Y. Zhu et al. / Electrochimica Acta 207 (2016) 308–312
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independently as electrolyte and also as the electrode, and to be
applied to the electro-oxidative activation of CÀÀH bonds. The
composite showed excellent electro-oxidative activity and selec-
tivity toward formation of carbonyl compounds and could easily be
recovered and reused. In addition, adjustment of the pH value of
the EmimAc/MWCNTs composite to the acid range, proved
beneficial to the electro-oxidation to the carbonyl group, with
yields for the conversion of p-methoxy toluene (p-MT) to
p-methoxybenzaldehyde (p-MBA) improving from 55-63% to 87%.
employed as the electrolyte. When the composite and the graphite
electrode (5 mm diameter) were used as the working electrode,
0.02 M LiClO4 was used as the supporting electrolyte in an aqueous
solution. The major products were detected using GC–MS (Thermo
Fisher). The yields (Y) were determined by GC (Agilent 7890A)
analysis.
The pH of the different electrolysis systems was measured using
a PHS-3C acidometer (Shanghai REX, China) at room temperature.
2.2. Preparation of EmimAc/MWCNTs
2. Experimental section
The MWCNTs were first mixed with EmimAc (the mass ratio of
EmimAc to MWCNTs was 1:1, 2:1 and 4:1), using methylene
chloride as a dispersant. The dispersion was stirred for 12 h at room
2.1. Chemicals and measurements
EmimAc was purchased from Lanzhou Institute of Chemical
Physics (Chinese Academy of Sciences), and used without further
purification. MWCNTs, (97%, 40–60 nm in diameter) were pur-
chased from Shenzhen Nanotech. Port. Co. Ltd. (China) and
vigorously stirred in 65% HNO3 solution for 4 h at 423 K. Following
treatment of the MWCNTs with nitric acid, they were filtered and
repeatedly washed with water until the aqueous filtrate tested
neutral, then dried at 353 K for 12 h before use. p-MT and
p-methoxybenzyl alcohol were purchased from Aladdin (China),
1-methoxy-4-propylbenzene was purchased from Sigma Aldrich
(Iceland), p-xylene was purchased from Sinopharm Chemical
Reagent Co. Ltd (China). All the reagents were analytical grade.
Scanning electron microscopy (SEM) images were obtained
using a Hitachi S4700 (Japan) system with an accelerating voltage
of 15 kV. Before observation, the surface of the sample material was
coated with a thin layer of gold. Transmission electron microscopy
(TEM) was obtained by using JEM-2010Ex (Japan) with an
accelerating voltage of 200 kV.
temperature using a magnetic stirrer. Then, the resulting
composite materials, referred to as EmimAc/MWCNTs, were dried
at 353 K for 12 h.
Following electrolysis when the composite was used as the
electrolyte, the composite was filtered, and the solid containing the
EmimAc/MWCNTs composite was washed with ether. The filtrate
containing the products and some desorbed EmimAc, was washed
using distilled water. The product, contained in the organic phase,
was detected by GC while the desorbed EmimAc was extracted
using ether from the aqueous phase and combined with the solid,
thereby constituting the recovered EmimAc/MWCNTs composite
(marked as Re-EmimAc/MWCNTs).
2.3. Preparation of composite electrode
One hundred (100) mg of composite material, 1 mL of ethanol,
1 mL of distilled water and 100
combined to form a slurry. Then, 150
m
L of Nafion solution (5 wt%) were
L of the slurry was added
m
Cyclic voltammetry (CV) was carried out using a CHI 660D
electrochemical workstation. A platinum sheet (1 cm  0.5 cm)
was used as the working electrode, a 2 cm  2 cm platinum sheet as
the counter electrode, and a platinum wire (0.5 mm diameter)
electrode as the quasi-reference electrode. Except when noted, the
CV measurements were performed at room temperature.
dropwise onto carbon paper (1 cm  1 cm) and dried at room
temperature for 12 h. After electrolysis, the resulting “composite
electrode” was washed with distilled water, and dried at room
temperature for reuse.
3. Results and discussion
Each controlled potential electrolysis was performed in a 10 mL
undivided electrochemical cell. The concentration of the aromatic
substrate was 0.04 M. The electrolysis potential used for experi-
ments conducted using different electrolytes was based on the
oxidation peak potential recorded using CV. All the electrolysis
experiments were performed at 323 K for 6 h while the solution
was stirred using a magnetic stirrer. When the composite was used
as the electrolyte, the 1 cm  0.5 cm platinum sheet was used as
the working electrode. For each controlled potential electrolysis,
comparison experiments involving the use of different electrolytes
for the electro-oxidative electrolysis of p-MT, 0.16 g of EmimAc,
0.04 g of MWCNTs and 0.2 g of composite were independently
The surface morphology of the nitrated MWCNTs and the
EmimAc/MWCNTs composites were characterized by SEM (Fig. 1)
and TEM (Fig. 2). After nitration, some of the ends of the MWCNTs
were opened as evidenced by Fig. 1 a, but most of the tubes were
tangled because of self-assembly and the nano-size effect [20].
After combining with the EmimAc, the MWCNTs became
untangled (Fig. 1 b, d). The dispersion of the tubes was improved
and the affinity of the ILs to the surface of the MWCNTs was
ensured after they were combined due to the interaction between
the electron deficient imidazolium cation and the
p-electron-rich
surface of the nitrated MWCNTs [21].
Fig. 1. SEM images of (a) the nitrated MWCNTs, and (b) EmimAc/MWCNTs (mass ratio = 4:1).