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Impact of Heating on Quantum Yield
Quantum yield as a function of heating time. (Inset is heating times after 30 min.)
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Heating Time (min)
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tum
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ld MPA
GLU
MSA
TGA
TGL
CYS
TIO
Quantum yield as a function of time after 8 months of TIO-CdSe QDs.
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12 24 38Time (min)
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2/2/2010
6/2/2009
Used by 9th century artisans for pottery
Wires
Resistors
Switches
Transistors
Diodes
Capacitors
Chemical sensors1
Optoelectronics2
Photovoltaics3
Fluorescent display devices3
Light-mediated binding & release of biomolecules3
Absorbance
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1e+7
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7e+7Rhodamine 6G (347 nm; R2 = 0.998)Fluorescein (323 nm; R2 = 0.989)
Relative Quantum Yield Equation5
ФX = Quantum yield of QDsФST = Quantum yield of standardη = Refractive indexGrad = Slope of integrated intensities from the plot
Reaction Mixture Metal perchlorate: Cd(ClO4)2·H2O, Zn(ClO4)2·6H2O or
Pb(ClO4)2·3H2O in Type 1 water. Water-soluble thiols added in 2.4:1 thiol:metal ratio
Procedure The pH is adjusted to ≥ 11 using 1 M NaOH while stirring Mixture was deaerated for ~30 minutes with N2
Selenium source comes from either Al2Se3 or NaHSe Mixture was allowed to reflux over a period of time
Impact of Structure on Quantum Yield
Previous research explored quantum yields of CdSe quantum dots produced using Al2Se3 (tHEAT = 0).
Note: Different excitations were used
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GLU TIO MPL TGL MSA MPA TGA CYS
Thiols
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ld Al2Se3 at 480 nm
NaHSe at 347 nm
QDs with ZnSe and CdSe core and different thiols (tHEAT= 0).
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GLU TIO MPL TGL MSA MPA TGA CYS
Thiols
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ZnSe
CdSe
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Project Overview Water-Soluble, Monolayer-Protected QDs Monolayer-Protected Gold NanoparticlesA study of quantum yield in water–soluble, monolayer-protected quantum dots (QDs) was completed. The study examined the changes in quantum yield from the effects of heating, method of selenide addition, type of surrounding thiol, and material lifetime. Subsequent modifications of the QD surface were characterized using electrochemistry.
Monolayer-protected gold nanoparticles were prepared using several different synthetic methods. The nanoparticles were characterized by UV-visible spectroscopy, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and mass spectrometry. Different thiols were used in the synthetic scheme in order to monitor differences in surface chemistry.
KIM Synthesis8
Add HAuCl4·3H2O to a solution of Oct4NBr in toluene Remove aqueous phase Add 1-hexanethiol in 5:1 ratio thiol/gold ratio Cool to 0°C, reduce with NaBH4, and stir for 30 min Collect black organic phase and wash 4x with Type 1 H2O Remove solvent under reduced pressure Add slowly DMSO to the MPC and allow to stand overnight Collect black product Add acetone to the flask to extract Au25 Remove acetone with reduced pressure Wash with acetonitrile and ethanol 1) J.W. Grate et al. Anal. Chem. 2003, 75, 1868-1879.
2) Kamat, P.V. J. Phys. Chem. B 2002, 106, 7729-7744. 3) Thomas, K.G.; Kamat, P.V. Acc. Chem. Res. 2003, 36, 888-898.4) N.Gaponik et al. J. Phys. Chem. B 2002, 106, 7177-7185. 5) M.Grabolle et al. Anal. Chem. 2009, 81, 6285-6294.6) M. Brust et al. J. Chem. Soc. Chem. Commun. 1995, 1655-1656.7) M. S. Devadas et al. J. Phys. Chem. C, 2010, 114 (51), 22417-22423.8) J. Kim et al. Langmuir. 2007, 23 (14), 7853-7858.9) Z.Wu et al. Adv. Funct. Mater. 2011, 21, 177-183.
NSF CHE-095940, Faculty Research Grants, Academic Initiatives, Conduff Scientific Grants, and Croom Beatty Chemistry Research Internship
References/Acknowledgements
DEVADAS Synthesis7
Make solution of 3:1 thiol/HAuCl4·3H2O ratio Reduce with NaBH4 and stir for 30 min Obtain Au25 by stepwise recrystallization with methanol Centrifuge at 3000 rpm for 10 minutes Wash with a 4:1 H2O:methanol mixture
WU Synthesis9 Dissolve HAuCl4·3H2O in H2O, and cool to 0°C for 30 min Add thiol to solution in a 4:1 ratio with gold and stir for 1.5 hr Solution was reduced with NaBH4 and stirred for >12 hours Add methanol to reaction mixture Collect precipitate by centrifugation (3800 rpm, 10 minutes) Wash solid with MeOH/H2O and wash repeatedly w/ MeOH Dry under reduced pressure for 4 days
DPV of ferrocene modified TGL-CdSe QDs and ferrocene monomer.
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1.00E-06
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0.00.20.40.60.81.0
Potential (V) vs. Ag/AgCl
Curr
ent (
A)
Fc-modifiedQDsFerroceneCOOH
Surface Modification of QDs
The Synthesis and Analysis of Metallic and Semiconducting Nanoparticles
HS OH
O
HS OH
OH
O
HS
HS
OH
OH
HO
OH
O
O
SH
NH
OH
SH
O
O
HOHN
NH
OH
O
NH2
O
HS
O
O
glutathione (GLU)tiopronin (TIO)
3-mercaptopropionic acid (MPA)
mercaptosuccinic acid (MSA)
3-mercapto-1-propanol (MPL)
thioglycolic acid (TGA)
thioglycerol (TGL)
HS
NH2
OH
O
cysteine (CYS)
Water-Soluble Thiols
Elizabeth M. Henry and Deon T. Miles The University of the South, Department of Chemistry, Sewanee, TN
Applications
Brust/Schiffrin MPC Synthesis6
[Au(I)SR]n
0 ºC
AuCl4– + RSH
AuIII
AuI
Au0
3X
10X
BH4–
Small core of Au atoms that are stabilized by a monolayer of chemisorbed alkanethiolate ligands
Monolayer-Protected NanoCluster (MPC)
Synthetic Methods for Au25 MPCS
Spectral and Electrochemical Analysis
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E(V) vs Ag/AgCl
Cu
rre
nt
(A)
DPV CYS-Au25 MPC (Wu Synthesis) in 0.05 M tetra-n-butylammonium bromide/H2O using Pt WE, Pt CE
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Wavelength (nm)
UV-vis spectrum of MSA-Au25 MPC (Wu Synthesis)
Au140
Synthesis of QDs4
Image: http://www.mdpi.com/1422-0067/11/1/154/
ewaneecholarshipSewaneecholarshipS
Professor. . MilesElizabeth
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Counts vs. Mass-to-Charge (m/z)200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
-ESI Scan (0.693 min) Frag=225.0V 03_07_2011_01.d
260.9975
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1170.9094
Mass Spectrum of CYS-Au25 MPC (Wu Synthesis)
Anticipated MW = 5173 Da
Aliquots were collected based on visible change in color.Color change progresses towards red region.
