A non-thermogenic source of black carbon in peat and coal

Hartman, Blaine E.; Chen, Hongmei; Hatcher, Patrick G.

doi:10.1016/j.coal.2015.03.011

Cited by 17 publications

(9 citation statements)

References 43 publications

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“…Soil humic acids from varying locations, soil types and degrees of humification are characterized by a common set of molecular formulas and structural entities whose presence has been debated to either derive from lignin and modified lignin, sugars and proteins, fungal or microbial phenols, or a combination of all these (Stevenson, 1994). Some recent studies in our group (Chen et al, 2014) The DOM from the Dismal Swamp is dominated by molecules derived predominantly from lignin (Hartman et al, 2015). Although primarily light-induced in the Chen et al study, hydroxyl radicals responsible for catalyzing this oxidation are also present in soil systems.…”

Section: Discussionmentioning

confidence: 86%

Potential origin and formation for molecular components of humic acids in soils

DiDonato

Chen

Waggoner

et al. 2016

Geochimica et Cosmochimica Acta

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143

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Soil humic acids are the base soluble/acid insoluble organic components of soil organic matter. Most of what we know about humic acids comes from studies of their bulk molecular properties or analysis of individual fractions after extraction from soils. This work attempts to better define humic acids and explain similarities and differences for several soils varying in degrees of humification using advanced molecular level techniques. Our investigation using electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) and nuclear magnetic resonance spectroscopy (NMR) has given new insight into the distinctive molecular characteristics of humic acids which suggest a possible pathway for their formation. Humic acids from various ecosystems, climate regions and soil textural classes are distinguished by the presence of three predominant molecular components: lignin-like molecules, carboxyl-containing aliphatic molecules and condensed aromatic molecules that bear similarity to black carbon. Results show that humification may be linked to the relative abundance of these three types of molecules as well as the relative abundance of carboxyl groups in each molecular type. This work also demonstrates evidence for lignin as the primary source of soil organic matter, particularly condensed aromatic organic molecules often categorized as black carbon and is the first report of the non-pyrogenic source for these compounds in soils. We also suggest that much of the carboxyl-containing aliphatic molecules are sourced from lignin. Abbreviations ESI-FTICR-MS, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry; NMR, Nuclear Magnetic Resonance Spectroscopy; DBE, double bond equivalents; CRAM, carboxyl-rich alicyclic molecules; CCAM: carboxyl containing aliphatic molecules; BC, Black carbon; CPMAS, cross-polarization magic angle spinning; DPMAS, direct polarization magic angle spinning; KMD, Kendrick mass defect; Ai mod , modified aromaticity index

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Section: Discussionmentioning

confidence: 86%

Potential origin and formation for molecular components of humic acids in soils

DiDonato

Chen

Waggoner

et al. 2016

Geochimica et Cosmochimica Acta

Self Cite

143

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“…Notably, HAb and HAp isolated from low-mire peat samples with a high degree of decomposition (Peat 5–9) were characterized by more aromatic structures compared to HA fractions obtained from raised bog peat samples (Peat 1–4), which is consistent with our previous publications [ 11 , 39 ]. The HAb fractions were mainly aliphatic in nature and were comprised mainly of molecules having H/C values centered at 1.3–1.4 [ 47 ]. There was no difference in the average O/C values of the HAb and HAp fractions, which is indicative of their similar carbohydrate content, carboxylic groups, and degree of oxidation.…”

Section: Resultsmentioning

confidence: 99%

Physicochemical Characterization and Antioxidant Activity of Humic Acids Isolated from Peat of Various Origins

et al. 2018

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Although humic acids (HAs) from peat exhibit various therapeutic properties, there is little information available concerning their physicochemical and antioxidant properties. To address this issue, nine different types of peat, including oligotrophic, mesotrophic, and minerotrophic peat samples, were used for isolation of HA fractions by basic (HAb) and pyrophosphate (HAp) extractions. Physical parameters of the HAs were analyzed by UV-Vis, fluorescent, infrared (IR), and electron paramagnetic resonance (EPR) spectroscopy. Average Mr of the fractions ranged from 17.2 to 39.7 kDa, while their humification index (HIX) varied from 0.49 to 1.21. HAp fractions had a higher content of aromatic structures compared to HAb fractions. Moreover, HAp fractions had a significantly higher content of phenolic OH groups (3.6 ± 0.5 mmol/g) versus HAb (3.1 ± 0.5 mmol/g). All HA fractions exhibited antioxidant activity in radical scavenging and electrochemical assays, and their EPR signal had a single line with g = 2.0035, which is consistent with semiquinone type radicals. Furthermore, the HIX was found to be important in determining the number of semiquinone-type free radicals in the HA structures. Overall, these data provide a molecular basis to explain at least part of the beneficial therapeutic properties of peat-derived HAs.

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“…These may be derived from lignin or tannin, which include a wide variety of polycondensed aromatics (Hernes and Hedges, 2000;Waggoner et al, 2015). Other non-pyrogenic OM sources of condensed aromatic OM are abundant in the geosphere, including woody peat, coal, kerogen, and oil (Yoshioka and Ishiwatari, 2005;Hammes et al, 2007;Wang et al, 2012;Hartman et al, 2015;Li et al, 2017). Still other studies have found that nonpyrogenic OM can be readily transformed to condensed aromatic OM, which would appear to be pyrogenic, through photolytic, microbial, or chemical degradative processes (Glaser and Knorr, 2008;Chen et al, 2014;Waggoner et al, 2015;DiDonato et al, 2016).…”

Section: Methodology/conceptual Issuesmentioning

confidence: 99%

Trial by Fire: On the Terminology and Methods Used in Pyrogenic Organic Carbon Research

Zimmerman

Mitra

2017

Front. Earth Sci.

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Our understanding of the cycling of fire-derived, i.e., pyrogenic organic matter (pyOM), as well as the goals of the community of researchers who study it, may be inhibited by the many terms and methods currently used in its quantification and characterization. Terms currently used for pyOM have evolved by convention, but are often poorly defined. Further, each of the different methods now used to quantify solid and dissolved pyrogenic carbon (pyC) comes with its own biases and artifacts. That is, each detects only a fraction of the total pyrogenic products produced by fire, while, at the same time, include some fraction of non-pyrogenic OM. This may be evident in the commonly observed correlations between pyC and total organic C reported for both soils and dissolved OM in many different systems. We suggest that our research area can be placed on a stronger footing by: (1) agreement upon a common set of terms tied to the method used for detection (e.g., of the form pyC method ), (2) implementation of another "ring trial" study with a wider set of natural soil and water samples that cross-compare more recently developed methods, and (3) further investigation of the processes which preserve/degrade/transport pyOM in the environment.

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A non-thermogenic source of black carbon in peat and coal

Cited by 17 publications

References 43 publications

Potential origin and formation for molecular components of humic acids in soils

Potential origin and formation for molecular components of humic acids in soils

Physicochemical Characterization and Antioxidant Activity of Humic Acids Isolated from Peat of Various Origins

Trial by Fire: On the Terminology and Methods Used in Pyrogenic Organic Carbon Research

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