Speciation of uranium (VI) at the solid/solution interface: sorption modeling on zirconium silicate and zirconium oxide

RADIOC

Sorption of uranium (VI) species on zircon: structural investigation of the solid/solution interface

RADIOC

Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields

When a micron-sized magnetizable particle is introduced into a suspension of nanosized magnetic particles, the nanoparticles accumulate around the microparticle and form thick anisotropic clouds extended in the direction of the applied magnetic field. This phenomenon promotes colloidal stabilization of bimodal magnetic suspensions and allows efficient magnetic separation of nanoparticles used in bioanalysis and water purification. In the present work, the size and shape of nanoparticle clouds under the simultaneous action of an external uniform magnetic field and the flow have been studied in detail. In experiments, a dilute suspension of iron oxide nanoclusters (of a mean diameter of 60 nm) was pushed through a thin slit channel with the nickel microspheres (of a mean diameter of 50 μm) attached to the channel wall. The behavior of nanocluster clouds was observed in the steady state using an optical microscope. In the presence of strong enough flow, the size of the clouds monotonically decreases with increasing flow speed in both longitudinal and transverse magnetic fields. This is qualitatively explained by enhancement of hydrodynamic forces washing the nanoclusters away from the clouds. In the longitudinal field, the flow induces asymmetry of the front and the back clouds. To explain the flow and the field effects on the clouds, we have developed a simple model based on the balance of the stresses and particle fluxes on the cloud surface. This model, applied to the case of the magnetic field parallel to the flow, captures reasonably well the flow effect on the size and shape of the cloud and reveals that the only dimensionless parameter governing the cloud size is the ratio of hydrodynamic-to-magnetic forces - the Mason number. At strong magnetic interactions considered in the present work (dipolar coupling parameter α≥2), the Brownian motion seems not to affect the cloud behavio

A Humins-Derived Magnetic Biochar for Water Purification by Adsorption and Magnetic Separation

International audienceIn this study, the use of magnetic biochar particles recovered from biorefinery by-products (humins) for adsorption of hydrophilic organic pollutants was investigated. The biochar was prepared by thermal treatment of crude humins followed by a grinding step after which a magnetic iron oxide was co-precipitated on the biochar surface. The resulting iron oxide content of the biochar composite was found to be 9 % by volume, and the presence of a characteristic Fe-O vibrational band was observed by FTIR-ATR. XPS analysis of Fe2p spectrum enabled the nature of iron oxide to be identified as maghemite. Finally, magnetometry measurements demonstrated the superparamagnetic properties of maghemite

Enhancing microfluidic separation of magnetic nanoparticles by molecular adsorption

International audienceMicrofluidic manipulation of magnetic nanoparticles is a smart tool for various environmental and biomedical applications, such as water remediation from pollutant molecules (heavy metals, pesticides, …), high-sensitivity immunoassays, cancer treatment by controlled drug delivery, hyperthermia or mechanical destruction of cells, protein purification, gene transfection, etc. In most of these applications, magnetic nanoparticles bear on their surface adsorbed molecules (either pollutants or biomolecules), which should either be delivered to the target site (drug delivery, gene transfection) or be extracted from the solvent (immunoassays, protein purification, water remediation). Unfortunately, these technics have strong limitations related to low efficiency of the magnetic manipulation of nanoparticles because of their strong Brownian motion and low efficiency of their separation from the suspending fluid (magnetic separation) under flows in microfluidic devices. However, molecules adsorbed on the nanoparticle surface often reduce repulsive colloidal interactions between nanoparticles and provoke a weak agglomeration of nanoparticles. Such agglomeration in the absence of applied magnetic field leads to an increase of the effective size of nanoparticles (or rather primary aggregates) and, once the magnetic field is applied, the magnetic force acting on primary aggregates is strongly amplified as compared to the situation of single non-aggregated nanoparticles. In this case the adsorbed molecules not only fulfill their function in water remediation or biomedical applications but allow a drastic enhancement of nanoparticle manipulation by magnetic fields, thereby broadening the application fields of nanoparticles. In the present work, we consider two different systems which follow the aforementioned behavior: iron oxide nanoparticles (of an average size of 8 nm) with either methylene blue (MB) dye adsorbed on their surface or monoclonal antibodies (AB) grafted on their surface and destined for realization of immunoassays. Dynamic light scattering (DLS), zeta-potential measurements along with experiments on kinetics of primary (at zero field) and secondary (field-induced) aggregation and microfluidic magnetic separation allow assessing the quantitative effect of the surface coverage of nanoparticles by MB or AB on the efficiency of nanoparticle clustering and magnetic separation in the presence of external magnetic fields as low as 5-10 mT

Incorporation of europium and nickel in calcite studied by Rutherford backsattering and spectrometry

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Interaction of europium and nickel with calcite studied by Rutherford Backscattering Spectrometry and Time-Resolved Laser Fluorescence Spectroscopy

International audienceThis study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO3). Calcite powders or single crystals (some mm sized) were put into contact with Eu or Ni solutions at concentrations ranging from 10 −3 to 10 −5 mol.L −1 for Eu and 10 −3 mol.L −1 for Ni. The sorption durations ranged from one week to one month. Rutherford Backscattering Spectrometry (RBS) well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance), has been carried out. Moreover, using the fluorescence properties of Europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage were also performed. Results showed that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption. Ni was found to accumulate at the surface of calcite without incorporation

Microfluidic separation of magnetic nanoparticles on an ordered array of magnetized micro-pillars

International audienceMicrofluidic separation of magnetic particles is based on their capture by magnetized micro-collectors while the suspending fluid flows past micro-collectors inside a micro-channel. Separation of nanoparticles is often challenging because of strong Brownian motion. Low capture efficiency of nanoparticles limits their applications in bio-analysis. However, at some conditions, magnetic nanoparticles may undergo field-induced aggregation that amplifies the magnetic attractive force proportionally to the aggregate volume and considerably increases nanoparticle capture efficiency. In this paper, we have demonstrated the role of such aggregation on an efficient capture of magnetic nanoparticles (about 80 nm in diameter) in a microfluidic channel equipped with a nickel micro-pillar array. This array was magnetized by an external uniform magnetic field, of intensity as low as 6-10 kA/m, and experiments were carried out at flow rates ranging between 0.3-30 µL/min. Nanoparticle capture is shown to be mostly governed by Mason number Ma, while the dipolar coupling parameter α does not exhibit a clear effect in the studied range, 1.4 < α < 4.5. The capture efficiency Λ shows a strongly decreasing Mason number behavior, Λ∝Ma-1.78 within the range, 32 ≤ Ma ≤ 3250. We have proposed a simple theoretical model, which considers destructible nanoparticles chains and gives the scaling behavior, Λ∝Ma-1.7 , close to the experimental findings