Thermodynamic Adsorption States of TNT and DNAN on Corundum and Hematite

Abstract

Adsorption isotherms are a critical tool in determining the transport of environmental contaminants through a particular media. Owing to the inherent heterogeneity of soils, the determination of which soil components are responsible for the adsorption and retention of a particular contaminant remains a challenge. In the current study, we consider several thermodynamic adsorption states in order to predict whether or not 2,4,6-trinitrotoluene (TNT) or 2,4-dinitroanisole (DNAN) would be either a ground-water contaminant or a soil contaminant. In order to reduce the complexity, we only consider two metal oxides (hematite and corundum) that are commonly found in arid regions. We have shown that TNT and DNAN bind favorably across all concentrations, temperatures, and surface hydration considered for α-Al 2 O 3 ; however, only TNT was found to be bound for α-Fe 2 O 3 . Our results indicate that for soils rich in iron oxides, DNAN would be a ground-water contaminant.

Effect of Concrete Composition on the Thermodynamic Binding of Dopamine: A DFT Study

“…The thermal corrections were then added to the DFT energies from the finite difference calculations. This setup gave errors in the binding energy less than 0.1 eV, and gave nearly a magnitude in terms of speed-up …”

“…Our binding energies ( E BE ) were calculated in the usual fashion, i.e., where E dopamine+surface is the total energy of the adsorbate and oxide surface, E dopamine is the gas-phase adsorbate energy, and E surface is the energy of the bare oxide surface. In order to translate this into surface coverages of the individual concrete components, we follow our recent methodology by starting with the Boltzmann distribution where Δ G BE, i is the Gibbs free energy of binding for component i . Here, Δ G BE, i is defined similarly to eq where we replace the electronic energies with the Gibbs free energies.…”

“…Upon adsorption of dopamine, only the top stoichiometric layers of the surface were allowed to relax (in addition to the dopamine). In regard to the vibrational calculations, we followed the procedure of Jenness et al 33 Here, the vibrational modes were calculated using the LCAO geometry with a LCAO basis set. The thermal corrections were then added to the DFT energies from the finite difference calculations.…”

“…Examination of the existing literature located nine different oxide surfaces (summarized in Table 1 and discussed in further detail below) for our consideration. The calculation of the binding energy of different binding modes with utilization of the thermodynamic binding model of Jenness et al 33 allows us to examine how dopamine would interact with these oxide materials under ambient conditions. Consequently, we predict that dopamine would bind favorably to the alkaline earth oxides Na 2 O and K 2 O in a manner resulting in the deprotonation of the dopamine.…”

Adventures in DFTB: Toward an Automatic Parameterization Scheme

“…Throughout the last several years, our group has extensively examined Munition interactions with components of natural water − and components of arid soil. − These computational studies have demonstrated several important factors in how these compounds are affected by the environment, including the solvation of munitions, decoupling interactions between various environmental components (e.g., studies on individual soil components), optical spectra, and degradation (vide supra). Further detailed analysis requires solutions that will allow for interactions between environmental components while simultaneously reducing empiricism.…”