Sheet Silicates Research Articles

Triple oxygen and hydrogen isotopes of glacial diamictites record crustal maturation and changing surface conditions through geologic time

The triple oxygen and hydrogen stable isotopic compositions of 24 glacial diamictite composites with depositional ages from 2.9 to 0.3 Ga are used to reconstruct the evolution of the continental crust and surface environments. The δ18O of the diamictite composites increases from the Archean to the Phanerozoic by ~4 ‰ (3–5 ‰ in Mesoarchean to 13.5 ‰ in Neoproterozoic), a trend that is comparable to those seen in shales and granites, although the diamictites plot on the lower δ18O end of the range seen in shales. The Δ’17O0.528 decreases from −0.04 to −0.15 ‰, overlapping with shales and granites. Nine zircon separates extracted from individual diamictites also show a ~3 ‰ increase in δ18O from 3.75 to 4.5 ‰ to 7 ‰ between 2.9 and 0.6 Ga. The δ18O of diamictites and zircon separates negatively correlates with ɛNd(i) of the diamictites, suggesting that the longer the rocks reside in the upper continental crust (the lower the ɛNd), the more they are subjected to repeated weathering cycles, thus acquiring a higher δ18O and lower Δ’17O0.528 during each cycle. On a triple O isotope plot (δ17O vs δ18O), diamictites define an array with a slope of 0.523, analogous to granites and shales.The δD values of nearly all diamictites overlap with the typical mantle and crustal ranges of −58 ± 12 ‰ and − 69 ± 24 ‰, respectively, but are on the lower end of coeval shale values. Water, contained primarily in sheet silicates, ranges from 2.85 wt% (pre-2.4 Ga) and 2.35 wt% (post-2.4 Ga), showing no temporal change. The youngest diamictites (0.3 Ga Dwyka Group) exhibit low δD values of −105 to −111 ‰, lower than the typical crustal values, potentially reflecting the near-polar position of South Africa at the time of their deposition, which is corroborated by the reconstructed δ18O value of −26 ‰ based on triple oxygen isotopic systematics.The chemical index of alteration (CIA) allows inverting measured δ18O and Δ’17O values of diamictite composites into a pure weathering product (wp) end member by subtracting values of coeval unweathered crust based on tzircon δ18O. This reveals that the δ18Owp also increases with time, suggesting that the increase in δ18O (decrease in Δ’17O) of the maturing crust is insufficient to fully explain the trends. Therefore, at least part of the increasing δ18Owp likely reflects increasing δ18O of the hydrosphere. Reconstructed surface temperatures around the time of diamictite deposition using δ18Owp and Δ’17Owp display a general decrease since the Archean. Given the diagenetic and post-diagenetic history experienced by the diamictites, the temporal and global trends should be interpreted with caution. Nonetheless, reconstructed δ18Owater shows an increase from −21 ‰ at 2.9 Ga to −11 ‰ at 0.6 Ga. Thus, diamictites, like shales, broadly monitor the evolution of surface conditions on Earth from warmer to colder and from lower to higher δ18Owater values of the hydrosphere.

Ti- and Ba-rich phlogopitic micas in alkaline basic and upper mantle igneous rocks; stoichiometry, stability, and Fe valence estimation reassessed and rationalised

Ti- and Ba-rich tri-octahedral micas occur in fractionated basic igneous rocks, metasomatized mantle peridotites, metamorphosed pelites/carbonates, and hydrothermally altered mineral deposits. Electron microprobe analyses (EMP), with all iron reported as FeO, were widely used in the 1970/80s to interpret Ti and Ba substitution mechanisms, based on 22 O2– unit cell calculations, implying that cation vacancies occur in octahedral and/or intersheet sites. In 1996 EMP with chemical and physical analyses for ferric and total Fe, H2O, (OH), and element-specific Fe X-ray Absorption Spectroscopy (both K and L-edges) established valence states for Fe and Ti and cation site occupancies, that ∼50 % O replaces (OH) molecules, and that 24 anion cell formulae show the absence of cation vacancies. Cell formula calculation protocol for phlogopitic micas is refined here and results tested against the stoichiometric formula for vacancy-free phlogopite, XIIK2VIMg6IV[Si6Al2]O20(OH)4. Hypothetical sheet silicate compositions, calculated with fixed contents of vacancies linked to particular mixed-valence element substitutions, confirm that reliable unit cell formulae for natural mica solids require that each stoichiometric vacancy must be accounted for. If reliable estimates for ‘excess O’ (denoted WO2−) are assigned to EMP analyses, the proportion of the oxy-mica component in a mica solid solution can be defined. This approach is tested using published analyses for Ti- and Ba-rich biotites from fractionated basic and ultramafic volcanic igneous rocks (oxymica range 2.5–45 %; TiO2 up to 14 %; BaO up to 23 %), upper mantle peridotites (equivalent values 7–18 %; 6 %; 0.7 %), and metasomatised upper mantle (2–37 %; 9 %; 23 %). Enrichments of Ti and Ba in micas are clearly linked to the extra oxygen charge required to neutralise the more highly charged Ba2+ and Ti4+ replacing K+ and Mg2+.Substitution mechanisms involving Ba, Ti, and Fe3+ in ideal phlogopite involve coupled inter-site / inter-valence interactions so both site-ordering and valence-balance between the different cation sites must be accounted for. The cation exchange 2XIIK+ + 4VI(Mg2+ + Fe2+) + 4IVSi4+ ↔ XIIBa2+ + 3VITi4+ + 4(Altotal + Fe3+ + Crtotal)3+ is used here so that valence and site order can be considered together. Compositional variations show well-defined trends towards high-oxymica content and vacancy-free Ti and Ba mica end-members, rather than to oxy-free end-members with essential vacancies. Average compositions for different source rock micas are used to assess compositional trends; molecular WO2− values are refined by relating initial estimates directly to the wt.% TiO2 contents; and refined WO2− and stoichiometrically calculated Fe3+/Fetotal ratios ranging ∼0.1–0.5) are correlated with possible primary magmatic values.

Montmorillonite Clay-Based Electrocatalyst for Water Splitting Applications

The goal of reaching net-zero emissions by the year 2050 requires a strategic overhaul to be realistically achievable. Hydrogen energy is considered an ideal substitute for fossil fuels, which leave carbon footprints and release hazardous chemicals into the atmosphere. Thus, large-scale commercialization of hydrogen energy could meet future energy demands with zero emissions. Electrochemical water splitting (EWS) is the most sustainable and efficient method to produce hydrogen for the next century. Thus, designing an electrocatalyst with an enhanced surface structure and abundant earth materials makes it a highly adoptable and affordable green energy. Smectite clay minerals are abundant on earth, non-hazardous, and easy to fabricate due to their clay nature. Among the smectites, montmorillonite is a promising candidate for electrocatalysts due to its unique physicochemical properties like expandable layered structure (TOT layers), high cation exchange, water adsorption, and swelling properties. Due to the high cationic exchange capacity of montmorillonite clays (70-110 meq/100g), the structural and interlayer cations can be tuned according to the water adsorption and desorption properties. When we look into the mineral structure, montmorillonite smectites belong to 2:1 phyllosilicate-layered sheets, composed of two tetrahedral silicate sheets (T) and one octahedral sheet (O). In each layer, an octahedral sheet is sandwiched between the two tetrahedral sheets (TOT), which is shown in Figure a. In the tetrahedral sheets, the dominant cation is Si4+, which is often substituted by the trivalent cation Al3+. The isomorphic substitution of Si4+ by Al3+ in the tetrahedral layer raises charge deficiency in the tetrahedral sheet, which is balanced by the absorbed interlayer cations like K+, Na+, and Ca2+ between the water molecules. In octahedral sheets, the common cations are Al3+, Mg2+, Fe3+, or Fe2+, and other cations like Ni2+, Li2+, and Cr2+. When the Mg2+ ions are substituted by Al3+ ions, it gives rise to a positive charge in the octahedral sheet. Depending upon the charges within the tetrahedral and octahedral sheets, the layered structure properties are altered. By considering their cation-rich and expandable properties, we have employed montmorillonite clay materials [Na,Ca)0.3 (Al,Mg)2 Si4O10(OH)2. nH2O] in electrocatalytic water splitting reactions for the first time. In our observation, annealing the montmorillonite at high temperatures such as 300 oC (Mont300/NF), 600 oC (Mont600/NF), and 900 oC (Mont900/NF), reconstruct the surface, and induce structural defects, which enables isomorphic substitution of bivalent (M2+) or trivalent cations (M3+). The annealed samples were prepared as slurry using binder additives (PVDF and NMP solvent) and coated on nickel foam (NF). The electrochemical performance was tested in a three-electrode potentiostat system in 1M KOH electrolyte, where the prepared sample was employed as the working electrode, graphite rod as the counter electrode, and Hg/HgO as the reference electrode. Figure b and c shows the electrochemical performances of the HER and OER reactions. Initially, the Mont600/NF catalysts show lower overpotential of 178 mV and 250 mV at 10 mA/cm2 for HER and OER reactions respectively. The pristine sample (Mont/NF) show much higher overpotential (240 mV for HER and 360 mV for OER). Thus, annealing promotes the formation of dangling bonds by generating cationic and anionic vacancies, which act as active sites for the adsorption of intermediates, which in turn reduces the requirement for higher overpotential. Furthermore, the pristine montmorillonite is mixed with functionalized CNT powder and annealed at the best performing temperature of 600oC (Mont+CNT600/NF). As a result, Mont+CNT600/NF sample shows much higher performance than Mont600/NF by requiring lower overpotential of 168 mV and 220 mV at 10 mA/cm2 for HER and OER reflecting the higher intrinsic kinetics owing to increased electrical conductivity due to CNT which enhances the electron transport properties and the water splitting kinetics. Interestingly, the used clay materials can be treated with organic solutions and can be reused due to their physicochemical retaining properties even after being treated at high temperatures. This would reduce the amount of solid catalyst waste going into landfills. Therefore, montmorillonite clay materials are the new era of catalyst’s material with recyclability due to their self-retaining physicochemical properties, water hydration, and dehydration properties. In this work, we have successfully optimized the montmorillonite properties by annealing at high temperatures, which helps to reconstruct the surface by breaking the OH lattice ions and creating dangling bonds. The formation of dangling bonds increases the rate of water splitting processes by acting as a surface-active site for the adsorption and desorption of H+ and OH- ions. Thus, tuning montmorillonite clays helps in achieving different water splitting properties. Figure 1

High-temperature behaviour of fluorcarletonite, KNa4Ca4Si8O18(CO3)4(F,OH)⋅H2O, from the Murun Alkaline Complex, Russia, appraised by experimental and theoretical methods

AbstractThe thermal behaviour of fluorcarletonite, KNa4Ca4Si8O18(CO3)4(F,OH)⋅H2O, from the charoitites of the Severny district at the Malyy Murun massif, Murun complex, NW Aldan Shield, Siberia, Russia, has been investigated in order to understand the temperature-induced changes in the crystal structure of this rare silicate. The study has been carried out combining in situ high-temperature single-crystal X-ray diffraction (T range 25–550°C), ex situ high-temperature Fourier-transform infrared spectroscopy (25–700°C) and ab initio calculations. An increasing trend of lattice parameters and cell volume was observed in the 150–550°C temperature range, when the mineral underwent a progressive dehydration process. At 550°C ~40% water loss was detected. If compared with the fluorcarletonite structure at room temperature, the partially dehydrated fluorcarletonite shows: the same space group (P4/mbm); increased distances between the oxygens of the H2O molecules (O11w and O12w) and their Na-centred octahedral cations (Na1 and Na2, respectively); distortion of the four- and six-member tetrahedral rings of the double silicate layer. The dehydration process mainly involves the oxygen at the O11w site which has a different local environment with respect to the oxygen at the O12w site. At T > 600°C, the complete dehydration is accompanied by deprotonation of the OH groups substituting for the F atoms and by the collapse of the structure when the CO2 is released. The adopted approach allowed definition of the temperature thresholds at which modifications occur in the fluorcarletonite crystal structure when subjected to controlled heating conditions. Our findings contribute to assessment of stability, reactivity and, more generally, the thermal behaviour of sheet silicates with fluorcarletonite-like topology.

Soil development trajectories, chemical weathering and pedogenic mineral (trans)formation on glauconitic calcarenites in a Mediterranean area

Glauconite forms in shallow marine basins under oxic to suboxic conditions. It is an Fe-rich sheet silicate often found in calcareous sandstones. How soils evolve on glauconitic sandstones (calcarenite) is poorly addressed: therefore, we investigated the evolutional trajectories. These soils should be enriched in Fe, depleted in K and contain kaolinite and smectite resulting from weathering. We investigated 11 soil profiles on glauconitic calcarenite in a Mediterranean area. The elemental contents, fractions of Fe and Al, soil mineralogy, magnetic susceptibility and stable isotopic composition (C, O) of the bulk soil and carbonates were analysed to explore pedogenesis.The carbonates reflect a former marine basin having onshore organic matter resulting from freshwater input. With soil formation, the primary carbonates were replaced by pedogenic carbonates having a lower δ13C and δ18O signal. Several sites were influenced by human activity since ancient times, reflected by the magnetic susceptibility. The shallow soils had a low weathering degree (CIA of 55 to 70). The better developed Vertisols exhibited a CIA value of up to 85. All soils contained smectite and quartz and, depending on the weathering degree, calcite. Kaolinite formation was connected to high Ca, K, Mg and Na losses. The high oxalate- and dithionite-extractable Fe contents are explained by glauconite weathering. Kaolinite is inherited from the parent material but also actively forms in the soils probably through precipitation from soil water. Due to the presence of smectite and oxyhydroxides the soils sequester a high amount of soil organic carbon (up to 30 kg/m2). Topography exerts a distinct influence on weathering and soil formation. Deepest soils and an advanced weathering stage were measured on footslope sites and shallow soils having a low weathering degree on crest/shoulder sites. Soils on glauconitic calcarenite represent a unique weathering environment that should be investigated even more at the micro-scale.

Applications of X-ray Powder Diffraction Microstructural Analysis in Applied Clay Mineralogy

Clay minerals and sheet silicates are the main constituents of lutites and clays. These materials are relevant in earth science research as well as in economic geology because of the great variety of applications, based on their particular features at different levels of aggregation in mineral assemblages and on the microstructural and structural characteristics of the mineral constituents frequently characterized by micro- and nanocrystalline appearance. Thus, X-ray diffraction is a main tool for fundamental and applied research of these materials. The present review concerns their microstructural research from powder X-ray diffraction data.

Hyperbranched polyglycidol grafted with rosin by a natural catalyst under ultrasound: Synthesis, characterization and antimicrobial activity

This study aimed to apply a novel green polymerization process to produce a new copolymer with potential antimicrobial activity for industrial application. The glycidol was polymerized into hyperbranched polyglycidol (HPG) polymer which in turn has been esterified with rosin to produce hyperbranched copoly(glycidol-Rosin) (HPGR), a new co-polymer. The process used Maghnite-H+, a montmorillonite silicate sheet clay, as an eco-catalyst and ultrasound was applied to enhance the interaction during polymerization. Different catalyst amounts were tested to assess their effects on the polymerization process. Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) were used to analyze the polymer products. The antimicrobial activity of HPGR was assessed against six human standard microbial strains using the agar disc diffusion method. The catalyst percentage of 10% resulted in the best yield for HPGR (35%). Thermogravimetric Analysis (TGA) revealed a best thermal stability of HPGR compared to that of HPG. The HPGR co-polymer displayed the best antibacterial activity against Klebsiella pneumonia, Bacillus cereus, Staphylococcus aureus, and Escherichia coli, producing inhibition zones of 12.33 ± 0.57, 11.00 ± 1.00, 10.66 ± 1.15, and 10.33 ± 1.15 mm, respectively. The hyperbranched copoly(glycidol-Rosin), an eco-catalyst-synthesized co-polymer, displayed interesting physical and antimicrobial properties for industrial application.

Effects of nanosized organic‐rectorite fillers on the morphologies and properties of PVDF UF membrane

AbstractIn this study, polyvinylidene fluoride/organic rectorite (PVDF/OREC) organic–inorganic nanocomposite membrane was prepared by phase conversion method. TEM and X‐ray diffraction (XRD) results demonstrate the successful fabrication of nanocomposite ultrafiltration membranes. When the OREC is less than 3 wt%, the nanosheets are mainly stripped and dispersed in the polymer matrix, with different numbers of intercalations. When the impurity content is 5%, the intercalation distribution dominates. When the impurity content increases to 7% and above, it becomes increasingly difficult for PVDF chain segments to enter the OREC interlayer and the OREC particles are dominated by simple blends on the order of micrometers in the polymer matrix. The inclusion of inorganic fillings significantly improved the mechanical properties of the membrane. The yield strength and tensile modulus of the membrane were increased by 53.7% and 574.9%, respectively, with an inorganic filler content of 5 wt%, while the elongation at the break was slightly decreased to 16.2%. This suggests a strong interaction between the OREC nanosheets and the polymer matrix. XRD and FTIR analyses indicate that OREC particles are effective heterogeneous nucleating agents that favor the formation of β‐phase crystals in the film. SEM surface and cross‐section results show that when joining can significantly reduce the average pore size of the membrane surface, large holes tend to reduce the number of holes in the skin layer distribution more uniformly. The AFM results show that the addition of OREC can significantly alter the surface roughness of ultrafiltered membranes, and that the changes in surface roughness and surface pore morphology of membranes with different clay contents are closely related to the distribution of nanoscale silicate sheets in the PVDF matrix.Highlights Prepared PVDF/OREC nanocomposite membranes via a phase‐inversion process. OREC acted as a potent nucleation agent, favoring β crystal formation. OREC resulted in smaller pore sizes and fewer large pores in the skin layer. The hydrophilicity of PVDF membranes was reformative by filling OREC. OREC led to increased water flux and BSA rejection due to pores and hydrophilicity.

Ammonium concentration in stream sediments resulting from decades of discharge from a wastewater treatment plant

A study of ammonium pollution in the sediments of a stream that receives wastewater treatment plant (WWTP) discharge has been carried out. It is urgently necessary to find environmental indicators that can help prevent and detect potential contamination of water, as water is an increasingly scarce resource. To understand the behaviour of ammonium ions introduced by a historical (50-year) contamination process, vertical boreholes were drilled in the stream banks to depths between 30 and 120 cm. Moisture, pH, ammonium (soluble and exchangeable), and clay fraction content were analysed. The variation profile of these parameters was evaluated as a function of depth to determine factors related to the distribution of ammonium in several locations along the stream banks.The ammonium concentration was asymmetrically distributed among samples collected in near-surface locations, with ammonium concentrations between 0.3048 mmol/kg soil and 0.0007 mmol/kg soil. Ammonium was typically concentrated at sediment depths of 30–40 cm, which also exhibited the highest clay fraction content. High positive correlations were detected (r > 0.8; p < 0.0001) among the different ammonium variables (exchanged and dissolved species). No contamination effect was observed below 60–70 cm depth, which was due to ammonium retention in a natural barrier layer of clayey sediment.The clays in our study area (previously identified as smectite, a 2:1 sheet silicate) were able to control the contamination by retaining ammonium in the interlayers, which retarded nitrification. It is suggested that clay could serve as a geo-indicator of ammonium pollution evolution.

Mobility and bioavailability of mercury in sediments of the southern Baltic sea in relation to the chemical fractions of iron: Spatial and temporal patterns

Marine sediments play a significant role as reservoirs for mercury (Hg), a bioaccumulative toxic pollutant that poses risks to human and ecosystem health. Iron (Fe) has been recognized as an influential factor in the complexation and bioavailability of Hg in sediments. However, limited studies have investigated the interactions between the chemical fractions of these elements in natural settings. This study aims to examine the fractions of Hg and Fe in sediments of the Baltic Sea, a region historically impacted by Hg pollution. The Hg fractions were determined using the thermodesorption technique, while sequential extraction was employed to identify the Fe fractions. The findings confirm the crucial role of Fe in the formation, as well as the horizontal and vertical distribution of labile and stable Hg in marine sediments. Factors such as the contribution of organic matter, the presence of reactive Fe, and Fe associated with sheet silicates emerged as significant drivers that positively influenced the content of the most labile Hg fractions, potentially affecting the mobility and bioavailability of Hg in the marine environment.

Systematic review of the association between talc and female reproductive tract cancers.

Talc is a hydrous magnesium sheet silicate used in cosmetic powders, ceramics, paints, rubber, and many other products. We conducted a systematic review of the potential carcinogenicity of genitally applied talc in humans. Our systematic review methods adhere to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and incorporated aspects from the US Institute of Medicine (IOM, now the National Academy of Medicine) and several US EPA frameworks for systematic reviews, evaluating and integrating the epidemiological, animal, and mechanistic literature on talc and cancer. We conducted a comprehensive literature search. Detailed data abstraction and study quality evaluation, adapting the Toxic Substances Control Act (TSCA) framework, were central to our analysis. The literature search and selection process identified 40 primary studies that assessed exposure to talc and female reproductive cancer risks in humans (n = 36) and animals (n = 4). The results of our evaluation emphasize the importance of considering biological plausibility and study quality in systematic review. Integrating all streams of evidence according to the IOM framework yielded classifications of suggestive evidence of no association between perineal application of talcum powders and risk of ovarian cancer at human-relevant exposure levels. We also concluded that there is suggestive evidence of no association between genital talc application and endometrial cancer, and insufficient evidence to determine whether a causal association exists between genital talc application and cervical cancer based on a smaller but largely null body of literature.

Structure and Properties of Water in a New Model of the 10-Å Phase: Classical and Ab Initio Atomistic Computational Modeling

The 10-Å phase is an important member of the family of dense hydrous magnesium silicates (DHMSs) that play a major role in the water budget in the Earth’s upper mantle. Its nominal composition is usually written as Mg3Si4O10(OH)2·xH2O, and its structure is often described as layers of talc with some amount of water present in the interlayer space. However, its actual structure and composition and the detailed mechanisms of retaining H2O molecules within the mineral are not yet sufficiently known. In particular, more recent spectroscopic and diffraction data indicate the presence of Si vacancies in the tetrahedral silicate sheets of the 10-Å phase leading to the formation of Q2-type Si sites terminated by silanol groups. These silanols are, in turn, hydrogen bonded to interlayer H2O molecules. Here, we use classical and ab initio molecular dynamics (MD) simulations to compare the structures and properties of ideal and defect models of the 10-Å phase under ambient conditions. For classical MD simulations, the most recent modification of the ClayFF force field is used, which can accurately account for the bending of Mg–O–H and Si–O–H angles in the mineral layers, including the structural defects. The crystal lattice parameters, elastic constants, structure, and dynamics of the interlayer hydrogen bonding network for the model 10-Å phase are calculated and compared with available experimental data. The results demonstrate that the inclusion of Si vacancies leads to better agreement with crystallographic data, elastic constants, and bulk and shear moduli compared to a simpler model based on the idealized talc structure. The results also clearly illustrate the importance of the explicit inclusion of Mg–O–H and Si–O–H angular bending terms for accurate modeling of the 10-Å phase. In particular, the properly constrained orientation of the silanol groups promotes the formation of strong hydrogen bonds with the interlayer H2O molecules.

High-performance low-smoke halogen-free flame-retardant composites for Fuxing electric multiple units via synergistic effects of char formation and anti-dripping of clay-based organic sheet silicates

High-performance low-smoke halogen-free flame-retardant composites for Fuxing electric multiple units via synergistic effects of char formation and anti-dripping of clay-based organic sheet silicates

Low content of highly reactive iron in sediments from Prydz Bay and the adjacent Southern Ocean: Controlling factors and implications for sedimentary organic carbon preservation

Examining iron (Fe) speciation in marine sediments is critical to understand Fe and carbon biogeochemical cycling in polar regions. In this study, we investigated the speciation of Fe in sediments from Prydz Bay and the adjacent Southern Ocean, and examined the factors controlling Fe speciation and its relationship with total organic carbon (TOC). Our results reveal that unreactive silicate Fe (FeU) is the dominant pool of total Fe (FeT), followed by poorly reactive sheet silicate Fe (FePRS), reducible crystalline Fe oxides (Feox2), easily reducible amorphous/poorly crystalline Fe oxides (Feox1), and magnetite (Femag), with carbonate-associated ferrous Fe (Fecarb) being the smallest pool. The highly reactive Fe (FeHR)/FeT ratios (0.13 ± 0.06) in our study area are among the lowest end-member globally, primarily due to weak bedrock weathering and slow glacier melting. The Feox1/FeT ratios are similar to those in continental shelf and marginal seas containing highly weathered materials, while the Feox2/FeT ratios are significantly lower. This result implicates that low temperature inhibits the aging of iceberg melting-sourced Feox1 potentially, and accordingly the regulation of weathering on the FeHR/FeT ratio is mainly reflected in Feox2/FeT ratio. There are no significant correlations between TOC and FeHR, Fecarb, Feox1 or Feox2 in the research region. Four distinct patterns of TOC/FeHR ratio can be discerned by summarizing the global data set: (a) high TOC/FeHR ratios (&amp;gt; 2.5) are likely the result of high marine primary productivity and low chemically weathered source materials; (b) low TOC/FeHR ratios (&amp;lt; 0.6) are caused by high rates of FeHR inputs and OC remineralization; (c) mid-range TOC/FeHR ratios (0.6 – 2.5) typical of most river particulates and marginal sea sediments indicate the same FeHR and OC sources and/or interactions between each other; (d) both low TOC and FeHR content is the result of low marine primary productivity and weak chemical weathering. Our findings provide new insights into the relationship between FeHR and TOC in polar sediments.

Green Synthesis of Functionalized Poly(3-Glycidoxypropyl-Trimethoxysilane) Using an Eco-Catalyst (Treated Montmorillonite)

Telechelic poly(3-glycidoxypropyltrimetho¬xysilane) (PGPTMS) with acetate and methacrylate end groups was successfully synthesized by an efficient and solvent-free approach, with anhydrides (acetic anhydride (AA) and methacrylic anhydride (MA)), by cationic ring-opening polymerization of 3 glycidoxypropyl¬trimetho-xysilane (GPTMS), using an ecologic solid catalyst Maghnite-H+ (Mag-H+), instead of electrophilic catalysts, such as, Bronsted and Lewis acids which are very noxious and corrosive. Mag-H+ is a montmorillonite sheet silicate clay exchanged with protons. The structure of the obta¬ined macromonomers was confirmed by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic reso¬nance (NMR) and UV-visible spectroscopy. The presence of the methacrylate end groups of bis-macromonomers was determined by UV-visible spectroscopy. In order to find the optimal reaction conditions, effects of reaction time and the amount of anhydrides (AA and MA) on the yield of macromonomers were investigated.

Crystal-chemical characterisation and spectroscopy of fluorcarletonite and carletonite

AbstractThe minerals of carletonite group, fluorcarletonite, KNa4Ca4[Si8O18](CO3)4(F,OH)·H2O and carletonite, Na4Ca4[Si8O18](CO3)4(OH,F)·H2O, were investigated using a multi-method approach. A detailed comparative chemical study of the minerals was carried out using electron probe microanalysis and Fourier transform infrared spectroscopy. Using X-ray techniques and the results obtained, geometrical and distortion characteristics of the mineral structures are calculated and the successful crystal-structure refinement of these two natural compounds are given. Using spectroscopic and luminescence methods and ab initio calculations, it is shown that hole defects (CO3)•– are responsible for the colouration of the samples studied. Luminescence due to 5d–4f transition in Ce3+ ions is observed in both investigated compounds. Moreover, luminescence attributed to intrinsic luminescence, corresponding to the decay of electronic excitations of (CO3)2– complexes in the carletonite sample, is registered for the first time in phyllosilicates. An analysis of the optical absorption spectra and g-tensor values suggests that (CO3)•– defects in the crystal structure are localised in the C1 positions. Identification of these specific properties for these sheet silicates, with a two-dimensional infinite tetrahedral polymerisation, indicates that carletonites could be prospective materials for novel phosphors and luminophores.

Crystal chemistry of turkestanite, Dara-i-Pioz massif, Tajikistan

AbstractThe results of combined single-crystal X-ray diffraction, electron probe microanalysis, Fourier microspectroscopy, and photoluminescence spectroscopy study of crystals of turkestanite from the Dara-i-Pioz deposit, Tien-Shan Mountains, Tajikistan are reported. It is a single-layer sheet silicate belonging to the ekanite group with a steacyite structural type. Averaged major-element analysis provided (wt.%): K2O 4.13(6), CaO 8.1(1), Na2O 2.3(1), ThO2 25.8(4), UO2 3.6(4) and SiO2 55.9(1). The averaged crystal-chemical formula for the studied turkestanite is (Th0.84U0.12)Σ0.96(Ca1.24Na0.65)Σ1.89(K0.75☐0.25)Σ1.00Si8O19.72(OH)0.28. Single-crystal structural refinement of turkestanite gave tetragonal, space group P4/mcc, a = 7.5708(3) Å, c = 14.7300(11) Å, V = 844.27(6) Å3 and Z = 2. Luminescence of the uranyl ion (UO2)2+ is observed in turkestanite. In the excitation spectrum, the bands corresponding to a charge transfer transition from the 2p states of the ligand to the 5f state of uranium were found.

Granite alteration as the origin of high lithium content of groundwater in southeast Hungary

The study aimed to find the origin of the high lithium content of groundwater in southeast Hungary. To be concerned with assessing the economic potential of lithium in these waters, it is necessary to investigate the lithium-releasing geochemical processes. For this purpose, granite and pegmatite samples were analysed for lithium content and alteration from various Battonya Complex locations. The key alteration processes are the chloritisation of biotite and the sericitisation of feldspar, which are hypothesised to mobilise Li from minerals into the geothermal waters. Whole-rock analyses show that the 36 ppm Li concentration in one sample (S1) exceeded the average crustal Li concentration (∼20 ppm), while three samples have near-average crustal concentrations. The Li content of rock samples decreases along with the increasing intensity of alteration. The Li concentration of biotite, muscovite, chlorite, feldspar and quartz from granites and pegmatite was measured using laser-induced-breakdown-spectrometry (LIBS). A total of 180 data points were analysed. Biotite and muscovite of the relatively fresh granites contain Li up to ∼3800 and ∼2500 ppm, respectively. Chloritisation is a hydrothermal alteration process in granites that can be described by the following reaction: biotite + plagioclase → chlorite + epidote + titanite + muscovite. As a function of chloritisation, Li concentration decreases two- and three orders of magnitude from biotite to chlorite in the more altered cases. A similar trend is observed for muscovite in parallel. Feldspars have Li of 17–141 ppm, while there is no correlation between the Li content of feldspars and the degree of alteration. Quartz contains constant low concentrations around the 1 ppm detection limit, with one outlier value of 48 ppm. Chloritisation of biotite is a possible explanation for the high Li content of the geothermal waters in the study area and possibly elsewhere. The main Li-bearing minerals of the Battonya Complex are biotite and muscovite. Chloritisation and subordinate sericitisation result in significant lithium loss. Chlorite can incorporate Li in its crystal lattice but to a lesser degree than the other sheet silicates, like biotite and muscovite.

Pd Thickness Optimization on Silicate Sheets for Improving Catalytic Activity

AbstractMaximizing surface‐to‐body ratio demands ever smaller metallic palladium (Pd) nanoparticles for catalytic applications. The quest for miniaturization is now reaching the single‐atom limit. However, if the supported Pd is below a critical size, the Pd hybridization with the supporting material can detrimentally reduce the labile electrons that facilitate the catalytic reactions. Thus, the smallest attainable size, i.e., single‐atom Pd, may not offer the best efficiency. Here, it is demonstrated that Pd with at least six atomic layers (or thickness of ≈1 nm) on the silicate sheets, synthesized via the partial exfoliation of a layered silicate, exhibits a metallic‐like electronic property, yielding an excellent catalytic activity (e.g., turnover frequency) for dehydrogenating formic acid higher than both isotropic Pd nanoparticles and single‐atom Pd.

Some new results on the face index of certain polycyclic chemical networks.

Silicate minerals make up the majority of the earth's crust and account for almost 92 percent of the total. Silicate sheets, often known as silicate networks, are characterised as definite connectivity parallel designs. A key idea in studying different generalised classes of graphs in terms of planarity is the face of the graph. It plays a significant role in the embedding of graphs as well. Face index is a recently created parameter that is based on the data from a graph's faces. The current draft is utilizing a newly established face index, to study different silicate networks. It consists of a generalized chain of silicate, silicate sheet, silicate network, carbon sheet, polyhedron generalized sheet, and also triangular honeycomb network. This study will help to understand the structural properties of chemical networks because the face index is more generalized than vertex degree based topological descriptors.