Sébastien Abramson

Magnetic alginate beads for Pb(II) ions removal from wastewater

A magnetic adsorbent (called magsorbent) was developed by encapsulation of magnetic functionalized nanoparticles in calcium-alginate beads. The adsorption of Pb(II) ions by these magnetic beads was studied and the effect of different parameters, such as initial concentration, contact time and solution pH value on the adsorption of Pb(II) ions was investigated. Our magsorbent was found to be efficient to adsorb Pb(II) ions and maximal adsorption capacity occurred at pH 2.3-6. The classical Langmuir model used to fit the experimental adsorption data showed a maximum sorption capacity close to 100 mg g(-1). The experimental kinetic data were well correlated with a pseudo second-order model, 50% of the Pb(II) ions were removed within 20 min and the equilibrium was attained around 100 min. Moreover our magsorbent was easily collected from aqueous media by using an external magnetic field. These results permitted to conclude that magnetic alginate beads could be efficiently used to remove heavy metals in a water treatment process.

Chitosan/maghemite composite: A magsorbent for the adsorption of methyl orange

In this study, magnetic beads were prepared by encapsulation of magnetic nanoparticles in epichlorohydrin cross-linked chitosan beads. Their adsorption characteristics were assessed by using methyl orange (MO) as an adsorbate. MO adsorption onto chitosan beads was found to be optimal in the pH range of 3-5. The adsorption isotherm was well described by the Langmuir model and showed high MO adsorption capacity (2.38 mmol/g, i.e. 779 mg/g). MO adsorption kinetics followed a pseudo-second-order kinetic model, indicating that adsorption was the rate-limiting step. At 0.305 mmol/L, only 19 min was required to reach 90% adsorption and 50% of the MO was adsorbed in 2 min. Desorption studies of MO using NaOH showed the reusability of the magsorbent. No release of iron species was observed at pH>2.4.

New covalent bonded polymer–calcium silicate hydrate composites

New covalent bonded polymer–calcium silicate hydrate (C–S–H) composites were prepared. For this purpose, two sets of hydrosoluble copolymers, both containing trialkoxysilane (T-silane) and/or methyldialkoxysilane (D-silane) functions, were synthesized. The addition of these polymers during the synthesis of C–S–H by the sol–gel method allowed us to obtain hybrid materials. The influence of different synthesis parameters, such as the silane content and the nature of the silane functions grafted to the polymer backbone, was studied. Characterisation of the composite materials by thermogravimetry and elemental analysis showed that chemical interaction of polymers and C–S–H is due only to the presence of T-silane functions. 29Si CP MAS NMR analysis confirmed the existence of covalent linkages between the inorganic silicate chains of the C–S–H crystallites and the T-silane functions. The specific incorporation of these new classes of silane-modified polymers in C–S–H structure may be successfully used in the preparation of new polymer–cement composites with reinforced mechanical properties.

Highly porous and monodisperse magnetic silica beads prepared by a green templating method

We describe the preparation of magnetic silica nanocomposite millimetric beads using alginate as a green biopolymer template. The simple and soft method which is used here is particularly suitable since the alginate template allows a multiscale control of the structure of the material, both its morphological characteristics at the millimetric scale and its porosity at the nanometric level. These nanocomposites are characterised by a high monodispersity, a perfect spherical shape, a very large and multiscale porosity with pore diameters ranging from 2 nm to more than 50 nm, a homogeneous dispersion of the magnetic nanoparticles in the silica matrix and a high magnetic susceptibility which increases linearly with the volume fraction of the nanoparticles. These highly porous materials which can be used as magnetic adsorbents in water treatment, showed a good sorption capacity for methylene blue, chosen as a model dye.

Adsorption of a cationic surfactant by a magsorbent based on magnetic alginate beads.

Adsorption of cetylpyridinium chloride (CPC), a cationic surfactant, by magnetic alginate beads (MagAlgbeads) was investigated. The magnetic adsorbent (called magsorbent) was prepared by encapsulation of magnetic functionalized nanoparticles in an alginate gel. The influence on CPC adsorption of several parameters such as contact time, pH and initial surfactant concentration was studied. The equilibrium isotherm shows that adsorption occurs through both electrostatic interactions with charge neutralization of the carboxylate groups of the beads and hydrophobic interactions inducing the formation of surfactant aggregates in the beads. The dosage of calcium ions released in the solution turns out to be a useful tool for understanding the adsorption mechanisms. Adsorption is accompanied by a shrinking of the beads that corresponds to a 45% reduction of the volume. Adsorption kinetic experiments show that equilibrium time is strongly dependent on the surfactant concentration, which monitors the nature of the interactions. On the other hand, since the pH affects the ionization state of adsorption sites, adsorption depends on the pH solution, maximum adsorption being obtained in a large pH range (3.2-12) in agreement with the pKa value of alginate (pKa=3.4-4.2). Finally, due to the formation of micelle-like surfactants aggregates in the magnetic alginate beads, they could be used as a new efficient magsorbent for hydrophobic pollutants.

An eco-friendly route to magnetic silica microspheres and nanospheres

A green and inexpensive alternative to existing methods for the preparation of magnetic iron oxide/silica nanocomposite particles has been investigated. The use of water-in oil emulsions based on vegetable oils instead of usual solvents led to microsized or nanosized magnetic silica spheres exhibiting similar characteristics to those of classical procedures. Furthermore this approach is very general since a large class of porous magnetic colloids differing in size or iron oxide fraction has been obtained. This work emphasizes the importance of the level of the shearing during the emulsification step with regard to the size and monodispersity of the prepared beads. All the materials prepared were fully characterized (SEM and TEM microscopies, SQUID magnetometry, N(2) sorption volumetry, etc.). In addition, samples functionalized by thiol groups have been synthesized and successfully tested for the removal of heavy metals in water-treatment.

Preparation of Highly Anisotropic Cobalt Ferrite/Silica Microellipsoids Using an External Magnetic Field

Magnetic cobalt ferrite/silica microparticles having both an original morphology and an anisotropic nanostructure are synthesized through the use of an external magnetic field and nanoparticles characterized by a high magnetic anisotropy. The association of these two factors implies that the ESE (emulsion and solvent evaporation) sol-gel method employed here allows the preparation of silica microellipsoids containing magnetic nanoparticles aggregated in large chains. It is clearly shown that without this combination, microspheres characterized by an isotropic distribution of the magnetic nanoparticles are obtained. While the chaining of the cobalt ferrite nanoparticles inside the silica matrix is related to the increase of their magnetic dipolar interactions, the ellipsoidal shape of the microparticles may be explained by the elongation of the sol droplets in the direction of the external magnetic field during the synthesis. Because of their highly anisotropic structure, these microparticles exhibit permanent magnetic moments, which are responsible, at a larger scale, for the existence of strong magnetic dipolar interactions. Therefore, when they are dispersed in water, the microellipsoids self-assemble into large and irregular chains. These interactions can be reinforced by the use of external magnetic field, allowing the preparation of very large permanent chains. This research illustrates how nanostructured particles exhibiting complex architectures can be elaborated through simple, fast, and low-cost methods, such as the use of external fields in combination with soft chemistry.