Jocelyne Miehé-Brendlé

Catalytic wet peroxide oxidation of phenol over Fe-exchanged pillared beidellite

This study presents an evaluation of the catalytic performances of a Fe-exchanged Al-pillared synthetic beidellite for the wet hydrogen peroxide oxidation of phenolic aqueous wastes. The catalyst was prepared by a cation doping technique, its properties being determined by DRX, BET and chemical analysis techniques. All the tests were performed on a laboratory scale set-up. Important factors affecting catalyst activity and phenol removal efficiencies were studied, i.e. the effect of pH, temperature, catalyst concentration and the stability of the catalyst. The experimental results indicate that the use of this catalyst allows a total elimination of phenol and a significant removal of chemical oxygen demand, without significant leaching of Fe ions. Thus, considering the lowest Fe concentrations in solution after oxidation, at pH=5, 50 degrees C, and 180 min. COD removal efficiency of 87.9% was obtained. It was also observed that by using this catalyst, it is possible to extend the range of pH values for which Fenton-type oxidations can occur.

Interactions of oxytetracycline with a smectite clay: a spectroscopic study with molecular simulations.

Binding of antibiotics to clay minerals can decrease both their physical and biological availability in soils. To elucidate the binding mechanisms of tetracycline antibiotics on smectite clays as a function of pH, we probed the interactions of oxytetracycline (OTC) with Na-montmorillonite (MONT) using X-ray diffraction (XRD), infrared (IR), and solid-state nuclear magnetic resonance (NMR) spectroscopies, and Monte Carlo molecular simulations. The XRD patterns demonstrate the presence of OTC in the MONT interlayer space at acidic pH whereas complexation of OTC by external basal and edge sites seems to prevail at pH 8. At both pH, the (1)H-(13)C NMR profile indicates restricted mobility of the adsorbed OTC species; and, -CH(3) deformation and C-N stretching IR vibration bands confirm a binding mechanism involving the protonated dimethylamino group of OTC. Changes in the (23)Na NMR environments are consistent with cation-exchange and cation complexation reactions at the different sites of adsorption. Molecular simulations indicate that MONT interlayer spacing and structural charge localization dictate favorable binding conformations of the intercalated OTC, facilitating multiple interactions in agreement with the spectroscopic data. Our results present complementary insights into the mechanisms of adsorption of TETs on smectites important for their retention in natural and engineered soil environments.

New range of Al–Mg organoclays with tailored hydrophobicity: incorporation of fluoride as a local probe to study the octahedral character

Abstract A series of inorganic–organic hybrids with a phyllosilicate-like structure were prepared using a single-step templating sol–gel procedure. The synthesis involves reaction of magnesium nitrate and aluminum acetylacetonate with octyltriethoxysilane, to give products where saponite is the inorganic parent. These hybrids were characterized by X-ray diffraction, solid-state 29 Si, 13 C and 27 Al nuclear magnetic resonance, infrared spectroscopy and thermogravimetry. The results showed that the hybrid materials exhibit lamellar structures, similar to those found in natural inorganic silicate saponite. The influence of the substitution of magnesium and silicon by aluminum was evident from 29 Si and 13 C NMR studies. A high degree of condensation was obtained. The hydrophobic character was evaluated by wettability measurements. These materials hold promise as sorbents for solid-phase extraction of organic pollutant molecules, due to their highly hydrophobic character.

Enhanced interlayer trapping of a tetracycline antibiotic within montmorillonite layers in the presence of Ca and Mg

The formation of a ternary antibiotic-metal-clay complex is hypothesized as the primary adsorption mechanism responsible for the increased adsorption of tetracycline antibiotics on smectites in the presence of divalent metal cations under circumneutral and higher pH conditions. To evaluate this hypothesis, we conducted a spectroscopic investigation of oxytetracycline (OTC) interacting with Na-montmorillonite in the presence and absence of Ca or Mg salts at pH 6 and pH 8. Despite a two-fold increase in OTC adsorbed in the presence of Ca or Mg, both solid-state nuclear magnetic resonance and infrared signatures of the OTC functional groups involved in metal complexation implied that the formation of an inner-sphere ternary complexation was not significant in stabilizing the adsorbate structures. The spectroscopic data further indicated that the positively-charged amino group mediated the OTC adsorption both in the absence and presence of the divalent metal cations. Focusing on the experiments with Mg, X-ray diffraction analysis revealed that the metal-promoted adsorption was coupled with an increased intercalation of OTC within the montmorillonite layers. The resulting interstratified clay layers were characterized by simulating X-ray diffraction of theoretical stacking compositions using molecular dynamics-optimized montmorillonite layers with and without OTC. The simulations uncovered the evolution of segregated interstratification patterns that demonstrated how increased access to smectite interlayers in the presence of the divalent metal cations enhanced adsorption of OTC. Our findings suggest that specific aqueous structures of the clay crystallites in response to the co-presence of Mg and OTC in solution served as precursors to the interlayer trapping of the antibiotic species. Elucidation of these structures is needed for further insights on how aqueous chemistry influences the role of smectite clay minerals in trapping organic molecules in natural and engineered soil particles.

Fe(II) sorption on a synthetic montmorillonite. A combined macroscopic and spectroscopic study.

Extended X-ray absorption fine structure (EXAFS) and Mössbauer spectroscopy combined with macroscopic sorption experiments were employed to investigate the sorption mechanism of Fe(II) on an iron-free synthetic montmorillonite (Na-IFM). Batch sorption experiments were performed to measure the Fe(II) uptake on Na-IFM at trace concentrations as a function of pH and as a function of sorbate concentration at pH 6.2 and 6.7 under anoxic conditions (O2 < 0.1 ppm). A two-site protolysis nonelectrostatic surface complexation and cation exchange sorption model was used to quantitatively describe the uptake of Fe(II) on Na-IFM. Two types of clay surface binding sites were required to model the Fe(II) sorption, the so-called strong (≡S(S)OH) and weak (≡S(W)OH) sites. EXAFS data show spectroscopic differences between Fe sorbed at low and medium absorber concentrations that were chosen to be characteristic for sorption on strong and weak sites, respectively. Data analysis indicates that Fe is located in the continuity of the octahedral sheet at trans-symmetric sites. Mössbauer spectroscopy measurements confirmed that iron sorbed on the weak edge sites is predominantly present as Fe(II), whereas a significant part of surface-bound Fe(III) was produced on the strong sites (∼12% vs ∼37% Fe(III) species to total sorbed Fe).

Na-magadiite prepared in a water/alcohol medium: synthesis, characterization and use as a host material to prepare alkyltrimethylammonium- and Si-pillared derivates

Abstract Syntheses of Na-magadiite were performed under hydrothermal conditions in a water/alcohol medium. It is only possible to obtain a pure and well crystallized magadiite sample using a water/ethanol medium at a water/ethanol molar ratio of ~0.12. As shown by thermal analysis and 1H liquid nuclear magnetic resonance spectroscopy, ethanol is not incorporated into the magadiite. Intercalation of dodecyl- and hexadecyltrimethylammonium cations in the interlayer space of Na-magadiite at different theoretical ion-exchange rates shows that the experimental ion- exchange rates are in good agreement with the theoretical ones. However, scanning electron micrographs of the sample having a theoretical ion exchange rate of 25-75% shows that the exchanges are not homogeneous (both thin and thick platelets are present). Attempts to obtain a Si- pillared compound starting from C16TMA-magadiite as the host material leads to a microporous compound having a BET surface area of 778 m2g-1.

Competitive Fe(II)-Zn(II) uptake on a synthetic montmorillonite.

The interaction of Fe(II) with clay minerals is of particular relevance in global geochemical processes controlling metal and nutrient cycles and the fate of contaminants. In this context, the influence of competitive sorption effects between Fe(II) and other relevant transition metals on their uptake characteristics and mobility remains an important issue. Macroscopic sorption experiments combined with surface complexation modeling and extended X-ray absorption fine structure (EXAFS) spectroscopy were applied to elucidate competitive sorption processes between divalent Fe and Zn at the clay mineral-water interface. Sorption isotherms were measured on a synthetic iron-free montmorillonite (IFM) under anoxic conditions (O2 <0.1 ppm) for the combinations of Zn(II)/Fe(II) and Fe(II)/Zn(II), where the former metal in each pair represents the trace metal (<10(-7) M) and the latter the competing metal at higher concentrations (10(-7) to 10(-3) M). Results of the batch sorption and EXAFS measurements indicated that Fe(II) is competing with trace Zn(II) for the same type of strong sites if Fe(II) is present in excess, whereas no competition between trace Fe(II) and Zn(II) was observed if Zn(II) is present at high concentrations. The noncompetitive behavior suggests the existence of sorption sites which have a higher affinity for Fe(III), where surface-induced oxidation of the sorbed Fe(II) to Fe(III) occurred, and which are not accessible for Zn(II). The understanding of this competitive uptake mechanism between Fe(II) and Zn(II) is of great importance to assess the bioavailability and mobility of transition metals in the natural environment.

Synthesis and characterization of a new one-dimensional sodium silicate named Mu-29

Abstract The synthesis and the structure of a new one-dimensional sodium silicate, named Mu-29, are reported. This material was prepared in a quasi-non-aqueous medium using ethanol as the main solvent. Its structure was determined by single crystal X-ray diffraction. The symmetry is orthorhombic, space group Pna2 1 , with the following unit-cell parameters: a =27.32(2) A, b =15.40(2) A and c =8.241(8) A. Mu-29 is a new chain-like silicate. Its structure consists of double-crankshaft––[Si 2 O 5 ] 2− ––chains which are in strong interaction with hydrogen atoms and sodium cations. The material was characterized by elemental and thermal analyses, XRD, SEM and 1 H, 23 Na and 29 Si solid state NMR spectroscopy.

Organoclays: Preparation, Properties and Applications

Publisher Summary This chapter summarizes the most important aspects of the synthesis and the application of organoclays. These include intercalation, grafting, and in situ incorporation of the organic moieties. This new class of porous solids attracted the attention of researchers in recent years with their unique properties and potential areas of application, which are beyond those of conventional layered type materials. Smectites, a subgroup of the phyllosilicates, attracted plenty of interest due to their swelling properties. Other subgroups include micas, kaolins, vermiculites, chlorites, talc, and pyrophyllite. These minerals are characterized by a 2:1 layer structure in which two tetrahedral sheets are attached on each side of an octahedral sheet via sharing of apical oxygens. The research effort is aimed at developing of synthesis methods to better control the physicochemical characteristics of organoclays. The synthesis of covalently linked inorganic–organic lamellar composites with ion exchange properties and tailored hydrophobicity were carried out using a single-step templating sol–gel procedure. The syntheses involved reaction of magnesium nitrate and aluminum acetylacetonate with octyltriethoxysilane. The applications vary from heavy metal remediation and catalysis to adsorption of organic pollutants and immobilization of biomolecules. The organoclays are also considered as promising materials as environmental barriers, polymer fillers, catalytic supports, chemical sensors, and porous vehicles for chemotherapy drugs.

Characterization of natural and chemically modified kaolinite from Mako (Senegal) to remove lead from aqueous solutions

Abstract The chemical and sorption properties of clay minerals from the Mako area, Senegal, were investigated using FTIR spectroscopy, X-ray diffraction, scanning electron microscopy equipped with an X-ray energy dispersion spectrometer, thermal analysis and chemical analysis. The clay sample is essentially dominated by kaolinite and quartz as also shown by treatment with ethylene glycol and dimethylsulfoxide (DMSO). The clay fraction of this natural clay was organically modified by grafting with 3-aminopropyltriethoxysilane (APTES) in order to improve significantly its retention ability of heavy metals. The silane groups of the APTES reagent were partly grafted on the surface of platy kaolinite particles and the remaining ethoxy groups could be hydrolysed by aqueous treatment. The natural clay, its clay fraction and the organo-functionalized clay (with APTES) were investigated as adsorbents for the removal of Pb(II) from aqueous solutions. Evidence for an organic grafting has been demonstrated by comparing the spectroscopic characteristics of the natural clay and those of its chemically modified derivatives. The effects of different parameters (i.e. initial Pb(II) concentration and contact time) on the adsorption efficiency were studied. For an initial concentration of 10 mg L-1 Pb(II), the adsorption was maximized after 30 min contact time both for the raw material and its clay fraction and after 90 min for the APTES grafted clay. Although the maximum of sorption for the APTES grafted clay is reached with slower kinetics, this maximum amount of Pb(II) uptake at room temperature (Xmax) is significantly higher since it is 0.99 mg g-1 for the raw clay, 1.46 mg g-1 for its clay fraction and 3.02 mg g-1 for the organically modified clay, i.e. three times greater than the raw clay.