Controllable and Scalable Engineered Soil Surrogates Utilizing Simulated Soil Organic Matter for the Study of Environmental, Ecological, and Agricultural Processes

Abstract

An entirely new, tunable, and scalable platform (model) approach for the detailed study of important molecular processes that take place in geomacromolecular matrices, such as soils, using block copolymer materials at inorganic interfaces has been developed and applied to gain a molecular-level understanding of environmental pollutant/soil interactions. This approach provides a scalable platform with molecular-level control of the soil organic matter (SOM) chemical composition and structure, allowing one to examine proposed SOM interactions with agricultural chemicals (ACs). Accordingly, a series of engineered soil surrogates (ESSs) utilizing simulated SOM was synthesized, in which multiblock oligomers were tethered to silica particles, creating one-, two-, and three-tiered ESSs, via controlled radical polymerization. Using norflurazon (NOR) as a model AC sorbate for batch mode sorption experiments, it was found that binding interactions with the ESSs are not just organic content-driven but are also dependent on the nature of the chemical structure of an ESS. By a stepwise increase in the polarity of the second and third tiers, it is shown that the ability of the ESS to sorb NOR decreases, pointing to a largely hydrophobic driving force for NOR adsorption to the ESSs. The ESS platform approach also allows for the investigation of other, more nuanced interactions with this study, directly showing that hydrogen bonding, electrostatic interactions, conformation, and π-stacking strongly influence NOR binding. This approach can also be applied to a range of other environmentally and agriculturally important issues, such as soil remediation, microbial community dynamics and evolution, nutrient cycling, and carbon sequestration, where soil variability between replicate samples has limited research advances.