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One-step approach for synthesis of nanosized Cu-doped zeolite A crystals using the Cu–EDTA-complex.
No full textCopper-doped nanosized zeolite A crystals were synthesized by an in situ templating approach using [Cu(EDTA)]2−-complex. The structural properties of the copper containing zeolite crystals were characterized by a suite of different techniques including SEM–EDX, ESR, mid-IR and Far-IR, Raman, in situ XRD and non-ambient neutron powder diffraction. The SEM investigations on the morphology show spheroidal zeolite A crystals with average size ∼200 nm. The asymmetric ESR spectrum shows that the Cu2+ ion is in a tetragonal-distorted octahedral crystal field. FT-IR and Raman spectroscopies provide information on coordination environment of the copper ion. The band due to stretching vibration of C–N bond, where N is coordinated to the copper ion (C–N–Cu), was observed at 1109 cm−1 in the mid-infrared region. The Raman band due to the Cu–O bond is present at 630 cm−1 indicating the coordination of the Cu2+-cation to COO−-group of the EDTA-ion. The XRD data shows an enlarged d-spacing between the adjacent zeolite lattice planes due to the presence of the [Cu(EDTA)]2−-complex in comparison to template-free LTA zeolite structure. LeBail fitting approach on temperature-dependent in situ X-ray and neutron diffraction profiles have demonstrated the expansion of the zeolite cell during the thermal treatment followed by subsequent contraction with the decomposition of the organic template. © 2014, Elsevie
Incorporation of uranium in pyrochlore oxides and pressure-induced phase transitions.
No full textUranium-doped gadolinium zirconates with pyrochlore structure were studied at ambient and high-pressure conditions up to 40 GPa. The bonding environment of uranium in the structure was determined by x-ray photoelectron and Raman spectroscopies and x-ray diffraction. The uranium valence for samples prepared in air is mainly U6+, but U4+ is present in pyrochlores fabricated in an argon atmosphere. Rietveld refinement of the XRD pattern suggests that uranium ions in pyrochlores are on the 16d site in 6-fold coordination with oxygen. At pressures greater than 22 GPa, the pyrochlore structure transformed to a cotunnite-type phase. The cotunnite high-pressure phase transformed to a defect fluorite structure on the release of pressure. © 2014 Elsevier Inc
Zirconium organophosphonates as high capacity, selective lanthanide sorbents
No full textNovel and versatile zirconium organophosphonate coordination networks have been developed as sorbent platforms via simple, low-temperature hydrothermal reactions of zirconium propoxide with amino tris(methylene phosphonic acid) (ATMP). The resulting materials exhibited hierarchical porosity and possessed exceptional selectively for lanthanide elements over mono- and divalent metal ions during competitive sorption experiments in 0.1 M HNO3, as well as modest intra-lanthanide selectivity. As such, the present materials have potential as solid phase extractants for lanthanide separations in applications including mining, radioactive waste treatment and environmental remediation. Lanthanide sorption was shown to occur via uncoordinated Psingle bondO groups in the ATMP molecule. The structure, porosity and sorption properties of the coordination network platform could be tuned through varying the molar ratio of phosphorus to zirconium. Interestingly, the sample with the lowest surface area (<2 m2/g) demonstrated the highest sorption capacity. Optimal compositions demonstrated europium sorption with fast kinetics and very high capacities of up to 0.63 g/mg min and 60 mg/g respectively. As such, these highly stable zirconium organophosphonates, prepared from inexpensive precursor chemicals using one-pot methods, perform comparably to costly commercially available polymer resins. © 2014, Elsevier B.V
High-yield synthesis and crystal structure of a green Au30 cluster co-capped by thiolate and sulfide
No full textA green gold-cluster, Au30S(StBu)18, was successfully prepared in high yield and crystallographically characterized. Each cluster consists of an Au22 core capped by a mixed layer of staple Au-thiolate units, bridging thiolates and a μ3-S2−.© 2014, The Royal Society of Chemistry
Compatibility of atmospheric 14CO2 measurements: comparing the heidelberg low-level counting facility to international accelerator mass spectrometry (AMS) laboratories
No full textCombining atmospheric Δ14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare Δ14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric Δ14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for Δ14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal. © 2016 by the Arizona Board of Regents on behalf of the University of Arizon
Use of stable and radioactive isotopes to unravel surface water groundwater interactions in a developed catchment. International Symposium on Isotope Hydrology: Revisiting Foundations and Exploring Frontiers.
No full textAbstract: Traditionally surface water groundwater interactions are estimated using
hydrometric and water balance methods. However, the hydrometric methods, based on
hydraulic gradients, have huge uncertainties related to the mostly unknown and often highly heterogeneous permeability distribution. Similarly, the surface water groundwater exchange can be relatively small compared to other components of the water balance (e.g. differential steam flow gauging) and consequently its estimation is associated with large uncertainties
when using a water balance method. Environmental tracers such as isotopes on the other hand integrate what has actually taken place. However, each individual isotopic tracer has particular advantages and disadvantages and therefore limited use. For instance each radioactive isotope is limited to provide residence time estimations within a certain age range
whereas stable isotopes only work when different water sources have distinctly different
isotopic compositions. In this study, of a highly developed catchment subject to groundwater
depletion it is demonstrated that by combining different tracers (14C, 3H, 2H and 18O) a more complete picture of the surface water groundwater interactions can be obtained
Statistical analysis of ITRAX XRF data to identify marine incursion, sediment source, and saltwater leaching in tsunami deposits
No full textGeochemical investigation of fine-grained tsunami sediments has found that a characteristic salinity signature can be commonly found in tsunami deposits and underlying soils following an event. We extend this method to assess historic and paleotsunami deposits and investigate a wider range of particle sizes, with the aim of identifying whether salinity signatures are present and determining the source material of the deposits. Geochemical and mineralogical investigation of seven short cores was undertaken at four sites in New Zealand, where historic and/or palaeotsunami deposits were present as sand, silt or gravel layers intercalated between soils. Geochemical signatures were measured using a high-resolution ITRAX X-ray fluorescence (XRF) core scanner and results were analysed using Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA). We were able to explore the signatures of historical events, verify that prehistoric deposits were laid down by tsunamis, and compare these sediments with the background depositional environment. A t-test of means was applied for salinity marker elements (S, Cl, Br) in the soils immediately above and below tsunami sand layers, to test for evidence of saltwater leaching. The dominant mineralogy of the sediments was determined using portable X-ray diffraction and the data used to consider source material and interpret the corresponding XRF data. Geochemical signatures were found to be site specific, depending primarily on the composition of the material. PCA and HCA results clearly distinguished the signature of the tsunami deposits from the background material at each individual site and were able to confirm or deny palaeodeposits as tsunami-related, by comparison with the signatures of known events in the same core or nearby
Marine water from mid-Holocene sea level highstand trapped in a coastal aquifer: Evidence from groundwater isotopes, and environmental significance
No full textA multi-layered coastal aquifer in southeast Australia was assessed using environmental isotopes, to identify the origins of salinity and its links to palaeo-environmental setting. Spatial distribution of groundwater salinity (electrical conductivity values ranging from 0.395 to 56.1 mS/cm) was examined along the coastline along with geological, isotopic and chemical data. This allowed assessment of different salinity sources and emplacement mechanisms. Molar chloride/bromide ratios range from 619 to 1070 (621 to 705 in samples with EC > 15 mS/cm), indicating salts are predominantly marine. Two distinct vertical salinity profiles were observed, one with increasing salinity with depth and another with saline shallow water overlying fresh groundwater. The saline shallow groundwater (EC = 45.4 to 55.7 mS/cm) has somewhat marine-like stable isotope ratios (δ18O = − 2.4 to − 1.9 ‰) and radiocarbon activities indicative of middle Holocene emplacement (47.4 to 60.4 pMC). This overlies fresher groundwater with late Pleistocene radiocarbon ages and meteoric stable isotopes (δ18O = − 5.5 to − 4.6‰). The configuration suggests surface inundation of the upper sediments by marine water during the mid-Holocene (c. 2–8 kyr BP), when sea level was 1–2 m above today's level. Profiles of chloride, stable isotopes, and radiocarbon indicate mixing between this pre-modern marine water and fresh meteoric groundwater to varying degrees around the coastline. Mixing calculations using chloride and stable isotopes show that in addition to fresh-marine water mixing, some salinity is derived from transpiration by halophytic vegetation (e.g. mangroves). The δ13C ratios in saline water (− 17.6 to − 18.4‰) also have vegetation/organic matter signatures, consistent with emplacement by surface inundation and extensive interaction between vegetation and recharging groundwater. Saline shallow groundwater is preserved only in areas where low permeability sediments have slowed subsequent downwards propagation. The configuration is unlikely to be stable long-term due to fluid density; this may be exacerbated by pumping the underlying aquifer. © 2015, Elsevier B.V
Measurements of 14C in ancient ice from Taylor Glacier, Antarctica constrain in situ cosmogenic 14CH4 and 14CO production rates.
No full textCarbon-14 (14C) is incorporated into glacial ice by trapping of atmospheric gases as well as direct near-surface in situ cosmogenic production. 14C of trapped methane (14CH4) is a powerful tracer for past CH4 emissions from “old” carbon sources such as permafrost and marine CH4 clathrates. 14C in trapped carbon dioxide (14CO2) can be used for absolute dating of ice cores. In situ produced cosmogenic 14C in carbon monoxide (14CO) can potentially be used to reconstruct the past cosmic ray flux and past solar activity. Unfortunately, the trapped atmospheric and in situ cosmogenic components of 14C in glacial ice are difficult to disentangle and a thorough understanding of the in situ cosmogenic component is needed in order to extract useful information from ice core 14C. We analyzed very large (≈1000 kg) ice samples in the 2.26–19.53 m depth range from the ablation zone of Taylor Glacier, Antarctica, to study in situ cosmogenic production of 14CH4 and 14CO. All sampled ice is >50 ka in age, allowing for the assumption that most of the measured 14C originates from recent in situ cosmogenic production as ancient ice is brought to the surface via ablation. Our results place the first constraints on cosmogenic 14CH4 production rates and improve on prior estimates of 14CO production rates in ice. We find a constant 14CH4/14CO production ratio (0.0076 ± 0.0003) for samples deeper than 3 m, which allows the use of 14CO for correcting the 14CH4 signals for the in situ cosmogenic component. Our results also provide the first unambiguous confirmation of 14C production by fast muons in a natural setting (ice or rock) and suggest that the 14C production rates in ice commonly used in the literature may be too high. © 2016, Elsevier Ltd
Magnetic structures of βI-Li2CoSiO4 and γ0-Li2MnSiO4: Crystal structure type vs. magnetic topology
No full textThe magnetic structure and properties of the candidate lithium-ion battery cathode materials Pbn21(≡Pna21) Li2CoSiO4 and P21/n Li2MnSiO4 have been studied experimentally using low-temperature neutron powder diffraction and magnetometry. Both materials undergo long-range antiferromagnetic ordering, at 14 K and 12 K respectively, due to super–super-exchange mediated by bridging silicate groups. Despite having different crystal structures (wurtzite- vs. “dipolar”-type), Li2CoSiO4 and Li2MnSiO4 have the same topology in terms of magnetic interactions, and adopt collinear magnetic structures of the same type with the propagation vectors (0, 1/2, 1/2) and (1/2, 0, 1/2), respectively. The magnetic moments in the two materials are aligned in parallel and obliquely to the distorted closed-packed layers of oxygen atoms. The experimentally observed values of the ordered magnetic moments, 2.9 μB and 4.6 μB, are close to those expected for d7 Co2+ and d5 Mn2+, respectively.© 2014, Elsevier Inc