Document Type

Dissertation - Open Access

Award Date

2017

Degree Name

Doctor of Philosophy (PhD)

Department / School

Chemistry and Biochemistry

First Advisor

James A. Rice

Keywords

Natural Organic Matter, Pulsed Field Gradient NMR, SANS, Self-Assembly

Abstract

This investigation focuses on the determination of the architecture of the natural organic matter (NOM) contained within a soft coal-like material, an agricultural soil and a peat material. NOM has been extracted from bulk materials, fractionated, reassembled, then characterized by 13C Solid State NMR, Pulsed-Field Gradient NMR (PFG-NMR), and Small Angle Neutron Scattering (SANS). Interpretation of the data obtained by SANS has established that the majority of the components of NOM are mass fractals in solution and surface fractals in the solid state. Surface-to-volume ratios calculated with PFGNMR data indicate the NOM components studied have varying disk-like shapes. These components self-assemble to form somewhat spherical assemblies that are more space filling but still retain their mass fractal characteristics. 13C Solid State and PFG-NMR gave evidence that aromaticity increases from the fractionated components that comprise NOM to the final assembly which also includes carbon types containing polar functional groups and aliphatics. It was also determined that NOM shares numerous similarities with asphaltenes and resins extracted from petroleum. The similarities include a hierarchical self-assembly of components with distinctly different chemical characteristics, comparable fractal dimension values, surface-to-volume ratios, and differences in diffusion coefficients dependent upon component. The model proposed by these findings suggests that the self-assembled architecture of NOM is dependent upon a polyaromatic hydrocarbon ring system with polar functional groups and peripheral alkanes. This architecture is consistent for the three materials studied, indicating that the amount of organic carbon present in a material or the materials geographic origin does not affect how NOM self-assembles in the environment. This assembly is created by a composite consisting of two lower level components, one of which is primarily a lipid and the other is an amphiphile. This composite then interacts with a large upper level component comprised mainly of aromatics with a few aliphatic and polar functional groups. Experimental data suggests that the composite component inserts into the aromatic ring system of the larger component then chemical interactions occurring between the two components causes the final assembly to be smaller than the components from which it is comprised. It is further suggested that this decrease in size is due to functional groups that tend to associate through short range inter/intra-molecular interactions such as van der Waals, π-π interactions, and hydrogen bonding which pull the molecules of the components into closer proximity to one another. Therefore, the proposed model herein is an example of a hierarchical aggregation occurring between distinct components of NOM which retain their similar chemical and physical characteristics regardless of material type.

Library of Congress Subject Headings

Humus -- Analysis.
Self-assembly (Chemistry)

Description

Includes bibliographical references (page 108-121)

Format

application/pdf

Number of Pages

133

Publisher

South Dakota State University

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Rights Statement

In Copyright