Understanding Environmental Reactions of Carbon Tetrachloride, Trichloroethylene, Perchloroethylene, and Arsenic Applying Computational Chemistry Methods

Persistent Link:
http://hdl.handle.net/10150/195287
Title:
Understanding Environmental Reactions of Carbon Tetrachloride, Trichloroethylene, Perchloroethylene, and Arsenic Applying Computational Chemistry Methods
Author:
Zhang, Nianliu
Issue Date:
2006
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
In recent years, as the progress of computational abilities has increased, computational chemistry has become an interesting tool for researchers for investigating mechanisms of environmental reactions when results of experimental explorations are not sufficiently clear. In this research, several environmental reactions have been investigated using ab initio and density functional theory (DFT) methods.This research investigated the effect of the reaction energy on the reaction pathway for C-Cl bond cleavage in carbon tetrachloride (CT). Ab initio and density functional theories were used to study adiabatic electron transfer to aqueous phase CT. The potential energies associated with fragmentation of the CT anion radical into a trichloromethyl radical and a chloride ion were explored as a function of the C-Cl bond distance during cleavage. The effect of aqueous solvation was simulated using a continuum conductor-like screening model. Solvation significantly lowered the energies of the reaction products, indicating that the dissociative electron transfer was enhanced by solvation. It was found that reductive dissociation electron transfer of CT undergoes a change from an inner-sphere to an outer-sphere mechanism as the reaction energy is increased. The results showed a liner relationship between the activation energy for the dissociation and the overall energy change, which is in good agreement with the results of the Marcus model.This research also investigated the thermodynamic favorability and resulting structures for chemisorption of trichloroethylene (TCE) and perchloroethylene (PCE) on iron surfaces using periodic DFT with the non-local Perdew-Burke-Enzerhof (PBE) functional. Chemisorption structures were obtained for four physically adsorbed initial configurations. An initial configuration with two carbons (C-bridge) physically adsorbed at bridge sites between adjacent iron atoms was shown to be the most stable configuration for TCE, while the mode with two carbons (C-hollow) physically adsorbed at hollow site was verified to be the most stable configuration for PCE. C-Fe bonds were formed via sigma or pi bonds in the complexes formed at C-bridge, top and hollow site. Upon binding with the iron surface, the interaction of the C=C bond still remained as sp2 hybridization. Moreover, the strong chemisorption induced dissociations of C-Cl bonds and formation of Cl-Fe bonds. For both TCE and PCE, modes with two Cl atoms (Cl-bridge) physically adsorbed at bridge sites were found to be the least favorable configuration, in which only two Cl atoms formed bonds with the Fe surface and no C-Fe bonds were formed. Negative net Mulliken charges on TCE and PCE indicated they are reduced upon adsorption to the iron surface.Finally, in this research, we evaluated the accuracies and costs of several DFT methods including Harris, PWC LDA, and BLYP GGA functionals for interaction of arsenite with ferric hydroxides by comparison to calculated and experimental properties of surface complexes. It was found that the approach of using low-level structures coupled with high level single-point energies was much less expensive than the approach of using high level functionals for both structures and energies and could obtain similar computed binding energies. Further work has been done to investigate the appropriate models for interaction of arsenite with ferric hydroxide between pH values of -4 through +4. The effect of solvation on single point energy was calculated using COSMO models. The bidentate corner-sharing complexes were more energetically favorable than monodentate corner-sharing complexes for the entire pH range. Lower binding energies at some pH values indicated monodentate binding may contribute to adsorption at low pH values and at high pH values. Adsorbed arsenite species were found to be fully protonated at low pH values and partly protonated at high pH values for the most favorable complex. Models for the interaction of arsenite with ferric hydroxide provided a relationship of adsorption and pH values that the adsorption of arsenite increased as pH value increased and there was a maximum point around pH 8.5-9.
Type:
text; Electronic Dissertation
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Chemical Engineering; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Blowers, Paul; Farrell, James
Committee Chair:
Blowers, Paul; Farrell, James

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleUnderstanding Environmental Reactions of Carbon Tetrachloride, Trichloroethylene, Perchloroethylene, and Arsenic Applying Computational Chemistry Methodsen_US
dc.creatorZhang, Nianliuen_US
dc.contributor.authorZhang, Nianliuen_US
dc.date.issued2006en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractIn recent years, as the progress of computational abilities has increased, computational chemistry has become an interesting tool for researchers for investigating mechanisms of environmental reactions when results of experimental explorations are not sufficiently clear. In this research, several environmental reactions have been investigated using ab initio and density functional theory (DFT) methods.This research investigated the effect of the reaction energy on the reaction pathway for C-Cl bond cleavage in carbon tetrachloride (CT). Ab initio and density functional theories were used to study adiabatic electron transfer to aqueous phase CT. The potential energies associated with fragmentation of the CT anion radical into a trichloromethyl radical and a chloride ion were explored as a function of the C-Cl bond distance during cleavage. The effect of aqueous solvation was simulated using a continuum conductor-like screening model. Solvation significantly lowered the energies of the reaction products, indicating that the dissociative electron transfer was enhanced by solvation. It was found that reductive dissociation electron transfer of CT undergoes a change from an inner-sphere to an outer-sphere mechanism as the reaction energy is increased. The results showed a liner relationship between the activation energy for the dissociation and the overall energy change, which is in good agreement with the results of the Marcus model.This research also investigated the thermodynamic favorability and resulting structures for chemisorption of trichloroethylene (TCE) and perchloroethylene (PCE) on iron surfaces using periodic DFT with the non-local Perdew-Burke-Enzerhof (PBE) functional. Chemisorption structures were obtained for four physically adsorbed initial configurations. An initial configuration with two carbons (C-bridge) physically adsorbed at bridge sites between adjacent iron atoms was shown to be the most stable configuration for TCE, while the mode with two carbons (C-hollow) physically adsorbed at hollow site was verified to be the most stable configuration for PCE. C-Fe bonds were formed via sigma or pi bonds in the complexes formed at C-bridge, top and hollow site. Upon binding with the iron surface, the interaction of the C=C bond still remained as sp2 hybridization. Moreover, the strong chemisorption induced dissociations of C-Cl bonds and formation of Cl-Fe bonds. For both TCE and PCE, modes with two Cl atoms (Cl-bridge) physically adsorbed at bridge sites were found to be the least favorable configuration, in which only two Cl atoms formed bonds with the Fe surface and no C-Fe bonds were formed. Negative net Mulliken charges on TCE and PCE indicated they are reduced upon adsorption to the iron surface.Finally, in this research, we evaluated the accuracies and costs of several DFT methods including Harris, PWC LDA, and BLYP GGA functionals for interaction of arsenite with ferric hydroxides by comparison to calculated and experimental properties of surface complexes. It was found that the approach of using low-level structures coupled with high level single-point energies was much less expensive than the approach of using high level functionals for both structures and energies and could obtain similar computed binding energies. Further work has been done to investigate the appropriate models for interaction of arsenite with ferric hydroxide between pH values of -4 through +4. The effect of solvation on single point energy was calculated using COSMO models. The bidentate corner-sharing complexes were more energetically favorable than monodentate corner-sharing complexes for the entire pH range. Lower binding energies at some pH values indicated monodentate binding may contribute to adsorption at low pH values and at high pH values. Adsorbed arsenite species were found to be fully protonated at low pH values and partly protonated at high pH values for the most favorable complex. Models for the interaction of arsenite with ferric hydroxide provided a relationship of adsorption and pH values that the adsorption of arsenite increased as pH value increased and there was a maximum point around pH 8.5-9.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineChemical Engineeringen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBlowers, Paulen_US
dc.contributor.advisorFarrell, Jamesen_US
dc.contributor.chairBlowers, Paulen_US
dc.contributor.chairFarrell, Jamesen_US
dc.contributor.committeememberBlowers, Paulen_US
dc.contributor.committeememberJarrell, Jamesen_US
dc.contributor.committeememberSaez, Eduardoen_US
dc.identifier.proquest1726en_US
dc.identifier.oclc659747483en_US
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