Investigation of Organic Matter Interactions at Geologically Relevant Mineral Interfaces and Metal Cations
EMSL Project ID
51879
Abstract
Clays are porous materials with large surface areas that are very abundant in in the earth's crust. Many geochemical processes including environmental transport of naturally occurring and anthropogenic organic and inorganic species in ground and surface waters are greatly affected by reactions at clay mineral surfaces and in their interlayers. In our recent combined computational and NMR studies we have focused on understanding the molecular scale processes that control the interaction of water and common inorganic species with clays and have also made substantial progress in understanding the interactions of dissolved NOM with clays. Like clay minerals, NOM is ubiquitous in near-surface geochemical environments, and it is a critical and chemically active component of many geochemical reactions. It is a complicated mixture of organic molecules with diverse chemical structures and functional groups with different molecular masses. Many critical questions regarding the mechanisms of its interaction with mineral surfaces, hydrated ions, other organic species, and water molecules the effects of such factors as solution concentration and pH remain poorly understood. Computational molecular simulations have become one of the most important tools in the study of such complex, nano-scale systems by providing invaluable atomistic information on the underlying chemical and physical process. Some of the important factors we will consider in the study is to consider when modeling such complex systems are (i) the adsorption and diffusion of different hydrated metal ions in clays, (ii) NOM complexation with different metal ions, (iii) the effect of metal cation on the NOM adsorption and its reactivity at mineral surfaces. Our project will concentrate on the last two of these factors, because the first ones have been previously studied extensively over the last decade. In general, these studies have shown that the metal cations with higher hydration energies and smaller ionic radii are more prone to be hydrated and less likely to be directly coordinated to the mineral surface (inner sphere complexation) than those cations with lower hydration energies and large ionic radii. They have also shown that as the hydration energies increases, bidentate complexation of metal ion with carboxyl groups of NOM is highly preferred. In recent studies, our group has investigated the sorption of NOM on to the surface of the smectite mineral and found that both cation bridging and hydrophobic interactions plays important roles for complexation. Thus, to address the questions above, our computational molecular modeling efforts in the upcoming period will focus on using use classical molecular dynamics (MD) and potential of mean force calculations to investigate the organo-mineral complexation.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2021-10-01
End Date
2023-10-01
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members