In situ potassium and hydrogen ion exchange into a cubic zirconium silicate microporous material.

The selective separation of ions from aqueous systems, and even in the human body, is a crucial to overall environmental management and health. Nanoporous materials are widely known for their selective removal of cations from aqueous media, and therefore have been targeted for use as a pharmaceutical to treat hyperkalemia. This study investigated the detailed crystallographic molecular mechanisms that control the potassium ion selectivity in the nanoporous cubic zirconium silicate (CZS) related materials. Using time-resolved in situ Raman spectroscopy and time-resolved in situ X-ray diffraction, the selectivity mechanisms were determined to involve a synchronous cation-cation repulsion process that serves to open a favorable coordination bonding environment for potassium, not unlike the ion selectivity filter process found in potassium ion channels in proteins. Enhancement of ion exchange was observed when the CZS material was in a partial protonated state (≈3:1 Na:H), causing an expansion of the unit-cell volume, enlargement of the 7 member-ring window, and distortion of framework polyhedra, which allowed increased accessibility to the cage structures and resulted in rapid irreversible potassium ion exchange.

A Proposed Geobiology-Driven Nomenclature for Astrobiological In Situ Observations and Sample Analyses.

As the exploration of Mars and other worlds for signs of life has increased, the need for a common nomenclature and consensus has become significantly important for proper identification of nonterrestrial/non-Earth biology, biogenic structures, and chemical processes generated from biological processes. The fact that Earth is our single data point for all life, diversity, and evolution means that there is an inherent bias toward life as we know it through our own planet's history. The search for life "as we don't know it" then brings this bias forward to decision-making regarding mission instruments and payloads. Understandably, this leads to several top-level scientific, theoretical, and philosophical questions regarding the definition of life and what it means for future life detection missions. How can we decide on how and where to detect known and unknown signs of life with a single biased data point? What features could act as universal biosignatures that support Darwinian evolution in the geological context of nonterrestrial time lines? The purpose of this article is to generate an improved nomenclature for terrestrial features that have mineral/microbial interactions within structures and to confirm which features can only exist from life (biotic), features that are modified by biological processes (biogenic), features that life does not affect (abiotic), and properties that can exist or not regardless of the presence of biology (abiogenic). These four categories are critical in understanding and deciphering future returned samples from Mars, signs of potential extinct/ancient and extant life on Mars, and in situ analyses from ocean worlds to distinguish and separate what physical structures and chemical patterns are due to life and which are not. Moreover, we discuss hypothetical detection and preservation environments for extant and extinct life, respectively. These proposed environments will take into account independent active and ancient in situ detection prospects by using previous planetary exploration studies and discuss the geobiological implications within an astrobiological context.

Plastic ingestion by freshwater turtles: a review and call to action.

Plastic pollution, and especially plastic ingestion by animals, is a serious global issue. This problem is well documented in marine systems, but it is relatively understudied in freshwater systems. For turtles, it is unknown how plastic ingestion compares between marine and non-marine species. We review the relevant turtle dietary literature, and find that plastic ingestion is reported for all 7 marine turtle species, but only 5 of 352 non-marine turtle species. In the last 10 years, despite marine turtles representing just 2% of all turtle species, almost 50% of relevant turtle dietary studies involved only marine turtles. These results suggest that the potential threat of plastic ingestion is poorly studied in non-marine turtles. We also examine plastic ingestion frequency in a freshwater turtle population, finding that 7.7% of 65 turtles had ingested plastic. However, plastic-resembling organic material would have inflated our frequency results up to 40% higher were it not for verification using Raman spectroscopy. Additionally, we showcase how non-native turtles can be used as a proxy for understanding the potential for plastic ingestion by co-occurring native turtles of conservation concern. We conclude with recommendations for how scientists studying non-marine turtles can improve the implementation, quality, and discoverability of plastic ingestion research.

Uppermost Triassic phosphorites from Williston Lake, Canada: link to fluctuating euxinic-anoxic conditions in northeastern Panthalassa before the end-Triassic mass extinction.

The end-Triassic mass extinction (ETE) is associated with a rise in CO2 due to eruptions of the Central Atlantic Magmatic Province (CAMP), and had a particularly dramatic effect on the Modern Fauna, so an understanding of the conditions that led to the ETE has relevance to current rising CO2 levels. Here, we report multiple phosphorite deposits in strata that immediately precede the ETE at Williston Lake, Canada, which allow the paleoenvironmental conditions leading up to the mass extinction to be investigated. The predominance of phosphatic coated grains within phoshorites indicates reworking in shallow water environments. Raman spectroscopy reveals that the phosphorites contain organic carbon, and petrographic and scanning electron microscopic analyses reveal that the phosphorites contain putative microfossils, potentially suggesting microbial involvement in a direct or indirect way. Thus, we favor a mechanism of phosphogenesis that involves microbial polyphosphate metabolism in which phosphatic deposits typically form at the interface of euxinic/anoxic and oxic conditions. When combined with data from deeper water deposits (Kennecott Point) far to the southwest, it would appear a very broad area of northeastern Panthalassa experienced anoxic to euxinic bottom water conditions in the direct lead up to the end-Triassic mass extinction. Such a scenario implies expansion and shallowing of the oxygen minimum zone across a very broad area of northeastern Panthalassa, which potentially created a stressful environment for benthic metazoan communities. Studies of the pre-extinction interval from different sites across the globe are required to resolve the chronology and spatial distribution of processes that governed before the major environmental collapse that caused the ETE. Results from this study demonstrate that fluctuating anoxic and euxinic conditions could have been potentially responsible for reduced ecosystem stability before the onset of CAMP volcanism, at least at the regional scale.

In Situ Cs and H Exchange into Gaidonnayite and Proposed Mechanisms of Ion Diffusion.

The microporous mineral gaidonnayite Na2ZrSi3O9·2H2O was studied to better understand its ion-exchange mechanisms, specifically for Cs+ and H+ ions. In situ Raman spectroscopy, in situ X-ray diffraction (XRD), simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), and in situ X-ray fluorescence were used to determine the exchange processes involved. The Raman spectra contain strong peaks that can be attributed to the vibrational modes for the 3MR symmetric stretch at 500 cm-1, Si-O-Zr-O chain stretches at 938 cm-1, and Si-O stretching in the 1000-1100 cm-1 range. The most prominent Raman shift during ion exchange is found near the 520 cm-1 peak, which corresponds to distortions of the 3MR substructure of gaidonnayite. In all instances of this study, the 3MR exhibited the highest amount of distortion during ion exchange, and the evolution of this distortion is compared to unit-cell changes as measured from XRD data and elemental changes via XRF. The correlations between the Raman, XRD, and XRF data show rapid deformation of the 3MR during the onset of H+ ion exchange in the Na form of gaidonnayite. Even when unit-cell volume changes were small (<3 Å3) as in the cases for Cs+ into Na-gaidonnayite and Cs+ into H-gaidonnayite, significant changes in the ≈520 cm-1 peak were measured. By comparing XRD data and Raman data, and verifying the cation uptake by XRF, we were able to identify and confirm conformational changes and distortions in the crystal structure before, during, and after Cs+ and H+ exchange. Cs exchange occurred the fastest and with the greatest capacity when starting in the H-form at room temperature, and at elevated temperatures when starting in the Na-form.

Structure Determination and Time-Resolved Raman Spectroscopy of Yttrium Ion Exchange into Microporous Titanosilicate ETS-4.

The ion exchange of yttrium, one of the five most critical rare-earth elements as outlined by the U.S. Department of Energy, into ETS-4 is a dynamic, multistep ion exchange process. The ion exchange process was followed using in situ time-resolved Raman spectroscopy, and the crystal structures of the pre-exchange and post-exchange forms were determined by single-crystal X-ray diffraction. In situ Raman spectroscopy is an ideal tool for this type of study, as it measures the spectral changes that are a result of molecular geometry changes at fast time intervals, even where symmetry and unit volume changes are minimally detected by X-ray diffraction. By tracking the stepwise changes in the peak positions and intensities in the spectra, where we focused primarily on the strong spectral features corresponding to titania quantum wires and three-membered-ring bending and breathing modes, we constructed molecular models to explain the changes in the Raman spectrum during ion exchange. The multistep ion exchange process started with rapid absorption of Y into the Na2 site, causing titania quantum wires to kink. After this initial uptake, the exchange process slowed, likely caused by hydration coordination changes within the channels. Next, Y exchange accelerated again, during which time the Y site moved closer to the framework O2-. Crystal structures of the maximal Y exchanged ETS-4 material were determined and confirmed the splitting of the Y site. Inductively coupled plasma optical emission spectroscopy was also used to quantify the extent of Y exchange and to measure if there were indications of titania leaching from the framework.

Effects of hydration during strontium exchange into nanoporous hydrogen niobium titanium silicate.

A Nb-substituted titanium silicate with the sitinakite (NbTS) topology was exchanged with Sr(2+) to determine the mechanisms and pathways of ion diffusion through this mixed polyhedral nanoporous framework. The refined structural models yield unit cell parameters and atomic positions of Sr(2+) and suggest that there was a two-step process during cation diffusion. The starting material of the exchange experiment was the H(+)-exchanged material, H(1.4)Nb(0.6)Ti(1.4)SiO(7)·1.9H(2)O, with space group P4(2)/mcm. In the beginning of the exchange process, Sr filled the 8-membered-ring channel near the 4(2) axis in the center. Once the Sr(2+) fractional occupancy reached approximate 0.11, Sr positions and extra-framework H(2)O molecules shifted away from the central 8-membered-ring toward the framework, and an increase in Sr hydration and framework bonding was observed. The new H(2)O positions resulted in a lowering of symmetry to the P ̅42m space group, and it is thought that the Sr migration served to enhance Sr(2+) ion diffusion capacity into the channels of NbTS since the exchange rate briefly accelerated after the 0.11 fractional occupancy level was passed. Exchange of Sr(2+) into the nanoporous material reached maximum fractional site occupancy of approximately 0.20 using a 10.0 mM SrCl(2) solution.

In situ X-ray diffraction study of cesium exchange in synthetic umbite.

The exchange of Cs(+) into H(1.22)K(0.84)ZrSi(3)O(9)·2.16H(2)O (umbite-(HK)) was followed in situ using time-resolved X-ray diffraction at the National Synchrotron Light Source. The umbite framework (space group P2(1)/c with cell dimensions of a = 7.2814(3) Å, b = 10.4201(4) Å, c = 13.4529(7) Å, and ß = 90.53(1)°) consists of wollastonite-like silicate chains linked by isolated zirconia octahedra. Within umbite-(HK) there are two unique ion exchange sites in the tunnels running parallel to the a-axis. Exchange Site 1 is marked by 8 member-ring (MR) windows in the bc-plane and contains K(+) cations. Exchange Site 2 is marked by a larger 8-MR channel parallel to [100], and contains H(2)O molecules. The occupancy of the Cs(+) cations through these channels was modeled by Rietveld structure refinements of the diffraction data and demonstrated that there is a two-step exchange process. The incoming Cs(+) ions populated the larger 8-MR channel (Exchange Site 2) first and then migrated into the smaller 8-MR channel. During the exchange process a structural change occurs, transforming the exchanger from monoclinic P2(1)/c to orthorhombic P2(1)2(1)2(1). This structural change occurs when Cs(+) occupancy in the small cavity becomes greater than 0.50. The final in situ ion exchange diffraction pattern was refined to yield umbite-(CsK) with the molecular formula H(0.18)K(0.45)Cs(1.37)ZrSi(3)O(9)·0.98H(2)O and possessing an orthorhombic unit cell with dimensions a = 10.6668(8) Å, b = 13.5821(11) Å, c = 7.3946(6) Å. Solid state (133)Cs MAS NMR showed there is only a slight difference between the two cavities electronically. Valence bond sums for the completely occupied Exchange Site 1 demonstrate that Cs-O bonds of up to 3.8 Å contribute to the coordination of the Cs(+) cation.

The mechanism responsible for extraordinary Cs ion selectivity in crystalline silicotitanate.

Combining information from time-resolved X-ray and neutron scattering with theoretical calculations has revealed the elegant mechanism whereby hydrogen crystalline silicotitanate (H-CST; H2Ti2SiO7 x 1.5 H2O) achieves its remarkable ion-exchange selectivity for cesium. Rather than a simple ion-for-ion displacement reaction into favorable sites, which has been suggested by static structural studies of ion-exchanged variants of CST, Cs(+) exchange proceeds via a two-step process mediated by conformational changes in the framework. Similar to the case of ion channels in proteins, occupancy of the most favorable site does not occur until the first lever, cooperative repulsive interactions between water and the initial Cs-exchange site, repels a hydrogen lever on the silicotitanate framework. Here we show that these interactions induce a subtle conformational rearrangement in CST that unlocks the preferred Cs site and increases the overall capacity and selectivity for ion exchange.

Dehydration-induced water disordering in a synthetic potassium gallosilicate natrolite.

A new potassium gallosilicate zeolite with a natrolite topology (approximate formula K8.2Ga8.2Si11.8O40.11.5H2O) was synthesized under hydrothermal conditions and characterized as a function of temperature using monochromatic synchrotron X-ray powder diffraction and Rietveld analyses. Unlike the previously known tetragonal K8Ga8Si12O40.6H2O phase, the as-synthesized material contains twice the amount of water molecules in an ordered arrangement throughout the channels in an orthorhombic (I212121) symmetry. The ordered configuration of water molecules is stabilized below 300 K, whereas heating above 300 K results in a selective dehydration and subsequent disordering of water molecules in a tetragonal (I2d) symmetry. Above 400 K, the material transforms to a fully dehydrated tetragonal phase with a concomitant volume reduction of ca. 15%. The fully dehydrated material transforms back to its original state when rehydrated over a period of up to 2 weeks. The distribution of potassium cations within the channels remains largely unperturbed during the water rearrangements and their order-disorder transition within the channels.

Role of the hydroxyl-water hydrogen-bond network in structural transitions and selectivity toward cesium in Cs0.38(D1.08H0.54)SiTi2O7.(D0.86H0.14)2O crystalline silicotitanate.

The crystal structure of the selective Cs+ ion exchanger D1.6H0.4Ti2SiO7.D2.66H0.34O1.5, known as crystalline silicotitanate or CST, has been determined in both native (D-CST) and in the Cs+-exchanged forms ((Cs, D)-CST) from angle-dispersive and time-of-flight neutron diffraction studies. The final fully exchange Cs+ form transformed from D-CST with unit cell parameters a = 11.0704(3) A c = 11.8917(5) A and space group P42/mbc, to one with a = 7.8902(1) A c = 11.9051(4) A and space group P42/mcm. Rietveld structure refinements of both D-CST and (Cs, D)-CST suggest the transition, and ultimately the selectivity, is driven by changes in the positions of water molecules, in response to the initial introduction of Cs+. The changes in water position appear to disrupt the D-O-O-D dihedral associated with the CST framework in space group P42/mbc which ultimately leads to the structural transition. The new geometric arrangement of the water-deuteroxyl network in (Cs, D)-CST suggests that Dwater-Ddeuteroxyl repulsion forced by Cs+ exchange drives the structural transformation.

Solid-state structural characterization of a rigid framework of lacunary heteropolyniobates.

In our ongoing investigations of heteropolyniobate chemistry, a phase featuring decorated, A-type trivacant alpha-Keggin ions linked by their charge-balancing sodium cations has been isolated and structurally characterized. This is the first heteropolyniobate reported that has a true lacunary structure type. Na15[(PO2)3PNb9O34] x 22 H2O (1) [triclinic space group P1 (No. 2); a = 12.242 (2) A, b = 12.291 (3) A, c = 22.056 (4) A; alpha = 93.12 (3) degrees, beta = 99.78 (3) degrees, gamma = 119.84 (3) degrees; Z = 4, V = 2799.2 (10) A3] is composed of bilayers of the heteropolyanions alternating with layers of hydrated Na+ cations. Sodium cations also bridge the clusters within their layers through Na-O(t)-Nb, Na-O(b)-Nb2, and Na-O(t)-P bonds (t = terminal and b = bridging). This phase is poorly soluble in water, suggesting that it is more characteristic of a framework of linked heteropolyanions rather than a water-soluble heteropolyanion salt. Two-dimensional solid-state 23Na multiple-quantum magic angle spinning (MAS) NMR of 1 reveals five distinctive chemical and structural environments for sodium, which agrees with the crystallographic data. The 23Na and 1H MAS NMR studies further illustrate the rigid and immobile nature of this framework of cations and anions.

Tribasic lead maleate and lead maleate: synthesis and structural and spectroscopic characterizations.

We report on the synthesis and structure of tribasic lead maleate hemihydrate ([Pb4O3]C2H2(CO2)2.(1/2)H2O, TRIMAL) and lead maleate (PbC2H2(CO2)2, PBMAL). The structure of [Pb4O3]C2H2(CO2)2.(1/2)H2O, solved ab initio from X-ray powder diffraction data, consists of infinite slabs of edge-sharing OPb4 tetrahedra, of composition [Pb4O3], running along the c axis and linked together into a three-dimensional network by tetradentate maleate anionic ligands. The structure of PbC2H2(CO2)2, solved from single crystal diffraction data, is lamellar and contains double layers of heptacoordinated lead atoms, bonded only to the oxygen atoms of the maleate ligands. In both compounds, lead is in the oxidation state 2+ and the coordination polyhedra around the Pb2+ exhibit a hemidirected geometry and are strongly distorted as a result of the lone pair of electrons. The absence of protons on the acidic portion of the maleate moieties was confirmed by Raman spectroscopy and by 1H MAS and 1H-13C CP MAS NMR experiments. The two compounds were further characterized using chemical and thermogravimetric analyses.

High-pressure neutron diffraction study of superhydrated natrolite.

Neutron powder diffraction data were collected on a sample of natrolite and a 1:1 (v/v) mixture of perdeuterated methanol and water at a pressure of 1.87(11) GPa. The natrolite sample was superhydrated, with a water content double that observed at ambient pressure. All of the water deuterium atoms were located and the nature and extent of the hydrogen bonding elucidated for the first time. This has allowed the calculation of bond valence sums for the water oxygen atoms, and from this, it can be deduced that the key energetic factor leading to loss of the additional water molecule upon pressure release is the poor coordination to sodium cations within the pores.

(K4Li4)Al8Ge8O32.8H2O: an Li+-exchanged potassium aluminogermanate with the zeolite gismondine (GIS) topology.

The title compound, lithium potassium dialuminium digermanium octaoxide dihydrate, (K,Li)-(Al,Ge)-GIS (GIS is gismondine), is the result of a 50% Li(+) exchange into the K-(Al,Ge)-GIS structure. The (K,Li)-(Al,Ge)-GIS structure was determined from a 4 x 4 x 2 micro m octahedral single crystal at the ESRF synchrotron X-ray source. The ion exchange results in a symmetry transformation from I2/a for K-(Al,Ge)-GIS to C2/c for (K,Li)-(Al,Ge)-GIS. The structural change is due to disordering of K(+) ions with Li(+) ions along the [001] channel and ordering of water molecules in the [101] channels. The distance between sites partially occupied by K(+) ions increases from 2.19 (3) A in K-(Al,Ge)-GIS to 2.94 (3) A in (K,Li)-(Al,Ge)-GIS. The Li(+) ions occupy positions along the twofold axis at the intersection of the eight-membered-ring channels in a twofold coordination with water molecules. For the four closest framework O(2-) anions, the Li.O distances are 3.87 (4) A.