Synthesis and characterization of magnetically separable Fe3O4@AHBA@Ni(0) [AHBA?=?3-amino-4-hydroxybenzoicacid] nanocatalyst: Applications for carbonyl hydrogenation and alcohol oxidation

Article abstract of DOI:10.1016/j.ica.2018.01.009

A simple, facile and convenient practical method has been developed for the preparation of a magnetically separable nanocatalyst, Fe₃O₄@AHBA@Ni(0) [AHBA = 3-amino-4-hydroxybenzoicacid]. The synthesized nanocatalyst was characterized

Full text of DOI:10.1016/j.ica.2018.01.009

Accepted Manuscript
Research paper
Synthesis and characterization of magnetically separable Fe O @AH-
3
4
BA@Ni(0) [AHBA = 3-amino-4-hydroxybenzoicacid] nanocatalyst: applica-
tions for carbonyl hydrogenation and alcohol oxidation
Sanchari Dasgupta, Aratrika Chakraborty, Sourav Chatterjee, Tanmay
Chattopadhyay
PII:
S0020-1693(17)30281-5
https://doi.org/10.1016/j.ica.2018.01.009
ICA 18083
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
24 February 2017
5 January 2018
8 January 2018
Please cite this article as: S. Dasgupta, A. Chakraborty, S. Chatterjee, T. Chattopadhyay, Synthesis and
characterization of magnetically separable Fe O @AHBA@Ni(0) [AHBA = 3-amino-4-hydroxybenzoicacid]
3
4
nanocatalyst: applications for carbonyl hydrogenation and alcohol oxidation, Inorganica Chimica Acta (2018), doi:
https://doi.org/10.1016/j.ica.2018.01.009
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Synthesis and characterization of magnetically separable Fe
3-amino-4-hydroxybenzoicacid] nanocatalyst: applications
hydrogenation and alcohol oxidation
3
O
4
@AHBA@Ni(0) [AHBA
=
for carbonyl
Sanchari Dasgupta,a Aratrika Chakraborty,a Sourav Chatterjee,b Tanmay
*
,b
Chattopadhyay
aDepartment of Chemistry, University of Calcutta, 92 A. P. C. Road, Kolkata-700009, India
b
Department of Chemistry, Panchakot Mahavidyalaya, Sarbari, Purulia, 723121, India.
E-mail: tanmayc2003@gmail.com
ABSTRACT
A simple, facile and convenient practical method has been developed for the preparation of a
magnetically separable nanocatalyst, Fe
3
4
O @AHBA@Ni(0) [AHBA = 3-amino-4-
hydroxybenzoicacid]. The synthesized nanocatalyst was characterized by electron
microscopy techniques (SEM, TEM with EDX), Power X-Ray Diffraction (PXRD), Fourier
transform infrared spectroscopy (FT-IR) and solid state UV-Vis spectroscopy techniques. X-
Ray photoelectron spectroscopy (XPS) study and time of flight secondary ion mass
spectroscopy (TOF-SIMS) study unambiguously prove the presence of nickel(0) on the
2
-1
surface of Fe
3
O . The surface area of prepared catalyst has been achieved 330 m g from
4
BET surface area analysis. This catalyst exhibits appreciable activity towards carbonyls
reduction and alcohols oxidation by changing the reaction conditions. The salient feature of
the present protocol is that the catalyst can be separated simply through an external magnetic
field and recycled for several times without any significant deterioration in its activity.
Moreover, ambient reaction conditions, easy workup process, extensive substrate scope and
cost effectiveness are some of the other wonderful features of this procedure that make it
cheap and sustainable.
Key words: Magnetic nanoparticles, Nickel(0), Catalysis, Recyclable, Oxidation, Reduction
1. Introduction
The field of nanoparticles has invited appreciable success because they have tremendous
potential to serve as catalysts owing to their active surface and interfacial atom effect, easy
recovery and reusability.[1-4] But unsupported nanoparticles are often unstable, and
agglomeration is frequently unavoidable during the reactions.[5] Thus, to overcome this
1

difficulty, nanoparticles have been immobilized on different solid supports.[6-12] But, again
the separation of these catalysts from reaction medium is very difficult.[13] Therefore,
surface modified magnetically separable super paramagnetic nanoparticles appear as a
redeemer.[14-22] Considering the fact that the position of nickel lies just above palladium
and platinum in the periodic table hence it can perform many of the same basic reactions as
palladium or platinum. The oxidation and reduction of organic functionalities is extremely
important in organic synthesis and has wide application in industry. In particular, very costly
metal nanoparticles, such as Pd, Pt and Au etc. have been evaluated for their ability to
catalyze these reactions.[23-24] Currently, nickel catalysed reactions is encountering a period
of escalated interest.[25] Practically speaking, the cost of nickel is lower than noble metals.
Again, as a first row transition metal, nickel has a small atomic radius, thus Ni-ligand bond
lengths are often relatively short and strong.[26] Although the field of nickel catalysis has
rapidly expanded over the last decade,[27-32] still there are many challenges that are yet to
be conquered. Presently, we are deeply involved in the field of catalysis to find out new cost
effective catalytic systems.[14,33-35] Here, we have reported a magnetically separable new
nickel catalyst that is highly active for both alcohol oxidation and carbonyl reduction. To the
best of our knowledge, this is the first example of such a catalyst that performs the two
reactions by changing the conditions only. Moreover, the catalyst can be easily recovered by
magnet and recycled several times without significant loss its activity. In this perspective a
novel Fe
synthesized (Scheme 1). Topark et al employed carboxylate group of piperidine-4-carboxylic
acid to modify the surface of Fe nanoparticles.[36] Here we have used AHBA for similar
purpose and it acts as a connector between Fe and Ni(0). Attachment of the carboxylate
group of AHBA to Fe nanoparticles and formation of five member chelate ring by its free
3
O
4
@AHBA@Ni(0) [AHBA=3-amino-4-hydroxybenzoicacid] catalyst has been
3
O
4
3
O
4
3
O
4
amino and hydroxyl group with Ni(0) enhances the stability of our synthesized nanocatalyst.
Moreover this newly synthesized catalyst is cost effective. Fortunately our prepared catalyst
can work for two types of catalytic reaction: (i) carbonyl reduction, and (ii) alcohol oxidation.
2

Scheme 1. Schematic diagram of preparation of Fe
3
4
O @AHBA@Ni(0) catalyst.
2. Experimental details
2
.1. Materials and methods.
All chemicals were obtained from commercial sources and used as received. Solvents were
dried according to standard procedure and distilled prior to use. FeSO .7H O, FeCl .6H O,
NiCl .6H O, sodium borohydride, hydrogen peroxide, alcohols and aldehydes were
purchased from merck and 3-amino-4-hydroxybenzoicacid, CDCl was purchased from sigma
4
2
3
2
2
2
3
-1
ο
Aldrich. Infrared spectra (2000–500 cm ) were recorded at 27 C using a Perkin-Elmer RXI
FT-IR spectrophotometer with KBr pellets. Electronic spectra (800–200 nm) were obtained at
o
2
7 C using a Shimadzu UV-3101PC with methanol as solvent and reference. Thermal
analyses (TG-DTA) were carried out on a Mettler Toledo (TGA/SDTA851) thermal analyzer
3
-1
in flowing dinitrogen (flow rate: 30 cm min ). Scanning Electron Microscope (SEM)
measurement was carried out with JEOL JSM-6700F field-emission microscope. X-ray
powder diffraction (PXRD) was performed on a XPERT-PRO Diffractometer
3

monochromated Cu-K radiation (40.0 kV, 30.0 mA) at room temperature. The spectra of the
α
samples were recorded at room temperature in solid phase. The light irradiation dependent
study was done after different irradiation times with a white light source compiled with a
<420 nm cut off filter. A vibrating sample magnetometer (EV-9, Microsense, ADE) was
utilized for obtaining the magnetization curves. Electrospray mass spectra have been recorded
on a WATERS Xevo G2-S Q Tof mass spectrometer.
2
.2. Synthesis of Fe
3
4
O NPs.
Preparation of magnetically responsive Fe
procedure as reported earlier.[37]
3
4
O NPs was prepared following the same
2
.3. Synthesis of Fe
3
4
O @AHBA.
3
g of 3-amino-4-hydroxybenzoicacid (AHBA) was dissolved in 10 mL of ethanol. This
and was stirred for 24 h at room
solution was added to ethanolic suspension of 3 g of Fe
3
O
4
temperature. The product was then allowed to settle, collected by centrifugation and washed
several times with ethanol. The products were air dried.
2
.4. Synthesis of Fe
3
O
4
@AHBA@Ni(II).
Fe @AHBA was dispersed in water and NiCl
3
O
4
2
.6H O solution in water was added drop
2
wise to get the 10 weight % of nickel. The reaction mixture was stirred for 24 h at room
temperature. The product was allowed to settle and was washed several times with water and
ο
acetone and dried under vacuum at 60 C for 2 h.
2
.5. Synthesis of Fe
3
4
O @AHBA@Ni(0).
Fe
3
O
4
@AHBA was dispersed in water and NiCl
2
.6H
2
O solution in water was added drop
was added portion wise. The
wise to get the 10 weight % of nickel. After that 0.1 g of NaBH
4
reaction mixture was stirred for 24 h at room temperature. The product was allowed to settle
ο
and was washed several times with water and acetone and dried under vacuum at 60 C for 2
h.
2
.6. General procedure of reduction of aldehydes.
Aldehydes (1 mmol), KOH ( 2 mmol), catalyst 30 mg) were stirred in 3 mL of glycerol at
room temperature for appropriate time. The progress of the reaction was monitored by TLC.
The catalyst was separated magnetically and the product was extracted with ethyl acetate and
4

the organic layer was evaporated in vacuum. The crude product thus obtained was purified by
column chromatography on silica gel using n-hexane and ethyl acetate as eluent.
2
.7. General procedure of oxidation of alcohols.
The alcohol (1 mmol), catalyst (20 mg),PhI(OAc)
2
(403 mg, 1.25 mmol) and MgSO (about
4
3
00 mg) were stirred in ethylenedichloride (EDC, 25 mL) at room temperature until the
reaction was complete. The progress of the reaction was monitored by TLC. The reaction
mixture was filtered through sintered funnel and residue was washed with EDC. Then the
EDC layer was washed with water and dried over anhydrous MgSO . The solvent was
4
removed using rotary evaporator at room temperature under reduced pressure. The crude
product was purified by column chromatography over silica gel using ethyl acetate–
petroleum ether as eluent.
3
.Results and discussions.
.1. Characterization of Fe
Magnetically active Fe
same procedure as reported earlier.[14, 32-34] Fe
AHBA (3 gm) and Fe NPs (3 gm) for 24 h in ethanolic medium.
3
3
O
4
@AHBA@Ni(0).
nanoparticles (here after Fe
@AHBA was prepared by stirring of
3
O
4
3
O NPs) were prepared following the
4
3
O
4
3
O
4
Primarily the UV-Vis spectra was taken in solution phase for homogeneous catalyst to ensure
the reduction of Ni(II)-AHBA complex to Ni(0)-AHBA. Before the reduction was performed
the d-d band of Ni(II)-AHBA complex is observed at 761 nm which gradually vanishes upon
addition of NaBH
4
. The reduced Ni(0)-AHBA was then separated and FT-IR and Solid state
UV-Vis spectra was recorded (Fig.1).
(
a)
(b)
Fig. 1. (a) Reduction of d-d band of Ni(0) upon addition of NaBH
4
and (b) Solid state UV-
Vis Spectra of Ni(0)-AHBA complex
5

-1
The Fourier transform infra-red (FT-IR) contains a band at 1600 cm which is a signature of
C=O stretching of carboxylic acid group of AHBA moiety which is also present in case of
-1
Ni(0)-AHBA complex [14]and the bands at 620 and 586 cm are due to Fe
signature of Fe-O vibration(Fig. S1). The characteristics band for NiO is not observed in FT-
IR spectrum of Fe @AHBA@Ni(0).[38]
We did not observe of any characteristics bands of Ni in the solid state UV-Vis spectrum of
the Fe @AHBA@Ni(0). This result hints that Ni(0) present at the surface of
Fe @AHBA (Fig. S2).
Thermal stability of Fe
thermo gravimetric analysis(TGA).The thermo gram of the Fe
of weight in the range of 30-800 °C. The TGA curve of Fe @AHBA@Ni(0) demonstrates
a weight loss about 19% from 260 to 800°C, due to the decomposition of organic materials
grafting to the Fe surface (Fig. S3). This result confirms the successful grafting of AHBA
and Ni(0) on the Fe NPs.
3
O
4
NPs which is
3
O
4
2
+
3
O
4
3
O
4
3
O
4
, Fe
3
O
4
@AHBA and Fe
3
O
4
@AHBA@Ni(0) was studied by
consist of about 6.5% loss
3
O
4
3
O
4
3
O
4
3
O
4
The X-Ray photoelectron spectroscopy (XPS) study was carried out to determine the surface
composition of the nanoparticle. Oxygen appears as most abundant element with percentage
ratio 60.7 and the percentage of Ni present to the surface of catalyst is 7.6. The characteristic
bands of nickel (Ni 2p) is depicted in Fig. 2. The peaks at 854.3 and 871.9 eV are assigned to
Ni(0) 2p3/2 and Ni(0) 2p1/2 and, respectively. Two lower intensity peaks at 860.1 and 878.09
eV can be assigned to Ni(II) 2p3/2and Ni(II) 2p1/2, respectively which suggests that NiO was
present as impurity in very low concentration. From the peak position it can be easily
concluded that Nickel(0) is present at the surface of the catalyst.[39-43]
(
a)
(b)
Fig. 2. X-ray photoelectron spectroscopy of Fe
3
O
4
@AHBA@Ni(0) (a) taken in full range
and (b) characteristics band of Ni(0)
6

Oxidation of nickel(0) nanoparticles during the XPS sampling procedure is a well known
phenomenon.[44,45] FT-RAMAN spectral analysis was performed to ensure the presence of
NiO on the surface of the catalyst since FT-RAMAN is a very useful technique to detect
metal oxide. The RAMAN spectra of Fe
3
O
4
and Fe
3
4
O @AHBA@Ni(0) resemble closely.
Thus it can be concluded that NiO nanoparticles formed during XPS study as impurity.
Fig. 3. FT-RAMN spectrum of Fe
3
O
4
and Fe
3
4
O @AHBA@Ni(0) catalyst
The presence of Ni(0) on the surface of Fe
3
4
O @AHBA@Ni(0) was further confirmed by
time of flight secondary ion mass spectrometry (TOF-SIMS), a commonly used technique for
surface characterization. The spectra of catalyst in positive ion mode consist of two peak at
m/z= 58 and 60 due to two most abundant isotopes of Nickel which suggest the presence of
5
6
+,
Ni at the surface of it. The peak at m/z= 56 arises for Fe present in the Fe
3
4
O moiety. In
the range of m/z = 60 to 100 an additional peak at m/z=61, 62, 69 and 73 appears due to
6
1
+
62
+
+
Ni , Ni , FeO and FeOH respectively (Fig. 4).
7

Fig. 4. TOF-SIMS positive ion spectra of Fe
3
4
O @AHBA@Ni(0) catalyst
The degree of crystalline nature of magnetic Fe
from Power X-Ray Diffraction (PXRD) measurements (Fig. S4). The PXRD data fit well
with the standard Fe sample. The same peaks were observed among the
Fe @AHBA@Ni(0) in PXRD patterns, signifying that the grafting process does not induce
any phase change of Fe as we observed earlier.[14, 33-34] Scanning electron microscopy
SEM) image of Fe @AHBA@Ni(0) was quite different from those of our prepared
Fe -NPs. [14, 33-34]
3
O
4
and Fe
3
O
4
@AHBA@Ni(0) were verified
3
O
4
3
O
4
3
O
4
(
3
O
4
3
O
4
The SEM images of nanocatalyst contained agglomerated particle and this alteration in
morphology confirms the surface modification process (Fig. 5). A close verification of
transmission electron microscopy (TEM) image of Fe
3
4
O @AHBA@Ni(0) revealed that these
magnetic nanoparticles are spherical with an average diameter of 10.0853±4.36 nm (Fig. 6a).
From the histogram of TEM image it is observed that most abundant average diameter of
nanoparticles is 10.085 nm (Fig. 6b).
8

Fig. 5. SEM images of Fe
3
4
O @AHBA@Ni(0)
(
a)
(b)
@AHBA@Ni(0)
Fig. 6. (a) TEM images and (b) histogram of Fe
3
O
4
The Energy-dispersive X-ray (EDX) spectra of Fe
depicted in (Fig. S5). The well-defined peaks of nickel in the EDX spectrum of nanocatalyst
confirm its presence in nanocatalyst. Magnetization behaviour of Fe NPs and
Fe @AHBA@Ni(0) was studied under applied magnetic field and is shown in Fig. 7. The
curves exhibit very similar phenomenon as we have observed earlier. [14, 33-34] The
decrease in the values of the saturation magnetization (M ) from the Fe nanoparticles
@AHBA@Ni (35.1 emu g ) due to gradual increment of organic
NPs to Fe @AHBA@Ni. However, the net magnetism showed by the
3
O
4
@AHBA@Ni(0) nanocatalyst are
3
O
4
3
O
4
s
3
O
4
−
1
-1
(
62.5 emu g ) to Fe
3
O
4
moiety from Fe
3
O
4
3
O
4
final nanocatalyst is satisfactorily good for an effective separation from the solution medium
through the use of an external magnetic force.
9

Fig. 7. Magnetic curves of Fe
3
O
4
, Fe
3
O
4
@AHBA and Fe
3
4
O @AHBA@Ni(0)
The measurement of the hydrodynamic size of Fe
light scattering (DLS) shows stable non-aggregated particles with a mean diameter of 40 nm
Fig. S6). They show good stability in water.
The textural properties of the Fe @AHBA@Ni(0) nanocatalyst was investigated by
3
O
4
@AHBA@Ni nanocatalyst by dynamic
(
3
O
4
Brunauer-Emmett-Teller (BET) gas-sorption measurements carried out at 77 K for the as-
dried powder sample under vacuum, as shown in (Fig. 8). BET surface area of
2
-1
Fe
3
O
4
@AHBA@Ni(0) nanocatalyst was 330 m g , very similar close to earlier report. The
= 0.55. The pore size
nitrogen adsorption isotherm holds a sharp inflection point at P/P
0
distribution adsorption curve is situated at 15.0 nm. It is evident that our synthesized
nanocatalyst has high BET surface areas which provide a platform for the catalytic organic
transformation.
(
a)
(b)
10

Fig. 8. (a) Nitrogen sorption isotherm and (b) BJH pore size distribution of the
Fe @AHBA@Ni(0)
3
O
4
3
.2. Reduction of carbonyl catalyzed by Fe
3
4
O @AHBA@Ni(0). In order to explore the
efficacy of the catalyst towards organic reaction, reduction of carbonyls were carried out
using glycerol as hydrogen source as well as solvent. All the carbonyl compounds mentioned
in Table 1 were successfully reduced to their corresponding alcohols. In this study,
optimization of the reaction conditions for carbonyls reduction was also carried out, making
an allowance for substrate (benzaldehyde)/ reductant(glycerol) molar ratio and the duration of
reaction time . It was observed that the conversion remains constant after 3 h of reaction. The
effect of the concentration of the catalyst with respect to the model substrate was also studied.
In absence of catalyst the conversion was significantly low (Table S1, entry 1). The
maximum conversion is observed when the reduction was performed in presence of 30 mg of
catalyst and 3 ml of glycerol (Table 1, entry 5). Interestingly, the conversion decreased with
an increased amount of catalyst (Table 1, entry 8) in case of reduction of carbonyl. This is
probably due to a decrease in the surface area of the nanocatalyst caused by adsorption of
reduced or oxidized products on the active surface. Further, the reduction reactions were
extended to a variety of carbonyls using the optimized reaction conditions as tabulated in
Table 2. Here we thought similar mechanistic path as reported in literature. [46]
Table 1.
Optimization of reaction conditions for reduction of benzaldehyde
a
Entry
Catalyst(mg)
Amount of reductant (mL)
Conversion (%)
1
2
3
4
5
6
7
8
0
3.0
3.0
3.0
3.0
3.0
2.5
3.5
3.0
<1
17
38
74
90
85
82
16
5
10
20
30
30
30
35
a
Reaction conditions: substrate 1 mmol, time(3 h)
11

Table 2
Fe @AHBA@Ni(0) catalyzed reduction of carbonyls
a
3
O
4
Entry
Compound
Product
Time (h)
3
Conversion
%)
Yield
(%)
90
(
1
93
2
3
4
3
3
3
89
91
92
87
89
88
5
6
3
3
94
95
92
90
7
8
3
3
89
93
87
88
9
3
3
88
87
85
83
1
0
a
Reaction conditions: substrate 1 mmol, KOH 2 mmol, Fe
glycerol 3 mL.
3
4
O @AHBA@Ni(0) 30 mg,
12

3
.3. Oxidation of alcohol catalyzed by Fe
3
4
O @AHBA@Ni(0).
Herein we report a novel protocol that employs Fe
efficient catalyst for oxidation of alcohols. Here we have chosen iodobenzene diacetate
PhI(OAC) ] as reagents oxidation, due to its unique properties.[47] The results for the
3
O
4
supported Ni(0)-nanoparticles as an
[
2
oxidation of a variety of alcohols are summarized in Table 4. In this case optimization of the
reaction conditions for alcohols oxidation by the nanocatalyst was also monitored, taking into
account the influence of substrate (benzyl alcohol)/oxidant molar ratio and duration of the
reaction time (Table 3). It was observed that the conversion remains constant after a reaction
time of 3 h. The effect of the concentration of the catalyst with respect to the model substrate
was studied. A significant conversion with 20 mg of the catalyst was observed for alcohol
oxidation respectively (Table 3, entry 5). The conversion observed in the absence of the
catalyst was very low (Table 3, entry 1).This revealed the catalytic role of our synthesized
Fe
3
O
4
@AHBA@Ni(0). The conversion decreased with an increased amount of catalyst
(
Table 3, entry 8) also in case of oxidation of alcohol. This is probably due to a decrease in
the surface area of the nanocatalyst caused by adsorption of reduced or oxidized products on
the active surface. The oxidation reactions were extended to a variety of alcohols using the
optimized reaction conditions (Table 4).
Table 3
Optimization of reaction conditions for oxidation of benzyl alcohol
a
Entry
Catalyst(mg)
Amount of oxidant (mmol)
Conversion (%)
1
2
3
4
5
6
7
8
0
1.25
1.25
1.25
1.25
1.25
1.00
1.50
1.25
<1
21
48
77
92
88
84
18
5
10
15
20
20
20
25
a
Reaction conditions: substrate 1 mmol, ethylenedichloride 25 mL, time(3 h)
13

Table 4
a
Fe
3
4
O @AHBA@Ni(0) catalyzed oxidation of alcohols
Entry
1
Compound
Product
Time (h)
Conversion
%)
Yield
(%)
92
(
3
83
2
3
3
3
80
75
90
82
4
5
3
3
80
79
86
87
6
7
3
3
75
76
80
80
8
3
78
82
a
Reaction conditions: substrate 1 mmol, PhI(OAc)
mg, ethylenedichloride 25 mL.
2
(1.25 mmol), Fe
3
4
O @AHBA@Ni(0) 20
3
.4. Probable mechanistic pathway for oxidation of alcohol.
In order to establish a plausible mechanism for the oxidation of alcohol ESI-MS study of
reaction mixture was carried out after 1 hour of the reaction. The reaction was performed
using benzyl alcohol as substrate. The intermediates are characterized by the ESI-MS study
after careful separation of the catalyst from reaction mixture. Firstly, the catalyst ruptured one
14

-
+
+
of the I-OAc bond of [PhI(OAC)
2
] to generate OAc and [PhI(OAC)] ions. [PhI(OAC)] ion
plays an important role for oxidation of the substrates. Peaks at m/z= 262.9653 amu for
+
+
[
PhI(OAC)] ion and 344.9710 amu for [PhI(OAC)
2
]-Na are observed along with the peak at
+
3
70.0390 amu assigned to [PhI(OAC)] -PhCH
2
OH adduct as reported earlier.[48]The
proposed mechanism for alcohol oxidation with [PhI(OAC)
Scheme 2. The unreduced Fe
was generated during the catalytic reaction leached Ni(II) from Fe
2
] as oxidant is represented in
-
3
O
4
@AHBA@Ni(II) can oxidized alcohol but OAc ion which
3
4
O @AHBA@Ni(II) and
deactivated its catalytic property (Fig. S7). Thus we reduced Ni(II) to Ni(0) to overcome this
problem.
15

Scheme 2.ESI-MS study of reaction solution of oxidation of alcohol
3
.5. Reusability of Fe
3
4
O @AHBA@Ni(0). Application of a simple bar magnet at the end of
the reaction ensures the separation of our synthesized nanocatalyst. This was washed with
ο
acetone, dried at 60 C which can be reused further for seven times (Fig. 9) without significant
loss of catalytic activity in the model reactions.
16

(
a)
(b)
@AHBA@Ni(0) towards: (a) reduction of benzaldehyde and (b)
oxidation of benzyl alcohol
Fig. 9. Reusability of Fe
3
O
4
The used catalyst has been further characterized by SEM after second, fourth and seventh
cycle in case of both oxidation and reduction (Fig. S8,S9) and TEM (Fig. S10). The size,
shape and morphology of the nanoparticles is same as was before the reaction, which clearly
indicates that no structural deformation takes place in catalyst active site. This was the
possible key factor for its reusability.
4. Conclusions
In summary, we have developed an economically viable and energy efficient catalytic a
new method using nickel based nanocatalyst for the reduction of carbonyls and oxidation of
alcohols in ambient condition at room temperature. Our synthesized catalyst showed
excellent catalytic properties towards oxidation as well as reduction (Yield  80%) reactions.
Here, we have also demonstrated that nickel in its zero oxidation state which can play a very
interesting role and also established a new mechanistic path for oxidation of alcohol. The
simple process, stability of catalyst, use of economical and gentle magnetic nanoparticles as
support, effortless recoverability and reusability, and above all, the yield in short reaction
time with little effluent discharge makes it an environmentally acceptable and greener
alternative, when compared to the other reported method. The recyclability test confirmed
that the catalyst could be reused at least seven times without any major degradation in its
activity. We speculate that this novel catalytic system would find functions in several other
industrially important catalytic processes as well as the common synthetic organic
transformations.
17

Acknowledgements
Financial support by the Science and Engineering Research Board (a statutory body under
DST, New Delhi, India (F. No. SB/FT/CS-185/2013 dt. 30-06-2014) is gratefully
acknowledged by TC. SD is thankful to UGC and University of Calcutta [UGC/485/Fellow
(
univ)] for providing fellowship.
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20

Highlights
A magnetically separable Ni(0) nanocatalyst has been prepared and explored for its dual
catalytic activity.
21

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