2
Z. Liu et al. / Journal of Molecular Structure 1221 (2020) 128744
furfural of 100% with only 0.75mol% loaded with 40 ꢀC in half an
hour. This heterogeneous catalyst also showed up to six times
recycle without significant catalytic activity decreased.
2.4.4. Universal applicability tests
To determined the universal applicability of catalyst 2, a series of
parallel experiment was designed. Generally the homolog 5-
hydroxymethylfurfural and other heterocyclic aldehyde pyr-
idinaldehyde and thiophenecarboxaldehyde was used to replace
furfural as reaction substrate. Moreover, the conversion efficiency
of benzaldehyde and its homologues was also determined. Finally,
we also tested the applicability of others active methylene
substance.
2. Experimental section
2.1. Materials
All the chemicals were obtained from commercial and without
further purification. Cobaltous nitrate(Co(NO3)2, 99.9%), 5-
aminoisophthalic acid(AR), 4-pyridine formaldehyde(AR), 2-
acetylpyridine(AR), 25% ammonia, potassium hydroxide(KOH,AR),
4-imidazole formaldehyde(AR), furfural(AR), malononitrile(AR)
and their homologous. Methanol(AR), Ethanol(AR), N,N-
Dimethylaniline(DMA), N,N-Dimethylformamide(DMF), ethyl ace-
tate, toluene and Tetrahydrofuran(THF) were purchased from
Hengshan Chemistry Co., Ltd.The Pyridine ligand pytpy was syn-
thesized based on literature reported [27].
2.5. Characterization
Powder X-ray diffraction (PXRD) measurements were achieved
by using Rigaku Ultimate IV with Cu-K
The crystal structure of [Co(pytpy)(AIP)]n was purchased by Bruker
SMART APEX CCD instrument with using Mo-K radiation
¼ 0.71073 A) and solved by SHELEX and Olex2. The element
a
radiation (
l
¼ 0.15405 nm).
a
(l
analysis was purchased by vario EL CUBE from elementary. The FT-
IR was measured by Nicolet iS50 from Thermofisher Scientific. The
production of Knoevenagel reaction was determined by GC method
of FID detector. (GC, Agilent, GC6890 N, column: HP-5,
30 m ꢁ 0.25 mm ꢁ 0.25 mm, hydrogen flame ion detector). N2
adsorption was determined by ASAP2460 from the American
micromeritics company. The SEM was determined by Shimadzu SS-
550 from Shimadzu company. The TEM was determined by Tecnai
G2 F20 from FEI company. The TG-DSC was determined by TA from
Naichi company. The XPS was determined by Thermo ESCALAB
250XI.
2.2. Synthesis of [Co(pytpy)(AIP)·H2O]n (1)
Generally pytpy(31 mg, 0.1 mmol), AIP(18.1 mg, 0.1 mmol),
Co(NO3)2$6H2O(29.1 mg, 0.1 mmol), 8 ml H2O and 4 ml DMF was
taken in a 20 ml Teflon-lined autoclave and ultrasonic dispersed for
several minutes, and then 20ul of concentrated nitric acid was
added to the mixture and heated at 120ꢀ for 3 days. After cooling
down to room temperature, the resulting product contained red-
colored blocky crystals. The red crystals were filtered and washed
with DMF and water for three times, and then dried at 60 ꢀC. (The
yield was 54.8% based on Co)
3. Results and discussion
The crystal data and structure refinement for [Co(pytpy)(AIP)$
H2O]n was showed in Table S1. [Co(pytpy)(AIP)$H2O]n is crystallized
in C2/c space group. Fig. S1 shows the 3D crystal structure of
[Co(pytpy)(AIP)$H2O]n. The coordination center Co(II) is coordi-
nated with four O from three AIP ligands and two N from two pytpy
ligands and forms a distorted octahedral configuration. As Fig. S1a
shows, one of the carboxyl group from AIP ligands formed double
tooth coordination mode while other formed single tooth coordi-
nation mode and bridging two Co(II). As Fig. S1b shows, two pyri-
dine nitrogen from pytpy ligand participate in coordination. Then
the AIP and pytpy liagnd forms two mutually perpendicular
planes(Figs. S1c and d). That two planes stack into 3D structure
through further bridging(Figs. S1e and f).
Thanks to the large number of amino groups in 1, imidazole
group can modified into the Co MOFs by schiff base post-
modification. As Fig. 1 shows, the imidazole group is introduced
into 1 by C]N, then a large conjugate system is formed which can
produce more electronic during Knoevenagel Condensation Reac-
tion. Fig. 2 shows the XRD patterns comparison of simulated 1, 1
and 2. The simulation is from “Mercury 1.4.1”. The characteristic
peak almost have no change at all, that is to say, the skeleton
structure of 1 has no change in the schiff base post-modification
reaction. The C, H, N elements analysis result(showed in Table S2)
in Experimental section also prove the success of post-
modification. The N element content rise by 3.43% after post-
modification, which attributed to the successful introduction of
imidazole groups. Moreover, the macroscopic color of 1 also has
significant changes after post-modification showed in Fig. S2.
The comparison of TG-DSC analysis data was showed in Fig. S3.
About 10 mg sample was putted into Thermal Analysis System
which N2 flows rate was 15 ml/min. The test temperature risen
from room temperature to 800 ꢀC at a scan rate of 10 ꢀC/min. The TG
results of 1 and 2 are analogous. The thermal stability do not change
significantly after PSM. Both MOF-based materials is relatively
2.3. Post-synthetic modification of [Co(pytpy)(AIP)·H2O]n (2)
100 mg Co-MOFs and 100 mg 4-imidazole formaldehyde were
added into a 250 ml round-bottom flask. And then 100 ml ethanol
was added to formed a suspension solution and refluxed for 6 h.
The purple product was collected by filtering and washed with
ethanol for three times before drying at 60 ꢀC.
2.4. Knoevenagel reaction catalytic decontamination
2.4.1. Catalytic conditions
The Knoevenagel reaction was carried out into a 10 ml round-
bottom flask. Generally 1 mmol furfural, catalyst 2 and 5 ml sol-
vent (methanol, ethanol, DMF, DMA, THF, ethyl acetate, toluene)
were putted into the flask which was placed in constant tempera-
ture water bath heater. After getting reaction temperature(from 25
to 70 ꢀC), 1.1 mmol malononitrile was added into the reaction
system. After reaction, the mixture was centrifuge at 6000 rpms for
2min. Then the supernatant was putted into gas chromatography to
characterization the yield.
2.4.2. Comparative experiment
To verify the reaction activity sites, Co-MOFs 1 and blank con-
dition was chosen for Knoevenagel reaction for furfural. Then the
yield of every condition was summed up together.
2.4.3. Catalyst recycling
To determined the recycling stability of catalyst 2, the catalyst
was separated by centrifugation and wished with methanol for
three times and then dried by air after the reaction, then catalysis
the reaction at same condition. Then the yield was also determined
by gas chromatography.