Electronic Supplementary Information
One-step Synthesis of α-Fe2O3 Nanorods and Nanorod
Assemblies Induced by Imidazolium Ionic Liquid for
Lithium-ion Battery
Shuting Xiea, Fei Lub, Shaojie Liuc, Liqiang Zhengb, Mingliang Jina, Guofu Zhoua and
Lingling Shuia*
a)
Institute of Electronic Paper Displays, South China Academy of Advanced Optoelectronics
& Joint International Research Laboratory of Optical Information of the Chinese Ministry of
Education, South China Normal University, Guangzhou, 510006, China
b)
Key laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of
Education, Jinan, 250100, China
c)
National Engineer Technology Research Center for Colloidal Materials, Shandong
University, Jinan, 250100, China
Corresponding author: Lingling Shui
E-mail address: [email protected]
Phone number: +86-20-39314813
Fax number: +86-20-39314813
Experimental Section
1. Preparation of ionic liquids [Cnmim]+[PhCOO]-, n = 4, 8, 12
The 1-butyl-3-alkylimidazolium chloride ([Cnmim]Cl, n=4, 8, 12) were freshly prepared
based on the procedures described in reference.1 An aqueous solution of [Cnmim]Cl was
purified by passing through a column filled with anion exchange resin to obtain
[Cnmim][OH].2 The reaction termination was tested by AgNO3. No AgCl precipitation could
be found, representing chloride ions were completely replaced by hydroxide ions.
1-butyl-3-alkylimidazolium benzoate ([Cnmim]+[PhCOO]-, n=4, 18, 12) (chemical structures
is shown in Fig. S1) was obtained by neutralization of [Cnmim][OH] and benzoic acid by
stirring in a flask at 40 °C for 10 h and dried in a vacumm dryer at 60 °C for 72 h. The
structures of the resulting ionic liquids were confirmed by 1H-NMR.
O
O
N
N
n
FIG. S1. Molecular structure of 1-butyl-3-alkylimidazolium benzoate ([Cnmim]+[PhCOO]-).
2. Fabrication of α-Fe2O3 nanoparticles
0.12 mmol of [C4mim]+[PhCOO]- was added to 10 mL of triply distilled water under stirring
to form a homogenous solution. Subsequently, 0.3 mmol of FeSO47H2O was added into the
above solution under continuous stirring. After stirring for 30 minutes, the total solution was
placed in a 25 mL Teflon-lined stainless steel autoclave and maintained at 150 °C for 3 h, 5 h
or 10 h in an electric oven. After that, the autoclave was cooled down naturally to room
temperature. The final product was separated by centrifugation, and then washed five times
with water and ethanol before drying in a vacuum oven at 60 °C for 12 h. In this procedure,
the amount of [C4mim]+[PhCOO]- could be adjusted to 0.3 mmol and 0.24 mmol. For
comparison, α-Fe2O3 samples were also prepared in the presence of [C8mim]+[PhCOO]- and
[C12mim]+[PhCOO]- under the same condition. The chemical composition of the obtained
α-Fe2O3 nanoparticles was characterized using X-ray photoelectron spectroscopy (XPS,
ESCALAB 250 spectrometer, ThermoFisher Scientific, USA) (Fig. S2a), D/max-Ra X-ray
diffractometer (XRD, Rigaku D/max 2550/PC, Japan) (Fig. S2b) and confocal microprobe
Raman spectrometer (Jobin-YvonHR800, France) (Fig. S2c). The binding energies obtained
in the XPS analysis were corrected for specimen charging by referencing the C1s line to 285
eV. And the carbon peak came from the adventitious carbon on the surface of the sample.
CKLL and OKLL is the Auger electron. The morphologies of these products were observed
by transmission electron microscopy (TEM, JEOLJEM-100CX II, Japan), scanning electron
microscopy (SEM, JEOLJSM-6700F, Japan) and high resolution transmission electron
microscopy (HR-TEM, JEOLJEM-2100, Japan).
FIG. S2. (a) XPS spectrum of the synthesized α-Fe2O3 nanorods. XRD spectrum (b) and
Raman spectrum (c) of the α-Fe2O3 nanorods and nanorod assemblies.
The XPS spectrum, as shown in Fig. S2a, contains the signal of Fe 2p3/2 (~724 eV), Fe 2p1/2
(~711 eV) and O1s (531 eV), confirming the existence of α-Fe2O3. Fig. S2b shows the
typical XRD patterns of nanorods and nanorod assemblies. All detectable diffraction peaks
match well with JCPDS no.33-0664 for rhombohedral α-Fe2O3. No other peaks from
impurities are observed. The intense and sharp diffraction peaks confirm that the nanorods
and nanorod assemblies are well-crystallized. The Raman spectra in Fig. S2c is consistent
with those of α-Fe2O3 reported in the literature.3 The Raman signal group of 225 and 494 cm-1
is ascribed to A1g; and 245, 292, 410 and 605 cm-1 is ascribed to Eg modes of α-Fe2O3. All
these results confirm that the as-prepared samples are purely stoichiometric α-Fe2O3. Table
SI presents the synthesized nanorods morphologies at different conditions.
TABLE SI. Experimental conditions and corresponding nanorod morphologies
Ionic Liquid
T/ºC
t/h
Morphology
L/nm
D/nm
L/D
[C4mim]+[PhCOO]-
150
3
Nanorods
250-400
～15
20
[C8mim]+[PhCOO]-
150
3
Nanorods
200-300
25
10
[C12mim]+[PhCOO]-
150
3
Nanorods
150
100
1.5
T-reaction temperature, t-reaction time, L-length, D-diameter, L/D-length/diameter
Figure S3 is the XRD patterns of the primary nanoparticles (nanospheres, nanorods and
nanoplates). All detectable diffraction peaks match well with JCPDS no.33-0664 for
Intensity / a. u.
rhombohedral α-Fe2O3. No other peaks from impurities are observed.
（ 012）
（ 104）
（ 110）
（ 116）
（ 214）（ 300）
（ 113） （ 024）
Nanorods
Nanoplates
Nanospheres
20
30
40
50
2  / degree
60
70
FIG. S3. XRD patterns of α-Fe2O3 nanospheres, nanorods and nanoplates.
2. Photocatalytic activity experiments
Photocatalytic activity of the as-prepared α-Fe2O3 nanostructures was evaluated by the
degradation of Rhodamine B (RhB) under 300 W Xe lamp with a 400 nm cutoff filter. In a
typical procedure, 10 mg of α-Fe2O3 nanorods material was added to 50 mL of RhB aqueous
solution (0.02 mM).Then the suspension was magnetically stirred in dark for 30 min to reach
the adsorption–desorption equilibrium and uniform dispersity. After that, 0.255 mL of
hydrogen peroxide solution (H2O2, 30 wt%) was added to the system. The Pyrex
photocatalytic reactor was then exposed to a visible light irradiation with maximum
illumination time up to 180 min. During the irradiation, the suspension was continuously
stirred and the reaction temperature was kept at 20 ºC. At different time intervals, analytical
samples were extracted, centrifuged and filtered to remove the photocatalyst powders. The
dye concentration in the filtrate was analyzed by measuring the absorption intensity of RhB at
554 nm.
The photocatalytic performance was investigated to understand the correlation between
the photocatalytic property and the morphology of α-Fe2O3 nanostructures. Fig. S4a shows a
time course of RhB degradation with different shapes (Ct/C0 with Ct and C0 the RhB
concentration at time t and after adsorption equilibrium, respectively). The degradation curves
can be described as a quasi-first-order limiting step rate expression of Langmuir-Hinshelwood
kinetic model. The blank test confirms that 10% of RhB can be degraded after 180 min of
irradiation without photocatalyst. The degradation rates are 48%, 59% and 99% for
nanospheres, nanoplates and nanorods, respectively. The degradation rate of nanorods is about
twice of that of nanospheres. Both nanorods and nanorod assemblies could degrade RhB
completely within 3 h (Fig. S4b). The photocatalytic efficiency of nannorods varies with L/D.
The nanorods with high value of L/D could degrade RhB completely in shorter time. It took
60 min and 40 min for the nanorods-1 (L/D = 20) and their assemblies to completely degrade
RhB.
FIG. S4. Photocatalytic degradation efficiency of the α-Fe2O3 (a) nanoplates, nanospheres
and nanorods and (b) nanorods with different value of L/D and nanorod assembly.
It is generally accepted that anisotropic nanorods can enhance the photo-reactivity by
minimizing the e--h+ recombination by tuning the direction and path of photo induced charge
carriers through quantum confinement. Well-defined long nanorods with more surface oxygen
vacancy defects as electron acceptors can temporarily trap the photo-generated electrons to
reduce the surface recombination of photo-induced electron-hole pairs. Therefore, it is
beneficial to the photocatalytic reaction.4,5
4. Electrochemical characterization
The electrochemical measurements were performed using 2032 coin-type cells. Pure lithium
foil is the counter and the reference electrodes. For the electrode preparation, 70 wt% of the
as-prepared α-Fe2O3 nanorod assemblies, 20 wt% conducting carbon black, and 10 wt%
organic binder polyvinylidene fluoride (PVDF) were mixed with methyl-2-pyrrolidinone
(NMP). The obtained slurry was coated on a copper foil to form working electrodes, and dried
under vacuum at 80 ºC for 12 h. The resulting foil was rolled pressed and cut into a disc. The
loading density of Fe2O3 nanorods on the electrode is about 1.2 mg·cm-2. The electrochemical
measurements were performed using 2032 coin-type cells with lithium metal as the
counter/reference electrode. The separator is Celgard 2400 membrane. The electrolyte used
was 1 M LiPF6 in a 50:50 w/w mixture of ethylene carbonate (EC) and dimethyl carbonate
(DMC). The total volume of electrolyte dripped in working electrode and separator in every
cell is about 0.5 mL. The cells were assembled in a high-purity argon-filled glove box (H2O
＜1 ppm, O2＜0.5 ppm, MBaun, Unilab). The galvanostatic charge/discharge measurements
were performed between 0.01 and 3.0 V at a constant current density of 0.5 C on a Land
battery tester (Wuhan, China). Cyclic voltammetry (CV) study was performed on a
Solartron-1470E Cell Test at 25 °C between 0.01 V and open circuit voltage (2.63 V) at a
sweep rate of 0.5 mV·s−1. In the evaluation of rate performance, the cell was charged and
discharged at various currents of 0.2 C, 0.5 C, 1 C, 2 C, 4 C and 0.2 C. Electrochemical
impedance spectroscopy (EIS) was performed on Autolab (PGSTAT302N) in a frequency
range of 105-0.1 Hz with potential amplitude of 5 mV.
To elaborate the aforementioned discussion for the α-Fe2O3 nanorod assemblies in
half-cell configurations, we did EIS analysis. A fresh cell has been prepared to record the EIS
data, and then subjected to five cycles of charge–discharge at the current rate of 0.2 C. After 5
cycles, the EIS measurement was performed again and the corresponding Nyquist plots are
shown in Fig. S5. Both plots contain a semicircle at the high frequency zone and a sloping
line at the low frequency region. The high frequency zone (width of the semicircle) explains
the efficiency of the charge-transfer process [J. Mater. Chem. 21, 2470(2011)]. After 5 cycles,
the cell exhibits a lower charge transfer resistance (RCT, 41 Ω) than the fresh cell (160 Ω).
This reduction in RCT is mainly due to the nature of the chemical composition of the SEI layer
formed over the α-Fe2O3 nanorod assemblies. This result of the EIS analysis is the lower
value of cell impedance after cycling. It confirms that may improve the wetting ability of the
interconnected α-Fe2O3 nanorod assemblies by the electrolyte molecules thereby providing
better electrochemical performance than during the initial cycles.
Fig. S5. Nyquist plots for the Li/α-Fe2O3 nanorod assemblies cell.
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