Preparation of a ZIF-67 Derived Thin Film Electrode via Electrophoretic Deposition for Efficient Electrocatalytic Oxidation of Vanillin

Article abstract of DOI:10.1021/acs.inorgchem.8b03281

The electrophoretic deposition method is employed to deposit uniform metal organic framework thin films. ZIF-67 particles dispersed in isopropanol move to a cathode as an electric field is applied on two conducting glass electrodes, the uniform ZIF-67 thi

Full text of DOI:10.1021/acs.inorgchem.8b03281

Article
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Preparation of a ZIF-67 Derived Thin Film Electrode via
Electrophoretic Deposition for Efficient Electrocatalytic Oxidation of
Vanillin
Haijuan Han, Xiaoxuan Yuan, Zhixin Zhang, and Jingbo Zhang*
Key Laboratory of Inorganic−Organic Hybrid Functional Material Chemistry, Ministry of Education, Tianjin Key Laboratory of
Structure and Performance for Functional Molecules, College of Chemistry, Tianjin Normal University, Tianjin 300387, China
S
* Supporting Information
ABSTRACT: The electrophoretic deposition method is
employed to deposit uniform metal organic framework thin
films. ZIF-67 particles dispersed in isopropanol move to a
cathode as an electric field is applied on two conducting glass
electrodes, the uniform ZIF-67 thin film can be formed on the
conducting glass substrate. As the deposition time is fixed at 1
min, the prepared film thickness can be adjusted from 1.0 to
7.0 μm by applying different electric fields from 20 to 60 V·
cm−1. The deposited ZIF-67 thin film is further converted into
porous Co9S8 thin films by the vulcanization with S powder.
The porous thin films vulcanized at different temperatures are
characterized by the measurements of scanning electron
microscope, X-ray photoelectron spectroscopy, X-ray powder
diffraction, high resolution transmission electron microscopy, and Fourier transform infrared spectra. The prepared porous
Co9S8 thin films are used as the thin film electrode to catalyze the degradation of vanillin. The Co9S8 thin film vulcanized at 500
°C shows better catalytic performance than the bare glassy carbon electrode and the electrodes vulcanized at other
temperatures. The electrocatalytic degradation enhancement mechanism is analyzed by the measurements of Tafel curves and
electrochemical impedance spectroscopies. It can be developed as a feasible method for the electrocatalytic detection of vanillin.
films have been explored, such as direct solvothermal,12 layer
1. INTRODUCTION
by layer or liquid phase epitaxy,13 electrochemical deposition,14
Metal organic frameworks (MOFs), as a new type of periodic
porous materials formed through self-assembly of metal ions
and organic ligands, have been applied in some fields such as
microwave-induced thermal deposition, electrospinning,15 and
hot-pressing.16 Although each method has its advantages, no
gas storage,1 separation,2 catalysis,3 chemical sensing,4 and
method has been proved to be universally applicable.
proton conduction.5 In recent years, copper or cobalt-based
MOFs were used excellent precursors or sacrificial templates to
construct porous functional materials for electrochemical
Therefore, it is very challenging to find a quick and ease
preparation method of MOF thin films on the unmodified low
cost substrate.
catalysis.6 As a subfamily of MOFs, zeolitic imidazolate
Electrophoretic deposition (EPD) has attracted wide
attention due to its lower cost, short fabrication time,
frameworks (ZIFs) created by bridging N-containing imida-
effectively controlled thickness and uniformity of the obtained
zolate linkers and zinc or cobalt ions within tetrahedral
frameworks have attracted great attention. They have been
utilized for selective syntheses of porous carbon, metal oxides,
films, and ease of scaling up. In the EPD process, the charged
particles move to the oppositely charged electrode and deposit
on the base surface under an applied electric field. It is an
and metal sulfide nanocomposites that have promising
applications in catalytic aspects.7
economical and universal processing technique that has already
For some applications such as chemical sensing,8 batteries,9
been applied to deposit coatings and films such as phosphor
for display.17
and supercapacitors,10 a MOF film is a requirement; therefore,
studying the preparation of MOF thin films has become a hot
research topic. Fabricating MOF thin films on the desired
substrate is a crucial challenge. In addition, the MOF thin films
grown on solid substrates have several advantages over the
powder samples. As chemical catalysis, they are easily
separated from the liquid medium and the number of catalytic
active sites at each MOF thin film is approximately constant.11
Recently, some interesting methods to fabricate MOF thin
Vanillin (4-hydroxy-3-methoxybenzaldehyde) is derived
from the beans or pods of tropical vanilla orchids and used
as an indispensable smell additive in a wide range of products
such as beverages, milk powders, confectionery, and
cosmetics.18 In addition, vanillin has been used to treat a
Received: November 23, 2018
© XXXX American Chemical Society
A
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taken out and the film color was changed from purple to grayish black.
The thin films vulcanized at 400, 450, 500, 550, and 575 °C were
named as S-400, S-450, S-500, S-550, and S-575, respectively.
2.3. Characterization of Materials. The morphologies of the
thin films were observed using a scanning electron microscope (SEM,
FEI Nova Nano SEM 230). The elemental compositions were
analyzed by energy dispersive spectroscopy (EDS) attached to the
SEM. The crystalline structure of the samples was characterized by an
X-ray powder diffractometer (XRD, RigakuD/max-2500, Cu Kα).
The microstructures of samples were determined by high resolution
transmission electron microscopy (HRTEM, Tecnai G2 F20). The
chemical composition and the valence states of the samples were
analyzed on an X-ray photoelectron spectrometer (XPS, AXIS
ULTRA Al Kα). Fourier transform infrared spectra (FTIR) were
measured on a FTIR spectrophotometer (Nicolet 360) using KBr as
pellets. The absorption spectra of ZIF-67 thin films were measured
using a spectrophotometer (UV-2600, SHIMADZU) at room
temperature.
2.4. Electrochemical Measurements. All electrochemical
measurements were performed on a potentiostat (Solartron 1287/
1260) with the prepared thin film electrode or bare glassy carbon
electrode (GCE, diameter 3 mm) as the working electrode, Pt wire as
the counter electrode, and saturated calomel electrode (SCE) as the
reference electrode. Cyclic voltammetry (CV) was performed in 30
mM vanillin electrolyte with 0.05 M phosphate buffer solution (PBS)
(pH = 7.0) at a scan rate of 50 mV·s−1. Before measurement, the
electrolyte was purged with Ar for 20 min to remove oxygen. The area
of the working electrode was 0.7 cm2. Electrochemical impedance
spectroscopy (EIS) and Tafel polarization curves were measured on
the symmetrical cells fabricated by two identical electrodes. The
frequency range of EIS is from 105 to 10−1 Hz. The scan rate for Tafel
measurements is 10 mV·s−1.
variety of diseases, including stress, digestive problems, anxiety,
stomach pain, and vomiting.19 Although vanillin is widely used
in our lives, too much ingestion of vanillin can have serious
adverse effects on our bodies and affect the function of the liver
and kidney.20 Therefore, the simple and low-cost determi-
nation of vanillin content is of great significance to people’s
health. Several methods to detect vanillin have been reported
such as ultraviolet−visible spectrum,21 gas chromatography,22
and colorimetric23 and electrochemical techniques.18 Among
these techniques, the electrochemical technique is simple, low
cost, and rapid for the determination of vanillin.19 Some
chemically modified glassy carbon electrodes (GCE) have
been employed. However, their performance was still not
enough good.24 Thus, it is important to search for a rapid and
efficient detection way of vanillin with new materials such as
nanomaterials.
Here, we deposited ZIF-67 powders on conducting glass
using the EPD method to prepare large-scale, uniform, and
continuous thin films and the film thickness can be adjusted by
applying different electric fields. Especially, isopropanol is used
as a dispersant with the advantages of low pollution and large-
scale production compared to the previously reported toluene
and dichloromethane dispersants.25,26 Moreover, the used the
EPD process has the advantages of short time and low electric
field. For example, it only takes 1 min to complete the film
preparation under 20 V·cm−1. The as-prepared films are then
used as the sacrificial templates and react with sulfur powders
under nitrogen to form porous cobalt sulfide thin film, which
could subsequently act as electrode for electrocatalytic
oxidation of vanillin. It provided a viable way to detect vanillin
through a thin film electrode.
3. RESULTS AND DISCUSSION
3.1. Characterization of the Deposited ZIF-67 Thin
Films. As shown in Figure 1a, the synthesized ZIF-67 particles
2. EXPERIMENTAL SECTION
2.1. Electrophoretic Deposition of ZIF-67 Thin Films. All the
chemicals were directly used after purchase without further
purification. ZIF-67 particles powder was synthesized in an ambient
condition according to the reported method.27 Solution A was
prepared by dissolving 2.9 g Co(NO3)2·6H2O in 100 mL methanol.
Solution B was formed by dissolving 6.5 g 2-methylimidazole in 100
mL methanol. In a typical synthesis process of ZIF-67, the solution B
was added to the solution A under vigorous stirring at room
temperature, and the stirring was kept for 1 h. After the resultant
mixed solution was aged at room temperature for 24 h, the purple
precipitate was collected by the centrifugation, washed three times
with fresh methanol, and then dried at 80 °C in vacuum for 12 h.
In order to prepare the ZIF-67 suspension for EPD, 100 mg ZIF-67
powder and 4 mL isopropanol were ground in a ball mill for 4 h to
obtain a homogeneous blend without any small clumps. ZIF-67
suspension of 1 mL was diluted with isopropanol to 10 mL and
sonicated for 15 min. For the deposition of ZIF-67 thin film, the as-
prepared ZIF-67 suspension was poured into a specially designed
vessel. Then, two FTO (10 Ω·sq−1, Nippon Sheet Glass Co., Ltd.,
Japan) coated glass substrates were immersed vertically into the
vessel, with one serving as an anode and another as a cathode. The
distance between two electrodes was fixed at 1 cm. In the EPD
process, various constant electric fields ranging from 20 to 60 V·cm−1
were applied using a DC power supply. When a stable electric field is
applied, the positively charged ZIF-67 nanoparticles begin to travel
toward the cathode. After 1 min deposition, the FTO based cathode
was taken out and dried naturally.
Figure 1. SEM images of as-prepared powders (a), as-ground
powders (b), and EPD thin film (c) of ZIF-67.
exhibit a rhombic dodecahedron metal framework structure.
SEM image of the ZIF-67 powder after being ground in the
ball mill was shown in Figure 1b, and the morphology of the
thin film formed by electrophoresis of ZIF-67 particles at an
applied electric field of 20 V·cm−1 was shown in Figure 1c. It
was found that the particles after being ground and on the
deposited thin film did not retain the complete rhombic
dodecahedron structure of the original ZIF-67 particles. After
being ground in the ball mill, the surface of the particles is
2.2. Vulcanization of ZIF-67 Thin Films. A combustion boat
containing the as-prepared ZIF-67 thin film and 400 mg S powders
was placed in a tube furnace. Then, the furnace was heated to a target
temperature at a rate of 5 °C·min−1 and maintained at the target
temperatures for 2 h in N2 atmosphere. After the furnace was
completely cooled to room temperature, the combustion boat was
B
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worn and defective. More cobalt ions are exposed on the
surface due to the lack of ligand links, resulting in a partial
positive charge on the surface of the ZIF-67 particle, which is
very beneficial for electrophoresis. During the EPD process,
the particles with the positive electrical charge were driven
toward the negatively charged electrode. Furthermore, XRD
patterns of the thin films (Figure 2) were measured to verify
Figure 2. XRD patterns of ZIF-67 thin film, the standard ZIF-67, and
powders.
Figure 3. SEM cross sectional images of the thin films deposited
under different electric fields of EPD: (a) 20, (b) 30, (c) 40, (d) 50,
and (e) 60 V·cm−1.
the crystalline structural integrity of ZIF-67 deposited on the
FTO electrode. The crystalline structure of the deposited thin
films is similar to that of the powders, which demonstrates that
the crystalline structure is not damaged during the EPD
process. In order to better understand the effect of applied
electric field during electrophoresis on the thickness and
surface coverage of the deposited films, a series of ZIF-67 thin
films were prepared under different electric fields from 20 to 60
V·cm−1. The corresponding SEM cross section images of
different ZIF-67 thin films were shown in Figure 3. It is clear
that the film thickness can be controlled by the applied electric
field as the deposition time is fixed as 1 min. Upon changing
the electric field from 20 to 60 V·cm−1, the film thickness could
increase from 1.2 to 7.0 μm. In addition, the continuous and
dense ZIF-67 thin films could be obtained on the FTO
substrate under different applied electric fields, when the films
were deposited within 1 min (Figure 1S). Figure 4 shows UV−
vis absorption spectra of ZIF-67 thin films grown at different
electric fields of EPD and ZIF-67 powder in solution. The
absorption peak position of different thin films is almost same,
and it is also same as that of ZIF-67 powder in solution. It can
be obviously seen that the absorption value of the ZIF-67 thin
films increases as the deposition electric field was increased.
However, the absorbance is not linearly increased with the film
thickness (Figure 2S), indicating that the density of the
deposited thin film is increased with the film thickness.
3.2. Characterization of the Vulcanized ZIF-67 Thin
Films. Due to the flexibility of electrophoretic depositions,
other MOF materials can also be deposited by this method to
form the thin film electrode. In addition, the prepared thin film
can be calcined to form some new film electrode materials,
which have been applied in various aspects.28 Here, the
deposited ZIF-67 thin films were vulcanized with S powders to
further form porous Co9S8 thin films. The XRD patterns of the
ZIF-67 thin films vulcanized at different temperatures were
shown in Figure 5. The diffraction peaks marked with rhombus
are indexed to Co9S8 phase (JCPDS No. 02-1459) except one
Figure 4. UV−vis absorption spectra of ZIF-67 thin films deposited
under different electric fields and ZIF-67 in solution.
peak marked with heart belonging to Co2C phase (JCPDS No.
65-1457). Obviously, ZIF-67 is not fully converted into single
Co9S8 phase. The complicated phases mainly consist of Co9S8
phase with a small amount of Co2C phase. However, almost all
the peaks corresponding to ZIF-67 disappear indicating the
rapid conversion from ZIF-67 thin film to Co9S8 thin film by
the vulcanization process. Using the Scherrer equation, the
average crystal size of the Co9S8 nanoparticles formed at 500
°C is estimated to be about 53 nm based on the full width at
half-maximum (0.153°) of the (311) peak.
SEM images of the thin films vulcanized at different
temperatures were shown in Figure 6. It is obvious that the
morphologies of the Co9S8 thin film depend on the
vulcanization temperature. After the controlled reaction with
S powders under N2, the carbon skeleton shrinks sharply with
the loss of other elements in ZIF structure, and some cracks
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indicates that the vulcanization reaction has occurred inside
the film. The N2 adsorption isotherm of S-500 thin film at 77 K
showed a Brunauer−Emmett−Teller (BET) surface area of
102.1 m2·g−1 (Figure S5), which can provide a large interface
to fully contact the electrolyte to promote the electrode
reaction. The pore size distribution calculated using the
Barrett−Joyner−Halenda (BJH) method showed the meso-
porosity of the material with a relatively wide pore-size
distribution in the range of 2−20 nm (inset in Figure S5).
In HRTEM image of the S-500 sample (Figure 7), it can be
clearly seen that the nanoparticles are highly crystalline with
Figure 5. XRD patterns of the Co9S8 thin films vulcanized at different
temperatures and FTO.
Figure 7. HRTEM of particles scraped from the S-500 thin film.
two sets of continuous lattice fringes with the d-spacing of
0.300 and 0.248 nm, which are correlated with the (311) and
(400) crystal planes of Co9S8 phase, respectively.
The thin films of S-500 and ZIF-67 were further
characterized using FT-IR spectroscopy (Figure 8). ZIF-67
exhibits two intense bands at 1582 and 1309 cm−1, which
could be attributed to the CN aromatic stretching and C−H
vibration. The peak at 426 cm−1 is attributed to the Co−N
Figure 6. SEM images (low and high magnification) of the thin films
of S-400 (a), S-450 (b), S-500 (c), S-550 (d), and S-575 (e).
appear between adjacent Co9S8 structures. At 400 and 450 °C,
the ZIF-67 thin films are not still completely corroded by the
sulfur, maintaining the edges and corners of the carbon
skeletons. However, after the vulcanization at 500 °C, the
particles became round. It is worth noting that the film shows
more porous structure composed of many nanoparticles, which
facilitates easy penetration of the electrolyte into the thin film.
However, at 550 and 575 °C, the high temperature
vulcanization leads to the fusion and aggregation of the
crystals to some extent, and the pores among the nanoparticles
are significantly reduced and agglomeration occurs. In
addition, the existence of Co, S, and C was confirmed in the
composite thin film as shown in Figure S3. The cross-sectional
images and corresponding element mapping of the S-500 thin
film (Figure.S4) further demonstrate the uniform distribution
of the Co and S elements throughout the cross section, which
Figure 8. FTIR spectra of the thin film of S-500 and ZIF-67.
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stretching. After the vulcanization process at 500 °C, the
strong peak at 452 cm−1 is contributed to the Co−S stretching.
The sulfur atom coordinates with the cobalt atom to form the
Co−S bond, accompanied by the breaking of the Co−N bond,
and as a result, ZIF-67 is transformed into Co9S8.29,30
To determine the chemical states on the S-500 thin film,
XPS spectra were measured and shown in Figure 9. It clearly
suggests the presence of Co, C, S, N, O, and Sn in the as-
obtained sample. Sn and O are from FTO, and C and N from
the residual ZIF-67 skeleton. The high resolution XPS
spectrum of Co 2p was shown in Figure 9b, where the peaks
at 778.7, 781.7, and 786.6 eV can be specified as Co 2p3/2. The
fitting of Co 2p1/2 peak shows three peaks with binding
energies centered at 793.8, 797.6, and 803.2 eV, respectively.
The peaks at 786.6 and 803.2 eV are the satellite peaks of 2p3/2
and 2p1/2, respectively. The doublets appearing at 778.7 and
793.8 eV can be assigned to Co3+ 2p3/2 and 2p1/2 states, while
the doublets appearing at 781.7 and 797.6 eV belong to Co2+
2p3/2 and 2p1/2. In the S 2p XPS spectrum (Figure 9c), the
curve was fitted to show four peaks. They can be attributed to
S in Co9S8 (161.5 and 162.5 eV), C−S−C (163.8 eV), and
SO42−(168.6 eV), which is in good agreement with the
previous report.31 The presence of SO4 may be related to
2−
partial oxidation of sulfur species by air on the surface of
material.31
3.3. Electrocatalytic Performance of the Co9S8 Thin
Films. Based on the above discussions, the porous Co9S8 thin
film on FTO can be prepared from the ZIF-67 thin film. To
explore potential applications of the porous Co9S8 thin film, we
used the Co9S8 thin film electrodes to catalyze the oxidation of
vanillin. The electrocatalytic activity of the Co9S8 thin films
were determined by cyclic voltammetry (CV) tests. And CV
curves of the Co9S8 thin film electrodes and bare GCE (Figure
10a) were recorded, respectively. There is an apparent
Figure 10. CV curves (a) and oxidization peak current density (b) of
the thin films vulcanized at different temperatures and bare GCE.
oxidation peak of vanillin at 0.56 V vs SCE on bare GCE. In
addition, for the Co9S8 thin film electrodes prepared by
vulcanization at different temperatures, the apparent oxidation
peak of vanillin is located at around 0.60 V. In Figure 10b, it is
clearly shown that the thin film electrode of S-500 has the
largest peak current density compared to other electrodes.
These results indicate that the thin film electrode of S-500
Figure 9. XPS spectra of the S-500 thin film: (a) survey spectrum, (b)
Co 2p, (c) S 2p.
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show better catalytic activity to oxidize vanillin than the bare
GCE and others.30,32
The Tafel polarization curves of these samples were shown
in Figure 11a, and the corresponding key parameters were
film electrode, EIS were performed by preparing typical
sandwich structure of Co9S8 electrode/electrolyte/Co9S8
electrode. The EIS of the Co9S8 thin film electrodes and the
related equivalent circuit diagram were shown in Figure 11b.
The interface properties can be evaluated by the resistance of
the interface transfer electron (Rct). By fitting the EIS with the
equivalent circuit, Rct values were obtained and summarized in
Table 1. The Rct values of the Co9S8 electrodes were in order
of S-500 < S-550 < S-450 < S-575 < S-400. The smaller
semicircle of the Co9S8 electrodes obtained at different
temperatures corresponds to the smaller Rct, and the lower
Rct value of the electrodes indicates that the oxidation reaction
at the electrode/electrolyte interface is faster. The results
showed that S-500 has better electrocatalytic activity for
vanillin than other electrodes. According to the various
characterization measurements on the samples, we thought
the best electrocatalytic activity of S-500 is attributed to its
porous structure can be mostly survived and organic ligands of
ZIF-67 can be almost removed after vulcanization under the
optimized vulcanization temperature of 500 °C.
4. CONCLUSIONS
In summary, uniform ZIF-67 thin films were prepared on FTO
substrate by the electrophoretic deposition method. The film
thickness can be adjusted by adjusting the applied electric field
as the deposition time was fixed at 1 min. The deposited ZIF-
67 thin films were further vulcanized to form the Co9S8 thin
films. The vulcanization temperature can affect the composi-
tion and porous structure. The Co9S8 thin film show a satisfied
catalytic activity to degrade vanillin, and the thin film electrode
prepared by vulcanization at 550 °C has the best catalytic
performance. It provides a viable method for the electro-
catalytic detection of vanillin. The electrophoretic deposition
method is very promising in the film formation of MOF
materials and has better industrial application prospects.
Figure 11. Tafel curves (a) and EIS (b) of the thin films vulcanized at
different temperatures obtained by using symmetrical cells with two
identical electrodes in 30 mM vanillin electrolyte.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b03281.
Table 1. Parameters Derived from Nyquist Plots of EIS and
Tafel Polarization Curves
SEM morphologies of ZIF-67 thin films deposited under
different electric fields, relationship of the absorbance
and the thickness of ZIF-67 thin films, the element
mapping images, and N2 sorption isotherms of the S-500
thin film (PDF)
electrode
Rct (Ω)
J0 (mA·cm−2
)
S-400
S-450
S-500
S-550
S-575
3659.0
739.4
116.5
241.1
1347.0
0.0466
0.1824
0.8586
0.4421
0.0910
AUTHOR INFORMATION
Corresponding Author
*Email: hxxyzjb@mail.tjnu.edu.cn (J.Z.).
■
elaborated in Table 1. The exchange current density (J0) is the
extrapolated intercepts of the anodic and cathodic branches of
the corresponding Tafel curves and the higher values of J0
indicate the better catalytic activity.33 As can be seen from
Table 1, the thin film electrode of S-500 showed the highest J0
among all samples, and the tendency of the J0 totally agrees
with the tendency of the peak current density observed in
Figure 10b.
The interfacial properties of the electrode and the electrolyte
affect the catalytic activity of the electrode toward vanillin. In
order to further investigate the charge transfer process on the
interface between the electrolyte of vanillin and the Co9S8 thin
ORCID
Jingbo Zhang: 0000-0002-6672-2650
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the National Nature
Science Foundation of China (Grant No. 21273160), the
Nature Science Foundation of Tianjin (Grant No.
14JCYBJC18000), and the Program for Innovative Research
Team in University of Tianjin (TD13-5074).
F
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Foods by Multivariate Calibration and Artificial Neural Networks.
Food Chem. 2005, 89, 465−473.
REFERENCES
■
(1) Furukawa, H.; Ko, N.; Go, Y. B.; Aratani, N.; Choi, S. B.; Choi,
E.; Yazaydin, A. O.; Snurr, R. Q.; O'Keeffe, M.; Kim, J.; Yaghi, O. M.
Ultrahigh Porosity in Metal-Organic Frameworks. Science 2010, 329,
424−428.
(21) Ainscough, E. W.; Brodie, A. M. The Determination of Vanillin
in Vanilla extract: An Analytical Chemistry Experiment. J. Chem. Educ.
1990, 67, 1070−1072.
́
(22) Lopez, R.; Aznar, M.; Cacho, J.; Ferreira, V. Determination of
(2) Li, J. R.; Sculley, J.; Zhou, H. C. Metal-Organic Frameworks for
Separations. Chem. Rev. 2012, 112, 869−932.
Minor and Trace Volatile Compounds in Wine by Solid-Phase
Extraction and Gas Chromatography with Mass Spectrometric
Detection. J. Chromatogr. A 2002, 966, 167−177.
(3) Ma, L. Q.; Abney, C.; Lin, W. B. Enantioselective Catalysis with
Homochiral Metal-Organic Frameworks. Chem. Soc. Rev. 2009, 38,
1248−1256.
(23) Peng, H.; Wang, S.; Zhang, Z.; Xiong, H.; Li, J.; Chen, L.; Li, Y.
Molecularly Imprinted Photonic Hydrogels as Colorimetric Sensors
for Rapid and Label-free Detection of Vanillin. J. Agric. Food Chem.
2012, 60, 1921−1928.
(4) Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van Duyne,
R. P.; Hupp, J. T. Metal-Organic Framework Materials as Chemical
Sensors. Chem. Rev. 2012, 112, 1105−1125.
(24) Bettazzi, F.; Palchetti, I.; Sisalli, S.; Mascini, M. A Disposable
Electrochemical Sensor for Vanillin Detection. Anal. Chim. Acta 2006,
555, 134−138.
(5) Taylor, J. M.; Dawson, K. W.; Shimizu, G. K. A Water-Stable
Metal-Organic Framework with Highly Acidic Pores for Proton-
Conducting Applications. J. Am. Chem. Soc. 2013, 135, 1193−1196.
(6) Mao, J.; Yang, L.; Yu, P.; Wei, X. W.; Mao, L. Q. Electrocatalytic
four-electron reduction of oxygen with Copper (II)-based Metal-
Organic Frameworks. Electrochem. Commun. 2012, 19, 29−31.
(7) Hu, H.; Han, L.; Yu, M. Z.; Wang, Z. Y.; Lou, X. W. Metal-
Organic-Framework-Engaged Formation of Co Nanoparticle-Embed-
ded carbon@Co9S8 double-shelled nanocages for efficient oxygen
reduction. Energy Environ. Sci. 2016, 9, 107−111.
(25) Feng, F.; Yang, X.; Gao, S. Y.; Shi, J. L.; Cao, R. Facile and
Rapid Growth of Nanostructured Ln-BTC Metal-Organic Framework
Films by Electrophoretic Deposition for Explosives Sensing in Gas
and Cr3+ Detection in Solution. Langmuir 2017, 33, 14238−14243.
(26) Hod, I.; Bury, W.; Karlin, D. M.; Deria, P.; Kung, C. W.; Katz,
M. J.; So, M.; Klahr, B.; Jin, D.; Chung, N. Y. W.; Odom, T. W.;
Farha, O. K.; Hupp, J. T. Directed Growth of Electroactive Metal-
Organic Framework Thin Films Using Electrophoretic Deposition.
Adv. Mater. 2014, 26, 6295−6300.
(8) Gao, Y. X.; Yu, G.; Liu, K.; Wang, B. Luminescent Mixed-Crystal
Ln-MOF Thin Film for the Recognition and Detection of
Pharmaceuticals. Sens. Actuators, B 2018, 257, 931−935.
(9) Ferey, G.; Millange, F.; Morcrette, M.; Serre, C.; Doublet, M. L.;
Greneche, J. M.; Tarascon, J. M. Mixed-valence Li/Fe-based Metal-
Organic Frameworks with both Reversible Redox and Sorption
Properties. Angew. Chem., Int. Ed. 2007, 46, 3259−3263.
(10) Diaz, R.; Orcajo, M. G.; Botas, J. A.; Calleja, G.; Palma, J. Co8-
MOF-5 as Electrode for Supercapacitors. Mater. Lett. 2012, 68, 126−
128.
(27) Jiang, Z.; Li, Z. P.; Qin, Z. H.; Sun, H. Y.; Jiao, X. L.; Chen, D.
R. LDH Nanocages Synthesized with MOF Templates and Their
High Performance as Supercapacitors. Nanoscale 2013, 5, 11770−
11775.
(28) Xu, W. J.; Sun, Y. X.; Ding, B.; Zhang, J. B. Zeolitic-Imidazolate
Frameworks Derived Pt-free Counter Electrodes for High-Perform-
ance Quantum Dot-Sensitized Solar Cells. R. Soc. Open Sci. 2018, 5,
180335.
(29) Jin, M.; Lu, S. Y.; Ma, L.; Gan, M. Y.; Lei, Y.; Zhang, X. L.; Fu,
G.; Yang, P. S.; Yan, M. F. Different Distribution of In-situ Thin
Carbon Layer in Hollow Cobalt Sulfide Nanocages and Their
Application for Supercapacitors. J. Power Sources 2017, 341, 294−301.
(30) Sivakumar, M.; Sakthivel, M.; Chen, S. M. Simple Synthesis of
Cobalt Sulfide Nanorods for Efficient Electrocatalytic Oxidation of
Vanillin in Food Samples. J. Colloid Interface Sci. 2017, 490, 719−726.
(31) Feng, L. L.; Fan, M. H.; Wu, Y. Y.; Liu, Y. P.; Li, G. D.; Chen,
H.; Chen, W.; Wang, D. J.; Zou, X. X. Metallic Co9S8 Nanosheets
Grown on Carbon Cloth as Efficient Binder-Free Electrocatalysts for
the Hydrogen Evolution Reaction in Neutral Media. J. Mater. Chem. A
2016, 4, 6860−6867.
(32) Hardcastle, J. L.; Paterson, C. J.; Compton, R. G. Biphasic
Sonoelectroanalysis: Simultaneous Extraction From, and Determi-
nation of Vanillin in Food Flavoring. Electroanalysis 2001, 13, 899−
905.
(33) Niu, Y. D.; Qian, X.; Zhang, J.; Wu, W. M.; Liu, H. Y.; Xu, C.;
Hou, L. X. Stepwise Synthesis of CoS2-C@ CoS2 Yolk-shell
Nanocages with much Enhanced Electrocatalytic Performances both
in Solar Cells and Hydrogen Evolution Reactions. J. Mater. Chem. A
2018, 6, 12056−12065.
(11) Shekhah, O.; Liu, J.; Fischer, R. A.; Woll, Ch. MOF thin films:
Existing and Future Applications. Chem. Soc. Rev. 2011, 40, 1081−
1106.
̈
(12) Hermes, S.; Schroder, F.; Chelmowski, R.; Woll, C.; Fischer, R.
A. Selective Nucleation and Growth of Metal-Organic Open
Framework Thin Films on Patterned COOH/CF3-Terminated Self-
Assembled Monolayers on Au(111). J. Am. Chem. Soc. 2005, 127,
13744−13745.
(13) Shekhah, O.; Wang, H.; Kowarik, S.; Schreiber, F.; Paulus, M.;
Tolan, M.; Sternemann, C.; Evers, F.; Zacher, D.; Fischer, R. A.; Woll,
C. Step-by-Step Route for the Synthesis of Metal-Organic Frame-
works. J. Am. Chem. Soc. 2007, 129, 15118−15119.
(14) Yoo, Y.; Jeong, H. K. Rapid fabrication of Metal Organic
Framework Thin Films using Microwave-Induced Thermal Deposi-
tion. Chem. Commun. 2008, 0, 2441−2443.
(15) Wu, Y.; Li, F.; Liu, H.; Zhu, W.; Teng, M.; Jiang, Y.; Li, W.; Xu,
D.; He, D.; Hannam, P.; Li, G. Electrospun Fibrous Mats as Skeletons
to Produce Free-Standing MOF Membranes. J. Mater. Chem. 2012,
22, 16971−16978.
(16) Chen, Y.; Li, S.; Pei, X.; Zhou, J.; Feng, X.; Zhang, S.; Cheng,
Y.; Li, H.; Han, R.; Wang, B. A Solvent-Free Hot-Pressing Method for
Preparing Metal-Organic-Framework Coatings. Angew. Chem., Int. Ed.
2016, 55, 3419−3423.
̈
(17) Vander Biest, O. O.; Vandeperre, L. J. Electrophoretic
Deposition of Materials. Annu. Rev. Mater. Sci. 1999, 29, 327−352.
(18) Veeramani, V.; Madhu, R.; Chen, S. M.; Veerakumar, P.; Syu, J.
J.; Liu, S. B. Cajeput Tree Bark Derived Activated Carbon for the
Practical Electrochemical Detection of Vanillin. New J. Chem. 2015,
39, 9109−9115.
(19) Deng, P.; Xu, Z.; Zeng, R.; Ding, C. Electrochemical Behavior
and Voltammetric Determination of Vanillin Based on an Acetylene
Black Paste Electrode Modified with Graphene-Polyvinylpyrrolidone
Composite Film. Food Chem. 2015, 180, 156−163.
(20) Ni, Y.; Zhang, G.; Kokot, S. Simultaneous Spectrophotometric
Determination of Maltol, Ethyl Maltol, Vanillin and Ethyl Vanillin in
G
DOI: 10.1021/acs.inorgchem.8b03281
Inorg. Chem. XXXX, XXX, XXX−XXX