Department of Chemical & Environmental Engineering Characterization of Bare and Surface-Modified...

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?