Transport Mechanisms of Titanium Dioxide Nanoparticles in Porous Media

Persistent Link:
http://hdl.handle.net/10150/247277
Title:
Transport Mechanisms of Titanium Dioxide Nanoparticles in Porous Media
Author:
Cox, Hazel Anne
Issue Date:
2012
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:
Nanoparticles are an emerging contaminant of concern. They are used in many products and industries and, due to a lack of regulation, are entering the natural environment through our waste streams. Studies examining the transport of nanoparticles in porous media have observed divergences between data and theory. Transport data also varies greatly across studies, adding complexity to the determination of the important factors in nanoparticle transport. These main factors and key areas of deviation from theory were determined by comparing and contrasting various studies of nanoparticle transport. To further examine behavior and retention mechanisms of nanoparticles in porous media, nano-sized titanium dioxide (nano-TiO₂) was used in miscible-displacement transport experiments, followed by force measurements by Atomic Force Microscopy (AFM) between the same nanoparticles and porous media. Ionic strength ranged from 0.0015 - 30 mM, and solution chemistries were varied from pH 4.5 (favorable attachment) to 8 (unfavorable attachment). To determine the possible presence of secondary minima attachment, detachment transport experiments were performed for the unfavorable attachment conditions. Calculations were performed using DLVO theory, which is often used to describe colloid and nanoparticle retention, and compared to measured force profiles. Mass recoveries for the transport experiments ranged from 28-80%. Retention under favorable conditions was much greater than under unfavorable conditions, as was anticipated. Detachment was observed, indicating the potential presence of secondary minima. Large adhesive forces were measured by AFM and were affected by solution chemistry. Force profiles were highly variable, especially under unfavorable attachment conditions. Secondary minima were observed, even at a 0.0015 mM ionic strength. DLVO theory, while qualitatively accurate, largely under-predicted attractive and repulsive forces and their range of influence. Variability in the force profile and potential conformational changes of nanoparticle aggregates were postulated to be influential in nanoparticle transport. Retention of the nanoparticles under unfavorable conditions was postulated to involve secondary minima and the effects of surface roughness. These mechanisms, which are not represented in DLVO theory, are likely causes of the observed divergence of experimental results from theory. Improved understanding of retention mechanisms will hopefully enhance our understanding of the potential impacts of nanoparticles on the natural environment.
Type:
text; Electronic Dissertation
Keywords:
Soil, Water & Environmental Science
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Soil, Water & Environmental Science
Degree Grantor:
University of Arizona
Advisor:
Brusseau, Mark L.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleTransport Mechanisms of Titanium Dioxide Nanoparticles in Porous Mediaen_US
dc.creatorCox, Hazel Anneen_US
dc.contributor.authorCox, Hazel Anneen_US
dc.date.issued2012-
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.abstractNanoparticles are an emerging contaminant of concern. They are used in many products and industries and, due to a lack of regulation, are entering the natural environment through our waste streams. Studies examining the transport of nanoparticles in porous media have observed divergences between data and theory. Transport data also varies greatly across studies, adding complexity to the determination of the important factors in nanoparticle transport. These main factors and key areas of deviation from theory were determined by comparing and contrasting various studies of nanoparticle transport. To further examine behavior and retention mechanisms of nanoparticles in porous media, nano-sized titanium dioxide (nano-TiO₂) was used in miscible-displacement transport experiments, followed by force measurements by Atomic Force Microscopy (AFM) between the same nanoparticles and porous media. Ionic strength ranged from 0.0015 - 30 mM, and solution chemistries were varied from pH 4.5 (favorable attachment) to 8 (unfavorable attachment). To determine the possible presence of secondary minima attachment, detachment transport experiments were performed for the unfavorable attachment conditions. Calculations were performed using DLVO theory, which is often used to describe colloid and nanoparticle retention, and compared to measured force profiles. Mass recoveries for the transport experiments ranged from 28-80%. Retention under favorable conditions was much greater than under unfavorable conditions, as was anticipated. Detachment was observed, indicating the potential presence of secondary minima. Large adhesive forces were measured by AFM and were affected by solution chemistry. Force profiles were highly variable, especially under unfavorable attachment conditions. Secondary minima were observed, even at a 0.0015 mM ionic strength. DLVO theory, while qualitatively accurate, largely under-predicted attractive and repulsive forces and their range of influence. Variability in the force profile and potential conformational changes of nanoparticle aggregates were postulated to be influential in nanoparticle transport. Retention of the nanoparticles under unfavorable conditions was postulated to involve secondary minima and the effects of surface roughness. These mechanisms, which are not represented in DLVO theory, are likely causes of the observed divergence of experimental results from theory. Improved understanding of retention mechanisms will hopefully enhance our understanding of the potential impacts of nanoparticles on the natural environment.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectSoil, Water & Environmental Scienceen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineSoil, Water & Environmental Scienceen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBrusseau, Mark L.en_US
dc.contributor.committeememberCurry, Joanen_US
dc.contributor.committeememberTuller, Markusen_US
dc.contributor.committeememberPapuga, Shirleyen_US
dc.contributor.committeememberBrusseau, Mark L.en_US
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