Date of Award

Spring 2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry & Biochemistry

Committee Director

Patrick G. Hatcher

Committee Member

James Lee

Committee Member

John Donat

Committee Member

Jingdong Mao

Committee Member

Sandeep Kumar

Abstract

Radicals drive the transformation of organic matter in natural and engineered systems, altering its structure, reactivity, and stability. Condensed aromatic carbon (ConAC) and condensed aromatic nitrogen (ConAN) are among the most persistent forms of organic matter in soils and are traditionally interpreted as products of biomass burning. This dissertation challenges the long-standing assumption that these materials are exclusively pyrogenic, showing that iron-mediated radical chemistry can generate condensed aromatic structures under ambient conditions.

Chapters II and III show that Fenton-like radical oxidation of lignin-rich biomass produces condensed aromatic structures compositionally similar to pyrogenic black carbon and black nitrogen when assessed with conventional analytical methods. Spatially resolved analyses of long-term iron-exposed wood subjected to natural outdoor weathering reveal progressive aromatic condensation, nitrogen incorporation, and heterocyclic nitrogen formation in the absence of fire. These findings demonstrate that non-pyrogenic pathways can contribute to global reservoirs of condensed aromatic matter, with implications for carbon and nitrogen budgets and for interpreting fire-derived environmental stocks and fluxes.

Chapter IV provides mechanistic insight into abiotic nitrogen immobilization by probing covalent interactions between oxidized lignin and nitrogenous compounds using a 15N-labeled peptide. These experiments establish lignin as a reactive scaffold capable of stabilizing nitrogen through covalent bonding, representing a potential precursor step toward condensed aromatic formation. Chapter V extends these findings to natural systems by characterizing condensed aromatic matter in Amazonian anthrosols, revealing nitrogen as a key component of aged, polycarboxylated aromatic acids, with polycyclic nitrogen-containing aromatic acids dominating the molecular signature and suggesting a central role of nitrogen in their long-term fertility.

Chapter VI explores an applied perspective by investigating Fenton oxidative pretreatment of lignin-rich biomass for bioenergy applications. This treatment produced aliphatic-rich intermediates that, under hydrothermal liquefaction, generate more hydrocarbons and improve bio-oil quality than non-pretreated or conventionally processed lignin-rich biomass.

Collectively, this dissertation advances our understanding of how radical chemistry controls the transformation of organic matter in natural and engineered systems, and underscores lignin-rich biomass as a versatile precursor that shapes the persistence and reactivity of carbon and nitrogen in the environment.

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DOI

https://doi.org/10.25777/xrff-zn31

ISBN

9798197808967

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