Doctor of Philosophy (PhD)
Soil is an important environmental component, and the study of soil processes have many practical implications such as improvement in agriculture, mitigation of climate change etc. The widespread use of Agricultural Chemicals (ACs) in modern agriculture has resulted in adverse effects in environment and human health mostly through contamination into food and water sources. Study of fate, bioavailability, and transport of ACs involves molecular level understanding of their interactions with soil. This can be challenging due to complex and heterogeneous nature of soil. One common approach used is the correlation of macroscopic properties of soil, (e.g. sorption) with empirical parameters such as carbon content, elemental ratios etc. While these metrics provide insight into important soil characteristics, the results are not sufficient to elucidate in-depth molecular level interactions of soil with ACs. Several attempts to synthesize artificial test soil substrates have been proposed to overcome this limitation. However, the exact composition of these “artificial soils” are also ill-defined as they use organic components from plant derived materials. This work demonstrates the design and synthesis of Engineered Soil Surrogates (ESSs) using controlled radical polymerization for use in study of geomacromolecular processes including sorption of ACs into the soil. The initial design of ESSs consisted of SiO2 as an inorganic matrix tethered with multi-block oligomers containing alky (tier-1), O-aryl (tier-2) and polar (tier-3) blocks carefully selected to echo hydrophobic, aromatic and hydrophilic components of the Soil Organic Matter (SOM) respectively. A series ESSs of increasing complexity were used in concert with sorption isotherm data obtained by batch mode experiments using Norflurazon (NOR) as a model AC. As the polarity of the second tier increased, the ability of the ESS to sorb NOR decreased, as was the case when a polar third tier was added, pointing to a largely hydrophobic driving force for NOR adsorption to the ESSs. Hydrogen bonding, pi-stacking, confirmation and hydration were also shown to influence binding of NOR to ESS. Additionally, the results from isotherm based sorption studies of ESS are compared with that of chemically modified real soil in a quest to develop realistic soil model.
Pandey, Arjun, "Development of a Tunable Platform for the Study of Geomacromolecular Matrices Using Controlled Radical Polymerization" (2019). LSU Doctoral Dissertations. 5071.