Inorganic Chemistry
Article
products possessing outstanding ORR catalytic activity, whose
performance is superior to that of Pt/C at the same loading in
alkaline media.37 Yin et al. successfully obtained a Co SAs/N-C
species where the stabilization of Co SAs is strictly related to
the N-doped porous carbon support.38 Two-dimensional
catalysts have been a hot field of research in recent years
because the low-dimensional design of the catalyst can increase
the catalytic efficiency.39,40 2D nanocomposites derived from
2D MOFs have shown excellent performance in the field of
catalysis.41−43 Therefore, we designed and synthesized a novel
2D Co-containing MOF with a ligand containing N atoms and
used this Co-MOF as a sacrificial template for preparing
transition-metal nanocarbon materials. The design of MOF
precursors can be used to achieve microcontrol of the
properties of nanomaterials.
Figure 1. Schematic illustration for the synthesis of Co-MOF and the
highly efficient catalysis of Co@NC derived from Co-MOF.
In this work, [Co(TPT)(fma)(H2O)2]·3H2O (TPT = 2,4,6-
tris(4-pyridyl)-1,3,5-triazine, fma = fumaric acid) was success-
fully synthesized under solvothermal conditions. The novel
Co-MOF was heat-treated under an N2 atmosphere to form
Co-carbon composites, denoted Co@NC. In the presence of
NaBH4, the prepared Co@NC has significant catalytic activity
for 4-NP and dye (RhB, MB) catalytic reduction in aqueous
solution. In addition, we conducted a series of experiments,
including the carbonization temperature for preparing the
catalyst, the effect of NaBH4 concentration, and the cycle
practicality of the catalyst, to comprehensively evaluate the
catalytic characteristics of the composite material.
4.00; N, 14.41. IR (KBr, cm−1): 426.33 (w), 882.08 (w), 1550.09 (w),
1861.06 (w), 1953.20 (w), 587.57 (m), 1151.92 (m), 1199.63 (m),
1313.16 (m), 511.88 (s), 640.22 (s), 681.35 (s), 798.17 (s), 974.22
(s), 1059.78 (s), 1374.04 (s), 1510.60 (s).
2.4. Synthesis of Co@NC. The synthesized Co-MOF was placed
in an alumina crucible that was then placed in a tube furnace for heat
treatment. As shown in Figure 1, under an N2 atmosphere, the
mixture was heated at a heating rate of 5 °C/min from room
temperature to T °C (T = 600, 700, 800) and was naturally cooled to
room temperature after being held for 2 h to obtain Co@NC-T
materials.
2.5. Reduction of 4-NP. A UV−vis spectrophotometer was used
to monitor the catalytic activity of the Co@NC catalyst. The catalytic
reduction of 4-NP was carried out in a quartz cuvette at room
temperature. First, 0.2 mL of a 2.5 mM solution of 4-NP and 2.5 mL
of deionized water were placed in the quartz cuvette, and then 0.2 mL
of a newly prepared NaBH4 solution (0.1, 0.2, and 0.3 M) was
dropped in. The solution quickly turned from light yellow to bright
yellow. Subsequently, 0.1 mL of a 1 mg/mL solution of the water-
dispersed complex where the catalyst homogeneously dispersed in
ultrapure water was dropped in. The absorbance of the solution was
measured at different times. The rate and progress of the reduction
reaction were monitored by recording UV−vis spectra at different
time intervals of the reaction system.
2.6. Reduction of RhB and MB. The catalytic reduction of RhB
and MB was also performed in a quartz cuvette, and the experimental
conditions of RhB and MB were the same as those for 4-NP. First, 10
mg of Co@NC-600 catalyst was dispersed in 25 mL of a 20 mg/L dye
solution and the mixture transferred into a cuvette. Then, 5 mL of 0.1
M NaBH4 was placed in the cuvette containing the system mixed
above, and the color of the mixed system quickly disappeared. Finally,
the progress of the reduction reaction was monitored by observing the
absorbance at the characteristic peak.
2. EXPERIMENTAL SECTION
2.1. Materials. The chemicals and solvents used in this study were
of analytical grade and were purchased from commercial sources and
used without further purification: Co(NO3)2·6H2O, 2,4,6-tris(4-
pyridyl)-1,3,5-triazine (TPT), fumaric acid (fma), 4-nitrophenol (4-
NP), sodium borohydride (NaBH4), Rhodamine B (RhB), and
Methylene blue (MB) were purchased from Energy Chemical. N,N-
Dimethylformamide (DMF) was obtained from Sigma-Aldrich.
2.2. Instrumentation and Characterization. Single-crystal data
were collected on a Bruker Smart Apex II CCD X-ray diffractometer
at room temperature. Mo Kα radiation (λ = 0.71073 Å)
monochromated with a graphite monochromator was used as the
incident light source. The SHELXTL-97 program package was used
to analyze the crystal structure, and the obtained data were corrected
for absorption with the SADABS program. The morphologies of the
material were examined ny field-emission scanning electron
microscopy (FE-SEM) and transmission electron microscopy
(TEM). When an X-ray diffractometer (Bruker) was used to study
the crystal phase, the scanning range was 5−80° and the scanning
speed was 5°/ min. A Renishaw Model 2000 confocal microscope
Raman spectrometer was used to characterize the vibration character-
istics of the sample. The magnetic properties of the sample at 300 K
were determined on a superconducting quantum interferometer
magnetometer (SQUID). X-ray photoelectron spectroscopy (XPS)
was used to study the changes in the surface element composition and
chemical state. a Jasco V-770 spectrophotometer was used to obtain
UV spectral data.
2.3. Synthesis of the Novel 2D Co-MOF. A mixture of TPT
(15.6 mg, 0.05 mmol), fma (5.8 mg, 0.05 mmol), and Co(NO3)2·
6H2O (29.1 mg, 0.1 mmol) was dissolved in a mixed solution of 3 mL
of DMF and 3 mL of deionized water. The mixture was charged into a
polytetrafluoroethylene high-pressure reactor (15 mL) and placed at
100 °C for 3 days under autogenous pressure to react (Figure 1).
After the reaction was completed, the reaction kettle was naturally
cooled to room temperature to obtain yellow-brown block crystals.
The obtained crystalline products were washed three times with the
mother liquor and dried at room temperature before use. Anal. Calcd
for C22H24N6O9Co: C, 45.92; H, 4.20; N, 14.61. Found: C, 45.72; H,
3. RESULTS AND DISCUSSION
3.1. Structure and Characterization of Co-MOF. An
analysis of single-crystal X-ray test data shows that Co-MOF
has a 2D structure and crystallizes in the monoclinic C/2c
space group. The molecular formula is [Co(TPT)(fma)-
(H2O)2]·3H2O (Co-MOF). The crystallographic parameters
of this compound are shown in Table S1. As shown in Figure
2a, the asymmetric unit of Co-MOF contains one Co atom,
two TPT ligands, two fma ligands, and two H2O molecules.
Each Co(II) adopts a six-coordinated coordination form,
which is coordinated with two oxygen atoms (O1) from two
carboxyl groups, two nitrogen atoms (N) from pyridine, and
two oxygen atoms (O2) from water (Co−O1 2.0513 Å, Co−N
2.196 Å, Co−O2 2.103 Å). The coordinated oxygen and
nitrogen atoms are derived from different ligands. These
ligands act as bridges, and the other end coordinates with other
B
Inorg. Chem. XXXX, XXX, XXX−XXX