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Toxicity mechanisms of metal oxide nanoparticles towards bacteria and underlying roles of membrane composition are still debated. Herein, the response of lipopolysaccharide-truncated Escherichia coli K12 mutants to TiO2 nanoparticles (TiO2NPs, exposure in dark) is addressed at the molecular, single cell, and population levels by transcriptomics, fluorescence assays, cell nanomechanics and electrohydrodynamics. We show that outer core-free lipopolysaccharides featuring intact inner core increase cell sensitivity to TiO2NPs. TiO2NPs operate as membrane strippers, which induce osmotic stress, inactivate cell osmoregulation and initiate lipid peroxidation, which ultimately leads to genesis of membrane vesicles. In itself, truncation of lipopolysaccharide inner core triggers membrane permeabilization/depolarization, lipid peroxidation and hypervesiculation. In turn, it favors the regulation of TiO2NP-mediated changes in cell Turgor stress and leads to efficient vesicle-facilitated release of damaged membrane components. Remarkably, vesicles further act as electrostatic baits for TiO2NPs, thereby mitigating TiO2NPs toxicity. Altogether, we highlight antagonistic lipopolysaccharide-dependent bacterial responses to nanoparticles and we show that the destabilized membrane can generate unexpected resistance phenotype., Pagnout et al investigate the multiscale response of deep rough Escherichia coli mutants to TiO2 nanoparticle exposure and find that TiO2 strips the cell membrane, which triggers osmotic and then oxidative stresses. Depending on their lipopolysaccharide surface-phenotype, the bacteria respond by releasing membrane vesicles that act as electrostatic baits for TiO2 nanoparticles.

International audience; It is a common practice to alter the undesirable behavior of clayey soils (i.e. swelling-shrinkage and high plasticity) with lime addition. However, the reaction mechanism involved in the early stage (first minute up to 24 h after mixing) of lime treatment is still not well explored. In the present work, the surface chemistry of lime ([Ca] = -22 mmol/l and pH = 12.63) treated kaolinites (Kaol) was studied using argon and nitrogen gas adsorption. The effect of pH ([Ca] = 22 mmol/l and. pH = 12.63 vs. [Ca] = 22 mmol/l and pH = 7) was also examined. The derivative low-pressure adsorption isotherms were analyzed using derivative isotherm summation (DIS), focusing on the analysis of surface heterogeneity. After the treatment with lime, the specific surface area and adsorption energy distribution of Kaol were modified. The adsorption of the calcium cation at both investigated pH (i.e. pH 7 and pH 12.63) takes place on the basal and lateral face of Kaol, however, the species of adsorbed calcium cation appeared to be different. The treatment also leads to a decrease in basal surface area due to basal face-basal face particle aggregation. The basal surface of Kaol treated with lime exhibited polar sites when probed with nitrogen molecule. These sites may have promoted linkage and flocculation of Kaol particles, which in turn play a role in the short-term modification of the macroscopic behavior of lime treated kaolins.

Smectites are 2:1 type swelling clay minerals widely distributed in the earth’s crust. The unique structures and properties endow them with various applications in many fields. However, their growt...

International audience; The surface properties of five kaolinites of various origins were analyzed using potentiometric titration, electrokinetic measurements and low-pressure gas adsorption associated to derivative isotherm summation (DIS) modeling. The data show that sample structure is important in determining the surface properties. The combined analytical results clearly shows the existence of a permanent negative layer charge for all the samples. The general features that could be observed for the five kaolinites are: the titration curves are shifted to lower pH with increasing ionic strength due to the layer charge; the amount of consumed proton is influenced by the permanent layer charge; although low, the permanent charge determines the electrokinetic behavior. The shape anisotropy and the charge distribution on the basal and edge surfaces are crucial parameters to understand the behavior of kaolinite particles in aqueous media. The Cameroonian sample of the set exhibits a significant permanent charge together with large specific surface area associated to fine particle size and considerable shape anisotropy.

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International audience; River suspended particulate matter (SPM) plays a crucial role in the fate and behavior of pollutants such as Zn, a widespread trace metal commonly encountered in continental surface waters. SPM comprises particles and colloids and is described as complex, heterogeneous particles composed of mineral, organic and microbiological components with high surface reactivity. In this study, the surface properties of river SPM and its capacity to bind Zn were probed using electrophoretic mobility (EM) experiments, specific surface area (SSA) measurements, Zn adsorption tests and X-ray absorption spectroscopy (XAS). The external characteristics and reactivity of lab-controlled mineral phases (illite, ferrihydrite, illite-iron (hydr)oxide composite, and calcite) were investigated as for natural SPM. The electrophoretic mobility (EM) of the SPM exhibited low variations among the samples and was essentially assigned to the clay particles that dominate the mineralogical composition. Except for two samples, Zn adsorption experiments evidenced comparable adsorption capacity in relation to their different mineral and chemical compositions. Zn K-edge XAS data revealed that at low Zn loadings, the binding mode of this metal with environmental particles was controlled by its mineralogical composition. Indeed, linear combination fitting of the XAS curves, completed by shell-to-shell fitting, revealed that Zn is associated with SPM by surface complexation. The XAS results showed that for SPM samples collected in the high flow regime, Zn was mainly bound to clay minerals. In contrast, for the SPM sample collected during the low flow regime, Zn was bound not only to clay minerals but also to iron (hydr)oxides

International audience; Atomic Force Microscopy (AFM) is a powerful technique for the measurement of mechanical properties of individual cells in two (x  y) or three (x  y  time) dimensions. The instrumental progress makes it currently possible to generate a large amount of data in a relatively short time, which is particularly true for AFM operating in so-called PeakForce tapping mode (Bruker corporation). The latter corresponds to an AFM probe that periodically hits the sample surface while the pico-newton level interaction force is recorded from cantilever deflection. The method provides unprecedented high-resolution (a few tens of nm) imaging of the mechanical features of soft biological samples (e.g. bacteria, yeasts) and of hard abiotic surfaces (e.g. minerals). The rapid conversion of up to several tens of thousands spatially resolved force curves typically collected in AFM PeakForce tapping mode over a given cell surface area into comprehensive nanomechanical information requires the development of robust data analysis methodologies and dedicated numerical tools. In this work, we report an automated algorithm for (i) a rapid and unambiguous detection of the indentation regimes corresponding to non-linear and linear deformations of bacterial surfaces upon compression by the AFM probe, (ii) the subsequent evaluation of the Young modulus and cell surface stiffness, and (iii) the generation of spatial mappings of relevant nanomechanical properties at the single cell level. The procedure involves consistent evaluation of the contact point between the AFM probe and sample biosurface and that of the threshold indentation value marking the transition between non-linear and linear deformation regimes. For comparison purposes, the former regime is here analyzed on the basis of Hertz and Sneddon models corrected or not for effects of finite sample thickness. Analysis of AFM measurements performed on a selected Escherichia coli strain is detailed to demonstrate the feasibility, rapidity and robustness of the here-proposed PeakForce data treatment process. The flexibility of the algorithm allows consideration of force curve parameterizations other than that detailed here, which may be desired for investigation of e.g. eukaryotes nanomechanics. The performance of the adopted Hertz-based and Sneddon-based contact mechanics formalisms in recovering experimental data and in identifying nanomechanical heterogeneities at the bacterium scale is further thoroughly discussed.

Contamination of water with steroid residues can cause a number of environmental damages, affecting exposed organisms including man. The development of technologies for treatment or removal of this type of micropollutant from water is of paramount importance. In this study, citric acid was used to functionalize β-Cyclodextrin (bCD) on the silica surface generating an organic-inorganic hybrid composite for application in molecular sequestration. The functionalization percentage was high, with about 62.6% of the composite mass corresponding to the organic part of the material. 13C NMR and infrared spectroscopic analysis indicate that the functionalization mechanism occurs by an esterification reaction between the citric acid with the silanol groups from silica and the primary hydroxyls of the bCDs. Fast adsorption of the methyltestosterone steroid was observed at acid pH, with a high adsorption capacity of 11 mg g−1. The best kinetic and isotherm models fit indicated that the adsorption occurred by a physical mechanism at independent sites with the steroid molecule possibly captured by two bCDs. The removal process was spontaneous and exothermic, with the existence of weak interactions between the hormone and the composite, and its regeneration is quite fast efficient with the displacement of the complexation equilibrium. The results obtained in this study demonstrate the considerable potential of the composite for use in the treatment of wastewater containing the steroid studied, and its efficacy should be evaluated for other steroid molecules.

International audience; Mutations in the rfa operon leading to severely truncated lipopolysaccharide (LPS) structures are associated with pleiotropic effects on bacterial cells, which in turn generates a complex phenotype termed deep-rough. Literature reports distinct behavior of these mutants in terms of susceptibility to bacteriophages and to several antibacterial substances. There is so far a critical lack of understanding of such peculiar structure-reactivity relationships mainly due to a paucity of thorough biophysical and biochemical characterizations of the surfaces of these mutants. In the current study, the biophysicochemical features of the envelopes of Escherichia coli deep-rough mutants are identified from the molecular to the single cell and population levels using a suite of complementary techniques, namely microelectrophoresis, Atomic Force Microscopy (AFM) and Isobaric Tag for Relative and Absolute Quantitation (iTRAQ) for quantitative proteomics. Electrokinetic, nanomechanical and proteomic analyses evidence enhanced mutant membrane destabilization/permeability, and differentiated abundances of outer membrane proteins involved in the susceptibility phenotypes of LPS-truncated mutants towards bacteriophages, antimicrobial peptides and hydrophobic antibiotics. In particular, inner-core LPS altered mutants exhibit the most pronounced heterogeneity in the spatial distribution of their Young modulus and stiffness, which is symptomatic of deep damages on cell envelope likely to mediate phage infection process and antibiotic action. Lipopolysaccharides (LPS) cover surface of the outer membrane of Gram-negative bacteria. They are tripar-tite molecules composed of lipid A, core oligosaccharides usually containing glucose, heptose, galactose, 2-keto-3-deoxyoctonate (KDO), and a highly variable O-antigen component (O-antigen is missing in Escherichia coli K-12). LPS act as a protective and permeable barrier against large molecules and hydrophobic compounds from the environment. They are positioned among phospholipids and proteins of the outer membrane, and contribute to the structural properties of the latter. In Escherichia coli, genes involved in the LPS synthesis are organized according to three operons in the rfa (also known as waa) locus (Fig. 1A). The first operon contains rfaD (or gmhD), rfaF, rfaC and rfaL genes. The three first genes encode proteins involved in the biosynthesis and transfer of the two first heptose residues in the inner core of LPS, whereas rfaL encodes a ligase required for the attachment of O-antigen. The second operon contains (i) rfaQ and rfaK (or waaU) that encodes the heptosyltransferases adding the third and fourth heptose residues, respectively, (ii) genes rfaG (or waaG), rfaI (or waaO) and rfaJ (or warR /waaJ) encoding the gluco-syltransferases that add the three glucose residues in the LPS outer core, (iii) rfaB that encodes the galactosyl-transferase adding the galactose residue to the first glucose, (iv) rfaY and rfaP that encodes kinases responsible for phosphorylation of heptoses, (v) rfaZ involved in the KDO attachment during LPS core biosynthesis, and finally (vi) rfaS that encodes a protein necessary for the attachment of rhamnose to the LPS core by linkage to the KDOII residue. The short kdtA operon contains kdtA (or waaA) that encodes the KDO transferase adding the two KDO residues to the lipid A and kdtB (or coaD) that is not involved in the LPS synthesis 1-3. A defining feature of E. coli LPS is the presence of phosphoryl substituents on the LPS core-heptose residues, essential for

International audience; Chlordecone (Kepone) (CLD) is a highly persistent pesticide formerly used in the French West Indies. High levels of this pesticide are still found in soils and represent a subsequent source of contamination for outdoor-reared animals which may ingest involuntary non negligible amounts of soil. In that context, sequestering matrices like activated carbons (ACs) may be used to efficiently decrease the bioavailability of such organic pollutants. The present study intends to assess the respective efficiency of two sequestering strategies where two different ACs were provided either via feed incorporation or via soil amendment. This study involved 20 piglets randomly distributed into 5 experimental groups (4 replicates). All groups were exposed to 10 mu g of CLD per kg of BW per day during 10 days via a contaminated soil. In both "Soil-ACs" treatment groups, the contaminated soil was amended by 2% (mass basis) of one of the two ACs. The two "Feed-ACs" groups received the contaminated soil and one dough ball containing 0.5% (mass basis) of one of the ACs. The piglets were then euthanized before collection of pericaudal adipose tissue and the whole liver and CLD analysis. A significant decrease of CLD concentrations in liver and adipose tissue was observed only in the "Soil-ACs" groups in comparison with the control group (P < 0.001). This decrease was particularly important for the coconut shell activated carbon where relative bioavailability was found lower than 1.8% for both tissues.

International audience; DDB2, known for its role in DNA repair, was recently shown to reduce mammary tumor invasiveness by inducing the transcription of IκBα, an inhibitor of NF-κB activity. Since cellular adhesion is a key event during the epithelial to mesenchymal transition (EMT) leading to the invasive capacities of breast tumor cells, the aim of this study was to investigate the role of DDB2 in this process. Thus, using low and high DDB2-expressing MDA-MB231 and MCF7 cells, respectively, in which DDB2 expression was modulated experimentally, we showed that DDB2 overexpression was associated with a decrease of adhesion abilities on glass and plastic areas of breast cancer cells. Then, we investigated cell nanomechanical properties by atomic force microscopy (AFM). Our results revealed significant changes in the Young's Modulus value and the adhesion force in MDA-MB231 and MCF7 cells, whether DDB2 was expressed or not. The cell stiffness decrease observed in MDA-MB231 and MCF7 expressing DDB2 was correlated with a loss of the cortical actin-cytoskeleton staining. To understand how DDB2 regulates these processes, an adhesion-related gene PCR-Array was performed. Several adhesion-related genes were differentially expressed according to DDB2 expression, indicating that important changes are occurring at the molecular level. Thus, this work demonstrates that AFM technology is an important tool to follow cellular changes during tumorigenesis. Moreover, our data revealed that DDB2 is involved in early events occurring during metastatic progression of breast cancer cells and will contribute to define this protein as a new marker of metastatic progression in this type of cancer.

International audience; 17 The release of engineered nanoparticles (NPs) in the environment may have profound implications 18 for the health of aquatic biota. In this study, we evidence that the initial stage of NPs action on 19 bacteria can be detected upon measurement of the electrophoretic fingerprints of mixed NPs-cells 20 dispersions. Such electrokinetic signatures reflect a modification of the physicochemical cells and NPs 21 surface properties following changes in cell envelope organization, subsequent intracellular material 22 release and/or biomolecules cell excretion. The demonstration is based on a thorough investigation 23 of the electrohydrodynamic features of genetically engineered Escherichia coli bacteria exhibiting 24 distinct surface phenotypes (presence of adhesive YeeJ large proteins or F-pili proteinaceous 25 filaments) exposed to silica NPs (65 nm radius) functionalized by-NH 2 terminal groups. At pH 7, 26 electrostatics prevents interactions between bacteria and SiNH 2 NPs, regardless of the NPs 27 concentration considered (0-10-2 g L-1 range). At pH 3, electrostatically-driven interactions allow 28 intimate contacts between NPs and bacteria. In turn, significant modulation of the electrophoretic 29 determinants of cells and NPs are generated due to cells envelope alteration and bio-corona 30 acquisition by NPs. Differentiated roles of the cell surface appendages in the mediation of NPs 31 impacts are evidenced by the measured dependence of electropherograms on cell surface 32 phenotype and NPs concentration. Cell morphology and surface roughness, evaluated by Atomic 33 Force Microscopy (AFM) in liquid, confirm the pH and NPs concentration conditions where NPs-cells 34 interactions are operational. Combination of electrokinetics and AFM further pinpoints 35 heterogeneities in cells response at the single cell and population scales. Altogether, results show 36 that electrokinetics is suitable to detect the preliminary stage of events leading to NPs toxicity 37 toward microorganisms. 38 Environmental context: 39 Attractive interactions and subsequent contacts between NPs and microorganisms are the first steps 40 of a chain of events leading to adverse NPs effects toward cells. Herein we show that the 41 electrophoretic response of complex mixtures of engineered NPs (silica NPs) and bacteria (E. coli) 42 Page 2/27 reflects initial NPs-mediated cell surface damages. We thus provide a promising option for a rapid 43 electrokinetics-based detection of deleterious actions of NPs on biological cells. 44

International audience; Adsorption of prebiotic building blocks is proposed to have played a role in the emergence of life on Earth. The experimental and theoretical study of this phenomenon should be guided by our knowledge of the geochemistry of the habitable early Earth environments, which could have spanned a large range of settings. Adsorption being an interfacial phenomenon, experiments can be built around the minerals that probably exhibited the largest specific surface areas and were the most abundant, i.e., phyllosilicates. Our current work aims at understanding how nucleotides, the building blocks of RNA and DNA, might have interacted with phyllosilicates under various physico-chemical conditions. We carried out and refined batch adsorption studies to explore parameters such as temperature, pH, salinity, etc. We built a comprehensive, generalized model of the adsorption mechanisms of nucleotides onto phyllosilicate particles, mainly governed by phosphate reactivity. More recently, we used surface chemistry and geochemistry techniques, such as vibrational spectroscopy, low pressure gas adsorption, X-ray microscopy, and theoretical simulations, in order to acquire direct data on the adsorption configurations and localization of nucleotides on mineral surfaces. Although some of these techniques proved to be challenging, questioning our ability to easily detect biosignatures, they confirmed and complemented our pre-established model.

International audience; Although microorganisms seem to play an important role in the alteration processes of basaltic glasses in solution, the elementary mechanisms involved remain unclear in particular with regard to the role of organic ligands excreted by the cells. Two glasses, one with Fe and one without Fe were synthesized to model basaltic glass compositions. Fe in the glass was mostly Fe(III) for enhancing interaction with siderophores, yet with small but significant amounts of Fe(II) (between 10% and 30% of iron). The prepared samples were submitted to abiotic alteration experiments in buffered (pH 6.4) diluted solutions of metal-specific ligands, namely oxalic acid (OA, 10 mM), desferrioxamine (DFA, 1 mM) or 2,2′-bipyridyl (BPI, 1 mM). Element release from the glass into the solution after short term alteration (maximum 1 week) was measured by ICP-OES, and normalized mass losses and relative release ratios (with respect to Si) were evaluated for each element in each experimental condition. The presence of organic ligands had a significant effect on the dissolution of both glasses. Trivalent metals chelators (OA, DFA) impacted on the release of Fe3+ and Al3+, and thus on the global dissolution of both glasses, enhancing all release rates and dissolution stoichiometry (release rates were increased up to 7 times for Al or Fe). As expected, the mostly divalent metal chelator BPI interacted preferentially with Ca2+, Mg2+ and Fe2+. This study thus allows to highlight the central roles of iron and aluminium in interaction with some organic ligands in the alteration processes of basaltic glasses. It thus provides a step toward understanding the biological contribution of this fundamental geological process.

International audience; Mechanical and conformational properties of type 1 fimbriae were evaluated on live bacterial cells by Single Molecule Force Spectroscopy (SMFS) and Dynamic Force Spectroscopy (DFS) in buffered solutions whose pH varied from 3 to 9. We evidenced that both fimbrial extension and fimbrial binding force to mannosylated-surface are modulated with changing the externally applied shear force and the solution pH. In particular, intertwined FimA-FimA and FimH-mannose interactions lead to a 5 to 25-fold decrease of the fimbrial unwinding for pulling rates larger than 10 μm/s and for pH values outside the range 5 to 7. In this pH range, the FimH-mannose binding force is maximal with a magnitude of -150-200 pN and the fimbriae extension reaches 8 μm. The enhancement of the FimH-mannose binding force at neutral pH, as evidenced from molecular AFM analyses, strongly correlates with an optimum in yeast agglutination detected at pH 5 to 7. The results reported in this work suggest that "catch bond effect" was negligible over the range of pulling rates tested, and both FimA-FimA and FimH-mannose interactions under given pH and external shear force conditions modify the ability of the bacteria to efficiently colonize host surfaces.

The aim of this paper is to study the effect of the chemical modification on the photocatalytic properties of TiO2. The TiO2 Degussa-P25 nanoparticles are chemically modified using the hydrophobic organosilane hexadecyltrichlorosilane (HTS). The samples are employed as catalysts for salicylic acid photocatalytic oxidation in water-ethanol mixtures. The kinetics of salicylic acid photodegradation is investigated as a function of ethanol content in water-ethanol mixtures and initial HTS concentrations. The results indicate that the HTS groups are not degraded during the photocatalytic process. The TiO2 grafted by HTS is more efficient than bare TiO2 for the photodegradation process in presence of ethanol. The photodegradation process follows first order kinetics and the apparent rate constant increases linearly with the initial HTS concentration (amount of HTS grafted).

The surface energetic heterogeneity of Aerosil OX50 silica is investigated before and after modification by the grafting of various amounts of hydrophobic hexadecyltrichlorosilane (HTS). A detailed study is conducted to obtain new insight into the grafting process using volumetric techniques based on molecular probing. The surface of the silica particles has been thoroughly characterized using classical N2 Brunauer–Emmett–Teller measurements and by low-pressure quasi-equilibrium volumetry using nitrogen and argon as probe molecules. The experimental data are analyzed using the derivative isotherm summation method in order to gain quantitative information on the specific surface area, the surface energy and the polarity of the bare and HTS-covered silica, in terms of adsorption energy sites and heterogeneity. The modification process is also studied by Fourier transform infrared spectroscopy (FTIR) and total carbon mass measurements performed on solid samples (TOC). The combination of these three techniques leads to a better description of organosilane grafting onto the particles. The bare silica surface appears energetically heterogeneous due to the use of 5 different adsorption sites to describe the low pressure adsorption results. The HTS molecules are mainly located on the polar high and medium energy domains. At the largest HTS coverage (2.1 µmol/m2), the surface becomes energetically homogeneous (one site of low energy) and fully apolar. The data obtained from the low-pressure gas adsorption have been employed to estimate the grafted organic content in contact with the gas. The surface coverages derived from volumetry analysis and TOC measurements are in acceptable agreement but some difference can be recognized. The discrepancy is discussed in terms of conformation of the HTS molecules at the solid surface. The proposed conformational changes are supported by the FTIR results.

Smectitic clays from the Sabga and Bana areas, western Cameroon were treated with sulfuric-acid solutions of various concentrations – 0.5, 0.7, 1.0 and 4.0 N – at 80°C for 2 h. The mineralogical, physicochemical and morphological characteristics of the samples treated were analysed using several techniques. The sulfuric acid caused structural modification of the dioctahedral smectite. The accessory minerals such as cristobalite, quartz, feldspars and anatase remained unaltered by the acid attack. The supernatant solutions after acid treatment contain Mg, Ca, K, Na, Si, Al and Fe as a result of partial dissolution of octahedral and tetrahedral cations. The activated clay samples exhibited a smaller cation exchange capacity (CEC) and the specific surface area (SSA) increased with increasing concentration of sulfuric acid, ranging from 65 to 134 m2/g for the sample from Bana and from 74 to 84 m2/g for the sample from Sabga. The different SSAvalues were affected by the relative abundance of smectite and cristobalite (SiO2/Al2O3 = 2.2 and 6.5, respectively, from Bana and Sabga). The activated clays from Bana and Sabga displayed interesting physicochemical and textural properties and can be considered as promising adsorbents for the bleaching of vegetable oils.

In view to evaluate an alternative local cheaper source for vegetable oil refiners, three cameroonian clays containing swelling (smectites) and non-swelling (kaolinite) clay minerals were treated with sulphuric acid solutions at concentrations of 1, 2, 4 and 8 N at 80 °C for 2 h. Their alteration and resulting products were characterized by XRD, FT-IR-spectroscopy, chemical analyses, along with TEM-EDS, nitrogen adsorption isotherms at 77 K, and compared with industrial bleaching earths. Acid treatment of Cameroonian clays leads to the classically observed cristallochemical and textural modifications. The plot of TEM-EDS data in Al 2 O 3 /SiO 2 and Fe 2 O 3 /Al 2 O 3 diagrams indicate that upon acid treatment, clay particles principally move towards the SiO 2 pole, consistent with the formation of an amorphous compound mainly siliceous as the result of acid activation. Concomitantly, a progressive decrease in cation exchange capacity (CEC) was observed with increasing sulphuric acid concentrations while both specific surface area and mesoporosity of the studied materials increase. Elemental analyses, X-ray and spectroscopy data reveal that acid activation affects both the octahedral and the tetrahedral sheets. The analysis of their reactivity shows that clays with high amounts of smectite are more sensitive to acid leaching than those with relative large kaolinite contents. Further, upon acid treatment, most trace and rare earth elements are leached, and the amount of toxic elements (e.g. Cd, Pb, Ni, Cu, As, Zn) in the by-products is low (

Surface properties of two goethites have been studied in order to compare the amount of acid surface sites and their distribution over the various surface domains. For this purpose, ammonia, pyridine and nitrogen were used as basic molecular probes. Calorimetry measurements of ammonia adsorption provided the image of the average surface acidity being moderate. This conclusion was supported by the moderate resistance of the adsorbed pyridine molecules to degassing conditions. Adsorption and desorption of pyridine prior to gaseous nitrogen adsorption resulting in masking/unmasking of acid surface sites on the goethite surface allowed confirmation of the acid character of the specific adsorption sites characterized by the high-energy adsorption of electron-donating molecular nitrogen. The amount of acid sites probed by nitrogen and ammonia were of the same order of magnitude but systematically higher for ammonia. The subsequent analysis of the argon and nitrogen derivatives of first-layer adsorption isotherm led to determine the distribution of {101} and {121} crystallographic faces and discuss the location of acid sites on these surface domains.

Three talc deposits were discovered at Ngoung, Lamal Pougue and Bibodi Lamal (Cameroon). They derived from ultramafic rocks and are enclosed in a Pan-African garnet and muscovite-bearing mica schist of the Yaounde series. The physico-chemical properties of these talc deposits have been investigated by different techniques including Scanning Electron and Transmission Microscopy (SEM and TEM), chemical analyses, X-ray diffraction (XRD), infrared spectroscopy, particle size analysis by laser diffraction and low temperature gas absorption–desorption. The mineralogical composition deduced from XRD is wide (talc + chlorite + tremolite ± anthophyllite ± chromite ±serpentine ± brucite ± magnesite ± dolomite), but due to the high talc contents (≈ 90%) the samples are close to monomineralic. SEM studies reveal that all talc deposits comprise bundles of platy talc and a few prismatic crystals of amphiboles and other contaminating minerals. Laser diffraction confirms the coarse particle size of the talc crystals. Mode values are as high as 105–170 μm (except two samples displaying 76 and 42 μm) and d50 ranges from 107 to 25 μm. The values of specific surface area measured by BET and t -plot methods range from 1 to 6 m 2 /g and are correlated with external specific surface area measured by laser diffraction. Discrepancies from the trend are due to the semi-crystalline texture of the samples and mostly to intra-crystalline structural defects revealed by TEM observations. In infrared spectra, specific absorption bands are distinguished for talc, chlorite, tremolite, carbonates, serpentine, brucite and water. Occasional substitutions in minerals led to a shift in some absorption bands. The chemical composition criteria important for most of the industrial applications such as ceramics and pharmaceutics are closely complied with in untreated samples from these deposits. In summary, high talc proportions, chemical compositions, platy morphology and coarse grain size of its crystals lead to the conclusion that the studied deposits are economically attractive. The data set of the present work is an important tool for choosing the beneficiation methods for specific applications.

The Lembo clay deposit occurs on orthogneiss, but it also comprises clays with litho-relicts of volcanic rocks. In this study, ten samples from two sites were investigated. The mineralogical compositions consisted of kaolinite + halloysite + illite + quartz + hematite + anatase ± rutile ± orthoclase ± sanidine ± magnetite ± maghemite ± goethite ± Ba-Al-Fe-phosphates ± carbonates ± sulphates. Kaolinite-halloysite and quartz are the prevailing minerals. Some volcanicderived clays contain Fe-rich kaolinite-halloysite (9.6–14.1 wt.% Fe2O3). The chemical compositions, colours and specific surface area (SSA) measurements reveal two groups of clays: one with a positive whiteness index (IB), small SSA and small Fe content, and the other showing a large SSA, negative IB and relatively large Fe contents. The compositions of the first group are close to those of clays from the Mayouom deposit (Cameroon), and from some European commercial kaolins used in ceramics. Relatively Fe-rich clay materials may conform to most formulations of earthen bricks. As a whole, the Lembo clay deposit comprises various compositions of kaolinitic clays, which may yield the opportunity for extensive application in ceramics.

Physicochemical properties of representative samples from talc deposits discovered at Pout-Kelle and Memel in Cameroon have been investigated using a variety of techniques. The data allow the study of the mineral crystal-chemistry, chemical and modal compositions, grain size distribution, textures and surface heterogeneity, and morphometric characteristics. As a result, we found that talc (platy or round, Fe-rich) prevails (65–90%) over Cr-chlorite (7–26%), halloysite, chromite, rutile, brucite and magnesite. Chemically, talc ores are made up of SiO2, MgO, Fe2O3 and minor Al2O3. Mode values range from 50 to 55 μm at Memel and from 30 to 90 μm at Pout-Kelle. Specific surface areas measured by BET and t-plot methods range from 1.3 to 2.5 m2/g. The large values of morphometric characteristics are indicative of high crystallinity and platiness. Potential uses of these talc ores in the rubber, plastics and paper industries require beneficiation processes. Interestingly, the Memel deposit and most zones of the Pout-Kelle deposit are free of needle-shaped crystals, an advantage for environmental safety.

International audience; In order to better understand the possible interactions between steel canisters and a claystone host rock, in this case the Callovo-Oxfordian rock (COx), the present study investigated in detail, under conditions relevant to high-level radioactive waste repositories (anoxic conditions, temperature of 90°C), the reactions between metallic iron and: (1) COx; (2) the clay fraction extracted from COx (CF); and (3) mixtures of CF with quartz, calcite, or pyrite. Batch experiments were then carried out in the presence of NaCl-CaCl2 background electrolyte, for durations of 1, 3, and 9 months. Solid and liquid end-products were characterized by a combination of techniques including liquid analyses, transmission and scanning electron microscopies, X-ray diffraction, N2 adsorption at 77 K, and Mössbauer spectroscopy. The interaction between CF and metallic iron appeared to proceed by means of pathways similar to those illustrated in previous studies on interactions between metallic iron and purified clays. In spite of the many similarities with previous studies, significant differences were observed between the behavior of COx and CF, particularly in terms of pH and Eh evolution, iron consumption, chemical composition of the neoformed particles, and textural evolution. Such differences demonstrate the important role played by non-clay minerals in reaction pathways. The addition of carbonates or pyrite to CF did not lead to significant change in reactivity. In contrast, under the conditions used in the present study, i.e. for relatively low iron:clay ratios, the presence of quartz strongly influenced reaction pathways. In the presence of quartz, magnetite was observed only in trace abundances whereas the amounts of magnetite were significant in experiments without quartz. Furthermore, filamentous serpentine particles with a small Al:Si ratio appeared which could develop from an FeSiAl gel that only forms in the presence of quartz. Considering that most clay rocks currently being considered for radioactive waste disposal contain significant amounts of quartz, the results obtained in the present study may be of significant interest for predicting the long-term behavior of clay barriers in such sites.

International audience; Bactericidal effects of NP-TiO2 under dark condition are still the subject of debate. As an example, some authors found that NP-TiO2 have no effect on the laboratory model strain E. coli while others found for this strain EC50 values differing from 10 magnitude orders. Such contradictory results may be explained by multiple causal factors, including differences in the intrinsic characteristics of NP-TiO2 and bacterial cells used in these studies, exposure conditions for toxicity assessment and even the method used to assess the toxicity, the latter being often inappropriate for nanoparticle toxicity assessment. Increasing knowledge about exposition parameters which trigger NP toxicity and associated molecular mechanisms would contribute to properly evaluate and predict NP effects/fate in the environment.In our study, analysis of the interactions between nanoparticles (NPs) and bacteria highlighted the paramount role played by interfacial electrostatic interactions (NP-cell vs. NP-NP interactions) in determining the extent of NP toxicity and the importance of physico-chemical parameters such as pH and ionic strength in controlling these interactions. In condition of interaction, we showed that nanoparticles causes E.coli membrane depolarization and loss of membrane integrity leading to higher cell permeability. A transcriptomic analysis highlighted that deregulated genes are involved in the response to osmotic stress, metabolism of various cell envelope components and the uptake/metabolism of other endogenous and exogenous compounds. In addition, a significant number of deregulated genes encode proteins localized in the membrane and periplasmic space. All in all, results indicate that the primary effect of NP-TiO2 is initiated at the cell envelope level (membrane depolarization, loss of integrity) triggering an osmotic stress response in bacteria. These results are supported by the observed massive leakage of intracellular K+/Mg2

The interaction of biomolecules at the mineral–water interface could have played a prominent role in the emergence of more complex organic species in life’s origins. Serpentinite-hosted hydrothermal vents may have acted as a suitable environment for this process to occur, although little is known about biomolecule–mineral interactions in this system. We used batch adsorption experiments and surface complexation modeling to study the interaction of l -aspartate onto a thermodynamically stable product of serpentinization, brucite [Mg(OH) 2 ], over a wide range of initial aspartate concentrations at four ionic strengths governed by [Mg 2+ ] and [Ca 2+ ]. We observed that up to 1.0 μmol of aspartate adsorbed per m 2 of brucite at pH ∼ 10.2 and low Mg 2+ concentrations (0.7 × 10 −3 M), but surface adsorption decreased at high Mg 2+ concentrations (5.8 × 10 −3 M). At high Ca 2+ concentrations (4.0 × 10 −3 M), aspartate surface adsorption doubled (to 2.0 μmol m −2 ), with Ca 2+ adsorption at 29.6 μmol m −2 . We used the extended triple-layer model (ETLM) to construct a quantitative thermodynamic model of the adsorption data. We proposed three surface reactions involving the adsorption of aspartate (HAsp − ) and/or Ca 2+ onto brucite: 2 > SOH + H + + HAsp - → SOH 2 + > SAsp - + H 2 O, > SOH + HAsp - + Ca 2 + → SO - _ Ca ( HAsp ) + + H + , and > SOH + Ca 2 + + 2 H 2 O → SOH 2 + _ Ca ( OH ) 2 + H + . We used the ETLM to predict that brucite particle surface charge becomes more negative with increasing [Mg 2+ ], creating an unfavorable electrostatic environment for a negatively-charged aspartate molecule to adsorb. In contrast, our addition of Ca 2+ to the system resulted in Ca 2+ adsorption and development of positive surface charge. Our prediction of surface speciation of aspartate on brucite with Ca 2+ revealed that the calcium–aspartate complex is the predominant surface aspartate species, which suggests that the increase in aspartate adsorption with Ca 2+ is primarily driven by calcium adsorption. The cooperative effect of Ca 2+ and the inhibitive effect of Mg 2+ on aspartate adsorption onto brucite indicate that serpentinite-hosted hydrothermal fluids provide an ideal environment for these interactions to take place.

Textural and energetic proprieties of kaolinite were studied by low-pressure argon adsorption at 77 K. The heterogeneity of four kaolinites (two low-defect and two high-defect samples) modified on their surface by cation exchange with Li+, Na+, or K+ was studied by DIS analysis of the derivative argon adsorption isotherms. The comparison between the derivative adsorption isotherms shows that the nature of the surface cation influences the adsorption phenomena on edge and basal faces. In the case of basal faces, two adsorption domains are observed: for the first one, argon adsorption is slightly sensitive to the nature of the surface cation; for the second one, argon adsorption energy depends on the nature of surface cation suggesting their presence on theoretically uncharged basal faces. This study also shows that the shape of elementary particles, as derived from basal and edge surface areas, changes with the nature of cation. This anomalous result is due to the decrease of edge surface area with increasing the size of the cation. This surface cation dependence can be accounted for the area occupied by the edge surface cations in the first argon monolayer.

Noble gases trapped in meteorites are tightly bound in a carbonaceous carrier labeled “phase Q.” Mechanisms having led to their retention in this phase or in its precursors are poorly understood. To test physical adsorption as a way of retaining noble gases into precursors of meteoritic materials, we have performed adsorption experiments for Ar, Kr, and Xe at low pressures (10−4 mbar to 500 mbar) encompassing pressures proposed for the evolving solar nebula. Low-pressure adsorption isotherms were obtained for ferrihydrite and montmorillonite, both phases being present in Orgueil (CI), for terrestrial type III kerogen, the best chemical analog of phase Q studied so far, and for carbon blacks, which are present in phase Q and can be considered as possible precursors. Based on adsorption data obtained at low pressures relevant to the protosolar nebula, we propose that the amount of noble gases that can be adsorbed onto primitive materials is much higher than previously inferred from experiments carried out at higher pressures. The adsorption capacity increases from kerogen, carbon blacks, montmorillonite to ferrihydrite. Because of its low specific surface area, kerogen can hardly account for the noble gas inventory of Q. Carbon blacks in the temperature range 75 K-100 K can adsorb up to two orders of magnitude more noble gases than those found in Q. Irreversible trapping of a few percent of noble gases adsorbed on such materials could represent a viable process for incorporating noble gases in phase Q precursors. This temperature range cannot be ruled out for the zone of accretion of the meteorite precursors according to recent astrophysical models and observations, although it is near the lower end of the temperatures proposed for the evolving solar nebula.

Relationships between structural parameters of MnO2 and their surface properties at the solid–gas interface were investigated. The studied series ranged from ramsdellite to pyrolusite and encompassed disordered γ-MnO2 samples. The structural model used takes into account structural defects: Pr (rate of pyrolusite intergrowth in the ramsdellite network) and Tw (rate of microtwinning). Analysis of the N2 adsorption isotherm evidenced positive correlations between specific surface area and Tw for γ-MnO2 only and between the energetic constant C and (1-Pr). No microporosity is evidenced. Water adsorption isotherms evidenced the dependence of the H2O monolayer volume on Tw and showed a positive correlation between the cross-section area of water molecules adsorbed in the first monolayer and Pr, ranging from 13.5 A2 for Pr=1 to 6.3 A2 for Pr=0.2 (12 sites/nm2). Energetic heterogeneity is quantified from Ar and N2 low-pressure adsorption isotherms with the DIS procedure and correlated with H2O adsorption. High-energy adsorption domains are quantified and assigned to the different crystal faces: (110) faces with a common 1×1 octahedra layer of pyrolusite and ramsdellite and the (001) face of ramsdellite with 2×2 octahedra on which channels and plateaus are differentiated. The specific surface area ratio of ramsdellite high-energy sites to total ramsdellite content is shown to depend on Tw. The dependence on microtwinning of low cross-sectional area of N2 and much lower cross-sectional of residual H2O molecules leads us to assume that their adsorption sites on grain boundaries are represented by the twin planes between the structured nanocrystals generated by oxygen evolution during MD synthesis.

International audience; Because relatively little information about the crystal-growth process of smectite is available, the process was assessed here by studying the size and shape of nontronite particles synthesized at six different temperatures from 75 to 150 degrees C over a period of 4 weeks.The morphology of nontronites was studied using low-pressure isotherms of argon adsorption at 77 K, a method which enables the measurement of the basal and edge surface areas of the nontronite particles and of their mean diameter and thickness. During the crystal growth of nontronite, the mean particle length increased whereas their thickness (and the number of stacked layers) did not vary significantly.A specific two-dimensional crysial-growth process Was observed for smectite via the lateral extension of the layers. This process also appears to occur during the growth of neoformed natural smectite.

International audience; This paper addresses the surface modification of TiO2 nanoparticles with n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) using various initial aminosilane concentrations. The main objective of this article is to show experimentally the importance of the physisorption during the grafting process. The distinction between chemisorbed and physisorbed aminosilane molecules on TiO2 is thoroughly analyzed. The surface of bare and modified TiO2 particles has been characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) to gain a better understanding of the adsorption mechanism of AHAPS on TiO2. Quantitative information on surface energy of TiO2, in terms of adsorption energy sites and heterogeneity, has been investigated by quasi-equilibrium low-pressure adsorption technique using nitrogen and argon as probe molecules. The FTIR and XPS data are combined to estimate and discuss the chemisorbed and physisorbed contribution. The results demonstrate that both physisorption and chemisorption occurs but they display a different behavior. The physisorbed amounts are much higher than the chemisorbed amounts. This shows that the main part of the adsorbed layer is composed of physisorbed molecules. The physisorbed uptake depends highly on the AHAPS concentration while the chemisorbed amount remains constant. Quasi-equilibrium Ar derivative adsorption isotherms reveal that the AHAPS molecules are mostly located on the {101} and {001} faces of titania and that the two faces display the same reactivity toward AHAPS sorption. Nitrogen adsorption experiments show that the sorption takes place on the three polar surface sites of high energy. The molecules are chemisorbed onto the site displaying the highest energy while they are physisorbed on the two lower energy sites.

International audience; Al-Fe oxyhydroxy co-precipitates were synthesised by forced hydrolysis of Fe(NO3)(3)center dot 9H(2)O and Al(NO3)(3)center dot 9H(2)O solutions. Solids containing 0, 1, 10, 25, 50, 75, 90 mol% Al were characterised for composition, texture, mineral structure and local atomic environment. Cation substitution in the hydrous oxides was not observed. The solids consisted of hydrous ferric oxide (HFO) nuclei surrounded by Al-hydroxide. Below 50 mol% Al, unit particle size, high specific surface area and microporosity of HFO were preserved. Al-K-edge XANES showed ordered arrangements of Al-octahedra suggesting that some Al bound specifically to HFO surface sites. Above 50 mol%, Al precipitated in multiple layers around the nuclei and also as individual entities. The HFO nuclei exhibited the general characteristics of a 2-line ferrihydrite. However, as Al increased, the structure was slightly modified. While the symmetry of the FeO6 octahedra improved, the number of Fe-Fe linkages decreased, suggesting less polymerisation. An organisation of the Fe-octahedra, faintly resembling akaganeite, was expressed in Raman spectra. These changes in HFO structure were attributed to hindrance in the progressive olation/oxolation of the primary Fe-hydroxypolymers, caused by Al bound to the surface of nuclei. The presence of nitrate is suspected to have favoured the structural changes.

International audience; The knowledge about interfacial energy interactions and surface free energy is necessary for understanding and modeling many surface and interface processes. The aim of this paper is to study the effect of the chemical modification on the surface free energy components of Aerosil OX50. This fumed silica is chemically modified using the hydrophobic organosilane hexadecyltrichlorosilane (HTS). The modification process is studied by Fourier transform infrared spectroscopy (FTIR) and total carbon mass measurements performed on solid silica samples. The combination of these two techniques allows the determination of the adsorption isotherm of HTS onto silica showing the formation of a plateau for an initial concentration of 3 mM. The quantity adsorbed of HTS at maximum coverage is 2.14 mu mol/m(2). However, the chemical modification does not elaborate a compact layer. The HTS density is approximately 1.2 molecules/nm(2) which is close to the density of hydroxyl groups on the surface. A recent method, developed by Chibowski and Perea-Carpio, based on imbibition of probe liquids into a thin porous layer (capillary rise), is used for the determination of the surface free energy components. The surface free energy decreases continuously from 54.2 mJ/m(2) for bare silica to 46.7 mJ/m(2) for silica treated at an initial concentration of 4 mM following a linear diminution of gamma(s) with the HTS adsorbed amount. The apolar Lifshitz-van der Waals component gamma(LW)(s) is reduced from 41.1 mJ/m(2) to 35.8 mJ/m(2). The electron-donor parameter gamma(-)(s) drops from 53.9 mJ/m(2) to 27.5 mJ/m(2) while the electron-acceptor parameter gamma(+)(s) remains roughly constant (1 mJ/m(2)). Trends in the surface free energy components are notably linked to observations in infrared spectra and give additional information about the structure of the HTS layer.

International audience; The objective of this study is to determine the morphological properties of vermiculite particles obtained by sonication followed by separation into different size fractions (0.1-0.2, 1-2 and 10-20 mu m). These size fractions were chosen because they represent the wide range of particle sizes encountered in natural media. As previously reported, the crystal-chemistry of this vermiculite from Santa Olalla (Huelva, Spain) was found to be unaffected by the sonication process, although a loss of crystallinity and an increase in structural disorder might have occurred for the finest fraction. Using low-pressure argon adsorption analyses and a suite of microscopy techniques (i.e., atomic force, optical and transmission electron microscopy), the geometrical properties of the particles, including the distribution of the basal and lateral surfaces and aspect ratios, were obtained. Good agreement was observed between the gas adsorption experiments when applying the derivative isotherm summation procedure and the atomic force or optical microscopy analyses. However, the surface area was overestimated by transmission electron microscopy, which was attributed to the sample preparation technique. All of these data demonstrated that the particle aspect ratios are similar for all fractions, and the finest particles tend to show slightly more elongated surface morphologies than the coarser particles. Finally, a comparison of the distribution of lateral, basal and interlayer adsorption sites to the experimental cation-exchange capacity (CEC) showed that only the basal and interlayer sites are available in the conditions of CEC analysis. Based on these findings, the pertinence of using these size fractions as models to better understand the interactions between swelling clay minerals and water/solutes is discussed.

International audience; The aim of this study was to provide new insight into the evaluation of the effect of the crystallinity, size, and morphology of TiO2-anatase nanopartides on their acid-base properties at the solid liquid interface. This was achieved through monitoring the evolution in the surface charge density with the solution acidity and point of zero net proton charge (PZNPC) for a set of anatase nanoparticles with a mean size in the 5-20 nm range and various shapes. Different anatase nanoparticles were obtained by a sol-gel synthesis approach using different precursors, pH conditions, and various inorganic or organic additives. The measured PZNPC values were found to vary more than one pH unit depending on the degree of crystallinity and presence of differently exposed surfaces. To discriminate slight differences in the surface reactivity at the solid-water interface, high-resolution titration curves of surface charge for each anatase sample were recorded, and a fine analysis by the titration derivative isotherm summation (TDIS) method and proton affinity distributions (PADs) was performed. They provided accurate data on the strength (pK position) of various local domains of proton adsorption with their relative surface contributions in relation with the particle morphology. The increase in the proportion of sites that are more present on the {101} faces or that of medium acid sites largely present on the {100} faces shifted the point of zero net proton charge to more acidic pH values for particles possessing a majority of such surfaces. In addition to these experiments, the relative acidity of the surface sites on the different surfaces of anatase was evaluated with the multisite complexation model (i.e., MUSIC model) applied to the theoretically optimized surfaces, and a comparison was drawn.

International audience; The interaction between metallic iron and kaolinite was studied in conditions relevant to those that may be encountered in a high-level radioactive waste disposal facility in geological formation. Experiments were carried out under anoxic atmosphere at 90 C and in chloride solutions to simulate conditions close to disposal facilities. KGa-2 kaolinite was put in contact with powdered metallic iron in batch experiments for durations of 1, 3, and 9 months. Solutions extracted from the end-products were analyzed (pH, Eh, conductivity, and cation concentrations). End-products were characterized by a set of chemical (oxide analyses, CEC, EDXS) and mineralogical techniques (SEM, TEM, XRD, and FTIR), textural analyses (nitrogen adsorption and low-pressure argon adsorption), XPS, and Mossbauer spectroscopy. In another set of experiments the system was changed from anoxic to oxic conditions to evaluate the stability of the system in the presence of O-2.The interaction between metallic iron and kaolinite led to a fast initial reaction as major modifications took place during the first month. The partial oxidation of metallic iron resulted in a pH increase and negative Eh values. Iron was not found in solution but in two new Fe-rich phases: magnetite in very low amounts and a Fe-rich clay phase, belonging to the berthierine family. The Si and Al of the berthierine are derived from the partial alkaline dissolution of kaolinite, mostly along edge faces. TEM-EDXS local analyses showed that the composition of resulting particles consisted in mixtures of berthierine and kaolinite layers. Clay particles became thicker with the epitaxial growth of berthierine layers on the basal surfaces of pristine kaolinite.Neoformed berthierine was not stable in the presence of O-2 at 90 degrees C. Berthierine layers dissolved, iron was mobilized to form iron oxides and oxyhydroxides while kaolinite layers recrystallized from released Al and Si.

International audience; Various titanium dioxide nanoparticles were prepared by sol–gel method in order to obtain samples showing different sizes and morphologies. An original approach based on the adsorption of gaseous molecules from the gas phase was proposed to gain information about surface energy of nanosized TiO2 anatase in terms of interfacial reactivity and heterogeneity. Argon, nitrogen, and ammonia were selected as such surface molecular probes. The mainly observed crystallographic faces of anatase particles were the {101} and {001} surfaces together with the {100} one. Their abundance was correlated with the energy distribution inferred from the local isotherms of argon adsorption in the low-pressure range. The acid character of the anatase surface was probed by nitrogen molecules, and, consequently, the location of polar sites on the particle surface could be determined in correlation with the argon adsorption domains. Moreover, the number and the strength of surface acid sites were evaluated with the aid of two-cycle adsorption of gaseous ammonia supplemented by appropriate flow microcalorimetry measurements. This molecular probe revealed significant differences among the samples depending on their crystal shape or face distribution.

International audience; The effect of pH and Gibbs energy on the dissolution rate of a synthetic Na-montmorillonite was investigated by means of flow-through experiments at 25 and 80 degrees C at pH of 7 and 9. The dissolution reaction took place stoichiometrically at 80 degrees C, whereas at 25 degrees C preferential release of Mg over Si and Al was observed. The TEM-EDX analyses (transmission electronic microscopy with quantitative chemical analysis) of the dissolved synthetic phase at 25 degrees C showed the presence of newly formed Si-rich phases, which accounts for the Si deficit. At low temperature, depletion of Si concentration was attributed to incongruent clay dissolution with the formation of detached Si tetrahedral sheets (i.e., alteration product) whereas the Al behaviour remains uncertain (e. g., possible incorporation into Al-rich phases). Hence, steady-state rates were based on the release of Mg. Ex situ AFM measurements were used to investigate the variations in reactive surface area. Accordingly, steady-state rates were normalized to the initial edge surface area (11.2 m(2) g(-1)) and used to propose the dissolution rate law for the dissolution reactions as a function of Delta G(r) at 25 degrees C and pH similar to 9: r(mol m(-2) s(-1)) = 3.82 x 10(-12) [1 - exp(-8.23 x 10(-10)vertical bar Delta G(r)/RT vertical bar(5.47))].

The structural characterization of the composite film formed by physisorption of krypton on (0001) graphite pre-plated with a monolayer of cyclohexane has been performed by neutron and X-ray diffraction. The organization of the composite film predicted by means of volumetric measurements on a very uniform surface (exfoliated graphite) is mostly preserved on compressed exfoliated graphite (Papyex) used for diffraction experiments in spite of enhanced difficulties in reaching the adsorption equilibrium, resulting from the Papyex density. Krypton adsorption at 77 K results in the compression of the pre-adsorbed cyclohexane layer to its densest state, followed by its partial displacement and the formation of three-dimensional crystallites. The fraction of cyclohexane remaining in the adsorbed state is involved in a two-dimensional solution with krypton, of √3 x √3 commensurate structure. Beyond the first layer, krypton adsorbs on itself.

Krypton physisorption on (0001) graphite pre-plated with cyclohexane (C 6H12) also physisorbed has been studied between 71 and 83 K by means of classical volumetric methods. Krypton adsorption is strongly hindered by preadsorbed C6H12, and becomes significant at pressures definitely higher than on bare graphite. In the first layer range, a partial displacement of the preadsorbed C6H12 film by krypton adsorption, according to a first order phase transition process, was assumed, as well as 3D C6H12 crystallites formation and partial miscibility of the 2D phases. At higher coverages krypton adsorbs on itself.

In the context of the potential confinement of high-level radioactive wastes (HLW) within the clay engineered barrier system (EBS) in deep geological formations, the evolution of the retention properties of smectite when interacting with Fe(0) needs to be assessed. If some potential natural analogues describing iron–clay reactivity are easily found, metallic iron–clay interactions are poorly described in studies regarding the Earth. Therefore, experimental investigations are needed. Several parameters influence Fe(0)–clay interactions, such as temperature, the interlayer composition of swelling clays, and the presence of octahedral Fe 3+ , etc. From a geometrical point of view, it is thought that clay destabilization is mainly controlled by phenomena starting at the edge faces of the particles. In the present work, the rates of the smectite–Fe(0) reaction at 80 °C were assessed by XRD, Mossbauer, and CEC analyses for three smectites. The investigations show marked differences in the degree of stability, which cannot be explained by the crystal-chemistry rules established in previous studies. Therefore, the Fe(0)-smectite interactions were studied in view of textural and energetic surface quantitative analyses. The studied smectites have equivalent nitrogen BET-specific surface areas, equivalent argon edge surface areas and slightly different basal surface areas. This similarity in particle shape indicates that the edge surface area cannot be accounted for when explaining the observed differences in reactivity. However, a correlation is obtained between smectite reactivity and the energetic heterogeneity of its edge faces. This is interpreted in terms of a multiplication of the number of sites on the edge faces, where the electron transfer between Fe(0) and the smectite structure can occur.

The distribution of edge and basal surface areas of phyllosilicate particles is an essential parameter for understanding the interaction mechanisms at solid/gas or solid/liquid interfaces. Among the techniques proposed to determine the geometrical heterogeneities of flat solids, low pressure argon adsorption and AFM analysis are the most promising ones to derive the weight-averaged values of specific surface areas. A series of publications [1,2] have been recently dedicated to the combination of both methods showing the correlation between the two approaches. As the obtention of a large set of high resolution AFM images is time consuming it is necessary to test the ability of AFM routine analysis to derive systematically and statistically surface areas and aspect ratio, with all possible experimental and instrumental artefacts. In the present study, the expected agreement was found between AFM and argon adsorption determination for total, basal and edge specific surface areas of non swelling clay minerals, except for one kaolinite, which is very heterogeneous in sizes. In addition, it was observed that for a given sample, individual particles present similar shapes, whatever their size, allowing to derive statistical relationship between AFM basal and total surface areas. On the basis of the obtained results, recommendations are given to derive accurate edge, basal and total specific surface areas of phyllosilicates by combining conventional gas adsorption (nitrogen BET) and routine AFM techniques.

Short-range ordered aluminosilicates particles were synthesized on the basis of a sol–gel process with initial solutions containing decimolar concentrations of AlCl3 salts and Si alkoxide (tetraethyl ortho silicate) with varying Al/Si molar and hydrolysis OH/Al ratios. Transmission electron microscopy micrographs revealed more or less condensed aggregates displaying homogeneous elemental compositions, with Al/Si molar ratios ranging from 0.2 to 1.7. Owing to the high number of samples, a correlation could be drawn between microanalysis data and intensities ratios of vibrational bands centered around 960, 560 and 1060 cm−1. On the basis of final Al/Si ratios determined from vibrational spectra, textural properties, evidenced by nitrogen adsorption volumetry, could be rendered as a function of spherules composition. Indeed, it appeared that as Al/Si increases, allophane-like materials develop successively, macropores, mesopores and micropores, until Al/Si = 1.3. For Al-rich materials, Al/Si > 1.3, low surface area is developed. On the basis of theoretical values calculated from reported size and shape and assuming the conservation of structure upon Al/Si increase, experimental data could be interpreted as a continuous increasing condensation of particles leading to supplementary microporosity for Al/Si molar ratios ranging from 0.8 to 1.3, and for higher molar ratios, condensation of particles prevents nitrogen access.

Surface heterogeneity can be assessed by adsorption of different gaseous probes on solid materials. In the present study, four types of activated carbons were analyzed by classical N2 Brunauer-Emmett- Teller (BET) measurements and by low-pressure quasi-equilibrium volumetry (LPQEV) (Villie´ras, F.; Michot, L. J.; Bardot, F.; Cases, J. M.; Francüois, M.; Rudzinski, W. Langmuir 1997, 13, 1104). Three methods of data evaluation were applied: (a) the Frenkel-Halsey-Hill method for estimation of fractal dimensions from BET data, (b) the Horwath-Kawazoe method to calculate the pore size distribution from LPQEV Ar and N2 adsorption isotherms, and (c) the derivative isotherm summation (DIS) method to describe the solid's surface heterogeneity by a concept of local derivative isotherms. Similar Ar and N2 adsorption energy distributions were obtained on all carbons, which indicates the presence of mainly nonpolar surfaces. When adsorption was described by the van der Waals equation, the ratio between the interaction energy of different energetic sites with argon and nitrogen was 0.88. This value corresponded very well with a slope obtained when Ar and N2 positions of local isotherms by the DIS method were compared. This relationship has an important impact because it enables one to constrain the modeling of local isotherms. This study, besides the surface information, showed large possibilities of the DIS method for the surface analysis not only in terms of solid heterogeneity characterization but also in terms of polarity assessment.