Ag nanoparticle immobilized on functionalized magnetic hydrotalcite (Fe3O4/HT-SH-Ag) for clean oxidation of alcohols with TBHP

Article abstract of DOI:10.1016/j.inoche.2020.108081

Hydrotalcite (HT) modified with magnetic nanoparticle and thiol groups for the immobilization of silver to the preparation of Fe₃O₄/HT-SH-Ag was used. The catalyst was completely characterized using XRD, ICP, SEM, EDS, VSM, FT-IR, and TEM analyzes. The Fe₃O₄/HT-SH-Ag catalyst is useful in oxidizing of primary and secondary aliphatic and benzyl alcohols to the relevant carbonyl products (aldehyde/ketone). To demonstrate the effect of Ag over the reaction, Fe₃O₄/HT-SH catalyst performance, and also some other control tests were studied. For this purpose, the model reaction was carried out in the presence of AgNO₃, HT (I), and Fe₃O₄/HT (II), and low yield was obtained (20–50%). High to good efficiency were obtained for all entries, whether benzaldehyde derivatives, in short times. The catalyst can be reused for several continuous runs with a simple external magnet without losing significant reactivity.

Full text of DOI:10.1016/j.inoche.2020.108081

Journal Pre-proofs
Ag nanoparticle immobilized on functionalized magnetic hydrotalcite
(
Fe O /HT-SH-Ag) for clean oxidation of alcohols with TBHP
3
4
Mehri Salimi, Azadeh Zamanpour
PII:
S1387-7003(20)30671-7
DOI:
https://doi.org/10.1016/j.inoche.2020.108081
INOCHE 108081
Reference:
To appear in:
Inorganic Chemistry Communications
Received Date:
Revised Date:
Accepted Date:
6 June 2020
23 June 2020
28 June 2020
Please cite this article as: M. Salimi, A. Zamanpour, Ag nanoparticle immobilized on functionalized magnetic
hydrotalcite (Fe O /HT-SH-Ag) for clean oxidation of alcohols with TBHP, Inorganic Chemistry
3
4
Communications (2020), doi: https://doi.org/10.1016/j.inoche.2020.108081
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Ag nanoparticle immobilized on functionalized magnetic hydrotalcite
Fe O /HT-SH-Ag) for clean oxidation of alcohols with TBHP
(
3
4
Mehri Salimi*, Azadeh Zamanpour
Department of Chemistry, Faculty of Science, University of Birjand, P. O. Box 97175-615,
Birjand, Iran
*
Correspondence to: msalimi@birjand.ac.ir, m_salimi4816@yahoo.com
ORCID: 0000-0003-1755-7297
Abstract:
Hydrotalcite (HT) modified with magnetic nanoparticle and thiol groups for the immobilization
of silver to the preparation of Fe O /HT-SH-Ag was used. The catalyst was completely
3
4
characterized using XRD, ICP, SEM, EDS, VSM, FT-IR, and TEM analyzes. The Fe O /HT-
3
4
SH-Ag catalyst is useful in oxidizing of primary and secondary aliphatic and benzyl alcohols
to the relevant carbonyl products (aldehyde/ketone). To demonstrate the effect of Ag over the
reaction, Fe O /HT-SH catalyst performance, and also some other control tests were studied.
3
4
For this purpose, the model reaction was carried out in the presence of AgNO , HT (I), and
3
Fe O /HT (II), and low yield was obtained (20-50%). High to good efficiency were obtained
3
4
for all entries, whether benzaldehyde derivatives, in short times. The catalyst can be reused for
several continuous runs with a simple external magnet without losing significant reactivity.
Keywords: Oxidation of alcohol, TBHP, hydrotalcite, Fe O /HT-SH-Ag
3
4

1
. Introduction
Oxidation reactions catalyzed transition metal complexes are of paramount importance in
recent decades [1]. The presence of these active sites are abundant homogeneous transition
metal complex catalysts improve their performance, but this complex separation from the
reaction mixture is difficult without doubt [2]. Therefore heterogenization via immobilization
of transition metal complex onto solid supports to produce a powerful catalyst.
In the last several decades, similar to hydrotalcite compounds (HT) and magnetic hydrotalcite
(MHTs) have numerous applications, particularly as catalyst forerunner for the
transesterification and as catalysts used for the aldol condensation [3]. The hydrotalcite (HT)
has also been proven as efficient support for a wide variety of reactions like oxidation reaction
[4], the reduction chemoselective [5], and dehydrogenation [6], because it shows a basic site
surface tunable and uniform deposition of the active metal onto the surface
Therefore, the combination of magnetic nanoparticle (MNP) in the structure of hydrotalcite [7]
provides simple separation of the catalyst in the reaction medium with the modest magnetic in
addition to preventing MNP aggregation, too. To achieve specific goals, metal nanocomposites
can be utilized on a large scale. Nanocomposites based on silver have broad applications in
various fields like food packaging [8], biosensor [9], and wooden wardrobe [10]. Lately, based
on magnetic nanocomposite, silver nanoparticles have been reported as a catalyst and are
utilized in the oxidation reaction [11].
Amongst the organic transformation achieved with heterogeneous catalysis, the selective
oxidation reaction is widely utilized in synthetic organic chemistry [12–14]. The catalytic
oxidation of alcohols has gained considerable attention from an industrial and academic point
of view [15]. Carbonyl compounds like ketone and aldehyde derivatives act as important
intermediates and precursors in the agrochemical, cosmetics, pharmaceutical, biofuels,
insecticides, and confectionery, flame-retardants, and fragrances industries [16]. The oxidation

of alcohol to carbonyls requires not only costly, polluting, and toxic oxidants, for example
hypochlorite chromate, or permanganate, etc.) and difficult reaction circumstances, but also
(
produce significant amounts of pollutants and poisonous waste [17]. Newly, numerous efforts
have given to developing more eco-friendly procedures by utilizing cleaner oxidants to
minimizing the deficiencies of traditional oxidation methods [18,19]. For environmental
concerns and economics, the development of green oxidants has attracted much important
consideration.
In continuance of our ongoing project, with the aim of selective oxidation of primary and
secondary alcohols and their importance and given all of the reasons mentioned above (mainly
the environmentally good character of magnetic hydrotalcite) and silver nanoparticles, it
encouraged us to the preparation of Fe O /HT/SH/Ag to produce aldehydes and ketones. To
3
4
improve the separation of the catalyst, magnetic support was used to immobilize the Ag
nanoparticle (Scheme 1).
Scheme 1. Oxidation of alcohols with Fe O /HT-SH-Ag
3
4

2
2
. Experimental:
.1. General
All solvents and chemical reagents were purchased from Sigma-Aldrich and Merck companies
and were utilized as received without additional purification. Determinations of purity of the
products were performed by thin-layer chromatography on the silica gel plate’s polygram STL
G/UV 254. The FTIR spectrum was reported on KBr pressed pellet utilizing a spectrometer
-1
FTIR Nicolet 800 at room temperature (approximately 400-4000 cm ). All results related to
the product isolated purification afterward with recrystallization or thin-layer chromatography.
2
.2. HT synthesis (I)
Mg(NO ).6H O (40 mmol, 10.25 g) and Al(NO ) .9H O (20 mmol, 7.5 g) dissolved in water
3
2
3 3
2
(
60 mL) followed by dropwise addition of NaHCO (25 mmol, 2.1 g), and NaOH (100 mmol,
3
o
4
g) by heating at 60 C for 24 hours underwent vigorous magnetic stirring.
After this period, the acquired product (white solid) was separated by filtered and washed with
deionized (DI) water (pH=7). The Mg-Al hydrotalcite (I) obtained (molar ratio Mg/Al =2) was
o
dried for 12 hours at 80 C.
2
.3. Fe O /HT synthesis
3 4
In a 500 mL 3-necked flask, the inert atmosphere was retained via a continuous flow of argon
and a dropping funnel, a combination of FeCl (5.2 mmol, 1.05 g) and FeCl (8 mmol, 2.1 g)
2
3
was dissolved in deionized (DI) water (100 mL). At that time, the resultant mixture was stirred
o
mechanically under the argon atmosphere at 80 C for 10 min. After that, 4 grams of
hydrotalcite (I) and NaOH (100 mL, 5%) were added to the solution simultaneously. The
o
resultant brown mixture was stirred for 24 hours at 80 C. Eventually, the mixture was allowed
to cool to room temperature, and then Fe O /HT was separated magnetically using an external
3
4

magnetic field, washed several times with deionized (DI) water to reach pH=7. Consequently,
o
Fe O @HT (II) was dried overnight in a vacuum oven at 50 C.
3
4
2
.4. Fe O /HT-SH (III) synthesis
3 4
In the following, 1 gram of Fe O /HT was dispersed ultrasonically in 50 mL of dry toluene for
3
4
3
0 min. Then 3.5 mL (18.5 mmol) of (3-Mercaptopropyl)trimethoxysilane (MPTMS) was
added dropwise to the corresponding mixture and was refluxed for 48 hours. Afterward, the
resultant Fe O /HT-SH (III) was then separated using an external applied magnetic field and
3
4
o
washing with dry toluene (each 3 × 10 mL) and dried for 16 hours at 25 C.
2
.5. Fe O /HT-SH-Ag nanoparticles (IV) synthesis
3 4
1
.0 gram of Fe O /HT-SH-Ag was dispersed ultrasonically in 20 mL of deionized (DI) water
3 4
for 30 min at room temperature. Then 3.4 grams (20 mmol) of AgNO in 20 mL of deionized
3
o
(
DI) water was added to the mixture underwent stirred vigorously at 60 C. Later, the solution
of 0.02 g (20 mmol) of sodium borohydride in 20 mL of deionized (DI) water was added to the
o
corresponding reaction under stirred at 60 C for 10 h. Finally, Fe O /HT-SH-Ag (IV) was
3
4
separated by an external magnetic field, washed via deionized water (each 2 × 50 mL), and
o
then dried into the oven (50 C) for 12 hours.
2
.6. General procedure for the oxidation of benzyl alcohols:
Fe O /HT-SH-Ag (0.007 g, 4.0 mol%) was added to mixture of benzyl alcohol and TBHP (0.5
3
4
o
mmol) in EtOH (0.5 mL) at 65 C. The reaction process was monitored via TLC. In the end,
the Fe O /HT-SH-Ag was removed using an external magnetic field after reaction completion,
3
4
washed via EtOH, dried, and reused for several consecutive runs. The resultant product was
purified using plate chromatography by EtOAc/n-hexane (3:10) solvent mixture.
Selected spectral data:

1
2
7
1
-chlorobenzaldehyde (Compound 2, Table 3): H-NMR (CDCl , 300 MHz)  (ppm): 7.295-
3
1
3
.959 (m, 4H, Ph), 10.507 (s, 1H). C-NMR (CDCl , 300 MHz)  (ppm): 189.818 (C=O),
3
37.957 (C), 135.145 (CH), 132.476 (C), 130.625 (CH), 129.389 (CH), 127.313 (CH).
1
4
6
3
-hydroxybenzaldehyde (Compound 4, Table 3): H-NMR (CDCl , 300 MHz)  (ppm):
3
1
3
.944-6.972 (2H, Ph), 7.749-7.778 (2H, Ph), 9.789 (1H), 10.616 (1H, OH). C-NMR (CDCl ,
3
00 MHz)  (ppm): 191.247 (C=O), 163.814 (C), 132.534 (CH), 128.897 (C), 116.309 (CH).
1
4
-methylbenzaldehyde (Compound 6, Table 3): H-NMR (CDCl , 300 MHz) d (ppm): 2.435
3
1
3
(
s, 3H, CH ), 7.318-7.344 (d, 2H, Ph), 7.768-7.795 (d, 2H, Ph), 9.962 (s, 1H). C-NMR
3
(
CDCl , 300 MHz) d (ppm): 192.001 (C=O), 145.557 (C), 134.206 (CH), 129.844 (CH),
3
1
29.722 (CH), 21.855 (CH3).
3
. Results and discussion:
HT was effortlessly prepared with the co-precipitation procedure. For the preparation of
Fe O /HT (II), HT (I) was used through an alkaline mixed salt-solution of Fe and Fe3+.
2
+
3
4
Subsequently, the surface of Fe O /HT has been modified with (3-Mercaptopropyl)
3
4
trimethoxysilane (MPTMS) to obtain Fe O /HT-SH (III). Finally, Fe O /HT-SH-Ag (IV) was
3
4
3
4
prepared by the immobilization of Ag onto Fe O /HT-SH (III) in EtOH (Scheme 2).
3
4

Scheme 2. Preparation of catalyst (Fe O /HT-SH-Ag )
3
4
The catalyst was characterized by utilizing a variety of instrumental analyses like X-ray powder
diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform
infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), vibrating sample
magnetometer (VSM), thermogravimetric analysis (TGA), inductively coupled optical
emission spectroscopy (ICP-OES), energy-dispersive X-ray (EDX), and CHNS analysis.
The FTIR spectra of HT (I), Fe O /HT (II), Fe O /HT-SH (III), and Fe O /HT-SH-Ag (IV) are
3
4
3
4
3
4
-1
represented in Figure 1(a-d). The existence of a strong-broad peak at 3473 cm indicates
symmetric OH stretching vibration of Al-OH and Mg-OH onto the hydrotalcite surface (Figure
-1
1
a). Besides, vibration absorption at 1637 cm shows the stretching vibrations associated with
the water molecules in the hydrotalcite structure. Meantime, the presence of peaks at 1372, 671
-1
cm indicates the C-O asymmetric stretching vibration mode (representative the attendance of

CO ) and the bending frequency of CO 32 ― , respectively. This demonstration that the CO 23 ―
2
―
3
-1
is existing between hydrotalcite layers [7]. At 1366 cm , peak intensity decreased in the
Fe O /HT (II) compared with HT, indicating that the HT (I) was magnetized by the Fe O [20].
3
4
3
4
-1
Likewise, the broad absorption of approximately 565-789 cm shows the stretching vibration
associated with Fe-O, which was covered with Mg-O and Al-O bonds (Figure 1b). Figure 1c,
shows two new absorption bands have confirmed the FT-IR of Fe O /HT-(CH ) SH (III),
3
4
2 3
functionalization with (3-mercaptopropyl)trimethoxysilane (MPTMS) onto the surface of
-1
Fe O /HT (II) at 2851, and 2931 cm (relating to the stretching vibration of C-퐻
(푆푃3)
). As
3
4
-1
shown in Figure 1c, the presence of peak around 1000-1250 cm indicates Si-O-H and Si-O-
-1
Si bonds, and as well as –SH vibration is as well as seen in the 2500 cm region as a weak
peak.
Figure 1. FT-IR spectra of HT (a), Fe O /HT(b) and Fe O /HT-SH (c) Fe O /HT-SH-Ag (d),
3
4
3
4
3
4

The crystal structure of catalysts was examined by X-ray diffraction analysis. The XRD
patterns of HT (I), Fe O /HT (II), and Fe O /HT-SH-Ag (IV) have been shown in Figure 2 (a-
3
4
3
4
c). The peaks appearing in the diffraction pattern of hydrotalcite (HT) nanoparticles at 2 =
1.21, 22.61, 34.51, 38.01, 45.71, 60.31, and 61.51, respectively, belong to plates (003),
006), (012), (015), (018), (110), and (113) respectively [21]. The attendance of new peaks at
 = 30.36, 35.76, 43.47, 57.51, and 63.11 matched well with indices (220), (311), (400),
511), and (440), that were fully consistent with the existence of the magnetic Fe O in the HT
1
(
2
(
(
3
4
I) structure [20]. The four peaks appearing in 2 = 38.116, 44.3, 64.445, and 77.339 were
corresponding to (111), (200), (220), and (311) indices. The pattern was fully in agreement
with the Ag nanoparticle in the HT structure (refer. Code: 03-065-2871) [22–24]. The average
size of the catalyst was calculated using the Debye-Scherrer’s equations:
d = 0.9  /  cos 
Where  is the source wavelength (for Cu K = 0.154 nm),  is the width of the XRD peak at
half maximum height, and  is the Bergg diffraction angle Therefore, the particle size of
Fe O /HT-SH-Ag was calculated as 27 nm.
3
4

Figure 2. The XRD patterns of (a) HT (I), (b) Fe O /HT (II) and (c) Fe O /HT- SH-Ag
3
4
3
4
The morphology of Fe O /HT-SH-Ag (IV) was studied by the FE-SEM method (Figure 3).
3
4
According to Figure 3, the as-synthesis HT (I) reveals irregular plate-like morphology,
demonstrating the properties of layered materials.

Figure 3. SEM images of Fe O /HT-SH-Ag(IV)
3
4
Moreover, the EDS analysis proved Mg, Al, C, O, S, Fe, and Ag elements in the catalyst
structure (Figure 4). Also, great intensity Ag showed doping successfully and coordination of
Ag onto Fe O /HT-SH (III). The important point is no impurity elements were observed in the
3
4
catalyst structure.
Figure 4. The EDS analysis of Fe O /HT-SH-Ag (IV)
3
4
Likewise, TEM analysis was performed to get information about the morphology and structure
of Fe O /HT-SH-Ag (IV). As revealed in Figure 1S, HT (I) is plate-like in shape with the
3
4
nonuniformly entrapped Fe O nanoparticles in its matrix. Moreover, a distribution histogram
3
4

of Fe O /HT-SH-Ag (IV) showed that the average diameter of the catalyst is 13-25 nm (see
3
4
supporting information, Figure 2S).
Figure 3S illustrates the study of the magnetic behavior of Fe O /HT (II) and Fe O /HT-SH-
3
4
3
4
Ag (IV) using VSM analysis. The saturation magnetization of Fe O /HT (II) and Fe O /HT-
3
4
3
4
-1
SH-Ag (IV) catalysts are 18.837 and 12.715 emu.g , respectively (see supporting information,
Figure 3Sa,b). The magnetization decrease of 6.122 emu.g-1 shows the successful
functionalization of Fe O /HT with (3-mercaptopropyl) trimethoxysilane (MPTMS) and Ag
3
4
(see supporting information, Figure 3Sa,b). Despite this significant reduction, the nanoparticles
were effortlessly separated from the reaction environment with a simple external magnetic
field.
Besides, the ICP analysis revealed that 183.43 mg equal 1.7 mmol of Ag was anchored on 1
gram of the catalyst.
Catalytic studies:
The catalytic activity of Fe O /HT-SH-Ag (IV) was examined in the oxidation of alcohols. All
3
4
oxidation reactions of data are presented in Table 1. In the early stages of the study, 4-
chlorobenzyl alcohol (4-Cl BzOH) was selected as a model substrate to obtained optimum
circumstances for the oxidation of alcohol to relevant aldehyde. The reaction was done in the
absence of Fe O /HT-SH-Ag (IV) and the attendance of the tert-butyl hydroperoxide (TBHP)
3
4
o
in EtOH as a green solvent at 65 C (Table 1, entry 1). It was turned out that the corresponding
product was not produced even after a long time (120 min). The fundamental role of Fe O /HT-
3
4
SH-Ag was highlighted in the oxidation of alcohols (ROH), when in a set of tests, the model
reaction was carried out in the presence of AgNO , HT (I), Fe O /HT (II) (Table 1, entries 2-
3
3
4
4
).
According to Table 1, Fe O /HT-SH-Ag (IV) is the utmost effective catalyst that makes the
3
4
maximum yield of the relevant product in a shorter time in model reaction. To determine the

optimal circumstances, the effect of temperature, and the catalyst loading on the rate of the
reaction and also on the yield of the relevant product was also examined. It could be observed
that using 0.044 mol% of Fe O /HT-SH-Ag, a significant yield of the corresponding product
3
4
o
was seen at 65 C (Table 1, entry 5-12).
Additional to increase the product yield, the solvent effect was studied. For this aim, water and
also several organic solvents (EtOH, EtOH/H O, EtOAc, and CH CN) were investigated. The
2
3
results showed that EtOH and CH CN are the best solvents for the reaction. Newly, the request
3
for green chemical synthesis processes and good efficiency has become more necessary. Since
EtOH is a green solvent, it was chosen as the solvent (Table 1, Entry 6, 13-17).
Subsequently, we examined the requirement of the oxidant (TBHP) for the oxidation of
alcohols (ROH) with the Fe O /HT-SH-Ag (IV) catalyst.
3
4
Table 1. Optimization of various reaction parameters for alcohol oxidation
OH
O
Catalyst
Solvent
T ( C),
o
Cl
Cl
Temp.
(°C)
70
70
70
70
75
65
50
40
65
65
65
65
65
65
65
Catalyst
Time
(min)
45-120
45-120
45-120
45-120
45
Yield
(%)
-
Entry
1
Solvent
(mol%)
-
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
a
2
0.007 (g)
0.007 (g)
0.007 (g)
0.044
0.044
0.044
0.044
0.019
0.032
0.063
0.19
0.044
0.044
0.044
0.044
0.044
20
40
50
60
90
25
20
60
80
75
70
40
85
90
60
10
b
3
c
4
5
6
7
8
9
45
45
45
45
45
45
45
45
45
45
45
45
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
H O
2
EtOAc
MeCN
EtOH ( 1:1 ) H O
65
65
2
Toluene
Reaction conditions: 4-chlorobenzyl alcohol (0.25 mmol), TBHP (0.25 mmol)
a
b
The reaction was carried out in the presence of AgNO . The reaction was performed
3
c
in the presence of HT (I). The reaction was done in the presence of Fe O /HT (II)
3
4

Alcohol oxidation without TBHP does not indicate any product formation, which we examined
in the use of other oxidants like O , H O , air, and Oxone to the reaction model and seen that
2
2
2
these oxidants are not active for alcohol oxidizer and no the product is not produced with good
efficiency (Table 2, Entry 1-4).
The amount of oxidant (TBHP) is a significant factor influencing the conversion and selectivity
in the corresponding reaction. The influence of the substrate to an oxidizing molar ratio was
then investigated, and the outcomes are shown in Table 2, entries 5-8.
Table 2. optimization of various oxidants for alcohol
oxidation
Entry
Oxidant (mmol)
Yield
-
30
-
15
60
70
90
90
1
2
3
4
5
6
7
8
Air
H O
2
2
O2
Oxone
TBHP (0.125)
TBHP (0.187)
TBHP (0.25)
TBHP (0.35)
Reaction conditions: 4-cholro benzyl alcohol (0.25 mmol),
catalyst (0.044 mol%) in EtOH (0.5 ml)
To discover the amplitude and limitations of the reaction, as well as the efficacy of Fe O /HT-
3
4
SH-Ag (IV), many aromatic alcohols have both electron-releasing and electron-withdrawing
groups, were selected and carried out under optimal conditions (Table 3).
All of them were reacted effectively and obtained the products with good efficiency. It has
been shown that aromatic alcohols counting electron-releasing react faster than electron-
withdrawing groups.

Table 3. The oxidation of different alcohols with Fe O /HT-SH-Ag
3
4
Entry
Alcohol
Product
Time (min)
Yield
OH
OH
O
O
1
60
82
2
3
90
75
90
60
Cl
Cl
OH
O
O
4
5
Cl
Cl
OH
4
90
HO
HO
OH
O
5
6
120
60
60
90
OH
OH
OH
O
OH
H
O
7
CH3
CH3
60
60
82
95
OH
Br
O
Br
8
9
OH
O
O
90
80
65
50
MeO
MeO
OH
1
1
0
1
120
120
O N
O N
2
2
OH
O
NO2
OH
NO2
O
1
2
120
42
OH
O
1
1
3
4
120
150
40
60
O
O
OH
O
Reaction conditions: benzyl alcohol (0.25 mmol), TBHP (0.25 mmol) catalyst (0.044
mol%), at 65 °C in EtOH as solvent

Catalyst Recycling
Recyclability of Fe O /HT-SH-Ag was investigated towards oxidative alcohol (ROH) via
3
4
TBHP to found the general applicability of the catalyst system presented. During each run
catalytically, Fe O /HT-SH-Ag was separated from the reaction medium by using an external
3
4
magnetic field and washed three times with H O and hot ethanol to remove traces of organic
2
o
compounds are absorbed, followed with a vacuum oven (80 C) for 6 hours. The dried
Fe O /HT-SH-Ag was utilized for the next catalytic performance. The Fe O /HT-SH-Ag
3
4
3
4
utilized for six continuous runs with negligible reduction in the efficiency of product
demonstrating the Fe O /HT-SH-Ag reusability, the outcomes are presented in Table 4.
3
4
Also, the ICP-OES analysis presented that the freshly synthesized catalyst has 183.43 mg, or
th
1
.70 mmol of Ag per 1 gram of Fe O /HT-SH-Ag, while the 6 reused catalyst has 174.25 g,
3
4
or 1.615 mmol of Ag per 1 gram of Fe O /HT-SH-Ag. It shows that 95% of Ag can be found
3
4
in the catalyst structure after six runs. As shown in Figure 4S, the FT-IR spectrum of the
recovered catalyst is completely similar to that of the freshly prepared catalyst, reflecting
approval of the catalyst under reaction circumstances.
Table 4. Recycling of Fe O /HT-SH-Ag towards oxidation of alcohols
3
4
Entry
Run
Time (min)
Yield
90
90
87
85
1
2
3
4
5
6
1
2
3
4
5
6
45
45
45
45
45
45
85
82
Reaction conditions: 4-chlorobenzyl alcohol (0.25 mmol), TBHP (0.25 mmol),
o
Fe O /HT-SH-Ag (0.044 mmol%), 65 C, in EtOH as a solvent.
3
4
To understand the properties of Fe O /HT-SH-Ag, we compare the results of the oxidation of
3
4
benzyl alcohols with other heterogeneous catalysts, as presented in Table 5.

Table 5. Comparison of results by Fe O /HT-SH-Ag with various catalysts
3
4
Time
Yield
(%)
89
94
95
Entry
Catalyst
Solvent/Oxidant
Ref.
(min)
a
1
2
3
Fe O MNPs
H O/H O
30
2880
300
[25]
[26]
[27]
3
4
2
2
2
a
Fe O @C
H O/H O
3
4
2
2
2
b
Fe O @SiO /Ru(OH)
x
Toluene/O2
3
4
2
4a
Fe O /HT-SH-Ag
EtOH/TBHP
45
90
This work
3
4
a
b
Reaction condition: 4-chloro benzyl alcohol , benzyl alcohol
Conclusion:
In brief, we have successfully synthesized Ag immobilized on modified magnetic hydrotalcite
Fe O /HT-SH-Ag) from easily available materials. The exact characterization of Fe O /HT-
(
3
4
3
4
SH-Ag using spectroscopic and microscopic techniques showed that this novel catalyst has a
plate-like shape with an average size of 13-25 nm, superparamagnetic behavior, and 1.7
-1
mmol.g Ag loading. We have introduced a simple and efficient procedure for oxidizing
alcohols to the relevant carbonyl compounds in the presence of Fe O /HT-SH-Ag catalyst in
3
4
o
ethanol as a solvent with TBHP at 65 C. The advantages of this procedure are the use of cheap
and green materials, simple procedure, quick reaction periods, effortlessness, high efficacy,
and moderated reaction circumstances. Effortless separation of the catalyst with the help of an
external magnet and reusability of the catalyst to 6 runs without a noteworthy reduction in
activity, the hopeful points of the method are presented, which makes it a good and suitable
method for the synthesis of aldehydes and ketones. It is important to note that the catalyst is
not sensitive to moisture, and air and there is not much sense to use or maintain it.
Acknowledgments
We gratefully acknowledge the support of this work by the University of Birjand.

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Highlights


Oxidation of alcohols with TBHP were carried out under mild conditions.
The reused several times without significant loss of reactivity.


Fe O /HT-SH-Ag presented excellent efficiency for alcohol oxidation.
3
4
Concise reaction time and excellent yields of products.

Graphical Abstract