A survey of photogeochemistry

Doane, Timothy A.

doi:10.1186/s12932-017-0039-y

Cited by 34 publications

(27 citation statements)

References 372 publications

(147 reference statements)

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“…phototrophic | mineral coatings | birnessite | solar energy | redox (bio)geochemistry I nnumerable previous studies concerning the most critical influences of solar energy on the surface of this planet have mainly focused on its influence on Earth's climate (1), on photosynthesis and associated biological processes (2,3), and on geological and soil processes (4). However, although widely exposed natural minerals on Earth's surface receive solar irradiation over very long time periods, the electronic response of these interactions and how this process also shapes the planet on which we live have rarely received attention.…”

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confidence: 99%

Photoelectric conversion on Earth’s surface via widespread Fe- and Mn-mineral coatings

Ding

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

143

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Sunlight drives photosynthesis and associated biological processes, and also influences inorganic processes that shape Earth’s climate and geochemistry. Bacterial solar-to-chemical energy conversion on this planet evolved to use an intricate intracellular process of phototrophy. However, a natural nonbiological counterpart to phototrophy has yet to be recognized. In this work, we reveal the inherent “phototrophic-like” behavior of vast expanses of natural rock/soil surfaces from deserts, red soils, and karst environments, all of which can drive photon-to-electron conversions. Using scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and X-ray absorption spectroscopy, Fe and Mn (oxyhydr)oxide-rich coatings were found in rock varnishes, as were Fe (oxyhydr)oxides on red soil surfaces and minute amounts of Mn oxides on karst rock surfaces. By directly fabricating a photoelectric detection device on the thin section of a rock varnish sample, we have recorded an in situ photocurrent micromapping of the coatings, which behave as highly sensitive and stable photoelectric systems. Additional measurements of red soil and powder separated from the outermost surface of karst rocks yielded photocurrents that are also sensitive to irradiation. The prominent solar-responsive capability of the phototrophic-like rocks/soils is ascribed to the semiconducting Fe- and Mn (oxyhydr)oxide-mineral coatings. The native semiconducting Fe/Mn-rich coatings may play a role similar, in part, to photosynthetic systems and thus provide a distinctive driving force for redox (bio)geochemistry on Earth’s surfaces.

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confidence: 99%

Photoelectric conversion on Earth’s surface via widespread Fe- and Mn-mineral coatings

Ding

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

143

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“…Analyzing the Mössbauer spectroscopy data, Bogart et al [ 27 ] proposed the following mechanism of transformation of Fe 3 O 4 to γ-Fe 2 O 3 due to the release of Fe-ions from the particles: Fe 2+ are drawn from the nucleus by a concentration gradient arising due to surface oxidation; Fe 2+ is oxidized in situ, colliding with mobile electrons, then Fe 3+ ions are distributed to maintain the electroneutrality of the material. Dissolution of the solid phase and an increase in dissolved Fe 2+ and/or Fe 3+ as a result of incubation of NPs with humic substances was demonstrated by Sundman et al [ 25 ]: the magnetite incubated with native humic substances became more oxidized as compared with the control, i.e., bare magnetite.…”

Section: Introductionmentioning

confidence: 99%

“…Recent research has shown that humic acids (HA) have a high affinity to Fe 3 O 4 NPs and the sorption of HA on the Fe 3 O 4 NP enhanced the stability of Fe 3 O 4 nanodispersions by preventing their aggregation via electrostatic and steric effects [ 19 , 20 , 21 , 22 , 23 ]. However, weak Coulombic attraction, hydrogen, and hydrophobic (van der Waals, π-π, CH-π) bonds between Fe 3 O 4 and HA [ 24 ] seemed not to protect Fe 3 O 4 NPs from the oxidation in real environmental conditions [ 25 , 26 ]. Thus, redox-active HS play an important role in Fe redox speciation in magnetite and can influence their reactivity and role in biogeochemical Fe cycling.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Humic Acids on the Ecotoxicity of Fe3O4 Nanoparticles and Fe-Ions: Impact of Oxidation and Aging

et al. 2020

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The magnetite nanoparticles (MNPs) are increasingly produced and studied for various environmental applications, yet the information on their ecotoxicity is scarce. We evaluated the ecotoxicity of MNPs (~7 nm) before and after the addition of humic acids (HAs). White mustard Sinapis alba and unicellular ciliates Paramecium caudatum were used as test species. The MNPs were modified by HAs and oxidized/aged under mild and harsh conditions. Bare MNPs proved not toxic to plants (96 h EC50 > 3300 mg/L) but the addition of HAs and mild oxidation increased their inhibitory effect, especially after harsh oxidation (96 h EC50 = 330 mg/L). Nevertheless, all these formulations could be ranked as ‘not harmful’ to S. alba (i.e., 96 h EC50 > 100 mg/L). The same tendency was observed for ciliates, but the respective EC50 values ranged from ‘harmful’ (24 h EC50 = 10–100 mg/L) to ‘very toxic’ (24h EC50 < 1 mg/L). The ecotoxicity of Fe-ions with and without the addition of HAs was evaluated in parallel: Fe (II) and Fe (III) ions were toxic to S. alba (96 h EC50 = 35 and 60 mg/L, respectively) and even more toxic to ciliates (24 h EC50 = 1 and 3 mg/L, respectively). Addition of the HAs to Fe-ions yielded the respective complexes not harmful to plants (96h EC50 > 100 mg/L) but toxic to ciliates (24h EC50 = 10–100 mg/L). These findings will be helpful for the understanding of the environmental fate and toxicity of iron-based NPs.

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“…This input of energy is known to influence soil properties and development (Carter & Ciolkosz, 1991;Franzmeier et al, 1969;Rech et al, 2001). In addition to thermal energy, the Sun delivers visible and ultraviolet radiation (hereafter referred to as light), which is strong enough to effect discrete chemical reactions among many naturally occurring substances (Doane, 2017), but is rarely investigated past the plant canopy into soil. Research in environmental photochemistry does occasionally involve soil, but this work almost always focuses on the degradation of synthetic soil-borne contaminants (e.g., Frank et al, 2002;Gonçalves et al, 2006;Helz et al, 1994;Katagi, 2004;Marques et al, 2016;Miller & Donaldson, 1994;Zhang et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Exposure to Light Elicits a Spectrum of Chemical Changes in Soil

2019

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The significance of photochemically active solar radiation is well substantiated in Earth's air and water environments, but no broad connection has yet been ascertained between sunlight and the chemical properties of land surfaces. Since it is obvious that sunlight strikes Earth every day, an inquiry into this connection was made in a simple experiment with a diverse group of 20 soils. Light‐induced alteration of most of the major elements in soil was evident, including significant changes in dissolved organic carbon, inorganic nitrogen, pH, phosphorus availability and sorption capacity, and soluble and mineral forms of iron, manganese, aluminum, silicon, and calcium. In many instances the extent of these changes could be predicted from initial values. This broad response to light attests to the vivid photochemistry of soils and has both pedological and edaphological implications that reach beyond the surface. The phenomena reported here affirm the opportunity for novel inquiries into the chemistry of soils and land surfaces in general.

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A survey of photogeochemistry

Cited by 34 publications

References 372 publications

Photoelectric conversion on Earth’s surface via widespread Fe- and Mn-mineral coatings

Photoelectric conversion on Earth’s surface via widespread Fe- and Mn-mineral coatings

Effects of Humic Acids on the Ecotoxicity of Fe3O4 Nanoparticles and Fe-Ions: Impact of Oxidation and Aging

Exposure to Light Elicits a Spectrum of Chemical Changes in Soil

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