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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Behaviour of cadmium isotopes in sulfidic waters and sediments of the Black Sea: Implications for global cadmium cycling and the application of cadmium isotopes as a paleo-oceanographic proxy

The cadmium isotope system has found use as a tracer for biological productivity, redox and organic carbon burial in the oceans. There are, however, very few observational constraints on Cd isotopic behaviour in modern sulfidic marine conditions, limiting our understanding of the modern Cd cycle, and our ability to use Cd isotope measurements of ancient sedimentary deposits as a paleoceanographic proxy. Here we study the behaviour of dissolved Cd in the water column of the Black Sea and its incorporation into sediments on the basin floor. The isotopic composition of dissolved Cd in the upper ∼50 m of the Black Sea water column is controlled by a combination of biological uptake and regeneration along with mixing of river water and Mediterranean seawater. Cadmium declines to <2 % of its peak subsurface concentration within the zone of nitrate-reduction but above the sulfide chemocline. The isotopic composition of dissolved Cd below the sulfide chemocline evolves in a manner that is consistent with experimental Cd sulfide fractionation factors, providing field-based support for these earlier studies. In contrast, the stability of the dissolved Cd isotopic signature above the chemocline, despite a large reduction in dissolved Cd concentrations, is explained by diffusion towards the Cd-sulfide sink below the chemocline. Sediments accumulating in the deep Black Sea below the sulfide chemocline have isotopic compositions that are similar to dissolved Cd in its near-surface aqueous concentration maximum. Sediments accumulating at shallower depths have lighter isotopic compositions that are likely affected by non-sulfidic burial pathways mediated by macrofaunal mixing and diagenesis of shallow burial phases. Our study shows that the isotopic composition of bulk sediments accumulating under sulfidic conditions is similar to dissolved Cd in the upper water column, supporting its use as a paleo-chemical proxy for ancient seawater as long as basin-scale controls on open ocean seawater sources are considered. We show that Cd burial in the deep Black Sea, predominantly as CdS, accounts for ∼0.5–15 % of total annual Cd burial in the global ocean.

Biogeochemical cycles↗
DOE OSTI2016

Deletion of phytochelatin synthase modulates the metal accumulation pattern of cadmium exposed C. elegans

Here, environmental metal pollution is a growing health risk to flora and fauna. It is therefore important to fully elucidate metal detoxification pathways. Phytochelatin synthase (PCS), an enzyme involved in the biosynthesis of phytochelatins (PCs), plays an important role in cadmium detoxification. The PCS and PCs are however not restricted to plants, but are also present in some lower metazoans. The model nematode Caenorhabditis elegans , for example, contains a fully functional phytochelatin synthase and phytochelatin pathway. By means of a transgenic nematode strain expressing a pcs -1 promoter-tagged GFP ( pcs -1::GFP) and a pcs -1 specific qPCR assay, further evidence is presented that the expression of the C. elegans phytochelatin synthase gene (pcs-1) is transcriptionally non-responsive to a chronic (48 h) insult of high levels of zinc (500 μM) or acute (3 h) exposures to high levels of cadmium (300 μM). However, the accumulation of cadmium, but not zinc, is dependent on the pcs -1 status of the nematode. Synchrotron based X-ray fluorescence imaging uncovered that the cadmium body burden increased significantly in the pcs -1(tm1748) knockout allele. Taken together, this suggests that whilst the transcription of pcs -1 may not be mediated by an exposure zinc or cadmium, it is nevertheless an integral part of the cadmium detoxification pathway in C. elegans .

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Effect of surfactant in mitigating cadmium oxide nanoparticle toxicity: Implications for mitigating cadmium toxicity in environment

Cadmium (Cd), classified as human carcinogen, is an extremely toxic heavy metal pollutant, and there is an increasing environmental concern for cadmium exposure through anthropogenic sources including cigarette smoke. Though Cd based nanoparticles such as cadmium oxide (CdO) are being widely used in a variety of clinical and industrial applications, the toxicity of CdO nanoparticles has not been well characterized. Herein we report the toxicity of CdO nanoparticles employing zebrafish as a model. Two different CdO nanoparticles were prepared, calcination of Cd(OH){sub 2} without any organic molecule (CdO-1) and calcination of Cd-citrate coordination polymer (CdO-2), to evaluate and compare the toxicity of these two different CdO nanoparticles. Results show that zebrafish exposed to CdO-2 nanoparticles expressed reduced toxicity as judged by lower oxidative stress levels, rescue of liver carboxylesterases and reduction in metallothionein activity compared to CdO-1 nanoparticles. Histopathological observations also support our contention that CdO-1 nanoparticles showed higher toxicity relative to CdO-2 nanoparticles. The organic unit of Cd-citrate coordination polymer might have converted into carbon during calcination that might have covered the surface of CdO nanoparticles. This carbon surface coverage can control the release of Cd{sup 2+} ions in CdO-2 compared to non-covered CdO-1 nanoparticles and hence mitigate the toxicity in the case of CdO-2. This was supported by atomic absorption spectrophotometer analyses of Cd{sup 2+} ions release from CdO-1 and CdO-2 nanoparticles. Thus the present study clearly demonstrates the toxicity of CdO nanoparticles in an aquatic animal and also indicates that the toxicity could be substantially reduced by carbon coverage. This could have important implications in terms of anthropogenic release and environmental pollution caused by Cd and human exposure to Cd{sup 2+} from sources such as cigarette smoke. - Highlights: • Toxicity of CdO nanoparticles can be mitigated by the use of sodium citrate. • Sodium citrate covers the CdO surface and reduces Cd{sup 2+} ion release. • Use of sodium citrate reduces both biochemical and histopathological changes. • Sodium citrate can be a remediation strategy against CdO nanoparticles toxicity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Evolution of oxygenated cadmium sulfide (CdS:O) during high-temperature CdTe solar cell fabrication

Oxygenated cadmium sulfide (CdS:O) produced by reactive sputtering has emerged as a promising alternative to conventional CdS for use as the n-type window layer in CdTe solar cells. Here, complementary techniques are used to expose the window layer (CdS or CdS:O) in completed superstrate devices and combined with a suite of materials characterization to elucidate its evolution during high temperature device processing. During device fabrication amorphous CdS:O undergoes significant interdiffusion with CdTe and recrystallization, forming CdS1-yTey nanocrystals whose Te fraction approaches solubility limits. Significant oxygen remains after processing, concentrated in sulfate clusters dispersed among the CdS1-yTey alloy phase, accounting for ~30% of the post-processed window layer based on cross-sectional microscopy. Interdiffusion and recrystallization are observed in devices with un-oxygenated CdS, but to a much lesser extent. Etching experiments suggest that the CdS thickness is minimally changed during processing, but the CdS:O window layer is reduced from 100 nm to 60-80 nm, which is confirmed by microscopy. Alloying reduces the band gap of the CdS:O window layer to 2.15 eV, but reductions in thickness and areal density improve its transmission spectrum, which is well matched to device quantum efficiency. The changes to the window layer in the reactive environments of device fabrication are profoundly different than what occurs by thermal annealing in an inert environment, which produced films with a band gap of 2.4 eV for both CdS and CdS:O. These results illustrate for the first time the significant changes that occur to the window layer during processing that are critical to the performance of CdTe solar cells.

14 SOLAR ENERGY↗
DOE OSTI2015

Properties of reactively sputtered oxygenated cadmium sulfide (CdS:O) and their impact on CdTe solar cell performance

Oxygenated cadmium sulfide (CdS:O) is commonly used as the n-type window layer in high-performance CdTe heterojunction solar cells. This layer is deposited by reactive sputtering, but the optimal amount of oxygen in the sputtering ambient is highly dependent on the specific system and process employed. In this work, the intrinsic properties of CdS:O were measured as a function of the oxygen content (0%–10%) in the sputtering ambient and correlated to device performance with the goal of better defining optimal CdS:O properties for CdTe solar cells. Optimal performance was found using CdS:O films that contained ∼40 at. % oxygen as measured by Rutherford backscattering spectrometry. X-ray photoelectron spectroscopy confirmed these results and showed that oxygen is incorporated primarily as oxygenated sulfur compounds (SO{sub x}). Device efficiency improved from 10.5% using CdS to >14% with CdS:O due largely to increases in short-circuit current density as well as a modest improvement in open-circuit voltage. The transparency of the CdS:O films was well correlated with observed improvements in blue quantum efficiency with increasing oxygen content. The optical bandgap of as-deposited CdS:O was identified as a simple metric for process optimization and transfer, with 2.8 eV being ideal for the device architecture employed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Increase of lifetime cadmium intake dose-dependently increased all cause of mortality in female inhabitants of the cadmium-polluted Jinzu River basin, Toyama, Japan

Highlights: • The mortality risk ratios of LCd (+1 g) for all causes in women were dose-dependently increased (risk ratio: 1.08). • Relative risk of LCd for kidney and urinal tract disease, renal diseases and renal failure were higher in women. • Life prognosis was adversely affected by Cd-exposure, especially in women. Exposure to cadmium (Cd) via food is supposed to affect life prognosis of inhabitants of Cd-polluted area in Japan. However, there have been few reports demonstrating a significant relationship between the amount of Cd intake and mortality. We aimed to investigate the relationship between mortality and individual lifetime Cd intake (LCd) in inhabitants of the polluted Jinzu River basin, Toyama, Japan.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Cadmium isotope systematics in sedimentary carbonate: Extending the utility of the cadmium isotope palaeo-productivity proxy

The cadmium (Cd) isotope compositions of seven Holocene (<11.7 ka) carbonate sediments, including the bulk carbonate, as well as the > 140 μm (zooplankton), <63 μm and < 20 μm (phytoplankton) fractions, and individual species of foraminifera isolated from the bulk carbonate were obtained for sub-samples processed using the Cd-cleaning and Mg/Ca cleaning methods. The respective Cd isotope systematics of each carbonate archive were then compared with the Cd isotope signature within the ocean using modern seawater data. We show that a constant Cd isotope fractionation factor of -0.25 ± 0.03 ‰ (2SE, n = 4) describes the partitioning of Cd from seawater into the carbonate phase ($Δ^{114}Cd_{CdC O_3 - seawater}$), allowing for accurate reconstructions of the past seawater nutrient regime. The Cd isotope signature of the < 63 µm and < 20 µm (phytoplankton) fractions can display comparable values to those recorded in the modern surface ocean, and can be used to model the magnitude of Cd uptake and utilisation in the past ocean. Individual species of planktic and benthic foraminifera, which inhabit different depths of the water column, can provide a full surface to deep water column reconstruction of the Cd nutrient regime, while infaunal benthic foraminifera can be used to interrogate the Cd isotope systematics of sediment porewaters. Bulk sediment and the > 140 µm (zooplankton) fraction also retain important information relating to the overlying water column Cd isotope systematics and can serve as essential archives for palaeo-productivity reconstructions where the separation of individual components from the bulk sediment is not possible. This new Cd isotope palaeo-productivity toolkit can considerably aid reconstruction efforts and vastly improves the ability to quantify the role of phytoplankton in modulating carbon sequestration through transitions in Earth’s climate evolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Controlling Infrared Plasmon Resonances in Inverse-Spinel Cadmium Stannate Nanocrystals via Site-Selective Cation-Exchange Reactions

Doped metal oxide nanocrystals (NCs) exhibit tunable localized surface plasmon resonances (LSPRs) in the infrared spectral region. Compared to the binary oxides commonly studied, plasmonic NCs derived from ternary oxides remain far less explored primarily due to the difficulty of controlling NC phase-purity and stoichiometry. Here, we report the synthesis of inverse spinel-type cadmium stannate (Cd 2 SnO 4 ) NCs, for which cation-exchange reactions were developed to tailor their composition and LSPR properties. X-ray absorption spectroscopy studies revealed that the inequivalent tetrahedrally and octahedrally coordinated Cd 2+ can be selectively exchanged for Cu + and In 3+ ions, respectively, enabling broadband tunable LSPR and Cu-mediated cation-exchange with lanthanide ions that are otherwise difficult to incorporate. Here, our work paves the way for systematic compositional engineering to accelerate the design of complex metal oxide NCs with emerging plasmonic, electronic, and magnetic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Femtosecond optical polarization switching using a cadmium oxide-based perfect absorber

Ultrafast control of the polarization state of light may enable a plethora of applications in optics, chemistry and biology. However, conventional polarizing elements, such as polarizers and waveplates, are either static or possess only gigahertz switching speeds. Here, with the aid of high-mobility indium-doped cadmium oxide (CdO) as the gateway plasmonic material, we realize a high-quality factor Berreman-type perfect absorber at a wavelength of 2.08 μm. On sub-bandgap optical pumping, the perfect absorption resonance strongly redshifts because of the transient increase of the ensemble-averaged effective electron mass of CdO, which leads to an absolute change in the p-polarized reflectance from 1.0 to 86.3%. As a result, by combining the exceedingly high modulation depth with the polarization selectivity of the perfect absorber, we experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Understanding the role of selenium in defect passivation for highly efficient selenium-alloyed cadmium telluride solar cells

Electricity produced by cadmium telluride (CdTe) photovoltaic modules is the lowest-cost electricity in the solar industry, and now undercuts fossil fuel-based sources in many regions of the world. This is due to recent efficiency gains brought about by alloying selenium into the CdTe absorber, which has taken cell efficiency from 19.5% to its current record of 22.1%. Although the addition of selenium is known to reduce the bandgap of the absorber material, and hence increase the cell short-circuit current, this effect alone does not explain the performance improvement. Here, by means of cathodoluminescence and secondary ion mass spectrometry, we show that selenium enables higher luminescence efficiency and longer diffusion lengths in the alloyed material, indicating that selenium passivates critical defects in the bulk of the absorber layer. Here, this passivation effect explains the record-breaking performance of selenium-alloyed CdTe devices, and provides a route for further efficiency improvement that can result in even lower costs for solar-generated electricity.

14 SOLAR ENERGY↗
DOE OSTI2018

Investigation of cadmium telluride grown by molecular-beam epitaxy using micro-Raman spectroscopy below and above the laser damage threshold

The effects of visible laser light on cadmium telluride (CdTe), grown by molecular beam epitaxy, are studied at low (48 μ W/ μ m 2 ) and high (480 μ W/ μ m 2 ) laser power densities using micro-Raman spectroscopy. The Raman spectrum of CdTe shows no notable change at low power density ~48 μ W/ μ m 2 for prolonged laser exposure. At higher power density ~480 μ W/ μ m 2 , the Raman spectrum is significantly changed and strong Te-related peaks appear in the spectrum, even for short laser exposure times suggesting that photo-induced Te enrichment happens at the CdTe surface at high laser power density. The temperature rise is estimated from observed shifts in the Te and CdTe optical phonon peaks and modeled using finite-element simulations. At laser power 480 μ W/ μ m 2 , the CdTe exhibits a rise of ~44 °C above room temperature while the observed change in Te temperature is significantly higher, ~179 °C. Furthermore, the approach illustrates steps needed to establish the laser damage threshold for CdTe.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Two-Dimensional Cadmium Chloride Nanosheets in Cadmium Telluride Solar Cells

In this paper we make use of a liquid nitrogen-based thermomechanical cleavage technique and a surface analysis cluster tool to probe in detail the tin oxide/emitter interface at the front of completed CdTe solar cells. We show that this thermomechanical cleavage occurs within a few angstroms of the SnO 2 /emitter interface. An unexpectedly high concentration of chlorine at this interface, ~20%, was determined from a calculation that assumed a uniform chlorine distribution. Angle-resolved X-ray photoelectron spectroscopy was used to further probe the structure of the chlorine-containing layer, revealing that both sides of the cleave location are covered by one-third of a unit cell of pure CdCl 2 , a thickness corresponding to about one Cl-Cd-Cl molecular layer. We interpret this result in the context of CdCl 2 being a true layered material similar to transition-metal dichalcogenides. Exposing cleaved surfaces to water shows that this Cl-Cd-Cl trilayer is soluble, raising questions pertinent to cell reliability. Our work provides new and unanticipated details about the structure and chemistry of front surface interfaces and should prove important to improving materials, processes, and reliability of next-generation CdTe-based solar cells.

14 SOLAR ENERGY↗