F. Zamani, S. Kianpour / Catalysis Communications 45 (2014) 1–6
3
AA molecules exist on the surface of the nanocomposite, and coordi-
nate with the Ni nanoparticles.
In order to investigate about the state of Ni in the nanocomposite,
the XPS study was carried out on the Fe3O4/Ala-AA-Ni catalyst (Fig. 3)
(recorded with Shimadzu ESCA SSX-100). The Ni 2p spectrum exhibits
two main peaks at 851.8 and 868.9 eV which are attributed to Ni(0)
2p3/2 and Ni(0) 2p1/2, respectively (Fig. 3). It means that the Ni species
are stable as metallic state in the Fe3O4/Ala-AA-Ni nanocomposite.
Furthermore, it can be seen that the Ni(0) 2p3/2 and 2p1/2 binding
energy of 851.8 and 868.9 eV represented in Fig. 3 are slightly lower
than those of typical Ni nanoparticles (852.3 eV for Ni 2p3/2 and
869.7 eV for Ni 2p1/2 [41]). This may be due to the interaction
between N and O atoms of Ala-AA and Ni nanoparticles which causes
to increase in the charge density around Ni(0) and decrease in bind-
ing energy. In general, the binding energy of metal nanoparticles is
sensitive to the surrounding chemical environment which means
that when the metal species are interacted with ligands, the binding
energy will decrease slightly [43]. According to the XPS and IR
results, it can be concluded that the Ni nanoparticles were success-
fully incorporated onto the Fe3O4/Ala-AA nanocomposite.
Fig. 1. XRD patterns of (a) Fe3O4/Ala-AA and (b) Fe3O4/Ala-AA-Ni.
The morphology of the nanocomposite was observed on transmission
electron microscopy (performed on Phillips CM10 microscope). Fig. 4
shows TEM image of the Fe3O4/Ala-AA-Ni nanocomposite catalyst. As
can be seen, the Ni nanoparticles were found to be highly dispersed on
the surface of the Fe3O4/Ala-AA nanocomposite with the average
diameter size of ~3–4 nm.
Fig. 5 depicts the N2 adsorption–desorption isotherms of the
Fe3O4/Ala-AA and Fe3O4/Ala-AA-Ni nanocomposites (Fig. 5a,b) (recorded
with Series BELSORP 18). As can be seen, these isotherms are similar to
isotherms of type IV, according to the IUPAC nomenclature, which are
the typical characteristics of mesoporous structure [44]. The BET surface
areas of the Fe3O4/Ala-AA and Fe3O4/Ala-AA-Ni nanocomposites were
calculated to be 133.7 m2 g−1 and 96.4 m2 g−1 respectively. This reduc-
tion in the specific surface area may be due to the incorporation of Ni
nanoparticles onto the Fe3O4/Ala-AA magnetic support.
between the carboxylate head and the metal atom [39]. Since the wave-
number separation between the COO−as and COO−s bands is 173 cm−1
(1589 − 1416 = 173 cm−1), it can be concluded that the interaction
between the COO− group and the Fe atom is covalent and bridging
bidentate [39]. The presence of peak at around 2800–3000 cm−1 also
corresponds to the aliphatic C\H stretching of the methylene groups,
which is observable in the samples (Fig. 2a-c). In Fe3O4/Ala-AA
(Fig. 2b), the new band at 1668 cm−1 is due to stretching vibration of
C_O bond, indicating the presence of amide group in the nanocompos-
ite. Fe3O4/Ala-AA-Ni spectrum (Fig. 2c) shows that the bending vibra-
tion absorption band of N\H at 1447 сm−1 is shifted to the lower
wavenumbers (1447 → 1382 сm−1), which is possibly due to the
strong interaction between the N groups of amide and metal parti-
cles. Moreover, the band at around 1668 cm−1, which is related to
the carbonyl bond of AA, is also shifted to the lower wavenumbers
(1668 → 1631 сm−1). Furthermore, the peak intensity of the car-
bonyl bond in the spectrum of Fe3O4/Ala-AA-Ni is lower than that
of Fe3O4/Ala-AA. These observations may be due to the strong inter-
action between the Ni nanoparticles and C_O groups. In other
words, the double bond CO stretches become weak by coordinating
with the metal nanoparticles [40–42], which is confirmed that Ala-
The structural composition of the Fe3O4/Ala-AA-Ni nanocomposite
was further examined by energy-dispersive X-ray (EDX) analysis
(recorded with Phillips CM10 microscope which was equipped
with an energy-dispersive X-ray analyzer). A typical EDX spectrum
taken from the nanocomposite was shown in Fig. 6, where peaks
associated with Fe, C, O, N, and Ni can be distinguished. The
quantitative analysis gives weight ratios of
C (39.87%), Fe
(20.96%), O (27.62%), N (3.17%) and Ni (6.07%). Taking the
EDX analysis into consideration, the presence of Ala-AA-Ni in the
structure of magnetic nanocomposite can be further confirmed.
Fig. 2. FT-IR spectra of (a) Fe3O4/Ala, (b) Fe3O4/Ala-AA and (c) Fe3O4/Ala-AA-Ni.
Fig. 3. XPS spectrum of Ni 2p of Fe3O4/Ala-AA-Ni nanocomposite.