A magnetic composite material composed of magnetic nanoparticles and clay encapsulated in cross-linked chitosan beads was prepared, characterized and used as a magsorbent for the removal of a cationic dye, methylene blue (MB), from aqueous solutions. The magnetic properties of these beads represent an advantage to recover them at the end of the depollution process. The optimal weight ratio R=clay:chitosan for the removal of MB in a large range of pH was determined. For beads without clay, the maximal adsorption capacity of MB occurs in the pH range [9], [10], [11], [12], while for beads with clay, the pH range extends by increasing the amount of clay to reach [3], [4], [5], [6], [7], [8], [9], [10], [11], [12] for R>0.5. Adsorption isotherms show that the adsorption capacity of magnetic beads is equal to 82 mg/g. Moreover, the kinetics of dye adsorption is relatively fast since 50% of the dye is removed in the first 13 min for an initial MB concentration equal to 100 mg/L. The estimation of the number of adsorption sites at a given pH shows that the main driving force for adsorption of MB in a large range of pH is the electrostatic interaction between the positively charged dye and the permanent negative charges of clay.

L'objectif de ce travail est le developpement et la caracterisation de materiaux magnetiques (magsorbants) qui pourraient etre integres dans un procede assiste magnetiquement dont la finalite est de completer les procedes actuellement utilises dans les filieres de traitement des eaux. Pour s'inscrire dans une demarche d'ecoconception, nos materiaux sont des billes millimetriques constituees d'une matrice biopolymere (alginate ou chitosane) dans laquelle sont encapsulees des nanoparticules magnetiques. Ces billes sont bifonctionnelles, elles possedent des proprietes adsorbantes permettant l'extraction de polluants organiques. Mais leur originalite reside dans leurs proprietes magnetiques qui sont mises a profit pour les separer magnetiquement de l'eau a depolluer. Les proprietes d'adsorption des billes magnetiques vis-a-vis de polluants organiques modeles ont ete etudiees en regardant l'effet de differents parametres tels que le pH et la force ionique de la solution, la concentration initiale en polluant et le temps de contact. Dans un premier temps, les polluants modeles consideres sont des colorants charges. Nous avons montre que les billes d'alginate sont efficaces pour adsorber le bleu de methylene charge positivement alors que les billes de chitosane adsorbent le methylorange charge negativement. Par contre, le p-nitrophenol est faiblement adsorbe par les billes d'alginate et de chitosane. Pour pallier ce probleme, deux solutions ont ete proposees dans le but d'augmenter l'hydrophobicite des billes. La premiere consiste a ajouter un tensioactif cationique aux billes d'alginate. La deuxieme solution est d'encapsuler une organobentonite dans les billes.

The paper focuses on the removal of p-nitrophenol by an adsorption process. A magnetic adsorbent was synthesized by encapsulation of magnetic functionalized nanoparticles using alginate as a green biopolymer matrix. A cationic surfactant, cetylpyridinium chloride (CPyCl), was used to confer a hydrophobic character to the magnetic beads and thus to promote their adsorption efficiency. The effect of different parameters such as initial concentrations of both PNP and CPyCl, contact time and solution pH value on the adsorption of PNP in the presence of CPyCl was investigated. It should be noted that combination of magnetic and adsorption properties in a same material is an interesting challenge which could overcome the recovery problems of pollutant-loaded adsorbent.

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. (C) 2013 Elsevier Inc. All rights reserved.