The reduction of 4-nitrophenol and 2-nitroaniline by the incorporation of Ni@Pd MNPs into modified UiO-66-NH2 metal-organic frameworks (MOFs) with tetrathia-azacyclopentadecane

Article abstract of DOI:10.1039/c7nj03732e

We have found that UiO-66-NH₂ can be used as an excellent support for the synthesis of highly sparse nanoparticles. UiO-66-NH₂ has a high surface area that was functionalized with tetrathia-azacyclopentadecane (TTACP) groups acting as strong conjugation sites so that Ni@Pd nanoparticles were well dispersed without aggregation on the structures of the UiO-66-NH₂ microspheres (UiO-66-NH₂/TTACP/Ni@Pd). The synthesized UiO-66-NH₂/TTACP/Ni@Pd magnetic nanoparticles (MNPs) exhibited excellent catalytic activity for the reduction of 2-nitroaniline and 4-nitrophenol.

Full text of DOI:10.1039/c7nj03732e

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The reduction of 4-nitrophenol and 2-nitroaniline
by the incorporation of Ni@Pd MNPs into
modified UiO-66-NH2 metal–organic frameworks
(MOFs) with tetrathia-azacyclopentadecane
ab
Cite this:DOI: 10.1039/c7nj03732e
Seyed Mohsen Sadeghzadeh,
*
Rahele Zhianiab and Shokufe Emraniab
We have found that UiO-66-NH2 can be used as an excellent support for the synthesis of highly sparse
nanoparticles. UiO-66-NH2 has a high surface area that was functionalized with tetrathia-azacyclopentadecane
(TTACP) groups acting as strong conjugation sites so that Ni@Pd nanoparticles were well dispersed without
aggregation on the structures of the UiO-66-NH2 microspheres (UiO-66-NH2/TTACP/Ni@Pd). The synthesized
UiO-66-NH2/TTACP/Ni@Pd magnetic nanoparticles (MNPs) exhibited excellent catalytic activity for the reduction
of 2-nitroaniline and 4-nitrophenol.
Received 29th September 2017,
Accepted 4th December 2017
DOI: 10.1039/c7nj03732e
rsc.li/njc
the potential application of these catalysts. However, affordable
noble metal NP catalysts with passive cores, great catalytic
Introduction
Metal–Organic Frameworks (MOFs) have received an excellent activities, and impressive recoverable properties are extremely
response from the research community as they provide a wide rare.17–20
range of applications in gas storage and separation, carbon
Recently, green chemistry has attracted substantial considera-
dioxide capture, guest-dependent luminescence, and catalysis tion as it is difficult to overcome the environmental contamination
research.1–8 Heterogeneous catalysis using MOF-supported encountered by the world population.21–27 Processes that avoid
small metal NPs or NCs has attracted increasing research using harmful organic solvents to transform organic debris into
attention because the nanopores of MOFs can not only serve reusable combinations with less toxicity in aqueous solution have
as templates for synthesizing monodisperse metal NPs/NCs but received an excellent response from the research community. Much
also provide well-defined microenvironments that could induce research has been done on the disposal of nitroaromatic
selectivity control on the encapsulated NPs/NCs in catalytic compounds. Industrial and agricultural waste waters contain
reactions. The piling of metal NPs/NCs into MOFs was first carried nitrophenols, which are among the most common organic
out by chemical vapor deposition using volatile organometallic pollutants.28,29 Due to the potential carcinogenic and mutagenic
precursors in the gas phase.9–13 Palladium nanoparticles (Pd NPs) effects of nitrophenols, the presence of low concentrations of
are of particular importance among the noble metals, owing to nitrophenols in water is detrimental to aquatic life and human
their superior catalytic performances.14–16 Most noble metal NP health. Due to these reasons, 4-nitrophenol and 2-nitroaniline as
catalytic reactions happen only on the surface of the NPs and a hazardous waste compounds and toxic contaminants are in the
large fraction of atoms in the core are catalytically passive. So, to list published by the United States Environmental Protection
construct a great percentage of noble metal atoms accessible for Agency.30–34 Hence, it is important to develop effective methods
catalysis and to reduce their use, the internal noble metal atoms to eliminate them. Also, 4-aminophenol (4-AP) and o-phenylene-
should be exchanged by other non-noble metals such as Fe, Co, diamine (o-PDA) are important intermediates for the synthesis of
and Ni in order to reduce the use of the noble metal without drugs and dyes, which are synthesised from 4-NP and 2-NA.35–39
sacrificing the overall performance of the catalyst. In addition, the Previously, both the reduction of 4-NP and the HDC of 4-CP have
presence of Fe, Co, and Ni in hybrid, core–shell NPs provides been performed using palladium as a catalyst.40,41 Palladium
excellent stability, solvent adaptability, catalytic activity, and due to its premier catalytic efficiency is of particular significance
magnetic separability. All of these properties greatly enhance among the noble metals.42 Palladium is now receiving attention due
to its catalytic activity in the treatment of wastewaters containing
4-NP or 4-CP contaminants.43–46 Herein, we report the synthesis
of (UiO-66-NH2) supported tetrathia-azacyclopentadecane-Pd
(UiO-66-NH2/TTACP/Ni@Pd) and its application for the catalytic
reduction of 4-NP and 2-NA (Scheme 1).
a Department of Chemistry, Faculty of Sciences, Neyshabur Branch, Islamic Azad
University, Neyshabur, Iran. E-mail: seyedmohsen.sadeghzadeh@gmail.com
b Young Researchers and Elite Club, Neyshabur Branch, Islamic Azad university,
Neyshabur, Iran
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The reaction mixture was stirred for 36 h at 110 1C and was
subsequently filtered and washed thoroughly with DMF, and
dried in an oven at 80 1C for 24 h to form UiO-66-NH2/TTACP.
Then, the resulting solid (1 g), N,N-dimethylthiocarbamoyl chloride
(4 g) and K2CO3 (5.5 g) were stirred in acetone (100 mL) and were
refluxed for 48 h under a nitrogen atmosphere. After the suspension
had cooled, the solvent was removed in vacuo. The organic phase
was then separated, washed with water, 5% KOH, and saturated
NaCl, and dried over anhydrous Na2SO4.
Scheme 1 The reduction of 4-NP and 2-NA on the surface of the UiO-
66-NH2/TTACP/Ni@Pd catalyst.
General procedure for the preparation of UiO-66-NH2/TTACP/
Ni@Pd NPs
UiO-66-NH2/TTACP/Ni@Pd structures were prepared by the
reaction of UiO-66-NH2/TTACP with 49.7 mg of nickel(II) acetate
tetrahydrate (Ni(ac)2ꢁ4H2O, 0.2 mmol) and 53.4 mg of palladium(II)
bromide (PdBr2, 0.2 mmol), mixed with 18.0 mL of OAm and
0.3 mL of TOP at room temperature. The reaction was heated to
245 1C under a gentle argon flow for 1 h. Then the UiO-66-NH2/
TTACP was separated from the reaction mixture by an external
magnet and washed several times with deionized water and acetone.
Finally, UiO-66-NH2/TTACP was dried under vacuum at 50 1C.
Experimental
Materials and methods
Chemical materials were purchased from Fluka and Merck in
high purity. Melting points were determined in open capillaries
using an Electrothermal 9100 apparatus and are uncorrected.
The FTIR spectra were recorded on a VERTEX 70 spectrometer
(Bruker) in transmission mode in spectroscopic grade KBr
pellets for all the powders. The particle size and structure of
the nanoparticles were observed by using a Philips CM10
transmission electron microscope operating at 100 kV. Powder
X-ray diffraction data were obtained using a Bruker D8 Advance
model with Cu ka radiation. The thermogravimetric analysis
(TGA) was carried out on a NETZSCH STA449F3 at a heating
rate of 10 1C minꢀ1 under nitrogen. The 1H and 13C NMR spectra
were recorded on a BRUKER DRX-300 AVANCE spectrometer at
300.13 and 75.46 MHz, and on a BRUKER DRX-400 AVANCE
spectrometer at 400.22 and 100.63 MHz, respectively. The elemental
analyses for C, H, and N were performed using a Heraeus CHN–
O-Rapid analyzer. The purity determination of the products and
reaction monitoring were accomplished by TLC on silica gel
polygram SILG/UV 254 plates. The mass spectra were recorded
on a Shimadzu GCMS-QP5050 Mass Spectrometer.
General procedure for the reduction of 4-nitrophenol
First, 40 mL of aqueous 4-NP solution (1.26 ꢂ 10ꢀ2 mol Lꢀ1) was
added to H2O (2.5 mL), and then mixed with 0.5 mL of a freshly
prepared aqueous NaBH4 solution (0.5 M) and a deep yellow
solution was formed. Then, 0.4 mg of the catalyst was added to
the above yellow solution and the reaction was performed until
the solution became colorless. The reaction progress was
monitored by measuring the UV-vis absorption spectra of the
reaction mixture.
General procedure for the reduction of 2-nitroaniline
1 mg of catalyst was added to H2O (2.5 mL), and then mixed
with 40 mL of 2-NA aqueous solution (1.26 ꢂ 10ꢀ2 mol Lꢀ1) and
NaBH4 (0.5 M) solution was injected rapidly with stirring. The
color of the mixture vanished gradually, indicating the reduction
of 2-NA. The reaction progress was monitored by measuring the
UV-vis absorption spectra of the reaction mixture.
General procedure for the preparation of UiO-66-NH2
Zirconium(IV) chloride (12 g) and water (3 mL) were added to
800 mL N,N-dimethylformamide (DMF) and stirred until completely
soluble. 2-Aminoterephthalic acid (9.4 g) was added to 400 mL DMF
and stirred until entirely soluble. The solutions were mixed in a
BuchiGlasUsterEcoclave 075 batch reactor with a 1.6 L glass reactor
vessel. The reactor was stirred at 500 rpm and held at 120 1C for 24 h.
The pale yellow solid was isolated via filtration.
Results and discussion
The synthesis of UiO-66-NH2/TTACP/Ni@Pd NPs involved several
steps. The UiO-66-NH2 has many N–H groups on its surface; thus, it
was expected that the UiO-66-NH2 could easily be functionalized
General procedure for the preparation of compound (M3)
M2 (3 mmol), M1 (2.6 mmol), and 360 mg (15 mmol, 5 equiv.) LiOH with tetrathia-azacyclopentadecane (TTACP) to form UiO-66-NH2/
were mixed in 100 mL DMF, and the thus-formed solution was TTACP. Furthermore, tetrathia-azacyclopentadecane groups on the
refluxed for 10 h. The solvent was removed under reduced pressure UiO-66-NH2/TTACP could support Ni@Pd MNPs (Scheme 2).
and the resultant residue was purified by column chromatography
over silica gel with dichloromethane and methanol (v : v = 3 : 1).
The morphology and sizes of the synthesized UiO-66-NH2,
and UiO-66-NH2/TTACP/Ni@Pd nanocatalyst were analyzed by TEM.
The average diameter of the microspheres was about 100–120 nm
(Fig. 1a). This catalyst revealed that the UiO-66-NH2/TTACP was
loaded with well-dispersed Ni@Pd NPs (Fig. 1b). Further inspection
General procedure for the preparation of UiO-66-NH2/TTACP
NPs
UiO-66-NH2 (1 g), 3,5-dihydroxybenzoic acid (1.5 mmol), and of the TEM micrograph of the recovered catalyst demonstrates that
DMF (50 mL) were mixed together with a magnetic stirrer bar. the Ni@Pd nanoparticles throughout the UiO-66-NH2/TTACP
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Fig. 2 XRD analysis of (a) simulated UiO-66-NH2; (b) UiO-66-NH2/
TTACP; and (c) UiO-66-NH2/TTACP/Ni@Pd MNPs.
Scheme 2 Schematic illustration of the synthesis for UiO-66-NH2/
TTACP/Ni@Pd NPs.
Fig. 1 TEM images of (a) UiO-66-NH2; (b) UiO-66-NH2/TTACP/Ni@Pd
NPs; and (c) single Ni@Pd NPs.
are well distributed. This observation shows that while UiO-66-
NH2/TTACP/Ni@Pd NPs act as a substrate for highly active and
soluble Ni@Pd species, they may also operate as a nanoscaffold
Fig. 3 TGA diagram of UiO-66-NH2/TTACP/Ni@Pd NPs.
to recapture the Ni@Pd nanoparticles inside the tree structure was attributed to the decomposition of material oxides. UiO-66-
of UiO-66-NH2, thus preventing Ni@Pd agglomeration. Fig. 1c NH2/TTACP/Ni@Pd MNPs showed a good thermal stability at
shows a TEM image of the Ni@Pd NPs. The diameter of the NPs the reaction temperature.
was about 10 nm, and the morphology of the NPs is near-spherical.
Magnetization curves (Fig. 4) show the superparamagnetic
Powder X-ray diffraction (XRD) was used to search for the behavior of the Ni@Pd NPs and UiO-66-NH2/TTACP/Ni@Pd
correct synthesis of the Ni@Pd NP loaded UiO-66-NH2/TTACP. nanocatalyst. The magnetic saturation values of the Ni@Pd
The XRD templates of the as-synthesized UiO-66-NH2/TTACP NPs and UiO-66-NH2/TTACP/Ni@Pd nanocatalyst are 4.56 and
(Fig. 2b) matched well with the simulated XRD patterns 0.86 emu gꢀ1, respectively. Therefore, the Ni@Pd NP modified
(Fig. 2a). After the loading of Ni@Pd, there is no apparent loss UiO-66-NH2/TTACP/Ni@Pd nanocatalyst could be efficiently
of MOF crystallinity in the XRD patterns (Fig. 2c). The XRD separated from the solution by using an external magnetic
analysis can provide evidence for the composition of the Ni@Pd force, and could be reused and recycled.
NPs. Fig. 2c reveals that Ni@Pd NPs exhibit sharp peaks of
Ni(111), Pd(111), Pd(200), Pd(220), and Pd(311), which also supported catalyst (fresh and reused) were obtained using the
verify the existence of fcc-Pd and fcc-Ni. Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH)
The specific surface area and porosity of the parent MOF and the
The TG analysis of UiO-66-NH2/TTACP/Ni@Pd MNPs was methods, respectively. According to the results in Table 1, the surface
determined and shown in Fig. 3. For the UiO-66-NH2/TTACP/ area was decreased after post-synthesis and copper Ni@Pd deposi-
Ni@Pd MNP sample, between 50 1C and 280 1C a weight loss of tion as expected for porous materials. A dramatic reduction in the
7% was observed corresponding to physically adsorbed water. surface area of the fresh catalyst indicated that post-synthesis,
The amino functionalized analogues UiO-66-NH2 showed significant Ni@Pd formation mainly took place on the surface of the frame-
weight losses (18% to 20%) at B400 1C, presumably due to TTACP work. The N2 adsorption–desorption isotherms of UiO-66-NH2/
decomposition. As shown in Fig. 3, a significant weight loss TTACP/Ni@Pd MNPs showed a characteristic type IV curve, which
step appeared at the temperature range of 550–600 1C, which is consistent with literature reports on standard porous materials.
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Fig. 4 Room-temperature magnetization curves of the nanocatalyst.
Table 1 Structural parameters of UiO-66-NH2 and UiO-66-NH2/TTACP/
Ni@Pd materials determined from nitrogen sorption experiments
Catalysts
SBET (m2 gꢀ1
)
Vt (cm3 gꢀ1
)
DBJH (nm)
UiO-66-NH2
UiO-66-NH2/TTACP/Ni@Pd
1274
32.6
0.549
0.041
1.82
2.41
We investigated the catalytic performance of the UiO-66-
NH2/TTACP/Ni@Pd MNPs by using the reduction of 4-NP into
4-AP in the presence of NaBH4 as a probe reaction. The
evolution process with reaction time for the reduction of 4-NP
to 4-AP was monitored by UV-vis spectroscopy. The solution
of 4-NP exhibits a strong absorption peak at 300 nm which
is remarkably red-shifted to 400 nm (Fig. 5a). The addition of
UiO-66-NH2/TTACP/Ni@Pd MNPs (0.4 mg) into the system led
to a decrease in the peak intensity of 4-NP at 400 nm with the
concomitant increase in the peaks corresponding to 4-AP at
300 nm. The reaction proceeds rapidly with the conversion
exceeding 99.6% at a reaction time of about 150 s (Fig. 5b).
Based on our above results, we also used the UiO-66-NH2/
TTACP/Ni@Pd MNPs to perform the catalytic reduction of 2-NA.
The reduction of 2-NA can also be easily monitored because the
product for the reduction reaction was only, and the progress
of the reaction can be determined by measuring the change in
UV-vis absorbance. The yellow colored solution of 2-NA exhibited
two distinct absorption peaks at 280 and 400 nm, and the intensity
of the two peaks did not decrease with the addition of NaBH4
solution. However, the intensity of the two peaks decreased
gradually when adding UiO-66-NH2/TTACP/Ni@Pd NPs to 2-NA
and NaBH4 mixed solution (Fig. 5c).
Fig. 5 UV-vis spectra of (a) 4-NP before and after adding NaBH4 solution;
(b) the successive reduction of 4-NP to 4-AP; and (c) 2-NA to o-PDA over
the UiO-66-NH2/TTACP/Ni@Pd NP catalyst.
The reaction conversion is calculated from Ct/C0, measured
in terms of the relative intensity of UV-vis absorbance (At/A0) at order with respect to the reduction of 4-NP. Thus, the kinetic
400 nm. Herein, Ct is the concentration of 4-NP at the reaction equation of this catalytic reduction reaction can be shown as
time t and C0 is the initial concentration. The averaged values ln(Ct/C0) = ꢀkt, where k is the apparent first-order rate constant
of the reaction conversions with standard deviation were given (sꢀ1), and t is the reaction time. The reaction rate constant k
as shown in Fig. 6a. As shown in Fig. 6b, the linear correlation was calculated to be 1.42 ꢂ 10ꢀ2 sꢀ1 for the UiO-66-NH2/TTACP/
between ln(Ct/C0) and reaction time demonstrates that the Ni@Pd NP catalyzed reduction of 4-NP. For a quantitative
reaction is of first order with respect to the reduction of 4-NP. comparison, the activity parameter k0 = k/M was introduced,
As shown in Fig. 6b, the linear correlation between ln(Ct/C0) and defined as the ratio of the rate constant k to the weight of
and reaction time demonstrates that the reaction is of first the catalyst added,47 where M is the total mass of the catalyst
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Table 3 A comparison of catalytic activities for the reduction of 4-NP
with catalysts reported in the literature
Catalysts
Catalyst (mg) ka (sꢀ1
)
k/Mb (sꢀ1 gꢀ1
)
p(AMPS)–Ni48
p(AMPS)–Co49
p(AMPS)–Cu50
TAC-Ag-1.051
50
50
10
4.0
1.0
1.0
9.38 ꢂ 10ꢀ4 0.019
2 ꢂ 10ꢀ3
0.04
1.72 ꢂ 10ꢀ3 0.172
5.19 ꢂ 10ꢀ3 1.3
7.67 ꢂ 10ꢀ3 7.67
1.69 ꢂ 10ꢀ3 1.69
1.42 ꢂ 10ꢀ2 14.2
Fe3O4@SiO2–Ag52
Ag/C spheres53
UiO-66-NH2/TTACP/Ni@Pd 1.0
a
b
The reaction rate constant. The reaction rate constant per total
weight of used catalyst.
continued the research to improve the yield of the product by
adding the nanoparticles to the catalyst. These nanoparticles as
a cocatalyst are necessary to activate propargylic amine, thus
improving their catalytic activity. The catalytic activity of these
various nanoparticles was found to be of the order Pd B Ni@Pd 4
Ag 4 Au 4 Cu 4 Pt 4 ZnO 4 TiO2 4 RuO2 4 FeNi3. Therefore,
we chose Ni@Pd as a cocatalyst for the synthesis of our catalyst.
The activity parameters used for the comparison of the
catalytic activity of UiO-66-NH2/TTACP/Ni@Pd with the reported
Ag, Ni, Co, and Cu NP-based catalysts employed for the
reduction of 4-NP are listed in Table 3. It can be seen from
Table 3 that the rate constant k and activity parameter k0 of the
UiO-66-NH2/TTACP/Ni@Pd nanocatalyst are higher than those
of the reported p(AMPS)–Ni, p(AMPS)–Co, and p(AMPS)–Cu
catalysts. According to the literature, p(AMPS)–Ni NPs48 and
p(AMPS)–Co NPs49 have activity parameters of about 0.019 and
ꢀ1
0.04 sꢀ1
g
, respectively. p(AMPS)–Cu has a rate constant k0 of
Fig. 6 Plots of Ct/C0 (a) and ln(Ct/C0) (b) versus reaction time for the
reduction of 4-NP over the UiO-66-NH2/TTACP/Ni@Pd NPs.
0.172 sꢀ1 g
catalyst (1.3 sꢀ1
dopedcarbon sphere catalyst (1.69 sꢀ1 gꢀ1
.
ꢀ1 50 Our value is also higher than that of the TAC-Ag-1
g
ꢀ1), Fe3O4@SiO2–Ag NPs (7.67 sꢀ1
g
)
ꢀ1) and Ag
reported
added in the reaction. Thus, the reaction rate constant per unit previously.51–53 The catalytic activity of the UiO-66-NH2/TTACP/
mass was calculated to be 14.2 sꢀ1 gꢀ1 for the reduction of 4-NP. Ni@Pd nanocatalyst, obtained in this study, is 14.2 sꢀ1 gꢀ1 which
To further evaluate the efficiency of the catalyst, different is significantly higher than the catalytic activities of the above-
control experiments were performed and the obtained data are mentioned nanoparticle-based catalysts; thus the UiO-66-NH2/
shown in Table 2. Firstly, one separated reaction was examined TTACP/Ni@Pd nanocatalyst displayed superior catalytic activity
in the presence of UiO-66-NH2. The results of these studies for the reduction reactions.
showed that no amount of the desired product was formed
Scheme 3 is an illustrative representation of the reaction,
(Table 2, entries 1). Based on these frustrating results, we with the activation of the hydrides on the surface of the catalyst
and their transfer to the nitro group. In fact, according to the
literature, in the reduction of nitroarenes using NaBH4 catalyzed
Table 2 Comparison of the catalytic efficiency of UiO-66-NH2/TTACP/
by Ni@Pd NPs, first, a B–H bond cleavage is the rate-determining
Ni@Pd NPs with various catalysts
step to give the Pd–H species. The negatively charged hydrogen
Entry
Catalyst
Yielda (%)
in the metal–hydrogen structure can easily attack the positively
charged nitrogen in the nitro group of nitrophenols, and as a
result, the nitro group is reduced to the nitroso group, followed
by the reductive addition of two hydrogen atoms to form
hydroxylamine. Finally, the hydroxylamine is further reduced
to the aniline derivative.
It is important to note that the magnetic properties of
the UiO-66-NH2/TTACP/Ni@Pd MNPs facilitate their efficient
recovery from the reaction mixture after the completion of the
reaction. The activity of the recycled catalyst was also examined
for ten consecutive cycles without any significant loss in
1
2
3
4
5
6
7
8
UiO-66-NH2
—
95
85
58
69
95
87
80
41
73
95
UiO-66-NH2/TTACP/Pd
UiO-66-NH2/TTACP/Au
UiO-66-NH2/TTACP/TiO2
UiO-66-NH2/TTACP/ZnO
UiO-66-NH2/TTACP/Ag
UiO-66-NH2/TTACP/Cu
UiO-66-NH2/TTACP/FeNi3
UiO-66-NH2/TTACP/Pt
UiO-66-NH2/TTACP/RuO2
UiO-66-NH2/TTACP/Ni@Pd
9
10
11
a
Isolated yield.
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Table 4 The loading amount of Ni@Pd MNPs in UiO-66-NH2/TTACP
Entry
Catalyst
wt%
1
2
UiO-66-NH2/TTACP/Ni@Pd
UiO-66-NH2/TTACP/Ni@Pd after ten reuses
2.9
2.8
almost overlapping with each other, which suggests that the
catalyst did not deactivate during these recycling runs.
Ni@Pd MNP leaching was studied by the ICP analysis of the
catalyst, after ten cycles of reactions. The loading amount of
Ni@Pd MNPs was found to be 2.8 wt%, which shows negligible
Ni@Pd MNP leaching. These results confirmed the high recycl-
ability of the Ni@Pd nanocatalyst (Table 4).
Conclusions
Scheme 3 A plausible mechanism for the reduction of p-nitrophenol
catalyzed by the UiO-66-NH2/TTACP/Ni@Pd NP catalyst in the presence
of NaBH4.
In conclusion, we have successfully developed a novel, magnetic
nanocatalyst called UiO-66-NH2/TTACP/Ni@Pd MNPs. This
nanocatalyst, with Ni@Pd MNPs as the active sites, can not only
reduce the use of Ni@Pd MNPs without reducing catalytic
activity, but also confer super-paramagnetic properties to the
nanocatalyst, making the catalyst easy to recover for reuse. The
UiO-66-NH2/TTACP/Ni@Pd MNPs exhibited excellent catalytic
activity in the reduction of 4-NP and 2-NA. This feature can be
attributed to the high accessibility of the UiO-66-NH2/TTACP/
Ni@Pd MNP support material and the low amount of aggrega-
tion of the Ni@Pd MNPs on the UiO-66-NH2/TTACP support.
Moreover, UiO-66-NH2/TTACP/Ni@Pd MNPs can be reused at
least ten times without an obvious reduction in the catalytic
activity which may be attributed to the prevention of leaching of
Ni@Pd MNPs from the UiO-66-NH2/TTACP/Ni@Pd.
Fig. 7 The reusability of the catalysts for the reduction of 4-NP and 2-NA
with NaBH4.
Conflicts of interest
catalytic activity. After the completion of the reaction, the
catalyst was separated by an external magnet, washed with
methanol, and dried at the pump (Fig. 7). We also carried out
kinetic studies for the first 3 h in four recycling tests to further
examine the catalyst stability. As shown in Fig. 8, the conver-
sion continues to increase with reaction time, reaching B95%
after 3 h. The kinetic curves for the four recycling runs are
There are no conflicts to declare.
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