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The exceptional physico-chemical properties of ionic liquids are exploited for the synthesis and catalytic application of heterometallic nanoparticles. Pt/Sn-based nanoparticles with 2-3 nm diameter are synthesized by chemical reduction of the metal salt precursors in the ionic liquid (i.e., methyltrioctylammonium bis(trifluoromethylsulfonyl)imide) using triethylborohydride as reducing agent. Investigations by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy suggest the formation of randomly alloyed Pt/Sn-based nanoparticles. The tin precursor and the platinum to tin ratio of the precursors are shown to influence the nature of the nanoparticles. The selective hydrogenation of cinnamaldehyde is used to probe the catalytic performance of the Pt/Sn nanoparticles, demonstrating the effect of tin alloying on the catalytic activity and selectivity to the α,β-unsaturated cinnamic alcohol. [ABSTRACT FROM AUTHOR]

A novel method was developed to synthesize air-stable zerovalent iron nanoparticles (hereafter nZVI) utilizing a radiation grafting technique. The nZVI were synthesized by borohydrate reduction of FeCl and stabilized on a radiation grafted copolymer matrix. Polyacrylic acid (PAA) grafted non-woven polyethylene/polypropylene (NWPE/PP-g-PAA) was used as the copolymer matrix and Co-60 γ-radiation was applied. The nZVI adsorbed NWPE/PP-g-PAA (hereafter nZVI-Ads-NWP) polymer composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), vibrational spectroscopy, scanning electron microscopy (SEM), Mössbauer spectroscopy, proton titrations, and zeta potential techniques. The SEM images showed that PAA was properly grafted onto the NWPE/PP fabric during irradiation and that the nZVI were well dispersed and stabilized on the fabric surface. Vibrational spectroscopy showed supplementary evidence for the proper grafting of PAA onto the base polymer and suggested a monodentate configuration as the primary interaction between the carboxylate groups of PAA and the nZVI surface. XRD, XPS, and Mössbauer analyses revealed core zerovalent iron with a shell mainly consisting of iron oxides. The pH and pH values of nZVI-NaCl suspensions were 7.3. Zeta potential and surface charge data were modeled using the 1-pK Stern layer model with two dissimilar sites for electrolyte and proton binding to account for the observed charge asymmetry. [ABSTRACT FROM AUTHOR]

Although the oxidative capacity of manganese oxides has been widely investigated, potential changes of the surface reactivity in dynamic anoxic/oxic environments have been often overlooked. In this study, we showed that the reactivity of layer structured manganese oxide (birnessite) was highly sensitive to variable redox conditions within environmentally relevant ranges of pH (4.0 – 8.0), ionic strength (0–100 mM NaCl) and Mn(II)/MnO 2 molar ratio (0–0.58) using ofloxacine (OFL), a typical antibiotic, as a target contaminant. In oxic conditions, OFL removal was enhanced relative to anoxic environments under alkaline conditions. Surface-catalyzed oxidation of Mn(II) enabled the formation of more reactive Mn(III) sites for OFL oxidation. However, an increase in Mn(II)/MnO 2 molar ratio suppressed MnO 2 reactivity, probably because of competitive binding between Mn(II) and OFL and/or modification in MnO 2 surface charge. Monovalent cations (e.g., Na+) may compensate the charge deficiency caused by the presence of Mn(III), and affect the aggregation of MnO 2 particles, particularly under oxic conditions. An enhancement in the removal efficiency of OFL was then confirmed in the dynamic two-step anoxic/oxic process, which emulates oscillating redox conditions in environmental settings. These findings call for a thorough examination of the reactivity changes at environmental mineral surfaces (e.g., MnO 2) in natural systems that may be subjected to alternation between anaerobic and oxygenated conditions. Surface-catalyzed oxidation of Mn(II) by dissolved oxygen controls the reactivity of nanostructured birnessite. [Display omitted] • Birnessite reactivity was highly sensitive to variable redox condition. • Surface-catalyzed oxidation of Mn(II) enabled formation of reactive Mn(III) sites. • Increase in Mn(II)/MnO 2 molar ratio suppressed MnO 2 reactivity. • Reactivity enhancement was observed in dynamic two-step anoxic/oxic process. • Oscillating redox conditions in environmental settings may affect contaminant fate. [ABSTRACT FROM AUTHOR]

Abstract: Cubic boron nitride (c-BN) coatings produced by PVD and PECVD techniques usually exhibit very high compressive stresses and poor adhesion due to intense ion bombardments of the growing surface that are mandatory during the formation of the cubic phase. Our previous investigations indicate, however, that a controlled addition of oxygen during film deposition can lead to a drastic reduction of the detrimental stress, yet having minor effect on the cubic phase content in the resulting low-stress, oxygen-containing c-BN:O coatings (as already confirmed by various analytical methods like X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and electron diffraction, and Fourier transform infra-red spectroscopy (FTIR)). This stress-reduction technique makes possible the deposition of well-adhered, superhard c-BN:O layer about 2 μm thick through magnetron sputtering on top of an adhesion-promoting base layer and via a compositional-graded nucleation process. In the present paper, we report on the atomic bonding structure relating in particular to the incorporated oxygen within such a thick c-BN:O coating using X-ray photoelectron spectroscopy (XPS). The c-BN:O top layer was found to consist of about 49.8 at% boron, 42.2 at% nitrogen, 5.5 at% oxygen, as well as small amounts of carbon (1.4 at%) and argon (1.1 at%). Because of the low oxygen concentration, it was difficult to categorize the bonding state of oxygen according to the XPS spectra of B 1s and N 1s elemental lines. However, the detailed results in terms of the O 1s spectrum strongly indicated that the lattice nitrogen of c-BN was partially replaced by the added oxygen. [ABSTRACT FROM AUTHOR]

Abstract: Uranium(VI) mobility in groundwater is strongly affected by sorption of mobile U(VI) species (e.g. uranyl, ) to mineral surfaces, precipitation of U(VI) compounds, such as schoepite (UO2)4O(OH)6·6H2O), and by reduction to U(IV), forming sparingly soluble phases (uraninite; UO2). The latter pathway, in particular, would be very efficient for long-term immobilization of U. In nature, Fe(II) is an important reducing agent for U(VI) because it frequently occurs either dissolved in natural waters, sorbed to matrix minerals, or structurally bound in many minerals. Redox reactions between U(VI) and Fe(II) depend not only on the availability of Fe(II) in the environment, but also on the chemical conditions in the aqueous solution. Under natural groundwater condition U(VI) forms complexes with many anionic ligands, which strongly affect its speciation. Carbonate, in particular, is known to form stable complexes with U, raising the question, if U(VI), when complexed by carbonate, can be reduced to UO2. The goal of this study was to find out if Fe(II) when structurally bound in a mineral (as magnetite, Fe3O4) or sorbed to a mineral surface (as corundum, Al2O3) can reduce U(VI) to U(IV) in the presence of . Batch experiments were conducted under anaerobic conditions to observe U removal from the aqueous phase by the two minerals depending on addition (1mM), U concentration (0.01–30μM) and pH value (6–10). Immediately after the experiments, the mineral surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) to obtain information on the redox state of U bound to the solid surfaces. XPS results gave evidence that U(VI) can be reduced both by magnetite and by corundum amended with Fe(II). In the presence of the amount of reduced U on the mineral surfaces increased compared to carbonate-free solutions. This can be explained by the formation of Fe(II) carbonates on the mineral surfaces which represent an easily available Fe(II) pool for the U(VI) reduction. A facilitated U(VI) reduction is also considered possible when U is present as a carbonate complex compared to non-complexed U (e.g. uranyl). [Copyright &y& Elsevier]

Pentavalent uranium compounds are key components of uranium‘s redox chemistry and play important roles in environmental transport. Despite this, well‐characterized U(V) compounds are scarce primarily because of their instability with respect to disproportionation to U(IV) and U(VI). In this work, we provide an alternate route to incorporation of U(V) into a crystalline lattice where different oxidation states of uranium can be stabilized through the incorporation of secondary cations with different sizes and charges. We show that iriginite‐based crystalline layers allow for systematically replacing U(VI) with U(V) through aliovalent substitution of 2+ alkaline‐earth or 3+ rare‐earth cations as dopant ions under high‐temperature conditions, specifically Ca(UVIO2)W4O14 and Ln(UVO2)W4O14 (Ln=Nd, Sm, Eu, Gd, Yb). Evidence for the existence of U(V) and U(VI) is supported by single‐crystal X‐ray diffraction, high energy resolution X‐ray absorption near edge structure, X‐ray photoelectron spectroscopy, and optical absorption spectroscopy. In contrast with other reported U(V) materials, the U(V) single crystals obtained using this route are relatively large (several centimeters) and easily reproducible, and thus provide a substantial improvement in the facile synthesis and stabilization of U(V). [ABSTRACT FROM AUTHOR]

Scale formation processes in the surface installations of geothermal power plants may have a negative effect on power plant performance. In addition, scales formed within the geothermal water circuit frequently accumulate natural radionuclides. Consequently, scale formation may lead to radiation dose rates, which are of radiological concern, and deposits, which may have to be disposed as radioactive waste. In order to minimize these problems and to foster geothermal power plant availability, it is of major interest to understand scale formation processes and to develop methods for their inhibition. One important pre-requisite towards this goal is a sound mineralogical and geochemical characterization of the formed material. Geothermal brines at sites in the Upper Rhine Graben are in general highly mineralized and become, upon cooling in the heat exchanger, supersaturated with respect to sulfate solid-solutions, e.g. (Ba,Sr)SO 4 , and other mineral phases. Some geothermal power plants very successfully tested the application of sulfate scaling inhibitors. Here we present mineralogical analyses of scale samples from geothermal power plants in the Upper Rhine Valley deposited in absence and presence of sulfate scaling inhibitors. Solid samples are investigated using wet-chemistry (after digestion), XRPD, SEM-EDX, XPS, EA-IRMS, Raman spectroscopy, and XANES (for explanation of abbreviations, see main text). Samples of scales deposited in the absence of a sulfate scaling inhibitor mainly consist of two phases. The largest part is made up of a barite type (Ba,Sr,Ca)SO 4 solid-solution. Traces of Ra occurring in the scaling are assumed to be incorporated in the barite type solid solution. Further minor phases are sulfide phases, either an X-ray amorphous nano-particulate phase or galena (PbS). Since the application of the sulfate inhibitor, sulfate minerals are no longer detectable in the scale samples. Subsequent scalings are Pb-dominated and consist mainly of galena (PbS), elemental lead (Pb), arsenic (As) and antimony (Sb). As and Sb are likely present as a nanocrystalline intermetallic mixed compound ((Sb, As) or Pb 3 (Sb,As) 2 S 3 ). The absence of barite-type minerals demonstrates the success of the application of the sulfate inhibitor. The precipitation of elemental Pb, As, and Sb, which are more noble than iron, may enhance the corrosion of mild steel pipes in the geothermal water circuit. Elution tests and oxidation of the scalings upon storage at atmospheric conditions demonstrate that proper disposal of the toxic heavy metal and metalloid containing scalings may be challenging. [ABSTRACT FROM AUTHOR]

This research specifically focused on the development of a novel methodology to reduce excess nitrate in drinking water utilizing zerovalent iron nanoparticles (nZVI)-stabilized radiation-grafted copolymer matrix. nZVI was synthesized by borohydrate reduction of FeCl3 and stabilized on acrylic acid (AAc)-grafted non-woven polyethylene/polypropylene (NWPE/PP-g-AAc) copolymer matrix, which was grafted using gamma radiation. The use of nZVI for environmental applications is challenging because of the formation of an oxide layer rapidly in the presence of oxygen. Therefore, radiation-grafted NWPE/PP synthetic fabric was used as the functional carrier to anchor nZVI and enhance its spreading and stability. The chemical reduction of nitrate by nZVI-adsorbed NWPE/PP-g-AAc (nZVI-Ads-NWP) fabric was examined in batch experiments at different pH values. At low pH values, the protective layers on nZVI particles can be readily dissolved, exposing the pure iron particles for efficient chemical reduction of nitrate. After about 24 h, at pH 3, almost 96% of nitrate was degraded, suggesting that this reduction process is an acid-driven, surface-mediated process. The nZVI-water interface has been characterized by the 1-pK Basic Stern Model (BSM). An Eley-Rideal like mechanism well described the nitrate reduction kinetics. In accordance with green technology, the newly synthesized nZVI-Ads-NWP has great potential for improving nitrate reduction processes required for the drinking water industry. [ABSTRACT FROM AUTHOR]

Mobility and bioavailability of radionuclides in the environment strongly depend on their aqueous speciation, adsorption behavior and the solubility of relevant solid phases. In the present context, we focus on naturally occurring Th-232 at a location in central Sri Lanka presenting high background radiation levels. Four different soil samples were characterized using X-ray Absorption Spectroscopy (XAS) at the Th L3-edge (16.3 keV), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy. X-ray Absorption Near Edge Structure (XANES) spectra are applied as a fingerprint indication for Th existing in different chemical environments. Linear combination fitting (LCF) of the Extended X-ray Absorption Fine Structure (EXAFS) data involving reference Th-monazite (phosphate) and thorianite (oxide) compounds suggested that Th is mostly present as Th-phosphate (76 ± 2%) and Th-oxide (24 ± 2%), even though minor amounts of thorite (silicate) were also detected by SEM–EDX. Further studies on selected individual particles using micro-focus X-ray Fluorescence (μ-XRF) and micro-X-ray Absorption Spectroscopy (μ-XAS) along with SEM–EDX elemental mapping provided information about the nature of Th-bearing mineral particles regarding mixed phases. This is the first study providing quantitative and XAS based speciation information on Th-mineral phases in soil samples from Sri Lanka. [ABSTRACT FROM AUTHOR]

The adsorption of Zn 2+ ions onto biogenic elemental selenium nanoparticles (BioSeNPs) was investigated. BioSeNPs were produced by reduction of selenite (SeO 3 2− ) in the presence of anaerobic granules from a full scale upflow anaerobic sludge blanket (UASB) reactor treating paper mill wastewater. The BioSeNPs have an iso-electric point at pH 3.8 at 5 mM background electrolyte concentration. X-ray photoelectron spectroscopy showed the presence of a layer of extracellular polymeric substances on the surface of BioSeNPs providing colloidal stability. Batch adsorption experiments showed that the uptake of Zn 2+ ions by BioSeNPs was fast and occurred at a pH as low as 3.9. The maximum adsorption capacity observed was 60 mg of zinc adsorbed per g of BioSeNPs. The Zn 2+ ions adsorption on the BioSeNPs was largely unaffected by the presence of Na + and Mg 2+ , but was impacted by the presence of Ca 2+ and Fe 2+ ions. The colloidal stability of BioSeNPs decreased with the increasing Zn 2+ ions loading on BioSeNPs (increase in mg of zinc adsorbed per g of BioSeNPs), corresponding to the neutralization of the negative surface charge of the BioSeNPs, suggesting gravity settling as a technique for solid–liquid separation after adsorption. This study proposes a novel technology for removal of divalent cationic heavy metals by their adsorption on the BioSeNPs present in the effluent of an UASB reactor treating selenium oxyanions containing wastewaters. [ABSTRACT FROM AUTHOR]

The concentrations of magnesium (Mg) and calcium (Ca) in natural aqueous environments are controlled by sorption and dissolution–precipitation reactions. Ca binding in calcareous soils depends on the degree of solution saturation with respect to CaCO3. Mg may be bound in precipitating calcite. Here, we investigated Mg incorporation into calcite via the recrystallization of vaterite, which simulates a very low supersaturation in a wide range of Mg to Ca ratios and pH conditions. Increasing the Mg to Ca ratios (0.2 to 10) decreased the partition coefficient of Mg in calcite from 0.03 to 0.005. An approximate thermodynamic mixing parameter (Guggenheim a0 = 3.3 ± 0.2), that is valid for dilute systems was derived from the experiments at the lowest initial Mg to Ca ratio (i.e., 0.2). At elevated Mg to Ca ratios, aragonite was preferentially formed, indicating kinetic controls on Mg partitioning into Mg-calcite. Scanning electron microscopy (SEM-EDX) analyses indicated that Mg is not incorporated into aragonite. The thermodynamic mixing model suggests that at elevated Mg to Ca ratio (i.e., ≥1) Mg-calcite becomes unstable relative to pure aragonite. Finally, our results suggest that the abiotic incorporation of Mg into calcite is only effective for the removal of Mg from aqueous environments like calcareous soil solution, if the initial Mg to Ca ratio is already low. [ABSTRACT FROM AUTHOR]

Reductive immobilization of 99Tc by a synthetic FeS 2 mixture, i.e. marcasite-pyrite 60:40, was studied by a combined approach of batch experiments and powder X-ray diffraction, X-ray photoelectron spectroscopy as well as Raman microscopy. It was found that the FeS 2 mixture removes 100% of Tc from the suspension after 7 days in contact at 6.0 < pH ≤ 9.0. The retention outside that pH range was slower and incomplete. Spectroscopic analysis showed that the redox active species at pH 6.0 is Fe2+ as expected from previous works with pyrite. However, at pH 10.0 the surprising oxidation of S2− to SO 4 2− was found responsible for Tc immobilization. This was explained by the high reactivity of marcasite that is easily oxidized to produce H 2 SO 4. Our work provides new molecular insights into the reductive mobilization of Tc(VII) by oxidative formation of sulfate. The assigned molecular reactions may also be relevant for the assessment of other redox reactive contaminants. Technetium re-oxidation experiments showed that the fast oxidation of marcasite is associated to the reduction of the remaining Tc(VII) in solution, which gives marcasite the potential of Tc natural remediation since it delays the re-oxidation of Tc(IV). [Display omitted] • Marcasite-pyrite mixture removes 100% of Tc(VII) at 6 < pH ≤ 9 after 7 days. • Retention is due to the reduction from Tc(VII) to Tc(IV). • Main redox sensitive species of the FeS 2 mixture are Fe2+ at pH 6 and S2− at pH 10. • Tc(IV) started to re-oxidize only after two months under ambient atmosphere. •Tc(VII) and solid elemental sulfur are final products of the re-oxidation. [ABSTRACT FROM AUTHOR]

Magnetite nanoparticles are a promising cost-effective material for the remediation of polluted wastewaters. Due to their magnetic properties and their high adsorption and reduction potential, they are particularly suitable for the decontamination of oxyanion-forming contaminants, including the highly mobile selenium oxyanions selenite and selenate. However, little is known how the remediation efficiency of magnetite nanoparticles in field applications is affected by partial oxidation and the formation of magnetite/maghemite phases. Here we characterize the retention mechanisms and capacity of partially oxidized nanoparticulate magnetite for selenite and selenate in an oxic system at different pH conditions and ionic strengths. Data from adsorption experiments showed that retention of selenate is extremely limited except for acidic conditions and strongly influenced by competing chloride anions, indicating outer-sphere adsorption. By contrast, although selenite adsorption capacity of oxidized magnetite is also adversely affected by increasing pH, considerable selenite quantities are retained even at alkaline conditions. Using spectroscopic analyses (XPS, XAFS), both mononuclear edge-sharing (2E) and binuclear corner-sharing (2C) inner-sphere selenite surface complexes were detected, while reduction to Se(0) or Se(–II) species could be excluded. Under favourable adsorption conditions, up to ~pH 8, the affinity of selenite to form 2C surface complexes is higher, whereas at alkaline pH values and less favourable adsorption conditions 2E complexes become more dominant. Our results demonstrate that magnetite can be used as a suitable reactant for the immobilization of selenite in remediation applications, even under (sub)oxic conditions and without the involvement of reduction processes. [Display omitted] • Oxidized magnetite can effectively remediate selenite contaminated wastewaters. • No reduction processes are required to remove large amounts of Se oxyanions. • Selenite immobilization is driven by formation of inner-sphere adsorption complexes. • Partially oxidized magnetite nanoparticles behave like maghemite phases. [ABSTRACT FROM AUTHOR]

This article reports results from two distinct, originally unrelated studies that show unexpected behavior with respect to sodium sulfate solutions in contact with flat surfaces. On the one hand, we investigated immersion freezing of sulfate containing solutions (target salt was CaSO4 and Na2SO4 was used as one control) in the presence of flat sapphire‐0001 crystals using second‐harmonic generation (SHG) spectroscopy. Further control experiments were carried out with neat water and CaCl2. The SHG signals from CaSO4 and Na2SO4 solutions behave somewhat differently from those recorded for the two other cases, the neat water and CaCl2. The common pattern shows a decrease of the SHG signal with decreasing temperature down to about −15°C, whereupon the signal sharply drops, indicating freezing. With the Na2SO4 solution, although the signal initially follows closely the neat water curve, the trend increases sharply at about −10°C followed by a gradual decrease with further cooling. There is no plausible explanation for the distinct behavior of the Na2SO4 solution, and thermodynamic calculations do not suggest any precipitation of a sodium sulfate solid phase. At the end of the freeze–thaw cycle, the initial SHG for each system is retrieved, suggesting reversibility. On the other hand, in a separate investigation unrelated to the freezing study, it was repeatedly observed that sodium sulfate precipitates from solution on flat steel surfaces at room temperature. As in the freezing experiments, thermodynamic calculations for the bulk solution solubility of sodium sulfate indicate that precipitates should not be forming under the conditions of the studies. The crystals observed on the steel samples have snowflake shapes similar to one literature report. We conclude that Na2SO4 in the presence of flat surfaces shows unexpected behavior that should incite further detailed studies in the future to elucidate the phenomenon. [ABSTRACT FROM AUTHOR]

• Technetium (Tc) is sorbed (6.5%) on γ-Al 2 O 3 NPs in absence of Fe2+ (binary system). • Tc removal highly enhances when Fe2+ is pre-sorbed on γ-Al 2 O 3 NPs (ternary system). • Tc uptake in the ternary system and the rate of the process increase with pH. • Tc removal enhances with pH and is complete for pH > 6.5 in the ternary system. • Hematite, Fe(II)-Al(III) LDH and magnetite, among others, form in the ternary system. Technetium (Tc) retention on gamma alumina nanoparticles (γ-Al 2 O 3 NPs) has been studied in the absence (binary system) and presence (ternary system) of previously sorbed Fe2+ as a reducing agent. In the binary system, γ-Al 2 O 3 NPs sorb up to 6.5% of Tc from solution as Tc(VII). In the ternary system, the presence of previously sorbed Fe2+ on γ-Al 2 O 3 NPs significantly enhances the uptake of Tc from pH 4 to pH 11. Under these conditions, the reaction rate of Tc increases with pH, resulting in a complete uptake for pHs > 6.5. Redox potential (Eh) and X-ray photoelectron spectroscopy (XPS) measurements evince heterogeneous reduction of Tc(VII) to Tc(IV). Here, the formation of Fe-containing solids was observed; Raman and scanning electron microscopy showed the presence of Fe(OH) 2 , Fe(II)-Al(III)-Cl layered double hydroxide (LDH), and other Fe(II) and Fe(III) mineral phases, e.g. Fe 3 O 4 , FeOOH, Fe 2 O 3. These results indicate that Tc scavenging is predominantly governed by the presence of sorbed Fe2+ species on γ-Al 2 O 3 NPs, where the reduction of Tc(VII) to Tc(IV) and overall Tc retention is highly improved, even under acidic conditions. Likewise, the formation of additional Fe solid phases in the ternary system promotes the Tc uptake via adsorption, co-precipitation, and incorporation mechanisms. [ABSTRACT FROM AUTHOR]

In this work we present the results of two spent nuclear fuel leaching experiments in simulated granitic groundwater, saturated with hydrogen under various pressures. The results show a large impact of the dissolved hydrogen already at 1 bar H 2 and room temperature on the release of both the uranium and of the fission products contained in the fuel matrix. Based on the results of this study and on published data with fuel from the same rod, the importance of the oxidative dissolution of spent fuel under repository conditions as compared to its non-oxidative dissolution is discussed. The XPS-spectra of the fuel surface before the tests and after long-term leaching under hydrogen are reported and compared to reduced UO 2 and SIMFUEL surfaces. The overall conclusion is that in spite of the unavoidable air contamination, hydrogen pressures of 1 bar or higher counteract successfully the oxidative dissolution of the spent nuclear fuel. The stability of the 4d-element metallic particles during fuel leaching under such conditions is also discussed, based on data for their dissolution. The metallic particles are also stable under such conditions and are not expected to release their component metals during long-term fuel leaching. [ABSTRACT FROM AUTHOR]

This study investigates the adsorption of americium and its chemical analogue europium on magnetite, which is expected to form as a major long-term steel canister corrosion product under anoxic and highly saline conditions. The sorption of europium on magnetite (solid/liquid ratio = 0.5 g/L) was investigated batch wise in NaCl brines with ionic strength I = 1 m , 3.5 m , and 6.67 m , as a function of pH m for two europium concentrations (6 × 10−10 m , 1.2 × 10−5 m). Information on the chemical nature of the surface species was obtained by X-ray absorption spectroscopy (XAS) at the americium L 3 -edge. Retention of europium by magnetite of >99.5% was found above pH m 6.4 for all ionic strengths for europium concentration of 6 × 10−10 m. No ionic strength effect was observed in this pH m range. At 1.2 × 10−5 m europium concentration, 95 ± 4% sorption was found above pH m 7.5 for I = 1 m and above pH m 8.0 for I = 3.5 m and 6.67 m. A small ionic strength effect was observed in this case. X-ray absorption spectroscopy (XAS) results are consistent with the batch sorption experiment outcomes, showing an insignificant effect of ionic strength on the pH m dependent sorption. Results from potentiometric titrations of the solid phase, batch sorption experiments and spectroscopy were interpreted consistently with a charge distribution multi-site (CD-MUSIC) triple layer surface complexation model assuming surface coordination of the metal ion via a tridentate binding mode. [ABSTRACT FROM AUTHOR]

The stainless steel AISI 309 S used for containers for vitrified high-level radioactive waste was exposed to 90 °C under highly saline and anoxic conditions for different exposure times up to 294 days. The surface damage was limited and no pitting could be detected. The corrosion layer is made of an inner-layer mostly of chromium (hydr)oxides and an outer-layer made of Fe- and Ni-based spinel compounds with admixed nickel (hydr)oxides. Minor contributions of magnetite and layered double hydroxide could be identified. Dissolved amounts of metal ions were very low, the pH increased only slightly and the redox potential decrease was limited. • Stainless steel AISI 309 S was exposed to highly saline anoxic solutions up to 343 days. • The surface attack after 294 days contact time at 90 °C was evaluated. • Synchrotron-based techniques with small beam footprint were applied for analyses. • The corrosion inner-layer consists of chromium (hydr)oxides, corroborated by XPS analysis. • The outer-layer is made of Fe and Ni spinel-type compounds and admixed Ni compounds. [ABSTRACT FROM AUTHOR]

Environmental and health hazards associated with the trace element selenium are mainly related to the presence of the highly mobile selenium oxyanions selenite and selenate (oxidation states IV and VI). In this study, we investigated the immobilization of dissolved selenite and selenate during the formation of magnetite in coprecipitation experiments based on the progressive oxidation of an alkaline, anoxic Fe2+ system (pH 9.2). Up to initial selenium concentrations of 10−3 mol L−1 (mass/volume ratio = 3.4 g L−1), distribution coefficient values (log Kd) of 3.7 to 5.1 L kg−1 demonstrate high retention of selenium oxyanions during the mineral formation process. This immobilization is due to the reduction of selenite or selenate, resulting in the precipitation of sparingly soluble selenium compounds. By X-ray diffraction analysis, these selenium compounds were identified as trigonal elemental selenium that formed in all coprecipitation products following magnetite formation. Time-resolved analysis of selenium speciation during magnetite formation and detailed spectroscopic analyses of the solid phases showed that selenium reduction occurred under anoxic conditions during the early phase of the coprecipitation process via interaction with iron(ii) hydroxide and green rust. Both minerals are the initial Fe(ii)-bearing precipitation products and represent the precursor phases of the later formed magnetite. Spectroscopic and electron microscopic analysis showed that this early selenium interaction leads to the formation of a nanoparticulate iron selenide phase [FeSe], which is oxidized and transformed into gray trigonal elemental selenium during the progressive oxidation of the aquatic system. Selenium is retained regardless of whether the oxidation of the unstable iron oxides leads to the formation of pure magnetite or other iron oxide phases, e.g. goethite. This reductive precipitation of selenium induced by interaction with metastable Fe(ii)-containing iron oxide minerals has the potential to influence the mobility of selenium oxyanions in contaminated environments, including the behavior of 79Se in the near-field of nuclear waste repositories. [ABSTRACT FROM AUTHOR]

Stainless steels coupons have been exposed to transuranic species in conditions representative of those found in a spent nuclear fuel reprocessing plant. Stainless steel was prepared to different surface finishes and exposed to nitric acid of varying concentrations containing 237 Np, 239 Pu or 243 Am for one month at 50 °C. Contamination by these transuranics has been observed on all surfaces exposed to the solution through the use of autoradiography. This technique showed that samples held in 4 M HNO 3 bind 2–3 times as much radionuclide as those held in 10.5 M HNO 3 . It was also found that the polished steel surfaces generally took up more transuranic contamination than the etched and “as received” steel finishes. The extent of corrosion on the steel surfaces was found, by scanning electron microscopy, to be greater in solutions containing Np and Pu in comparison to that observed from contact with Am containing solutions, indicating that redox activity of transuranics can influence the mechanism of stainless steel corrosion. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dominant interlayer growth of Fe0 NPs on 2:1 bentonite form B-nZVI (−ve charge). • Non-swelling 1:1 kaolinite with surface coverage of Fe0 NPs led to K-nZVI (+ve). • Preferential sorption of toxic cations on B-nZVI (63 mg/g) than K-nZVI (33 mg/g). • Higher removal of oxy-anions with K-nZVI (248 mg/g) than B-nZVI (149 mg/g). • Removal mechanisms were redox transformation, complexation and co-precipitation. In the current study, contrasting growth behaviour of redox sensitive Fe0 nanoparticles (nZVI) was observed on different clay surfaces i.e., 1:1 non-swelling kaolinite (K-nZVI) and 2:1 swelling bentonite (B-nZVI). Osmotic swelling of bentonite led to Fe0 nucleation and growth of 5–7 nm size particles in the broadened interlayer spaces. B-nZVI had negative zeta potential due to the domination of the surface charge of bentonite clay. In contrast, kaolinite has shown dominant surface growth of nZVI particles (>24.8 ± 7.4 nm) and positive zeta potential, suggesting domination of Fe0 nanoparticles (nZVI) characteristics. This surface-dependent variation led to higher and faster removal of oxy-anions with K-nZVI, i.e., chromium and arsenic (87.5 and 157.35 mg/g) than B-nZVI (18.4 and 86.9 mg/g). In comparison, B-nZVI has shown higher sorption of cations i.e., nickel and cadmium (36 mg/g and 46 mg/g) than K-nZVI (25 and 27 mg/g). XPS and pXRD analysis of reaction precipitates confirmed reductive sorption of chromium, co-precipitation/ complexation of arsenic, electrostatic attraction and complexation of nickel and cadmium as major removal mechanisms. Drastically higher total contaminant sorption capacities of B-nZVI (327 mg/g) and K-nZVI (372 mg/g) in multi-contaminant (Cr + As + Ni + Cd) solutions than individual capacities in mono-ionic solutions was due to co-operative effects and newer sites induced via sorption and redox-transformation of other ionic species. K-nZVI removed chromium and arsenic to below drinking water permissible limits whereas B-nZVI succeeded in separating nickel and cadmium to drinkable levels in groundwater, freshwater, river water, and wastewater samples, emphasizing their applicability in high cationic—low anionic and low cationic-higher anionic species contaminated waters, respectively. [ABSTRACT FROM AUTHOR]

Se is an essential nutrient at trace levels, but also a toxic environmental contaminant at higher concentrations. The mobility of the trace element Se in natural environments is mainly controlled by the occurrence of the highly soluble Se oxyanions – selenite [Se(IV)] and selenate [Se(VI)] - and their interaction with geological materials. Since iron oxides are ubiquitous in nature, many previous studies investigated Se retention by adsorption onto iron oxides. However, little is known about the retention of Se oxyanions during the formation process of iron oxides. In this paper, we therefore studied the immobilization of Se oxyanions during the crystallization of hematite from ferrihydrite. In coprecipitation studies, hematite was synthesized by the precipitation and aging of ferrihydrite in an oxidized Se(IV)- or Se(VI)-containing system (pH 7.5). Hydrochemical data of these batch experiments revealed the complete uptake of all available Se(IV) up to initial concentrations of c(Se) 0 = 10 −3 mol/L ( m / V ratio = 9.0 g/L), while the retention of Se(VI) was low (max. 15% of c(Se) 0 ). In case of high initial Se(IV) concentrations, the results also demonstrated that the interaction of Se with ferrihydrite can affect the type of the final transformation product. Comparative adsorption studies, performed at identical conditions, allowed a distinction between pure adsorption and coprecipitation and showed a significantly higher Se retention by coprecipitation than by adsorption. Desorption studies indicated that Se coprecipitation leads to the occurrence of a resistant, non-desorbable Se fraction. According to time-resolved studies of Se(IV) or Se(VI) retention during the hematite formation and detailed spectroscopic analyses (XPS, XAS), this fraction is the result of an incorporation process, which is not attributable to Fe-for-Se substitution or the Se occupation of vacancies. Se initially adsorbs to the ferrihydrite surface, but after the transformation of ferrihydrite into hematite, it is mostly incorporated by hematite. In systems without mineral transformation, however, Se remains as a sorption complex. In case of Se(VI), an outer-sphere complex forms, while Se(IV) forms a mixture of bidentate mononuclear edge-sharing and bidentate binuclear corner-sharing inner-sphere complexes. The results of this study demonstrate that incorporation of Se oxyanions by hematite is an important retention mechanism in addition to pure adsorption, which may affect the migration and immobilization of Se oxyanions in natural systems or polluted environments. [ABSTRACT FROM AUTHOR]

The interaction of Tc(VII) with crushed crystalline rock (Äspö diorite; 1–2 mm size fraction) from the Äspö Hard Rock Laboratory (HRL) (Sweden) was studied by laboratory batch sorption and desorption experiments under Ar atmosphere using both natural and synthetic groundwater. The Äspö diorite used in the experiments was drilled, transported and handled as far as possible under anoxic conditions to preserve the in-situ rock redox capacity. For comparison, identical experiments using artificially oxidized Äspö diorite have been carried out to examine the effect of in-situ redox capacity on Tc uptake. According to the batch studies, Tc(VII) uptake on the Äspö diorite is strongly dependent on redox capacity. Uptake on un-oxidized rock is approximately 2 times higher compared to oxidized rock samples, most likely due to higher Fe(II) contents of the un-oxidized rock. Tc redox states and speciation both on the mineral surface and in the bulk were studied using X-ray photoelectron spectroscopy (XPS) and Tc K-edge X-ray absorption near edge structure (XANES) spectroscopy. The spectroscopic results verify a Tc(VII) reduction to Tc(IV) at the rock surface. Distribution coefficients (K d ) and surface normalized distribution coefficients (K a ) were determined and compared to available literature data. The formation of a Tc colloidal phase was not observed under the geochemical conditions prevailing in the experimental studies. Desorption of Tc is very low under anoxic conditions, but after artificial oxidation Tc mobility is strongly increased. The results of this work clearly highlight the effect of in-situ rock redox capacity on Tc retention. [ABSTRACT FROM AUTHOR]

Uranium redox states and speciation in magnetite nanoparticles coprecipitated with U(VI) for uranium loadings varying from 1000 to 10000 ppm are investigated by X-ray absorption spectroscopy (XAS). It is demonstrated that the U M4 high energy resolution X-ray absorption near edge structure (HR-XANES) method is capable to clearly characterize U(IV), U(V), and U(VI) existing simultaneously in the same sample. The contributions of the three different uranium redox states are quantified with the iterative transformation factor analysis (ITFA) method. U L3 XAS and transmission electron microscopy (TEM) reveal that initially sorbed U(VI) species recrystallize to nonstoichiometric UO2+x nanoparticles within 147 days when stored under anoxic conditions. These U(IV) species oxidize again when exposed to air. U M4 HR-XANES data demonstrate strong contribution of U(V) at day 10 and that U(V) remains stable over 142 days under ambient conditions as shown for magnetite nanoparticles containing 1000 ppm U. U L3 XAS indicates that this U(V) species is protected from oxidation likely incorporated into octahedral magnetite sites. XAS results are supported by density functional theory (DFT) calculations. Further characterization of the samples include powder X-ray diffraction (pXRD), scanning electron microscopy (SEM) and Fe 2p X-ray photoelectron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

Environmental scientists and geoscientists working in different fields regard the reactivity of calcite and corresponding changes in its trace elemental- or isotopic composition from diametrically opposed points of view. As one extreme, calcite based environmental remediation strategies rely on the fast recrystallization of calcite and the concurrent uptake and immobilization of pollutants. Paleo-ecological investigations denote the other extreme, and rely on the invariability of calcite composition over geological periods of time. We use long-term radiotracer experiments to quantify recrystallization rates of seven types of calcite powder with diverse morphology and particle size distribution. On the one hand our results demonstrate the long-term metastability of calcite with equilibrated crystal surfaces even at isotopic dis-equilibrium. On the other hand, we document the extremely high reactivity and interfacial free energy of freshly ground, rough calcite. Our results indicate that bulk calcite recrystallization is an interfacial free energy driven Ostwald-ripening process, in which particle roughness effects dominate over the effect of crystal habitus and particle size. We confirm that the dynamic equilibrium exchange of crystal constituents between kink sites involves an activation barrier of about 25 kJ/mol. At room temperature the equilibrium exchange is limited to a near surface region and proceeds at a rate of (3.6 ± 1.4)·10-13 mol/(m²·s). [ABSTRACT FROM AUTHOR]

Palladium compounds (Pd(OAc) 2 and Pd(acac) 2 ) were dissolved in commercially available epoxy resins (glycidyl derivatives of bisphenol A and p -aminophenol) and the formulations were polymerized employing the ionic liquid 1-ethyl-2-methylimidazolium acetate (EMIM acetate) as polymerization initiator. Thus, palladium species could be incorporated in the network of the resulting polyether materials. Polymerization reactions were investigated by DSC and the curing behavior of different formulations was compared. High polymerization enthalpies were observed indicating high crosslinking in the materials. Accordingly, the materials exhibited high glass transition temperatures and thermogravimetric data revealed high thermal stability. Due to the good solubility of the palladium compounds in the epoxy resins, a widely homogeneous dispersion of palladium species in the polyether matrix could be realized. This was confirmed by SEM-EDX and TEM measurements. XPS measurements revealed that reduction of Pd(II) to Pd(0) species occurred during catalyst preparation and this was also proven by XRD. The materials were ground and successfully employed as catalysts for the hydrogenation of several alkenes under mild reaction conditions. High conversions and selectivities could be reached within a few hours at room temperature and moderate hydrogen pressure of 2.5 bar. Palladium leaching from the catalysts to reaction solutions was investigated. To determine very low quantities, metal concentrations were enriched by removal of volatile components. Subsequent ICP-AES measurements revealed low palladium contents in the range of a few μg. These amounts correspond to values around 0.007% with respect to palladium originally loaded on the polymer. Catalyst recycling experiments were also carried out and it was shown that the catalysts can be employed in numerous consecutive reactions without any catalyst treatment and without loss of activity. Within a series of reactions, palladium leaching decreased while catalytic activity was not affected. [ABSTRACT FROM AUTHOR]

In this article we introduce and compare three techniques for low-cost and rapid bonding of stereolithographically structured epoxy components to polydimethylsiloxane (PDMS). In short, we first create a polysiloxane layer on the epoxy surface via silane surface coupling and polymerization. Afterwards, the modified epoxy surface can be bonded to a PDMS component at room temperature using a handheld corona discharger, which is a commonly used low-cost technique for bonding two PDMS components. Using these methods bonds of desirable strength can be generated within half an hour. Depending on the epoxy resin, we found it necessary to modify the silanization procedure. Therefore, we provide a total of three different silanization techniques that allow bonding of a wide variety of stereolithographically structurable epoxy resins. The first technique is a UV-light induced silanization process which couples a silane that contains an epoxy-ring ((3-glycidoxypropyl)trimethoxysilane (GPTMS)). For surfaces that cannot be modified with this silane we use dimethoxydimethylsilane (DMDMS). This silane can either be coupled to the surface by a sol–gel process or UV-light induced polymerisation. The sol–gel process which is a heat induced surface modification technique results in high bond strengths. Because of the heat which triggers the sol–gel process, this technique is limited to epoxy polymers with high glass transition temperatures. For the majority of stereolithographically structured epoxy resins which typically have glass transition temperatures of around 60 °C the light-induced bonding technique is preferable. For all three techniques we performed DIN EN-conform tensile testing demonstrating maximum bond strengths of up to 350 kPa which is comparable with bond strengths reported for PDMS-to-PDMS bonds. For all bond methods, long-term stability as well as hydrolytic stability was assessed. [ABSTRACT FROM AUTHOR]

Neptunium (Np(V)) sorption onto a purified illite is investigated as a function of pH (3–10) and [Np V O 2 + ] tot (3 × 10 −8 –3 × 10 − 4 M) in 0.1 M NaCl under Ar atmosphere. After about one week reaction time, only insignificant variation of Np sorption is observed and the establishment of reaction equilibrium can be assumed. Surprisingly, solid–liquid distribution ratios (R d ) are clearly higher than those measured for Np(V) sorption onto illite under aerobic conditions. The observation that R d increases with decreasing pe (pe = −log a e − ) suggests partial reduction to Np(IV), although measured redox potentials (pe values) at a first glance suggest the predominance of Np(V). Reduction to Np(IV) at the illite surface could indeed be confirmed by X-ray absorption near-edge spectroscopy (XANES). Np speciation in presence of the purified Na-illite under given conditions is consistently described by applying the 2 sites protolysis non-electrostatic surface complexation and cation exchange model. Measured pe data are taken to calculate Np redox state and surface complexation constants for Np(IV) are derived by applying a data fitting procedure. Constants are very consistent with results obtained by applying an existing linear free energy relationship (LFER). Taking Np(IV) surface complexation constants into account shifts the calculated Np(V)/Np(IV) redox borderline in presence of illite surfaces by 3–5 pe units (0.2–0.3 V) towards redox neutral conditions. Our study suggests that Np(V) reduction in presence of a sorbing mineral phase is thermodynamically favored. [ABSTRACT FROM AUTHOR]

The interaction of lanthanides and trivalent actinides with borate in dilute to concentrated alkaline NaCl, MgCl2 and CaCl2 solutions was investigated at 22 ± 2 °C by a comprehensive series of solubility experiments with Nd(OH)3(am), and complemented with Cm(iii)–TRLFS studies (TRLFS: time resolved laser fluorescence spectroscopy) under analogous pH and ionic strength conditions. Although there was clear evidence of borate complexation in the pH range of 8.5 to 10, overall no significant increase in Nd(iii) solubility occurred in any of the investigated salt systems in the presence of [B]tot≤ 0.4 M, compared with analogous borate-free solutions. On the contrary, a significant decrease in Nd(iii) concentration was observed at pHc≤ 9 in NaCl and MgCl2 systems with [B]tot≥ 0.16 M (diluted salt systems) or [B]tot≥ 0.04 M (concentrated salt systems). This observation, together with a clear change in the slope of the solubility curve and the further confirmation by XPS analyses, indicates the transformation of Nd(OH)3(am) into a so far unknown Nd(iii)–borate solid phase with significantly lower solubility. Similar Nd(iii) concentrations in the aqueous phase are obtained in undersaturation solubility experiments conducted with a synthesized crystalline phase Nd[B9O13(OH)4](cr). TRLFS confirmed the formation of aqueous Cm(iii)–borate complexes in dilute to concentrated NaCl and MgCl2 systems at pHc = 8 and [B]tot≥ 0.04 M. Two different Cm(iii)–borate species are proposed based on the peak shift of the spectra, although the resulting fluorescence emission bands do not allow the definition of an unequivocal chemical model for this system. TRLFS also shows that no Cm(iii)–borate complexes form under hyperalkaline conditions (pHc = 12), due to the stronger competition posed by hydrolysis and the predominance of weakly coordinating B(OH)4− in the aqueous phase. These results show the impact of An(iii)–borate interactions on An(iii) speciation and highlight the hitherto unknown role of borate in the immobilization of trivalent actinides under repository-relevant conditions due to the formation of borate-bearing solid phases with significantly lower solubility than the corresponding hydroxides. [ABSTRACT FROM AUTHOR]

Materials matter in microfluidics. Since the introduction of soft lithography as a prototyping technique and polydimethylsiloxane (PDMS) as material of choice the microfluidics community has settled with using this material almost exclusively. However, for many applications PDMS is not an ideal material given its limited solvent resistance and hydrophobicity which makes it especially disadvantageous for certain cell-based assays. For these applications polystyrene (PS) would be a better choice. PS has been used in biology research and analytics for decades and numerous protocols have been developed and optimized for it. However, PS has not found widespread use in microfluidics mainly because, being a thermoplastic material, it is typically structured using industrial polymer replication techniques. This makes PS unsuitable for prototyping. In this paper, we introduce a new structuring method for PS which is compatible with soft lithography prototyping. We develop a liquid PS prepolymer which we term as “Liquid Polystyrene” (liqPS). liqPS is a viscous free-flowing liquid which can be cured by visible light exposure using soft replication templates, e.g., made from PDMS. Using liqPS prototyping microfluidic systems in PS is as easy as prototyping microfluidic systems in PDMS. We demonstrate that cured liqPS is (chemically and physically) identical to commercial PS. Comparative studies on mouse fibroblasts L929 showed that liqPS cannot be distinguished from commercial PS in such experiments. Researchers can develop and optimize microfluidic structures using liqPS and soft lithography. Once the device is to be commercialized it can be manufactured using scalable industrial polymer replication techniques in PS – the material is the same in both cases. Therefore, liqPS effectively closes the gap between “microfluidic prototyping” and “industrial microfluidics” by providing a common material. [ABSTRACT FROM AUTHOR]

Speciation and fate of radionuclides in environment are strongly dependent on their interaction with various mineral surfaces. Presence of impurity atoms in minerals modifies these interactions. 237Np, a long-lived component of nuclear high-level waste, is highly mobile in environment as neptunyl (NpO 2 +) cation. Role of impurities in defining its interaction with mineral surfaces present in natural and engineered systems is yet to be completely understood. Manganese is a ubiquitous impurity present in naturally occurring iron corrosion product, magnetite. Here, a series of manganese (Mn)-doped magnetites (FM) was synthesized and the evolution of solid-sorbed speciation of Np(V) was investigated as a function of Mn doping (3–11 wt%) in near neutral pH condition. Combining Mn K-edge and Np L 3 -edge X-ray absorption fine structure spectra with Np M 5 -edge high energy-resolution X-ray absorption near-edge structure spectra, we found nanoparticulate NpIVO 2 solid as the single speciation of Np sorbed on both doped and undoped magnetites. Without changing the surface speciation of Np, Mn-O sites did show preference for sorbing Np(V) vis-á-vis Fe-O sites. Mn participates through Fe(II)/Mn(III) redox couple in reducing sorbed Np(V). Its participation, however, becomes significant only when the doped-magnetite contains a critical minimum concentration (> 6 wt%) of Mn. This study highlights the significant role of impurity atom wherein it interacts with sorbing species through redox process. [Display omitted] • Single phase manganese-doped (3–12 wt%) magnetites were synthesized. • Neptunium(V) interaction with Mn-doped magnetites in neutral pH condition. • HR-XANES confirmed single speciation of Np on undoped and doped magnetites. • Mn-O sites participates through Fe(II)/Mn(III) redox couple in reducing Np(V). [ABSTRACT FROM AUTHOR]

The mechanism of selenium(IV) uptake by maghemite was investigated on both the macroscopic and the molecular level. Maghemite nanoparticles exhibited fast adsorption kinetics toward selenium(IV). Batch experiments showed a decreased sorption with increasing pH (3.5-11). Ionic strength variations (0.01 to 0.1 M NaCl) had no significant influence on selenium(IV) uptake. Electrophoretic mobility measurements revealed a significant shift toward lower values of the isoelectric point of maghemite upon selenium(IV) uptake, suggesting the formation of inner-sphere surface complexes. At the molecular level, using X-ray Absorption Fine-Structure Spectroscopy (EXAFS), the formation of both bidentate binuclear corner-sharing (2C) and bidentate mononuclear edge-sharing (1E) inner-sphere surface complexes was observed, with a trend toward solely 1E complexes at high pH. The absence of a tridentate surface complex as observed for arsenic(III) and antimonite(III) might be due to the relatively small size of the SeIVO3 unit. These new spectroscopic results can be implemented in reactive transport models to improve the prediction of selenium migration behavior in the environment as well as its monitoring through its interaction with maghemite or maghemite layers at the surface of magnetite. Due to its chemical stability even at low pH and its magnetization properties allowing magnetic separation, maghemite is a promising sorbing phase for the treatment of Se polluted waters. [ABSTRACT FROM AUTHOR]

Deposition of latex colloids on a structured siliconsurface wasinvestigated. The surface with well-defined roughness and topographypattern served as an analogue for rough mineral surfaces with half-poresin the submicrometer size. The silicon topography consists of a regularpit pattern (pit diameter = 400 nm, pit spacing = 400 nm, pit depth= 100 nm). Effects of hydrodynamics and colloidal interactions intransport and deposition dynamics of a colloidal suspension were investigatedin a parallel plate flow chamber. The experiments were conducted atpH ∼ 5.5 under both favorable and unfavorable adsorption conditionsusing carboxylate functionalized colloids to study the impact of surfacetopography on particle retention. Vertical scanning interferometry(VSI) was applied for both surface topography characterization andthe quantification of colloidal retention over large fields of view.The influence of particle diameter variation (d=0.3–2 μm) on retention of monodisperse as well as polydispersesuspensions was studied as a function of flow velocity. Despite electrostaticallyunfavorable conditions, at all flow velocities, an increased retentionof colloids was observed at the rough surface compared to a smoothsurface without surface pattern. The impact of surface roughness onretention was found to be more significant for smaller colloids (d= 0.3, 0.43 vs. 1, 2 μm). From smooth to rough surfaces,the deposition rate of 0.3 and 0.43 μm colloids increased bya factor of ∼2.7 compared to a factor of 1.2 or 1.8 for 1 and2 μm colloids, respectively. For a substrate herein, with constantsurface topography, the ratio between substrate roughness and radiusof colloid, Rq/rc, determinedthe deposition efficiency. As Rq/rcincreased, particle–substrate overall DLVO interactionenergy decreased. Larger colloids (1 and 2 μm) beyond a criticalvelocity (7 × 10–5and 3 × 10–6m/s) (when drag force exceeds adhesion force) tend to detach fromthe surface irrespective of the impact of roughness. For polydispersesolutions, an increase in the polydispersity and flow velocity resultedin a reduction of colloid deposition efficiency due to the resultingenhanced double-layer repulsion. Quantification of surface topographyvariations of two endmembers of natural grain surfaces showed thathalf-pore depths and roughness of sedimentary quartz grains are mainlyin the micrometer range. Grains with diagenetically formed quartzovergrowths, however, show surface roughness mainly in the submicrometerrange. Thus, surface topography features applied in the here presentedanalogue study and resulting variation in particle retention can serveas quantitative analogue for particle reactions in diageneticallyaltered quartz sands and sandstones. The reported impact of particlepolydispersity can have an important application for quantitativeprediction of retention of varying types of minerals, such as differentclay minerals in the environment under prevailing unfavorable conditions. [ABSTRACT FROM AUTHOR]

Within the scope of a cooperation between Svensk Kärnbränslehantering AB and Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, a series of actinide migration experiments were performed both in the laboratory and at the Asp6 Hard Rock Laboratory in Sweden. The objectives of these experiments were to quantify the sorption of different actinide elements in single fractures of a granite host rock and to investigate the sorption mechanisms. To guarantee the most realistic conditions--as close to nature as possible--in situ experiments were performed in the Chemlab 2 borehole probe. These migration experiments were complemented by laboratory sorption and migration studies. The latter included batch experiments with flat chips of natural material extracted from fracture surfaces to identify the mineral phases relevant to radionuclide sorption by means of autoradiography. Scanning electron microscopy analyses provided information on the composition of sorption-relevant phases and X-ray photoelectron spectroscopy of Np, Tc, and Fe distribution revealed the redox states of these elements. Important mineral phases retaining all actinides and Tc were Fe-bearing phases. From the migration experiments, elution curves of the inert tracer (HTO), Np(V), U(VI), and to a small extent of Tc(VII) were obtained. Americium(III) and plutonium(IV) were not eluted. The mechanisms influencing the migration of the elements Np, U, and Tc depended on redox reactions. It was shown by various independent methods that Np(V) was reduced to the tetravalent state on the fracture surfaces, thus resulting in a pronounced dependence of the recovery on the residence time. Technetium was also retained in the tetravalent state. Elution of natural uranium from the granite drill cores was significant and is discussed in detail. [ABSTRACT FROM AUTHOR]

In this work, the adsorption behavior of Sr onto a synthetic iron(III) oxide (hematite with traces of goethite) has been studied. This solid, which might be considered a representative of Fe3+ solid phases (iron corrosion products), was characterized by X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS), and its specific surface area was determined. Both XRD and XPS data are consistent with a mixed solid containing more than 90% hematite and 10% goethite. The solid was further characterized by fast acid-base titrations at different NaCl concentrations (from 0.1 to 5 M). Subsequently, for each background NaCl concentration used for the acid-base titrations, Sr-uptake experiments were carried out involving two different levels of Sr concentration (1 × 10−5 and 5 × 10−5 M, respectively) at constant solid concentration (7.3 g/L) as a function of −log([H+]/M). A Surface Complexation Model (SCM) was fitted to the experimental data, following a coupled Pitzer/surface complexation approach. The Pitzer model was applied to aqueous species. A Basic Stern Model was used for interfacial electrostatics of the system, which includes ion-specific effects via ion-specific pair-formation constants, whereas the Pitzer-approach involves ion-interaction parameters that enter the model through activity coefficients for aqueous species. A simple 1-pK model was applied (generic surface species, denoted as >XOH−1/2). Parameter fitting was carried out using the general parameter estimation software UCODE, coupled to a modified version of FITEQL2. The combined approach describes the full set of data reasonably well and involves two Sr-surface complexes, one of them including chloride. Monodentate and bidentate models were tested and were found to perform equally well. The SCM is particularly able to account for the incomplete uptake of Sr at higher salt levels, supporting the idea that adsorption models conventionally used in salt concentrations below 1 M are applicable to high salt concentrations if the correct activity corrections for the aqueous species are applied. This generates a self-consistent model framework involving a practical approach for semi-mechanistic SCMs. The model framework of coupling conventional electrostatic double layer models for the surface with a Pitzer approach for the bulk solution earlier tested with strongly adsorbing solutes is here shown to be successful for more weakly adsorbing solutes. [ABSTRACT FROM AUTHOR]

Abstract: Feldspar minerals are thermodynamically unstable in the near-surface environment and their surfaces are well known to react readily with aqueous solutions, leading to incongruent dissolution at low pH values, but congruent dissolution at neutral and high pH values. Interactions with mineral surfaces are an important control on the environmental transport of trace elements and detrital feldspars are abundant in soils and sediments. However, the interactions of metal ions in solution with the reacting feldspar surface have not been widely explored. The interactions of Pb(II), U(VI) and Np(V) ions with the feldspar surface have therefore been studied. Lead is taken up by the microcline surface at pH 6 and 10, but no uptake could be measured at pH 2. There was measurable uptake of Pb(II) on the plagioclase surface at pH 2, 6 and 10. Uptake always increased with pH. In most conditions, Pb(II) reacts through cation exchange process although, at high pH, a discrete phase, probably hydrocerrusite, is observed by atomic force microscopy (AFM) to precipitate on the plagioclase surface. Supersaturation with hydrocerrusite in these conditions is expected from thermodynamic calculations. Uptake of uranyl ion , generally through surface complex formation, could only be measured at pH 6 and 10. At pH 6 and an initial U(VI) concentration above 21.0μM, precipitation of becquerelite (Ca[(UO2)3O2(OH)3]2·8H2O), identified by AFM and characterised by grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy, is observed on plagioclase. The U(VI) concentration range in which becquerelite precipitation begins (dissolved U(VI) 1–5μM) is consistent with that predicted from thermodynamic modelling. On plagioclase feldspar, secondary ion mass spectrometry showed diffusion of uranium into the altered surface layer. Uptake of the neptunyl ion (Np(V)) was found at pH 6 and 10 for microcline and at pH 2, 6 and 10 for plagioclase, and was generally lower than uptake of U(VI). By combining batch sorption experiments with imaging and surface analysis, and thermodynamic modelling, it has been possible to gain a mechanistic insight into the reactions of the feldspar surface with metal ions in solution. [Copyright &y& Elsevier]

Abstract: A series of low platinum loaded Pt:SnO2 electrocatalysts for dye-sensitized solar cells were prepared by the hydrogen reduction method at 120 °C. As prepared and annealed at 630 °C samples containing 1.2%, 2% and 3% platinum loaded antimony doped tin dioxide catalytic powders were characterized. The structure and particle sizes are studied by means of high resolution transmission electron microscopy and X-ray diffraction measurement. The metallic state of platinum nanoparticles was observed by X-ray photoelectron spectroscopy. For the paste preparation, differently loaded Pt:SnO2 powders were each mixed with the ethylcellulose/terpineol printing media. In order to produce symmetrical Pt/Electrolyte/Pt cells for the electrochemical study the pastes were applied onto transparent conductive oxide coated glass by screen printing technology. The charge transfer resistance of these electrodes to the iodide/triiodide redox system in different electrolytes after the thermal sealing of the cells at 630 °C was investigated by electrochemical impedance spectroscopy, which showed that catalytic performance can be improved by homogenous deposition of catalyst on substrate. The surface morphology of the printed catalytic stripes was imaged by field emission scanning electron microscopy and atomic force microscopy. [Copyright &y& Elsevier]

Abstract: X-ray photoelectron spectroscopy (XPS) has been used to analyse a series of mechanochemically synthesised, nanocrystalline calcium silicate hydrates (C-S-H). The samples, with Ca/Si ratios of 0.2 to 1.5, showed structural features of C-S-H(I). XPS analysis revealed changes in the extent of silicate polymerisation. Si 2p, Ca 2p and O 1s spectra showed that, unlike for the crystalline calcium silicate hydrate phases studied previously, there was no evidence of silicate sheets (Q3) at low Ca/Si ratios. Si 2p and O 1s spectra indicated silicate depolymerisation, expressed by decreasing silicate chain length, with increasing C/S. In all spectra, peak narrowing was observed with increasing Ca/Si, indicating increased structural ordering. The rapid changes of the slope of FWHM of Si 2p, Δ Ca–Si and Δ NBO–BO as function of C/S ratio indicated a possible miscibility gap in the C-S-H-solid solution series between C/S 5/6 and 1. The modified Auger parameter (α′) of nanocrystalline C-S-H decreased with increasing silicate polymerisation, a trend already observed studying crystalline C-S-H. Absolute values of α′ were shifted about −0.7 eV with respect to crystalline phases of equal C/S ratio, due to reduced crystallinity. [Copyright &y& Elsevier]

The migration behavior of [sup 241]Am(III) in a sandy aquifer was studied under near-natural conditions by long-term column experiments of more than 1 year duration. Columns with 50 cm length and 5 cm in diameter were packed with aeolian quartz sand and equilibrated with two different groundwaters having an original dissolved organic carbon concentration (D0C) of 1.1 and 7.2 mg·dm[sup -3], respectively, from the Gorleben site (Lower Saxony, Germany). In each experiment, 1 cm³ of Am-spiked groundwater ([Am] = 0.2 to 2 µmol·dm[sup -3]) was injected into the column. The flow rate of the groundwater was adjusted to 0.28 m·d[sup -1]. A small colloid-borne Am fraction was found to elute together with tritiated water. After 414 and 559 days, respectively, the experiments were terminated. Whereas the nonsorbing tracer of tritiated water would have covered a distance of about 350 m in that time period, the maximum of the Am activity was detected between 32 and 40 mm column length. Applying selective dissolution analysis to the sand surface, Am was found to be preferentially bound to iron hydroxide/oxide sites. From this Am distribution, a retardation factor R of about 10&sup4; was determined and compared to static batch experiments. The Am breakthrough was calculated for the conditions of the column experiment. [ABSTRACT FROM AUTHOR]

The solubility of Be(II) is investigated in carbonate-free dilute to concentrated HCl–NaCl–NaOH, KCl–KOH, NaOH and KOH solutions. Undersaturation experiments were performed under Ar atmosphere at T = (22 ± 2) °C. XRD, XPS, SEM and quantitative chemical analysis confirm that α-Be(OH) 2 (cr) is the solid phase controlling the solubility in all evaluated systems. No transformation of α-Be(OH) 2 (cr) to β-Be(OH) 2 (cr) or ternary solid phases Na/K–Be(II)–OH(s) is observed in the investigated systems within the timeframe of this study (t ≤ 600 days). An amphoteric solubility behaviour of Be(II) is observed with a solubility minimum at pH m ≈ 9.5 (with [Be(II)] ≈ 10−6.8 M), regardless of the ionic strength. The combination of solubility data determined in acidic pH m conditions and the hydrolysis scheme reported in the literature for cationic hydrolysis species of Be(II) is used for the determination of the solubility constant of α-Be(OH) 2 (cr), log * K ° s,0 = (6.9 ± 0.4). Slope analysis of the solubility data in alkaline to hyperalkaline conditions and 9Be NMR support the predominance of the monomeric hydrolysis species Be(OH) 2 (aq), Be(OH) 3 – and Be(OH) 4 2− within the strongly alkaline pH m -conditions relevant in cementitious systems. The comprehensive solubility dataset collected within this study in combination with extensive solid and aqueous phase characterization allow the development of a complete chemical, thermodynamic and (SIT) activity model for the system Be2+–Na+–K+–H+–Cl––OH––H 2 O(l). This model provides an accurate and robust tool for the evaluation of Be(II) solubility and speciation in a diversity of geochemical conditions, including source term calculations of beryllium in the context of the nuclear waste disposal Safety Case. • Systematic solubility and spectroscopic study with Be(II) in NaCl and KCl systems. • α-Be(OH) 2 (cr) controls the solubility of Be(II) in the investigated systems. • Comprehensive thermodynamic, chemical and SIT activity models derived. • Accurate description of the system Be2+–Na+–K+–H+–Cl––OH––H 2 O(l) provided. • Be(OH) 3 – and Be(OH) 4 2− confirmed as relevant species in cementitious systems. [ABSTRACT FROM AUTHOR]

Sorption of Eu(III) onto quartz from highly saline solutions (up to 5 M NaCl) for pH c 2–9 ha s been studied by measuring sorption edges. The acid-base titrations of the silica surface suggest the rather unusual presence of two different sites that has been the object of recent discussions in the literature. Europium uptake results show the usual behaviour with a steep pH-edge and nearly complete removal at sufficiently high pH. Previous spectroscopic data on this system suggest the presence of two bidentate surface complexes with different proton stoichiometry. Based on this, a self-consistent Surface Complexation Model (SCM) was fitted to the full set of experimental data, from 0.1 to 5 M NaCl, using a coupled Pitzer/surface complexation approach. The Pitzer model was applied to aqueous species. A Basic Stern Model was used for interfacial electrostatics of the system, which includes ion-specific effects via ion-pair formation. Parameter fitting was done using the general parameter estimation software UCODE coupled to a modified version of FITEQL2 involving separate calculations of the respective ionic strength corrections. At high ionic strength (>1 M), the surface potential is strongly screened by ion-pair formation and the diffuse layer potential is negligibly low, which justifies the extension of the standard electrostatic model to these harsh conditions. Overall, our model is able to describe the full set of analysed data. To the knowledge of the authors this is the first comprehensive work studying solid surface titrations and cation uptake up to high salt levels and applying electrostatics models to describe the solid interface at these particular conditions. It is expected that these first systematic data acquisition along with the detailed modelling can serve as a benchmark for the modelling of future studies on sorption in highly saline systems. [ABSTRACT FROM AUTHOR]

For more than 120 years, systematic studies of X-ray interaction with matter have been the basis for our understanding of materials—both of natural or man-made origin—and their structure-function relationships. Beginning with simple radiographic imaging at the end of the 19th century, X-ray based analytical tools such as X-ray diffraction, X-ray fluorescence and photoemission or X-ray absorption techniques are indispensable in almost any field of chemical and material sciences—including basic and applied actinide and radionuclide studies. The advent of dedicated synchrotron radiation (SR) sources in the second half of the last century has revolutionized the analytical power of X-ray probes, while—with increasing number of SR facilities—beamline instrumentation followed a trend towards increasing specialization and adaption to a major research topic. The INE-Beamline and ACT station at the KIT synchrotron source belong to the exclusive club of a few synchrotron beamline facilities—mostly located in Europe—dedicated to the investigation of highly radioactive materials. Since commissioning of the INE-Beamline in 2005, capabilities for synchrotron-based radionuclide and actinide sciences at KIT have been continuously expanded, driven by in-house research programs and external user needs. [ABSTRACT FROM AUTHOR]