Search results for "Specific surface area"
showing 10 items of 123 documents
Synthesis of micro-mesoporous aluminosilicates on the basis of ZSM-5 zeolite using dual-functional templates at presence of micellar and molecular te…
2017
Abstract Micro-mesoporous aluminosilicates consisting of agglomerates of the ZSM-5 nanoparticles were obtained using dual-functional templates [C6H13–N+(CH3)2–C6H12–N+(CH3)2–C6H13](Br−)2 (C6–6–6Br2), [C8H17–N+(CH3)2–C6H12–N+(CH3)2–C8H17](Br−)2 (C8–6–8Br2). Aluminosilicates with randomly oriented flake-like particles built from ZSM-5 layers were obtained using [C16H33–N+(CH3)2–C6H12–N+(CH3)2–C6H13](Br−)2 (C16–6–6Br2). Use of С8–6–8Br2 and additive of cetyltrimethylammonium bromide CTAB (CTAB concentration is lower than the first critical micelle concentration, CMC1) leads to an increase of the total specific surface area, mesopore surface area and the mesopore size uniformity in the product,…
Chemical modification of porous calcium hydroxyapatite surfaces by grafting phenylphosphonic and phenylphosphite acids
2006
Abstract It is well known that the incorporation of organic molecules can provide an effective route to modify the surface properties of apatite ceramics. The present study shows that phosphonates can react with calcium ions to control the formation of the hydroxyapatite structures. The grafting of C6H5PO(OH)2 (PPOH) and C6H5PO(OH)H (PPH) was used to increase the specific surface area as well as the porosity of hydroxyapatite materials. The higher specific surface area for HAp treated by PPOH is around 267 m2/g compared to the pure HAp (140 m2/g). The phenyl (C6H5) groups are removed by thermal treatment around 500 °C. After treatment at 800 °C, organoapatites (PP-HAp) are converted to stoi…
Phase analysis and oxygen strorage capacity of ceria-lanthana-based TWC promoters prepared by sol-gel routes
2002
Ceria–lanthana-based promoters of three-way catalysts are synthesized by two different sol–gel routes, involving nitrate precursors. The oxygen uptake ability of these compounds is measured by O2 chemisorption. The specific surface area is determined by N2 adsorption (BET). X-ray diffraction data are analyzed by Rietveld refinement, demonstrating that lanthanum forms solid solution with CeO2; its total amount in ceria depends on the competitive formation of La–Al mixed oxides and on the synthetic method. The O2 uptake ability is essentially determined by the La content in the ceria–lanthana solid solution, while it is independent on the surface area and on the CeO2 particle size. The O2 upt…
Preparation and photoactivity of nanocrystalline TiO2 powders obtained by thermohydrolysis of TiOSO4
2013
Nanocrystalline TiO2 photocatalysts were synthesized in mild conditions by thermohydrolysis of TiOSO4 in water at 100 °C and post-calcination treatment at various temperatures. The TiO2 powders were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, specific surface area determinations, scanning electron microscopy and electron paramagnetic resonance measurements. The photoactivity of the samples was tested employing the photodegradation of 4-nitrophenol in liquid–solid regimen and the photooxidation of gaseous 2-propanol. The best results were obtained with the powder calcined at 600 °C for 10 h. Surprisingly, the not calcined sample was the most active for the abatement…
Novel synthesis of spherical MCM-48
1999
Abstract A novel synthesis route was developed for the cubic member of the M41S family, MCM-48, with a three-dimensional pore system allowing the formation of submicrometre- to micrometre-sized beads with a narrow pore-size distribution. The synthesis is based on the modified Stober method applying tetraethoxysilane, ethanol, water, ammonia and n -hexadecyltrimethylammonium bromide as template. The specific surface area, the specific pore volume and the average pore diameter were varied in the following ranges: 900–1600 m 2 g −1 , 0.5–0.9 cm 3 g −1 and 2–3 nm. Aluminium-, chromium-, gallium-, niobium- and vanadium-MCM-48 were also synthesized following this procedure.
Synthesis and characterization of diatomaceous earth chemically modified with γ-aminopropyltrimethoxysilane
2003
A stationary phase for thin-layer chromatography has been prepared by bonding purified diatomaceous earth (rich in silica) with γ-aminopropyltrimethoxysilane. The phase has been characterized by elemental analysis, measurement of the specific surface area, IR spectroscopy, thermal analysis, and chromatographic testing.
Impact of acidic/hydrothermal treatment on pore structural and chromatographic properties of porous silicas
1991
Abstract A series of commercial silicas and a laboratory made product were subjected to acidic/hydrothermal treatment with solutions of HCI, HNO3, H2SO4 and HF. The concentration of acid and the temperature and duration of treatment were varied. The specific surface area, content of metal impurities, types and concentration of surface hydroxyl and siloxane groups and crystallinity were determined for native and treated silicas. Only changes in the structural order of the surface could be assessed by means of 19Si cross-polarization magic angle spinning NMR spectrometry and electron diffraction. The native and acid-treated silicas were surface modified to n-octyl derivatives and tested under…
Development of standard operation procedures for the manufacture of n-octadecyl bonded silicas as packing material in certified reference columns for…
2004
The development of standard operation procedures for the manufacture of a n-octadecyl bonded spherical silica packing from partially condensed tetraethoxysilane as silica source is described. The synthesis comprises five intermediate products and six synthesis steps which were examined according to their reproducibility and robustness. The results led to the optimisation of the manufacturing process for a n-octadecyl bonded silica. Correlations were drawn between the dynamic viscosity of the poly(ethoxy)siloxane (PES), the synthesis parameters, the resulting pore structural properties and particle size distribution of the silicas. Validated procedures were developed to manufacture spherical…
Synthesis and characterization of alumina R chemically modified withn-octyl for use as a stationary phase in TLC
2003
A stationary phase for thin-layer chromatography has been prepared by attaching 1-octene to alumina R. This stationary phase has been characterized by elemental analysis, measurement of specific surface area, IR spectroscopy, and by chromatographic testing.
Removal of trivalent chromium from tannery waste waters using bone charcoal
2002
International audience; The ability of bone charcoal to remove Cr(III) from aqueous solutions by adsorption has been investigated. The adsorbent used was first characterised and then the adsorption was studied as a function of time and amount of charcoal. Tests were carried out with synthetic solutions whose Cr concentrations (500 mg L-1) were similar to those found in some effluents of Moroccan tannery industries. Cr removal efficiencies higher than 90% were obtained at pH 3.5 using 3 g of bone charcoal and a stirring time of about 30 min. Results of Cr removal by all sieved fractions of bone charcoal had shown the same interesting capabilities for Cr(III) retention. The cross interference…