Size Control in The Synthesis of Ag:SG Nanoparticles

Yeakub Zaker

Department of Chemistry and Biochemistry

Nanoparticles (NPs)

Halpert J.E. et al. J. Am. Chem. Soc. 2006, 128, 12590-12591.

Kumar, S. et al. J. Am. Chem. Soc. 2010, 132, 13141-13143.

8

6

2

0100

4

Exhibit new properties – electronic and optical properties differ from bulk properties

2

Increasing Particle Size

CdSe NPs

Ag:SG NPs

scaling

molecular

Reported Monodispersed Synthesis of Au MNPs

Au10(SG)10

Au15(SG)13

Au18(SG)14

Au22(SG)16

Au22(SG)17

Au25(SG)18

Au29(SG)20

Au33(SG)22

Au39(SG)24

By modification of reaction conditions

Solvent

Temperature

Reaction time

Aging of products

3

Au25(SG)18

Negishi, Y. et al. J. Am. Chem. Soc. 2005, 127, 5261-5270.

Wu Z. et al. J. Mater. Chem., 2009, 19, 622–626.

Kitaev et al. ACS Nano, 2009, 3(1), 21–26.

Kitaev et al. J. Phy. Chem. C, 2010, 114, 16010-16017.

• single size large Ag NP synthesized

at high temperature and low pH

• single size small Ag NP synthesized

with mixed ligands and high pH

Synthesis of Ag:SG NPs

silver thiolate

precursor

Stir (30 minutes)

AgNO3 +

Glutathione (SG) in H2O

i. Precipitate with ethanol

ii. Centrifuge

Ag:SG

Nanoparticles

add NaBH4

Kumar, S. et al. J. Am. Chem. Soc. 2010, 132, 13141-13143.

Stir

~1 minutes

~2 minutes~5 minutes60 minutes 4

Aging of Ag:SG NPs as a Function of pH

Desireddy, A. et al. Nanoscale, 2013, 5, 2036-2044. 5

Glutathione

pKa = 2.12

pKa = 3.59

pKa = 8.75

could pH be a useful control parameter for synthesis?

Project

Possible control parameters: • pH

• Temperature

• Solubility of precursor

• Reducing agent

• Time

find what controls the products of

Ag:SG MNP syntheses

Problem - Polydispersity

6

Ag:SG NPs

Kumar, S. et al. J. Am. Chem. Soc. 2010, 132, 13141-13143.

Synthesis of Ag:SG NPs

as a Function of pH and Temperature

Courtesy of Nathan Diemler 7

pH affect the product of the reaction, T too but not a big effect

2 3 4 5 6 7 8 9pH

T=~1°C

T=~20°C

Glutathione

pKa = 3.59

pKa = 2.12

pKa = 8.75

Control

8

(i) charge states of polyprotic ligands depend on pH

(ii) solubility of precursor depends on pH

soluble is more homogeneous, which could be better

(iii) reaction could depend on buffer composition

silver chemistry can be sensitive to halogens

(iv) NaBH4 reduction rate depends on pH

reaction rate is fast at low pH and slow at high pH

Which is the important control parameter?

Possible Reasons for pH Dependence

2 3 4 5 6 7 8 9pH

Captopril

9

T=~1°C

T=~20°C

(+-0) (+--)

Synthesis of Ag:SG NPs

as a Function of pH and Temperature

Glutathione

pKa = 3.59

pKa = 2.12

pKa = 8.75

seems to be a correlation with second deprotonation

(+00)

Control

2 3 4 5 6 7 8 9pH

Captopril

10

T=~1°C

T=~20°C

(0) (-)

pKa = 4.02

no correlation with deprotonation charge state is NOT an important control parameter

Synthesis of Ag:Captopril NPs

as a Function of pH and Temperature

Solubility of the Precursor as a Function of pH

Ag:Captopril

Ag:SG

pH 6

Stir30 min (all pH)

soluble

solubleturbid

correlation for GSH but not captopril solubility of precursor is NOT an important control parameter

2 3 4 5 6 7 8 9pH

T=~1°C

T=~20°C

(0) (-)

cloudy whiteinsoluble

11

400 600 800 1000

0.0

0.2

0.4

0.6

0.8

1.0

Abs

orba

nce

Wavelength (nm)

rt6citbuffer

rt6trisbuffer

rt7citbuffer

rt7trisbuffer

Effect of Buffer Composition

Ag:SG Synthesis at ~20 °C and pH 6 & 7

7

Cit.

7

Tris

6

Tris6

Cit.

No correlation for GSH buffer composition is NOT an important control parameter 12

Effect of Reducing Agent

Ag:SG Synthesis At ~1 °C and pH 9

400 600 800

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Abso

rba

nce

Wavelength (nm)

BTBC

KBH4

NaBH4

LiBH4

BTBC KBH4 NaBH4 LiBH4

13

* BTBC – Borane Tert-Butylamine Complex

Rate of Reaction

slower reaction rate produced smaller NPs reaction rate MIGHT be an important control parameter

400 600 800

0.0

0.2

0.4

0.6

0.8

1.0

Ab

so

rba

nce

Wavelength (nm)

BTBC

KBH4

NaBH4

LiBH4

Effect of Reducing Agent

Ag:SG Synthesis At ~20 °C and pH 9

14

BTBC KBH4 NaBH4 LiBH4

Rate of Reaction

slower reaction rate produced smaller NPs reaction rate MIGHT be an important control parameter

…but something else might be going on too.

BTBC KBH4 NaBH4 LiBH4

400 600 800

0.0

0.2

0.4

0.6

0.8

Absorb

an

ce

Wavelength (nm)

BTBC

KBH4

NaBH4

LiBH4

Effect of Reducing Agent

Ag:SGSynthesis At ~20 °C and pH 7

15

Rate of Reaction

faster reaction rate produced small NPs something else IS going on too

Courtesy of Nathan Diemler

400 600 800 1000

0.0

0.2

0.4

0.6

0.8

1.0

Abso

rba

nce

Wavelength (nm)

Band 2(Orange)

Time Evolution

Ag:SG Synthesis At ~20 °C and pH 6

NaBH4

faster kinetics initially produced large NPs, which quickly fell apart into small NPs due to higher T

time and higher T can completely change the product 16

Time Evolution

Ag:SG Synthesis At ~1 °C and pH 9Courtesy of Nathan Diemler

17

400 600 800 1000

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Abso

rba

nce

Wavelength (nm)

Band 6 (Brown)

NaBH4

slower kinetics produced small NPs, product evolved as sizes systematically grew

seems to be the thermodynamic product

7 95 6 843

Ag:SG Synthesis with BTBC at ~20°C

and Various pH (3-9)

18

slower kinetics produced small NPs

charge state did not control the product

REDUCTION RATE is the important control parameter

19

Why did the initial synthetic protocol lead to a

polydisperse product?

(i) there was no pH control (i.e. no buffer)

(ii) NaBH4 reduces water to produce OH–

pH increases from 3 to 9 over the course of the reaction

(iii) NaBH4 reduction rate depends on pH

reaction rate begins fast and ends slow

(iv) reaction was done in an ice bath

aging/decay reaction was slow

The reaction likely favored large particles initially and smaller particles

toward the end, with little opportunity for aging and decay toward smaller

particles, therefore the final product size distribution was broad.

Kumar, S. et al. J. Am. Chem. Soc. 2010, 132, 13141-13143.

Ag:SG NPs

Conclusions

• Charge states and solubility of precursor are NOT important control

parameters, i.e. they did not control the product

• REDUCTION RATE is the important control parameter for synthesis

of Ag:SG NPs

• Aging at higher temperatures can lead to size focusing (known)

• Nearly monodispersed Ag:SG MNPs can be synthesized using

following conditions:• BTBC at pH 7 and RT produced Ag15(SG)11

• NaBH4 at pH 6 and RT produced Ag15(SG)11

• NaBH4 at pH 9 on ice produced mostly Ag32(SG)19 with some

Ag15(SG)11

20

Future Work

Use new knowledge to develop simple synthetic protocols for

making high-quality products (pure and high yield).

• refine chemistry to improve selectivity (purity) of individual sizes

• focus on high-yield synthesis of particular products without the

need for separation

21

Acknowledgement

Group members

Aydar AtnagulovBadri BhattaraiDr. Brian AshenfelterBrian ConnNathan DiemlerSameera Wickramasinghe

Advisory committee

Dr. Terry BigioniDr. Joseph SchmidtDr. Dragan IsailovicDr. Nikolas Podraza

Department of Chemistry and Biochemistry

University of Toledo