Oxidation State and Structure of Fe in Nontronite: From Oxidizing to Reducing Conditions

The redox reaction between natural Fe-containing clay minerals and its sorbates is a fundamental process controlling the cycles of many elements such as carbon, nutrients, redox-sensitive metals, and metalloids (e.g., Co, Mn, As, Se), and inorganic as well as organic pollutants in Earth's critical zone. While the structure of natural clay minerals under oxic conditions is well-known, less is known about their behavior under anoxic and reducing conditions, thereby impeding a full understanding of the mechanisms of clay-driven reduction and oxidation (redox) reactions especially under reducing conditions. Here we investigate the structure of a ferruginous natural clay smectite, nontronite, under different redox conditions, and compare several methods for the determination of iron redox states. Iron in nontronite was gradually reduced chemically with the citrate-bicarbonate-dithionite (CBD) method. 57Fe Mössbauer spectrometry, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy including its pre-edge, extended X-ray absorption fine structure (EXAFS) spectroscopy, and mediated electrochemical oxidation and reduction (MEO/MER) provided consistent Fe(II)/Fe(III) ratios. By combining X-ray diffraction (XRD) and transmission electron microscopy (TEM), we show that the long-range structure of nontronite at the highest obtained reduction degree of 44% Fe(II) is not different from that of fully oxidized nontronite except for a slight basal plane dissolution on the external surfaces. The short-range order probed by EXAFS spectroscopy suggests, however, an increasing structural disorder and Fe clustering with increasing reduction of structural Fe.

Thallium adsorption onto phyllosilicate minerals

The adsorption of thallium (Tl) onto phyllosilicate minerals plays a critical role in the retention of Tl in soils and sediments and the potential transfer of Tl into plants and groundwater. Especially micaceous minerals are thought to strongly bind monovalent Tl(I), in analogy to their strong binding of Cs. To advance the understanding of Tl(I) adsorption onto phyllosilicate minerals, we studied the adsorption of Tl(I) onto Na- and K-saturated illite and Na-saturated smectite, two muscovites, two vermiculites and a naturally Tl-enriched soil clay mineral fraction. Macroscopic adsorption isotherms were combined with the characterization of the adsorbed Tl by X-ray absorption spectroscopy (XAS). In combination, the results suggest that the adsorption of Tl(I) onto phyllosilicate minerals can be interpreted in terms of three major uptake paths: (i) highest-affinity inner-sphere adsorption of dehydrated Tl⁺ on a very low number of adsorption sites at the wedge of frayed particle edges of illite and around collapsed zones in vermiculite interlayers through complexation between two siloxane cavities, (ii) intermediate-affinity inner-sphere adsorption of partially dehydrated Tl⁺ on the planar surfaces of illite and muscovite through complexation onto siloxane cavities, (iii) low-affinity adsorption of hydrated Tl⁺, especially in the hydrated interlayers of smectite and expanded vermiculite. At the frayed edges of illite particles and in the vermiculite interlayer, Tl uptake can lead to the formation of new wedge sites that enable further adsorption of dehydrated Tl⁺. On the soil clay fraction, a shift in Tl(I) uptake from frayed edge sites (on illite) to planar sites (on illite and muscovite) was observed with increasing Tl(I) loading. The results from this study show that the adsorption of Tl(I) onto phyllosilicate minerals follows the same trends as reported for Cs and Rb and thus suggests that concepts to describe the retention of (radio)cesium by different types of phyllosilicate minerals in soils, sediments and rocks are also applicable to Tl(I).

Proposal of a formula mouth opening reduction assessment, for forensic purposes

OBJECTIVES

To propose a formula for determining reduced mouth opening due to oral and maxillofacial trauma, based on the normal standard of the Brazilian population.

MATERIALS AND METHODS

First, the maximum mouth opening was established, in millimeters, using a digital pachymeter, in patients between 22 and 60 years of age. The opening was measured from the upper to the lower incisor, at maximum amplitude, without pain and overbite. Second, the facial profile type and height were determined. A formula was developed to calculate the percentage of reduced mouth opening based on the normal average.

RESULTS

The average mouth opening was found to be 51.71 mm in men and 47.94 mm in women, thus establishing a statistically significant difference in mouth opening between sexes. However, there was no statistically significant difference between age and profile type with mouth opening. The following formulas were developed to calculate the reduced mouth opening, based on the averages found, by using RA= [100-(A.1.93)].0.3 for males and RA= [100-(A.2,08)] .0.3 for female patients.

CONCLUSION

Considering that mouth opening tends to be larger in men than in women, valid formulas can be used to determine the correct percentage of reduced mouth opening.

Fundamental Research on Radiochemistry of Geological Nuclear Waste Disposal

Currently, 5 · 10¹⁹ Bq of radioactive waste originating from the use of nuclear power for energy production, and medicine, industry and research, is maintained in Switzerland at intermediate storage facilities. Deep geological disposal of nuclear waste is considered as the most reliable and sustainable long-term solution worldwide. Alike the other European countries, the Swiss waste disposal concept embarks on the combination of engineered and geological barriers. The disposal cell is a complex geochemical system. The radionuclide mobility and consequently radiological impact depend not only on their chemical speciation but also on the background concentration of other stable nuclides and their behaviour in the natural environment. The safety assessment of the repository is thus a complex multidisciplinary problem requiring knowledge in chemical thermodynamics, structural chemistry, fluid dynamics, geo- and radiochemistry. Broad aspects of radionuclide thermodynamics and geochemistry are investigated in state-of-the-art radiochemical laboratories at the Paul Scherrer Institute. The research conducted over the last 30 years has resulted in a fundamental understanding of the radionuclides release, retention and transport mechanism in the repository system.

Iron Adsorption on Clays Inferred from Atomistic Simulations and X-ray Absorption Spectroscopy

The atomistic level understanding of iron speciation and the probable oxidative behavior of iron (Fe_aq²⁺ → Fe_surf³⁺) in clay minerals are fundamental for environmental geochemistry of redox reactions. Thermodynamic analyses of wet chemistry data suggest that iron adsorbs on the edge surfaces of clay minerals at distinct structural sites commonly referred as strong and weak sites (with high and low affinity, respectively). In this study, we applied ab initio molecular dynamics simulation to investigate the structure and the stability of the edge surfaces of trans- and cis-vacant montmorillonites. These structures were further used to evaluate the surface complexation energy and to calculate reference ab initio X-ray absorption spectra (XAS) for distinct inner-sphere complexes of iron. The combination of ab initio simulations and XAS allowed us to reveal the Fe-complexation mechanism and to quantify the Fe partitioning between the high and low affinity sites as a function of the oxidation state and loadings. Although iron is mostly present in the Fe³⁺ form, Fe²⁺ increasingly co-adsorbs at increasing loadings. Ab initio structure relaxations of several different clay structures with substituted Fe²⁺/Fe³⁺ in the bulk or at the surface site showed that the oxidative sorption of ferrous iron is an energetically favored process at several edge surfaces of the Fe-bearing montmorillonite.

Photocatalytic and antimicrobial multifunctional nanocomposite membranes for emerging pollutants water treatment applications

Emerging pollutants represent a new global problem for water quality. As these compounds get into the environment, they cause severe threats to aquatic environments and human health and are typically resistant to conventional wastewater treatments. In this work, TiO₂ nanoparticles surface was functionalized with silver (Ag) nanoparticles, and solvent cast and electrospun membranes of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) were prepared with different concentrations of TiO₂ and Ag-TiO₂ to produce a multifunctional material. The photocatalytic activity of the nanocomposites was evaluated through the degradation of norfloxacin under ultraviolet (UV) and visible radiation. It is shown that nanocomposites with Ag-TiO₂ show the highest degradation efficiencies: 64.2% under UV and 80.7% under visible radiation, for 90 and 300 min, respectively. Furthermore, the recyclability of the membranes has also been demonstrated. Finally, it is shown the antimicrobial activity of the nanocomposite membranes, demonstrating the suitability of the Ag-TiO₂/PVDF-HFP nanocomposites as multifunctional photocatalytic and antimicrobial membranes for water remediation applications.

Thallium Adsorption onto Illite

We investigated the adsorption of Tl⁺ onto purified Illite du Puy (IdP). Distribution coefficients (K_d) for trace Tl adsorption indicated a moderate pH-dependence from pH 2.5 to 11. Adsorption isotherms measured at Tl⁺ concentrations from 10^-9 to 10^-2 M at near-neutral pH on illite saturated with Na⁺ (100 mM), K⁺ (1 and 10 mM), NH₄⁺ (10 mM) or Ca²⁺ (5 mM) revealed a high adsorption affinity of Tl⁺ in Na⁺- and Ca²⁺-electrolytes and strong competition with K⁺ and NH₄⁺. Cation exchange selectivity coefficients for Tl⁺ with respect to Na⁺, K⁺, NH₄⁺, and Ca²⁺ were derived using a 3-site sorption model. They confirmed the strong adsorption of Tl⁺ at the frayed edges of illite, with Tl selectivity coefficients between those reported for Rb⁺ and Cs⁺. X-ray absorption spectra of Tl adsorbed onto Na-exchanged IdP indicated a shift from adsorption of (dehydrated) Tl⁺ at the frayed edges at low loadings to adsorption of (hydrated) Tl⁺ on planar sites at the highest loadings. Our results suggest that illite is an important adsorbent for Tl in soils and sediments, considering its often high abundance and its stability relative to other potential adsorbents and the selective nature of Tl⁺ uptake by illite.

Biocompounds from rapeseed oil industry co-stream as active ingredients for skin care applications

OBJECTIVE

Despite the great number of substances produced by the skincare industry, very few of them seem to truly have an effect on the skin. Therefore, given the social implications surrounding physical appearance, the search for new bioactive compounds to prevent or attenuate skin ageing and enhance self-image is a priority of current research. In this context, being rich in valuable compounds, such as proteins, phenolics, lipids and vitamins, this study is focused on the potential activity of rapeseed press cake hydrolysates to be used as raw materials for skincare applications.

METHODS

In this study, the protein-rich press residue from the rapeseed oil industry was converted enzymatically into short-chain biologically active peptides using four protease products with varying substrate specificity - Alcalase 2.4L FG, Protex 6L, Protamex and Corolase 7089. The antioxidant, anti-wrinkle and anti-inflammatory activities of the obtained hydrolysates were evaluated in vitro while their biocompatibility with human skin fibroblasts was tested.

RESULTS

All hydrolysates were biocompatible with skin fibroblasts after 24 h of exposure, while the non-hydrolysed extract induced cell toxicity. Alcalase 2,4L FG and Protex 6L-obtained hydrolysates were the most promising extracts showing improved bioactivities suitable for skin anti-ageing formulations, namely antioxidant activity, inhibiting approximately 80% cellular reactive oxidative species, anti-inflammatory and anti-wrinkle properties, inhibiting around 36% of myeloperoxidase activity and over 83% of elastase activity.

CONCLUSION

The enzymatic technology applied to the rapeseed oil industry costream results in the release of bioactive compounds suitable for skincare applications.

Fe(II) uptake on natural montmorillonites. I. Macroscopic and spectroscopic characterization

Iron is an important redox-active element that is ubiquitous in both engineered and natural environments. In this study, the retention mechanism of Fe(II) on clay minerals was investigated using macroscopic sorption experiments combined with Mössbauer and extended X-ray absorption fine structure (EXAFS) spectroscopy. Sorption edges and isotherms were measured under anoxic conditions on natural Fe-bearing montmorillonites (STx, SWy, and SWa) having different structural Fe contents ranging from 0.5 to 15.4 wt % and different initial Fe redox states. Batch experiments indicated that, in the case of low Fe-bearing (STx) and dithionite-reduced clays, the Fe(II) uptake follows the sorption behavior of other divalent transition metals, whereas Fe(II) sorption increased by up to 2 orders of magnitude on the unreduced, Fe(III)-rich montmorillonites (SWy and SWa). Mössbauer spectroscopy analysis revealed that nearly all the sorbed Fe(II) was oxidized to surface-bound Fe(III) and secondary Fe(III) precipitates were formed on the Fe(III)-rich montmorillonite, while sorbed Fe is predominantly present as Fe(II) on Fe-low and dithionite-reduced clays. The results provide compelling evidence that Fe(II) uptake characteristics on clay minerals are strongly correlated to the redox properties of the structural Fe(III). The improved understanding of the interfacial redox interactions between sorbed Fe(II) and clay minerals gained in this study is essential for future studies developing Fe(II) sorption models on natural montmorillonites.

Fe(II) uptake on natural montmorillonites. II. Surface complexation modeling

Fe(II) sorption edges and isotherms have been measured on low structural Fe-content montmorillonite (STx) and high structural Fe-content montmorillonite (SWy) under anoxic (O2 < 0.1 ppm) and strongly reducing conditions (Eh = -0.64 V). Under anoxic conditions Fe(II) sorption on SWy was significantly higher than on STx, whereas the sorption under reducing conditions was essentially the same. The uptake behavior of Fe(II) on STx under all redox conditions (Eh = +0.28 to -0.64 V) and SWy under reducing conditions (Eh = -0.64 V) was consistent with previous measurements made on other divalent transition metals. All of the sorption data could be modeled with the two-site protolysis nonelectrostatic surface complexation and cation exchange (2SPNE SC/CE) sorption model including an additional surface complexation reaction for Fe(II) which involved the surface oxidation of ferrous iron surface complexes (≡S(S,W)OFe(+)) to ferric iron surface complexes (≡S(S,W)OFe(2+)) on both the strong and weak sites. The electron acceptor sites on the montmorillonite are postulated to be the structural Fe(III).

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

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

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

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

Redox properties of structural Fe in clay minerals. 1. Electrochemical quantification of electron-donating and -accepting capacities of smectites

Clay minerals often contain redox-active structural iron that participates in electron transfer reactions with environmental pollutants, bacteria, and biological nutrients. Measuring the redox properties of structural Fe in clay minerals using electrochemical approaches, however, has proven to be difficult due to a lack of reactivity between clay minerals and electrodes. Here, we overcome this limitation by using one-electron-transfer mediating compounds to facilitate electron transfer between structural Fe in clay minerals and a vitreous carbon working electrode in an electrochemical cell. Using this approach, the electron-accepting and -donating capacities (Q(EAC) and Q(EDC)) were quantified at applied potentials (E(H)) of -0.60 V and +0.61 V (vs SHE), respectively, for four natural Fe-bearing smectites (i.e., SWa-1, SWy-2, NAu-1, and NAu-2) having different total Fe contents (Fe(total) = 2.3 to 21.2 wt % Fe) and varied initial Fe(2+)/Fe(total) states. For every SWa-1 and SWy-2 sample, all the structural Fe was redox-active over the tested E(H) range, demonstrating reliable quantification of Fe content and redox state. Yet for NAu-1 and NAu-2, a significant fraction of the structural Fe was redox-inactive, which was attributed to Fe-rich smectites requiring more extreme E(H)-values to achieve complete Fe reduction and/or oxidation. The Q(EAC) and Q(EDC) values provided here can be used as benchmarks in future studies examining the extent of reduction and oxidation of Fe-bearing smectites.

Keratin-based peptide: biological evaluation and strengthening properties on relaxed hair

A peptide based on a fragment of hair keratin type II cuticular protein, keratin peptide (KP), was studied as a possible strengthening agent for weakened relaxed hair. The peptide was prepared both in aqueous water formulation (WF) and organic solvent formulations (OF), to determine the effect of organic solvents on peptide interaction with hair and the differences in hair recovery. Both peptide formulations were shown to improve mechanical and thermal properties of weakened hair with peptide in OF showing the stronger effect. As a potential new hair care product, and so would necessitate contact with skin, the cytotoxicity and genotoxicity of the peptide were also evaluated through different methodologies (Alamar Blue assay, 2'-7'-dichlorofluorescein probe, cell morphology and growth and evaluation of DNA damage by an alkaline version of the comet assay) in skin fibroblasts. These tests are indicators of the potential of peptide to cause irritation on skin or to be carcinogenic, respectively. The peptide in WF did not cause cytotoxicity or genotoxicity in any of the concentrations tested. The presence of OF, however, induced a 20% decrease in cell viability in all of the range of concentrations used after 72-h incubation. Moreover, OF inhibited cell growth and was considered genotoxic at first contact with cells. The peptide was therefore considered a promising strengthening agent for hair and was shown to be innocuous when applied in WF.

The influence of carbonate complexation on lanthanide/actinide sorption on montmorillonite

The safety case for radioactive waste repositories is, to a large extend based on the physical and chemical retention of radionuclides on clay minerals which are important constituents in both the man-made engineered barriers and in argillaceous host rock formations. The presence of carbonate, one of the most important inorganic ligands for lanthanide and actinide ions in groundwaters and clay porewaters, can have a significant influence on their sorption behaviour on clay minerals. The sorption of Eu(III) on Na-montmorillonite in the absence and the presence of carbonate was investigated in batch sorption experiments. In the presence of carbonate two sets of experimental conditions were investigated. Eu(III) sorption measurements were performed as a function of pH in equilibrium with atmosphericpCO2(=10−3.5 bar) and at a variablepCO2(=10−1.4to 10−3.4 bar). The sorption data were modelled using the 2 site protolysis non-electrostatic surface complexation and cation exchange model. Both experimental data sets in the presence of carbon could be quantitatively modelled by including in the sorption model two additional surface complexation reactions on the strong sites forming ≡SSOEuCO30and ≡SSOEuOHCO3−surface complexes.