17 research outputs found
Nanosized inorganic metal oxides as heterogeneous catalysts for the degradation of chemical warfare agents
No full textNanosized inorganic metal oxides, such as TiO2, ZnO, -Al2O3, are proposed as heterogeneous catalysts for the oxidative degradation of chemical warfare agents (CWA), particularly of organosulfur toxic
agents, into oxidised products with reduced toxicity. The morphology, structural and textural properties
of the catalysts were investigated. Furthermore, their catalytic properties were evaluated in the oxidative abatement of (2-chloroethyl)ethylsulfide, CEES, a simulant of sulfur mustard (blistering CWA). Their
performance was also compared to a conventional decontamination powder and a commercial Nb2O5
sample. The metal oxides powders were then employed in the active oxidative decontamination of CEES
from a cotton textile substrate, mimicking a real contamination occurrence. Remarkable results in terms
of abatement and degradation into desired products were recorded, achieving good conversions and
decontamination efficiency with Nb2O5, TiO2 and -Al2O3, under very mild conditions, with hydrogen
peroxide (as aqueous solution or as urea-hydrogen peroxide adduct), at room temperature and ambient
pressure. In the aim of a real on-field use, the potential environmental impact of these solids was also
evaluated by bioluminescence toxicity tests on reference bacteria (Photobacterium leiognathi Sh1), showing a negligible negative impact for TiO2, -Al2O3, and Nb2O5. A major biotoxic effect was only found for
Zn
Advanced Catalytic Technologies for Improved Global Security
No full textThe abatement of toxic chemical warfare agents (CWA) is conventionally achieved via stoichiometric reactions using strong oxidants with high environmental impact and/or via thermal degradation. The international Project “NanoContraChem”, in the framework of NATO Science for Peace and Security Programme, aims at obtaining innovative nanostructured inorganic materials for the catalytic decontamination of CWA. In the first year of activity, a class of heterogeneous catalysts has been designed to transform selectively and under mild conditions toxic organosulfur chemical agents in non-noxious products with reduced environmental impact. Nb(V)-containing saponite clay was identified as an optimal catalyst for the CWA oxidative abatement. The conventional synthetic protocol used to obtain saponite materials was modified to allow the insertion of Nb(V) ions within the inorganic framework of the clay, thus obtaining a bi-functional catalyst with strong oxidizing and acid properties. The cataly
Methane-carbon budget of a ferruginous meromictic lake and implications for marine methane dynamics on early Earth
No full textThe greenhouse gas methane (CH4) contributed to a warm climate that maintained liquid water and sustained Earth’s habitability in the Precambrian despite the faint young sun. The viability of methanogenesis (ME) in ferruginous environments, however, is debated, as iron reduction can potentially outcompete ME as a pathway of organic carbon remineralization (OCR). Here, we document that ME is a dominant OCR process in Brownie Lake, Minnesota (midwestern United States), which is a ferruginous (iron-rich, sulfate-poor) and meromictic (stratified with permanent anoxic bottom waters) system. We report ME accounting for ≥90% and >9% ± 7% of the anaerobic OCR in the water column and sediments, respectively, and an overall particulate organic carbon loading to CH4 conversion efficiency of ≥18% ± 7% in the anoxic zone of Brownie Lake. Our results, along with previous reports from ferruginous systems, suggest that even under low primary productivity in Precambrian oceans, the efficient conversion of organic carbon would have enabled marine CH4 to play a major role in early Earth’s biogeochemical evolution.This article is published as Sajjad A. Akam, Pei-Chuan Chuang, Sergei Katsev, Chad Wittkop, Michelle Chamberlain, Andrew W. Dale, Klaus Wallmann, Adam J. Heathcote, Elizabeth D. Swanner; Methane-carbon budget of a ferruginous meromictic lake and implications for marine methane dynamics on early Earth. Geology 2024; doi: https://doi.org/10.1130/G51713.1. © 2024 The Authors.This paper is published under the terms of the CC-BY license
Evaluating a primary carbonate pathway for manganese enrichments in reducing environments
No full textMost manganese (Mn) enrichments in the sedimentary rock record are hosted in carbonate minerals, which are assumed to have formed by diagenetic reduction of precursor Mn-oxides, and are considered diagnostic of strongly oxidizing conditions. Here we explore an alternative model where Mn-carbonates form in redox-stratified water columns linked to calcium carbonate dissolution. In ferruginous Brownie Lake in Minnesota, USA, we document Mn-carbonates as an HCl-extractable phase present in sediment traps and in reducing portions of the water column. Mn-carbonate become supersaturated in the Brownie Lake chemocline where dissolved oxygen concentrations fall below 5 μM, and Mn-oxide reduction increases the dissolved Mn concentration. Supersaturation is enhanced when calcite originating from surface waters dissolves in more acidic waters at the chemocline. In the same zone, sulfate reduction and microaerobic methane oxidation add dissolved inorganic carbon (DIC) with negative δ13C. These observations demonstrate that sedimentary Mn enrichments may 1) develop from primary carbonate phases, and 2) can occur in environments with dissolved oxygen concentrations 200 μM), and where Mn and Fe are partitioned by S cycling, photoferrotrophy, or microaerophilic Fe-oxidation. A shallow lysocline enhances Mn-carbonate production by providing additional DIC and nucleation sites for crystal growth. This carbonate model for Mn-enrichments is expected to be viable in both euxinic and ferruginous environments, and provides a more nuanced view of the relationships between Mn and carbon cycling, with applications throughout the rock record.This is a manuscript of an article published as Wittkop, Chad, Elizabeth D. Swanner, Ashley Grengs, Nicholas Lambrecht, Mojtaba Fakhraee, Amy Myrbo, Andrew W. Bray, Simon W. Poulton, and Sergei Katsev. "Evaluating a primary carbonate pathway for manganese enrichments in reducing environments." Earth and Planetary Science Letters 538 (2020): 116201. doi:https://doi.org/10.1016/j.epsl.2020.116201
Carbon mineralization and oxygen dynamics in sediments with deep oxygen penetration, Lake Superior
No full textTo understand carbon and oxygen dynamics in sediments with deep oxygen penetration, we investigated eight locations (160-318-m depth) throughout Lake Superior. Despite the 2-4 weight percent organic carbon content, oxygen penetrated into the sediment by 3.5 to. >12 cm at all locations. Such deep penetration is explained by low sedimentation rates (0.01-0.04 cm yr-1), high solubility of oxygen in freshwater, and a shallow (~ 2 cm) bioturbation zone. In response mainly to oxygen variations in the bottom waters, the sediment oxygen penetration varied seasonally by as much as several centimeters, suggesting that temporal variability in deeply oxygenated sediments may be greater than previously acknowledged. The oxygen uptake rates (4.4-7.7 mmol m-2 d-1, average 6.1 mmol m-2 d-1) and carbon mineralization efficiency (~ 90% of deposited carbon) were similar to those in marine hemipelagic and pelagic sediments of comparable sedimentation rates. The reactivity of organic carbon was found to decrease with age similarly to the power-law documented in marine environments. The burial flux of carbon into the deep sediment (0.7 mmol m-2 d-1) was 2.5% of the previously estimated primary production. Maximum volume-specific carbon degradation rates were 0.3-1.5 μmol cm-3 d-1; bioturbation coefficient near the sediment surface was 3-8 cm2 yr-1. These results indicate that carbon cycling in large freshwater systems conforms to many of the same trends as in marine systems.</p
Methane-carbon budget of a ferruginous meromictic lake and implications for marine methane dynamics on early Earth
No full textThe greenhouse gas methane (CH4) contributed to a warm climate that maintained liquid water and sustained Earth’s habitability in the Precambrian despite the faint young sun. The viability of methanogenesis (ME) in ferruginous environments, however, is debated, as iron reduction can potentially outcompete ME as a pathway of organic carbon remineralization (OCR). Here, we document that ME is a dominant OCR process in Brownie Lake, Minnesota (midwestern United States), which is a ferruginous (iron-rich, sulfate-poor) and meromictic (stratified with permanent anoxic bottom waters) system. We report ME accounting for ≥90% and >9% ± 7% of the anaerobic OCR in the water column and sediments, respectively, and an overall particulate organic carbon loading to CH4 conversion efficiency of ≥18% ± 7% in the anoxic zone of Brownie Lake. Our results, along with previous reports from ferruginous systems, suggest that even under low primary productivity in Precambrian oceans, the efficient conversion of organic carbon would have enabled marine CH4 to play a major role in early Earth’s biogeochemical evolution
The biogeochemistry of tropical lakes: A case study from Lake Matano, Indonesia
No full textThis is the publisher's version, also available electronically from http://onlinelibrary.wiley.comWe examined the chemical composition of the water column of Lake Matano, Sulawesi Island, Indonesia, to document how the high abundances of Fe (hydr)oxides in tropical soils and minimal seasonal temperature variability affect biogeochemical cycling in lakes. Lake Matano exhibits weak thermal stratification, yet a persistent pycnocline separates an oxic epilimnion from anoxic meta- and hypolimnions. The concentration of soluble P in the epilimnetic waters is very low and can be attributed to scavenging by Fe (hydr)oxides. Chromium concentrations in the epilimnion are high (up to 180 nmol L−1), but below U.S. Environmental Protection Agency guidelines for aquatic ecosystems. The concentration of chromium decreases sharply across the oxic-anoxic boundary, revealing that the hypolimnion is a sink for Cr. Flux calculations using a one-dimensional transportreaction model for the water column fail to satisfy mass balance requirements and indicate that sediment transport and diagenesis play an important role in the exchange of Fe, Mn, P, and Cr between the epilimnion and hypolimnion. Exchange of water between the epilimnion and hypolimnion is slow and on a time scale similar to temperate meromictic lakes. This limits recycling of P and N to the epilimnion and removal of Cr to the hypolimnion, both of which likely restrict primary production in the epilimnion. Owing to the slow exchange, steep concentration gradients in Fe and Mn species develop in the metalimnion. These concentration gradients are conducive to the proliferation of chemoautotrophic and anoxygenic phototrophic microbial communities, which may contribute a significant fraction to the total primary production in the lake
Photoferrotrophs thrive in an Archean Ocean analogue
No full textUdgivelsesdato: October 14Considerable discussion surrounds the potential role of anoxygenic phototrophic Fe(II)-oxidizing bacteria in both the genesis of Banded Iron Formations (BIFs) and early marine productivity. However, anoxygenic phototrophs have yet to be identified in modern environments with comparable chemistry and physical structure to the ancient Fe(II)-rich (ferruginous) oceans from which BIFs deposited. Lake Matano, Indonesia, the eighth deepest lake in the world, is such an environment. Here, sulfate is scarce (<20 μmol·liter−1), and it is completely removed by sulfate reduction within the deep, Fe(II)-rich chemocline. The sulfide produced is efficiently scavenged by the formation and precipitation of FeS, thereby maintaining very low sulfide concentrations within the chemocline and the deep ferruginous bottom waters. Low productivity in the surface water allows sunlight to penetrate to the >100-m-deep chemocline. Within this sulfide-poor, Fe(II)-rich, illuminated chemocline, we find a populous assemblage of anoxygenic phototrophic green sulfur bacteria (GSB). These GSB represent a large component of the Lake Matano phototrophic community, and bacteriochlorophyll e, a pigment produced by low-light-adapted GSB, is nearly as abundant as chlorophyll a in the lake's euphotic surface waters. The dearth of sulfide in the chemocline requires that the GSB are sustained by phototrophic oxidation of Fe(II), which is in abundant supply. By analogy, we propose that similar microbial communities, including populations of sulfate reducers and photoferrotrophic GSB, likely populated the chemoclines of ancient ferruginous oceans, driving the genesis of BIFs and fueling early marine productivity
