Competitive adsorption mechanisms of Cd(II), Cu(II) and Pb(II) on bioinspired mesoporous silica revealed by complementary adsorption/isothermal titration calorimetry studies.

This study presents the adsorption properties of a bioinspired grafted mesoporous silica material and the competitive effects between Cd(II) or Cu(II) and Pb(II) during the adsorption process. Glutathione, a natural antioxidant known for its metal binding properties, has been successfully grafted to SBA-15 mesoporous silica and the optimum adsorption parameters were determined. This original and multidisciplinary approach combines classical adsorption studies with thermodynamic investigations to understand the adsorption behavior of Cd(II), Cu(II) and Pb(II) on this material. To this end, isothermal titration calorimetry (ITC) has been used to elucidate the mechanisms of single-metal and two-metal adsorption. The results showed affinity in the order Pb(II) > Cu(II) > Cd(II) in single metal systems. Cd(II) adsorption relied mainly on physical contributions while Cu(II) and Pb(II) adsorption was shown to be chemically driven. Two-metal systems highlighted that Cd(II) and Pb(II) are adsorbed on the same coordination sites, whereas Cu(II) and Pb(II) are adsorbed on different sites. The material showed good selectivity and encouraging results were obtained on real effluents.

Grafting of Crown Ether and Cryptand Macrocycles on Large Pore Stellate Mesoporous Silica for Sodium Cation Extraction.

Regulation of the sodium cations level in the case of renal failure diseases is a very challenging task for clinicians, and new pollutant extractors based on nanomaterials are emerging as potential treatments. In this work, we report different strategies for the chemical functionalization of biocompatible large pore mesoporous silica, denoted stellate mesoporous silica (STMS), with chelating ligands able to selectively capture sodium. We address efficient methods to covalently graft highly chelating macrocycles onto STMS NPs such as crown ethers (CE) and cryptands (C221) through complementary carbodiimidation reactions. Regarding sodium capture in water, C221 cryptand-grafted STMS showed better capture efficiency than CE-STMS due to higher sodium atom chelation in the cryptand cage (Na+ coverage of 15.5% vs. 3.7%). The sodium selectivity was hence tested with C221 cryptand-grafted STMS in a multi-element aqueous solution (metallic cations with the same concentration) and in a solution mimicking peritoneal dialysis solution. Results obtained indicate that C221 cryptand-grafted STMS are relevant nanomaterials to extract sodium cations in such media and allow us to regulate their levels.

Highly chelating stellate mesoporous silica nanoparticles for specific iron removal from biological media.

In this work, the design of a new generation of functionalized large pore silica nanoparticles is addressed for the specific removal of iron from biological environments. Herein, mesoporous silica with a large pore stellate morphology, denoted STMS, were grafted with the highly specific iron chelating agent desferrioxamine B, DFoB. The challenge of this work was the step by step elaboration of the nanoplatform and the evaluation of its chelating efficiency and selectivity. Hence, the controlled covalent grafting of DFoB specific iron chelator, was successfully achieved ensuring a high grafting rate of chelating ligand of 730 nmol·mg-1 (i.e., 0.85 ligand·nm-2). Furthermore, these highly chelating STMS silica were able to capture iron(III) stabilized with nitrilotriacetic acid (NTA) in solution at physiological pH with a fast kinetics (less than 30 min). For a stoichiometry 0.85:1 (FeNTA : DFoB), the STMS-DFoB nanoparticles allowed reaching capture capacity and efficiency of 480 nmolFe3+/mg SiO2 and 78%, respectively. Regarding the selectivity features of the removal process, studies were performed with two different media composed of various metal ions: (i) an equimolar solution of various metal cations and (ii) a Barth's buffer mimicking the brain solution composition. In both cases, the chelating STMS-DFoB showed a high selectivity for iron versus other ions at the same (Al3+) or different valency (Na+, K+…). Finally, this work paves the way for new nanosystems for metal overload treatments as well as for future highly chelating nanoplatforms that can be used at the interface between depollution and nanomedecine.

Lanthanide recovery by silica-Cyanex 272 material immobilized in alginate matrix.

Mesoporous silica impregnate with Cyanex 272 (bis/2,4,4-trimethylpentyl/phosphinic acid) extractant was immobilized into an alginate matrix to obtain a composite sorbent easy to use and applicable in fixed-bed column continuous systems. The sorption efficiency of this material was tested for the recovery of Eu(III) ions from aqueous solutions in batch and continuous mode. The competition among rare earths ions (europium, lanthanum, and lutetium) and among rare earths and calcium or sodium ions was investigated. High calcium concentrations strongly reduce the sorption capacity of the alginate matrix that composes the hybrid material and the Cyanex 272 impregnated into silica powder improves the rare earths' sorption performance in this calcium charged media. The experimental breakthrough curves obtained were satisfactory fitted by Thomas model.

Boron removal by a composite sorbent: Polyethylenimine/tannic acid derivative immobilized in alginate hydrogel beads.

A novel composite material was prepared by the grafting of tannic acid on polyethylenimine (PEI), which allows an efficient sorption of boron (sorption capacity close to 0.89 mmol B g-1). The encapsulation of this chelating sorbent (finely crushed) facilitates its use (readily solid/liquid separation, use in fixed-bed columns) at the expense of a loss in sorption capacity (proportionally decreased by the introduction of alginate having poor efficiency for boron uptake). Sorption isotherms are modeled using the Langmuir equation, while the kinetic profiles are presented a good fit by pseudo-second order rate equation. In addition, the encapsulating matrix introduces supplementary resistance to intraparticle diffusion, especially when the resin is dried without control: freeze-drying partially limits this effect. The stability (at long-term storage) of the sorbent is improved when the sorbent is stored under nitrogen atmosphere. The presence of an excess of NaCl was investigated. The degradation of the hydrogel (by ion-exchange of Ca(II) with Na(I)) leads to a decrease in the sorption performance of composite material but the action of Ca(II) ions in the solutions re-stabilizes the hydrogel.

Sargassum filipendula alginate from Brazil: seasonal influence and characteristics.

The aim of this work is focused on the extraction and characterization of the Brazilian seaweed Sargassum filipendula alginate. Alginates obtained at different seasons were characterized by liquid state nuclear magnetic resonance spectroscopy and scanning electron microscopy. The alginate extraction efficiency was about 20%. Different seasons of the year and different stages in the life cycle of Sargassum sp. in southeastern Brazil influenced the M/G and, consequently, the technological properties of extracted alginates.

Biosorption of chromium by alginate extraction products from Sargassum filipendula: investigation of adsorption mechanisms using X-ray photoelectron spectroscopy analysis.

The alginate extraction products from Brazilian brown seaweed Sargassum filipendula were studied for chromium biosorption. Batch experiments were conducted at pH 2 and 3 and 20°C to determine the sorption capacity of this biosorbents for chromium (VI) and (III). The biomass was characterized before and after metal binding by X-ray photoelectron spectroscopy (XPS) in order to determine the mechanisms of chromium biosorption. The residue has a high adsorption capacity, close the value obtained with seaweed and higher than that of alginate for both Cr(III) and Cr(VI). XPS analysis of the biosorbents revealed that carboxyl, amino and sulfonate groups are responsible for the binding of the metal ions. The analysis also indicated that the Cr(VI) bound to the biomass was reduced to Cr(III).