Synthesis and characterization of a novel TEMPO?FeNi3/DFNS-laccase magnetic nanocomposite for the reduction of nitro compounds

Article abstract of DOI:10.1039/d0ra03989f

Water is an essential substance for life on earth and for all living things. Plants and animals need almost pure water to live; if it is contaminated with harmful chemicals and micro organisms, it will be impossible for them to survive. This study has tried to investigate the performance of catalyst to reduce nitro-aromatic combinations in the attendance of NaBH4 solution duo to the hydrogen source. TEMPO?FeNi3/DFNS-laccase MNPs was prepared, and its features were reviewed using SEM, TEM, XRD, TGA, VSM, AFM, and FTIR. Then, its strength as a nanocatalyst for removal of nitro-aromatic combinations was tested in contact time, initial concentration, the effects of pH and nanocatalyst amount was study. The results of this research proved that TEMPO?FeNi3/DFNS-laccase MNPs has a good return in removal of nitro-aromatic combinations, as its easy synthesis and reliable recovery.

Full text of DOI:10.1039/d0ra03989f

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Synthesis and characterization of a novel
TEMPO@FeNi /DFNS–laccase magnetic
3
Cite this: RSC Adv., 2020, 10, 27297
nanocomposite for the reduction of nitro
compounds
a
b
a
Shima Saberi, Rahele Zhiani, * Jamshid Mehrzad*
b
and Alireza Motavalizadehkakhky
Water is an essential substance for life on earth and for all living things. Plants and animals need almost pure
water to live; if it is contaminated with harmful chemicals and micro organisms, it will be impossible for them
to survive. This study has tried to investigate the performance of catalyst to reduce nitro-aromatic
4 3
combinations in the attendance of NaBH solution duo to the hydrogen source. TEMPO@FeNi /DFNS–
laccase MNPs was prepared, and its features were reviewed using SEM, TEM, XRD, TGA, VSM, AFM, and
FTIR. Then, its strength as a nanocatalyst for removal of nitro-aromatic combinations was tested in
contact time, initial concentration, the effects of pH and nanocatalyst amount was study. The results of
Received 3rd May 2020
Accepted 14th July 2020
DOI: 10.1039/d0ra03989f
this research proved that TEMPO@FeNi
3
/DFNS–laccase MNPs has a good return in removal of nitro-
rsc.li/rsc-advances
aromatic combinations, as its easy synthesis and reliable recovery.
Various researches have reported the usage of supported
laccase for the preparation of materials, however, the applica-
Introduction
Water pollution has become a serious global concern, which tion of expensive intermediate reagents such as 2,2,6,6-
threatens the entire biosphere and inuences the lives of many tetramethyl-1-piperidinyloxy (TEMPO) are unavoidable for lac-
individuals around the globe. Different kinds of illnesses are case catalyzed reactions. For a large-scale reaction, the recycling
11
caused by this pollution and many people die every year due to of laccase and the mediator is in favor. The usage of porous
diseases caused by polluted water. Nitroarene hydrogenation is material in co-immobilizing both laccase and the mediator is
one of the most effective ways for producing aromatic amines. found to be effective as both species can be found in the indi-
12
The amine group is oen an important mediator for vidual cavity of the support. For this application, a magnetic
manufacturing many drugs, organic chemicals, rubber mate- material known as FeNi
rials, photographic, polymers and dyes. Many strategies have lent permeability, magnetic saturation and experience minimal
3
alloy is extensively used for its excel-
1
been developed for decreasing a nitro precursor such as metal/ energy loss. The concerns that arise for the synthesis of FeNi
3
2
–4
5
acid reduction, hydrogenation of catalytic, Hydrogenation at nanomaterials are the risks possessed by the individual metal.
6
homogeneous catalytic transition, and hydrogenation at It is especially alarming as nickel can be an allergen that causes
7
,8
heterogeneous catalytic transfer.
processes have some signicant disadvantages; for instance, concerns, FeNi
metal/acid system has demonstrated poor selectivity and this problem that persist is the instability of magnetic particle for
technique is ecologically hazardous; besides, hydrogenation of a long-term application as FeNi is highly chemically reactive
catalytic is not favored because of applying H2 gas at high and can go through oxidation in air. This contributes to the loss
Nonetheless, these dermatitis and possesses carcinogenic properties. Despite the
has not been reported to be harmful. The
3
3
13–19
temperature, it is not easy to separate the homogeneous or of magnetic properties and dispersion.
heterogeneous catalytic transfer hydrogenation from the ulti-
mate product.
In the recent years, the utilize of surfactant over so tem-
Accordingly, it is important to discover new plating caused the production of mesoporous silica along with
9,10
catalysts for hydrogenation of nitroarenes under favorable dendrimeric silica bers morphology (DFNS). For adsorption
situations.
and catalysis approaches as support material, silica having this
morphology are analyzed. For reactants for accessing the
functional materials more properly, the appearance radial
a
Department of Biochemistry, Faculty of Science, Islamic Azad University, Neyshabur widening of these silicas possesses higher surface area. More-
Branch, Neyshabur, Iran. E-mail: mehrzadjam@yahoo.com
over, DFNS possesses intrinsic mesoporous characteristics,
exhibits high activity and thermally stable. The production of
b
Department of Chemistry, Faculty of science, Islamic Azad University, Neyshabur
Branch, Neyshabur, Iran. E-mail: R_zhiani2006@yahoo.com
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DFNS needs microemulsion method that involves water, General procedure for the preparation of FeNi /DFNS/GMSI
3
surfactant, and oil. In addition, the morphology of DFNS and MNPs
particle size may be varied considering co-surfactant and
A mixture was prepared by mixing 200 mg of FeNi
3
/DFNS in
20–26
different co-solvents.
bifunctional hybrid catalyst is synthesized by co-
20 mL of THF followed by the addition of 20 mmol of NaH via
A
ultrasonication. Aer that, 22 mmol of (3-glycidyloxypropyl)tri-
immobilizing laccase and TEMPO into the cavities of
magnetic DFNS. In consideration on the environmental impact
caused by antibiotic residuals and the high oxidation of rate in
the removal of organic contaminants, this research is aimed at
investigating the photocatalytic efficiency of the bifunctional
hybrid catalyst synthesized for reduction of 4-NP to 4-AP from
aqueous environment.
methoxysilane were added into the mixture at room tempera-
ture and stirred for 16 h at 50 C. The resultant mixture was
ꢀ


3
ltered and washed with ethanol and deionized water. The
ꢀ
ltered solids were then dried in vacuum condition at 50 C for
28
h.
3
General procedure for the preparation of TEMPO@FeNi /
Experimental
DFNS–laccase MNPs
General procedure for the preparation of FeNi MNPs
Glycidyloxypropyl were used for the activation of FeNi /DFNS
3
3
(100 mg). This was then added to a mixture containing 10 mL of
The procedure involved in the preparation of FeNi3 MNPs
acetate buffer at 0.1 M and pH of 4.5, laccase and 4-hydroxy-
TEMPO. The mixture is stirred at 120 rpm for a few hours.
The resultant nanoparticles containing co-immobilized laccase
and TEMPO were ltered and rinsed with acetate buffer
multiple times. The ltered nanoparticles were kept and store
involved dissolving 0.01 mol FeCl $4H O and 0.03 mol NiCl -
2
2
2
$
6H O into 300 mL of distilled water and the subsequent
2
addition of 1.0 g of polyethylene glycol (PEG, MW 6000). To
achieve the pH range of 12 # pH # 13, sodium hydroxide
(
(
NaOH) were added to the solution. Next, hydrazine hydrate
$H O) at 80% concentration were added to the suspen-
ꢀ
28
under 4 C.
N
2
H
4
2
sion in varied quantity. The suspension was le to react
continuously for 24 h at room temperature. The pH of the
suspension was maintained at 12 # pH # 13 with periodical
dosing of NaOH. Aer that, the solid phase of resultant mixture
General procedure for reducing nitro compounds
Suspension of NaBH (1.5 mmol) in H O (5 mL) was added to
4
2
was ltered to obtain a black colored FeNi
3
MNPs and rinsed
ꢀ
nitro compound (1 mmol) and stirring was applied at 50 C in
27
with ionized water multiple times.
the presence of TEMPO@FeNi /DFNS–laccase (15 mg) in water.
3
TLC was applied for monitoring the reaction progress. Aer the
end of the reaction, the catalyst was removed and eluted with
ethanol. Ethyl acetate was applied to extract the reaction
mixture and dried with Na SO . The product was puried by
2 4
column chromatography using hexane–ethyl acetate as solvent
General procedure for the preparation of FeNi
3
2
/SiO MNPs
An aqueous solution containing 80 mL of ethanol, 20 mL of
ionized water and 2.0 mL of 28 wt% concentrated ammonia
aqueous solution (NH $H O) was prepared. 0.02 mol of FeNi
3 2 3
system in various concentrations to get the pure compound.
MNPs were dispersed in the mixture and 0.20 g of tetraethyl
orthosilicate (TEOS) were added subsequently. The mixture was
vigorously stirred for 24 h. The solid phase of the resultant
mixture was ltered and washed several times before being
ꢀ
27
dried in atmospheric condition at 60 C.
General procedure for the preparation of FeNi
Solution A was prepared with the addition of 30 mL aqueous
solution containing 0.3 g urea and dispersion of 0.25 g of FeNi
3
/DFNS MNPs
3
/
SiO . The mixture was placed in an ultrasonic bath for 1 h.
2
Solution B was prepared with the addition of 0.5 g cetylpyr-
idinium bromide (CPB) into 0.75 mL of n-pentanol and 30 mL of
cyclohexane. Solution A and solution B were mixed and stirred
at room temperature and 1.25 g TEOS was added in a drop wise
manner. The mixture was continuously stirred for 1 h at room
ꢀ
temperature and placed in an oven at 120 C for 5 h to incite
reaction. The completed reaction was cooled to room temper-
ature before applying a strong magnetic suction for the isola-
tion of FeNi /DFNS core–shell microspheres. The solid phase
3
was then washed several times with water and acetone. The
ꢀ
washed solid were dried in a drying oven at 40 C overnight and
Scheme 1 The process of co-immobilization of laccase and TEMPO
onto glycidyloxypropyl-functionalized FeNi /DFNS nanoparticles.
3
ꢀ
27
calcined at 550 C for 5 h in atmospheric condition.
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Results and discussion
The preparation of magnetic DFNS were done in accordance to
previously established procedures and then functionalized with
(3-glycidyloxypropyl)trimethoxysilane. The chemical process
involved in the construction of co-immobilized TEMPO and
enzyme is shown in Scheme 1.
TEM and FE-SEM were used for the morphological and
structural characterization of the FeNi /DFNS, and
3
TEMPO@FeNi /DFNS–laccase MNPs. The images from TEM
3
and FE-SEM showed spherical shaped solid composed of bers.
It is observed in Fig. 1a that FeNi
FeNi particle with nonporous silica layer and silica bres. A
uniform and monodispersed as-prepared magnetic core–shell
brous silica material FeNi /DFNS with brous structure were
3
/DFNS has a core made from
3

3
Fig.
2
3 3
XRD patterns of (a) FeNi , (b) FeNi /DFNS, and (c)
also observed. Fig. 1a and c displayed highly textured FeNi3/
DFNS samples containing spheres of uniform size (ꢁ300 nm)
with wrinkled radial structure. The wrinkled bres with an
approximate thickness of ꢁ8.5 nm is observed to be a three-
dimensional radial extension from the center of the sphere.
Also, cone-shaped open pores were formed as wrinkled radial
structure overlapped on each other. Nevertheless, mass transfer
of reactants was enhanced with the formation open hierarchical
channel structures and bers due to increase accessibility to
active sites. TEM and FE-SEM images also showed that there are
no morphological changes were experienced with modied
TEMPO@FeNi
3
/DFNS–laccase MNPs.
peak is observed in Fig. 2b which corresponded to the amor-
phous silica in FeNi /DFNS core–shell nanoparticles. XRD
pattern shown in Fig. 2c for TEMPO@FeNi /DFNS–laccase
MNPs were determined to be normal and had experienced no
changes.
TGA analysis of TEMPO@FeNi /DFNS–laccase MNPs were
illustrated in Fig. 3. The weight loss experienced below 150 C
were a consequence of the removal of physically and chemically
absorbed solvent from the surface of the TEMPO@FeNi /DFNS–
3
3
3
3
ꢀ
FeNi
Fig. 2 illustrates the powder X-ray diffraction patterns of
FeNi , FeNi /DFNS, and TEMPO@FeNi /DFNS–laccase MNPs
respectively. Prominent diffraction peaks were observed at 111,
00 and 220 for all samples. The XRD patterns obtained is in
3
/DFNS.
laccase material. A 23.2 wt% loss was experienced around 250–
3
3
3
ꢀ
4
50 C which corresponded to the organic group derivatives.
The weight decrement at this temperature is attributed to the
oxidation of TEMPO and laccase at around 180–350 C. In fact,
the remaining mass aer the organic decomposition in
TEMPO@FeNi /DFNS–laccase MNPs is due to the DFNS NPs.
2
ꢀ
good agreement to report in the JCPDS card (no. 19-0629) for
standard FeNi sample as shown in Fig. 2a. A broad amorphous
3
3
Atomic force microscopy (AFM) were utilized to determine the
surface roughness of TEMPO@FeNi /DFNS–laccase MNPs. The
3
resultant topographic images observed in Fig. 4 showed that
decreasing T/W is accompanied by greater height region rep-
resented by bright yellowish color. This suggested the incre-
ment in surface roughness of the catalyst.
Surface silanol, hydroxyl and phosphate groups were deter-
mined to be present in FeNi /DFNS, and aminofunctionalized
3
Fig. 1 TEM images of FeNi
laccase MNPs (b); FE-SEM images of FeNi
TEMPO@FeNi /DFNS–laccase MNPs (d).
3
/DFNS MNPs (a); TEMPO@FeNi
3
/DFNS–
3
/DFNS MNPs (c);
3
3
Fig. 3 TGA curves of TEMPO@FeNi /DFNS–laccase MNPs.
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3
Fig. 4 Three-dimensional of AFM images of TEMPO@FeNi /DFNS–
laccase MNPs.
Fig. 6 Room-temperature magnetization curves of (a) FeNi
3
, and (b)
FeNi /DFNS nanoparticles via FTIR analyses as shown in Fig. 5.
3
TEMPO@FeNi /DFNS–laccase MNPs.
3
For FeNi /DFNS, presence of Si–O–Si unsymmetrical stretching
3
ꢂ1
and OH are evident in the broad absorption bands at 1089 cm
and 3654 cm respectively. Symmetrical stretching of Si–O–Si
and bending is represented by the peaks observed at 799 cm
and 467 cm as shown in Fig. 5a. This signied that GMSI is
ꢂ1
3 3
Table 1 Structural parameters of FeNi /DFNS, and TEMPO@FeNi /
ꢂ1
DFNS–laccase MNPs
ꢂ1
2
ꢂ1
3
ꢂ1
Catalysts
S
BET (m g
a
) V (cm g ) DBJH (nm)
successfully graed on DFNS surface. Bands around 1091, 793
ꢂ1
and 462 cm were exhibited by GMSI–FeNi
3
/DFNS composite.
FeNi
TEMPO@FeNi
3
/DFNS
652
3.4
1.9
11
6
The occurrence of –OH and –NH stretching vibrations are
characterized by a strong and broad absorption band at 3000–
550 cm . Peak appeared at 2930 cm
stretching of the C–H aliphatic group (Fig. 5b).
Vibrating sample magnetometer (VSM) are utilized or the
specication of the nanoparticles magnetic characteristics by for FeNi /DFNS are specied through nitrogen physisorption
3
/DFNS–laccase 340
ꢂ1
ꢂ1
3
are due to the
TEMPO@FeNi /DFNS–laccase and BET specic surface area
3
3
2
ꢂ1
the magnetization curves of the archived nanocomposite analysis. It is determined to be 340 and 652 m g , respectively.
considered at the temperature of 300 K. Fig. 6 shows that no TEMPO@FeNi /DFNS–laccase reduced in surface area
3
residual magnetism was specied, so paramagnetic properties compared with FeNi /DFNS due to the supporting of laccase
3
were exhibited using the nanocomposites. Value of saturation and TEMPO in the FeNi /DFNS. In addition, reducing surface
3
ꢂ1
magnetization of 51.2 and 16.3 emu g are specied for FeNi3 area is more clear in TEMPO@FeNi /DFNS–laccase MNPs due
3
3
and TEMPO@FeNi /DFNS–laccase MNPs, respectively. External to poor bicontinuous concentric TEMPO as well as laccase
magnetic eld as well as the ability for rapid redispersion on morphology of the nanocatalyst. The attendance of mesopores
removal of magnetic eld has been introduced as a properties of in FeNi /DFNS was proved to the attendance of IV isotherm as
3
paramagnetic nanocomposites along with high magnetization well as H1-type hysteresis loop. To calculate pore size distribu-
amounts. Therefore, the resultant nanocomposite showed tion by BJH approach, the desorption branch of nitrogen
proper magnetic responsivity proposing potential application in isotherm was utilized. Table 1 shows that corresponding pore
the cases of targeting and separation.
size distribution presented a narrow pore size distribution
peaked at 11 nm (refer to Table 1). The high mesopore size of
3
FeNi /DFNS by great capacity can load TEMPO as well as lac-
case, which have relative large molecular size.
The catalytic performance of the new nanocatalyst
3
TEMPO@FeNi /DFNS–laccase was examined to decrease
fragrant nitro compounds. To improve the reaction conditions,
the reduction reaction of para-nitrophenol within the atten-
4
dance of NaBH as the hydrogen source was considered as
a model reaction. Initially, the solvent effect and molar ratio of
hydrogen sources on the model reaction were studied (Table 2,
entries 1–13). According to our ndings, water was the simplest
solvent for the model reaction when 1.5 mmol NaBH
applied; thus, the output was gotten by 99% yield (Table 2, entry
). Increasing the amount of NaBH from 1.0 mmol to 2.5 mmol
4
was
2
4
resulted in an improvement within the rate of para-nitrophenol
reduction (Table 2, entries 1–4). Reduction process was very
Fig. 5 FTIR spectra of (a) DFNS NPs, and (b) GMSI–DFNS NPs.
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Table 2 Reduction of para-nitrophenolin the attendance of various
4 3
values of NaBH in different solvents by TEMPO@FeNi /DFNS–laccase
MNPs
Entry
Source of hydrogen
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
1
1
1
1
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
NaBH
4
4
4
4
4
4
4
4
4
4
4
4
4
(1.0 mmol)
(1.5 mmol)
(2.0 mmol)
(2.5 mmol)
(1.5 mmol)
(1.5 mmol)
(1.5 mmol)
(1.5 mmol)
(1.5 mmol)
(1.5 mmol)
(1.5 mmol)
(1.5 mmol)
(1.5 mmol)
H
H
H
H
H
H
H
CH
EtOH
CH
CH
DMSO
2
2
2
2
2
2
2
O
O
O
O
O
O
O
5
5
5
5
3
2
1
2
2
2
2
2
2
39
99
99
99
99
99
63
90
82
30
36
27
12
3
OH
0
1
2
3
2
Cl
CN
2
3
n-Hexane
slow in aprotic solvents like CH Cl , CH CN, DMSO (Table 2,
2
2
3
entries 10–12) and non-polar solvent like n-hexane (Table 2,
entry 13). Using CH OH, H O, EtOH as protic solvents was the
most appropriate procedure for this catalytic system (Table 2,
entries 8 and 9); H O was chosen for the nitroarene reduction
3
2
2
because it is cheap, harmless, and ecologically green solvent.
The inuence of catalyst content on the model reaction was
explored. There was no advancement within the decrease of
nitro-aromatic combinations, in the absence of neither catalyst
Fig. 8 UV-vis spectra of (a) 4-NP before and after adding NaBH
solution; and (b) the consecutive reduction of 4-NP to 4-AP.
4
nor TEMPO@FeNi /DFNS–laccase MNPs. Fig. 7 shows that,
3
increasing the quantity of catalyst from 1 to 15 mg per mmol of
substrate leads to increased reaction efficiency; thus, the
maximum yield (99%) has been obtained from a 15 mg catalyst
attendance. The ndings t well with signicant increase in the
number of active positions.
1
3
5 mg TEMPO@FeNi /DFNS–laccase MNPs within the system
led to decrease the height severity of 4-NP (in 400 nm) with the
simultaneous increment within the peaks related to 4-AP at
3
The catalytic efficiency of TEMPO@FeNi /DFNS–laccase
MNPs by using the decrease of 4-NP in 4-AP under the existence
3
9
00 nm. The response swily occurred with the conversion of
9% in a very time interval of about 120 s (Fig. 8b).
of NaBH , which could be a probe reaction. Using UV-vis spec-
4
The reaction conversion is measured with C /C , obtained
t
0
troscopy, the expansion method with time of reaction within the
case of the reduction of 4-NP to 4-AP was evaluated. As observed
in Fig. 8a, 4-NP solution indicates a correct absorption peak in
the relative strength of UV-vis absorbance (A /A ) (at 400 nm). C
t
shows the concentration of 4-NP at the interval (t). C indicates
the primary concentration. Fig. 9 shows the mean value of the
t
0
0
300 nm, which is red-shied to 400 nm, dramatically. Using
Fig. 7 Effect of increasing amount of TEMPO@FeNi
MNPs on yield of reduction of para-nitrophenolin.
3
/DFNS–laccase Fig. 9 The scheme of C
t 0
/C against reaction time for the reduction of
4-NP over TEMPO@FeNi
3
/DFNS–laccase MNPs.
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Table
3
Reduction of different nitro-aromatic compounds over
3
TEMPO@FeNi /DFNS–laccase MNPs
a
ꢀ
Entry
1
Reactant Product
Yield (%)
Mp ( C)
91
99
Liquid
2
3
97–100
99
140–142
Fig. 10 The scheme of ln(C
tion of 4-NP over TEMPO@FeNi
t
/C
0
) against reaction time for the reduc-
/DFNS–laccase MNPs.
3
4
5
97
98
61–63
reaction conversions by standard deviation. Fig. 10 illustrates
the linear correlation between the time of reaction. ln(C /C )
t
0
103–105
shows that the reaction was rst-order considering that the
reduction of 4-NP. Fig. 10 indicates the linear correlation
among reaction time and ln(C
reduction is rst-order. Nevertheless, the kinetic relation of this
catalytic reduction reaction can be illustrated as ln(C /C
t 0
/C ) considering that the 4-NP
6
7
96
95
59–62
40–43
t
0
) ¼ ꢂkt.
Here, t shows the reaction time and k shows the apparent rst-
ꢂ1
order rate constant (s ). The k, reaction rate constant, be
ꢂ1
estimated 0.944 s in the case of the TEMPO@FeNi /DFNS–
3
0
laccase MNPs catalyzed 4-NP reduction. The activity factor, k ¼
k/M, is showed, for a quantitative comparison that introduced
as the ratio of k to the weight of the catalyst utilized. In addition,
M indicates the total mass of the catalyst that was utilized
8
9
98
96
184–186
107–109
during the reaction. Hence, the reaction rate constants per unit
ꢂ1 ꢂ1
mass was estimated to be 9.44 s
-NP.
As Table 3 shows, we used the enhanced situations for
g
in case of the reduction of
4
transforming of nitro aromatic comprising various functional
groups into the intended amino compounds (Table 3, entries 1–
12). Table 3 ndings suggest that electrons with substituents for
drawing/donating have no extraordinary effect on the reaction
time and yield (Table 3, entries 6–12). Dinitro compounds were
successfully converted to the intended diamines that are 10
signicant precursor for several heterocyclic combinations and
are utilized as a part for engineering polymers and composites
98
99
182–185
203–206
(Table 3, entries 3–5).
Scheme 2 was an illustrative representation of the reaction, 11
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 TEMPO cata-
lyzed by TEMPO and laccase, rst, a TEMPO–H bond cleavage is
the rate-determining step to give the laccase–H species. The
negatively charged hydrogen in the TEMPO–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
1
2
97
66–69
a
Isolated yield.
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for reduction of aromatic nitro compounds. In addition to its
easy synthesis method, recyclability and convenient recovery, it
is concluded that TEMPO@FeNi /DFNS–laccase MNPs can be
3
used in the removal and degradation of persistent, pharma-
ceutical organic pollutants.
Conflicts of interest
There are no conicts to declare.
Scheme 2 A plausible mechanism for the reduction of p-nitrophenol
2
catalyzed by the UiO-66-NH /TTACP/Ni@Pd NPs catalyst.
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3
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3
as well. It was found that TEMPO@FeNi
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3
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3
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