i Lights, Camera, Reaction! The Influence of Interfacial Chemistry on Nanoparticle Photoreactivity

253 Pages·2016·12.75 MB·English

Lights, Camera, Reaction!
The Influence of Interfacial Chemistry on Nanoparticle Photoreactivity
by
Jeffrey Michael Farner Budarz
Department of Civil and Environmental Engineering
Duke University

Date:_______________________
Approved:

___________________________
Mark R. Wiesner, Supervisor

___________________________
Claudia K. Gunsch

___________________________
Jerome Rose

___________________________
Richard T. Di Giulio

Dissertation submitted in partial fulfillment of
the requirements for the degree of Doctor
of Philosophy in the Department of
Civil and Environmental Engineering in the Graduate School
of Duke University

2016

i
v
ABSTRACT
Lights, Camera, Reaction!
The Influence of Interfacial Chemistry on Nanoparticle Photoreactivity
by
Jeffrey Michael Farner Budarz
Department of Civil and Environmental Engineering
Duke University

Date:_______________________
Approved:

___________________________
Mark R. Wiesner, Supervisor

___________________________
Claudia K. Gunsch

___________________________
Jerome Rose

___________________________
Richard T. Di Giulio

An abstract of a dissertation submitted in partial
fulfillment of the requirements for the degree
of Doctor of Philosophy in the Department of
Civil and Environmental Engineering in the Graduate School of
Duke University

2016
i
v
Copyright by
Jeffrey Michael Farner Budarz
2016
Abstract
The ability of photocatalytic nanoparticles (NPs) to produce reactive oxygen
species (ROS) has inspired research into several new applications and technologies,
including water purification, contaminant remediation, and self-cleaning surface
coatings. As a result, NPs continue to be incorporated into a wide variety of increasingly
complex products. With the increased use of NPs and nano-enabled products and their
subsequent disposal, NPs will make their way into the environment. Currently, many
unanswered questions remain concerning how changes to the NP surface chemistry that
occur in natural waters will impact reactivity. This work seeks to investigate potential
influences on photoreactivity – specifically the impact of functionalization, the influence
of anions, and interactions with biological objects - so that ROS generation in natural
aquatic environments may be better understood.
To this aim, titanium dioxide nanoparticles (TiO2) and fullerene nanoparticles
(FNPs) were studied in terms of their reactive endpoints: ROS generation measured
through the use of fluorescent or spectroscopic probe compounds, virus and bacterial
inactivation, and contaminant degradation. Physical characterization of NPs included
light scattering, electron microscopy and electrophoretic mobility. These systematic
investigations into the effect of functionalization, sorption, and aggregation on NP

iv
aggregate structure, size, and reactivity improve our understanding of trends that
impact nanoparticle reactivity.
Engineered functionalization of FNPs was shown to impact NP aggregation, ROS
generation, and viral affinity. Fullerene cage derivatization can lead to a greater affinity
for the aqueous phase, smaller mean aggregate size, and a more open aggregate
structure, favoring greater rates of ROS production. At the same time however, fullerene
1
derivatization also decreases the O2 quantum yield and may either increase or decrease
the affinity for a biological surface. These results suggest that the biological impact of
fullerenes will be influenced by changes in the type of surface functionalization and
extent of cage derivatization, potentially increasing the ROS generation rate and
facilitating closer association with biological targets.
Investigations into anion sorption onto the surface of TiO2 indicate that reactivity
will be strongly influenced by the waters they are introduced into. The type and
concentration of anion impacted both aggregate state and reactivity to varying degrees.
Specific interactions due to inner sphere ligand exchange with phosphate and carbonate
have been shown to stabilize NPs. As a result, waters containing chloride or nitrate may
have little impact on inherent reactivity but will reduce NP transport via aggregation,
while waters containing even low levels of phosphate and carbonate may decrease
“acute” reactivity but stabilize NPs such that their lifetime in the water column is
increased.

v
Finally, ROS delivery in a multicomponent system was studied under the
paradigm of pesticide degradation. The presence of bacteria or chlorpyrifos in solution
significantly decreased bulk ROS measurements, with almost no ŸOH detected when
both were present. However, the presence of bacteria had no observable impact on the
rate of chlorpyrifos degradation, nor chlorpyrifos on bacterial inactivation. These results
imply that investigating reactivity in simplified systems may significantly over or
underestimate photocatalytic efficiency in realistic environments, depending on the
surface affinity of a given target.
This dissertation demonstrates that the reactivity of a system is largely
determined by NP surface chemistry. Altering the NP surface, either intentionally or
incidentally, produces significant changes in reactivity and aggregate characteristics.
Additionally, the photocatalytic impact of the ROS generated by a NP depends on the
characteristics of potential targets as well as on the characteristics of the NP itself. These
are complicating factors, and the myriad potential exposure conditions, endpoints, and
environmental systems to be considered for even a single NP highlight the need for
functional assays that employ environmentally relevant conditions if risk assessments
for engineered NPs are to be made in a timely fashion so as not to be outpaced by, or
impede, technological advances.

vi
Dedication

No work is produced in a vacuum (don’t believe the particle physicists), and so
this dissertation is dedicated to everyone who has contributed to this endeavor. Truly
without your collaboration, ideas, and support, in ways both large and small, I would
not find myself here.

vii
Contents
Abstract .......................................................................................................................................... iv
List of Tables ................................................................................................................................ xv
List of Figures ............................................................................................................................. xvi
Acknowledgements .................................................................................................................. xxii
1. Introduction ............................................................................................................................... 1
1.1 Motivation ...................................................................................................................... 1
1.2 Scope ............................................................................................................................... 2
1.3 Hypotheses and Objectives .......................................................................................... 4
2. Background ................................................................................................................................ 7
2.1 Photocatalysis .................................................................................................................... 8
2.1.1 Reactive Oxygen Species .......................................................................................... 10
2.1.1.1 ROS Detection ..................................................................................................... 12
2.1.1.2 ROS Standard Generators ................................................................................. 15
2.1.1.3 ROS Quenchers .................................................................................................. 16
2.2 Photoreactive Nanoparticles ......................................................................................... 16
2.2.1 Fullerene Nanoparticles ........................................................................................... 19
2.2.1.1 FNP Reactivity .................................................................................................... 20
2.2.1.2 FNP Physical Transformations ........................................................................ 22
2.2.2 Titanium Dioxide ....................................................................................................... 23
2.2.2.1 TiO2 Reactivity .................................................................................................... 23

viii
2.2.2.2 P25 TiO2 ............................................................................................................... 25
2.3 Particle Stability and Aggregation ............................................................................... 27
2.3.1 Particle Attachment ................................................................................................... 27
2.3.2 Rectilinear Transport and Particle Collisions ........................................................ 30
2.3.3 Fractal Dimension ..................................................................................................... 32
2.3.4 Changes to the Smoluchowski Equation Due to the Fractal Nature of
Aggregates ........................................................................................................................... 33
2.3.5 Measuring Fractal Dimension via Light Scattering .............................................. 35
2.4 Effect of Aggregation on Reactivity ............................................................................. 38
2.5 NPs in Environmental Waters ...................................................................................... 40
2.6 Possible Risks Posed by Nanomaterials ...................................................................... 42
2.6.1 Need for Standardized Systems and Tests – Functional Assays ........................ 44
3. Methods .................................................................................................................................... 46
3.1 NP Suspension Preparation .......................................................................................... 46
3.1.1 FNP Suspensions ....................................................................................................... 46
3.1.2 TiO2 Suspensions ....................................................................................................... 47
3.2 UV Illumination .............................................................................................................. 48
3.3 ROS Measurements ........................................................................................................ 49
1
3.3.1 O2 Measurements with SOSG ................................................................................. 49
3.3.1.1 Standard Curve Preparation ............................................................................ 50
3.3.2 ŸOH Measurements with TA ................................................................................... 52
3.3.2.1 Standard Curve Preparation ............................................................................ 54

ix
-
3.3.3 O2Ÿ Measurements with HE .................................................................................... 54
3.4 Additional Reactivity Endpoints .................................................................................. 55
3.4.1 Viral Inactivation ....................................................................................................... 55
3.4.2 Bacterial Inactivation ................................................................................................ 56
3.4.3 Inactivation Kinetics and ROS Dose ....................................................................... 57
3.4.4 CPF Degradation ....................................................................................................... 57
3.5 Aggregate Characterization .......................................................................................... 58
3.5.1 Transmission Electron Microscopy ......................................................................... 58
3.5.2 Aggregate Size by Laser Diffraction ....................................................................... 58
3.5.3 Particle Size by Dynamic Light Scattering ............................................................. 59
3.5.4 Fractal Dimension by Static Light Scattering ........................................................ 59
3.5.5 Electrophoretic Mobility and pH Titrations .......................................................... 60
4. Results and Discussion ........................................................................................................... 62
4.1 Bacteriophage Inactivation by UV-A Illuminated Fullerenes: Role of
Nanoparticle-Virus Association and Biological Targets ................................................. 62
4.1.1 Introduction ................................................................................................................ 63
4.1.2 Materials and Methods ............................................................................................. 66
4.1.2.1 Cultures, Phage Purification and Enumeration ............................................. 66
4.1.2.2 Fullerene Suspensions ....................................................................................... 66
1
4.1.2.3 Irradiation and O2 Detection ............................................................................ 66
4.1.2.4 ATR-FTIR Spectroscopy .................................................................................... 67
4.1.2.5 OxyBlot Protein Oxidation Assay .................................................................... 68

x