Microfluidic manipulation of magnetic nanoparticles (MNPs) is a smart tool for various environmental and biomedical applications. Unfortunately, these techniques have a strong limitation related to the low efficiency of magnetic manipulation of MNPs due to their Brownian motion. However, molecules adsorbed on the surface of MNPs can cause their weak (primary) aggregation. Once the magnetic field is applied, the magnetic force exerted on the primary aggregates will be strongly amplified allowing for significant improvement of the remote control over the MNPs by the magnetic fields. In this paper, we check this concept on three different physicochemical systems covering different application: (i) methylene blue cationic dye adsorbed on citrate coated MNPs for water purification; (ii) curcumin bound to the & beta;-cyclodextrin modified MNPs for magnetic drug delivery; (iii) antigens bound to MNPs decorated with antibodies for model immunoassays. We find striking similarities of the magnetic-field induced behaviours of these different systems, with the dipolar coupling parameter, the supersaturation, the Mason number and the Peclet number being the main governing parameters. We also mention the possibility of using this concept for enhancement of the convective drug transport through the blocked blood vessels.

The aim of this work was to investigate the use of biorefinery industry by-products such as humins as adsorbents for methylene blue (MB). After thermal treatment, these by-products are called biochars. Three biochars were used as adsorbents for MB removal: (i) a biochar obtained after thermal treatment of humins (called raw biochar), (ii) a biochar obtained after NaOH treatment of the biochar from (i) (called biochar-OH), (iii) a biochar obtained after mixing humins with lignin, this mixture being then submitted to the same thermal treatment than (i) (called humins-lignin biochar). Structural characterization was done using ATR-FTIR, BET surface area analysis, and scanning electron microscopy (SEM). An elemental analysis was conducted to determine C, H, N, S, and O content in samples. Adsorption experiments were carried out as a function of time, pH, different background electrolytes (NaNO3 and CaCl2), and initial MB concentration. Kinetics data showed a good compatibility of all adsorbents with the pseudo-second-order model. The affinity of MB for biochar increased noticeably with the increase in pH, particularly for biochar-OH and humins-lignin biochar. Both the NaNO3 and CaCl2 background electrolytes had a negative effect on adsorption processes, and Ca2+ and Na+ acted as competitor ions with MB on the surface. The Langmuir model was more suitable for biochar-OH and humins-lignin biochar, whereas neither the Langmuir nor the Freundlich isotherms fitted experimental results for raw biochar due to its very low adsorption capacity. The maximum adsorption capacity predicted by the Langmuir model allowed us to establish the following classification of biochars: biochar-OH > humins-lignin biochar > > > raw biochar. Modifications of the surface had a positive impact on the adsorption capacity due to the additional available functional groups incorporated into the surface through lignin enrichment and the clean-up of blocked pores through NaOH treatment. Furthermore, formation of macropores on biochar-OH through the NaOH treatment created additional adsorption sites and probably promoted the adsorption of MB via a pore-filling mechanism.

Hydrochars obtained by hydrothermal carbonization (HTC) of Lavandula straws have been studied as an eco-friendly and economical valorization route of residual biomass from cosmetic industry into solid fuels. HTC process has been performed in a temperature range from 180 to 260 °C and retention time ranging from 1 to 20 h. The two key parameters (time and temperature) were normalized to severity factor (SF) ranging from 4.74 to 7.79, in order to compare the fuel characteristics of hydrochars according to the thermal treatment conditions. Proximate and ultimate analysis and microscopy and thermal analysis were used to characterize hydrochar surface, combustion behavior, and kinetics as a function of SF, and to compare them with those of the raw lavandin sample. Results showed that after HTC, hydrochar properties were close to sub-bituminous coal and lignite, and SF was a relevant optimization parameter for solid fuel application. In the case of Lavandula, SF = 6 was the optimal value for the HTC process. Nevertheless, in addition to SF, it is important to consider that HTC-temperature is a more influencing parameter than HTC-retention time for the fuel properties of the resulting hydrochars.

Lavandin hydrochar obtained by hydrothermal carbonization ( HTC) of lavandin straw has been studied as an eco-friendly and economical valorization route of residual biomass from cosmetic industry into adsorbent. Modified hydrochar was obtained after HTC of lavandin at 180 degrees C for 4 h followed by a throughout alkaline washing. Adsorption of Ni(II), Cd(II) and Pb(II) onto hydrochar surface was conducted as a function of initial metal concentration and pH in single and ternary systems. The metallic cations concentrations were measured by ICP-OES. Langmuir and Freundlich isotherms were used for the interpretation of adsorption isotherms as a function of initial concentration. The adsorption capacity followed the order of Pb(II) > Cd(II) > Ni(II) in single and ternary systems. In the single systems, the maximum sorption capacities of Ni(II), Cd(II) and Pb(II) obtained by the Langmuir model were 7.7, 16.7 and 50.0 mg g(-1), respectively. In the ternary system, a strong competition between Ni(II), Cd(II) and Pb(II) occurred at the hydrochar surface and adsorption capacities decreased compared to the one obtained for the single systems. Lavandin hydrochar has significant potential as an alternative adsorbent towards heavy metals removal from aqueous solution due to its easy and low-cost production.

In 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. The adsorption of methylene blue on the biochar composite was found to be fast (less than 1 h at pH 6 with an initial concentration of methylene blue of 2 × 10–5 mol L−1). Kinetics data were satisfactorily modelled by both first and second order models. Freundlich and Langmuir models were applied to adsorption isotherms data. Maximum adsorption capacity (3.35 × 10–5 mol g−1), and Langmuir and Freundlich constants (2.33 × 104 L mol−1 and 5.70 × 10–5 mol0.913 L0.087 g−1 respectively) were found to be comparable to the average of those found in the literature. Electrostatic attraction between oppositely charged methylene blue and magnetic biochar was presumed to be the dominant interaction governing adsorption at environmental pH values. Lastly, a laboratory-scale experimental device with magnetic filtration under flow allowed the complete separation of the magnetic biochar composite from the liquid phase. This study shows that this magnetic biochar composite is a promising and economically interesting recovery route for biorefinery by-products and could be used for adsorption purposes.

This paper (part II) is devoted to the effect of molecular adsorption on the surface of magnetic iron oxide nanoparticles (IONP) on the enhancement of their (secondary) field-induced agglomeration and magnetic separation. Experimentally, we use Methylene Blue (MB) cationic dye adsorption on citrate-coated maghemite nanoparticles to provoke primary agglomeration of IONP in the absence of the field. The secondary agglomeration is manifested through the appearance of needlelike micron-sized agglomerates in the presence of an applied magnetic field. With the increasing amount of adsorbed MB molecules, the size of the field-induced agglomerates increases and the magnetic separation on a magnetized micropillar becomes more efficient. These effects are mainly governed by the ratio of magnetic-to-thermal energy α, suspension supersaturation Δ0, and Brownian diffusivity Deff of primary agglomerates. The three parameters (α, Δ0, and Deff) are implicitly related to the surface coverage θ of IONP by MB molecules through the hydrodynamic size of primary agglomerates exponentially increasing with θ. Experiments and developed theoretical models allow quantitative evaluation of the θ effect on the efficiency of the secondary agglomeration and magnetic separation.

Humins as biorefineries by-product can be converted with a direct heating treatment into new rigid porous carbon materials known as humins foams. Currently, not many informations about this new material are known. Here, a preparation protocol in two steps involving foaming and carbonization is reported, while the materials have been investigated in terms of morphology, elemental content, water adsorption-desorption, stability to solvents and high temperatures, and thermal conductivity. In order to evaluate their potential uses in applications such as water purification, the pH associated to the zero charge point has been identified. Foams prepared under air ventilated condition revealed an extremely negative surface, which can be used in cation exchange applications. The surface's groups have been identified by Boehm titration, showing that this behavior can be associated to the presence of acid moieties, while the basic species result absent. The humins foams have been also tested through CO2 adsorption tests at realistic operation conditions, revealing that their performances can compete with materials reported in literature. Finally, activated carbon monoliths from carbonized humins foams using CO2 activation were tested, reaching a surface area of 1347 m(2) g(-1) after 20 min and 1482 m(2) g(-1) after 40 min of activation. These monoliths have been characterized in terms of morphology and elemental content. The results prove that the humins foams are very versatile materials, cost effective and easy to produce, with promising properties that can be further tailored for foreseen applications. (c) 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

In this work, magnetic nanoparticles of iron oxide (MNPs) were synthesized, and then the surface was recovered with an oleate double layer in order to investigate the ability of this material to adsorb nickel ions. First, the solution chemistry of oleate ions was investigated in order to determine the critical micellar concentration (CMC) value and the arrangements of ions above the CMC. Then, the synthesized oleate-modified MNP was characterized (TEM, DLS, XRD, FTIR, zeta potential, magnetometry). Finally, adsorption experiments were carried out as a function of pH and as a function of nickel concentration in 0.1 g L−1 suspensions of oleate-modified MNP. The results show that CMC of oleate ranges from 1 to 2.5∙10−3 mol L−1. Above CMC, arrangement of oleate ions as droplets, vesicles, or micelles depends on pH and influences the average size and solution absorbance. Potentiometric titrations allowed determining a pKa value of 7.8 for sodium oleate. The high stability in aqueous suspensions and characterization of oleate-modified MNP confirm that oleate ions are arranged as a bilayer coating at the surface of MNP. Retention of nickel was found to be highly dependent on pH, with a maximum adsorption (90%) beginning from pH = 7.5. The sorption isotherms were well fitted with the Langmuir model and the maximum nickel adsorption capacities were found to be 44 and 80 mg g−1 for pH = 6.8 and 7.2, respectively. The efficient removal of nickel combined with the magnetic properties of the NMP make the oleate-modified MNP an interesting water purification tool.

Microfluidic separation of magnetic particles is based on their capture by magnetized microcollectors while the suspending fluid flows past the microcollectors inside a microchannel. Separation of nanoparticles is often challenging because of strong Brownian motion. Low capture efficiency of nanoparticles limits their applications in bioanalysis. 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 micropillar 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 and 30 μL/min. Nanoparticle capture is shown to be mostly governed by the 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 nanoparticle chains and gives the scaling behavior, Λ∝Ma^{-1.7}, close to the experimental findings.

Predictive modelling of uranium speciation in natural waters can be achieved using equilibrium thermodynamic data and adequate speciation software. The reliability of such calculations is highly dependent on the equilibrium reactions that are considered as entry data, and the values chosen for the equilibrium constants. The working group "Speciation" of the CETAMA (Analytical methods establishment committee of the French Atomic Energy commission, CEA) has organized a modelling exercise, including four participants, in order to compare modellers' selections of data and test thermodynamic data bases regarding the calculation of U(VI) inorganic speciation. Six different compositions of model waters were chosen so that to check the importance of ternary alkaline earth carbonate species of U(VI) on the aqueous speciation, and the possible uranium solid phases as solubility-limiting phases. The comparison of the results from the participants suggests (i) that it would be highly valuable for end-users to review thermodynamic constants of ternary carbonate species of U(VI) in a consistent way and implement them in available speciation data bases, and (ii) stresses the necessary care when using data bases to avoid biases and possible erroneous calculations. (C) 2014 Elsevier Ltd. All rights reserved.

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 behavior.

This 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 10−5molL−1 for Eu and 10−3molL−1 for Ni. The sorption durations ranged from 1week to 1month. 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 160nm after 1month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.

Water pollution is an important problem for the environment. The presence of inorganic and organic pollutants, like metallic cations or polyaromatic hydrocarbons (PAHs), causes environmental damage and provokes different health diseases. Many techniques are currently used to extract these pollutants from water but most of them do not allow elimination of pollutants at trace concentrations. To solve this problem, we propose to use functionalized magnetic particles of two different sizes. The small nanoparticles will be used to adsorb pollutants on their surface and these nanoparticles will be removed from water with the help of magnetic micron-sized particles which exhibit a higher response to the applied magnetic field. First, we present experimental results on the magnetic separation of the magnetic iron oxide nanoparticles by magnetic microparticles under an external magnetic field. In the absence of flow, we see the attraction of nanoparticles around the microparticle and formation of thick nanoparticle clouds in the direction of the magnetic field. We compare these results with a theoretical model based on the equilibrium of chemical potentials of the captured and un-captured nanopartciles. Under flow, the size and the shape of the nanoparticle clouds strongly decreases with the Mason number (defined as a ratio of hydrodynamic -to magnetic forces). The range of Mason numbers within which the nanoparticle capture still takes place is determined. Finally we study adsorption of metallic cations on the iron oxide nanoparticles. The influence of various parameters (pollutant concentration, pH ...)will be discussed.

The adsorption capacity of a natural nanostructured clay (sepiolite) for the inorganic species: Ni2+ and As(V) has been studied using a batch method. The different parameters affecting sorption such as the mass of adsorbent, contact time, sorbate concentration or pH have been investigated and optimal experimental conditions have been determined. Langmuir and Freundlich equations, which are commonly used to describe sorption equilibrium, were applied to model experimental results. The maximum sorption capacity of sepiolite towards Ni2+ and As(V) was 2.236 mg g−1 and 0.006 mg g−1, respectively. The differences between the sorption capacities could be explained by different parameters like the charge of the ions or the free energy of hydration. The conclusion of this study is that natural sepiolite can adsorb cationic heavy metal and anionic metalloid species, which can have interesting applications in environmental applications such as the removal of these species from polluted waters.

Competition between selenium (IV) and silicic acid for the hematite (α-Fe2O3) surface has been studied during this work. Single batch experiments have been performed to study separately the sorption of selenium (IV) and silicic acid as a function of the pH. With the help of the 2-pK surface complexation model, experimental data have been fitted using the FITEQL 4.0 program. Two monodentate inner-sphere surface complexes have been used to fit selenite ions retention, FeSeO3- and FeHSeO3. In order to fit sorption of silicic acid, the two following surface complexes, namely FeH3SiO4, and FeH2SiO4-, have been used. Using the surface complexation constants coming from these two binary systems, prediction curves of the effect of silicic acid on the retention of selenium (IV) onto hematite have been obtained. Finally, performed experiments showed a competition between selenium (IV) and silicic acid for the surface sites of hematite. Experimental data matched DDLM predictions, confirming the ability of the surface complexation model to predict quantitatively and qualitatively the ternary system selenium (IV)/H4SiO4/hematite.

Sorption of selenium(IV) and silicic acid onto magnetite (Fe(3)O(4)) was investigated in binary systems, with concentrations of silicic acid under the solubility limit of amorphous silica. Using the double diffuse layer model (DDLM), surface complexation constants of selenium(IV) and H(4)SiO(4) onto magnetite were extracted using Fiteql 4.0. Then, prediction curves of the sorption of selenium(IV) in the presence of silicic acid onto magnetite were obtained, using the calculated surface complexation constants. Finally, laboratory experiments were performed and showed a competition between selenium(IV) and silicic acid for the surface sites of magnetite. Experimental results matched the model predictions, confirming its ability to model qualitatively and quantitatively the ternary system.

The interaction of glycine with SiOH silanols, which cover the surface of amorphous silica are modeled and investigated by means of the DFT B3LYP/6-31++G** method. The neutral and zwitterion form of glycine are considered. Cooperative hydrogen bonding, with one or several silanol groups, are studied. Different scenarii are modeled: adsorption from the gas phase at 0 and 430K and adsorption of the microsolvated glycine. It is shown that hydroxylated silica does not act to stabilize the zwitterion form of glycine and thus cannot be considered as a “solid solvent”: glycine remains more stable in the neutral state when bonded up to 3 silanols. In contrast, if water molecules are adsorbed on the silanols, they act as co-stabilizors of the zwitterionic state. Two distinct domains exist in the (T,P) phase diagram: in the first one, glycine is stabilized on silanols and in the second, glycine is more stable in the gas phase. Vibration frequencies are calculated and compared with experimental ones.