André Larbot

Spherical MSU-1 Mesoporous Silica Particles Tuned for HPLC

Among the mesoporous silica micellar templated structures (MTSs), MSU-X silica, obtained through an N0I0 assembly between non-ionic polyethyleneoxide-based surfactants (N0) and silica neutral inorganic precursors (I0), exhibits a regular ordered structure with a 3D wormhole porous framework and an easily controlled pore size. These materials have been tested for applications requiring both a narrow mesopore size distribution and isotropic properties. A specific double-step synthesis that we developed recently for MSU-X materials has allowed us to prepare mesoporous silica particles with the required shape, size, and properties. Both the particles’ synthesis and comparative HPLC separation tests with a commercial ungrafted silica HPLC powder of identical shape and size are reported.

Nanometric hollow spheres made of MSU-X-type mesoporous silica

Submicrometric hollow spheres with mesoporous walls were prepared by applying the synthesis of MSU-X type mesoporous silica at neutral pH. The application of ultrasound in the proper power range, to a mixture of nonionic polyoxyethylene surfactant and unreacted silicon alkoxide (tetraethylorthosilicate) gives a stable emulsion where the cavitation bubbles created by the ultrasound are trapped in the solution. Further hydrolysis and condensation of the silica by the addition of sodium fluoride freezes the structure and gives a powder that exhibits a single reflection in the X-ray diffraction pattern, characteristic of a 3D-wormhole ordered porous framework. Its main feature is a large hysteresis loop in the nitrogen adsorption/desorption isotherm. This hysteresis loop corresponds to the retention of condensed nitrogen within the voids of these particles that can play the role of tanks for volatile compounds.

Grafting of ceramic membranes by fluorinated silanes: hydrophobic features

Abstract One of the application of ceramic membranes can be the transfer of a gas into a liquid or the extraction of gas from a liquid through a membrane. The problem is the hydrophilic behaviour of the oxide materials that leads to a natural and important absorption of liquid into the different layers of a membrane. Pressures required, in order to bring the liquid back out of the membrane, especially when the pore diameters of the layers become smaller, are too high and systems cannot support such pressures. Consequently, a mean of making membrane material hydrophobic is developed. The membrane was impregnated by a solution of a fluorinated product. It grafts into the membrane material. Grafting using two different fluorinated silanes, C 6 F 13 C 2 H 4 Si(OMe) 4 and C 8 F 17 C 2 H 4 Si(OEt) 3 , was investigated. First experiments were made, for instance, on microfiltration membrane with C 8 F 17 C 2 H 4 Si(OEt) 3 . Results of grafting of microfiltration and ultrafiltration membranes with different fluorinated silanes will be given and discussed.

Elaboration of new ceramic microfiltration membranes from mineral coal fly ash applied to waste water treatment

This work aims to develop a new mineral porous tubular membrane based on mineral coal fly ash. Finely ground mineral coal powder was calcinated at 700 degrees C for about 3 h. The elaboration of the mesoporous layer was performed by the slip-casting method using a suspension made of the mixture of fly-ash powder, water and polyvinyl alcohol (PVA). The obtained membrane was submitted to a thermal treatment which consists in drying at room temperature for 24 h then a sintering at 800 degrees C. SEM photographs indicated that the membrane surface was homogeneous and did not present any macrodefects (cracks, etc...). The average pore diameter of the active layer was 0.25 microm and the thickness was around 20 microm. The membrane permeability was 475 l/h m(2) bar. This membrane was applied to the treatment of the dying effluents generated by the washing baths in the textile industry. The performances in term of permeate flux and efficiency were determined and compared to those obtained using a commercial alumina microfiltration membrane. Almost the same stabilised permeate flux was obtained (about 100 l h(-1)m(-2)). The quality of permeate was almost the same with the two membranes: the COD and color removal was 75% and 90% respectively.

Ozone–water contacting by ceramic membranes

Abstract A common process in water treatment is the wet oxidation for the removal of certain organic and inorganic pollutants. The strongest oxidant technically applied in this process is ozone, which is an unstable gas under normal conditions, and therefore is produced from oxygen on site, usually by electrical discharge. After that the ozone has to be transferred from that gas into the water to be treated. Conventionally ozone transfer is achieved by bringing the gas and water in direct contact by means of bubble columns, injectors or other similar devices. Under unfavorable conditions, however, these methods suffer from excessive formation of foam requiring an extra treatment and a high-energy demand for pumping gas or water. This projects approach was to improve the transfer by better control of gaseous and aqueous phases conditions at the contact surface. This was achieved by means of a membrane both separating the two phases and allowing for an ozone transfer between them. Due to ozones high oxidation potential, chemically inert ceramic membranes were chosen for that purpose. In experiments, it was found that the transfer of the unstable ozone molecules is not obstructed by ceramic membrane material. Transfer rates between gaseous ozone and model water were measured for conventional ceramic membranes, as well as specially designed ones. They are comparable to conventional methods or better on the base of mass transfer per reactor volume. In conventional oxide membranes, water enters the pores because of capillary effects in the hydrophilic material [Burggraaf, A.J. and Cot, L., 1996, Fundamentals of inorganic Membrane Science and Technology Elsevier Science, The Netherlands]. The water in the pores raises the diffusion resistance for the ozone thus decreasing the transfer itself. Consequently, the modification of the hydrophilic material features into a hydrophobic behavior was one promising approach for the optimization of the process. It was achieved through the application of a hydrophobic coating to the membrane surface, which greatly improved the transfer efficiency.

Membrane distillation properties of TiO2 ceramic membranes modified by perfluoroalkylsilanes

Abstract The tubular and planar TiO2 ceramic membranes were modified by grafting with perfluoroalkylsilanes (PFAS) molecules. Two types of PFAS were used for grafting process: 1H,1H,2H,2H-perfluorooctyltriethoxysilane (C6) and 1H,1H,2H,2H-perfluorotetradecyltriethoxysilane (C12). Studies showed that hydrophilic surface of titania ceramic membranes can be efficiently modified as a results of the proposed grafting method. Grafting efficiency of the tubular membranes was determined by measurement of liquid water entry pressure (LEPw), whereas grafting efficiency of planar membranes was verified by contact angle measurement. The contact angle values of the planar membranes are 130 and 140° for grafting with C6 and C12, respectively. The LEPw of the tubular membranes increased from 2 bar to 10 bar after modification by C12, whereas the LEPw values were constant at 2 bar when TiO2 membrane was modified by C6 molecules. It was found that water contact angle, LEPw, and water flux in the membrane distillation (MD)...

A double step synthesis of mesoporous micrometric spherical MSU-X silica particles

Spherical particles of mesoporous MSU-X silica in the micrometric size range have been obtained through a new double step process that led to an easy and highly reproducible synthesis pathway giving micelle templated structures with a large surface area and narrow pore size distribution

γ Alumina membranes grafting by organosilanes and its application to the separation of solvent mixtures by pervaporation

Abstract The selectivity and the membrane flux depend on the textural and also on the chemical composition of the materiel used to prepare the membrane. The surface properties of γ alumina membranes prepared by sol–gel route can be modified by grafting mono-, di- and tri-functional organosilanes (OCH 3 , OC 2 H 5 , Cl) in the goal to change the selectivity of the membrane towards the chemical solutes. The characterization of the different membranes showed that the grafting depends on the nature of the silanes used and is achieved with the multifunctional silanes. The modification of the surface properties of the membrane prepared after grafting has been confirmed by pervaporation tests on different binary mixtures of solvents (water+ethanol, methylethylketone+cyclohexane, cyclohexane+ethanol). In these conditions, the flux of the different solvents and the selectivity of the membranes depends clearly on the grafting conditions.

Elaboration and properties of TiO2–ZnAl2O4 ultrafiltration membranes deposited on cordierite support

The preparation and characterization of porous ceramic multilayer ultrafiltration (UF) membranes is described. The fist step consisted to prepare high-quality macroporous supports in cordierite (2MgO, 2Al2O3, 5SiO2). The microporous interlayer was then prepared by slip casting from Zirconia commercial powder suspension, and finally the active UF top layer was obtained by sol–gel route using TiO2 and ZnAl2O4 mixed sols. The water permeability of this membrane is 6.3 l h−1 m−2 bar−1, its thickness is 1.2 μm, the pore diameter of the active layer is centred on 4 nm and the cutoff is 3000 Da. The filtration tests performed with NaCl and Na2SO4 solution show the electric interactions govern the rejection rates of the solutes. The efficiency of the membrane is quite good for the elimination of methylene blue and of salts which contain Cr(III), Pb(II), Cd(II).

Elaboration and properties of TiO2–ZnAl2O4 ultrafiltration membranes

Abstract New ceramic ultrafiltration membranes with a pore size diameter in the range of 6 nm have been prepared by sol gel route using TiO 2 and ZnAl 2 O 4 mixed sols. The main characteristics of the membranes are given and their filtering properties discussed by taking into account of the electrophoretic behavior of powder suspension elaborated with the different sols used for the membrane preparation. As for other membrane materials, the salt rejection rate depends mainly on the surface charge of the material which is correlated to the ζ potential.