Date of Award
1-1-2024
Document Type
Thesis
Degree Name
M.S. in Engineering Science
First Advisor
Hunain Alkhateb
Second Advisor
Matteo D’Alessio
Third Advisor
Ahmed Al-Ostaz
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
The contamination of drinking water by per- and polyfluorinated alkyl substances (PFAS) is a global issue. PFAS have been widely utilized in a variety of applications, including water and stain-resistant coatings, fire suppression foams, cosmetics, paints, and adhesives. They have been detected in soils and rivers globally due to their widespread use and resistance to degradation. The strong C–F bonds of PFAS make them exceedingly stable and hard to remove. In order to remediate PFAS contamination in the environment, it is essential to develop selective adsorbent materials that can effectively capture a wide range of PFAS structures. On April 10, 2024, the U.S. Environmental Protection Agency (EPA) announced the final National Primary Drinking Water Regulation for six PFAS (PFOA, PFNA, GenX, PFBS, PFOS, and PFHxS), providing legally enforceable levels for these compounds. Consequently, there is an even more urgent need to identify effective as well as affordable treatment approaches including the use of new materials to remove PFAS compounds. The main objective of this thesis is to extract design principles from the molecular dynamic simulations of the six PFAS compounds with legally enforceable levels defined by the U.S. EPA, in the presence of graphene. The interaction between each of the individual PFAS compounds and graphene is analyzed through simulations, specifically in terms of the adsorption energy and diffusion coefficient. Additionally, to simulate a more realistic scenario, the interaction between a matrix containing the six PFAS compounds, water, and graphene was investigated. The simulation was conducted by constructing an amorphous cell with six graphene sheets, ten PFAS molecules in their anionic state (negatively charged), ten sodium atoms, and 1,000 water molecules for each specific type of PFAS. On the other hand, when the six PFAS compounds were added together, the cell comprised of six graphene sheets, two compounds of each PFAS molecule (totaling twelve molecules), twelve sodium atoms, and 1,000 water molecules. Prior to construct the amorphous cell, geometry optimization is applied to each component. After that, a constant number of particles (N), pressure (P), and temperature (T) are assigned, in an approach known as NPT-isothermal isobaric ensemble. Finally, COMPASS Ⅲ force field is assigned. When the six PFAS compounds were individually added, a strong relationship between increased molecular weight and enhanced adsorption was observed throughout the study. Compounds with sulfonic acid head groups are generally stronger than those with carboxylate head groups due to their higher adsorption energy, suggesting that the head group plays an essential role in relation to the number of carbon atoms. When the six PFAS compounds were added together, it was found that the adsorption energy changed significantly, showing weaker and less distinct adsorption energies due to competitive dynamic. However, graphene still effectively removes PFAS from water under these conditions. Furthermore, the diffusion coefficient findings indicate that the presence of graphene enhances the performance of PFAS compounds in water, exceeding the diffusion coefficients of PFAS in water without graphene. Therefore, the presence of graphene increases the diffusion coefficient outcomes of the system. Based on the results of the study, the ability of functionalized graphene with metal oxides (e.g., iron and or manganese oxides) and fluorine should be further investigated. Additionally, laboratory scale investigations using flow-through reactors as well as sorption studies should be conducted based on the results of the conducted simulation.
Recommended Citation
Awawdeh, Bashar Moufeed, "Atomistic Simulation of PFAS And Graphene: Interactions for Water Applications" (2024). Electronic Theses and Dissertations. 2915.
https://egrove.olemiss.edu/etd/2915