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Department of Chemical &Environmental Engineering
Characterization of Bare and Surface-Modified Gold Nanoparticles
Thi (Kathy) Nguyen HuynhGraduate student mentor: Hyunjung N. Kim
Advisor: Dr. Sharon Walker
Department of Chemical and Environmental EngineeringUniversity of California, Riverside
Background Objectives Experimental Approach Results
-Bare Gold Nanoparticles (GNPs)
-Surface-modified GNPs Conclusions to date Acknowledgements
Outline
Background Nanostructures are popular for many industrial applications
Ongoing studies investigating the interactions between nanostructures with living organisms
Nanostructures are source of environmental contamination
By the year of 2025, 48 countries will be short of fresh water water reuse/recycling will become standard
Therefore, the ability to remove these nanostructures must be determined.
◈ Overall project’s objective:To determine what physical and chemical mechanisms control the transport and fate of nanostructures in aquatic environments.
Task 1: Synthesis and Characterization of One-Dimensional Nanostructures Task 2: Radial Stagnation Point Flow (RSPF) experiments Task 3: Filtration experiments
◈ Specific objectives – initiating task 1:1. To establish methods to characterize surfaces of Gold Nanoparticles (GNPs)
2. To compare characteristics of bare and surface-modified GNPs (S-GNPs)
Objectives
◈ Model nanoparticles (GNPs)
◈ Surface Modification (S-GNPs)
Experimental Approach
GNPs + 1mM 3-Mercapto-1-Hexanol 3hrs Wash with DI water for 7
times: centrifuge at 12000 rpm for 2 minutes each time
(1mL) (2mL)
S
O
H
H
- Procedure
- 3-Mercapto-1-Hexanol (C6H14OS)
- Synthesis done by SUNRISE
student in Dr. Myung’s lab
- Diameter: 200 nm
- Length: 2.5 – 4.0 µm
- Size Measurement(Inverted microscope Olympus IX70)
Experimental Approach
◈ Surface Characterization
- Hydrophobicity (VCA Optima Goniometer)
- Electrokinetic properties (ZetaPALS)
What is Electrokinetic Property? A particle’s ability to move in the electromagnetic field ZetaPALS measures the particles’ mobility, and then
calculates to give zeta potentials or the surface charge values Mechanism:
Distance from surfaceP
oten
tial
Stern layer
Point of measurement
Results – Electrokinetic Properties of GNPs
◈ Effect of size◈ Effect of concentration
Mobility ≠ f (size)
for these particles and in this conditionOptimum concentration (OD546nm) : 0.15 - 0.30
pH: 5.8, DI water, 3 µm pH: 5.8, DI water
0
-1
-2
-3
-4
Mob
ilit
y,
[(
m/s
)/(V
/cm
)]
~ 3 m ~ 5 m ~ 8 m0
-1
-2
-3
-4
Mob
ility
, [
(m
/s)/
(V/c
m)]
A B S = 0 .1 2 5 A B S = 0 .2 0 6 A B S = 0 .2 9 0
◈ Effect of valence and ionic strength
1 E -0 0 5 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1
Io n ic S tren g th (M )
- 6
- 5
- 4
- 3
- 2
- 1
0
1
2
3
Mob
ilit
y,
[(
m/s
)/(V
/cm
)]
B are G N P s + C aC l2
B are G N P s + K C l• As ionic strength increased in the presence of salt solutions, mobility became less negative (charge on particle approached neutral)
• Valance had an important role on mobility: in the presence of divalent cations, mobility was less negative than that in the presence of monovalent cations.
pH: 5.8
Results – Electrokinetic Properties of GNPs
What is Hydrophobicity?
Hydrophobicity refers to a surface’s property of being water-repellent
Task: To what degree are GNPs hydrophobic? Contact Angle Method
SLSG
өHydrophobic: ө>90o
Hydrophilic: ө<90o
Water droplet
Solid surface
LG
◈ Contact angle measurement
Glass 20 μL 70 μL 100 μL 200 μL
- Solution concentration: OD546nm : 1.684 (2.5x dilution)
0 1 0 0 2 0 0 3 0 0
C o n cen tra tio n (L )
0
5 0
1 0 0
1 5 0
Con
tact
An
gle
(o )
Optimum concentration- Contact angle of Bare GNPs : 130.6 3.2 O
Surface of bare GNPs: Hydrophobic
Results – Hydrophobicity of GNPs
1 E -0 0 5 0 .0 0 0 1 0 .0 0 1 0 .0 1 0 .1
Io n ic S tren g th (M )
- 6
- 5
- 4
- 3
- 2
- 1
0
1
2
3
Mob
ilit
y,
[(
m/s
)/(V
/cm
)]
S -G N P s + C aC l2
B are G N P s + C aC l2
S -G N P s + K C lB are G N P s + K C l
- The mobility of S-GNPs was less
negative than that of bare GNPs in
the presence of KCl. However, the
difference was not significant in the
presence of CaCl2.
- Valence played an important role
on GNPs’ mobility regardless of the
presence of 3-mercapto-1-hexanol
groups.
pH: 5.8
Results – Electrokinetic Properties of Bare GNPs vs. S-GNPs
Why surface-modified?
Results – Hydrophobicity of GNPs vs. S-GNPs
0
40
80
120
160
Con
tact
Ang
le (
o )
B are G N P s S -G N P s
Bare GNPs S-GNPs
Contact angle of S-GNPs : 135.8 3.2 O
Surface of S-GNPs: Hydrophobic
Functional groups 3-mercapto-1-hexanol did not affect the hydrophobicity significantly.
Proposed Mechanisms
Why did mobility of GNPs decrease in the presence of 3-mercapto-1-hexanol?
SH end, hydrophilic with
greater affinity to GNPs
OH end, hydrophilic end
Increase in mobility of GNPs
and
Surface becomes more hydrophilic
Decrease in mobility of GNPs
and
Surface becomes more hydrophobic
Modification
◈ Proposed Changes: -Increase in concentration of 3-mercapto-1-hexanol-Increase in amount of time suspending the GNPs in the solution-Reduce the length of the GNPs when keeping the same concentration
Conclusions to date1. Methods to characterize the surface of GNPs has been established. Mobility of
GNPs was not a function of concentration nor size, over a range investigated in this study.
2. Solution chemistries (Ionic strength and valence) considerably influenced mobility of bare and surface-modified-3-mercapto-1-hexanol GNPs.
3. Mobility of S-GNPs was less negative than that of bare GNPs in the presence
of KCl, while the mobility was not sensitive to the presence of 3-mercapto-1-hexanol in the presence of CaCl2.
4. The surface of bare GNPs was determined to be hydrophobic. 5. The modification of 3-mercapto-1-hexanol did not make a significant differen
ce in hydrophobicity.
Acknowledgements
- The Coordinators of BRITE Program
- The bacterial adhesion research lab members
- Dr. Nosang Myung and Heather Yang
Thank you !!
Questions?