Graphene based magnetic nanohybrids as promising catalysts for the green synthesis of β-amino alcohol derivatives

Article abstract of DOI:10.1016/j.molstruc.2019.127522

The principle of green chemistry evolves around designing products and processes with catalyst retrieval as its foremost aim. In this regard, the present report encompasses the synthesis of graphene based magnetic nanohybrids (CoFe?rGO) and their catalyti

Full text of DOI:10.1016/j.molstruc.2019.127522

Journal Pre-proof
Graphene based magnetic nanohybrids as promising catalysts for the green synthesis
of β-amino alcohol derivatives
Ankush Sheoran, Jaspreet Kaur, Paramdeep Kaur, Vinod Kumar, K.B. Tikoo, Jyoti
Agarwal, S. Bansal, Sonal Singhal
PII:
S0022-2860(19)31631-X
DOI:
https://doi.org/10.1016/j.molstruc.2019.127522
MOLSTR 127522
Reference:
To appear in: Journal of Molecular Structure
Received Date: 4 October 2019
Revised Date: 8 November 2019
Accepted Date: 2 December 2019
Please cite this article as: A. Sheoran, J. Kaur, P. Kaur, V. Kumar, K.B. Tikoo, J. Agarwal, S. Bansal,
S. Singhal, Graphene based magnetic nanohybrids as promising catalysts for the green synthesis
of β-amino alcohol derivatives, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/
j.molstruc.2019.127522.
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Graphical abstract:
Graphene based magnetic nanohybrids as promising catalysts for the green synthesis of β-
amino alcohol derivatives.
O
NH2
OH
H
GO
O
X
X
X
N
H
GO
N
H2
O
NH2
OH
H
GO
O
X
X
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GO
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Graphene based magnetic nanohybrids as promising catalysts for the green synthesis of
β-amino alcohol derivatives.
Ankush Sheorana, Jaspreet Kaurb, Paramdeep Kaura, Vinod Kumarc, K.B. Tikooc, Jyoti
Agarwala, S. Bansald, Sonal Singhala*
aDepartment of Chemistry & Centre of Advanced Studies in Chemistry, Panjab University,
Chandigarh, India-160014
bEnergy Research Centre, Panjab University, Chandigarh, India-160014
cHR-TEM Facility Lab, National Institute of Pharmaceutical Education and Research,
(NIPER), SAS Nagar, 160062, Punjab, India
dDST, New Delhi, India
*sonal1174@gmail.com; sonal@pu.ac.in
CORRESPONDING AUTHOR: Sonal Singhal
Professor,
Department of Chemistry &
Centre of Advanced Studies in Chemistry,
Panjab University, Chandigarh, India-160014
Ph. No.+91-172-2534421(o)
+91-09872118810(m)
Fax No. +91-172-2545074
E-mail: sonal1174@gmail.com
1

Abstract
The principle of green chemistry evolves around designing products and processes with
catalyst retrieval as its foremost aim. In this regard, the present report encompasses the
synthesis of graphene based magnetic nanohybrids (CoFe@rGO) and their catalytic
evaluation for epoxide ring opening reactions. Numerous techniques were employed for
sample characterization. Powder X- Ray diffraction patterns confirm the single phase cubic
structure corresponding to CoFe2O4 with Fd-3m space group. The average crystallite size was
observed to be in the range of 8-12 nm for all the samples which was calculated in
accordance with Debye-Scherrer equation. The FE-SEM and HR-TEM techniques were
utilized to obtain detailed structural analysis of the nanohybrids displaying layered structure
of GO decorated with CoFe2O4 nanoparticles. The EDX spectra confirm the elemental purity
of the synthesized materials. Magnetic measurements were investigated by vibrating sample
magnetometer, displaying the increase in saturation magnetization values with increase in
CoFe2O4 concentration from 32.7 emu/g for CoFe@rGO (5%) to 38.6 emu/g for CoFe@rGO
(20%). The catalytic presentation of the synthesized nanohybrids was evaluated for epoxide
ring opening reactions under solvent free conditions displaying 100% conversion rates within
6 minutes of reaction time.
Keywords: Graphene based nanohybrids; magnetic nanocatalyst; heterogeneous catalyst;
epoxide ring opening; alcohol based products.
Highlights:
•
Synthesis of Graphene based magnetic nanohybrids (CoFe@rGO) using hydrothermal
technique.
•
•
•
Enhanced catalytic performance owing to large surface areas and active catalytic sites.
Magnetically retrievable catalyst displaying great recyclability.
Epoxide ring opening reactions with amines under solvent free conditions.
2

1. Introduction
Heterogeneous catalysis has procured gigantic appreciation in the contemporary span,
owing to ease of separation, regeneration and reusability of the catalyst. Payable to their
prodigious returns heterogeneous catalysts have been extensively used for numerous
applications such as organic transformations, environmental remediation etc. [1]. Diversity of
materials like semiconductors, metal oxides, iron based materials and inorganic matrices can
be utilized as heterogeneous catalyst [2- 4]. Recently, carbon based inorganic matrices like
graphene oxide (GO), carbon nanotubes (CNTs) have drawn immense attention of the
scientific community owing to their large surface areas, surface defects, admirable electrical
conductivity and high mechanical strength. The chemically active sites of these materials are
predominantly answerable for their catalytic performance; moreover these sites allow easy
functionalization and immobilization with various materials [5-7].
Amongst various inorganic moieties, implementation of graphene oxide (GO) as
heterogeneous catalyst is worthwhile owing to its large specific surface area, high thermal
stability, flexible structure, exceptional mechanical and electronic properties [8]. GO consists
of various functional groups like hydroxyl, carboxylic and epoxide which facilitates the
interactions with reactants and participates as heterogeneous catalyst in various reactions [9,
10]. Bhattacharya et al. [11] reported metal-free transamidation of aliphatic amide with
aromatic amine catalysed by graphene oxide (GO) providing a clean and practical method for
the formation of amines in good yields and with high selectivity. Shaikh et al. [12]
demonstrated metal-free GO as a proficient catalyst for the oxidative polymerization of 2-
naphthols in aqueous basic media and the homocoupling of 2-naphthols in organic media in
high yields. Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5- diformylfuran
(DFF) using GO as carbocatalyst was reported by Lv. et al. [13].
Besides, the impending use of GO as a catalyst for innumerable reactions, it dwells
certain drawbacks such as challenging separation from reaction mixture, poor dispersion,
inconstant multilayer thickness which restricts its practical use. Moreover, it is challenging to
recycle GO, which causes cost escalation and fetch secondary pollution [14, 15]. Fabricating
hybrids of GO with magnetic nanocatalyst can curb these downsides as well as shadow the
central aim of green chemistry, offering high catalytic performance, simplified seclusion of
products, easy recovery and recyclability of the catalyst [16]. But agglomeration of magnetic
nanocatalyst seems inescapable which declines their dispersal in solution phase thus limiting
their catalytic performance. Thus, functionalization of magnetic nanocatalyst with GO can
unravel the motive by reducing the agglomeration of magnetic particles providing large
3

surface areas [17, 18]. Numerous research associates have explored the catalytic exhibition of
composites of graphene oxide and magnetic nanomaterials. Maleki and Rahimi [19]
developed Fe3O4@GO as a capable heterogeneous nanocomposite for the synthesis of various
derivatives of quinazoline and quinazolinone fused heterocyclic compounds via modest
multicomponent reactions. Bahadorikhalili et al. [20] synthesized β-Cyclodextrin
functionalized PEGylated mesoporous silica nanoparticles-graphene oxide hybrid and
explored its catalytic performance for the synthesis of benzimidazoles and 1,2,3-triazoles.
Tanhei et al. [21] designed a novel 3-D graphene- magnetic palladium nanohybrid for Suzuki
and Heck cross-coupling reactions to produce 86% yield over 10 cycling tests. Lee et al. [22]
employed nanocomposites of ZnFe2O4 with GO and rGO (reduced graphene oxide) for the
synthesis of propene through oxidative dehydrogenation of propane. Eris et al. [23] fabricated
polyaniline – rGO decorated platinum catalyst and utilised for methanol oxidation reactions
displaying good catalytic activity and durability of the catalyst. Numerous organic
conversions have been reported in literature, out of which epoxide ring opening reactions are
highly beneficial as epoxides are versatile chemical intermediates which can be commonly
transformed via ring opening reactions with different nucleophiles such as water, alcohols,
amines and other substrates to produce a comprehensive range of bifunctional products.
Specifically, alcohol based products find great applications in pharmaceutical and solvent
industry [24- 28].
In present study, nanohybrids of cobalt ferrite and reduced graphene oxide
(CoFe@rGO) were utilized as heterogeneous catalyst for epoxide ring opening reactions, due
to the availability of large number of catalytic sites and magnetically separable nature. The
catalytic performance was evaluated by varying the concentration of cobalt ferrite in the
synthesized materials keeping the amount of GO constant. Although graphene based
nanocomposites have been utilized for numerous applications, but to the best of our
knowledge, such nanohybrids have been seldom used for ring opening reactions under
solvent free conditions following the principles of green chemistry. Comparison has been
made from literature, for epoxide ring opening reactions using different catalysts on the basis
of reaction completion time, % yield and recyclability of the catalyst.
2. Experimental section
2.1 Materials used
Cobalt nitrate hexahydrate (Co(NO3)3.6H2O, 98%), Ferric nitrate nonahydrate
(Fe(NO3)3.9H2O, 98%) and Potassium permanganate (KMnO4) were obtained from Central
4

Drug House (CDH). Graphite flakes were purchased from Otto chemicals. Sodium nitrate
(NaNO3) and Hydrogen peroxide (H2O2, 30% w/v) were provided by Fisher scientific.
Sulphuric acid (H2SO4) and liquor ammonia (Liq. NH3) were purchased from Merck. All the
mentioned chemicals were of analytical grade and were used as bought without any further
refining. All the solutions were prepared in ultrapure water obtained from an ultrafiltration
system (Milli-Q, Millipore).
2.2 Synthesis of nanocatalyst
2.2.1 Synthesis of Graphene Oxide (GO)
GO was synthesized using graphite flakes via modified Hummer’s method [10]. In this
method, 3g of natural graphite flakes were added to 70 ml conc. H2SO4, followed by addition
of fixed amount of NaNO3 (1.5g) and KMnO4 (9g) for about half an hour along with
continuous stirring, maintaining the temperature of the reaction mixture using ice bath at -
4˚C. Further, the reaction mixture was magnetically stirred for 24 h at room temperature.
Subsequently, the mixture was diluted by addition of distilled water and finally, 18 ml H2O2
was added slowly until the colour of the solution changes from brown to yellow which
indicates complete oxidation of graphite to graphene oxide. The resulting mixture was
repeatedly washed with distilled water until the pH of the solution became neutral; the
obtained product was then filtered and dried at 80 ˚C for 10 h.
2.2.2 Synthesis of CoFe@rGO nanohybrids
A facile hydrothermal method was employed for the synthesis of CoFe@rGO
nanohybrids [29], as depicted in Scheme 1. Primarily, GO was dispersed in distilled water
using ultrasonic technique. The stoichiometric amounts of metal nitrates (Co(NO3)3 and
Fe(NO3)3; 0.02M) were dissolved in minimum amount of water and pH of the solution was
adjusted to 7.5 using liquid ammonia. Subsequently, aqueous GO suspension was added to
metal nitrate solution followed by continuous stirring for 2 h. The solution was then
transferred to a Teflon autoclave maintained at 160 °C for 15 h. The obtained precipitates
were thoroughly washed with distilled water and acetone; followed by drying at 60 °C
overnight. The concentration of CoFe was varied as 5, 10, 15 and 20% and keeping the
amount of GO constant. The obtained nanohybrids were labelled as CoFe@rGO (5%).
CoFe@rGO (10%), CoFe@rGO (15%) and CoFe@rGO (20%).
2.3 Physical techniques
Various techniques were employed for the characterization of the synthesized
nanohybrids. For crystalline phase identification, Powder X-ray diffraction (XRD) analysis
was performed using Panalytical’s X’pert Pro diffractometer equipped with CuKα radiation
5

(λ=1.54Å) with scanning angle (2θ) range varying from 10o - 80o. The Fourier Transform
Infra-red (Perkin Elmer Spectrum 400, FT-IR/FT-FIR spectrometer) spectroscopy was
employed for all the samples in the range of 4000-400 cm-1; the samples were prepared using
KBr pellets, in order to confirm the functional groups present in the synthesized materials.
The surface morphology of the synthesized nanohybrids was perceived using Field Emission
Scanning Electron Microscopy (FE-SEM, Hitachi-SU8010) and High Resolution-
Transmission Electron Microscope (HR-TEM, FEI Tecnai (G2 F20) operating at 200 keV).
Vibrating sample magnetometer (VSM, Microsense EZ7) was used for magnetic
measurements. Thin layer chromatography (TLC) was performed using pre-coated silica 60
F254, 0.25 mm aluminium plates (Merck) and the progress of the reactions was visualized
and studied under UV chamber. Confirmation of the desired product formation was
scrutinized by Nuclear Magnetic Resonance (NMR) spectrometer (BRUKER AVANCE II
400 MHz) using CDCl3 as solvent and TMS as an internal standard.
2.4. Catalytic assessment
The catalytic study for the aminolysis of the epoxides was investigated using GO and
CoFe@rGO nanohybrid. The reactions were performed under solvent free conditions
amongst equimolar amounts of epoxide (1 mmol) and amine (1 mmol) using GO and
CoFe@rGO nanohybrid as catalyst (10 mg) at 80 °C. The progress of the reaction was
monitored using thin layer chromatography (TLC). After the completion of the reaction, the
catalysts were magnetically separated from the reaction mixture and thoroughly washed with
distilled water and acetone in order to remove the organic or inorganic part. The recovered
catalysts were then dried and recycled for further use. The final isolated products were
1
analysed using H NMR and the obtained records were matched with those reported in
literature [30].
3. Results and Discussion
3.1. Characterization of the nanohybrids
3.1.1 FT-IR Spectroscopy
The FT-IR spectra depict the presence functional groups present in the crystal lattice
through their vibrational modes. Here, FT-IR spectroscopy was used to investigate the
existence of oxygen containing functionalities and their variations after the formation of
nanohybrids. The FT-IR spectra of pure GO and CoFe@rGO nanohybrids are depicted in Fig.
1. In case of GO, a broad peak around 3400 cm-1 corresponding to stretching vibration of O-
H bonds of hydroxyl and carboxyl moieties was observed. Furthermore, five peaks around
1725, 1620, 1415, 1220, 1088 cm-1 were observed which could be ascribed to stretching
6

modes of C=O, aromatic C=C, carboxyl C-O, epoxy C-O, alkoxy respectively [31]. The
spectra of CoFe@rGO nanohybrids reveals all the signature peaks of GO except the peaks of
oxygen containing functional groups around 1625-1725 cm-1 and 1150 cm-1 in Fig.1 (b-e),
suggesting complete reduction of GO to rGO. Moreover, a new peak around 590 cm-1
appeared indicating the formation of metal-oxygen bond in CoFe@rGO nanohybrids [32].
3.1.2. Powder XRD Analysis
Powder XRD analysis was executed in order to determine the structural parameters and
phase purity of synthesized nanohybrids. The XRD patterns of GO and CoFe@rGO
nanohybrids are presented in Fig. 2. In case of GO, a strong diffraction peak at 2θ = 10.5º
corresponding to (011) crystal plane was observed. For CoFe@rGO hybrid, diffraction peaks
corresponding to (220), (311), (400), (511) and (440) planes were perceived, hence
confirming the formation of single phase cubic structure of CoFe2O4 with Fd-3m space
group. Furthermore, in case of nanohybrids the diffraction plane of GO at (011) plane was
absent indicating complete reduction of GO to rGO [33, 34]. However, in the nanohybrids the
diffraction peak corresponding to rGO at 2θ = 25º was not observed that could be attributed
to the damage and disorder generated in its layered structure by the crystal growth of ferrite
nanoparticles in its interlayers [35-37].
The average crystallite size of the synthesized materials was calculated using most
intense peak broadening of (311) plane using Debye-Scherrer equation [38]
Dhkl = kλ/βcosθ
(1)
Where Dhkl is the crystallite size, λ is the wavelength of radiation used, β is full width at half
maxima of the diffraction peak (FWHM), k is Scherrerˊs constant with a value of 0.9 and θ is
the angle of diffraction. The values of crystallite size in the range of 8-12 nm were observed
for all the samples and are listed in Table 1. Le Bail refinement method was employed to
estimate the lattice parameter (a) values of the synthesized materials which are tabulated in
Table 1.
3.1.3 Structural analysis
To gain insight into the structure and morphology of nanohybrids, FE-SEM analysis
was carried out. The typical FE-SEM micrographs of CoFe@rGO (20%) at resolution 500
nm and 300 nm are presented in Fig. 3. The FE-SEM micrographs revealed that rGO has
layered structure and cobalt ferrite (CoFe2O4) nanoparticles were randomly distributed on the
surface and edges of graphene sheets. Furthermore, it can be clearly perceived from the FE-
SEM micrographs that CoFe2O4 remain intact to the surface of rGO besides long period of
7

sonication and stirring suggesting strong interaction between rGO and CoFe2O4
nanoparticles. Owing to layered structure, rGO possess large surface area which in turn
proliferates the exposure of active sites of ferrites which ultimately enhances the catalytic
efficiency of nanohybrids [5, 23, 39, 40].
HR-TEM studies were carried out for the detailed structural analysis of the
synthesized nanohybrids. Fig.4 (a), (b) and (c) displays low resolution TEM images of
hydrothermally synthesized CoFe@rGO (20%) nanohybrid. The images reveal that the ferrite
nanoparticles were successfully sheathed over GO. Fig. 4 (d) displays the lattice spacing of
0.25 nm corresponding to (311) plane of CoFe@rGO nanohybrid. The interplanar distance
values obtained from the HR-TEM images well matched with the corresponding XRD
diffraction planes of CoFe@rGO(20%) nanohybrid.
The crystalline nature of the samples can be predicted from concentric electron
diffraction rings corresponding to different planes in the SAED pattern. Typical SAED
(selected area electron diffraction) pattern of CoFe@rGO(20%) nanohybrid is shown in Fig.
4(e). The presence of the concentric diffraction rings illustrates the highly crystalline nature
of the synthesized nanohybrid and all the planes observed from the SAED patterns matched
well with the planes observed in the powder XRD patterns.
Furthermore, the elemental composition of the synthesized nanohybrids was confirmed
from EDX spectra as presented in Fig. 4 (f) which demonstrates the presence of desired
elements. The presence of peaks corresponding to C and Cu were observed due to carbon
coated copper grid, which was utilized for the analysis. No additional peak corresponding to
other elements was perceived hence, confirming the purity of the synthesized nanohybrid.
3.1.4 Magnetic measurements
The magnetic characteristics of the synthesized nanohybrids were assessed by
recording room temperature hysteresis loops using vibrating sample magnetometer as
depicted in Fig. 5. The saturation magnetization (Ms) values were observed to increase with
increase in cobalt ferrite concentration from 32.7 emu/g for CoFe@rGO (5%) to 38.6 emu/g
for CoFe@rGO (20%). The enhancement in the Ms values could be attributed to coherent
magnetic nature of CoFe2O4. The values of saturation magnetization (Ms), coercivity (Hc),
remanence (Mr) and squareness ratio (Sq) for all the synthesized nanohybrids are listed in
Table 2.
3.2 Catalytic investigation of GO and CoFe@rGO nanohybrids for epoxide ring
opening reaction
8

The epoxide ring opening reactions were performed under solvent free conditions and
substrate scope was investigated via reactions between epoxides and aromatic amines at 80˚C
using GO and CoFe@rGO as heterogeneous catalysts. The substrate scope of GO and
CoFe@rGO (20%) catalysed ring opening reactions amongst various epoxides (2, 4, 6) and
aromatic amines bearing electron withdrawing and electron releasing groups are listed in
Table 3-5. The isolated products were obtained in excellent yields showcasing 100%
conversion within minutes; the yields were calculated using column chromatography. In case
of halogen substituted aromatic amines, longer reaction times were observed as listed in
entries b-g in Table 3-5. Amongst halogens, the reaction time was observed to be shortest for
iodine substituted amines followed by bromine and then by chlorines substituted amines. As
observed, completion time for the epoxide ring opening reaction was equivalent, irrespective
of the position of attached halogen. In case of p-OCH3 and p-CH3 anilines, rapid completion
times as well as excellent isolated yields (93 to 94%) were observed as mentioned in entries h
and i from Table 3-5. On comparing the results for the reaction of epoxides (cyclohexene
oxide (2) and cyclopentene oxide (4)) with various aromatic amines similar completion times
were observed except for the case of unsymmetrical epoxide i.e., styrene oxide (6) little
longer completion time was detected with all the aromatic amines. As inferred from all the
reaction results, CoFe@rGO (20%) nanohybrid showcased better catalytic performance
compared to that of pristine GO towards epoxide ring opening reactions which could be
attributed to large surface area of the nanohybrid showcasing better dispersal in the solution
phase. In case nanohybrids, both CoFe and GO act synergistically, hence augmenting the
catalytic performance towards epoxide ring opening reactions.
3.3 Characterization of product
The formation of all the desired products was confirmed and characterized using
1
1HNMR spectroscopy. The HNMR spectra and data of obtained products using GO and
CoFe@rGO nanohybrids as catalyst are provided as supplementary data (Fig. S1-S27).
3.4 Probable mechanistic pathway
The catalytic performance of GO is due to its capacity to function as an acid. GO
transfers a proton to the epoxide when the epoxide gets adsorbed on the surface of the GO.
This results in the increased electrophilicity at one of the epoxide carbon atoms which
prompts the attack of nucleophile and consequently, ring opening of epoxide takes place. The
schematic representation of the reaction mechanism for epoxide ring opening using GO as
catalyst is shown in the Fig. 6. The epoxide ring opening reaction catalysed by GO is
represented in equation (2) :
9

O
NH2
OH
H GO
O
(2)
X
X
X
N
H
GO
N
H2
In case of nanohybrids (CoFe@rGO), the adsorption of reactant molecule occurs at the
surface of the nanohybrid due to the presence of acidic sites on the surface. The plausible
mechanism for epoxide ring opening in the presence of CoFe@rGO as catalyst is depicted in
Fig. 7. On adsorption of the epoxide molecule at the surface of nanohybrid, epoxide gets
activated for the nucleophilic attack by the amine derivatives. This results in the formation of
intermediate (I) which can interchange with the intermediate (II) by proton transfer and
finally results in the formation of the desired product. The epoxide ring opening reaction
catalysed by CoFe@rGO is represented in equation (3) :
O
O-
NH2
CoFe2O4rGO
X
OH
(3)
X
X
rGO-CoFe2O4
N
H2
N
H
The results obtained in Tables 3 to 5 can be justified on the basis of the above
mentioned plausible mechanism. The higher reactivity of –OMe substituted amine is due to
its high nucleophilicity which results in the facile attack on the epoxide-nanohybrid complex
to form the desired product in lesser time. So, based on the nucleophilicity of different
groups, the order of reactivity for various amines follows the trend OMe > Me > H > I > Br >
Cl.
The presently prepared materials were compared with previous reports in terms of
completion time, % yield, use of solvent and magnetically separable nature which directly
relates with recyclability of the materials. [41-47]. The present study displays superior results
for epoxide ring opening reactions as compared to previously reported materials as mentioned
in Table 6.
3.5 Recyclability
10

Admirable stability and recyclability are the significant features of the synthesized
nanohybrids, CoFe@rGO. The recyclability of the nanohybrids was examined for six
catalytic cycles employing CoFe@rGO (20%) as catalyst. Owing to the magnetic nature of
the nanohybrid, it was separated from reaction mixture using an external magnet and washed
with distilled water and acetone. The obtained material was then dried and reused for
subsequent reactions. No significant decrease in the % yield was observed even after six
catalytic cycles signifying excellent reusability of the nanohybrid (Fig. 8). After each
catalytic run, the recovered catalyst was characterized using FT-IR and powder X-ray
diffraction; no significant change in the nanohybrid was observed suggesting high durability
of the nanohybrids. The FT-IR spectra and the powder XRD pattern of the recovered
nanohybrid are provided as supplementary data (Fig. S28-S29). The prepared materials were
found to be superior in comparison with the previously reported materials in terms of
recyclability.
4. Conclusions
To conclude, graphene based magnetic nanohybrids (CoFe@rGO) were synthesized
using a facile hydrothermal method and were characterized using various techniques. Powder
XRD pattern confirms the formation of single phase cubic structure of CoFe2O4 with Fd-3m
space group, absence of diffraction peak (011) indicates the complete reduction of GO to
rGO in the nanohybrids. From FE-SEM and HR-TEM images, ferrite nanoparticles sheathed
over reduced graphene oxide were observed. The saturation magnetization values were
observed to be more than 30 emu/g for all the prepared samples and were observed to
increase with increase in cobalt ferrite content. The catalytic performance of Graphene oxide
(GO) and magnetic nanohybrids (CoFe@rGO) was exploited for ring opening reactions of
epoxides with amines under solvent free conditions. The nanohybrids (CoFe@rGO) emerged
out as better candidates for the conversion of different aromatic amines to corresponding
amino alcohols with 100% conversion rate within 6 minutes of reaction time. Owing to the
magnetically separable nature of the prepared samples, excellent recyclability for upto 6
catalytic runs was observed. The present report exhibited short reaction time, simple work up
procedure, great recyclability and solvent free greener approach for the given reaction as
compared with previous reports. Thus, the synthesized magnetic nanohybrids could be
potentially used as green catalyst for the formation of various pharmaceutical and
intermediate chemicals in near future.
Acknowledgements
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The authors are highly thankful to CSIR (09/135(0783)/2017-EMR-I) and DST
(Technology Mission Division, TPN No. 24831) for providing necessary financial support;
SAIF-CIL, Panjab University, Chandigarh for the sample characterization.
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16

Table 1. Crystallite size Dhkl (nm) and Lattice parameter, a (Å) for GO and CoFe@rGO
nanohybrids.
Samples
Dhkl (±2 nm)
a (Å)
GO
11.4
8.7
9.9
9.9
9.9
8.250
8.418
8.374
8.320
8.371
CoFe@rGO (5%)
CoFe@rGO(10%)
CoFe@rGO (15%)
CoFe@rGO (20%)

Table 2. Remanence (Mr), coercivity (Hc), squareness ratio (Sq), saturation magnetization
(Ms) of the synthesized nanohybrids.
Mr
Hc
Ms
Catalyst
Sq×10-2
(emu/g)
(Oe)
(emu/g)
CoFe@GO(5%)
CoFe@GO(10%)
CoFe@GO(15%)
CoFe@GO(20%)
3.00
4.60
5.00
3.20
140
180
190
155
9.1
13
32.7
35
13
36
8.3
38.6

Table 3. GO and CoFe@rGO (20%) catalysed epoxide ring opening reaction of
cyclohexene oxide (2) with various aromatic amines (1a-i)
NH2
OH
GO/CoFe@rGO(20%)
O
X
X
Neat, 80 oC
N
H
3a-i
1a-i
2
GO
CoFe@rGO(20%)
Conversion Yield
Amine
-X
Conversion
100%
100
Yield
(%)
92
Time
(min)
Time
Product
(min)
(%)
100
100
100
100
100
100
100
100
(%)
92
86
86
90
89
88
88
93
1a
1b
1c
1d
1e
1f
H
3a
3b
3c
3d
3e
3f
4
14
14
12
12
9
3
12
12
8
2-Cl
4-Cl
2-Br
4-Br
2-I
100
86
100
86
100
90
100
90
8
100
89
7
1g
1h
4-I
3g
3h
9
100
88
7
4-Me
3
100
93
2
4-
1i
3i
3
100
94
2
100
94
OMe

Table 4. GO and CoFe@rGO (20%) catalysed epoxide ring opening reaction of
cyclopentane oxide (5) with various aromatic amines (1a-i)
NH2
OH
GO/CoFe@rGO(20%)
O
X
X
Neat, 80 oC
N
H
1 a-i
4
5 a-i
CoFe@rGO (20%)
GO
Time Conversion
Amine
-X
Yield Time Conversion Yield
Product
(min)
100%
100
100
100
100
100
100
100
100
100
(%) (min)
(%)
100
100
100
100
100
100
100
100
100
(%)
93
89
88
86
86
86
85
94
94
1a
1b
1c
1d
1e
1f
H
2-Cl
4-Cl
2-Br
4-Br
2-I
5a
5b
5c
5d
5e
5f
4
92
88
88
86
88
85
85
93
93
3
12
12
8
14
14
12
12
9
8
6
1g
1h
1i
4-I
5g
5h
5i
9
7
4-Me
4-OMe
3
2
3
2

Table 5. GO and CoFe@rGO (20%) catalyzed epoxide ring-opening reaction of styrene
oxide (8) with various aromatic amines (1a-i)
X
HN
NH2
O
OH
GO/CoFe@rGO(20%)
X
Neat, 80 o
C
1a-i
6
7a-i
GO
CoFe@rGO (20%)
Amine
-X
Conversion Yield
Conversion
(%)
100
Yield
(%)
90
Time
(min)
Time
(min)
Product
100%
100
100
100
100
100
100
100
100
100
(%)
90
84
84
84
85
82
82
90
92
1a
1b
1c
1d
1e
1f
H
2-Cl
4-Cl
2-Br
4-Br
2-I
7a
7b
7c
7d
7e
7f
8
6
24
24
20
20
18
18
6
20
20
18
18
15
15
5
100
84
100
84
100
85
100
85
100
83
1g
1h
1i
4-I
7g
7h
7i
100
82
4-Me
4-OMe
100
92
6
5
100
92

Table 6. Comparison of reaction time and % yield employing different catalysts for ring
opening reactions
Yield
(%)
Magnetically
recoverable
Catalyst
Solvent
Time
References
Yb(OTf)3
SmI2(THF)2
10% Bi(OTf)3
THF
CH2Cl2
H2O
10 h
18 h
7-9 h
94
75
83
No
No
No
[41]
[42]
[43]
Hexafluoro-2-
propanol
-
4 h
84
No
[44]
Samarium Iodo
Binaphthoxide
CH2Cl2
18 h
20 h
55
89
90
No
No
[45]
[46]
LiNTf2
-
-
CoFe@rGO
(20%)
6 min
Yes
This work

Scheme 1. Schematic representation for the synthesis of CoFe@rGO nanohybrids via
Hydrothermal route.

(e)
(d)
(c)
(b)
(a)
4000 3600 3200 2800 2400 2000 1600 1200 800
400
Wavenumber (cm-1)
Fig. 1. FT-IR spectra of (a) GO, (b) CoFe@rGO (5%), (c) CoFe@rGO (10%), (d)
CoFe@rGO (15%) and (e) CoFe@rGO (20%) nanohybrid.

CoFe@rGO (20%)
CoFe@rGO (15%)
CoFe@rGO (10%)
CoFe@rGO (5%)
GO
6
10
20
30
40
50
60
70
80
90
Angle (2θ)
Fig. 2. Powder XRD patterns of GO and CoFe@rGO nanohybrids.

Fig. 3. Typical FE-SEM micrographs of CoFe@rGO(20%) nanohybrid at (a) 500 nm and
(b) 300 nm magnification.

Fig. 4 Low Resolution TEM images at different magnification (a,b,c), High Resolution
TEM image (d), SAED pattern (e) and EDX spectra (f) of CoFe@rGO(20%) nanohybrid.