Laurence Bois

Functionalized silica for heavy metal ions adsorption

Abstract Heavy metals adsorbents were prepared by co-condensation of tetraethoxysilane and functionalized trialkoxysilane RSi(OR′)3. Functionalized porous silicas with aminopropyl (H2N(CH2)3-), [amino-ethylamino]propyl- (H2N-(CH2)2-NH(CH2)3), (2-aminoethylamino)-ethylamino]propyl (H2N-(CH2)2-NH-(CH2)2-NH(CH2)3-), and mercaptopropyl (HS-(CH2)3-) groups were synthesized using dodecylamine as structure directing agent. These materials have been characterized by elemental analysis, powder X-ray diffraction, nitrogen gas sorption, Fourier transform infrared and Raman spectroscopies and thermogravimetric analysis. These organo-silicas were prepared for use in the removal of heavy metal ions from aqueous solutions. Samples synthesized with [amino-ethylamino]propyl- and (2-aminoethylamino)ethylamino]propyl- functions show a high loading capacity for Cu2+, Ni2+, Co2+ and the anion Cr(VI). The sample synthesized with a mercaptopropyl function has a high loading capacity for Cd2+.

Comparison between SBA-15 silica and CMK-3 carbon nanocasting for mesoporous boron nitride synthesis

The synthesis of mesoporous boron nitride, using an aminoborazine as the boron nitride source, with silica (SBA-15) or mesoporous carbon (CMK-3) as the template is compared. Tri(methylamino)borazine (MAB) is converted to BN inside the mesopores of silica or carbon molecular sieves through a mild thermal process. Boron nitride is obtained after the removal of the hard template using an ammonia thermal treatment (carbon template) or an HF treatment (silica template). X-Ray diffraction, TEM and pore size analysis show that the structure of the BN molecular sieves synthesized from the carbon template consisted of a 2D regular array of uniform mesopores 3.4 nm in diameter. The hydrophilic nature of the silica template prevents successful pore filling with the aminoborazine precursor. Ordered BN molecular sieves are obtained at 1000 °C with a specific surface area of 500 m2 g−1 using mesoporous carbon molecular sieves as a hard-template.

Reversible and Irreversible Laser Microinscription on Silver‐Containing Mesoporous Titania Films

Silver species adsorbed on colloidal titania have been known for a long time to exhibit photochromism. [ 1 ] They reversibly change color in response to light exposure. Under UV illumination, i.e. at photon energy greater than the band-gap of TiO 2 (3.2 eV), the photogenerated electrons of titania migrate towards the positively charged Ag(I) species and reduce them, leading to the formation of silver nanoparticles. [ 2 ] These particles exhibit a grey-brown color caused by an inhomogeneous broadening of their surface plasmon resonance, which depends on the nanoparticle size, shape and close environment. [ 3–5a ] Reversibly, under visible light the material can bleach or change color. This multicolour photochromism has been reported recently on nanoporous titania fi lms loaded with silver nanoparticles. [ 5a,b ]

Chemical Growth and Photochromism of Silver Nanoparticles into a Mesoporous Titania Template

Elaboration of mesoporous titanium oxide film supporting silver nanoparticles is described. Mesoporous titanium oxide films are characterized by TEM analysis. Titania films are infiltrated with a silver salt solution and chemical reduction treatments are performed using either a NaBH(4) or a formaldehyde solution. Infiltrated films are then characterized by TEM, SEM, AFM, UV-visible spectroscopy, X-ray diffraction, and Rutherford Backscattering Spectrometry (RBS). The utilization of a mesoporous titania substrate allows to control the nanoparticle size and the interparticle distance. RBS experiments provide the evidence that NaBH(4) treatment induces a strong accumulation of silver nanoparticles in the subsurface of the layer, while formaldehyde treatment induces the formation of silver nanoparticles embedded into almost the whole depth of the titania film. Large silver nanocrystals are also formed at the film surface whatever the reducer used. A broad visible absorption band related to the surface plasmon resonance (SPR) is obtained in both cases and is strongly red-shifted compared to the SPR obtained for silver nanoparticles inside a silica matrix. Moreover, irradiation with visible light causes the photooxidation of silver nanoparticles by titania and a complete discoloration of the material. The photooxidation is related to a drastic decrease in the silver nanoparticle size and is found to be reversible, particularly in the case of the material obtained by the formaldehyde reduction.

Silicon Oxycarbide Glasses from Sol-Gel Precursors

Silicon oxycarbide glasses have been prepared from sol-gel precursors containing not only Si-CH 3 , but also Si-H bonds. Three systems have been chosen containing various Si units but the same C/Si ratio. Their pyrolysis process has been mainly followed by 29 Si MAS-NMR and the composition of the final glass extracted. This study shows that a suitable choice of Si-CH 3 and Si-H functionnalized silicon alkoxides can lead to a strong decrease in the free carbon content and to an almost pure silicon oxycarbide phase.

Aqueous alteration of lanthanum alumino-silicate glasses

Abstract The aqueous alteration behavior of glasses in the system Y–La–Al–Si–O–N has been investigated using the Soxlhet test. The altered surface was then studied by means of solid and solution analyses. In the case of La–Al–Si–O–N glasses, the formation of a crystallized lanthanum hydroxycarbonate was determined by X-ray diffraction (XRD) analysis. In the case of Y–La–Al–Si–O–N, X-ray photoelectron spectroscopy analysis (XPS) reveals a complete disappearance of silicon and aluminum at the glass surface (depth analyzed: 20 A). Rutherford backscattering spectrometry (RBS) gives some evidence that the glass surface is covered with a phase consisting mainly of yttrium and lanthanum compounds. Solution and solid analyses provide evidence that yttrium increases the chemical durability of the glass. Nitrogen seems to enhance glass corrosion by increasing the pH of the solution.

Silicon oxycarbides via sol-gel route: characterization of the pyrolysis process

Abstract Modified silicon alkoxides, R x Si(OR) 4− x , appear as very promising precursors to introduce Si C bonds inside a silica gel network and thus to obtain silicon oxycarbide glasses after pyrolysis under inert atmosphere. Copolymers between tetraethoxysilane and diethoxydimethylsilane have been prepared and the pyrolyzed products have been characterized mainly using infrared and magic angle spinning-nuclear magnetic resonance ( 29 Si, 13 C and 1 H). The pyrolysis process can be divided in three stages. Up to 400°C, the gels are thermally stable. Between 400 and 600°C, redistribution reactions between Si O and Si C bonds occur, but with no destruction of the organic groups. The transition between a polymeric and an inorganic material occurs only between 600 and 800°C with decomposition of the methyl groups. Samples pyrolyzed at 1000°C show the presence of Si C and can be described as a mixture of a silicon oxycarbide phase and free carbon.

Electroless Growth of Silver Nanoparticles into Mesostructured Silica Block Copolymer Films

Silver nanoparticles and silver nanowires have been grown inside mesostructured silica films obtained from block copolymers using two successive reduction steps: the first one involves a sodium borohydride reduction or a photoreduction of silver nitrate contained in the film, and the second one consists of a silver deposit on the primary nanoparticles, carried out by silver ion solution reduction with hydroxylamine chloride. We have demonstrated that the F127 block copolymer ((PEO)(106)(PPO)(70)(PEO)(106)), F type, mesostructured silica film is a suitable soft template for the fabrication of spherical silver nanoparticles arrays. Silver spheres grow from 7 to 11 nm upon the second reduction step. As a consequence, a red shift of the surface plasmon resonance associated with metallic silver has been observed and attributed to plasmonic coupling between particles. Using a P123 block copolymer ((PEO)(20)(PPO)(70)(PEO)(20)), P type, mesostructured silica film, we have obtained silver nanowires with typical dimension of 10 nm x 100 nm. The corresponding surface plasmon resonance is blue-shifted. The hydroxylamine chloride treatment appears to be efficient only when a previous chemical reduction is performed, assuming that the first sodium borohydride reduction induces a high concentration of silver nuclei in the first layer of the porous silica (film/air interface), which explains their reactivity for further growth.

Optical properties of silver nanoparticles thermally grown in a mesostructured hybrid silica film

The composition, the structure and the optical properties of mesostructured hybrid silica films elaborated by sol-gel routine are studied versus the temperature of the post treatment by comparing ellipsometric measurements, atomic force microscopy and electronic microscopy characterizations, X-ray diffraction and thermal analysis. This paper shows that the refractive index variation is a combination between the structure contraction, the solvent evaporation, the silica wall condensation and the pyrolysis of the copolymer. We also investigate the optical properties of thermally grown silver nanoparticles in the mesotructured films and we demonstrate that these properties depend on the optical properties of the host matrix and on the silver concentration profile in the film.

Laser-induced direct space-selective precipitation of CdS nanoparticles embedded in a transparent silica xerogel

A simple method, suitable for direct space-selective precipitation of semiconducting nanoparticles inside a transparent silica xerogel, is presented. The porous silica monoliths, prepared by the sol-gel method, are first loaded with specific CdS precursors. Then, the samples can be irradiated using either a femtosecond laser to generate the nanoparticles inside the deep volume of the silica matrix or a continuous visible laser to yield a nanocrystal growth under the surface. The resulting CdS nanoparticles are characterized using absorption and Raman spectroscopies, x-ray diffraction analysis and transmission electron microscopy.