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H. Veisi et al. / Journal of Catalysis 365 (2018) 204–212
analysis (TGA, TSTA Type 503) at a heating rate of 10 °C/min under
nitrogen atmosphere. The spectra were obtained using the Ther-
mofisher Scientific K-Alpha XPS spectrometer. Survey spectra were
initially obtained at low energy resolution (pass energy – 200 eV)
followed by the main regions of interest at higher resolution (pass
ions were instantly reduced to metallic Pd NPs using the
advantage of the existing active catechol and amine groups,
in situ. In the final phase, the Fe3O4@PMDP/Pd nanocatalyst were
isolated using a suitable magnet and dried under vacuum. The
synthetic route of the catalyst is summarized in Scheme 1. The
palladium content of the nanocomposite was 0.28 0.001 mmol
gÀ1 as obtained with atomic absorption spectroscopy. The FTIR,
X-ray photoelectron spectroscopy (XPS), FESEM, EDX, HR-TEM,
TGA, ICP and VSM were used to characterize the catalyst.
energy – 25 eV). A monochromatic Al K
nominal spot size of 400 m.
a X-ray was used, with a
l
2.2. Preparation of Fe3O4, Fe3O4@PDA and Fe3O4@PMDP/Pd magnetic
nanoparticles
FT-IR is used for studying the surface composition of the pre-
pared Fe3O4, Fe3O4@PMDP; and Fe3O4@PMDP/Pd(II) NPs. In the
spectrum of naked Fe3O4 (Fig. 1), the strong peak observed at
582 and 632 cmÀ1 are corresponded to the vibration of the FeAO
groups and the peaks appeared at 1625 and 3385 cmÀ1 are related
with the surface-adsorbed water and hydroxyl groups [45a]. The
FTIR spectra of Fe3O4@PMDP and Fe3O4@PMDP/Pd (Fig. 1b and c)
display FeAO vibrations in the similar vicinity. The peaks
appeared at 3380, 2928, 1600, 1465 cmÀ1 can be allocated to
OAH stretching, CAH stretching, C@C stretching and CAN
stretching relating to the existence of functional groups AOH of
phenol and AC@CANHA in the Fe3O4@PMDP [45a]. As can be
observed, the broad peak appeared at ꢀ2400–3400 cmÀ1 are
because of asymmetric and symmetric stretching of the COOH
and NAH stretching, which show the existence of bound amino
acid on the MNP surface (Fig. 1b and c). However, the peaks
observed at 1600 and 1512 cmÀ1 can be allocated to the
vibration of benzene ring skeleton [45a]. These outcomes offer
that immobilization of PMDP polymer on the surface of Fe3O4
NPs was performed effectively. Furthermore, the band at about
1656 cmÀ1, which relates to COOH bond of the supported PMDP
(Fig. 1b), is moved to lower wavenumbers (1638 cmÀ1) (Fig. 1c),
signifying a good interaction between carboxylic group and Pd
NPs. Moreover, the bending vibration absorption band
corresponding to NAH at 1436 cmÀ1 (Fig. 1b) was moved to
lower wavenumbers (1436 ? 1430), which is probably because
of the interaction of an amine group with Pd NPs (Fig. 1c).
Considering the above results, it can be stated that the
Fe3O4@PMDP/Pd nanocomposite was effectively synthesized
along with a strong interaction between amino acid, catechol and
amino groups of the supported PMDP and the Pd NPs. This
The magnetic Fe3O4 NPs were synthesized through the chemical
coprecipitation approach [45a], and the detailed process is
explained in the following. FeCl2Á4H2O (2 g) and FeCl3Á6H2O (5.2
g) were mixed into 25 mL deoxygenated water and 0.85 mL of
concentrated HCl was added to it. The obtained solution was
gradually poured into 250 mL of 1.5 M NaOH solution under
agitating and N2 protection at 353 K. The resulted MNPs were
isolated from the mixture using a strong magnet and washed by
200 mL distilled water three times. Lastly, the products were
dried at 40 °C to give Fe3O4 NPs.
Fe3O4 NPs (500 mg) were poured into 60 mL distilled water-
ethanol (2:1), following by addition of methyldopa (500 mg), and
the resulted solution was agitated mechanically for 24 h at reflux
condition. at the end of the reaction, the Fe3O4@PMDP NPs were
separated using a magnet and rinsed with distilled water and etha-
nol and dried at 40 °C to give Fe3O4@PMDP.
In the next phase, 500 mg of prepared Fe3O4@PMDP was soni-
cally dispersed in distilled water (100 mL) for 20 min. Conse-
quently, 0.02 g Na2PdCl4 was dissolved in 20 mL water and added
to reaction solution and agitated for 24 h at reflux conditions. In
the next step, Fe3O4@PMDP/Pd(0) was magnetically isolated and
rinsed with ethanol, deionized water and acetone, respectively to
remove probable unattached substrates. Furthermore, the palla-
dium level of the catalyst was determined 0.28 0.001 mmol gÀ1
by means of atomic absorption spectroscopy.
2.3. General procedure for cyanation reactions
A solution containing K4[Fe(CN)6] (0.17 mmol), aryl halide (1.0
mmol), Na2CO3 (1.5 mmol), Fe3O4@PMDP/Pd (45 mg, 1.5 mol%),
and DMF (3 mL) was mixed under stirring at 120 °C for the speci-
fied time. TLC was used to follow the reaction. At the end of the
reaction, the obtained solution was cooled to ambient temperature
and filtered, and the residue was rinsed using ethyl acetate (3 Â 10
mL) to isolate the catalyst using a suitable magnet. Water phase
containing ethyl acetate (30 mL) was mixed with the organic phase
to extreact the ethyl acetate from the water. The organic phase was
dried over Na2SO4. The products were resulted by evaporating the
organic solvent. If more purification was needed, the products
were passed through a short silica gel column using the eluent of
n‐hexane. All the products are known substances and were com-
pared with authentic specimens.
3. Results and discussion
This research has been aimed to continue our earlier research
[45] and design a new magnetic nanocomposite using the influ-
ence of both coordinator and stabilizer agent for immobilizing
metal ions, e.g. palladium. Firstly, Fe3O4 NPs was synthesized
according to our earlier report [45a]. Next, Fe3O4 NPs were
immobilized using PMDP, in situ, through polymerization of
methyldopa in water/ethanol (2:1) under reflux condition. Then,
the synthesized Fe3O4@PMDP nanocomposite was used for
absorbing palladium ions on their PMDP layers. The palladium
Fig. 1. FT-IR spectra of (a) Fe3O4, (b) Fe3O4@PMDP, and (c) Fe3O4@PMDP/Pd.