Incorporation of nanosized ZnWO4 and Fe3O4 on graphitic carbon nitride to fabricate a novel, highly active magnetically recoverable catalyst in Claisen–Schmidt condensation

Article abstract of DOI:10.1016/j.jpcs.2019.109117

Herein we outline a facile and viable approach for successful anchoring of ZnWO₄ and Fe₃O₄ nanoparticles on graphitic carbon nitride (g-C₃N₄) through ultrasonication and microwave irradiation. The as-synthesised nanocomposite, g-C₃N₄–Fe₃O₄–ZnWO₄, was characterised using Fourier transmission infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, vibrating-sample magnetometry, and X-ray photoelectron spectroscopy techniques. The nanocomposite exhibited appreciable catalytic performance in the Claisen–Schmidt condensation reaction between benzaldehyde and acetone producing dibenzalacetone with excellent yields. The as-prepared catalyst demonstrated excellent magnetically recyclable property for seven successive runs. The presence of g-C₃N₄ in the nanocomposite g-C₃N₄–Fe₃O₄–ZnWO₄ played a significant role in promoting the catalytic activity due to its inherent basic nature and efficient grafting of the substrates onto the g-C₃N₄ sheets.

Full text of DOI:10.1016/j.jpcs.2019.109117

Accepted Manuscript
Incorporation of nanosized ZnWO and Fe O on graphitic carbon nitride to
3 4
4
fabricate a novel, highly active magnetically recoverable catalyst in Claisen–Schmidt
condensation
Arijita Paul, Meghali Devi, Siddhartha Sankar Dhar
PII:
S0022-3697(19)30483-4
DOI:
https://doi.org/10.1016/j.jpcs.2019.109117
Article Number: 109117
Reference:
PCS 109117
To appear in: Journal of Physics and Chemistry of Solids
Received Date: 2 March 2019
Revised Date: 19 July 2019
Accepted Date: 22 July 2019
Please cite this article as: A. Paul, M. Devi, S.S. Dhar, Incorporation of nanosized ZnWO and Fe O
4
on graphitic carbon nitride to fabricate a novel, highly active magnetically recoverable catalyst in
Claisen–Schmidt condensation, Journal of Physics and Chemistry of Solids (2019), doi: https://
doi.org/10.1016/j.jpcs.2019.109117.
3 4
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ACCEPTED MANUSCRIPT
Graphical Abstract

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Incorporation of nanosized ZnWO4 and Fe3O4 on graphitic carbon nitride to fabricate a
novel, highly active magnetically recoverable catalyst in Claisen–Schmidt condensation.
Arijita Paula,b, Meghali Devib, Siddhartha Sankar Dharb*
aDepartment of Chemistry, Karimganj College, Karimganj-788710, Assam, India.
bDepartment of Chemistry, National Institute of Technology Silchar, Silchar-788010, Assam,
India.
*Corresponding Author. Tel: +91-03842-242915; Fax: +91-03842-224797
Email: ssd_iitg@hotmail.com (S. S. Dhar)
ABSTRACT
Herein we outline a facile and viable approach for successful anchoring of ZnWO4 and Fe3O4
nanoparticles on graphitic carbon nitride (g-C3N4) through ultrasonication and microwave
irradiation. The as-synthesised nanocomposite, g-C3N4–Fe3O4–ZnWO4, was characterised
using Fourier transmission infrared spectroscopy, X-ray diffraction, scanning electron
microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy,
vibrating-sample magnetometry, and X-ray photoelectron spectroscopy techniques. The
nanocomposite exhibited appreciable catalytic performance in the Claisen–Schmidt
condensation reaction between benzaldehyde and acetone producing dibenzalacetone with
excellent yields. The as-prepared catalyst demonstrated excellent magnetically recyclable
property for seven successive runs. The presence of g-C3N4 in the nanocomposite g-C3N4–
Fe3O4–ZnWO4 played a significant role in promoting the catalytic activity due to its inherent
basic nature and efficient grafting of the substrates onto the g-C3N4 sheets.
Keywords: Novel; g-C3N4–Fe3O4–ZnWO4; Catalyst; Claisen–Schmidt condensation;
Magnetically recoverable
1. Introduction

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Development of existing catalytic technologies for synthesis of important organic compounds
is viewed as a significant goal in scientific research. Such advances have been at the cutting
edge of research for several generations [1–3]. The base-catalysed organic transformations
such as Knoevenagel, aldol, Claisen–Schmidt condensations, and trans-esterification
reactions are of great significance in both industry and academic research [4]. The Claisen–
Schmidt or crossed aldol condensation is an efficient process for making carbon–carbon
bonds in the formation of various sorts of carbonyl compounds [5–8]. Such a reaction
between acetone and benzaldehyde leads to formation of dibenzalacetone (DBA), which is
synthetically quite useful owing to its property of absorbing harmful UV radiation from the
sun, which is used to protect human skin. It is thus an essential ingredient of sunscreens [9].
The DBA and some of its derivatives also exhibit anti-inflammatory [10], anti-parasitic [11],
and anti-mycobacterial [12] properties; DBA is also used as a ligand in organometallic
chemistry [13]. Such reactions often need stoichiometric amounts of the base together with
increased reaction time, lack of reusability, and harsh reaction conditions such as high
temperature. Presence of bases in the final reaction mix are often difficult to isolate, resulting
in tedious workup procedures like base neutralisation steps, difficult product separation, and
purification [4,5].
In recent times, organocatalysis has emerged as a promising approach for applications in
green catalysis [4]. The organocatalyst graphitic carbon nitride (g-C3N4), an attractive and
emerging two-dimensional material with large surface area, has attracted substantial attention
due to its high nitrogen content and excellent chemical and heat stability [14–16]. The
presence of nitrogen atoms in this material also results in its basic properties [17]. Moreover,
g-C3N4 is cost effective and environmentally benign since it can be easily prepared by direct
thermal condensation of nitrogen-rich materials like urea, melamine, cyanamide, thiourea,
and dicyanamide [16,18–20]. The basic sites inherent in g-C3N4 are due to the presence of

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some uncondensed primary and secondary amino groups lying at the edges of graphitic sheets
obtained during pyrolysis of suitable carbon nitride precursors. This gives it a Lewis and
Bronsted base character which can be exploited in base-catalysed organic reactions [17]. This
surface basic nature of g-C3N4 makes it an efficient catalyst for several base-catalysed
transformation reactions [21,22].
Recently, the immobilisation process has emerged as an efficient technique for improving
catalytic activity [23]. The incorporation of metal and metal oxide nanoparticles on g-C3N4
nanosheets results in increased charge separations at the metal–semiconductor heterojunction
interface. This further improves catalyst performance, preventing aggregation of these
nanoparticles and enhancing selectivity in addition to activity [24–27].
Metal tungstates have been widely explored due to their superior properties and significant
applications in diverse fields. These tungstate materials have been used as efficient catalysts
and photocatalysts in several organic transformation reactions such as oxidation of benzyl
alcohols, bromides and chlorides, esterification reactions, and degradation of dyes [28–33].
Fusing tungstates with g-C3N4 helps improve the overall catalytic performance of the
catalyst. However, both g-C3N4 and tungstate based catalysts face problems in their recovery
from the reaction medium. Combining these catalysts with a magnetic material helps the ease
of recovery of the catalyst from the suspension using an external magnet [34]. Moreover,
roles of magnetic materials are well established as efficient magnetically retrievable catalysts
in several organic reactions [35–37].
Thus, in continuation of our current studies of nanocatalysts and their applications, especially
magnetically recoverable catalysts [5,35–38], we contemplated fabrication of g-C3N4–Fe3O4–
ZnWO4 nanocomposite and evaluation of its catalytic performance in the Claisen–Schmidt
condensation reaction between benzaldehyde and acetone. To the best of our knowledge,

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there have been no reports on preparation and application of g-C3N4–Fe3O4–ZnWO4 as an
efficient magnetically separable catalyst.
2. Experimental
2.1. Materials and physical measurements
Melamine and the metal salt precursors ferric nitrate [Fe(NO3)3·9H2O], ferrous sulphate
(FeSO4·7H2O), zinc nitrate [Zn(NO3)3·6H2O], and sodium tungstate (Na2WO4·2H2O) were
purchased from Sigma Aldrich. Acetone, benzaldehyde, and 30% aqueous ammonia (NH3)
solution were obtained from Merck India Ltd. Double-distilled water was used throughout the
experimental process. The X-ray diffraction (XRD) measurements were done on a Philips
X’Pert Pro Powder X-ray Diffractometer with Cu-Kα radiation (λ = 1.5418 Å) and scan
speed of 2°/min. Fourier transmission infrared spectroscopy (FT-IR) spectra were recorded
on Thermo Nicolet, Avatar 370 on KBr matrix. Scanning electron microscopy (SEM)
micrographs were obtained using a JEOL Model JEM-6390LV instrument. Energy-dispersive
X-ray spectroscopy (EDX) was performed on OXFORD XMX N equipment. Transmission
electron microscopy (TEM) and high-resolution TEM (HRTEM) studies were performed
using a Tecnai G2 20. The X-ray photoelectron spectroscopy (XPS) analysis was conducted
on PHI 5000 Versa Prob II, Fei Inc. Vibrating-sample magnetometry (VSM) measurements
were conducted on a Lakeshore Model 7410 series.
2.2. Synthesis of g-C3N4
For preparation of g-C3N4, 5 g of melamine was placed in a semi-closed crucible and calcined
in a furnace at 550 °C for about 4 h. The obtained pale yellow sample was cooled at room
temperature, ground to a powdered form in a mortar, and stored for further use.
2.3. Synthesis of g-C3N4–Fe3O4–ZnWO4 nanocomposite
In preparing g-C3N4–Fe3O4–ZnWO4 nanocomposite, firstly 0.50 g of g-C3N4 was dispersed
into 100 ml of distilled water and irradiated ultrasonically for about 30 min. In one beaker,

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0.81 g of Fe(NO3)3·9H2O (2 mmol) was dissolved in 20 ml of distilled water; in another
beaker around 0.28 g of FeSO4·7H2O (1 mmol) was dissolved in 10 ml of distilled water.
Both solutions were then added to the prepared yellowish g-C3N4 suspension and stirred for
about 2 h. To maintain pH 9, aqueous NH3 (10 ml of 30% NH3 in 250 ml of distilled water)
was added. It was then subjected to 450-W microwave irradiation for about 10 min and
cooled at room temperature. The precipitate g-C3N4–Fe3O4 was obtained, and 0.16 g of
Zn(NO3)3·6H2O dissolved in 10 ml distilled water was added to it and stirred. An aqueous
solution of Na2WO4·2H2O (0.15 g in 10 ml) was added dropwise to the stirred suspension
and stirred for about 2 h. Afterwards, 10 ml of NH3 was added to the reaction mixture and
exposed to 450-W microwave irradiation for 10 min. The suspension obtained was
centrifuged and the precipitate heated in a Teflon-based autoclave at 180 °C for about 3 h.
The g-C3N4–Fe3O4–ZnWO4 obtained was then washed with ethanol and dried.
2.4. Claisen–Schmidt condensation of benzaldehyde with acetone
A mixture of acetone (5 mmol) and benzaldehyde (10 mmol) was placed in a 50-ml round-
bottomed flask fixed to a condenser. The prepared catalyst, g-C3N4–Fe3O4–ZnWO4 (20 mg)
was added to the reaction mixture and heated at 70 °C for about 1.5 h to obtain the desired
product DBA. After the reaction was complete, the catalyst was isolated from the reaction
mixture using an external magnet. The formed yellowish suspension was left undisturbed for
approximately 12 h to obtain a yellow crystalline product, then filtered, and recrystallised
from acetonitrile. The product was characterised by 1H and 13C NMR spectroscopy (Figs. S1
and S2 in Supporting Information).
3. Results and discussion
The g-C3N4 was obtained via thermal decomposition of precursor melamine at 550 °C. The
metal oxides ZnWO4 and Fe3O4 were then intercalated into the prepared g-C3N4 sheets using
microwave radiation followed by hydrothermal treatment.

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3.1. Structural analysis
The powder XRD studies were conducted to examine the crystalline phase and purity of the
synthesised g-C3N4–Fe3O4–ZnWO4 nanocomposite. The XRD patterns of g-C3N4, Fe3O4,
ZnWO4, and g-C3N4–Fe3O4–ZnWO4 are presented in Fig. 1. The XRD of ZnWO4 and Fe3O4
are in accordance with the literature values of JCPDS File No. 15-0774 and 89-3854,
respectively. A strong diffraction peak at 27.5° for g-C3N4 can be indexed to the (002) plane
and is symbolic of the stacking of a conjugated aromatic system [4]. This broad peak
indicates the amorphous nature of the synthesised g-C3N4.
Fig. 1. Powder XRD pattern of g-C3N4, Fe3O4, ZnWO4, and g-C3N4–Fe3O4–ZnWO4
nanomaterials.
The diffraction peaks of g-C3N4–Fe3O4–ZnWO4 nanocomposite can be indexed to the face-
centred cubic magnetite phase of Fe3O4 (JCPDS File No. 89-3854) and primitive monoclinic
sanmartinite phase of ZnWO4. The broad peak at 27.4° for g-C3N4 in the nanocomposite

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reflects its amorphous nature. These results confirm an effective fabrication of g-C3N4 sheets
with Fe3O4 and ZnWO4. The XRD pattern of g-C3N4–Fe3O4–ZnWO4 shows no impurity
peak, suggesting formation of a highly pure nanocomposite. The average crystallite sizes of
the incorporated ZnWO4 and Fe3O4 were calculated using the Debye–Schrerrer equation:
d = kλ/βcosθ
where d is average crystallite size, λ is wavelength of Cu-Kα radiation, β is the full width at
half maximum (FWHM) of the highest intensity diffraction peak, θ is the Bragg
diffraction angle, and k is a shape factor of value about 0.9. The values for crystallite
size of ZnWO4 and Fe3O4 were 14.65 and 13.02 nm, respectively.
The FT-IR spectra of the prepared g-C3N4 and as-fabricated g-C3N4–Fe3O4–ZnWO4
heterostructures are shown in Fig. 2. In the FT-IR spectrum of g-C3N4 (Fig. 2a), the sharp
peak at 803 cm−1 can be attributed to the characteristic ring breathing modes of s-triazine
units. The strong absorption bands centred in the range 1245–1620 cm−1 correspond to
stretching vibration modes of C–N heterocycles [4,38,39]. The broad band of 3000–3400
cm−1 may be assigned to stretching vibration modes of primary and secondary amines [14].
The FT-IR spectrum of g-C3N4–Fe3O4–ZnWO4 (Fig. 2b) shows absorption bands at 463 and
891 cm−1, which correspond to bending and stretching vibration modes of W–O, respectively.
The absorption peak around 720 cm−1 can be ascribed to the symmetric vibration mode of
bridged O atoms of Zn–O–W [28]. The peak at 570 cm−1 can be indexed to the characteristic
bond absorption of Fe–O [40]. The other bands correspond to the stretching vibration modes
exhibited by g-C3N4 (Fig. 2b).

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Fig. 2. FT-IR spectra of (a) g-C3N4 and (b) g-C3N4–Fe3O4–ZnWO4 nanocomposite.
3.2. Morphological analysis
The morphological attributes of the synthesised composite were studied using SEM images
(Fig. 3). The dispersal of ZnWO4 and Fe3O4 on g-C3N4 sheets is shown in the SEM image

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corresponding to g-C3N4–Fe3O4–ZnWO4 in Fig. 3. Further TEM studies investigated the size
and shape of components forming the nanomaterial g-C3N4–Fe3O4–ZnWO4 (Fig. 4). The
TEM images show the formation of rod-shaped g-C3N4 material (Fig. 4a and b). The ZnWO4
and Fe3O4 nanoparticles are well scattered on the synthesised rod-like g-C3N4 nanomaterial
(Fig. 4c–e). The HRTEM image of the nanohybrid is displayed in Fig. 4e. The lattice fringes
of 0.295 nm correspond to the (111) plane of ZnWO4 and 0.167 nm corresponds to the (511)
plane of Fe3O4. The electron diffraction (ED) pattern of the nanocomposite shows that the
ZnWO4 and Fe3O4 nanoparticles immobilised onto g-C3N4 rods exhibit a polycrystalline
nature (Fig. 4f). Peaks for C, N, O, Zn, W, and Fe are observed in the EDX spectrum of the
nanocomposite (Fig. 5).
Fig. 3. SEM images of g-C3N4, Fe3O4, ZnWO4, and g-C3N4–Fe3O4–ZnWO4 nanomaterials.

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Fig. 4. TEM images of (a, b) g-C3N4 and (c, d) g-C3N4–Fe3O4–ZnWO4; (e) HRTEM of g-
C3N4–Fe3O4–ZnWO4; and (f) ED pattern of g-C3N4–Fe3O4–ZnWO4 nanocomposite.
Fig. 5. EDX spectrum of g-C3N4–Fe3O4–ZnWO4 nanocomposite.

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In order to investigate the elemental composition and chemical status of the g-C3N4–Fe3O4-
ZnWO4 nanomaterial surface in detail, XPS was carried out. The wide-scan XPS spectrum of
the nanohybrid surface reveals the presence of elements C, N, Zn, W, Fe, and O (Fig. 6a).
This validates the effective fabrication of ZnWO4 and Fe3O4 on g-C3N4 rods. The high-
resolution spectra for C 1s, N 1s, Fe 2p, O 1s, Zn 2p, and W 4f are shown in Fig. 6b–g,
respectively. The C 1s spectrum shows two binding energy peaks at 286.1 and 282.57 eV
(Fig. 6b), which correspond to C–C and N=C–N [38]. The XPS spectrum of N 1s is
deconvoluted into three characteristic peaks centred at 396.65, 398.70, and 402.45 eV (Fig.
6c) which are ascribed to the C=N–C aromatic nitrogen in triazine rings, tertiary nitrogen in
N–(C)3, and nitrogen in the uncondensed terminal amino groups, respectively [38,41]. The
high-resolution spectrum for Fe 2p region shows two characteristic peaks at 709.23 and 722.
78 eV (Fig. 6d), which are indexed to Fe 2p3/2 and Fe 2p1/2 states, respectively. There is an
energy separation of 13.5 eV between the two states of iron, consistent with previous reports
[42]. The high-resolution spectrum for O 1s when deconvoluted shows two peaks with
binding energies 528.14 and 530.12 eV (Fig. 6e), which are characteristic of Fe–O and W–O–
W bonds, respectively. The high-resolution Zn 2p region shows two broad peaks at 1019.25
and 1042.45 eV (Fig. 6f) and correspond to the Zn 2p3/2 and Zn 2p1/2 states, respectively [43].
The W 4f spectrum shows two binding energy peaks at 33.39 and 35.45 eV (Fig. 6g)
representing W 4f7/2 and W 4f5/2 in the W6+ state, respectively [43,44]. These results further
validate the successful anchoring of ZnWO4 and Fe3O4 on g-C3N4 rods.

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Fig. 6. (a) Full scan XPS spectrum of g-C3N4–Fe3O4–ZnWO4; and high-resolution XPS
spectra of (b) C 1s, (c) N 1s, (d) Fe 2p, (e) O 1s, (f) Zn 2p, and (g) W 4f.
3.3. Magnetism studies

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Magnetic measurements were performed to examine the magnetic behaviour of the as-
synthesised nanohybrid g-C3N4–Fe3O4–ZnWO4 at 300 K with the applied external magnetic
field ranging from −20 000 to +20 000 Oe. The magnetic hysteresis curve (Fig. 7) shows
ferromagnetic character with retentivity (Mr) 27.52 emu/g and coercivity (Hci) 12.269 Oe.
Fig. 7. Room temperature hysteresis curve for g-C3N4-Fe3O4-ZnWO4 nanocomposite.
3.4. Evaluation of catalytic efficiency of the nanocomposite
After successful synthesis and detailed characterisation of the nanocomposite g-C3N4–Fe3O4–
ZnWO4 was accomplished, its ability as a catalyst was explored in the Claisen–Schmidt
condensation of benzaldehyde with acetone. The schematic representation of this reaction is
shown in Fig. 8.

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Fig. 8. Claisen–Schmidt condensation reaction between acetone and benzaldehyde in the
presence of catalyst g-C3N4–Fe3O4–ZnWO4 nanocomposite.
Optimisation studies for reaction parameters like temperature, catalyst quantity, and reaction
time were performed to obtain the best reaction conditions, and the results are shown in Fig.
9.
To optimise reaction temperature, Claisen–Schmidt condensation of benzaldehyde with
acetone was carried out at temperatures ranging from room temperature to 80 °C and the
corresponding DBA yields were recorded. The reaction showed maximum product yield at 70
°C. Following this, the catalyst quantity required was optimised. For this, the same reaction
was conducted using varying amounts of catalyst in the range of 10–50 mg. An increase in
catalyst amount from 10 to 20 mg resulted in increases in DBA yield; however, further
increases in catalyst amount did not significantly boost product yield. In the absence of
catalyst, the catalytic reaction did not proceed. Thus 20 mg is considered the ideal catalyst
amount required for this catalytic reaction at 70 °C. Finally, the time required to ensure
completion of the reaction was also optimised. Keeping other parameters constant, the same
reaction was performed for different reaction times of 1–3 h. A maximum yield of DBA
(95%) was achieved for a reaction time of 1.5 h. It should be noted that no self-condensation
product was observed in this reaction.

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Fig. 9. Effect of reaction parameters on the Claisen–Schmidt condensation reaction between
acetone and benzaldehyde: (a) catalyst amount (mg); (b) reaction temperature (°C); (c)
reaction time (h); and (d) recyclability test of the catalyst against number of runs.
Employing the best reaction conditions obtained from optimisation studies, the reaction was
performed using ZnWO4, Fe3O4, and g-C3N4 individually. Although g-C3N4 could aid in
formation of DBA due to its inherent basic nature, the yield significantly increased on using
g-C3N4–Fe3O4–ZnWO4 nanocomposite as catalyst. The corresponding yields of DBA
obtained when using Fe3O4, ZnWO4, and g-C3N4 individually and Fe3O4/ZnWO4, Fe3O4/g-
C3N4, ZnWO4/g-C3N4, and g-C3N4–Fe3O4–ZnWO4 in combinations as catalysts in the present
organic reaction are presented graphically in Fig. 10. Using g-C3N4 and g-C3N4–Fe3O4
nanocomposite as catalyst results in 62% and 70% DBA yield, respectively. However, the

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yield significantly increases to 95% on incorporation of ZnWO4 into the combination g-
C3N4–Fe3O4. This marked increase in DBA yield from 70% to 95% might be attributed to the
synergetic effects between g-C3N4, Fe3O4, and ZnWO4. Moreover, the catalyst ZnWO4/g-
C3N4 gives about 82% DBA yield. These results also emphasise the catalytic importance of
ZnWO4 in the prepared nanocomposite for DBA synthesis. It is noteworthy that no such
catalytic performance was observed on using ZnWO4 and Fe3O4 individually because of the
absence of g-C3N4 counterparts.
To ascertain that the high performance of catalyst g-C3N4–Fe3O4–ZnWO4 is probably due to
effective synergism between the various counterparts in the catalyst and not because of g-
C3N4 alone, the initial g-C3N4 was also subjected to ultrasonic treatment for 30 min followed
by 450-W microwave irradiation for 10 min prior to its use as the catalyst. However, there
was no increase in yield of the product, clearly suggesting that the enhanced activity is due to
synergism between its various components.
Fig. 10. Percentage yield of DBA obtained using different nanomaterials.
The possible mechanism for DBA formation can be explained as follows. The inherent basic
nature of g-C3N4 may have provided some degree of basicity to the nanocomposite g-C3N4–

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Fe3O4–ZnWO4, which resulted in the abstraction of protons from acetone forming the enolate
ion. Moreover, the presence of ZnWO4 and Fe3O4 on g-C3N4 may have facilitated better
interaction between substrates and the catalyst matrix, causing an increased rate of formation
of enolate ions. The enolate ions, being nucleophiles, then attacked the electron-deficient
carbonyl centre of benzaldehyde forming DBA. The HRTEM micrograph further shows that
ZnWO4 and Fe3O4 nanoparticles are in contact with each other while anchored onto g-C3N4
(Fig. 4e), suggesting interaction between these two metal oxide nanoparticles on the surface
of g-C3N4. Due to this possible interaction, a synergism might develop among ZnWO4,
Fe3O4, and g-C3N4, which may be responsible for the distinct enhancement of catalytic
performance in the synthesised g-C3N4–Fe3O4–ZnWO4 catalyst.
The reusability of the catalyst was then checked for the same condensation reaction under the
same optimised reaction conditions for seven consecutive runs (Fig. 9d). After each run the
catalyst was isolated magnetically from the reaction mixture, washed with water and acetone,
dried, and then reused for further cycles. Interestingly, the catalyst performed very well in
terms of product yield even after seven recycles.
The reused catalyst after the seventh cycle was easily isolated through magnetic separation
and was investigated for any significant change in its structure and morphology using powder
XRD, SEM, and TEM studies (Fig. 11). The powder XRD pattern of the spent catalyst shows
peaks indicating the presence of ZnWO4, Fe3O4, and g-C3N4. The SEM and TEM also reflect
no pronounced change in shape and morphology compared with fresh catalyst. However, the
TEM micrograph reflects a slight increase in agglomeration in structure of the recycled
catalyst.

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Fig. 11. (a) Powder XRD pattern and (b) SEM and (c) TEM micrographs of recycled catalyst.
4. Conclusion
A novel nanocomposite g-C3N4–Fe3O4–ZnWO4 was developed by microwave irradiation
followed by hydrothermal treatment. Detailed characterisation techniques confirmed the
successful anchoring of ZnWO4 and Fe3O4 nanoparticles on g-C3N4 sheets. The
nanocomposite performed very well as a catalyst in Claisen–Schmidt condensation of

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benzaldehyde and acetone to form DBA. The catalyst had excellent reusability even after five
recycles. Hence g-C3N4–Fe3O4–ZnWO4 nanocomposite has great prospects as a highly active
catalyst for other practical applications.
Acknowledgements
The authors are highly thankful to DST-SAIF, Kochi, CRF-IIT Delhi, ACMS- IIT Kanpur,
SAIF-Gauhati University, and CIF-IIT Guwahati for analysis. The Director, NIT Silchar, and
Advanced Institutional Biotech Hub, Karimganj College (BCIL/NER-BPMC/2010 dated 30th
November 2010) are acknowledged for providing infrastructural facilities. Financial
assistance from the Science and Engineering Research Board, Government of India is also
acknowledged (EMR/2016/005860).
References
1. A. Allahresani, B. Taheri, M.A. Nasseri, A green synthesis of spirooxindole derivatives catalyzed
by SiO2@g-C3N4 nanocomposite, Res. Chem. Intermed. 44 (2018) 1173–1188.
2. P.V.R.K. Ramacharyulu, Sk.J. Abbas, S.R. Sahoo, S. Ke, Mechanistic insights into 4-nitrophenol
degradation and benzyl alcohol oxidation pathways over MgO/g-C3N4 model catalyst systems, Catal.
Sci. Technol. 8 (2018) 2825–2834.
3. S. Sobhani, Z.P. Parizi, R. Nasseri, Nano n-propylsulphonated γ-Fe2O3, A novel magnetically
recyclable heterogeneous catalyst for the efficient synthesis of bis(pyrazolyl)methanes in water, J.
Chem. Sci. 125 (2013) 975–979.
4. P. Sharma, Y. Sasson, Highly active g-C3N4 as a solid base catalyst for Knoevenagel condensation
reaction under phase transfer conditions, RSC Adv. 7 (2017) 25589–25596.
5. B. Bhuyan, D.J. Koiri, M. Devi, S.S. Dhar, A novel MnFe2O4/ graphitic carbon nitride (g-C3N4)
nanocomposites as efficient magnetically retrievable catalyst in crossed aldol condensation, Materials
Letters, 218 (2018) 99–102.
6. G. Thirunarayanan, G. Vanangamudi, Synthesis of some 4-bromo-1-naphthyl chalcones using
silica-sulfuric acid reagent under solvent free conditions, ARKIVOC 2006 (2006) 58–64.

ACCEPTED MANUSCRIPT
7. S.R. Bankar, S.N. Shelke, Applicability of magnetically recyclable ferrite-L-cysteine nanocatalyst
for the green synthesis of quinoline and pyrazole derivatives under microwave irradiation, Current
Catalysis, 7 (2018) 43–51.
8. A. Maleki, P. Ravaghi, H. Movahed, Green approach for the synthesis of carboxycoumarins by
using a highly active magnetically recoverable nanobiocomposite via sustainable catalysis, Micro
Nano Lett., 13 (2018) 591–594.
9. L.A. Huck, W.J. Leigh, A better sunscreen: structural effects on spectral properties, J. Chem. Educ.,
87 (2010) 1384–1387.
10. R.V. Smerbeck, E.P. Pittz, Dibenzalacetone and benzylcinnamate as non-steroidal anti-
inflammatory compounds and compositions thereof. US patent 4587260. 1986 May 6.
11. I.S. Chauhana, G.S. Rao, J. Shankarc, L.K.S. Chauhan, G.J. Kapadia, N. Singh, Chemoprevention
of Leishmaniasis: In-vitro antiparasitic activity of dibenzalacetone, a synthetic curcumin analog leads
to apoptotic cell death in Leishmania donovani, Parasitol. Int. 67 (2018) 627–636.
12. V. Sedighi, P. Azerang, S. Sardari, Synthesis of dibenzalacetone derivatives and evaluation of
their antimycobacterial property, 3rd World Congress on Bioavailability & Bioequivalence,
Hyderabad, India (2012) 206.
13. A.G. Jarvis, A.C. Whitwood, I.J. Fairlamb, Cu(I) complexes containing a multidentate and
conformationally flexible dibenzylidene acetone ligand (dbathiophos): Application in catalytic alkene
cyclopropanation, Dalton Trans. 40 (2011) 3695–3702.
14. Q. Li, Y. He, R. Peng, Graphitic carbon nitride (g-C3N4) as a metal-free catalyst for thermal
decomposition of ammonium perchlorate, RSC Adv. 5 (2015) 24507–24512.
15. Y. Yang, C. Zhang, C. Lai, G. Zeng, D. Huang, M. Cheng, J. Wang, F. Chen, C. Zhou, W. Xiong,
BiOX (X=Cl, Br, I) photocatalytic nanomaterials: applications for fuels and environmental
management, Adv. Colloid Interface Sci. 254 (2018) 76–93.
16. C. Zhou, P. Xu, C. Lai, C. Zhang, G. Zeng, D. Huang, M. Cheng, L. Hu, W. Xiong, X. Wen, L.
Qin, J. Yuan, W. Wang, Rational design of graphic carbon nitride copolymers by molecular doping
for visible-light-driven degradation of aqueous sulfamethazine and hydrogen evolution, Chem. Eng. J.
359 (2019) 186–196.

ACCEPTED MANUSCRIPT
17. N.D. Shcherban, P. Mäki-Arvela, A. Aho, S.A. Sergiienko, P.S. Yaremov, K. Eränen, D.Y.
Murzin, Melamine-derived graphitic carbon nitride as a new effective metal-free catalyst for
Knoevenagel condensation of benzaldehyde with ethylcyanoacetate, Catal. Sci. Technol. 8 (2018)
2928–2937.
18. M.M.J. Sadiq, U.S. Shenoy, D.K. Bhat, Synthesis of BaWO4/NRGO–g-C3N4 nanocomposites with
excellent multifunctional catalytic performance via microwave approach, Front. Mater. Sci. 12 (2018)
247–263.
19. A. Wang, C. Wang, L. Fu, W. Wong-Ng, Y. Lan, Recent advances of graphitic carbon nitride-
based structures and applications in catalyst, sensing, imaging, and LEDs, Nano Micro Lett. 9 (2017)
doi: 10.1007/s40820-017-0148-2.
20. Y. Yang, C. Zhang, D. Huang, G. Zeng, J. Huang, C. Lai, C. Zhou, W. Wang, H. Guo, W. Xue, R.
Deng, M. Cheng, W. Xiong, Boron nitride quantum dots decorated ultrathin porous g-C3N4:
Intensified exciton dissociation and charge transfer for promoting visible-light driven molecular
oxygen activation, Appl. Catal., B 245 (2019) 87–99.
21. X. Jin, V.V. Balasubramaniam, S.T. Selvan, D.P. Sawant, M.A. Chari, G. Q. Lu, A. Vinu, Highly
ordered mesoporous carbon nitride nanoparticles with high nitrogen content: a metal free basic
catalyst, Angew. Chem. 121 (2009) 8024–8027.
22. S. Yin, J. Han, T. Zhou, R. Xu, Recent progress in g-C3N4 based low cost photocatalytic system:
activity enhancement and emerging, Catal. Sci. Technol. 5 (2015) 5048–5061.
23. H. Yi, M. Yan, D. Huang, G. Zeng, C. Lai, M. Li, X. Huo, L. Qin, S. Liu, X. Liu, B. Li, H. Wang,
M. Shen, Y. Fu, X. Guo, Synergistic effect of artificial enzyme and 2D nano-structured Bi2WO6 for
eco-friendly and efficient biomimetic photocatalysis, Appl. Catal., B 250 (2019) 52–62.
24. A. Allahresani, M.A. Nasseri, A. Nakhaei, SiO2/g-C3N4 nanocomposite-catalyzed green synthesis
of di-indolyloxindols under mild conditions, Res. Chem. Intermed. 43 (2017) 6367–6378.
25. N. Boonprakob, N. Wetchakun, S. Phanichphant, D. Waxler, P. Sherrell, A. Nattestad, J. Chen, B.
Inceesungvorn, Enhanced visible-light photocatalytic activity of g-C3N4/TiO2 films, J. Colloid
Interface Sci. 417 (2014) 402–409.

ACCEPTED MANUSCRIPT
26. J. Zhang, Z. Ma, Novel β-Ag2MoO4/g-C3N4 heterojunction catalysts with highly enhanced visible-
light-driven photocatalytic activity. RSC Adv. 7 (2017) 2163–2171.
27. H. Katsumata, Y. Tachi, T. Suzuki, S. Kaneco, Z-scheme photocatalytic hydrogen production over
WO3/g-C3N4 composite photocatalysts, RSC Adv. 4 (2014) 21405–21409.
28. M.J.S. Mohamed, K.B. Denthaje, Novel RGO-ZnWO4-Fe3O4 Nanocomposite as an efficient
catalyst for rapid reduction of 4-nitrophenol to 4-aminophenol, Ind. Eng. Chem. Res. 55 (2016) 7267–
7272.
29. M. Sadanandan, B. Raveendran, Synthesis and characterization of tin (IV) tungstate nanoparticles
– a solid acid catalyst, BCREC 7 (2012) 105–111.
30. P.F.S. Pereira, A.F. Gouveia, M. Assis, R.C. de Oliveira, I.M. Pinatti, M. Penha, R.F. Gonçalves,
L. Gracia, J. Andrés, E. Longo, ZnWO4 nanocrystals: synthesis, morphology, photoluminescence and
photocatalytic properties, Phys. Chem. Chem. Phys. 20 (2018) 1923–1937.
31. S. Kundu, L. Ma, Y. Chen,, H. Liang, Microwave assisted swift synthesis of ZnWO4
nanomaterials: material for enhanced photo-catalytic activity, J. Photochem. Photobiol. 346 (2017)
249–264.
32. S.M. AlShehri, J. Ahmed, A.M. Alzahrani, T. Ahamad, Synthesis, characterization, and enhanced
photocatalytic properties of NiWO4 nanobricks, New J. Chem. 41 (2017) 8178–8186.
33. M. Hao, X. Meng, Y. Miao, Synthesis of NiWO4 powder crystals of polyhedron for photocatalytic
degradation of Rhodamine, Solid State Sci. 72 (2017) 103–108.
34. S. Huang, Y. Xu, M. Xie, H. Xu, M. He, J. Xia, L. Huang, H. Li, Synthesis of magnetic
CoFe2O4/g-C3N4 composite and its enhancement of photocatalytic ability under visible-light, Colloids
and Surfaces A: Physicochem. Eng. Aspects 478 (2015) 71–80.
35. B. Bhuyan, B. Paul, A. Paul, S.S. Dhar, Paederia foetida Linn. promoted synthesis of CoFe2O4
and NiFe2O4 nanostructures and their photocatalytic efficiency, IET Nanobiotechnol. 12 (2018) 235–
240.
36. B. Paul, D. Purkayastha, S.S. Dhar, One-pot hydrothermal synthesis and characterization of
CoFe2O4 nanoparticles and its application as magnetically recoverable catalyst in oxidation of
alcohols by periodic acid, Mater. Chem. Phys. 181 (2016) 99–105.

ACCEPTED MANUSCRIPT
37. B. Paul, D. Purkayastha, S.S. Dhar, Size-controlled synthesis of NiFe2O4 nanospheres via a PEG
assisted hydrothermal route and their catalytic properties in oxidation of alcohols by periodic acid,
Appl. Surf. Sci. 370 (2016) 469–475.
38. M. Devi, S. Ganguly, B. Bhuyan, S.S. Dhar, V. Sethumathavan, A novel [Fe(acac)3] interspersed
g‐C3N4 heterostructure for environmentally benign visible‐light‐driven oxidation of alcohols, Eur. J.
Inorg. Chem. 44 (2018) 4819–4825.
39. S. Wang, D. Li, C. Suna, S. Yanga, Y. Guanb, H. Hea, Synthesis and characterization of g-
C3N4/Ag3VO4 composites with significantly enhanced visible-light photocatalytic activity for
triphenylmethane dye degradation, Appl. Catal. B. 144 (2014) 885–892.
40. V.A.J. Silva, P.L. Andrade, M.P.C. Silva, A. Bustamante D., L.D.L.S. Valladares, J.A. Aguiar,
Synthesis and characterization of Fe3O4 nanoparticles coated with fucan polysaccharides, J. Magn.
Magn. Mater. 343 (2013) 138–143.
41. B. Zhu, P. Xia, Y. Li, W. Ho, J. Yu, Fabrication and photocatalytic activity enhanced mechanism
of direct Z-scheme g-C3N4/Ag2WO4 photocatalyst, Appl. Surf. Sci. 391 (2017) 175–183.
42. R. Madhuvilakku, S. Alagar, R. Mariappan, S. Piraman, Green one-pot synthesis of flowers-like
Fe3O4/rGO hybrid nanocomposites for effective electrochemical detection of riboflavin and low-cost
supercapacitor applications, Sens. Actuator B-Chem. 253 (2017) 879–892.
43. M.M.J. Sadiq, U.S. Shenoy, D.K. Bhat, Novel RGO–ZnWO4–Fe3O4 nanocomposite as high
performance visible light photocatalyst, RSC Adv. 6 (2016) 61821–61829.
44. M.I. Osotsi, D.K. Macharia, B. Zhu, Z. Wang, X. Shen, Z. Liu, L. Zhang, Z. Chen, Synthesis of
ZnWO4−x nanorods with oxygen vacancy for efficient photocatalytic degradation of tetracycline, Pro.
Nat. Sci-Mater. 28 (2018) 408–415.
Supplemental Files
Incorporation of nanosized ZnWO4 and Fe3O4 on graphitic carbon nitride to fabricate a
novel, highly active magnetically recoverable catalyst in Claisen–Schmidt condensation.

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Arijita Paula,b*, Meghali Devib, Siddhartha Sankar Dharb
aDepartment of Chemistry, Karimganj College, Karimganj-788710, Assam, India.
bDepartment of Chemistry, National Institute of Technology Silchar, Silchar-788010, Assam,
India.
*Corresponding Author. Tel: +91-+91-03842-242915; Fax: +91-03842-224797
Email: ssd_iitg@hotmail.com (S. S. Dhar)
Contents
Page Numbers
General information.........................................................................................1-2
Experimental………………................................................................................2
Spectral & analytical data of compounds.....................................................3-4
References..................................................................................................... .....4
1. General information
Melamine and the metal salt precursors ferric nitrate [Fe(NO3)3·9H2O], ferrous sulphate
(FeSO4·7H2O), zinc nitrate [Zn(NO3)3·6H2O], sodium tungstate (Na2WO4·2H2O) were
purchased from Sigma Aldrich. Acetone, benzaldehyde, and 30% aqueous ammonia (NH3)
solution were obtained from Merck India Ltd. Double-distilled water was used throughout the
experimental process. The XRD measurements were done on a Philips X’Pert Pro Powder X-
ray Diffractometer with Cu-Kα radiation (λ = 1.5418 Å) with a scan speed of 2°/min. The
FT-IR spectra were recorded on a Thermo Nicolet, Avatar 370 on KBr matrix. The SEM
micrographs were obtained using a JEOL Model JEM-6390LV instrument. The EDX was
performed on OXFORD XMX N equipment. The TEM and HRTEM studies were performed

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using a Tecnai G2 20. The XPS analysis was conducted on a PHI 5000 Versa Prob II, Fei Inc.
The VSM measurements were conducted on Lakeshore, Model 7410 series.
2. Experimental
2.1. Synthesis of Fe3O4 nanoparticles
The Fe(NO3)3·9H2O (2 mmol, 0.81 g) and FeSO4·7H2O (1 mmol, 0.28 g) were dissolved
separately in a minimum volume of distilled water. The two solutions were then mixed
together and stirred for 30 min. To this, aqueous NH3 (5 ml of 30% NH3 in 250 ml of distilled
water) was added and stirred at about 80 °C for about 2 h. The reaction mixture was then
subjected to 450-W microwave irradiation for 10 min. It was finally shifted into a 150-ml
Teflon-lined autoclave and heated at 180 °C for about 3 h. The reddish brown suspension
obtained was then centrifuged, washed with water and ethanol, and dried.
2.2. Synthesis of ZnWO4 nanoparticles
In a typical synthesis, 0.30 g of Zn(NO3)2·6H2O (1 mmol) was dissolved in 10 ml of distilled
water. To this Na2WO4·2H2O solution (0.26 g, 0.80 mmol in 10 ml distilled water) was added
dropwise under constant stirring for about 30 min. Afterwards, 5 ml of aqueous NH3 (30%
NH3 in 250 ml of distilled water) was added to it and stirred at 80 °C for 2 h. The reaction
mixture was then treated with 450-W microwave irradiation for about 10 min. It was finally
subjected to hydrothermal heating in a 150 ml Teflon-lined autoclave at 180 °C for 3 h. The
obtained white precipitate was centrifuged, washed with water and ethanol, and dried.

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3. Spectral and analytical data of dibenzalacetone
DBA: Pale yellow solid; H1 NMR (400 MHz, CDCl3): δ 7.72 (d, 2H), δ 7.62 (d, 4H), δ
7.26–7.46 (t, 6H), δ 7.07 (d, 2H).
C13 NMR (400 MHz, CDCl3): δ 184.6, 140.18, 139.21, 138.51, 129.3, 128.46, 125.24.
Fig. S1 H1 NMR spectrum of dibenzalacetone.

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Fig. S2 C13 NMR spectrum of dibenzalacetone
.
References
1. S. Ni, X. Wang, G. Zhou, F. Yang, J. Wang, Q. Wang, D. He, Hydrothermal synthesis of
Fe3O4 nanoparticles and its application in lithium ion battery, Mater. Lett. 63 (2009) 2701–
2703.
2.
J. Yan, Y. Shen, F. Li, T. Li, Synthesis and photocatalytic properties of ZnWO4
nanocrystals via a fast microwave-assisted method, Sci. World J. 2013 (2013) doi:
10.1155/2013/458106.

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3.
Z. Luo, D. Xu, S. Zhang, J. Shen, Facile hydrothermal synthesis of ZnWO4 for enhanced
photocatalytic performance, J. Nanosci. Nanotechnol. 18 (2018) 7241–7245.