Electronic Supplementary Material
Journal of Nanoparticle Research
Double Stabilization of Nanocrystalline Silicon: a Bonus from Solvent
Yury G. Kolyagin, Valery N. Zakharov, Alexandr V. Yatsenko, Ksenia A. Paseshnichenko,
Sergei V. Savilov, Leonid A. Aslanov*
Department of Chemistry, M.V. Lomonosov Moscow State University, Leninskie Gory,
Moscow, 119991, Russia
Experimental Section
1. Synthesis of silicon nanoparticles
Chemicals:
1,3-dimethylimidazolium iodide (mmimI) (99%), glyme ( 99%), methylbenzene( 99%),
potassium (99,5%), sodium (99,5%) and silicon tetrabromide (99 %) were purchased from SigmaAldrich.
Synthesis of sample 1. The reagents used were: SiBr4 – 0.016 mol; K – 0.07 mol (with a 10% excess)
and glyme, 35 ml.
The Schlenk vessel with a magnetic stirrer was purged with argon and 30 ml of glyme and 0.07 mol of
potassium were introduced. The reaction mixture was heated to 85 ºС with a glycerol bath. Potassium
was dispersed to spheres of 1–3 mm using a stirrer. Then a solution of 0.016 mol of SiBr4 in 5 ml of
glyme was added under Ar until the violet color appeared. After one hour, the color of the dispersion
changed to yellow. The overall reaction time was about 3 h.
Synthesis of sample 2. The reagents used were: SiBr4 – 0.016 mol; Na – 0.07 mol (with a 10% excess)
and methylbenzene, 35 ml.
The Schlenk vessel with a magnetic stirrer was purged with argon and 30 ml of methylbenzene and 0.07
mol of sodium were introduced. Previously sodium was dispersed in methylbenzene to spheres of 1-1,5
mm by ultrasonication. The reaction mixture was heated to 85 ºС using a glycerol bath. Then a solution
of 0.016 mol of SiBr4 in 5 ml of methylbenzene was added under Ar . The overall reaction time was
about 2 h.
S1
Synthesis of sample 3. The reagents used were: SiBr4 – 0.016 mol; K – 0.08 mol (with a 15% excess);
mmimI – 0,009 mol and glyme, 50 ml.
The Schlenk vessel with a magnetic stirrer was purged with Ar and 40 ml of glyme and 0,08 mol of
potassium were introduced. The reaction mixture was heated to 85 ºС using a glycerol bath and then
mmimI was added. The color of solution changed to yellowish-red. The reaction mixture was heated to
90 ºС and then solution of 0.016 ml of SiBr4 in 10 ml of glyme was added under Ar .The color of
dispersion changed to yellowish-brown. The overall reaction time was about 5 h.
Synthesis of sample 4. The reagents used were: SiBr4 – 0.008 mol; Na – 0.04 mol; mmimI – 0.004 mol
and methylbenzene, 50 ml.
The Schlenk vessel with a magnetic stirrer was purged with Ar and 40 ml of methylbenzene and 0,03
mol of sodium were introduced. The reaction mixture was heated to 100 ºС using a glycerol bath and
then mmimI was added. Then solution of 0.008 mol SiBr4 in 10 ml of methylbenzene was added under
Ar. The color of solution changed to brown and then to black during 1 h.. The overall reaction time was
about 6 h. After sedimentation a black precipitate was observed on the bottom of the Schlenk vessel,
and nanosilicon dispersion was bright-yellow.
Synthesis of sample 5. The reagents used were: SiBr4 – 0.008 mol; K – 0.04 mol; mmimI – 0.004 mol
and methylbenzene, 35 ml.
The Schlenk vessel with a magnetic stirrer was purged with Ar and 30 ml of methylbenzene and 0.04 of
potassium were introduced. The reaction mixture was heated to 90 ºС using a glycerol bath and then
mmimI was added. Then solution of 0.008 mol SiBr4 in 5 ml of methylbenzene was added under Ar.
The color of solution changed to brown and then to black during 1 h.The overall reaction time was
about 5 h. After sedimentation a black precipitate was observed on the bottom of the Schlenk vessel,
and nanosilicon dispersion was yellow.. The latter was decanted. Methylbenzene (10 ml) was added to
the black precipitate and dry HCl was purged for 15 min in order to remove traces of metallic
potassium. Then 10 ml of glyme was added and the reaction mixture was heated to 90 ºС for 90 min.
The color of precipitate changed from black to brown. Solvents were removed and brown precipitate
was isolated in a dry camera for NMR studies.
2. NMR MAS spectroscopy
The
13
С and
29
Si MAS NMR experiments were performed using a Bruker AVANCE-II 400
spectrometer (v1H = 400.1 MHz, v13С=100.4 MHz, v29Si= 79.5 MHz). The
13
С CP/MAS NMR spectra
were recorded using a 4mm HX MAS probe with spinning rate of 12 kHz. The 29Si MAS NMR spectra
were recorded using a 7mm HX MAS NMR probe with spinning rate of 4 kHz.
S2
The 29Si MAS NMR experiments were recorded by one-pulse sequence with 90-degree pulse length of 6
µs, a recycle delay of 60 s and number of scans from 1000 to 2400.
To record the
1
13
C spectra, a RAMP cross-polarization pulse sequence was used [1-2] with ramping of
H-channel power from 100 to 70% and 2 ms contact time. For high-power proton decoupling during
the acquisition, the SW-TPPM sequence (τ = 8μs, φ= 15°) was used [3]. The recycle delay was 2s and
the length of the proton 90-degree pulse was 5 μs. The number of transients collected for spectrum was
from 10000 to 20000. Si(CH3)4 was a reference for 13C and 29Si (0 ppm).
References
1. Cook R. L. Ramped-amplitude cross polarization in magic-angle-spinning NMR. Anal. Bioanal.
Chem. 2004, 378, 1484-1503.
2. Metz G.; Wu X. L.; Smith S. O. Coupling NMR to NOM. J. Magn. Reson. Ser. A 1994, 110, 219227.
3. Thakur R.S.; Kurur N.D.; Madhu P.K. Swept-frequency two-pulse phase modulation for
heteronuclear dipolar decoupling in solid-state NMR, Chem. Phys. Lett. 2006, 426, 459–463.
3. HRTEM
TEM images were obtained using a TITAN 80-300 high-resolution electron microscope (FEI, USA)
with correction of spherical aberration in light- and dark-field modes at accelerating voltage 300 kV and
a JEOL JEM 2100F/Cs electron microscope (JEOL Co. Ltd) with field emission generator (FEG)
equipped with a spherical aberration corrector (CEOS GmbH, Germany), Tridiem energy filter and
electron energy loss spectrum analyzer (Gaton Inc., USA) at accelerating voltage 200 kV. The data were
processed and interpreted using Digital Micrograph (Gatan), TIA (FEI) and JEMS (Switzerland)
packages.
For TEM studies, samples were prepared by deposition of suspension on the standard copper electron
microscope grids with solid ultrathin carbon film (~3 nm) or precoated with polyvinylformale.
4. XPS
The XPS patterns were obtained using a Kratos Axis Ultra DLD spectrometer, AlKa radiation with a
neutralizer calibrated for C1s of hydrocarbons (284.8 эV), transmission energy being 160 eV (general
spectrum) and 20 eV (separate lines).
S3
5. Figures
| |
50
0
- 50
-108.9
-99.6
-91.2
-76.5
-67.5
Fig.S7
| | |
- 100
ppm
Fig. S1. 29Si MAS NMR spectrum of sample IV.
Peaks at -108.9, -99.6 and -91.2 ppm are assigned as Q4, Q3 and Q2 sites,
respectively. The peaks in a range from –76.5 ppm to –67.5 ppm belong to
silicon nanoparticles with a broad size distribution (Si4Si site).
S4
A)
B)
Fig. S2. XPS pattern of sample IV.
a) panoramic spectrum, b) spectral line Si2p consists of two major components:
103.6 eV caused by silicon atoms of SiO2 and 102.0 eV usually assigned to
silicon atoms bonded to hydrocarbon ligands.
S5
Fig. S3. HRTEM image of sample IV.
S6
150
100
50
12.5
18.5
21.3
26.5
38.1
45.1
59.7
61.3
63.8
74.4
72.1
124.4
125.6
128.4
129.2
137.9
Fig. S9
0
ppm
Fig. S4. 13С CP/MAS NMR spectrum of sample V.
A peak at 38.1 ppm was assigned to the methyl groups of imidazolium. Peaks in
the range 124.4 – 137.9 ppm also indicate the presence of imidazolium in
sample V. Peaks in the range 59.7 – 74.4 ppm are assigned as the adsorbed
glyme molecules. Peaks in the range 12.5 – 26.5 ppm require additional
experiments for their interpretation.
S7