Co3O4 nanoparticles embedded in triple-shelled graphitic carbon nitride (Co3O4/TSCN): a new sustainable and high-performance hierarchical catalyst for the Pd/Cu-free Sonogashira–Hagihara cross-coupling reaction

Article abstract of DOI:10.1007/s11164-021-04466-y

Inspired by the synthesis of triple-shelled periodic mesoporous organosilica hollow spheres, a straightforward and controllable approach for the preparation of Co₃O₄ NPs embedded in triple-shelled graphitic carbon nitride has been es

Full text of DOI:10.1007/s11164-021-04466-y

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-021-04466-y
Co3O4 nanoparticles embedded in triple‑shelled
graphitic carbon nitride (Co3O4/TSCN): a new sustainable
and high‑performance hierarchical catalyst for the Pd/
Cu‑free Sonogashira–Hagihara cross‑coupling reaction
in solvent‑free conditions
Sara S. E. Ghodsinia1 · Batool Akhlaghinia1 · Roya Jahanshahi1
Received: 5 January 2021 / Accepted: 10 April 2021
© The Author(s), under exclusive licence to Springer Nature B.V. 2021
Abstract
Inspired by the synthesis of triple-shelled periodic mesoporous organosilica hol-
low spheres, a straightforward and controllable approach for the preparation of
Co3O4 NPs embedded in triple-shelled graphitic carbon nitride has been estab-
lished through a combinatorial route comprising the hard-templating technique and
impregnation method. A series of various techniques such as FT-IR, XRD, BET,
TEM, FE-SEM, EDX, EDX mapping, TGA, and ICP-OES have been used for the
full characterization of the catalyst. It was found that the Co3O4/TSCN has a high
performance to promote Sonogashira–Hagihara cross-coupling reaction in solvent-
free conditions. Interestingly, the architecture of the catalyst provides not only the
high dispersion loading of the Co3O4 NPs on the support, but also facilitates the
favorable mass transfer through the catalyst structure. The catalyst could be readily
separated from the reaction mixture by fltration method and used again up to fve
times without any evident decrease in catalytic activity.
* Batool Akhlaghinia
akhlaghinia@um.ac.ir
1
Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad,
9177948974 Mashhad, Iran
Vol.:(0123456789)
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S. S. E. Ghodsinia et al.
Graphical abstract
The superior catalytic performance of the Co3O4/TSCN as a new sustainable hierar-
chical catalyst has been presented for Pd/Cu-free Sonogashira–Hagihara cross-cou-
pling reaction under solvent-free conditions
Keywords Co3O4 nanoparticles embedded in triple-shelled graphitic carbon nitride
(Co3O4/TSCN) · Sonogashira–Hagihara cross-coupling reaction · Pd/Cu-free ·
Solvent-free conditions
Introduction
The most widely utilized transformations in the agrochemical, pharmaceutical, and
fne chemical industries, ranging from the discovery phase to multi-ton scale pro-
ductions, include the carbon–carbon bond formation reactions [1–9]. The Sonoga-
shira–Hagihara cross-coupling reaction, as one of the most useful reactions in
organic synthesis from both academic and industrial viewpoints, provides a strong
tool for C(sp)–C(sp2) construction via the reaction of aryl halides with terminal
acetylenes. In the standard Sonogashira–Hagihara cross-coupling reaction, Pd or Pd/
Cu complexes are used as catalysts [10–18]. Nevertheless, these approaches have
witnessed a number of difculties including the high toxicity and cost of the pal-
ladium, formation of undesirable Glaser-type alkyne homocoupled products, and
complicated instability and recovery of the copper(I) salt, which is often involved
in the Pd/Cu based catalytic systems. To overcome these shortcomings, extensive
eforts have been devoted to seeking more sustainable, cost-efective, and conveni-
ent metal-based catalytic systems such as copper, cobalt, iron, and nickel-based cat-
alysts, for operating under more mild conditions [13, 19–32]. By exploiting the mer-
its of heterogeneous catalytic systems and based on the ideology of green chemistry,
the advent of the conceptually new, straightforward, efective, and practical catalytic
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Co3O4 nanoparticles embedded in triple-shelled graphitic…
approach accompanied with the reduction of operational costs and waste materials
to efciently drive the Sonogashira–Hagihara cross-coupling reaction is a substan-
tial criterion. It is worth noting that despite the more availability, non-toxicity, and
cheap of the cobalt-based catalytic systems, the applicability of these metal catalysts
in the C–C cross-coupling reactions is in the introductory stages and highly recom-
mended [20].
In recent years, considerable endeavors have been devoted to the fabrication of
hollow materials with multiple shells (hybrid materials or organic–inorganic solid
materials) to improve the catalytic activity and stability in organic transformations
[33]. Recently, the design and preparation of noble-metal nanocatalysts with hol-
low interiors and porous shells have developed due to the favorable mass transfer of
the substrates into and out of the catalytic active sites, which leads to high catalytic
activity and selectivity [34]. Signifcantly, periodic mesoporous organosilica (PMO)
structures (as a promising class of inorganic–organic mesoporous hybrid materi-
als, formed by surfactant-directed self-assembly process) have been intensively
investigated as they have reachable ordered mesopores, high specifc surface area,
structural diversity, and sufcient high thermo-mechanical stability [35, 36]. PMO
materials are widely utilized for a broad range of applications such as adsorption,
catalysis, hard-templating, and high-performance liquid chromatography [37, 38].
The mpg-C3N4, as an important class of mesoporous materials, is the most stable
allotrope of the carbon nitride family [39]. It has attracted great attention in design-
ing catalysts due to its well-ordered porous structure, unparalleled high surface area,
interesting physicochemical properties, strong chemical and mechanical stability,
and diversity of the hierarchical nanostructures [40–43]. Generally, mpg-C3N4, as an
ideal and unique green carrier, is synthesized by the nano-hard-templating approach
using mesoporous silica as the template [44]. Metal-embedded (such as palla-
dium, cobalt, copper, and zinc) g-C3N4 materials provide an opportunity to design
efective heterogeneous catalysts for diferent reactions, especially the photocata-
lytic performances [45, 46]. Considering all the aforementioned potential benefts,
herein, we have reported a suitable strategy for the controlled synthesis of Co3O4
NPs embedded in triple-shelled graphitic carbon nitride (Co3O4/TSCN) using triple-
shelled SiO2 nanospheres as the proper templates in a stepwise procedure including
the three major steps (Scheme 1). According to what we know, this study repre-
sents the prime example of fabricating embedded Co3O4 NPs in the triple-shelled
graphitic carbon nitride (Co3O4/TSCN) as a new sustainable and high-performance
hierarchical catalyst, towards the C(sp)–C(sp2) bond formation, through the Sonoga-
shira–Hagihara cross-coupling reaction, under solvent-free conditions.
At the outset, monodispersed triple-shelled hollow SiO2 nanospheres were pro-
vided utilizing a well-known sol–gel process [38]. A number of shell layers of SiO2
nanospheres was achieved via a cetyltrimethylammonium bromide (CTAB) sur-
factant-directed sol–gel process using a mixture of tetraethyl orthosilicate (TEOS)
and 1,2-bis(triethoxysilyl)ethane (BTSE), as the silane precursors, in aqueous
ethanolic solution. Typically, triple-shelled SiO2 (TSS) nanospheres are acquired
through the step-by-step addition of a TEOS and BTSE mixture into the reaction
solution with a time slot of 24 h. This time interval could efciently control the num-
ber of shells in the obtained multi-shelled PMO hollow spheres. The transformation
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S. S. E. Ghodsinia et al.
Scheme 1 Overall fowchart for the preparation of Co3O4/TSCN
of solid-state to hollow structure was accomplished by the hydrothermally treating
of the successively grown PMOs nanospheres at 120 °C for 5 h.
The triple-shelled PMO could be acquired after the extraction of surfactant
(CTAB) by acidic ethanol. Afterward, the triple-shelled PMO hollow spheres (which
next annealing at 600 °C in the atmospheric air for 2 h) were applied as a sacrif-
cial template to provide triple-shelled graphitic carbon nitride (TSCN). Mesopores
existing in the triple-shelled facilitate the fast dispersion of the g-C3N4 precursor
(cyanamide) into the pores [47]. Well-developed g-C3N4 materials have privileged
thermal and mechanical stabilities at high temperatures. The second step in the
overall synthetic procedure of TSCN includes the interpenetration of some cyan-
amide molecules into the mesopores of the shells, adsorption of some cyanamide
1 3

Co3O4 nanoparticles embedded in triple-shelled graphitic…
molecules onto the SiO2 nanosphere shells to get the cyanamide-bearing silica nano-
spheres, the transformation of nanospheres into the silica/g-C3N4 nanospheres via
the thermal polycondensation process of cyanamide under the N2 atmosphere for
3 h at 550 °C, and removing the silica template by Na2CO3 solution to create TSCN.
In the following step, the obtained TSCN was used as potent support to prepare the
Co3O4/TSCN, through an impregnation method. To this end, after the dispersion of
TSCN in the water–alcohol binary mixture, a certain amount of Co(NO3)2.6H2O
was enhanced successfully to the resulting suspension. After the slow solvent evapo-
ration, the resultant solid was dried at 70 °C overnight and then calcined at 400 °C
for 2 h with a heating ramp rate of 2 °C min−1, in the atmospheric air to produce the
black Co3O4/TSCN, which was subsequently used as a potent catalyst towards the
Sonogashira–Hagihara cross-coupling reaction of various aryl halides with terminal
acetylenes. (see Scheme 2).
Experimental section
General
All chemical reagents and solvents were procurement from Merck chemical compa-
nies and were utilized as received without further purifcation. The purity determi-
nation of the products and the progress of the reactions were accomplished by a thin
layer or column chromatography on silica gel polygram STL G/UV 254 plates and
GC-FID (Agilent 6890, Santa Clara, USA) device. The melting points of the prod-
ucts were determined with an Electrothermal Type 9100 melting point apparatus.
The FT-IR spectra were recorded on an Avatar 370 FT-IR Therma Nicolet spec-
trometer. The NMR spectra were recorded on 400 MHz Bruker Avance instruments
in CDCl3 in the presence of tetramethylsilane as the internal standard and the cou-
pling constants (J values) are given in Hz. Mass spectra were recorded with a CH7A
Varianmat Bremem instrument at 70 eV electron impact ionization, in m/z (rel %).
Scheme 2 The Sonogashira–Hagihara cross-coupling reaction in the presence of the Co3O4/TSCN (III)
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S. S. E. Ghodsinia et al.
X-ray powder difraction (XRD) was performed on a PANalytical Company X’Pert
Pro MPD difractometer with Cu Kα radiation (λ=0.154 nm) radiation. BET sur-
face area and pore-size distribution were measured on a Quantachrome Instruments
version 2.2 at −196 °C using N2 as the adsorbate. Transmission electron micros-
copy (TEM) was performed with an EM10C-100 kV microscope (Zeiss, Germany).
FE-SEM images, EDX, and EDX mapping were recorded using a TESCAN (model:
Sigma VP) scanning electron microscope operating at an acceleration voltage of
15.00 kV and resolution of about 500 nm (Zeiss, Germany).
Thermogravimetric analysis/diferential thermogravimetric analysis (TGA/DTG)
was performed using a Shimadzu Thermogravimetric Analyzer (TG-50) in the tem-
perature range of 25–900 °C at a heating rate of 10 °C min−1, under air atmosphere.
Inductively coupled plasma optical emission spectroscopy (ICP-OES) was imple-
mented with a Varian VISTA-PRO, CCD (Australia). All yields refer to the isolated
products after purifcation by a thin layer or column chromatography.
Materials
Cyanamide (99%), tetraethyl orthosilicate (TEOS), 1,2-bis(triethoxysilyl)ethane
(BTSE), cetyltrimethyl ammonium bromide (CTAB), concentrated ammonia (30
wt.%), absolute ethanol, and HCl (37%) were bought from Merck chemical com-
pany. Deionized water was used in all experiments with a resistivity of 18.2 MΩ
cm−1.
Synthesis of triple‑shelled SiO2 nanospheres (TSS) (I)
Triple-shelled SiO2 nanospheres (I) were frst obtained by the sol–gel process in
agreement with a modifed previously described procedure [38]. Typically, CTAB
(0.16 g, 0.44 mmol) was dissolved in a mixed solution of concentrated ammonia
(1.0 mL, 30 wt %), ethanol (30 mL), and deionized water (75 mL). After stirring
at 35 °C for one hour, a mixture of silane precursors containing BTSE (0.119 g,
0.33 mmol) and TEOS (0.116 g, 0.56 mmol) was rapidly added to the resultant solu-
tion, under drastic stirring (1100 rpm). Mesostructured organosilica spheres were
obtained as a white precipitate after stirring the resultant mixture at 35 °C for 24 h.
Thereafter, a mixed solution of BTSE (0.119 g, 0.33 mmol) and TEOS (0.116 g,
0.56 mmol) was quickly added again under the same conditions; keep stirring for
another 24 h (to obtain two-layered mesostructured organosilica spheres). Fol-
lowing the preparation procedure and the same experimental conditions described
above, for the third time, a mixed solution of BTSE (0.119 g, 0.33 mmol) and TEOS
(0.116 g, 0.56 mmol) was quickly added into the resultant suspension. Three-layered
mesostructured organosilica spheres, after stirring for another 24 h at the same tem-
perature, were acquired. Afterward, the obtained triple-layered organosilica spheres
were harvested by centrifugation and washed with ethanol. To carry out the multi-
interface transformation, the mesostructured organosilica spheres were re-dispersed
in 540 mL of deionized water and transferred to a Tefon-lined stainless-steel auto-
clave. The autoclave was further heated in an airfow electric oven at 120 °C for
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Co3O4 nanoparticles embedded in triple-shelled graphitic…
5 h to accomplish the multi-interface conversion. Next, the autoclave was cooled
down to room temperature, and the products were collected by centrifugation (3000
Rpm, 15 min). Subsequently, CTAB was removed from the products by the solvent-
extraction process (a solution containing ethanol (180 mL) and concentrated HCl
(360 µL, 37%) at 60 °C for 3 h). Finally, triple-shelled hollow SiO2 nanospheres (I)
were obtained after washing with ethanol three times, dried under a high vacuum
at 80 °C for overnight, and annealed at 600 °C for 2 h with a heating ramp rate of
2 °C min−1 in the air atmosphere.
Synthesis of triple‑shelled g‑C3N4 (TSCN) (II)
The obtained triple-shelled SiO2 nanosphere (I) (0.1 g) was poured into deionized
water (5 mL) and then mixed with cyanamide (2 g, 47.57 mmol), keep stirring at
40 °C for 8 h [47]. Next, the mixed suspension was centrifuged, freezing-dried, and
heated at 550 °C for 3 h (with a heating ramp rate of 1 °C min−1, under the N2
protective fow of 50 mL min−1). The resulting powder was treated with Na2CO3
solution (0.3 mol L−1, 20 mL) at 60 °C for 24 h to remove the SiO2 templates. At
last, the product (triple-shelled g-C3N4 (II)) was centrifuged (3000 Rpm, 15 min)
and washed with distilled water and ethanol several times and dried at 70 °C for
overnight.
Synthesis of Co3O4 NPs embedded in triple‑shelled graphitic carbon nitride
(Co3O4/TSCN) (III)
To prepare the Co3O4/TSCN (III), 1.0 g of TSCN (II) was dispersed in 100 mL of
a water–alcohol binary mixture (1:1, v/v) in the ultrasonic bath for 30 min. Then,
Co(NO3)2.6H2O (1.5 g, 5.19 mmol) was added successively to the resulting suspen-
sion. After the slow solvent evaporation, the resultant pink solid was dried in a vac-
uum oven at 70 °C overnight. The Co3O4/TSCN (III) was obtained after annealing
at 400 °C for 2 h with a heating ramp rate of 2 °C min−1 in the air atmosphere. The
obtained product is referred to 20.33 wt.% Co3O4/TSCN (where ’20.33 wt.%’ repre-
sents the weight percentage of Co3O4 in the fnal catalyst (III).
A typical procedure for the Sonogashira–Hagihara cross‑coupling reaction
A round-bottomed fask equipped with mechanical stirring was charged by a mixture
of phenylacetylene (1.2 mmol, 0.102 g), iodobenzene (1.0 mmol, 0.203 g), trieth-
ylamine (1 mmol, 0.101 g), and catalyst (0.007 g, 2.41 mol% Co), under solvent-
free conditions at 70 °C. The progress of the reaction was monitored using TLC.
After completion of the reaction (4 h), the mixture was diluted with ethyl acetate.
Thereafter, the mesostructured catalyst was separated by simple fltration, washed
with EtOH (3×10 mL), and dried at 60 °C under vacuum overnight to remove the
organic residuals and solvents for use in the next run. The crude product was then
extracted with ethyl acetate, and the combined organic layer was dried over anhy-
drous Na2SO4. After solvent evaporation, the residue was purifed by thin-layer
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S. S. E. Ghodsinia et al.
chromatography using n-hexane/ethyl acetate (6:1) to aford white crystals of diphe-
nylacetylene (0.174 g, 98% yield).
Results and discussion
At the preliminary stage, the successful synthesis of Co3O4/TSCN was evaluated
using some spectroscopic and microscopic techniques including Fourier trans-
form infrared spectroscopy (FT-IR), powder X-ray difraction (PXRD), Brunauer,
Emmett, and Teller (BET) surface area analysis, transmission electron microscopy
(TEM), feld emission scanning electron microscopy (FE-SEM), energy-dispersive
X-ray (EDX), energy-dispersive X-ray (EDX) elemental mapping, thermogravimet-
ric analysis/diferential thermogravimetric analysis (TGA/DTG), and inductively
coupled plasma optical emission spectroscopy (ICP-OES). In the following of our
previous studies [48–56] and based on the successful preparation of the Co3O4/
TSCN, the catalytic capability of the aforesaid nanocatalyst was studied in the
Sonogashira–Hagihara cross-coupling reactions of aryl halides with various acety-
lenic compounds without using any palladium or copper species, under solvent-free
conditions.
The FT-IR spectra of TSS nanospheres (I), TSCN (before template removal) (II),
TSCN (after template removal) (II), Co3O4/TSCN (III), and the 5th reused Co3O4/
TSCN (III) are shown in Fig. 1. As it is evident from Fig. 1a, the typical absorption
bands located at 1087, 811, and 460 cm−1 are assigned to the asymmetric, sym-
metric, and bending vibrations of Si–O–Si bond, respectively. The broad absorp-
tion band at 3443 cm−1 and the distinctive band at 1625 cm−1 can be related to the
Fig. 1 FT-IR spectra of TSS nanospheres (I) (a), TSCN (before template removal) (II) (b), TSCN (after
template removal) (II) (c), Co3O4/TSCN (III) (d), and the 5th reused Co3O4/TSCN (III) (e)
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Co3O4 nanoparticles embedded in triple-shelled graphitic…
stretching and bending modes of the surface-attached hydroxyl groups (ν O–H) and
adsorbed water molecules in TSS nanospheres (I), respectively [57–60]. In the FT-IR
spectrum of TSCN (before template removal) (II) (Fig. 1b), a broad absorption band
at 3168 cm−1 could be ascribed to the stretching modes of the terminal NH2 or NH
groups at the defect sites of the aromatic rings. The characteristic stretching vibra-
tion of O–H (attributed to the triple-shelled SiO2) is detected in nearly the same
region, which is worn by the absorption bands of the amino groups in the triple-
shelled g-C3N4. Based on the literature data, the appearance of strong absorption
bands at 1640 and 1568 cm−1 can correspond to the C=N stretching vibration mode
of TSCN [60]. Furthermore, three absorption bands at 1410, 1319, and 1252 cm−1
are allocated to the stretching vibrations of aromatic C-N bonds. Besides, it is worth
mentioning that the absorption band at 809 cm−1 could be ascribed to the s-triazine
ring vibration mode [61, 62]. In the case of TSCN after template removal (II), as
can be clearly observed in Fig. 1c, the disappearance of the strong absorption band
at 460 cm−1 (attributed to the bending vibrations of Si–O-Si bond) corroborated the
removal of SiO2 nanosphere templates. The FT-IR spectrum of the Co3O4/TSCN
(III) is shown in Fig. 1d. Notably, the strong absorption bands at 659 and 563 cm−1
are related to the vibrations of the bridging O–Co–O bond and Co–O stretching
vibration mode, respectively, which indicate the defnite presence of Co3O4 on the
graphitic carbon nitride [62–64]. A good agreement was obtained from the spectral
information with the XRD analysis results described in the following.
The phase purity and crystal structures of TSS nanospheres (I), TSCN (after
template removal) (II), Co3O4/TSCN (III), and the 5th reused Co3O4/TSCN (III)
are clearly corroborate via surveying the powder X-ray difraction (PXRD) pat-
terns (Fig. 2). As it is evident from Fig. 2a, the strong and broad difraction peak at
- Triple-shell SiO2 (I) (a)
- TSCN (II) (b)
- Co3O4/TSCN (III) (c)
- 5th reused Co3O4/TSCN (III) (d)
(d)
(c)
(b)
(a)
10
20
30
40
50
60
70
2θ (degree)
Fig. 2 XRD patterns of TSS nanospheres (I) (a), TSCN (after template removal) (II) (b), Co3O4/TSCN
(III) (c), and the 5th reused Co3O4/TSCN (III) (d)
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S. S. E. Ghodsinia et al.
2θ=22.8° can be assigned to the amorphous structure of triple-shelled SiO2 (TSS)
nanospheres (I) [65]. The PXRD pattern of TSCN (Fig. 2b) exhibited two difraction
peaks at 2θ=13.34° (1 0 0) and 27.16° (0 0 2), which can be corresponded to the
interlayer structural packing of s-triazine units and the periodic inter-planar stacking
peak (with the interlayer distance of 0.326 nm) of conjugated aromatic systems in
graphitic carbon nitride, respectively (Ref. Code: 01-087-1526). Meanwhile, the dis-
appearance of the characteristic peak at 22.8°, which is attributed to the SiO2 in the
PXRD pattern of TSCN (Fig. 2b), along with the FT-IR spectrum results of the TSS
(Fig. 1c) and EDX results (Fig. 5) together indicates the approximate removal of the
SiO2 template. As could be distinguished from the PXRD pattern of Co3O4/TSCN
(III) (Fig. 2c), the apparent peaks at 2θ=31.35° (2 2 0), 36.93° (3 1 1), 44.99° (4
0 0), 59.37° (5 1 1), and 65.31°(4 4 0) are imputed to the cubic Co3O4 spinel struc-
ture, which is in accordance with the standard cubic structure of Co3O4 (Ref. Code:
98-001-5024). Nevertheless, no difraction peaks of any crystalline phase of g-C3N4
appear in the patterns of all Co3O4/TSCN catalysts is possibly due to either the small
quantity of g-C3N4 matrix in the catalysts or limited detection of X-ray difraction
[66–69] Benefting from the electrostatic attraction efect, the cobalt ions can be
absorbed into the surface of the TSCN layers (the in situ formed Co3O4 might attach
to the surfaces of TSCN), which are prevented their aggregation and restacking. It
can weaken the characteristic peak of g-C3N4 matrix in the catalyst [69–71].
It is known that the BET surface area and pore structure of the catalysts are sig-
nifcant factors, which infuence the catalytic activity. N2 adsorption–desorption
analysis determines the contact area between the catalyst and the reactant, and the
difusion of the reactants into the catalyst. To gain further insights into the textural
properties (the pore-size distributions and BET surface areas), N2 adsorption–des-
orption analysis of TSS nanospheres (I) and Co3O4/TSCN (III) were investigated
(Fig. 3). As can be seen in Fig. 3a and 3b, both samples exhibit typical type IV
isotherms with H3-type hysteresis loop according to the IUPAC classifcation [72].
The achieved data including the specifc surface area, total pore volume, and pore
Fig. 3 The nitrogen adsorption–desorption isotherms of TSS nanospheres (I) (a), Co3O4/TSCN (III) (b),
and the corresponding pore-size distribution curves (c and d)
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Co3O4 nanoparticles embedded in triple-shelled graphitic…
diameter of TSS (I) and Co3O4/TSCN (III) are listed in Table 1. Also, the pore-
size distribution of the hierarchical structure of TSS (I) and Co3O4/TSCN (III) is
also estimated using the Barrett–Joyner–Halenda (BJH) method, which indicates a
broad range (from 1.2 to 95 nm), and the presence of diferent sizes of mesopores
and macropores structures (Fig. 3c and d). Additionally, it is found that the mean
pore size of the Co3O4/TSCN (22 nm) is slightly greater than the pore size of triple-
shelled SiO2 template (7 nm), while the BET surface area of the Co3O4/TSCN (III)
(56 m2 g−1) is smaller than that of TSS template (224 m2 g−1) (Table 1). Triple-
shelled g-C3N4 can facilitate the high dispersion of Co species.
To explore more details concerning the morphology and structure of the pris-
tine triple-shelled structure of the SiO2 (I), TEM analysis was employed. Figure 4a
and b shows that the triple-shelled structure of the SiO2 (I) possess uniform hol-
low spheres with three shells. The sizes of the external, middle, and internal shells
were about 398, 333, and 263 nm, sequentially. The average thickness of the shells
was approximately 20 nm. By implementing templates, the size of the Co3O4/
TSCN (III) became smaller (the sizes of the external, middle, and internal shells
were about 365, 301, and 240 nm, respectively), while the thickness of the shells
increased (Fig. 4e and f). In particular, the existence of bright and dark areas in the
shells and cavities observed from TEM images suggested the presence of radially
mesoporous channels on the surface of the Co3O4/TSCN (III). The SEM images
with diferent magnifcations further revealed the uniform diameter (with an average
diameter of about 368 nm) and spherical morphology of the SiO2 template (I) in the
triple-shelled hollow structures (the thickness, size, and shape of the triple-shelled
structure of the SiO2 (I) was well agreed with the TEM images) (Fig. 4c and d).
The SEM images of the as-synthesized hierarchical structure (after removing the
synthesized silica templates) are displayed in Fig. 4g. Compared to the SiO2 tem-
plate (I), the surface of the Co3O4/TSCN (III) is rougher and wrinkled. Moreover,
the uniformly spherical shape, monodisperse size distribution, and tunable spherical
wrinkles pointed to the high surface area and excellent mechanical strength of this
nanocatalyst. The average diameter of the Co3O4/TSCN (III) was estimated to be
about 338 nm, which is very close to the particle size determined using TEM data.
EDX technique is conducted to scrutiny the type of elements in the Co3O4/TSCN
(III) (Fig. 5). Surveying the EDX spectrum confrmed the existence of C, O, N, and
Co elements in the Co3O4/TSCN (III) structure.
Besides, to explore the elemental composition uniformity of the Co3O4/TSCN
(III), the EDX mapping analysis is provided and the results are shown in Fig. 6.
Table 1 Specifc surface area
Samples
SBET
Vt (cm3 g−1
)
Mean
pore
(SBET), total pore volume (Vt),
and pore diameter of TSS
nanospheres (I) and Co3O4/
TSCN (III)
(m2 g−1
)
diameter
(nm)
TSS nanospheres (I)
223.86
56.446
51.433
12.969
7.7159
22.055
Co3O4/TSCN
(III)
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S. S. E. Ghodsinia et al.
Fig. 4 TEM (a & b) and FE-SEM images (c & d) of TSS nanospheres (I), TEM (e & f) and FE-SEM
images (g) of Co3O4/TSCN (III), FE-SEM image (h) of the 5th reused of Co3O4/TSCN (III)
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Co3O4 nanoparticles embedded in triple-shelled graphitic…
Fig. 5 EDX spectrum of the Co3O4/TSCN (III)
Fig. 6 EDX mapping of the Co3O4/TSCN (III)
As can be seen in this fgure, the simultaneous existence of C, O, N, and Co
elements with homogeneous distribution on the entire surface of the catalyst is
proved properly.
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S. S. E. Ghodsinia et al.
To investigate the thermal and structural stability of the TSCN (II) and Co3O4/
TSCN (III), TGA analysis was performed under an air atmosphere at a heating rate
of 10 ºC min−1 from 25 to 900 °C (Fig. 7). As is shown in Fig. 7a, a sharp weight
loss in the temperature range from 480 to 670 °C is attributed to the decomposi-
tion of TSCN (II). It is illustrated that TSCN (II) has good thermal stability and
can be utilized to modify the sensing materials, and also it is not decomposed in
the process of the gas sensing tests [47]. The as-synthesized catalyst exhibits three
mass loss steps (Fig. 7b). The frst negligible mass loss, which eventuated in the
temperature range from 25 to 140 °C, is responsible for the output of the physically
adsorbed water located inside and on the surface of the pores (4% weight loss). Pro-
gressive removal of the adsorbed water from the surface hydroxyl groups on metal
oxides [73] and the excess oxygen in the non-stoichiometric oxide, is occurred dur-
ing the second weight loss step (36%) from 390 to 440 °C [74, 75]. The third weight
loss (35%) at 440–560 °C is due to the decomposition of TSCN [76]. Therefore, the
Co3O4 contents in Co3O4/TSCN (III) (between 700–900 °C) [77] are estimated to
be 21 wt.%. A good agreement was observed between the ICP-OES analysis (20.33
wt.%, 3.45 mmol g−1) and TGA data, according to the obtained results.
Catalytic performance of the Co3O4/TSCN (III) in the Sonogashira–Hagihara
cross‑coupling reaction
After full characterization of Co3O4/TSCN (III) as a new, highly efcient, reusable,
eco-friendly, and promising heterogeneous hierarchical nanocatalyst, its catalytic
activity was investigated towards the Sonogashira–Hagihara cross-coupling reaction
of various aryl halides with acetylenic compounds (Scheme 2).
Hence, in order to evaluate the optimum reaction profle for the Sonoga-
shira–Hagihara cross-coupling reaction, the reaction of iodobenzene with
100
(a)
80
60
40
(b)
20
Co3O4/TSCN
TSCN
0
200
400
600
Temperature (°C)
Fig. 7 TGA thermogram of the Co3O4/TSCN (III)
1 3

Co3O4 nanoparticles embedded in triple-shelled graphitic…
phenylacetylene in the presence of the Co3O4/TSCN (III) was chosen as a model
reaction by taking into account several important parameters such as solvent, tem-
perature, base and catalyst loading (Table 2). As expected, the control experiment
indicated that no cross-coupled product was obtained in the absence of the catalyst
and base (in H2O at 70 °C), and the reaction did not proceed even after a long time
(Table 2, entry 1). Likewise, conducting the model reaction with no addition of cata-
lyst in the presence of base did not lead to the formation of the target compound even
after lengthening the reaction time to 24 h (Table 2, entry 2). No satisfying yield
of the desired product (15%, after 24 h) was achieved in the presence of 0.005 g
(1.72 mol% Co) of the Co3O4/TSCN (III), without using the base in H2O at 70 °C
Table 2 Optimization of the reaction conditions for the Sonogashira–Hagihara cross-coupling reaction of
iodobenzene with phenylacetylene in the presence of the Co3O4/TSCN (III)
Entry
Catalyst
(mol %)
Base
Solvent
Temperature
(˚C)
Time
(h)
Isolated
(1 mmol)
yield (%)
1
2
3
4
5
6
7
8
–
–
1.72
1.72
1.72
1.72
1.72
1.72
1.72
1.72
1.72
1.72
1.72
1.38
2.41
3.09
–
Et3N
–
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
–
–
–
–
–
–
–
–
–
70
70
70
70
70
70
70
70
70
70
70
80
60
70
70
70
70
70
70
70
24 h
24 h
24 h
6 h
12 h
9 h
0
0
15
85
75
73
80
75
80
75
90
90
70
80
98
98
55
75
–
Et3N
K2CO3
K3PO4
KOH
NaOH
NaOAc
Pyridine
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
Et3N
9 h
10 h
12 h
15 h
5 h
5 h
8 h
7 h
4 h
4 h
4 h
4 h
24 h
15 h
9
10
11
12
13
14
15
16
17a
18b
19c
20d
0.007 (g)
0.007 (g)
0.007 (g)
2.41
–
40
aThe reaction was performed in the in the presence of Co3O4/SSCN,
bThe reaction was performed in the in the presence of Co3O4/DSCN,
cThe reaction was performed in the presence of TSCN,
dThe reaction was performed in the presence of Co3O4 NPs.
1 3

S. S. E. Ghodsinia et al.
(the bridging tertiary N atoms had the superior base intensity to other N-containing
functional groups in g-C3N4) (Table 2, entry 3) [78]. To improve the product yield
and enhance the reaction rate, the model reaction was carried out in the presence
of diferent bases comprising the Et3N, K2CO3, K3PO4, KOH, NaOH, NaOAc, and
pyridine (Table 2, entries 4–10). As can be seen, among the bases mentioned, Et3N
was found to be highly efcient in the preparation of the corresponding coupling
product in H2O at 70 °C (Table 2, entry 4). Then, the model cross-coupling reaction
was tested under solvent-free conditions (Table 2, entry 11). Surprisingly, accurate
studies demonstrated that the best result was obtained in solvent-free conditions (to
modernize the classical chemical procedures and concerning the principle of green
chemistry, it is now often claimed that “the best solvent is no solvent”) [79]. Subse-
quent experiments identifed the efect of temperature in the Sonogashira–Hagihara
cross-coupling reaction, which revealed that the best yield of the desired product was
obtained at 70 °C (Table 2, entries 11–13). Next, the infuence of the catalyst load-
ing was scrutinized using the model reaction to achieve the optimal reaction condi-
tions (Table 2, entries 11 and 14–16). After a few attempts, it was found that 0.007 g
(2.41 mol% Co) of the catalyst was required to achieve the reasonable yield of the
desired product (98% after 4 h) (Table 2, entry 15). A higher amount of the catalyst
0.009 g (3.09 mol% Co) did not have any efect on the product yield or the reaction
rate (Table 2, entry 16), whereas a signifcant decrease in the reaction progress was
observed by applying 0.004 g (1.38 mol% Co) of the catalyst (Table 2, entry 14).
To gain further evidence towards the catalytic efciency of Co3O4/TSCN (III), the
catalytic activity of Co3O4 NPs embedded in single-shelled graphitic carbon nitride
(Co3O4/SSCN) and Co3O4 NPs embedded in double-shelled graphitic carbon nitride
(Co3O4/DSCN) was separately studied in the model reaction (Table 1, entries 17
and 18). As clearly understood from the results, the reaction progress was far from
satisfactory in such cases. In a follow-up investigation, the model reaction was sepa-
rately carried out in the presence of TSCN (II) and Co3O4 NPs under the optimized
reaction conditions (Table 2, entries 19 and 20). As expected, the results indicated
that no desired product was obtained in the presence of TSCN (II) (Table 2, entry
19). Furthermore, in the presence of Co3O4 NPs, the cross-coupling reaction pro-
ceeded slowly with a lower yield (Table 2, entry 20). These fndings clearly afrmed
the crucial role of the Co3O4 NPs in accompanied with the existence of the triple-
shelled graphitic carbon nitride, which provides the high dispersion and appropriate
loading of the cobalt oxide NPs on the support and facilitates the favorable mass
transfer through the catalyst structure, which is strong evidence for the unique cata-
lytic activity of Co3O4/TSCN.
Motivated by the profound initial studies on the optimized reaction conditions
and having the obtained results in hand, we next focused on investigating a diver-
sity of the substrate scope of the Sonogashira–Hagihara cross-coupling reaction
in the presence of the Co3O4/TSCN (III) under the optimized reaction conditions.
It is evident from Table 3 that the cross-coupling reactions of aryl iodides with
phenylacetylenes are faster than that of aryl bromides or aryl chlorides due to
the lower C–I bond strength versus C–Br and C–Cl bonds (C–Cl> C–Br > C–I)
(Table 3, entry 1 versus 22 and 29) [80, 81].
1 3

Co3O4 nanoparticles embedded in triple-shelled graphitic…
Table 3 Sonogashira–Hagihara cross-coupling reactions of aryl halides with diferent terminal acety-
lenes in the presence of the Co3O4/TSCN (III)
Entry
Aryl halides
Terminal acetylenes
Product
Time (h)
Isolated yield (%)
1
4
98
2
3
4
5
6
7
3.5
98
98
85
68
55
96
3
6
12
8
3.5
8
9
3
95
94
2.5
10
11
3
85
80
2.5
1 3

S. S. E. Ghodsinia et al.
Table 3 (continued)
Entry
Aryl halides
Terminal acetylenes
Product
Time (h)
Isolated yield (%)
75
12
2.5
13
3.5
70
14
15
3
75
80
2.5
16
10
85
9
90
17
8
80
18
19
20
21
22
12
10
10
7.5
91
82
85
85
1 3

Co3O4 nanoparticles embedded in triple-shelled graphitic…
Table 3 (continued)
Entry
Aryl halides
Terminal acetylenes
Product
Time (h)
7
Isolated yield (%)
80
23
24
25
26
6
11
7
86
67
70
27
28
11
14
55
50
29
30
31
32
33
9
8
65
70
75
70
55
8
8.5
15
Comparatively,
the
electron-poor
aryl
halides
(substituted
by
1 3

S. S. E. Ghodsinia et al.
Scheme 3 Plausible mechanism for the Sonogashira–Hagihara, cross-coupling reaction in the presence
of the Co3O4/TSCN
electron-withdrawing groups such as –NO2, –CN, and –Cl) aforded the desired
products with excellent yields, more quickly than the electron-rich aryl halides (sub-
stituted by electron-donating groups such as –Me, –OMe, and –NH2) in the cou-
pling process with phenylacetylene (Table 3, entries 7–15, 26, and 32 versus 16–21,
27, and 33). It means that the electron density enhancement over the aromatic ring
slowed down the elimination of halide from intermediate I in the oxidative-addition
step of the Sonogashira–Hagihara cross-coupling reaction, based on the previous
reports in the literature [80, 81] and also the proposed mechanism in Scheme 3.
Thereupon, the reactivity of the diferent phenylacetylenes was surveyed in the
Sonogashira–Hagihara cross-coupling reaction in the presence of the Co3O4/TSCN
(III). Similarly, efcient catalytic activity and higher yields of the products were
achieved with phenylacetylenes endowed with electron-withdrawing groups than
the electron‐donating ones (Table 3, entries 2, 3 versus 4, and 23, 24 versus 25).
Electron-poor phenylacetylenes with more acidic strength facilitated the formation
of intermediate III (Scheme 3).
To study the chemo-selectivity of the present method, the reaction of 1-chloro-
4-iodobenzene (as a di-halogenated aryl halide) with phenylacetylene was probed,
which demonstrated that the iodide substitution is much more reactive than the
chloride one, which further confrmed by mass spectroscopy (Table 3, entries
13–15). Additionally, the Sonogashira–Hagihara cross-coupling reaction of aliphatic
1 3

Co3O4 nanoparticles embedded in triple-shelled graphitic…
terminal alkynes was investigated in the presence of the Co3O4/TSCN (III). The
attained results noticeably revealed that the aliphatic alkynes could also couple with
aryl halides under the optimized reaction conditions and the desired products were
obtained in moderate yields (Table 3, entries 5, 6, and 28).
In the present study, the reaction progress was periodically monitored by the
disappearance of the starting materials and further formation of the desired cross-
coupled products on TLC. All of the synthesized compounds were known and iso-
lated as oil or solid products. The obtained products were characterized by com-
paring their melting points with those reported in the literature. The molecular ion
peaks of certain selected products exhibited their respective m/z values, according
to the mass spectrometric data. Besides, the structure of some selected compounds
1
was efectively corroborated by surveying their high-feld H NMR, 13C NMR,
and FT-IR spectral data. FT-IR spectra of the coupling products from the Sonoga-
shira–Hagihara cross-coupling reactions displayed a characteristic absorption band
at 2225–2739 cm−1 due to the carbon–carbon triple bonds. Furthermore, in the
13CNMR spectra, the resonating signals at δ 94.74–89.39 ppm were corresponded
to C≡ C bonds of the resultant coupled products from Sonogashira–Hagihara cross-
coupling reaction (see Supporting Information fle).
The detailed mechanism of the Sonogashira–Hagihara cross-coupling reac-
tion with the Co3O4/TSCN is not clear at this point. With the above results taken
into consideration and according to the previous reports [82–85], the proposed
catalytic cycle has been depicted in Scheme 3. The reaction initially proceeded
through the oxidative-addition of the aryl halide to the active Lewis acidic sites
present on the Co3O4/TSCN (III) (which plays a signifcant role in enhancing the
electrophilic property of alkyl halide and activation of C–H bond in acetylene)
to aford intermediate I. Upon the insertion of a terminal alkyne into intermedi-
ate I, followed by deprotonation of alkyne under basic conditions, π-coordinated
complex II and intermediate III were formed, respectively. Finally, the coupled
product IV was obtained via the reductive-elimination step with the simultaneous
generation of the Co3O4/TSCN for the next catalytic cycle. We propound that the
Fig. 8 Reusability of the Co3O4/TSCN (III) in Sonogashira–Hagihara cross-coupling reactions under the
optimized reaction conditions
1 3

S. S. E. Ghodsinia et al.
presence of TSCN (containing the basic structural units based on triazine groups)
facilitates the substrate approach to the catalytic active sites. On the other hand,
the high surface area of the Co3O4/TSCN increases the catalytic activity of the
system to perform an efcient coupling reaction. More studies dealing with the
detailed mechanism of the reaction will be accomplished in the near future.
Considering the economic and environmental factors, and encouraged by the
signifcance of the reusability of the heterogeneous catalyst, from the perspec-
tive of green chemistry, the long-term durability experiment of the catalyst was
carried out. In this regard, to check the reusability behavior of the Co3O4/TSCN
(III), the model reaction of the Sonogashira–Hagihara cross-coupling reaction
was performed under the optimized reaction conditions. The recycling efciency
is demonstrated in Fig. 8, and the obtained results are discussed in detail. Briefy,
after the completion of each run of the cross-coupling reaction, which was moni-
tored by TLC, the Co3O4/TSCN (III) was separated from the reaction media by
a simple fltration process, washed with EtOH (3 × 10 mL), and vacuum-dried at
60 °C overnight to remove the organic residuals and solvents for use in the next
run. As it is evident from Fig. 8, no obvious decrease in the product yield and
conversion was detectable after fve consecutive runs, indicating the high cata-
lytic activity and long-term durability of the Co3O4/TSCN (III) in the Sonoga-
shira–Hagihara cross-coupling reaction.
Moreover, to confrm the stability of the Co3O4/TSCN (III) after fve-cycles in
the Sonogashira–Hagihara cross-coupling reaction, any structural changes of the
aforesaid nanocatalyst were investigated by several techniques including FT-IR,
XRD, FE-SEM, and ICP-OES.
Through surveying the FT-IR spectrum of the 5th reused Co3O4/TSCN (III),
it could be concluded that all of the characteristic absorption bands are well pre-
served in terms of the frequencies, intensities, positions, and shapes even after
fve recycle runs (Fig. 1e). Additionally, it is interesting to note that no signif-
cant broadening or shifting was observed in the typical difraction peaks of the
XRD pattern of the 5th reused Co3O4/TSCN (III). Satisfyingly, the FE-SEM
image of the 5th reused Co3O4/TSCN (III) confrmed that no changes in the
particle size, dispersion, shape, and morphology of the catalyst was observed
(Fig. 4h). As a fnal point, in order to estimate the exact amount of cobalt in the
fresh and the 5th reused Co3O4/TSCN (III), ICP-OES technique was applied.
The obtained results illustrated that the Co contents of the fresh and the 5th
reused Co3O4/TSCN (III) were 20.33 wt.% and 20.16 wt.%, respectively. These
results clearly proved that a negligible amount of cobalt was leached from the
surface of the hierarchically structured catalyst during the recycling process.
Based on the obtained data from FT-IR, XRD, FE-SEM, and ICP-OES analysis,
it could be asserted certainly that the Co3O4/TSCN (III) is completely stable in
terms of functional groups, crystalline structure, morphology, and metal content
even after fve consecutive recycle runs. The high catalytic activity and excel-
lent reusability of the Co3O4/TSCN (III) can be possibly attributed to the stable
embedded metal oxide in the triple-shelled carbon nitride (TSCN).
1 3

Co3O4 nanoparticles embedded in triple-shelled graphitic…
Fig. 9 Hot fltration experiment in the model reaction of the Sonogashira–Hagihara cross-coupling reac-
tion in the presence of Co3O4/TSCN (III)
Scheme 4 Structure of some components with Sonogashira–Hagihara cross-coupling reaction
1 3

S. S. E. Ghodsinia et al.
Hot fltration test
To approve the heterogeneous nature of the Co3O4/TSCN (III) in the Sonoga-
shira–Hagihara cross-coupling reaction, the hot fltration test was performed. The
hot fltration test is one of the substantial methods to defne the nature of the cat-
alytic species based on the comparison of the reaction progress before and after
removal of the solid catalyst. For this purpose, the model Sonogashira–Hagihara
cross-coupling reaction was carried out under the optimal reaction conditions. After
2 h (55% conversion), the catalyst was separated from the reaction mixture by sim-
ple fltration. Subsequently, the remaining mixture was permitted to stir without a
catalyst for an additional 2 h. In this context, no more reaction progress well sug-
gested that no leaching of metal species takes place during the reaction and that the
catalytic process is purely heterogeneous in nature. ICP-OES analysis of the fltrate
also revealed that during the reaction only 0.1 wt.% of the Co species were leached.
The results of the hot fltration test for the Sonogashira–Hagihara cross-coupling
reaction are presented in Fig. 9.
The versatility of the Sonogashira–Hagihara cross-coupling products in the cur-
rent study makes them vital building blocks in the synthesis of the various structur-
ally diferent molecules in the felds of the natural product (pyrrhoxanthin), polymer
synthesis (y-POP-NH2) (Scheme 4), pharmaceutical synthesis, and drug discovery
(DC324) [86–88].
In order to confrm the importance of the industrial-scale application of the
synthesized Co3O4/TSCN (III) and by considering the performing importance of
large-scale reactions, in the next experiment, we evaluated the scalability of the
Sonogashira–Hagihara cross-coupling reaction. To this purpose, the reaction of phe-
nylacetylene, iodobenzene, and triethylamine in a scaled-up procedure (50 times) in
the presence of Co3O4/TSCN (III) was assessed successfully under the optimized
reaction conditions. Interestingly, the scaled-up reaction was accompanied by the
85% isolated yield of the desired product after 9 h.
To approve the privileged features of the Co3O4/TSCN (III) in the Sonoga-
shira–Hagihara cross-coupling reaction, the catalytic activity of this new fabricated
hierarchical nanostructure was compared with some of the previously reported cata-
lysts in the literature (Table 4). Undoubtedly, all of the listed catalysts in Table 4
signifcantly can produce the desired product in good to excellent yield. But it can
be found that the current methodology is much superior to almost all of the methods
presented in Table 4, in terms of the reaction times (entries 2, 5–7 and 9–14), tem-
perature (entries 3, 4, and 8–12), solvents (entries 1–5, 8 and 10–14), catalyst price
(entries 1–6), and reaction medium (entries 7,14).
Conclusion
In the present study, we have successfully fabricated the Co3O4 NPs embedded in
triple-shelled graphitic carbon nitride (Co3O4/TSCN) (III), via a simple thermo-
polymerization of cyanamide (as a single molecular C and N precursor), using the
1 3

Co3O4 nanoparticles embedded in triple-shelled graphitic…
1 3

S. S. E. Ghodsinia et al.
periodic mesoporous organosilica (PMO) as a hard-template. The newly synthe-
sized catalyst was fully characterized by diferent techniques including the FT-IR,
XRD, BET, TEM, FE-SEM, EDX, EDX mapping, TGA, and ICP-OES analysis.
In the presence of this catalyst, diverse aryl halides react with various acetylenic
compounds to aford the corresponding products in good to excellent yields, under
mild reaction conditions. Interestingly, the hierarchical triple-shelled architecture of
the catalyst, in association with the coexistence of micro-, meso-, and macropores
and the nano-sized crystalline structure (from 1.2 to 95 nm), provides not only the
high dispersion and appropriate loading of the cobalt oxide NPs on the support but
also facilitates the favorable mass transfer through the catalyst structure, which is a
strong evidence for the unique catalytic activity of Co3O4/TSCN. To the best of our
knowledge, this study represents the frst example of fabricating embedded Co3O4
NPs in the Co3O4/TSCN as a new sustainable and high-performance hierarchical
catalyst, towards the C(sp)–C(sp2) bond formation, through the Sonogashira–Hagi-
hara cross-coupling reaction, under solvent-free conditions. Notably, this new cata-
lyst could remain quite stable during the reaction conditions, as it can be readily sep-
arated from the reaction mixture using a simple fltration method, and reused for at
least fve recycle runs. Further studies are underway in our laboratory to extend the
capability of this hierarchically structured catalyst to prompt other cross-coupling
reactions. The present investigation could be considered as an attractive alternative
to the currently reported methods for C(sp)–C(sp2) coupling reactions, which would
open a new front for designing and modifcation of environmentally friendly, renew-
able, low-cost, and high-performance nanostructured catalysts with a well-controlled
morphology for other cross-coupling reactions.
Supplementary Information The online version contains supplementary material available at https://doi.
org/10.1007/s11164-021-04466-y.
Acknowledgements The authors gratefully acknowledge the partial support of this study by Ferdowsi
University of Mashhad Research Council (Grant no. p/3/39491).
Declarations
Confict of interest There is no confict of interest for each contributing author.
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