title: Immobilization of selenite on Fe3O4 and Fe/Fe3C ultrasmall particles.
abstract: The sorption of selenite ions onto Fe3O4 and Fe/Fe3C nanoparticles (NPs) was studied in aqueous solutions under anoxic conditions using gamma spectrometry and X-ray absorption spectrometry (XAS) techniques. This is the first study related to the remedial applications of Fe/Fe3C NPs. FesO4 NPs have been prepared by conventional coprecipitation of Fe(II) and Fe(III) in basic solutions. Stable Fe/Fe3C NPs have been prepared by Fe(CO)5 sonicating in diphenylmethane solutions and subsequently annealing the as-prepared product. Kinetic study demonstrated that Se(IV) sorption is extremely rapid: the equilibrium is reached in approximately 10 and 30 min for Fe3O4 and Fe/Fe3C NPs, respectively, at pH = 4.9-5.1 in solutions of 0.1 M NaCl. The distribution coefficients are also very high for both kinds of NPs (Kd > 3000). Increasing the pH to 10.3 or adsorption of organic ligands, like L-lysine or dodecanoate, at the surface of NPs causes the decrease in Kd values. However, even in these cases Kd values exceed 150. Magnetic NPs loaded with selenium can be easily and completely removed from solution with a 0.4 T permanent magnet. XAS study revealed the absence of Se(IV) reduction during the sorption onto Fe3O4 NPs in the pH range of 4.8-8.0. By contrast, the removal of Se(IV) with Fe/Fe3C NPs in anaerobic conditions occurs via Se(IV) reduction to Se(-II) and subsequent formation of iron selenide at the particle surface. Thus, the Fe/Fe3C NPs are superior to Fe3O4 NPs due to their ability to immobilize rapidly and irreversibly Se(IV) via reductive mechanism. Presumably these particles could be also effective for the removal of other contaminants such as hexavalent chromium, actinides, technetium, and toxic organic compounds.
authors.affiliation: Chimie Nucléaire Analytique et Bioenvironnementale, Université de Bordeaux I,II, CNRS, BP 120 Le Haut Vigneau, 33175 Gradignan, France.
authors.forename: Raquel López de Arroyabe
authors.initials: RL
authors.lastname: Loyo
authors.forename: Sergei I
authors.initials: SI
authors.lastname: Nikitenko
authors.forename: Andreas C
authors.initials: AC
authors.lastname: Scheinost
authors.forename: Monique
authors.initials: M
authors.lastname: Simonoff
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D007700:Kinetics; D053758:Nanoparticles; D010316:Particle Size; D018038:Sodium Selenite / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D014965:X-Rays
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D018038:Sodium Selenite