement ratio and micro-silica (silica fume) addition

Dependence of the durability of mortars on sand/cement ratio and micro-silica (silica fume) addition

Histograms comparing number of freeze-thaw cycles producing 0.1% residual expansion for mortars containing 0% and 10% silica fume.. that the specimens had undergone the ind[r]

17 En savoir plus

Permeability of porous liquids

Permeability of porous liquids

This project proposes to evaluate a new approach allowing to maintain the existing separation installations, by replacing the organic phases of liquid-liquid extraction processes, with a porous liquid. Porous liquids were discovered in 2014 by the Oak Ridge Corporation. They are solid materials made up with hollow nanoparticles of silica, that present the particularity to become liquid when grafted with ionic functions. To date, these materials have only been tested for gas separation. Being at the exact junction between liquid- liquid and solid-liquid extraction processes, porous liquids would allow exploiting the advantages of the two processes.
En savoir plus

3 En savoir plus

Perfectly plastic flow in silica glass

Perfectly plastic flow in silica glass

d ESPCI ParisTech CNRS UPMC, Soft Matter Science and Engineering, Paris, France Abstract The plastic behavior of silicate glasses has emerged as a central concept for the understanding of glass strength. Here we address the issue of shear- hardening in amorphous silica. Using in situ SEM mechanical testing with a high stiffness device, we have been able to compress silica pillars to large strains while directly monitoring radial strain. The sizeable increase of pillar cross-section during compression directly demonstrates the significant role of homogeneous shear flow. From the direct evaluation of the cross section, we have also measured true stress-strain curves. The results demonstrate that silica predominantly experiences plastic shear flow but that there is no shear- induced hardening. The consequence of this finding for our understanding of glass strength is discussed.
En savoir plus

35 En savoir plus

FNA fluorescence reporting within silica-zirconia porous thin films

FNA fluorescence reporting within silica-zirconia porous thin films

Porous materials, when adequately tailored, offer the possibility to entrap various biomolecules without altering their conformation or function. The sol-gel process enables the formation of porous glasses or ceramics through polymerization at room temperature of liquid precursors (mainly metal or metalloid alkoxides). Upon fine-tuning, the resulting materials may display interesting properties such as optical transparency, tailored porosity, thermal or mechanical stability. In addition, such materials can be produced in a great variety of shapes (thin films, powders, monoliths, fibers, etc.). The sol-gel process is thus ideally versatile to prepare biohybrid materials, and has been applied to the encapsulation of all kinds of biological species, from proteins to cells, usually in order to develop biosensors.
En savoir plus

2 En savoir plus

Show all 1193 documents...