Facile synthesis of a recyclable Pd-rGO/CNT/CaFe2O4 nanocomposite with high multifunctional photocatalytic activity under visible light irradiation

Article abstract of DOI:10.1039/c9ta02882j

We report a facile method to synthesize a magnetically separable Pd-rGO/CNT/CaFe₂O₄ photocatalyst. The incorporation of CNTs into rGO can form a conductive network structure to bridge the gaps between rGO sheets. This conductive netw

Full text of DOI:10.1039/c9ta02882j

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January 2016 Pages 1–330
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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS nanocages as a lithium ion battery anode material
2
rsc.li/materials-a

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Facile synthesis of recyclable Pd-rGO/CNT/CaFe O nanocomposite with high
2
4
multifunctional photocatalytic activities under visible light irradiation
a
a
a
Mojtaba Bagherzadeh,* Reyhaneh Kaveh and Hamed Mahmoudi
a
Chemistry Department, Sharif University of Technology, Tehran, P.O. Box 11155-3615, Iran;
bagherzadeh@sharif.edu
Abstract:
2 4
We report a facile method to synthesize a magnetically separable Pd-rGO/CNT/CaFe O photocatalyst. The
incorporation of CNTs into rGO can be performed with a conductive network structure to bridge between the gaps of
rGO sheets. This conductive network can prevent the restacking of GO nanosheets during the reduction process. Also,
for photocatalysis, the aforementioned conjugated network can provide rapid electronic conducting channels. It was
2 4
found that the Pd-rGO/CNT/CaFe O nanocomposite is an efficient photocatalyst for Heck-Mizoroki coupling
reaction under irradiation of visible light. Interestingly, the electrons which exited by the photon can be transferred to
the palladium nanoparticles causes an increase in the electron density of Pd in consequence increases the catalytic
activity of these nanoparticles in Heck-Mizoroki coupling reactions under visible light. In this regard, we tested the
catalytic activity of these nanocomposites in Heck-Mizoroki coupling reaction under visible light to obtain the product
in good to excellent yields. As compared to pure CaFe
the prepared Pd-rGO/CNT/CaFe photocatalyst exhibits remarkably increased photocatalytic degradation of
methylene blue (MB). The presence of Pd nanoparticles can act as a co-catalyst and delay the recombination of
photoinduced electron-hole pairs of CaFe
2 4 2 4 2 4
O , rGO/CaFe O , and rGO/CNT/CaFe O nanocomposites,
2
O
4
2
4
O .
2 4
Keywords: Photocatalyst, rGO, CNT, Pd, CaFe O , photocatalytic Heck-Mizoroki coupling, MB degradation
1
. Introduction
Solar energy as a renewable source of energy plays an important role in acquiring higher
activity without high energy consumption. In other words, coupling solar energy with active
1
catalysts enhances the overall performance of the catalysts and environmental protection. The
field of heterogeneous photocatalysis has been studied for nearly four decades due to their
2
interesting advantages in the sustainable transformation of organic molecules. Recently, the
interest in photocatalysis has concentrated on the use of semiconductor materials. Most of the
3
organic reactions are performed exposure heating condition, which is energy intensive. One of
the twelve principles of green chemistry is to minimize the energy requirements of chemical
processes so it would be an outstanding breakthrough if the catalytic reaction can be performed at
4
room temperature under visible light irradiation. Considering the explosive growth of green and
environmentally benign synthetic process, light-catalyzed chemical reactions have attracted a lot
of attention as zero valent metal nanoparticles, especially Pd nanoparticles can be used as a
catalytically active species for a great number of main chemical reactions.5
The palladium-catalyzed Heck-Mizoroki coupling reaction is one of the most important
carbon-carbon coupling reactions with a considerably wide scope in organic synthesis. Also, this
coupling reaction has been extensively used for the synthesis of pharmaceuticals, polymers and
6
natural products. Conventional Pd catalysts for Heck-Mizoroki coupling reaction which has been
widely investigated are mostly inhomogeneous with different additives or ligands.3b, 3d-h Most of
the time, these reactions require difficult conditions, such as high temperature and long reaction

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7
time. Difficult separations and the poor thermal stability of these Pd catalysts significantly hinder
their applications in the chemical industry. Although heterogeneous catalysts can overcome those
challenges, they are generally less efficient than their homogeneous counterparts. In addition, a
great number of heterogeneous catalysts have difficulties in their separation from the mixture of
reaction by centrifugation and filtration.3a, 8 These problems would be removed by preparation of
magnetic catalysts that can be easily separated by an external magnet from the mixture of reaction.
Many works are available on the Heck-Mizoroki coupling reaction in which palladium was
9
supported on different silica, zeolite, metal oxides and carbon-based materials. Carbon-based
materials such as graphene oxide and carbon nanotubes can be good choice as support for
palladium nanoparticles due to their unique properties including the high surface area,
1
0
morphology, good chemical stability, and good electrical conductivity. According to the previous
studies, nanosheets of graphene and its derivatives show superior mechanical and chemical
properties also, extraordinary interaction with the loaded nanoparticles and good conductivity for
electron capture and transport make them effective in catalysis, pollutant degradation, etc.11
However, graphene-based materials are very easily aggregated due to the π-π stacking interaction
between the sheets. Consequently, the further modification should be carried out to remove this
problem. In fact, the rGO/CNT network as a catalyst supporting material has been used for
preparing of this nanocomposite. Introduction of CNT between sheets of graphene via van der
Waals forces, hydrogen bonding, and π-π stacking can bridge the adjacent sheets of graphene,
avoiding graphene sheets aggregation and increase the conductivity and specific surface area.12
Supporting Pd nanoparticles on rGO/CNT composite not only provide a large surface area but also
increase thermally stable system.13
The interest in photocatalysis has concentrated on the use of semiconductor materials
recently. In fact, a great number of semiconductor materials have been used as photocatalysts for
1
4
15
environmental protection. The large band gap semiconductors, such as titanium oxide (TiO ),
2
1
6
17
18
zinc oxide (ZnO), strontium titanate (SrTiO ), and Zinc sulfide (ZnS), are capable of utilizing
3
only a small portion of sunlight (UV light), while spinel ferrites (MFe O ) can effectively utilize
2
4
1
9
visible light due to their narrow band gaps. In addition, recovery and reusability of the
2
0
photocatalysts are very important. The magnetic property of the spinel ferrites is another reason
for making them useful in preparing of the photocatalysts.21 Therefore, MFe O as magnetic
2
4
materials with thermally and chemically stabilities and narrow band gaps have been used for
2
2
preparing of effective photocatalysts. The nontoxic and inexpensive CaFe O , as a member of
2
4
the spinel ferrites, has paid lots of attention because of the interesting catalytic and magnetic
properties. This narrow band-gap semiconductor is found to be a perfect photocatalyst under
visible-light irradiation.23
However, spinel ferrites cannot exhibit satisfied photocatalytic performance alone. This
issue is related to the high recombination rate of photoinduced electron-hole pairs. One of the best
ways to solve this problem is to combine spinel ferrites with carbon-based materials such as porous
carbon, carbon nanotubes (CNTs)13a, 13b, and graphene.13c-f Unique physicochemical properties
2
4

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of carbon materials make them perfect supporting materials for various nanoparticles loading, such
as spinel ferrites, to improve their photocatalytic performance. Among different carbon-based
materials, carbon nanotubes and graphene sheets show a promising performance due to their high
specific area, corrosion resistance, and intrinsic excellent conductivity.25
In this report, we successfully synthesized quadruple Pd-rGO/CNT/CaFe O
2
4
nanocomposite as an effectiveness photocatalyst for Heck-Mizoroki coupling reaction at room
temperatures under irradiation of visible light. Also, the prepared photocatalyst can be easily
separated from the system of reaction via an external magnetic. We also demonstrate that Pd-
rGO/CNT/CaFe O nanocomposite photocatalyst exhibits remarkably increased photocatalytic
2
4
methylene blue (MB) degradation as compared to pure CaFe O , rGO/CaFe O , and
2
4
2
4
rGO/CNT/CaFe O nanocomposites. MB is one of the most dangerous pigments which are
2
4
important pollutants in the wastewater of a great number of industries like textiles and chemicals.14
Experimental
2
.1. Preparing of rGO/CNT nanocomposite
g of the purchased MWCNTs were suspended in 200 mL of a mixture of concentrated
H SO (98 wt%) and HNO (65 wt%) with a volume ratio of 3:1 and then was sonicated for 3 h.
1
2
4
3
The obtained solid was collected by centrifugation, washing repeatedly with distilled water until
the pH of 7 and drying at 80 °C for 5 h under vacuum. The purpose of CNTs treatment is removing
the impurity and functionalize the surface of CNTs. Also, Graphene oxide (GO) synthesized from
2
6
purified graphite powder by using the Hummers method. Then 120 mg of acid-treated CNTs
were added into the 60 mL of homogeneous GO aqueous dispersion (2 mg/mL). In order to develop
an interconnected structure between GO and acid-treated CNTs, they mixed together with a mass
ratio of 1:1. After being sonicated for 30 min, the mixture was transferred into a 100 mL sealed
Teflon-lined autoclave for 12 h at 180 °C. Finally, the obtained mixture was cooled in room
temperature and the black-colored rGO/CNT nanocomposite was collected.
2
.2. Preparing of Pd-rGO/CNT nanocomposite
A 50 mL round-bottom flask equipped with a magnetic stirrer was charged with PdCl (72
2
mg, 0.4 mmol) and KCl (668 mg, 9 mmol), in 15 mL water. The flask was heated at 80 °C until
PdCl was dissolved. This solution was cooled at room temperature and added dropwise to a
2
suspension of rGO/CNT (400 mg) in 15 mL water. The suspension was stirred at room temperature
for 2 h, then filtered under reduced pressure, washed with water and methanol and dried in air. The
product Pd-rGO/CNT was obtained as a black solid.
2
.3. Preparing of Pd-rGO/CNT/CaFe O nanocomposite
2 4
To synthesize the CaFe O nanoparticles, calcium nitrate Ca(NO ) .6H O and ferric
2
4
3 2
2
nitrate Fe(NO ) .9H O with a molar ratio of (1:2) were dissolved in 60 mL ethylene glycol (EG)
3
3
2
and the mixture was sonicated for 10 min. An appropriate KOH solution was used to adjust the

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pH of the solution to 10. Then the resulting mixture was sealed in a 100 mL Teflon-lined
autoclave and maintained at 125 °C for 24 h. After collection and being washed with ethanol, the
product was dried and the brown-colored CaFe O nanoparticles were obtained. The Pd-
2
4
rGO/CNT/CaFe O nanocomposite with various loadings of CaFe O was prepared using the
2
4
2
4
following procedure. 0.5 g of Pd-rGO/CNT and various weight percents of CaFe O (30%, 40%,
2
4
and 50%) were dispersed in 60 mL of ethanol by sonication for 2 h. In order to get a
homogeneous suspension, the resulting mixture kept under continuous stirring for 12 h. Then the
suspension was transferred into a 100 mL Teflon lined autoclave. The autoclave was sealed and
maintained at 120 °C for 6 h. The final product was centrifuged and dried at 70 °C in an oven.
The loading of Pd was determined to be 1.72% w/w Pd by ICP-OES analysis. For comparison,
rGO/CaFe O and rGO/CNT/CaFe O were synthesized using the same preparation method of
2
4
2
4
Pd-rGO/CNT/CaFe O without the addition of Pd in both composites (rGO/CaFe O and
2
4
2
4
rGO/CNT/CaFe O ) and acid treated MWCNT in first composite (rGO/CaFe O ). The synthesis
2
4
2
4
process for the Pd-rGO/CNT/CaFe O nanocomposite is depicted in scheme 1.
2
4
2
.4. Photocatalytic Heck-Mizoroki Reaction
In a 25 mL round bottom flask equipped with a magnetic stirrer, aryl iodide (1 mmol),
alkene (1.2 mmol), TEA (1.5 mmol), catalyst (0.1 mol%, 6.2 mg) and dimethylacetamide (DMA,
M, 1 mL) were consecutively added and the resulting mixture was left under visible light
1
illumination (a 250-W mercury lamp with the UV cut-off filter). The distance between the
aforementioned flask and the light source were 50 cm and the reaction temperature was maintained
at (25 °C ± 2 °C) by using a water bath circulator system. The reaction monitored by gas
chromatography system. A Parallel reaction was performed as a dark control under the same
condition in a dark environment to check the ability of photocatalyst in the transformation of
organic materials in Heck–Mizoroki coupling reaction.
2
.5. Thermocatalytic Heck-Mizoroki Reaction
In a 5 mL round bottom flask equipped with a magnetic stirrer and condenser, aryl iodide
(1 mmol), alkene (1.2 mmol), TEA (1.5 mmol), catalyst (0.1 mol%, 6.2 mg) and
dimethylacetamide (DMA, 1 M, 1 mL) were consecutively added and the resulting mixture was
left under stirring at 130 °C and the reaction monitored by gas chromatography system.
2
.6 General procedure for extraction work-up of catalytic product in Photocatalytic and
Thermocatalytic Heck-Mizoroki Reaction
After 5h, the catalyst was separated by using an external magnetic field, and 2 mL of Ethyl
acetate was added to the remain solution. The liquid extraction was performed by adding water
(3×2 mL) to extracting dimethylacetamide. Finally, the product was obtained by distillation of
Ethyl acetate. Final purification of the catalytic product was performed by using flash
chromatography.
2
.
Results and discussion
3
.1. Characterizations

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The prepared materials were characterized by using several techniques such as FT-IR,
PXRD, Raman, Magnetometer, electrochemical impedance spectroscopy, and Photoluminescence.
Full characterization details are available in supporting information.
To investigate the morphologies of the synthesized F-MWCNT, rGO/CNT, Pd-
rGO/CNT/CaFe O nanocomposites, the FESEM images of these samples are presented in Fig. 1.
2
4
As observed in Fig. 1a, due to the presence of functional groups after acid treatment, the bundle-
liked MWCNTs appeared dispersed. Also, white impurities were observed on the surface. In
addition, the smooth wall of the MWCNTs became less smooth and a little bent because of the
side attachment of the -COOH groups during acid treatment. Fig. 1b shows that F-MWCNTs were
significantly distributed on the surface of GO sheets, also F-MWCNTs inserted into the GO sheets.
The F-MWCNTs nanotubes can act as bridges to prevent GO sheets from restacking and increase
the spaces between sheets. The presence of interaction between the synthesized nanoparticles (Pd,
CaFe O ) with the rGO/CNT nanocomposite can be vividly seen in Fig. 1-c.
2
4
The EDX spectrum of Pd-rGO/CNT/CaFe O nanocomposite indicate that the elements C,
2
4
O, Fe, Ca, and Pd present in this nanocomposite. The EDX-mapping (Fig. 1d-h) that is related to
the FESEM image in Fig. 1c shows that the Ca, Fe and Pd Elements have a uniform dispersity in
the rGO/CNT nanocomposite.
In order to investigate the optical absorption performance of the prepared samples, UV-Vis
diffuse reflectance spectra (DRS) of neat CaFe O , rGO/CNT/CaFe O and Pd-
2
4
2
4
rGO/CNT/CaFe O nanocomposite in Fig. 2. As can be seen in Fig. 2a, the CaFe O has significant
2
4
2
4
absorption in the visible region due to its narrow bandgap but after the formation of Pd-
rGO/CNT/CaFe O , the nanocomposite exhibits increased absorption in the visible region,
2
4
indicating that the Pd-rGO/CNT/CaFe O4 nanocomposite possess better visible-light
2
photocatalytic activity (Fig. 2c). This phenomenon not only can be related to the electronic
transition between rGO/CNT and CaFe O but also can be attributed to the inherent absorption of
2
4
rGO/CNT nanocomposite. On the other hand, the presence of rGO/CNT nanocomposite can lead
to a bridge between the CaFe O and light. The DRS test for rGO/CNT/CaFe O also showed that
2
4
2
4
the presence of Pd nanoparticles in Pd-rGO/CNT/CaFe O nanocomposite does not significantly
2
4
change the optical properties of rGO/CNT/CaFe O nanocomposite (Fig 2b).
2
4
3
.2. Catalytic activity in Heck-Mizoroki coupling reactions
Since Pd is widely known to be a catalytically active species for a large number of organic
reactions under thermal conditions, for finding the ability of the catalytic system in the cross-
coupling reactions, we tested the catalytic system in the Mizoroki-Heck coupling reaction. For this
reason, iodobenzene and methyl acrylate were chosen as model substrates and triethylamine as a
base. Interestingly, with only 0.1 mol% Pd content the reaction was completed in 5h. This result
showed that this catalyst is perfect under this condition for the Heck-Mizoroki coupling reaction.
In the next step, we start to change the source of energy to the visible light and we perform
one reaction under visible light, in parallel, a dark control reaction was performed with the same
condition under dark environment. Surprisingly, the photocatalytic reaction showed perfect

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conversion in comparison with dark control reaction. A summary of this study has been gathered
in Table 1.
To verify the efficiency of the catalytic system, we investigated the Heck–Mirozoki
coupling reaction using a series of aryl iodides and alkyl acrylates or styrenes (Table 2) Using both
thermal and photocatalytic reaction and obtaining after 5 h with good to excellent yields of isolated
products. This study Emphasis that the thermal condition slightly better than photocatalytic
reaction, but photocatalytic reaction also showed very promising results and given the importance
of using light rather than heat in such reactions, this catalyst can be a good alternative to the
1
traditional thermal methods of cross-coupling reactions. The products H NMR spectra are
depicted in Fig. S17-S32 respectively (the supplementary materials).
To verify the efficiency of these well-defined materials in photocatalytic Heck-Mizoroki
coupling reaction, authors made a comparison between the catalytic system introduced in this work
and some other previously published photocatalytic systems. Suresh B. Waghmode et al. prepared
PdCl /TiO catalyst, and they showed that the catalytic activity of this heterogeneous system in
2
2
Heck-Mizoroki coupling is perfect under UV-Vis light and 45C.27 Saurabh S. Soni et al.
synthesized the Pd(0)-doped mesoporous TiO nanoparticles (Pd/TiO ) and showed that the
2
2
catalytic activity of Pd/TiO nanoparticles is remarkably increased under solar light irradiation for
2
8
a
the Heck reaction. X. Wei Guo et al. showed that Pd nanoparticles, supported on carbon nanocoils
2
8
(
Pd/CNCs), has unexpected high photocatalytic activity for Heck coupling reaction at 40°C. H.
Shin et al. showed that the incorporation of MoS nanosheets with Pd nanodots can be a good
2
1
b
strategy for promoting the visible-light-induced Suzuki–Miyaura C–C coupling reaction. The
results of this comparison are summarized in Table 3. These comparisons clearly show the
efficiency of the present catalytic system considering TOF, which is very important in the point of
view of the atom economy in green chemistry.
3
.3. catalytic activity on Methylene Blue degradation
Fig. S11 shows the photocatalytic activities of prepared samples for the degradation of MB
−
1
−1
(
12 mg L , 50 mL, and 3 g L catalyst) under visible light illumination. The obtained results
show that the MB photolysis under visible light irradiation is not considered in the absence of
photocatalyst. In a dark situation, no electron-hole pairs can be formed and since the photocatalytic
performance of photocatalysts depends on formation, separation, and migration of charges,
decomposition of MB is ignorable after 30 min. As observed, the Pd-rGO/CNT/CaFe O (40%)
2
4
nanocomposite exhibits higher photocatalytic activity than that of the other samples. The
degradation of MB via Pd-rGO/CNT/CaFe O (40%) is > 98% during 75 min however the
2
4
photodegradation of MB by the pure CaFe O , rGO/CaFe O (40%) and rGO/CNT/CaFe O (40%)
2
4
2
4
2
4
is 24%, 35% and 90% in 75 min, respectively. The synergistic effect of rGO and CNTs can be a
good contribution to increase the photocatalytic activity of pure CaFe O . Also, the obtained result
2
4
demonstrates that Pd-rGO/CNT shows low photoactivity, indicating that the increased
photocatalytic activity of Pd-rGO/CNT/CaFe O cannot be related to the intrinsic catalytic activity
2
4
of Pd nanoparticles. So, Pd nanoparticles only can play a co-catalyst role in the photodegradation
of MB. In other words, the presence of Pd nanoparticles can be effective for trapping the

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photogenerated electrons and it can improve the separation efficiency of the charge carriers, so a
higher photodegradation of MB was obtained.
In Fig. S12, the photocatalytic kinetics of the synthesized samples were also studied. Kapp
values for photodegradation of MB are gained by plotting the curve of ln (C /C ) versus t. The
0
t
obtained results displayed that the kinetic simulation curves are close to linear curves. So that all
2
of the correlation coefficients (R ) were higher than 0.9, the pseudo-first-order kinetics model
significantly fit the experimental data.29 Fig. S13 shows that the optimized photocatalyst (Pd-
rGO/CNT/CaFe O (40%)) has the highest removal efficiency of MB and the value of K for this
2
4
app
-1
photocatalyst is 0.0548 min .
Also, the degradation of MB as a sample of pollutants was investigated quantitatively via
COD method. The results are depicted in Fig. S14. The COD values of the treated MB solution
were decreased and this issue shows that in the presence of Pd-rGO/CNT/CaFe O (40%)
2
4
nanocomposite acceptably degradation/ mineralization of MB was carried out.
.6. Possible photocatalytic mechanism
One of the major factors for limiting the conversion efficiency of light energy is charge
3
recombination for semiconductor photocatalysts. The synergistic effect of rGO and CNTs can be
a good contribution to overcome this issue and improve the photocatalytic performance. In fact,
the incorporation of CNTs into rGO not only can be caused a conductive network structure in order
to bridge between the gaps of rGO sheets but also can prevent the restacking of GO nanosheets
during the reduction. This conjugated network remarkably enhances the electrical conductivity.
Also for photocatalysis, this conjugated network can provide rapid electronic conducting channels.
In addition, Pd nanoparticles are an effective material for trapping the photogenerated electrons
because of their electron reservoir capacity so, facilitating the photodegradation of organic
pollutants such as MB and enhancing photocatalytic performance. In other words, Pd nanoparticles
can play as a co-catalyst role in the photodegradation of MB and these nanoparticles can delay the
recombination of photoinduced electron-hole pairs of CaFe O .
2
4
¯
⦁
The photoinduced electrons react with surface adsorbed O to generate O , that then react
2
2
+
•
•
with H to generate OOH, followed by rapid decomposition to OH. Additionally, the
photoinduced holes could oxidize H O and OH‾ to generate OH which is involved in the
photodegradation process of organic pollutants. On the other hand, the process of generating OH
radicals can occur by two pathways. So, the reactive species involved in the photodegradation
•
2
•
3
0
⦁
¯⦁
+
process are hydroxyl radicals ( OH), superoxide radicals (O ) and photogenerated holes (h ). In
2
order to identify the role of these species taking part in the photodegradation process, 2 mmol KI
+
¯⦁
(
a hole (h ) scavenger), 2 mmol BZQ (a superoxide radical (O ) scavenger), 2 mmol t-BuOH (a
2
•
hydroxyl radical ( OH) scavenger) were added into the photocatalytic system using Pd-
rGO/CNT/CaFe O (40%) nanocomposite. As observed in Fig. S15, the presence of KI hardly
2
4
+
decreases the rate of degradation in the photocatalytic reaction. As a consequence, the h cannot
play an important role in the photodegradation of MB. The photodegradation rate of MB is
significantly decreased in the presence of BZQ and especially t-BuOH. This issue indicates that
the O2¯ and especially OH is the main reactive species. In conclusion, first OH and second O
⦁
⦁
⦁
¯⦁
2

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are the predominant reactive species for the photodegradation of MB over the Pd-
rGO/CNT/CaFe O (40%) photocatalyst under the visible light illumination.
2
4
To find the mechanism of visible-light-driven Heck-Mizozroki coupling reaction, a control
-
test was carried out in order to investigate the role of the photoinduced e . The result showed that
-
after adding 2 mmol of K S O as e scavenger only 9% conversion was gained under visible light
2
2
8
irradiation. According to the published literature,20, 31 upon visible light illumination, electrons
from VB of CaFe O are excited into the CB of CaFe O and then they easily transfer from the CB
2
4
2
4
of CaFe O to the Pd nanoparticles. These nanoparticles can trap the photoinduced electrons
2
4
-
because of their e reservoir capacity. The photoinduced electrons that transferred onto the
nanoparticles of Pd can increase the inherent catalytic activity of palladium nanoparticles. These
electrons finally transferred to the carbon-iodine bond, which caused weakening of this bond (Fig.
3
). When the bond is weakened, with an oxidative addition reaction, this bond is added to the
palladium and generate the active species of Ar-Pd-I complex and start the traditional Heck-
Mizozroki coupling cycle. The final products can be obtained by β-hydrogen elimination.
Therefore, both the photoinduced electrons and energetic nanoparticles of palladium act as active
centers to attack the C-I bond of aryl halide.
3
.6. Reusability
Stability and reusability of the synthesized heterogeneous catalysts are crucial parameters
for the practical application. Both the photodegradation of MB solution and Heck-Mizoroki
coupling reaction are selected to investigate the reusability of Pd-rGO/CNT/CaFe O (40%)
2
4
nanocomposite under the optimized conditions. After each test, the catalyst was separated by an
external magnetic field and washed several times with distilled water and dried at 90 °C. Based on
the obtained results the Pd-rGO/CNT/CaFe O (40%) photocatalyst can be reused ten runs for the
2
4
MB photodegradation process with no significant loss in degradation efficiency (Fig. S16) and six
consecutive reaction runs for the Heck-Mizoroki coupling reaction without a dramatic loss of
catalytic activity (Fig. 4). It can be indicated that the synthesized photocatalyst is stable during the
photocatalytic process.
3
.
Conclusions
The magnetically recyclable Pd-rGO/CNT/CaFe O nanocomposite has been successfully
2
4
synthesized by a facile method. This nanocomposite exhibits the effective photocatalytic Heck-
Mizoroki coupling reaction under room temperature that can completely replace the
thermocatalytic Heck reaction. Also, this nanocomposite shows increased photodegradation of
organic pollutants such as MB. Both the increased photocatalytic activities are attributed to the
effective electron spatial transfer route because of the Pd nanoparticles. These nanoparticles not
only can act as the electron mediator on the rGO/CNT nanocomposite and CaFe O but also can
2
4
trap photogenerated electrons. In addition, the incorporation of CNTs into rGO can be caused by
a conductive network structure to bridge between the gaps of rGO sheets and this can prevent the
restacking of GO Nanosheets during the reduction. This conjugated network significantly
increases the electrical conductivity and it can provide rapid electronic conducting channels.
Further, the Pd-rGO/CNT/CaFe O exhibits perfect reusability for both the photodegradation of
2
4

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dye and photocatalytic chemical reaction. The prepared photocatalyst can be easily recovered by
an external magnet.
Acknowledgments
M.B. acknowledges the research council of the Sharif University of Technology for the
research funding of this work.

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Figure Captions:
Fig. 1. FESEM image of (a) F-MWCNT, (b) rGO/CNT (c) Pd-rGO/CNT/CaFe O (40%) and
2
4
EDX-mapping of C (d), O (e), Ca (f), Fe (g), and Pd (h) of Pd-rGO/CNT/CaFe O (40%)
2
4
nanocomposite in the green frame of (c).
Fig. 2. The UV–Vis DRS spectra of (a) CaFe O , (b) rGO/CNT/CaFe O (40%) (c) Pd-
2
4
2
4
rGO/CNT/CaFe O (40%).
2
4
Fig. 3. The effect of visible light on the activation of C-I bond through transfer electron from CB
of CaFe O to Pd nanoparticles.
2
4
Fig. 4. Recycling studies of the Pd-rGO/CNT/CaFe O (40%) catalyst in the Heck-Mizoroki
2
4
coupling reaction.

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Table Captions:
Table. 1. Checking the capability of Pd-rGO/CNT/CaFe O as a catalyst of Heck-Mizoroki
2
4
coupling in different conditions
Table. 2. Heck-Mizoroki coupling of aryl iodide with different olefins in the presence of Pd-
rGO/CNT/CaFe O catalyst under thermocatalytic VS photocatalytic conditions
2
4
Table. 3. A comparative study of Pd-rGO/CNT/CaFe O with the previously reported catalysts in
2
4
Heck-Mizoroki coupling reactions.

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List of Figures:
Fig. 1.

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Fig. 2.

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Fig. 3.

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Fig. 4.a
0.1 mol%
Pd-rGO/CNT/CaFe O
O
2
4
O
TEA (1.5 mmol)
I +
O
DMA
O
5h
1
00
90
80
70
60
50
40
30
20
10
0
TCR
PCR
Run 1
Run 2
Run 3
Run 4
Run 5
Run 6
Run number
a
;
;
Reaction conditions: iodobenzene 1 mmol, methyl acrylate 1.2 mmol, TEA 1.5 mmol, 1 mL DMA and 5 h.
Measured by GC analyses.
b
TCR=Thermocatalytic Reaction; Conditions: 130 C in dark environment.
PCR=Photocatalytic Reaction; Conditions: 25 C controlled by water bath circulator under visible light
illumination, a 250-W mercury lamp with the UV cut-off filter.

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Table. 1.a
0.1 mol%
Pd-rGO/CNT/CaFe O
O
2
4
O
TEA (1.5 mmol)
I +
O
DMA
O
5h
Visible
light
No
entry mol % cat
Temp.
130 C 5 h
Convb
Description
Time
1
2
3
0.1
0.1
0.1
>99%
73%
0%
Thermocatalytic Reactionc
Photocatalytic Reactiond
Dark controle
Yes
No
25 C
25 C
5 h
5 h
a
;
;
Reaction conditions: iodobenzene 1 mmol, methyl acrylate 1.2 mmol, TEA 1.5 mmol, 1 mL DMA and 5 h.
Measured by GC analyses.
130 C in a dark environment.
b
c
;
d
;
25 C controlled by water bath circulator under visible light illumination, a 250-W mercury lamp with the UV
cut-off filter.
c
;
25 C controlled by water bath circulator in a dark environment.

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Table. 2.a
0.1 mol%
Pd-rGO/CNT/CaFe O
2
4
TEA (1.5 mmol)
R1 I +
R2
R2
R1
DMA
5h
Yield%c
Yield%c
Entry
R1
R2
Product
(
TCRd)
(PCRe)
O
O
1
O
94
67
O
O
O
O
2
3
O
84
91
61
72
O
O
O
O
O
O
O
O
O
O
O
4
95
76
O
O
O
O
O
O
5
6
7
88
87
93
71
63
74
O
O
O
O
O
O
O
O
O
O
O
O
O
8
9
96
83
77
66
O
O
1
0
1
81
89
59
68
1
O
O

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O
1
1
2
3
91
87
69
73
O
Cl
Cl
Cl
1
1
4
5
89
93
72
78
Cl
Cl
O
Cl
O
Cl
O
1
6
94
81
Cl
O
a
c
;
;
;
Reaction conditions: aryl iodide 1 mmol, olefin 1.2 mmol, TEA 1.5 mmol, 1 mL DMA and 5 h.
Isolated yield of the pure product after flash chromatography.
TCR=Thermocatalytic Reaction; conditions: 130 C in dark environment.
d
e; PCR= Photocatalytic Reaction; conditions: 25 C controlled by water bath circulator under visible
light illumination, a 250-W mercury lamp with the UV cut-off filter.

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Table. 3.a
entry Catalytic
system
Light source
Temperature
Time
(h)
5
TOF Refrence
(h-1)
38.8
8.61
23.4
146
(C)
45
2
7
1
2
3
4
PdCl /TiO
UV-Vis
Vis (sun light)
Vis
2
2
8
a
Pd/TiO2
r.t.
40
72
3
2
8
Pd/CNCs
This work
Vis
r.t.
5
-

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Scheme. 1. Schematic illustration of the preparation process of Pd-rGO/CNT/CaFe O
2
4
nanocomposite.

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3
38x190mm (96 x 96 DPI)

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Graphical Abstract
Facile synthesis of recyclable Pd-rGO/CNT/CaFe O nanocomposite with high
2
4
multifunctional photocatalytic activities under visible light irradiation
Mojtaba Bagherzadeh *, Reyhaneh Kaveh and Hamed Mahmoudi
A magnetically separable Pd-rGO/CNT/CaFe O nanocomposite photocatalyst synthesized and
2
4
its photocatalytic activity in the presence of visible-light were investigated. This photocatalyst not
only presents remarkably increased photocatalytic activity toward MB degradation under visible irradiation
but also presents significantly catalytic activity in Heck-Mizoroki coupling reactions under visible light to
obtain the product in good to excellent yields. Moreover, the synthesized photocatalyst is so stable
during the photocatalytic process.