Silver doped reduced graphene oxide as a promising plasmonic photocatalyst for oxidative coupling of benzylamines under visible light irradiation

Article abstract of DOI:10.1039/c9nj00852g

Visible light assisted photocatalytic transformations have been considered as an efficient and sustainable approach for the production of high-value chemicals. The present paper describes the synthesis of plasmonic silver nanoparticle incorporated reduced

Full text of DOI:10.1039/c9nj00852g

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PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Silver doped reduced graphene oxide as promising plasmonic photocatalyst
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for oxidative coupling of benzylamines under visible light irradiationDOI: 10.1039/C9NJ00852G
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Anurag Kumar,1,2 Aathira M. Sadanandhan,1 and Suman L. Jain1*
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1Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Dehradun India 248005
2Academy of Scientific and Innovative Research (AcSIR), New Delhi India 110001
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Abstract
Visible light assisted photocatalytic transformations have been considered as an efficient and sustainable approach for the production of
high-value chemicals. The present paper describes the synthesis of plasmonic silver nanoparticles incorporated reduced graphene oxide
and its photocatalytic performance for the selective oxidation of various benzylamines to the corresponding imines using molecular
oxygen as oxidant under ambient temperature condition. The developed photocatalyst was found to be highly stable and exhibited
excellent photoactivity with consistent recycling ability for several runs without loss in activity. Moreover, to the best of our
knowledge, the developed photocatalyst represents the first example of a graphene-based photocatalyst for the oxidative coupling of
amines.
33-35
Introduction
applications.
Further immobilization of silver nanoparticles
on reduced graphene oxide is known to improve the performance
mainly due to the increased reactive surface area, as well as the
superior charge separation. The unique electron collecting and
transporting properties of graphene through conjugated system
drive the hot electrons to the reactive sites, and suppressing the
recombination. Owing to these advantages we have chosen
Ag@rGO photocatalyst for the present study.
Accordingly, we herein report the synthesis, characterization and
performance evaluation of the silver NPs decorated reduced
graphene oxide, i.e. Ag@rGO for the oxidative coupling of
benzylamines with molecular oxygen under ambient conditions
using visible light irradiation (Scheme 1). To the best of our
knowledge the present study represents the first report on the use
of graphene-based photocatalyst for oxidative coupling of
benzylamines.
Imines and their derivatives have found extensive applications as
key intermediates for preparation of various nitrogen containing
heterocyclic compounds mainly in alkaloid synthesis.1,2
Oxidative coupling of amines is a straight forward approach for
the synthesis of these valuable intermediates.3-8 Furthermore, the
use of abundantly available solar energy and molecular oxygen
as oxidant make this methodology greener and sustainable.6,9-12
However, limited reports mainly using semiconductor-based
photocatalysts are known in the previous literature for the
oxidation of benzylamines to imines using molecular oxygen as
oxidant. Su and co-workers investigated mesoporous graphite
carbon nitride (mpg-C3N4) for the oxidation of benzylic alcohols
and amines with O2 under visible light. 13 Jin et al. demonstrated
the selective oxidation of amines using O2 catalyzed by cobalt
thioporphyrazine under visible light.14 Raza et al. reported
15
oxidative coupling of amines by photoactive WS2 nanosheets.
Furukawa et al. demonstrated the use of Nb2O5 as an efficient
heterogeneous photocatalyst for the oxidation of various amines
into respective imines in the presence of molecular oxygen as an
oxidant.16 Sun et al. reported visible-light-assisted photocatalytic
oxidation of amines to imines over NH2-MIL-125(Ti)
photocatalyst.17 Very recently Kumar et al. reported a hybrid
photocatalyst consisting of iron bipyridine complex immobilized
Scheme 1: Oxidative coupling of benzylamines under visible light.
to graphitic carbon nitride under visible light irradiation 18
.
Graphene, the newest member of carbon family, possesses
two-dimensional layered structure of sp2 hybridized carbon
atoms and unique properties that are useful in catalysis and
photovoltaic devices.19 Due to the abundance of delocalized
electrons from the conjugated sp2 bonded carbon network,
graphitic carbon enhances the transport of photo-generated
electrons and increases the photo-conversion efficiency of the
system.20-25 Although, graphene oxide (GO)/ reduced graphene
oxide (rGO) owing to their lower bandgap have been used as
visible light active semiconductor photocatalyst, albeit the
conversions were found to be poor due to fast recombination of
electron-hole pairs on the surface24-26. In order to enhance the
photo-conversion efficiency of GO/rGO based photocatalysts by
Results and discussion
Synthesis and characterization of the photocatalyst
The desired photocatalyst (Ag@rGO) was obtained by in-situ
synthesis of silver nanoparticles (Ag NPs) followed by reduction
of graphene oxide into rGO in the presence of formic acid at 80
oC as shown in Scheme 2. Loading of Ag NPs in photocatalyst
was found to be 5 wt% as determined by ICP-AES analysis.
suppressing
the
electron-hole
recombination,
surface
modifications with noble metal ions, such as platinum,
palladium, silver and gold nanoparticles (NPs) has been well
established.27-32 Among the most studied noble metals, silver
owing to its low cost, unique optical properties, higher chemical
stability and non-toxic nature has considered to be promising for
the modifications of graphene and its analogs for photocatalytic
Scheme 2: Synthesis of Ag@rGO photocatalyst
1

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DOI: 10.1039/C9NJ00852G
The surface morphology of the photocatalyst was determined by
HR-TEM analysis. The HR-TEM images showed in Fig. 1a-b
revealed the wrinkled nanosheets like morphology with
encapsulation of Ag NPs in rGO nanosheets. Fig. 1c-d showed
lattice spacing around 0.235 nm corresponded to (111) plane of
Ag NPs according to the JCPDS No. 04-0783.36 The average
particle size of the Ag NPs obtained from the HR-TEM image
was approximately in the range of 10-12 nm. The SAED pattern
showed that the synthesized material was crystalline in nature.
The elemental mapping confirmed the homogeneous dispersion
of the Ag NPs throughout the material (Fig. S1). Furthermore,
the EDX (Fig. S1) confirmed the presence of all the desired
elements i.e. C, O and Ag in the hybrid material.
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Fig. 2 FTIR Spectra of a) GO, b) rGO, c) Ag@rGO
The crystalline nature and phase structure of the synthesized
samples was determined by XRD analysis (Fig. 3). The
diffractogram of GO showed a sharp peak at 2θ=10.27
corresponded to (001) plane (Fig. 3a).39 In case of rGO an
intense broad peak at 25.4° and a small peak at 43.6°
corresponding to (002) and (111) planes, respectively were
appeared (Fig. 3b).40 In hybrid Ag@rGO photocatalyst, the
peaks observed at 38.1°, 44.3°, 64.5° and 77.3° were
corresponded to (111), (200), (220) and (311) crystallographic
planes of Ag NP phase. The average particle size in the
photocatalyst was estimated by using the Debye-Scherrer
formula.
D = 0.9λ / βCosθ .......................................................................(1)
where “λ” is wavelength of X-ray (1.5418 Å), “β” is FWHM
(full width at half maximum), “θ” is the diffraction angle and
“D” is particle diameter size. The average particle size of Ag
NPs was found to be in the range of 12 nm. The peak at 25.4°
indexed to (002) planes with 0.235 nm interlayer distance is
attributed to the presence of graphene in the hybrid material (Fig.
3c).41 The average estimated crystallite size of the Ag NPs at
optimum condition was found to be in the range of 8-10ꢀnm that
matches well with the sizes of Ag NPs obtained from HR-TEM
analysis.
Fig. 1 HR-TEM images: a) Ag@rGO; b) at 20 nm showing the
presence of Ag NPs; c) at 10 nm show the fringes d) 5 nm scale
bar showing interplanar d-spacing; f) SAED pattern.
Fig. 2 demonstrates the FTIR spectra of GO, rGO and Ag@rGO
photocatalyst. FTIR spectrum of GO showed the characteristic
bands related to –OH (3000-3500 cm-1), C-H (υC-H at 2923 cm-1),
C=C (υC=C at 1574 cm-1), C-OH (υC-OH at 1383 cm-1), C-O-C (υC-
at 1249 cm-1), C-O (υC-O at 1055 cm-1) and C=O (υC=O at
O-C
1725 cm-1) of the oxygen functionalities present on the basal
plane of graphene sheets (Fig. 2a).37,38 FTIR spectrum of rGO
showed the reduced intensity of all the bands related to the
oxygen functionalities and exhibited mainly two absorption
bands at 1249 cm-1 (υC-O-C) and 1574 cm-1 (υC=C), which
indicated the successful reduction of the GO to rGO (Fig. 2b).
After the intercalation of Ag NPs between the graphitic sheets of
rGO or deposition onto the surface of nanosheets, the FTIR
spectrum of hybrid remains almost similar to rGO with reduced
intensity of the bands. The bands at 3411 cm-1 (OH), 1574 cm-1
(C=C) and 1249 cm-1 (C-O-C) could be clearly seen in the FTIR
spectrum of the photocatalyst with slightly reduced intensity
(Fig. 2c).
2

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Fig. 5: UV-vis absorption spectra of a) GO, b) rGO, c) Ag@rGO
photocatalyst.
X-ray photoelectron spectroscopy was used to determined the
surface chemical composition of the photocatalyst. The XPS
survey scan shows the binding energies of all desired elements
such as C1s (285.0 eV), O1s (531.5 eV), Ag3d (368 eV) and Ag3d
(374 eV) in hybrid material (Fig. 6a). The high-resolution XPS
spectra of C1s shows three peaks at ~284, 285.3 and 288.2 eV
due to C-C and C-O and C=O bonds, respectively confirmed the
presence of reduced graphene oxide (Fig. 6b).44 For the
comparison, we added the XPS of graphene oxide which
exhibited C1s peaks at binding energy 285.8 and 287.9 eV due to
the C–C and C–O bond respectively (Fig. 6b). The XPS high-
resolution spectrum of O1s deconvoluted into two peaks at 532.3
and 530.8 eV corresponded to O-H and C=O, respectively (Fig.
6c). Fig 6d shows the high-resolution spectrum of Ag3d, in which
two peaks appeared at 374 and 368 eV with spin energy
separation of 6 eV attributed to Ag3d5/2 and Ag3d3/2, respectively
(Fig. 6c). These values confirm that silver is present as Ag0 in
the hybrid photocatalyst. The reduction of Ag+ to Ag0 occurred
on the surface of rGO sheets during the reduction process.45,46
Fig. 3 XRD pattern of a) GO, b) rGO, c) Ag@rGO photocatalyst.
Fig. 4 shows the Raman spectra of the reduced graphene oxide
and Ag@rGO hybrid material. In case of rGO two bands, i.e., D
band and G band at 1335 and 1594 cm-1 respectively are
obtained (Fig. 4a). The intensity ratio of D to G defines the
degree of distortion in the graphitic sheets. The integral intensity
ratio of D to G bands (ID/IG) in rGO was found to be 0.97. After
intercalation of the Ag NPs, the integral intensity ratio ID/IG
was found to be increased, i.e. 1.18, which suggested the
presence of a large number of defects in the form of Ag NPs in
the hybrid (Fig. 4b).42
Fig. 4: Raman spectra of a) rGO, b) Ag@rGO photocatalyst.
UV-Vis spectroscopy was used to determine the absorbance of
GO, rGO, and Ag@rGO photocatalysts. In case of GO, the
absorbance in the region between 250-280 nm owing to the π-π*
transitions of aromatic C-C bonds indicated the restoration of the
extensive conjugated framework of sp2 carbons and a shoulder at
about 300 nm assigned to n- π* transition of C=O bonds (Fig.
5a). For rGO the absorption peak corresponds to π-π* transition
of the aromatic C-C bond was found to be redshifted to 270 nm,
confirmed the reduction of GO (Fig. 5b). UV-Vis spectrum of
Ag@rGO hybrid exhibited strong absorption in the visible
region 350-370 nm due to the surface plasmonic resonance
(SPR) of Ag NPs, which further confirmed its application as a
visible light active photocatalyst for organic transformations
(Fig. 5c).43 Furthermore, the band gap observed for rGO and
Ag@rGO hybrid was 1.72 and 1.5 eV, respectively as calculated
with the help of a Tauc plot with linear extrapolation (Fig. S2).
The rate of charge recombination was analyzed with the help of
Photoluminescence spectroscopy. The PL spectra of rGO
displayed a peak at 478 nm with high intensity. However, the
significant lowering in peak intensity in hybrid photocatalyst
confirmed the reduced charge recombination (Fig. S3).
Fig. 6: High-resolution XPS spectra of Ag@rGO photocatalyst.
The thermal stability of the synthesized hybrid was measured by
thermo-gravimetric analysis (TGA). Thermogram of Ag@rGO
photocatalyst showed an initial weight loss at temperature 100
°C due to the evaporation of moisture and a gradual weight loss
in the range of 300-500 °C owing to the combustion of the
carbon skeleton of graphene (Fig. S4). The nitrogen adsorption-
desorption isotherm for Ag@rGO was of type-IV that confirmed
the mesoporous nature of the material. The higher absorption
capacity of the photocatalyst could be attributed to the larger
surface area of the material. The SBET and pore volume for
Ag@rGO were found to be 88.2 m2g-1 and 0.25 cm3g-1
3

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respectively (Fig. S5).
higher concentration of the substrate on the vicinity of the
reactive sites through the π-π interaction. Hence, theVpierwesAertniccleeOonfline
rGO support improved the reactivity of theDpOhIo:t1o0c.1a0ta3l9y/sCt9. NJ00852G
The scope of the reaction was extended for various substituted
benzylamines under optimized reaction conditions. The results
of these experiments are summarized in Table 2. As shown in
Table 2, all the reactants containing either electron donating or
withdrawing groups were selectively and efficiently converted to
the corresponding N-benzylidene benzylamines with excellent
yields without any evidence of the formation of any by-product.
Among the various substrates, benzylamines substituted with
electron-donating groups i.e. OCH3, CH3 (Table 2, entries 2-4)
were found to be more reactive as compared to those having
electron withdrawing groups, i.e. Cl, F, Br (Table 2 entries 6-9
The higher reactivity of the electron-rich substrates may be
assumed due to the facile formation of cation radical followed by
imine intermediate after donating electron to VB of the
photocatalyst during the reaction. Substrates like aniline,
cyclohexylamine and n-butyl amine did not show any reaction
under the described protocol, and original substrates could be
isolated at the end of the reaction (Table 1, entry 10-12).
Photocatalytic oxidative coupling of benzylamines
The photocatalytic activity of the synthesized photocatalyst was
evaluated for the oxidative coupling of benzylamines to imines
with molecular oxygen under visible luminance at room
temperature using acetonitrile as reaction medium (Scheme 1).
At first, the oxidative coupling of benzylamine was chosen as a
representative reaction for screening experiments. The results of
these experiments are summarized in Table 1. To evaluate the
effect of loading of Ag NPs in the hybrid photocatalyst, two
more samples using different amount of Ag NPs (3 and7 wt%)
was prepared and tested under identical conditions. The activity
order of these materials was found to be in the order
3%Ag@rGO <5%Ag@rGO> 7%Ag@rGO (Table 1, entry 1).
The poor product yield in 3% Ag@rGO might be due to the less
concentration of the reactive Ag0-sites on the surface; whereas
leaching of active Ag0-content from the surface in 7% Ag@rGO
was responsible for the poor reactivity. Hence, 5%Ag@rGO was
considered to be optimum photocatalyst for this transformation.
Among the different solvents such as DMF, methanol, ethanol,
THF and acetonitrile studied, acetonitrile was found to be best
for this transformation (Table 1, entry 2). Visible light irradiation
was found to be essential and there was no reaction occurred in
the dark under described conditions (Table 1, entry 3). Similarly,
there was no reaction observed in the absence of photocatalyst
under visible irradiation even after the prolonged reaction time
(Table 1, entry 3). The use of individual components, such as
rGO and Ag NPs as photocatalysts under the identical conditions
afforded only 13 and 17% conversion of benzylamine,
respectively (Table 1, entry 4-5). Molecular oxygen was found to
be vital, and a negligible yield of the desired product was
obtained when nitrogen was used in place of oxygen (Table 1,
entry 6).
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Table 2: Ag@rGO catalyzed oxidative coupling of amines under visible
light irradiation.
Entr
y
1
Reactants
Products
Conv
(%)b
98
Yield
(%)c
97
TOF
(h-1)
8.0
NH2
N
NH2
N
2
3
96.5
94
7.8
H3CO
H3CO
OCH3
NH2
N
93
91
7.5
H3
C
H3
C
CH3
NH2
NH2
N
4
5
88
85
87
83
7.2
6.9
Table 1: Results of screening experiments.a
N
N
Conv.
Visible
light
Entry
1
Photocatalyst
Solvent
CH3CN
(%)b
NH2
6
7
8
83
86
89
82
84
87
6.8
7.0
7.2
Br
Br
Br
5%Ag@rGO
3%Ag@rGO
7%Ag@rGO
98
56
84
91
72
54
75
NH2
NH2
N
NC
CN
NC
Yes
N
F
F
F
DMF
MeOH
THF
5%Ag@rGO
N
2
3
Yes
9
NH2
84
-
82
-
6.8
Cl
Cl
EtOH
Cl
NH2
10
11
12
-
-
-
-
-
-
No
5%Ag@rGO
-
-
CH3CN
c
Yes
-
NH2
-
-
Ag NPs
rGO
4
5
Yes
Yes
Yes
CH3CN
CH3CN
CH3CN
17
13
-
-
-
NH2
aReaction conditions: substrate (1 mmol), 5%Ag@rGO (25 mg),
acetonitrile (10 mL) under visible light irradiation with white cold LED λ
> 400 nm; time: 12 h using molecular oxygen as oxidant; Power at
reaction vessel: 70 W/m2; bdetermined by GC-MS; cIsolated yield.
5%Ag@rGO
6d
aReaction conditions: benzylamine (1 mmol), photocatalyst (25 mg),
solvent (10 mL), light source: white cold LED λ > 400 nm, time: 12h
using molecular oxygen as oxidant; bdetermined by GC-MS; cReaction
time, 24h; dIn the absence of molecular oxygen (under N2 atmosphere).
Further, the recyclability experiments were perfromed by
selecting the oxidative coupling of benzylamine as
a
representative example. After completion of the reaction, the
photocatalyst was easily separated by filtration, washed with
acetonitrile, dried and reused for subsequent experiment with
fresh substrate. The results of recycling experiments are depicted
in Fig. 7. The conversion and product yield remained almost
same for seven cycles, confirming that the developed catalyst
was highly stable and reusable with consistent efficiency.
Further to check the leaching of Ag NPs during the reaction,
selected filtrate samples were analyzed by ICP-AES analysis.
Based on these experiments, it can also be concluded that the
main reactive sites for this transformation in the developed
photocatalyst were Ag NPs. However supporting them to rGO
significantly improved the reactivity and provided higher
conversion and product yield. The presence of rGO support in
the photocatalyst mainly provided increased surface area, facile
collection and transportation of the electrons on the surface to
suppress the recombination of electrons and holes, and finally
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There was no detectable amount of Ag NPs observed, which
conversion reached up to 98% under same reaction conditions.
These experimental results confirmed theDgOeIn: 1e0ra.1t0io3Vn9i/eCwo9fANrstJiic0nle0gO8len5tl2inGe
oxygen (1O2) in the photocatalytic system under visible light
irradiation.
eliminated the possibility of leaching of Ag during the
photoreactions. Furthermore, the metal loading in the recovered
photocatalyst after 7th run was found to be 4.98 wt% which was
almost similar to the fresh one (5 wt%). These results indicated
that the developed photocatalyst was highly stable,
heterogeneous and no leaching had occurred during the
photocatalytic experiments.
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Fig. 8: Conversion of benzylamine using Ag@rGO photocatalyst as such
and with adding NaN3 as a quencher.
Conclusions
We have demonstrated an efficient, easily synthesized and cost-
effective heterogeneous photocatalyst prepared by single step in-
situ grafting of the Ag NPs onto the surface of rGO for the
oxidative coupling of benzylamines to imines under visible light
at room temperature. The developed photocatalyst exhibited
higher efficiency as compared to its individual components such
as rGO and Ag NPs and reported photocatalysts in the prior art
(Table S1). More importantly, the photocatalyst showed
consistent recycling for several runs without any remarkable loss
of the activity. This study promotes the synthesis of graphene-
based heterogeneous materials for visible light assisted organic
transformations.
Fig. 7: Results of recycling experiments
The exact mechanism of the reaction is not known at this stage.
Based on the existing reports, a plausible mechanism of the
reaction is proposed as shown in Scheme 2. Under the light
irradiation, charge separation takes place in the photocatalyst and
photo-generated electrons are produced in the conduction band
(CB) and photo-generated holes remain in the valence band
(VB). The presence of rGO owing to its 2D planar conjugated
structure facilitated the charge separation and provided mobility
of these electrons on the photocatalyst surface.47 These hot
electrons react with oxygen molecules adsorbed on the rGO
surface and converted to O2·– radicals.48 These O2 ·– radicals are
very powerful oxidizing agents and can oxidize benzylamine to
imine under visible-light irradiation. At the same time, reactive
holes in the VB of Ag are able to oxidize benzylamine molecule
directly due to their strong oxidizing ability. As a result, the
separated electrons and holes are fully involved in the
photocatalytic reactions and provided improved activity.
Experimental
Materials
All chemicals were analytical reagent grade and used as received
without further purification. Graphite flakes, potassium
permanganate (99%), sodium nitrate (99%), silver nitrate
(AgNO3), sodium borohydride (NaBH4) was purchased from
Sigma-Aldrich. Hydrogen peroxide (30%), acetonitrile, formic
acid, hydrochloric acid and sulphuric acid (H2SO4) procured
from Alfa Aesar. The deionized (DI) water used throughout the
experiments was of HPLC grade. Graphene oxide was
synthesized from graphite powder according to the modified
method reported by Hummers and Offeman49.
Synthesis of in situ Ag@rGO hybrid photocatalyst50
Graphene oxide (1.0 g) was sonicated with 50 ml DI water, and
then 2 mL of formic acid was mixed in the reaction mixture.
Subsequently, AgNO3 (50 mg) was added as a precursor of Ag
NPs in the hybrid material. The reaction mixture was heated at
80 °C for 6 h under continuous stirring. The solid was separated
by filtration and washed with deionized water for several times
followed by a saturated solution of sodium bicarbonate to
remove the excess formic acid. Finally the solid was washed
with deionized water and dried under vacuum for overnight at 60
0C for 6h. For the comparative study, bare reduced graphene
oxide (rGO) was prepared by following the similar procedure
without adding silver nitrate. Similarly, other Ag@rGO samples
containing different amount of Ag NPs were prepared for the
comparative study.
Scheme 2: Plausible mechanism of photocatalytic oxidative coupling of
benzylamine in the presence of Ag@rGO photocatalyst.
Furthermore, in order to verify the suggested mechanism we
performed the quenching experiments by using NaN3 as
quencher. A comparison between the original photocatalytic
experiment and that obtained after the addition of sodium azide
(NaN3) at different time intervals followed by the analysis by
GC-MS (Fig. 8) was made to visualize the quenching effect of
azide ions. After adding NaN3 as quencher the maximum
conversion of benzylamine in the presence of hybrid
photocatalyst was reached only up to 13.7% after 12h. While in
case of original photocatalytic experiment, the maximum
Characterization Techniques
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Surface morphology of the samples was determined by High-
resolution transmission electron microscopy (HR-TEM) with
JEM 2100, Japan operated at an accelerating voltage of 200 kV
using lanthanum hexaboride as a source of electrons. X-ray
photoelectron spectroscopy (XPS) measurement of photocatalyst
was carried out using ESCA+ (omicron nanotechnology, Oxford
instruments Germany) XPS system having an angle between
analyzer to the source is 90 o. All the binding energies were
referenced to the C1s peak at 284.6 eV of the surface
adventitious carbon. Fourier Transform Infrared (FT-IR) spectra
were recorded on Perkin-Elmer spectrum RX-1 IR
spectrophotometer using potassium bromide window. The
crystalline structure of the samples was determined by Bruker
D8 Advance diffractometer with Cu Ka radiation, (λ= 1.5418 Å)
in the range of 2θ = 20-80 and a scan rate of 40 min-1. UV-
visible spectra of the samples were collected on Perkin Elmer
Lambda-19 UV-VIS-NIR spectrophotometer using a 10 mm
quartz cell while absorption spectra of solid samples were
recorded by using fine powder of BaSO4 as a reflectance
standard. Raman spectra of samples were measured at room
temperature using a Raman Microprobe (HR-800 Jobin-Yvon)
with 532 nm Nd-YAG excitation source. The specific surface
area of the samples was determined by nitrogen adsorption-
desorption isotherm at 77 K by using VP; Micromeritics
ASAP2010. Thermal degradation pattern of the materials was
calculated by TG-DTA analysis by using a thermal analyzer TA-
SDT Q-600 in the temperature range of 40 to 800 °C under
nitrogen flow with a heating rate 10 °C/min. 1H NMR of the
reaction products was collected at 500 MHz by using a Bruker
Advance-II 500 MHz instrument.
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Acknowledgments
Authors are grateful to Director IIP for granting permission to
publish these results. AK express their sincere thanks to CSIR,
New Delhi, for providing financial assistance in terms of
research fellowship. DST, New Delhi is kindly acknowledged
for funding under the project GAP-3125. The analytical division
is acknowledged for providing support in the analysis of the
samples
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