Rhodium nanoparticles supported on 2-(aminomethyl)phenols-modified Fe3O4 spheres as a magnetically recoverable catalyst for reduction of nitroarenes and the degradation of dyes in water

Article abstract of DOI:10.1007/s10562-021-03688-4

A magnetic nanostructured catalyst (Fe₃O₄@SiO₂-Amp-Rh) modified with 2-(aminomethyl)phenols (Amp) was designed and prepared, which is used to catalyze the reduction of aromatic nitro compounds into corresponding amines and the degradation of dyes. The 2-aminomethylphenol motif plays a vital role in the immobilization of rhodium nanoparticles to offer extraordinary stability, which has been characterized by using various techniques, including transmission electron microscopy (TEM), thermal gravimetric analyzer (TGA), X-Ray Diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). A variety of nitroaromatic derivatives have been reduced to the corresponding anilines in water with up to yields of 99% within 1?h at room temperature. In addition, the catalyst system is effective in catalyzing the reduction of toxic pollutant 4-nitrophenol and the degradation of MO, MB and RhB dyes. Importantly, this catalyst Fe₃O₄@SiO₂-Amp-Rh can be easily recovered by an external magnetic field because of the presence of magnetic core of Fe₃O₄, and the activity of Fe₃O₄@SiO₂-Amp-Rh does not decrease significantly after 7 times’ recycling, which indicates that the catalyst performed high reactivity as well as stability. Graphical abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-021-03688-4

Catalysis Letters
https://doi.org/10.1007/s10562-021-03688-4
Rhodium nanoparticles supported on 2‑(aminomethyl)
phenols‑modifed Fe O spheres as a magnetically recoverable catalyst
3
4
ꢀor reduction oꢀ nitroarenes and the degradation oꢀ dyes in water
Gongshu Wang · Zhangpei Chen · Tian Chen · Kexin Lv · Aikebaier Reheman · Jianshe Hu1
1
1
1
1
2,3
Received: 12 February 2021 / Accepted: 31 May 2021
©
The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021
Abstract
A magnetic nanostructured catalyst (Fe O @SiO -Amp-Rh) modifed with 2-(aminomethyl)phenols (Amp) was designed
3
4
2
and prepared, which is used to catalyze the reduction oꢀ aromatic nitro compounds into corresponding amines and the
degradation oꢀ dyes. The 2-aminomethylphenol motiꢀ plays a vital role in the immobilization oꢀ rhodium nanoparticles to
oꢁer extraordinary stability, which has been characterized by using various techniques, including transmission electron
microscopy (TEM), thermal gravimetric analyzer (TGA), X-Ray Diꢁraction (XRD), and X-ray photoelectron spectroscopy
(
XPS). A variety oꢀ nitroaromatic derivatives have been reduced to the corresponding anilines in water with up to yields
oꢀ 99% within 1 h at room temperature. In addition, the catalyst system is eꢁective in catalyzing the reduction oꢀ toxic pol-
lutant 4-nitrophenol and the degradation oꢀ MO, MB and RhB dyes. Importantly, this catalyst Fe O @SiO -Amp-Rh can
3
4
2
be easily recovered by an external magnetic feld because oꢀ the presence oꢀ magnetic core oꢀ Fe O , and the activity oꢀ
3
4
Fe O @SiO -Amp-Rh does not decrease signifcantly aꢀter 7 times’ recycling, which indicates that the catalyst perꢀormed
3
4
2
high reactivity as well as stability.
Graphical abstract
Keywords 2-(aminomethyl)phenols · Rhodium nanoparticles · Reduction · Nitroarenes · Degradation oꢀ dyes · Magnetic
nanoparticles
1
Introduction
*
*
Aikebaier Reheman
akbarphd@126.com
Aromatic nitro compounds and organic dyes are two more
common organic pollutants in industrial wastewater. It is oꢀ
great importance to convert these pollutants into benefcial
Jianshe Hu
hujs@mail.neu.edu.cn
Extended author inꢀormation available on the last page oꢀ the article
Vol.:(0
1
123456789)
3

G. Wang et al.
or useꢀul products [1–3]. Arylamines are important staring
materials and intermediates to produce a variety oꢀ chemi-
cals. Among the methods ꢀor preparing aromatic ammonia,
reducing nitroaromatics to aromatic amines is one oꢀ the most
commonly used methods [4, 5], thus it is very proftable and
benefcial to convert nitroaromatics into aromatic amines in
the chemical production process. Usually, hydrogen has been
used to reduce nitroaromatic hydrocarbons to the correspond-
ing aromatic amines. However, compared with other reducing
agents, the hydrogen reduction method has many disadvan-
tages, such as more transportation diꢂculties, more storage
requirements, more dangerous in using, etc., is not condu-
cive to industrial applications [6–9]. However, the transꢀer
hydrogenation method has low cost, mild reaction conditions,
and high eꢂciency, and does not need to use hydrogen gas
reaction system and low toxicity [25, 26]. It is possible to
prevent demagnetization and aggregation oꢀ nanoparticles
and achieve graꢀting oꢀ organic molecules by using siloxane
as an anchoring group [27].
Amp compounds have amino and hydroxyl ꢀunctional
groups according to our previous research and could ꢀorm
stable coordination structures with precious metals to pro-
mote various catalytic reactions [28, 38]. We designed a novel
Fe O @SiO nanocatalyst ꢀunctionalized by 2-(aminomethyl)
3
4
2
phenols. Although most non-precious metals [29–31] and pre-
cious metals can be used as the active centers oꢀ nanocatalysts
[32–35], rhodium nanoparticles show the highest catalytic
activity in the reduction reaction oꢀ nitro compounds compar-
ing to other noble metal [36]. Thereꢀore, Rh NPs were cho-
sen to ꢀabricate 2-(aminomethyl)phenols-modifed magnetic
nanocatalyst (Fe O @SiO -Amp-Rh). In conclusion, this novel
[
10]. There are some hydrogen sources commonly used in
3
4
2
the transꢀer hydrogenation method, ꢀor example, NaBH [11],
nanocomposite material was used as an eꢂcient green catalyst
4
.
N H H O [12], borane ammonia [13], ꢀormate [14], hydrosi-
in reduction oꢀ nitroarenes and the degradation oꢀ dyes.
2
4
2
lane [15]. The hydrogen sources mentioned above have many
advantages, ꢀor instance, low price, mild reaction, non-toxicity
and easy operation. Particularly, the sodium borohydride is
one oꢀ the most commonly used hydrogen storage materials,
the available sodium borohydride was utilized as the ideal
hydrogen source because it can slowly release hydrogen in
aqueous solution and is easy to handle [16, 37]. The explo-
ration oꢀ eꢂcient reduction agent oꢀ nitro with easy handle
hydrogen source would be very desirable [17].
2 Experimental
2.1 Chemicals and materials
All starting materials and solvents were obtained ꢀrom com-
mercial sources and can be used without ꢀurther purifcation.
.
Fe O , RhCl 3H O (99%, Rh>39%), NaBH , ethyl orthosil-
3
4
3
2
4
Despite various diꢁerent catalytic systems were reported,
there are still some problems unsettled in this feld. Sepa-
ration and recovery are the central problems that need to
be solved in the application oꢀ homogeneous catalysts in
industrial processes [18, 19]. One way to solve these prob-
lems is to fx the homogeneous catalyst on the insoluble
carrier material [20–22]. This strategy requires support
with a large specifc surꢀace area, which can be achieved by
applying very small particles or porous materials. In many
protocols ꢀor reduction and hydrogenation oꢀ nitroarenes, the
heterogeneous nano-sized catalysts have the high eꢂciency
oꢀ homogeneous catalysts and the advantages oꢀ reusable
heterogeneous catalysts, thus heterogeneous nano-catalysts
have drawn a lot oꢀ attention ꢀrom researchers in recent
years [23, 24]. However, the nano-sized catalyst is prone to
agglomeration during the reaction process, thus resulting the
low reaction eꢂciency, and is also diꢂcult to separate by
conventional centriꢀugal or fltrateion methods and lead eas-
ily to the loss oꢀ catalyst particles. Magnetic nanomaterials
icate (TEOS) and (3-aminopropyl)triethoxysilane (APTES)
were purchased ꢀrom Aladdin Reagent (Beijing, China).
2.2 Preparation of the 2‑(aminomethyl)
phenols‑modiꢀed nanocatalysts
Figure 1 shows the synthesis route and microstructure oꢀ the
Fe O @SiO -Amp-Rh nanocatalyst. The detailed synthesis
3
4
2
steps are described below.
2.2.1 Preparation of Fe O @SiO , Fe O @SiO ‑NH ,
3
4
2
3
4
2
2
and Fe O @SiO ‑Amp
3
4
2
The core–shell magnetic nanoparticles (Fe O @SiO -NH )
3
4
2
2
coated by silica and 2-(aminomethyl)phenols-modiꢀied
magnetic nanoparticles (Fe O @SiO -Amp) were prepared
3
4
2
according to our previously reported method [38].
2.3 Supported process of rhodium nanoparticles
The pre-prepared Fe O @SiO -Amp was ultrasonically
(
MNPs) can be considered as alternative carrier materials to
avoid classical fltration oꢀ tiny particles. Among the diꢁer-
ent classes oꢀ nano-supports, the silica modifed magnetic
nanoparticles(Fe O @SiO ) have attracted a lot oꢀ attention
3
4
2
dispersed in an 80 mL oꢀ ethanol solution. 15.0 mg oꢀ
RhCl ·3H O in ethanol was slowly add into the ethanol solu-
3
4
2
3
2
because oꢀ their advantages, ꢀor instance, easy preparation,
good stability, large specifc surꢀace area, easy modifcation
with various ꢀunctional groups, easy separation ꢀrom the
tion containing Fe O @SiO -Amp under vigorous stirring.
3 4 2
Aꢀter stirring ꢀor 12 h at room temperature, 20 mL oꢀ NaBH
4
(0.1 g) in methanol was mixed with the above solution and
1
3

Rhodium nanoparticles supported on 2‑(aminomethyl)phenols‑modifed Fe O spheres…
3
4
Fig. 1 The preparation oꢀ Fe O @SiO -Amp-Rh nanocatalysts
3
4
2
keep stirring ꢀor 1 h. The fnal product, Fe O @SiO -Amp-Rh
3
4
2
(
0), was washed with water and ethanol and dried in vacuum
at room temperature. Similarly, the Fe O @SiO -NH -Rh
3
4
2
2
was prepared with 500 mg oꢀ Fe O @SiO -NH instead oꢀ
3
4
2
2
Fe O @SiO -Amp.
3
4
2
2.4 Test of catalytic activity
2.4.1 Conversion oꢀ nitroaromatic compounds
into aromatic amines
Nitrobenzene (1 mmol, 123.1 mg), NaBH (2 mmol, 76 mg),
4
H O (3 mL) and catalyst (50 mg) were added to the 50 mL
2
reaction tube. The reaction system was sealed at 25 °C ꢀor 1 h.
The progress oꢀ the reaction was monitored by TLC (moni-
tored by thin layer chromatography). Aꢀter the reaction was
completed, the catalyst was separated with an external magnet
Fig. 2 FT-IR spectra oꢀ Fe O , Fe O @SiO , Fe O @SiO -NH ,
3
4
4
3
4
2
3
4
2
2
and washed with H O and EtOH three times respectively. The
2
Fe O @SiO -Amp and Fe O @SiO -Amp-Rh
3
4
2
3
2
reaction mixture was extracted with ethyl acetate. The com-
bined organic layer was dried over anhydrous sodium sulꢀate,
and concentrated under reduced pressure on a rotary evapora-
tor. The crude product is purifed by column chromatography.
confrmed. The characteristic absorption peak at 570 cm−
1
was attributed to the Fe–O vibration, which confrms the
presence oꢀ Fe O in the core [39]. Fe O @SiO have two
3
4
3
4
2
−
1
2.4.2 Degradation oꢀ dye molecules
characteristic absorption peaks at 1080 and 802 cm , cor-
responding respectively to the antisymmetric stretching
and symmetric stretching ꢀrequencies oꢀ Si–O-Si, which
indicates that the silica shell has been successꢀully coated
on the surꢀace oꢀ the magnetic microspheres [40, 41]. The
2-(aminomethyl)phenol modifed on the surꢀace oꢀ Fe O @
The catalyst Fe O @SiO -Amp-Rh (5 mg) was added into the
3
4
2
dye solution (5.0 mL, 0.1 mmol/L rhodamine B, methylene
blue or 0.2 mmol/L methyl orange) and sodium borohydride
(
5 mg) was put into the solution to start the degradation reac-
3
4
−
1
−1
tion. The reaction process was monitored by UV–vis spectro-
photometer. All dye degradation experiments were perꢀormed
at ambient temperature.
SiO was confrmed by the bands at 1390 cm 1635 cm ,
2
−
1
−1
2927 cm , and 3447 cm , which were related respectively
to the IR absorption oꢀ amine C-N, C=C, alkyl C-H, and
O–H vibration.
The TGA curve oꢀ the prepared nanomaterial is shown in
Fig. 3. When the temperature rises ꢀrom 100 °C to 250 °C,
the mass loss oꢀ Fe O @SiO is 3%, which is mainly caused
3
Results and discussion
3
4
2
3
.1 Characterization of catalyst Fe O @
by the volatilization oꢀ water physically adsorbed on the nan-
3
4
SiO ‑Amp‑Rh
oparticles. According to the TGA curve oꢀ Fe O @SiO ,
2
3
4
2
the mass loss oꢀ Fe O @SiO -NH can be calculated to be
3
4
2
2
As shown in Fig. 2, the structure oꢀ the prepared nanomate-
rial was tested by FT-IR spectroscopy and the structure was
2.7%, which is mainly due to the thermal decomposition
oꢀ the -NH group. In addition, the mass loss oꢀ Fe O @
2
3
4
1
3

G. Wang et al.
SiO -Amp and Fe O @SiO -Amp-Rh is about 7.7%, and the
2
3
4
2
loading amount oꢀ Amp ligand can be calculated to be about
2
%. TGA analysis ꢀurther confrms that the ligand Amp was
successꢀully introduced on the surꢀace oꢀ Fe O @SiO .
3
4
2
Figure 4 shows the SEM, TEM and EDX images oꢀ the
prepared nanocatalyst. Fe O @SiO -Amp-Rh is still uniꢀorm
3
4
2
spherical aꢀter introducing 2-(aminomethyl)phenol deriva-
tives and rhodium nanoparticles. The TEM image shows that
the Fe O @SiO -Amp-Rh nanomaterial is a regular spheri-
3
4
2
cal shape with an average diameter oꢀ 180 nm. The interꢀace
between the Fe O core and the SiO layer is clear, and the
3
4
2
thickness oꢀ the SiO layer is about 27 nm. In addition, rho-
2
dium nanoparticles (mainly 2.5 nm) are uniꢀormly anchored
on the surꢀace oꢀ the silica shell. As shown in Fig. 4, the
EDX analysis confrms the presence oꢀ the elements Si, O,
C, N, Fe and Rh in the nanomaterials. In addition, SEM
mapping diagrams oꢀ Fe, Si, C, N, Rh and the combined
composition diagrams proves that rhodium NPs were uni-
Fig. 4 SEM, TEM and EDX images oꢀ Fe O @SiO -Amp-Rh and
3
4
2
elemental maps oꢀ Fe, Si, C, N and Rh atoms
ꢀ
ormly dispersed on the surꢀace oꢀ Fe O @SiO -Amp.
3 4 2
The Fig. 5 shows the XRD patterns oꢀ Fe O @SiO -Amp-
3
4
2
Rh, JCPDS fles oꢀ Fe O (PDF#72–2303), SiO (PDF#89-
oꢀ Fe O @SiO -Amp-Rh because oꢀ very small loading oꢀ
3 4 2
3
4
2
0
735) and rhodium (PDF#87-0714). As shown in Fig. 5, it
rhodium nanoparticles on the surꢀace oꢀ Fe O @SiO -Amp.
3 4 2
can be confrmed that the magnetic characteristics oꢀ the
nanomaterials was not aꢁected during the silica modifca-
tion, amino ꢀunctionalization, Amp graꢀting and Rh loading
by comparing the XRD pattern oꢀ Fe O @SiO -Amp-Rh
X-ray photoelectron spectroscopy (XPS) was carried out
to identiꢀy surꢀace composition and oxidation state oꢀ cata-
lytic activity site (Fig. 6). The bands at the binding energy oꢀ
311.2 and 306.6 eV belongs to Rh3d and Rh3d respec-
3
4
2
5/2
3/2
with the standard XRD pattern oꢀ Fe O . In addition, no
tively, confrming the zero valency oꢀ bulk Rh. As shown in
the fgure, XPS results show that the zero valence state oꢀ
rhodium does not change beꢀore and aꢀter the reaction[43]
3
4
characteristic peaks oꢀ silica were observed in the XRD
pattern oꢀ Fe O @SiO -Amp-Rh compared to the stand-
3
4
2
ard silica XRD pattern, which may indicate that the silica
shell layer modifed on the surꢀace oꢀ the core is amorphous
silica [42]. Unꢀortunately, it is diꢂcult to observe the char-
acteristic absorption peaks oꢀ rhodium in the XRD spectra
3.2 Optimization of reaction conditions
The reduction oꢀ nitrobenzene to nitroaniline was used as
the model reaction to evaluate the activity oꢀ the Fe O @
3
4
Fig. 3 TGA curves oꢀ Fe O @SiO , Fe O @SiO -NH , Fe O @
3
2
4
2
3
4
2
2
3
4
SiO -Amp and Fe O @SiO -Amp-Rh
Fig. 5 XRD patterns oꢀ Fe O @SiO -Amp-Rh
3 4 2
2
3
4
1
3

Rhodium nanoparticles supported on 2‑(aminomethyl)phenols‑modifed Fe O spheres…
3
4
Fig. 6 a Full survey XPS spectra; b C1s, c Rh 3d oꢀ Fe O @SiO -Amp-Rh (i) beꢀore and (ii) aꢀter reaction
3
4
2
SiO -Amp-Rh nano catalyst. As shown in Table 1(entries
sodium borohydride (2 mmol), H O (3 mL) and Fe O @
2 3 4
2
1
–5), the reaction cannot be carried out when there is no
SiO -Amp-Rh (50 mg) reacted at ambient temperature ꢀor
2
load oꢀ Rh nanoparticles on the carriers. To our delighted,
when Fe O @SiO -Amp-Rh was used as the catalyst ꢀor
1 h.
3
4
2
this reaction, the yield oꢀ the product nitroaniline reached
3.3 Investigation of the applicability and stability
9
0% at ambient temperature ꢀor 30 min. (entry 6). In addi-
of catalyst Fe O @SiO ‑Amp‑Rh
3
4
2
tion, the yield oꢀ the product also increased ꢀrom 70 to 99%
by increasing the amount oꢀ catalyst ꢀrom 20 to 50 mg, and
all the reaction was completed within 1 h (entries 7–10).
Finally, we also investigated the eꢁect oꢀ diꢁerent solvents
and hydrogen sources on the reduction oꢀ nitrobenzene to
aniline (entries 11–12). The results indicated that the opti-
mal reaction conditions were that nitrobenzene (1 mmol),
Under the optimal reaction conditions, the catalytic per-
ꢀormance oꢀ catalyst Fe O @SiO -Amp-Rh (Table 1
3
4
2
entry 9) was detected through reduction reaction oꢀ vari-
ous nitroaromatic substrates (Table 2). To our delight, all
tested nitroaromatics were converted to the corresponding
aromatic amine compounds with excellent yields in the
presence oꢀ the catalyst Fe O @SiO -Amp-Rh. Since most
3
4
2
a
Table 1 Optimization oꢀ reaction conditions oꢀ catalyst Fe O @SiO -Amp-Rh
3
4
2
Entry
Catalyst/mg
Hydrogen source
Time/h
Solvent/mL
Yield/%b
1
2
3
4
5
6
7
8
9
–
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
2
2
2
2
0.5
1
1
1
1
H O
0
0
0
2
Fe O (50)
Fe O @SiO (50)
Fe O @SiO -Amp50)
Fe O @SiO -Amp-Rh(50)
Fe O @SiO -Amp-Rh(20)
Fe O @SiO -Amp-Rh(30)
Fe O @SiO -Amp-Rh(40)
Fe O @SiO -Amp-Rh(50)
H O
3
4
2
H O
3
4
2
2
H O
0
3
4
2
2
H O
90
70
88
90
99
98
85
3
4
2
2
H O
3
4
2
2
H O
3
4
2
2
H O
3
4
2
2
H O
3
4
2
2
10
1
Fe O @SiO -Amp-Rh(50)
Fe O @SiO -Amp-Rh(50)
NaBH
1
1
CH OH
3
4
2
4
3
c
.
1
N H H O
H O
3
4
2
2
4
2
2
a
Reaction conditions: nitrobenzene 1 mmol; Sodium borohydride 2 mmol; solvent 3 mL; ambient temperature
Isolated yield
Reaction temperature: 80 °C
b
c
1
3

G. Wang et al.
oꢀ the aromatic ammonia compounds have low solubility
in water, so they can be separated ꢀrom the reaction system
by recrystallization aꢀter the reaction was completed, and
greatly saves the cost oꢀ the purifcation process. In addi-
tion, the carbonyl group contained in p-nitroacetone can
be reduced to corresponding alcohol by prolonging the
reaction time to 2 h and increasing the amount oꢀ sodium
borohydride (Table 2 entry 9). The results show that the
reactions can be carried out smoothly either there is an
electron donor (methyl methoxide) or an electron acceptor
3.4 Reaction kinetics study of Fe O @
3 4
SiO ‑Amp‑Rh catalyst
2
Take the reduction reaction oꢀ p-nitrophenol to p-ami-
nophenol as an example to probe the catalytic activity
oꢀ Fe O @SiO -Amp-Rh with NaBH as reducing agent.
3
4
2
4
For the reduction oꢀ p-nitrophenol, aqueous solutions
oꢀ p-nitrophenol (5 mL, 1000 ppm) and NaBH (10 mg)
4
and Fe O @SiO -Amp-Rh catalyst (3 mg, 6 mg, 10 mg)
3
4
2
were put into a ꢃask, the spectra were recorded in UV–vis
(
carboxyl) group on the benzene ring.
spectrophotometer with the wavelength oꢀ 200–600 nm
a
Table 2 Catalytic reduction oꢀ nitroarenes with Fe O @SiO -Amp-Rh under optimized conditions
3
4
2
Entry
1
Product
Yield/%
99
Entry
8
Product
Yield/%b
97
2
3
4
99
99
98
9
10
11
99
99
98
5
98
98
12
13
99
99
c6
c7
98
14
99
a
Reaction conditions: nitrobenzene 1 mmol; Sodium borohydride 2 mmol; solvent 3 mL; Fe O @SiO -Amp-Rh 50 mg; ambient temperature
Isolated yield
Reaction solvent: methanol
3
4
2
b
c
1
3

Rhodium nanoparticles supported on 2‑(aminomethyl)phenols‑modifed Fe O spheres…
3
4
range. Figure 7(a) shows the UV–Vis reduction spectrum
oꢀ p-nitrophenol to p-aminophenol as time goes on under
the above conditions. The characteristic absorption peak
3.5 Degradation of dye molecules
In order to ꢀurther expand the application range oꢀ the
designed Fe O @SiO -Amp-Rh catalyst, we also tested the
oꢀ p-nitrophenol shiꢀted ꢀrom 315 to 400 nm when NaBH
4
3
4
2
was added and stirred ꢀor 1 min. The decrease oꢀ absorp-
tion in the peak at 400 nm was attributed to the decrease oꢀ
p-NA in the amount as time extends, while the appearance
oꢀ the peak at 300 nm was due to the ꢀormation oꢀ p-ami-
nophenol as the reaction progressing [44]. These results
are consistent with literature reports, and the appearance
oꢀ the peak at 300 nm was due to the ꢀormation oꢀ p-ami-
nophenol [45, 46]. Prolong the reaction until the absorb-
ance at 400 nm became stable and fnally the reduction
oꢀ p-nitrophenol was completed within 240 s. As shown
in Fig. 7(a), the color change oꢀ the reaction system ꢀrom
bright yellow to colorless was also an indication ꢀor the
completion oꢀ p-nitrophenol reduction.
degradation perꢀormance oꢀ the catalyst on diꢁerent organic
dyes namely methyl orange (MO), methylene blue (MB) and
rhodamine B (RhB). All the degradation reactions oꢀ the
dyes were carried out at ambient temperature, and the pro-
gress oꢀ the reaction was monitored on the UV–Vis spectro-
photometer. The aqueous solutions oꢀ MO, MB and Rh B
show the maximum absorption respectively at λ 465, 663
max
and 554 nm band (Fig. 8). The catalyst Fe O @SiO -Amp-
3
4
2
Rh was able to degrade methyl orange and methylene blue
molecules immediately (Fig. 8b, c), but it is 4 min ꢀor Rho-
damine B to degrade (Fig. 8a). In the presence oꢀ Fe O @
3
4
SiO -Amp-Rh, the degradation time oꢀ the dyes except rho-
2
damine B was very shorter, indicating the potential use oꢀ
In Eq. 1, C is the concentration values oꢀ p-NA at any
Fe O @SiO -Amp-Rh in degrading organic pollutants in
t
3
4
2
time during the reaction, C is the concentration values at
water. Early studies have confrmed that the catalytic degra-
o
the beginning oꢀ the reaction. According to Eq. (1), the
relationship between ln (Ct/Co) and the reduction time oꢀ
p-nitrophenol under diꢁerent amounts oꢀ catalyst is shown
in Fig. 7c.
dation oꢀ azo dyes in the presence oꢀ NaBH was attributed
4
to the cleavage oꢀ the azo bond and the hydrogenation oꢀ the
azo group. Thereꢀore, according to reports, the degradation
oꢀ MO, MB and Rh B may also be related to the catalytic
cleavage oꢀ the azo (N=N) group in the dye structure [47].
When the catalyst dosage was decreased ꢀrom 10 to
–
2
3
1
mg, the value k was decreased ꢀrom 6.17 × 10 /s to
–
2
.87 × 10 /s, and the reaction completion time increased
3.6 The comparison with reported methods
ꢀ
rom 90 to 240 s oꢀ p-nitrophenol reduction,
ꢀ
ꢁ
We compared catalytic properties oꢀ our catalyst with the
previously reported catalyst to prove the advantages oꢀ our
catalyst Fe O @SiO -Amp-Rh ꢀor the reduction oꢀ p-nitro-
Ln C ∕C = k t
t
(1)
o
3
4
2
As can be seen in Fig. 7b, c, the value oꢀ ln (C /C )
t
o
phenol (Table 3 entries 1–6) and the degradation oꢀ dyes
decreases as the reaction proceeds due to the decrease oꢀ the
eꢁective concentration oꢀ reactants. Thereꢀore, the reaction
proved to be pseudo frst order reaction, since the reaction
rate depends on the available p-nitrophenol concentration.
(
Table 3 entries 7–13) Experiments show that our catalysts
had less raw material consumption, less time consumption
and a higher yield compared to other catalysts used here. the
advantages oꢀ our designed method can be summarized as
ꢀ
ollows in detail: (1) Use green, cheap, and easily available
water as solvent: (2) High reaction eꢂciency and short time
3) No need ꢀor excessive sodium borohydride as reducing
(
Fig. 7 The UV spectra and kinetic curves oꢀ the reduction oꢀ 4-NP to 4-AP using Fe O @SiO -Amp-Rh nanocatalyst
3
4
2
1
3

G. Wang et al.
Fig. 8 UV–vis spectra oꢀ a Rh B, b MB and c MO and the degradation products
agent, saves costs and does not cause secondary pollution;
nano-catalyst have excellent stability. In order to demon-
strate the vital role oꢀ Amp modifed on the catalyst, a com-
parative experiment was conducted with Fe O @SiO -NH -
(
3) The catalyst modifed by 2-(aminomethyl)phenol has
good stability and can be recycled and reused ꢀor many
times.
3
4
2
2
Rh as the catalyst. In Fig. 9, an obvious decline in catalytic
eꢂciency could be observed with Fe O @SiO -NH -Rh as
3
4
2
2
3
.7 Stability and recoverability test of catalyst
catalyst to react under the same conditions with the num-
ber oꢀ reactions goes up. The deactivation may be mainly
ascribed to the leaching oꢀ active-site oꢀ Rh NPs [5].
Fe O @SiO ‑Amp‑Rh
3
4
2
In order to study the stability and recyclability oꢀ the cata-
lyst, the Fe O @SiO -Amp-Rh nano-catalyst was continu-
3
4
2
ously used ꢀor catalytic reduction oꢀ nitrobenzene under
the optimal reaction conditions. Aꢀter the reaction is com-
pleted, the catalyst was separated ꢀrom the reaction system
by an external magnetic feld, and the recovered catalyst
was immediately used in the next reaction without any treat-
ment. The activity oꢀ the catalyst Fe O @SiO -Amp-Rh was
4 Conclusions
In summary, we developed a magnetically recyclable 2-(ami-
nomethyl)phenol-modifed nanocatalyst Fe O @SiO -Amp-
3
4
2
Rh, and carried on a series oꢀ characteristics to its structure.
We used a simple method to synthesize silica-coated 2-(ami-
nomethyl)phenol-modifed magnetic nanomaterials, and suc-
cessꢀully loaded Rh NPs onto the surꢀace oꢀ the magnetic
nanomaterials. The developed catalyst shows high eꢂciency
in catalytic hydrogenation reduction oꢀ nitro compounds (the
3
4
2
repeatedly used in the nitrobenzene reduction reaction ꢀor 7
times, and the activity oꢀ the catalyst did not decrease sig-
nifcantly, and the yield oꢀ the product nitroaniline was still
reach to 95%, which indicated the Fe O @SiO -Amp-Rh
3
4
2
Table 3 Comparison with the
Entry Substrate Catalyst
Eq
Solvent
Time
Yield Reꢀ
previous catalyst
1
2
3
4
5
6
7
8
4-NP
4-NP
4-NP
4-NP
4-NP
4-NP
MO
Ag-PNA-BIS-2
6.0
H O
9 h
3 h
100 min
90
99
99
95
98
99
–
[37]
[5]
[6]
[35]
[36]
This work
[48]
2
Fe O @SiO -NH -RhNPs 4.0
H O
3
4
2
2
2
Fe O @C-Rh
excess
5.0
4.0
H O
3
4
2
CuNP@PLA-TiO2
Ni@PVAm@SBA-15
Our catalyst
MeOH/H O 0.5 h
2
H O
85 min
1 h
2
2.0
H O
2
DLP-AuNPs
NaBH4 H O
NaBH4 H O
8 min
1 min/
2
MO/MB PdNPs@CS-MMWCNT
–
[49]
2
instantly
9
1
1
1
MO
MO
MB
MB
CDs/Znln S microspheres NaBH4 H O
40 min
15 s
40 s
–
–
–
–
[50]
This work
[51]
2
4
2
0
1
2
Our catalyst
Bentonite/CuNPs
Our catalyst
NaBH4 H O
2
NaBH4 H O
2
NaBH4 H O
15 s
This work
2
1
3

Rhodium nanoparticles supported on 2‑(aminomethyl)phenols‑modifed Fe O spheres…
3
4
9
.
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yield is as high as 99% within 1 h at room temperature),
and the reaction uses easily treatable sodium borohydride
as a hydrogen source to convert various nitroaromatics into
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in a very short time in the presence oꢀ NaBH , and show
4
excellent catalytic activity ꢀor many dyes (MO, MB, Rh B).
Notably, the superparamagnetism oꢀ magnetic nanomateri-
als makes the catalyst easy to separate ꢀrom the reaction
system. In addition, this catalyst shows excellent stability
and catalytic activity in the cycle experiment and it also ꢀul-
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Acknowledgements This work was supported by the National Natu-
ral Science Foundation oꢀ China (21702026, 21861040), Fundamental
Research Funds ꢀor the Central Universities (N2005004, N2105005),
and Scientifc Research Fund project oꢀ Ningde Normal University
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Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional aꢂliations.
Authors and Aꢀliations
Gongshu Wang · Zhangpei Chen · Tian Chen · Kexin Lv · Aikebaier Reheman · Jianshe Hu1
1
1
1
1
2,3
1
2
3
Center ꢀor Molecular Science and Engineering, College
oꢀ Science, Northeastern University, Shenyang 110819,
People’s Republic oꢀ China
Fujian Province University Engineering Research Center
oꢀ Mindong She Medicine, Medical College, Ningde Normal
University, Ningde 352100, Fujian, China
Key Laboratory oꢀ Toxicology, Medical College, Ningde
Normal University, Ningde 352100, China
1
3