Fire-derived organic matter retains ammonia through covalent bond formation

Fire-derived organic matter, often referred to as pyrogenic organic matter (PyOM), is present in the Earth's soil, sediment, atmosphere, and water. We investigated interactions of PyOM with ammonia (NH₃) gas, which makes up much of the Earth's reactive nitrogen (N) pool. Here we show that PyOM's NH₃ retention capacity under ambient conditions can exceed 180 mg N g⁻¹ PyOM-carbon, resulting in a material with a higher N content than any unprocessed plant material and most animal manures. As PyOM is weathered, NH₃ retention increases sixfold, with more than half of the N retained through chemisorption rather than physisorption. Near-edge X-ray absorption fine structure and nuclear magnetic resonance spectroscopy reveal that a variety of covalent bonds form between NH₃-N and PyOM, more than 10% of which contained heterocyclic structures. We estimate that through these mechanisms soil PyOM stocks could retain more than 600-fold annual NH₃ emissions from agriculture, exerting an important control on global N cycling.Rachel Hestrin, Dorisel Torres-Rojas, James J. Dynes, James M. Hook, Tom Z. Regier, Adam W. Gillespie, Ronald J. Smernik, Johannes Lehman

Magnetic Frustration in a Mn Honeycomb Lattice Induced by Mn-O-O-Mn Pathways

We investigated the electronic structure of layered Mn oxide Bi3Mn4O12(NO3) with a Mn honeycomb lattice by x-ray absorption spectroscopy. The valence of Mn was determined to be 4+ with a small charge-transfer energy. We estimated the values of superexchange interactions up to the fourth nearest neighbors (J1, J2, J3, and J4) by unrestricted Hartree-Fock calculations and a perturbation method. We found that the absolute values of J1 through J4 are similar with positive (antiferromagnetic) J1 and J4, and negative (ferromagnetic) J2 and J3, due to Mn-O-O-Mn pathways activated by the smallness of charge-transfer energy. The negative J3 provides magnetic frustration in the honeycomb lattice to prevent long-range ordering.Comment: 4 pages, 3 figure

Linking structural and chemical characteristics of soot particles to their optical absorption in the UV-visible

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Suie carbonnée aéronautique : production d'analogues de laboratoire et étude de leur propriétés physico-chimiques à l'échelle nanométrique par HRTEM, XPS et NEXAFS.

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Suie carbonée aéronautique : production d’analogues de laboratoire et étude de leur propriétés physico-chimiques à l’échelle nanométrique par HRTEM, XPS et NEXAFS

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Structural and chemical study of collected aircraft soot and generated surrogates

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Linking structural and chemical characteristics of soot particles to their optical absorption in the UV-visible

International audienceYe

Structural and chemical study of collected aircraft soot and generated surrogates

International audienc

Suie carbonnée aéronautique : production d'analogues de laboratoire et étude de leur propriétés physico-chimiques à l'échelle nanométrique par HRTEM, XPS et NEXAFS.

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Linking structural and chemical characteristics of soot particles to their optical absorption in the UV-visible

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