size control in the synthesis of ag:sg nanoparticles
TRANSCRIPT
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