Electronic Supplementary Material (ESI) for Dalton Transactions
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Electronic Supplementary Information
(NH4)2S, A Highly Reactive Molecular Precursor for Low Temperature Anion Exchange
Reactions in Nanoparticles
Haitao Zhang, Louis V. Solomon, Don-Hyung Ha, Shreyas Honrao, Richard G. Hennig, and
Richard D. Robinson*
Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853
* To whom correspondence should be addressed. E-mail: [email protected].
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Electronic Supplementary Material (ESI) for Dalton Transactions
This journal is © The Royal Society of Chemistry 2013
General Procedures
All of the manipulations were carried out in a dinitrogen atmosphere by employing
standard Schlenk line and glove box techniques unless otherwise noted. Hexanes (≥98.5%),
ethanol (≥99.5%), 1-octadecene (90%), oleic acid (99.9%), ammonium sulfide (40-48 wt%
solution in water), oleylamine (70%), trioctylphosphine oxide (TOPO, 99%), 1,2dichlorobenzene (99%), and cobalt carbonyl (Co2(CO)8, 90%) were purchased from Aldrich;
molecular sieves (UOP type 3 Å) were purchased from Aldrich and activated at 300 oC under
dynamic vacuum for 3 hours before use.
The conventional transmission electron microscopy (TEM) images were recorded on an
FEI Tecnai T12 transmission electron microscope operating at 120 kV; the high-resolution TEM
(HRTEM) images were collected on an FEI Tecnai F20 transmission electron microscope
operating at 200 kV. Samples for TEM analysis were prepared by putting a drop of solution
containing nanoparticles on the surface of a copper grid coated with an amorphous carbon film.
X-ray powder diffraction data were collected on a Scintag Theta-Theta X-ray diffractometer (Cu
Kα radiation). X-ray photoelectron spectroscopy (XPS) data were collected on a Surface Science
Instruments SSX-100 with operating pressure < 2×10-9 Torr and monochromatic AlKax rays at
1486.6 eV. Elemental analysis (Inductively coupled plasma mass spectrometry (ICP-MS)) was
performed at ALS Environmental, Tucson, AZ.
Density-functional calculations were performed with the Vienna Ab-initio Software
Package (VASP)1-4 using the PBE exchange-correlation functional5 and the projector augmented
wave method.6,7 The Brillouin zone integration was performed using a Monkhorst and Pack kpoint mesh.8 8×8×8 and 6×6×6 k-point meshes were employed for structural relaxations and
nudged-elastic band (NEB) calculations,9 respectively. The kinetic energy cutoff for the plane
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Electronic Supplementary Material (ESI) for Dalton Transactions
This journal is © The Royal Society of Chemistry 2013
wave basis was set to 360 eV for the structural relaxations and 270 eV for the NEB calculations
of the diffusion barriers. The corresponding cutoff energies for the augmentation functions were
set to 650 eV and 480 eV, respectively. POSCAR files taken from the Materials Project
Website10 are used in our calculations.
Synthesis of CoO Nanoparticles
In a typical synthesis, trioctylphosphine oxide (TOPO) (0.2 g) was mixed with 99.9% oleic
acid (0.2 mL) and 1,2-dichlorobenzene (24 mL). The solution was heated to 180oC under N2
flow and a solution of 1.04 g CO2(CO)8 in 8 mL 1,2-dichlorobenzene was quickly injected. The
reaction was allowed to proceed for 5 mins and then an air stream (50 mL/min) was blown
through the reaction solution for 270 minutes. The reaction solution was cooled down in air and
ethanol was added to the solution to precipitate out NCs, which were separated by centrifugation
and washed one more time with hexanes/ethanol. The purified NCs were dissolved in hexanes.
Synthesis of Cobalt Sulfide Amorphous Nanoparticles
A mixture of 85 mg CoO, 5 mL octadecene and 5 mL oleylamine was heated to 100 oC.
Molecular sieve-dried (NH4)2S oleylamine solution (10 mL, 0.36 mmol/mL) was injected at
100 °C. Temperature was dropped down to 70 °C. The reaction was allowed to proceed for 5
mins at 70 °C and cooled down by water bath. Ethanol was added to the solution to precipitate
out NCs, which were separated by centrifugation and washed one more time with
hexanes/ethanol. The purified NCs were dissolved in hexanes. Elemental analysis (wt%): Co,
27.30; S, 19.49.
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Electronic Supplementary Material (ESI) for Dalton Transactions
This journal is © The Royal Society of Chemistry 2013
Synthesis of Cobalt Sulfide Crystalline Nanoparticles
In a typical synthesis, a mixture of 80 mg cobalt sulfide amorphous nanoparticles, 4 mL
octadecene and 1 mL oleylamine was heated to 200 oC and kept at this temperature for 1 hour.
The solution was then cooled down in air and ethanol was added to the solution to precipitate out
NCs, which were separated by centrifugation and washed one more time with hexanes/ethanol.
The purified NCs were dissolved in hexanes.
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Electronic Supplementary Material (ESI) for Dalton Transactions
This journal is © The Royal Society of Chemistry 2013
a)
Co 2p3/2
b)
Co 2p1/2
Co 2p3/2
ΔE = 15.8 eV
Intensity
ΔE = 15.1 eV
Intensity
775
Co 2p1/2
780
785
790
Binding Energy (eV)
795
800
775
780
785
790
Binding Energy (eV)
795
800
Figure S1. Co 2p XPS spectra of CoO (a) and amorphous Co3S4(b) NPs. ΔE represents the 2p3/22p1/2 spin orbit splitting of Co ions.
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Electronic Supplementary Material (ESI) for Dalton Transactions
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100 nm
Figure S2. TEM image of cobalt sulfide nanoparticles synthesized by reacting CoO with (NH4)2S at
140 oC. The reaction produced small sized (ca. 1-3 nm) impurity nanoparticles, which might originate
from the partial decomposition of nanoparticles.
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Electronic Supplementary Material (ESI) for Dalton Transactions
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Co3S4 (PDF 47-1738)
Intensity (a.u.)
CoS1.097 (PDF 19-0366)
25
30
35
40
45
50
55
60
65
70
2 Theta (degree)
Figure S3. XRD pattern of cobalt sulfide nanoparticles after annealing at 200 oC for 1 hour. The
major peaks in this pattern can be indexed to cubic Co3S4 (PDF 47-1738; blue stick pattern). Two
additional peaks at ca. 35o and 47o can be assigned to a secondary minor phase of CoS1.097 (PDF
19-0366).
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Electronic Supplementary Material (ESI) for Dalton Transactions
This journal is © The Royal Society of Chemistry 2013
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