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The surface charge of colloidal particles is usually determined by potentiometric titration. These acid-base titrations make it possible to measure the pH of point-of-zero charge (pzc) for oxide minerals. This macroscopic property is the most important parameter used in surface complexation modeling to reproduce experimental data. The pzc values of goethite reported in the literature vary between 7.0 and 9.5. Carbonate adsorption and/or surface morphology are thought to account for this wide range.We demonstrate a procedure for the removal of the carbonate ions that initially adsorb on goethite and strongly affect the titration curves and pzc determination. We also investigated the crystal-face-specific reactivity of two morphologically different goethites. The z-profiles obtained from atomic force microscopy (AFM) images showed that the goethite with the smallest specific surface area (S = 49 m2/g, denoted G49) exhibits 70% of the (001) face, whereas this value is only 30% for the goethite with largest specific surface area (S = 95 m2/g, denoted G95). This morphologic difference results in slightly different pzc values: 9.0 for G49 goethite and 9.1 for G95 geothite. These experimental pzc values have been correlated with multisite complexation calculations using both the full-site and the 1-pK approaches. We used the full-site approach to consider all of the configurations of hydrogen bond interactions with surface site. The resulting mean charges gave estimated pzc values of 8.9 and 9.2 for the (001) and (101) faces, respectively. Considering these theoretical pzc values for individual faces and the face distributions obtained from AFM analysis, the calculated pzc values are in full agreement with the experimental pzc values. However, this morphologic difference is more expressed in surface charge values than in the pzc values. Indeed, the surface charge of G49 goethite is much higher than that of G95 goethite, and the 1-pK calculations make it possible to fit the titration data satisfactorily. [Copyright &y& Elsevier]

Presents a study on the initial oxidation of pyrite surfaces in air using X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) and scanning tunneling microscopy. Comparison of valence-bond photoemission spectra for cleaned pyrite; Pyrite valence-band electronic structure; UPS valence-band spectra; XPS valence-band spectra.

Abstract: Adapting and combining specific biochemical and physical methods to investigate the properties of fat is the first step of an integrated approach conducted on fat-filled dairy powders, which have an economic and qualitative importance. The study includes the isolation, quantification and characterization of the free fat fraction, and the investigation of fat properties in situ in the powder. Free fat isolation is achieved by solvent extraction; the extracted fat can be quantified and further studied from thermal profile features by differential scanning calorimetry (DSC). Fat droplet sizes are investigated by laser light scattering: measurements are achieved on emulsions obtained after the rehydration of the powders. In situ methods mainly include investigation of the thermal properties by DSC, composition of the surface by X-ray photoelectron spectroscopy and qualitative observations by confocal laser scanning microscopy. After this study, reliable and connected methods are available (i) to quantify and locate the different types of fat within a powder particle and (ii) to investigate fat composition, structure and thermal properties. The need to combine several methods to conclude on a data set was demonstrated. [Copyright &y& Elsevier]

Abstract: X-ray photoelectron and Raman spectroscopies were used to investigate the chemical and the structural properties of thin diamond films synthesised by Plasma Assisted Chemical Vapour Deposition (PACVD). Continuous polycrystalline diamond films were grown under different plasma conditions and based on the combination of detailed XPS and Raman spectroscopic analysis two main topics are highlighted (i) the stress measurements were discussed by distinguishing clearly the chemical effects from the mechanical effects; (ii) an electronic gap at 2.7eV probed by Raman resonance that corresponds to an energy loss peak on the XPS carbon signal, was related to the surface hydrogenation. [Copyright &y& Elsevier]

The ability of mackinawite, an iron(II) monosulphide, to reduce Cr(VI) was studied at pH values of 5 and 7, Cr(VI) solution concentrations ranging from 10-4 to 6 × 10-3M and fixed ionic strength. Mackinawite suspensions (0.6gL-1 and 1.2gL-1) and Cr(VI) solutions were reacted for 4.5h in a nitrogen atmosphere. The oxidation of mackinawite was determined by analysing both solutions and solid phases after Cr(VI) reaction. The solid phases were characterised by using complementary electrokinetic measurements and X-ray Photoelectron Spectroscopy and by Transmission Electron Microscopy. Solutions were analysed using colorimetric methods for Fe(II) and Cr(VI) and capillary electrophoresis for sulphur speciation. Mackinawite was found to be a very effective reductant of Cr(VI) under the conditions of the experiments. The removal capacity was determined to be around 130mg Cr(VI)/g FeS at pH 7 and 240mg Cr(VI)/g FeS at pH 5. The presence of an iron(III) and chromium(III) (oxyhydr)oxide layer covering the mackinawite crystals was evidenced with a constant Cr to Fe ratio of 1.4 ± 0.2. The extent of the metal (oxyhydr)oxide layer increases with the initial Cr(VI) concentration, thus probably limiting the Cr(VI) reduction at high initial Cr(VI) concentrations. [Copyright &y& Elsevier]

In the goal of finding efficient scavengers for radioiodide in conditions (pH, pE) close to those encountered in deep geological sites, sorption of iodide ions on cuprous sulfide minerals (especially roxbyite, Cu1.75S) has been studied. Surface analysis by X-ray photoelectron spectroscopy has shown that commercial cuprous sulfides are covered by an oxidized overlayer (mainly in the form of CuSO4). Therefore, a synthetic procedure to get roxbyite (typically by mixing Na2S with an aqueous suspension of commercial Cu2O) was applied to produce pure samples with clean surfaces. Batch equilibration of cuprous sulfide particles suspended in aqueous solutions containing iodide species has revealed significant consumption of iodide. The sorption mechanism involves the formation of a surface complex via the exchange of surface hydroxyl groups by iodide anions, as highlighted by a transient pH increase during the immobilization process. Other copper and mixed copper–iron sulfides (e.g. CuS, CuFeS2), which are stable over wide pH and potential ranges are also likely to accumulate iodide species. Because of the specific interaction between iodide and copper(I) centers on the minerals, high distribution coefficients (>1000 ml/g) were observed. [Copyright &y& Elsevier]

Describes the chemical mechanisms governing transport and reduction of hexavalent chromium (Cr) in soils of a contaminated industrial waste landfill. Characterization of the metal pollution distribution in the groundwater of the industrial site; Determination of the bearing phases of Cr contamination in soil samples; Identification of the mechanisms responsible for chromium immobilization in soils.

Abstract: Biotite is a constituent Fe-bearing mineral of Delta subsoils in India and Bangladesh and has been hypothesized as a primary source of arsenic (As). The adsorption behavior of As onto structural Fe(II, III)-bearing biotite fractions (<50μm) was investigated in the pH range of 4–8 under a CO2-free, anoxic condition (O2 <1ppmv) using X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The batch experiments indicate that As adsorption is strongly pH dependent and that As(V) adsorbs more efficiently than As(III). X-ray Absorption Near-Edge Structure (XANES) spectra show no oxidation or reduction of As by biotite after reaction with As(III) or As(V) solutions for 3days. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic results suggest that As(III) forms bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C) surface complexes at pH 7.7 as indicated by average As–Fe bond distances at 3.00±0.02Å and 3.37±0.03Å respectively. The surface speciation retrieved by XPS does not provide any evidence of reduction of As(V) on biotite after 30days further confirming the thermodynamic prediction and the XANES results. This study has therefore significant environmental implications for As contaminated areas, where biotite retards the release of As into reducing groundwater. The changes in soil redox conditions and weathering of biotite may likely contribute to the occurrence of high As in groundwater. [ABSTRACT FROM AUTHOR]

The influence of surface-bound Fe(II) on uranium oxidation state and speciation was studied as a function of time (6 min-72 h) and pH (6.1-8.5) in a U(VI)-Fe(II)-montmorillonite (Ca-montmorillonite, MONT) system under CO2-free, anoxic (O2 <1 ppmv) conditions. The results show a rapid removal of U(VI) from the aqueous solution within 1 h under all pH conditions. U LIII-edge X-ray absorption near-edge structure spectroscopy shows that 96% of the total sorbed U(VI) is reduced at pH 8.5. However, the extent of reduction significantly decreases at lower pH values as specifically sorbed Fe(II) concentration decreases. The reduction kinetics followed by X-ray photoelectron spectroscopy during 24 h at pH 7.5 demonstrates the presence of partially reduced surface species containing U(VI) and U(IV). Thermodynamically predicted mixed valence solids like U3O8/β-U3O7/U4O9 do not precipitate as verified by transmission electron microscopy and extended X-ray absorption fine-structure spectroscopy. This is also supported by the bicarbonate extraction results. The measured redox potentials of Fe(II)/Fe(III)-MONT suspensions are controlled by the Fe(II)/hydrous ferric oxide [HFO(s)] couple at pH 6.2 and by the Fe(II)/lepidocrocite [γ-FeOOH(s)] couple at pH 7.5. The key finding of our study is the formation of a sorbed molecular form of U(IV) in abiotic reduction of U(VI) by sorbed Fe(II) at the surface of montmorillonite. [ABSTRACT FROM AUTHOR]

Vetiver roots have been utilized for the preparation of activated carbon (AC) by chemical activation with different impregnation ratios of phosphoric acid, X P (gH3PO4/g precursor): 0.5:1; 1:1 and 1.5:1. Textural characterization, determined by nitrogen adsorption at 77K shows that mixed microporous and mesoporous structures activated carbons (ACs) with high surface area (>1000m2/g) and high pore volume (up to 1.19cm3/g) can be obtained. The surface chemical properties of these ACs were investigated by X-ray photoelectron spectroscopy (XPS) and Boehm titration. Their textural and chemical characteristics were compared to those of an AC sample obtained by steam activation of vetiver roots. Classical molecules used for characterizing liquid phase adsorption, phenol and methylene blue (MB), were used. Adsorption kinetics of MB and phenol have been studied using commonly used kinetic models, i.e., the pseudo-first-order model, the pseudo-second-order model, the intraparticle diffusion model and as well the fractal, BWS (Brouers, Weron and Sotolongo) kinetic equation. The correlation coefficients (R 2) and the normalized standard deviation Δq (%) were determined showing globally, that the recently derived fractal kinetic equation could best describe the adsorption kinetics for the adsorbates tested here, indicating a complex adsorption mechanism. The experimental adsorption isotherms of these molecules on the activated carbon were as well analysed using four isotherms: the classical Freundlich, Langmuir, Redlich–Peterson equations, but as well the newly published deformed Weibull Brouers–Sotolongo isotherm. The results obtained from the application of the equations show that the best fits were achieved with the Brouers–Sotolongo equation and with the Redlich–Peterson equation. Influence of surface functional groups towards MB adsorption is as well studied using various ACs prepared from vetiver roots and sugar cane bagasse. Opposite effects governing MB and phenol adsorption mechanism on ACs are demonstrated. The various effects involved in adsorption mechanisms of each molecule are demonstrated. [Copyright &y& Elsevier]

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, and :inf loc="post">3. In order to fit sorption of silicic acid, the two following surface complexes, namely f loc="post">3SiO4, and , 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. [Copyright &y& Elsevier]

Abstract: Sorption of selenium(IV) and silicic acid onto magnetite (Fe3O4) 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 H4SiO4 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. [Copyright &y& Elsevier]

Abstract: The sorption of europium(III) species from EuCl3 solution at pH=5.4 onto dickite particles is investigated using spectroscopic methods. Thanks to the neutrality of phyllosilicate sheets of dickite, cation exchange is prevented. X-ray photoelectron spectroscopy reveals that chloride atoms probably remain in the ligand sphere of the europium(III) cation. The edge site-specific reactivity is evidenced by epifluorescence microscopy and Raman spectroscopy. Comparison between dickite/europium(III) samples rinsed or not with distilled water shows that the surface processes not only involve inner-sphere complex formation, but also either outer-sphere complex or surface precipitation. Raman spectra also indicate that europium(III) surface complexes are preferentially localised at the edge of tetrahedral silica sheets. [Copyright &y& Elsevier]

Sorption of H4SiO4 (including experiments as a function of time, Kd measurement with different m/v ratios and sorption edges) onto different iron (hydro)oxides as goethite (α-FeOOH), hematite (α-Fe2O3), and magnetite (Fe3O4) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namely ≡ FeH3SiO4 and ≡ FeH4SiO− 4, are needed to describe properly the experimental observations. [Copyright &y& Elsevier]

Abstract: The efficiencies of two methods of functionalizing single wall carbon nanotubes (SWCNTs) are compared, either through a radical addition of 4-methoxyphenylhydrazine hydrochloride by a classical thermally activated procedure, or via a microwave-assisted method. X-ray photoelectron spectroscopy and thermal gravimetric analysis clearly indicate the efficiency of both methods. Raman and absorption spectroscopy further confirm the functionalization and reveal the covalent nature of the bonds created at the carbon nanotube surface. For the microwave-assisted reaction, 5–15min is enough to functionalize the SWCNTs. Longer microwave exposure times reduce the functionalization yield and lead to a removal of groups which were bonded in a previous stage. An optimal choice of microwave irradiation time allows reducing the reaction time from days to minutes. [Copyright &y& Elsevier]

Abstract: We report a new SWNT functionalization method through 4-methoxyphenyl free radical addition. The 4-methoxyphenyl radicals are generated by air oxidation of 4-methoxyphenylhydrazine hydrochloride. Absorption and Raman spectroscopy show the covalent nature of the bond between the nanotubes and the functional groups. The XPS and TGA data furnish quantitative information on the degree of functionalization. [Copyright &y& Elsevier]

The aim of this study is to understand the sorption of tributyltin (TBT) onto natural quartz sand by classical batch experiments and spectroscopic surface analyses. At pH<6, the major species of TBT is the cation TBT+. Due to the presence of both the cationic part and the butyl chains, TBT should present amphiphilic properties. For concentrations lower than 40 μM, TBT sorption occurs as a homovalent 1:1 cation exchange between either H+ or Na+ and TBT+. The increasing affinity of TBT with respect to the different materials follows the series kaolinite≪natural sand. From XPS analyses, where the chemical environment of Sn did not change, indicating possible complete reversibility of the TBT sorption, it seems that inner-sphere surface complexes could be formed due to the increase in the 3d-level binding energy. At TBT concentrations higher than 100 μM, we showed by flotation experiments and XPS analysis that the surface becomes hydrophobic. After one monolayer was formed, the TBT sorption could thus be due to hydrophobic interaction between the butyl chains of the sorbed TBT and those of the TBT still available from the bulk solution. This mechanism is consistent with surface condensation and the shape of the sorption isotherm. [Copyright &y& Elsevier]

In the framework on a study of the acido-basic and sorption properties of iron oxides, a thorough characterization of two types of goethite powders was performed in several laboratories joined in a common project. Chemical analysis by ICPAES; high-resolution SEM, TEM, and AFM observations; XRD with line width analysis; and argon and nitrogen sorption isotherms were used for that purpose. The main crystallographic faces of goethite particles could be identified as {001}, {101}, and {121}, and their abundance correlated with the distribution of low-pressure argon adsorption local isotherms. These results will be very useful for further studies on the relationship between surface reactivity in aqueous solution and orientation of solid surfaces. [Copyright &y& Elsevier]

Tetragonal FeS 1− x mackinawite, has been synthesized by reacting metallic iron with a sodium sulfide solution and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), transmission Mössbauer spectroscopy (TMS) and X-ray photoelectron spectroscopy (XPS). Based on XRD and TEM analyses, synthetic mackinawite exhibits crystallization and is identical to the natural mineral. Unit cell parameters derived from XRD data are a = b = 0.3670 nm and c = 0.5049 nm. The bulk Fe:S ratio derived from the quantitative dispersive energy analysis is practically 1. XPS analyses, however, showed that mackinawite surface is composed of both Fe(II) and Fe(III) species bound to monosulfide. Accordingly, monosulfide is the dominant S species observed at the surface with lesser amount of polysulfides and elemental sulfur. TMS analysis revealed the presence of both Fe(II) and Fe(III) in the mackinawite structure, thus supporting the XPS analysis. We propose that the iron monosulfide phase synthesized by reacting metallic iron and dissolved sulfide is composed of Fe(II) and S(-II) atoms with the presence of a weathered thin layer covering the bulk material that consists of both Fe(II) and Fe(III) bound to S(-II) atoms and in a less extent of polysulfide and elemental sulfur. [ABSTRACT FROM AUTHOR]