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Ag core–shell nanoparticles: Synthesis, characterization and properties
Accepted Manuscript Bi-phase dispersible Fe3O4/Ag core–shell Synthesis, characterization and properties
nanoparticles:
Chunyan Li, Zheng Guan, Chenguang Ma, Ning Fang, Hongling Liu, Mingxue Li PII: DOI: Reference:
S1387-7003(17)30508-7 doi: 10.1016/j.inoche.2017.08.019 INOCHE 6742
To appear in:
Inorganic Chemistry Communications
Received date: Revised date: Accepted date:
12 June 2017 7 August 2017 16 August 2017
Please cite this article as: Chunyan Li, Zheng Guan, Chenguang Ma, Ning Fang, Hongling Liu, Mingxue Li , Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles: Synthesis, characterization and properties, Inorganic Chemistry Communications (2017), doi: 10.1016/j.inoche.2017.08.019
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ACCEPTED MANUSCRIPT Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles: synthesis, characterization and properties Chunyan Lia, Zheng Guanb, Chenguang Maa, Ning Fanga, Hongling Liua,* and Mingxue Lia,*
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Henan Key Laboratory of Polyoxometalates, Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical
Engineering, Henan University, Kaifeng 475004, PR China
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Henan Chemical Technician College, Kaifeng 475004, Henan China
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*Corresponding author. Fax: +86-371-23881589. E-mail address: [email protected] (H.L. Liu)
ACCEPTED MANUSCRIPT ABSTRACT
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Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles were successfully synthesized via non-aqueous nanoemulsion process using the triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as the surfactant. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses confirm the structure and morphology of the polymer-capped Fe3O4/Ag nanoparticles. The measurements obtained using ultraviolet-visible light absorbance spectrometry (UV-vis), vibrating sample magnetometry (VSM) demonstrate that the nanoparticles exhibit a surface plasmon resonance (SPR) absorption band around 430 nm from nanostructured Ag and a unique magnetic nature at room temperature. This kind of bifunctional optical-magnetic core–shell nanoparticles could be of interest in interfacial proximity effects due to the unique spatial nanostructure configuration and have potential applications in various areas. Keywords: Core–shell; Nanoparticles; Nanoemulsion; Polymer; Bi-phase dispersible
ACCEPTED MANUSCRIPT Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles: synthesis, characterization and properties Chunyan Lia, Zheng Guanb, Chenguang Maa, Ning Fanga, Hongling Liua,* and Mingxue Lia,* a
Henan Key Laboratory of Polyoxometalates, Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, PR China b Henan Chemical Technician College, Kaifeng 475004, Henan China ____________________________________________________________________________________________________________ ABSTRACT: Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles were successfully synthesized via nanoemulsion
process
using
the
triblock
copolymer
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non-aqueous
poly(ethylene
glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as the surfactant. X-ray
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diffraction (XRD) and transmission electron microscopy (TEM) analyses confirm the structure and morphology of the polymer-capped Fe3O4/Ag nanoparticles. The measurements obtained using ultraviolet-visible light absorbance spectrometry (UV-vis), vibrating sample magnetometry (VSM)
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Aritcle history: Received xx xx 2017 Received in revised form xx xx 2017 Accepted xx xx 2017 Available online xx xx 2017 Keywords: Core–shell Nanoparticles Nanoemulsion Polymer Bi-phase dispersible
demonstrate that the nanoparticles exhibit a surface plasmon resonance (SPR) absorption band around 430 nm from nanostructured Ag and a unique magnetic nature at room temperature. This kind of bifunctional optical-magnetic core–shell nanoparticles could be of interest in interfacial
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ARTICLEINFO
proximity effects due to the unique spatial nanostructure configuration and have potential applications in various areas.
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synthesis of Fe3O4/Ag core–shell nanoparticles with narrow size distribution and bi-phase dispersibility remains a one of the
and good biocompatibility [1–7]. However, the applications of
most challenging issue.
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The preparation of Fe3O4 magnetic nanoparticles has been
extensively studied because of their unique magnetic properties
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Fe3O4 have been limited due to its inherent properties. For
In this work, we report a simple and efficient method for the synthesis of polymer-capped Fe3O4/Ag nanoparticles using
aggregate, easily oxidized or dissolved in an acid medium and
triblock
have fewer activating groups [8]. In order to overcome these
PEO-PPO-PEO
problems, numerous studies are available with respect to the
non-charging trait, biocompatibility, non-toxicity, and aqueous
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example, pure magnetic nanoparticles are likely to form a large
copolymer
PEO-PPO-PEO
demonstrates
as
distinct
the
surfactant.
advantages
of
solubility and has been employed in a variety of field [19-23].
well-known composite system that have shown enhanced
In nanoemulsion process, the PEO-PPO-PEO molecules not
optical, magnetic, and catalytic properties compared to their
only participate as a surfactant, but also play a role in stabilizing
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addition of noble metals [9-14]. Core-shell nanostructures are a
individual single-component materials [15]. An outer noble
the nanoparticles formed, as attested in our reports on long-term
metallic shell on the surface of iron oxide nanoparticle, not only
stable,
provides the stability to the nanoparticle in solution but also
Fe3O4/ZnO, Fe3O4/Au, and FeAu nanoparticles [24-27]. The
help binding various biological ligands at the nanoparticle
PEO-PPO-PEO-capped Fe3O4/Ag core-shell nanoparticles as
surface for various biomedical applications [16]. Silver is a kind
prepared herein show high crystallinity, monodispersity,
of well studied material, possessing localized surface plasmon
excellent magnetic and optical performance. In particular, the
resonance, surface-enhanced Raman scattering, and is applied in
resulting nanoparticles could be directly dispersed in both
chemical and biological sensing [17]. The combination of
aqueous
magnetic nanoparticles with silver can retain the optical and
modification.
highly
and
crystalline,
organic
monosized
media
without
Fe3O4/Ca3(PO4)2,
further
surface
magnetic properties of the respective components and provide
The Fe3O4/Ag nanoparticles were prepared by the
synergistically enhanced performance and functionalities which
controlled sequential synthesis of the Ag capping onto the
could go beyond those of the individual components. In
surface of the Fe3O4 seeds. The reactions were completed in a
addition, the binary system can be removed from the medium
250 mL flask in a heating mantle, equipped with a cooling
by means of an external magnetic field [18]. However, the
condenser and a thermocouple. In a typical experiment, the
ACCEPTED MANUSCRIPT Fe3O4 seeds were first produced by the reduction of Fe(acac)3
Fe3O4(0.375)/Ag(0.125) nanoparticles (thin shell) and Fe3O4
by 1,2-hexadecanediol (2.5 mmol) at high-temperature in the
nanoparticles are shown in Fig. 1. As shown in Fig. 1,
presence of the polymer surfactant molecules of PEO-PPO-PEO
Fe3O4(0.125)/Ag(0.375) (thick
(0.1358 mmol) dissolved in dioctyl ether (10 mL). The reaction
nanoparticles (thin shell) exhibit diffraction peaks at 38.2 ○ ,
mixture was first heated to 125 ℃ in 1 h and maintained for 1 h
44.4○ , 64.59○ , 77.59○ and 81.75 ○ , which can be indexed to
at 125 ℃, then rapidly raised to 280 ℃ in 15 min and refluxed at
(111), (200), (220), (311) and (222) planes of silver, respectively.
the temperature for 1 h. After cooling down to room
In the thicker Ag-shell sample (Fig. 1 (a)), only silver peaks,
temperature, Ag(acac) with 2 mL dioctyl ether was added to the
possibly overlapped with iron peaks for they are very near to
solution for coating Ag nanolayers. At this stage, the reaction
each other in some positions, are visible. In contrast, the thinner
mixture started with heating to 80 ℃ in 1 h, maintained for 2 h
Ag-shell sample (Fig. 1 (b)) demonstrates two weak peaks (311)
at 80 ℃, then rapidly heated to 215 ℃ and refluxing for 2 h at
and (440) of Fe3O4 nanoparticles (Fig. 1 (c)), in addition to the
215 ℃. After the completion of the reaction, a pale brown
normal silver. It implies that X-ray can penetrate to the core of
product was separated from the supernatant by centrifugation,
Fe3O4 if the silver shell is not sufficiently thick, otherwise the
which was washed with ethanol–hexane in a volume ratio of 1 :
signal from the core is shielded to become visible in the XRD
2 several times, and re-dispersed in ethanol for further use.
pattern. The absence of any diffraction peaks for magnetite is
Three compositions in the ratios of Fe(acac)3 to Ag(acac) 1:3,
most likely due to the heavy atom effect from silver as a result
1:1 and 3:1 were prepared and named Fe3O4(0.125)/Ag(0.375),
of the formation of Ag-coated Fe3O4 nanocrystals.
Fe(acac)3 are 0.125 mmol, 0.25 mmol and 0.375 mmol, respectively, corresponding to the amounts of Ag(acac) are
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Fe3O4(0.375)/Ag(0.125)
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0.375 mmol, 0.25 mmol and 0.125 mmol, respectively. For
and
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Fe3O4(0.25)/Ag(0.25) and Fe3O4(0.375)/Ag(0.125). The amounts of
shell)
comparison, Fe3O4 and Ag nanoparticles were synthesized
similarly using only Fe(acac)3 and Ag(acac) respectively as the precursor.
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In the paper, the microstructure and grain size of the
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Fe3O4/Ag core-shell nanoparticles were acquired by X-ray diffraction (XRD, Philips X'Pert Pro, Philips, Amsterdam, Netherlands;
λ=1.54056Å)
using
Cu
Kα radiation
Fig. 1. XRD patterns for the respective Fe3O4/Ag and Fe3O4
transmission electron microscopy (TEM, JEM-2010) including
nanoparticles. (a) Fe3O4(0.125)/Ag(0.375) nanoparticles (thick shell), (b)
the mode of high resolution (HRTEM). The UV-vis spectra
Fe3O4(0.375)/Ag(0.125) nanoparticles (thin shell), (c) Fe3O4 nanoparticles.
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and
were measured by a UV-vis spectrometer (UV-vis near IR
Bar diagram for the JCPDS of Fe3O4 (in square) and Ag (in circle).
spectrophotometer, Hitachi U4100), revealing the band edge
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and surface plasmon resonance features of the nanostructured
The morphology and particle size of the prepared
Fe3O4 and Ag materials in the composite nanoparticles. In the
Fe3O4(0.125)/Ag(0.375) nanoparticles were recorded by TEM. As
Fourier transform infrared spectroscopy (FTIR) studies, the
shown in Fig. 2 (a), the nanoparticles apparently are highly
washed PEO-PPO-PEO capped Fe3O4/Ag nanoparticles and the
crystalline, virtually uniform and nearly spherical or polyhedral
pure PEO-PPO-PEO polymer were separately crushed with a
in shape. The size distribution of the nanoparticles acquired
pestle in anagate mortar. The individually crushed material was
from Fig. 2 (a) is presented in Fig. 2 (b), in which the histogram
mixed with KBr in about 1 : 100 proportion. The mixture was
has a tight size distribution and gives an average particle size of
then compressed into a 2 mm semi-transparent disk by applying
~15.9 nm in diameter. The size distribution is described quite
a force of 10 T for 2 min. The FTIR spectra were recorded in
satisfactorily by the Gaussian function. Fig. 2 (c) represents the
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the wavenumber range of 4000–400 cm using an Avatar 360
high-resolution TEM image of a single Fe3O4(0.125)/Ag(0.375)
FTIR spectrometer (Nicolet Company, USA). The magnetic
core–shell nanoparticle with highly regular lattices running over
properties were subsequently studied by VSM (Lakeshore
the nanocrystal. As labeled, the spacing of 2.75 Å is assigned to
7300).
the projection of the (311) Fe3O4 plane, whereas the spacing of
XRD patterns for Fe3O4(0.125)/Ag(0.375) (thick shell),
1.44 Å is originated from the (220) Ag plane. Nevertheless, the
ACCEPTED MANUSCRIPT lattices showing the core material of Fe3O4 and the coating
chains to the metal atoms in the hybrid nanostructure [18]. As
substance of Ag in high resolution imaging are in essence
the extra PEO-PPO-PEO molecules were removed by the
consistent with the XRD observation as analyzed above.
purification process, the outcome overtly draws to the conclusion of covering of the PEO-PPO-PEO molecules onto the surface of the Fe3O4/Ag nanoparticles, which can be further corroborated by the other relevant absorption bands in the
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spectra.
nanoparticles. (a) Bright-field image, (b) particle size histogram with
nanoparticle.
Fig. 3. FTIR spectra of (a) the PEO-PPO-PEO- capped Fe3O4(0.125)/Ag(0.375) nanoparticles and (b) the pure PEO-PPO-PEO
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Gaussian fit, (c) HRTEM of an individual Fe3O4(0.125)/Ag(0.375)
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Fig. 2. TEM analyses of the PEO-PPO-PEO-capped Fe3O4(0.125)/Ag(0.375)
+
polymer.
The magnetic properties of the Fe3O4/Ag nanoparticles were studied against the Fe3O4 nanoparticles at room temperature, as presented in Fig. 4. Ag and the PEO-PPO-PEO
was undertaken by comparatively assessing the FTIR spectra of
macromolecules are nonmagnetic in nature, thus the magnetism
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The determination of existence of the PEO-PPO-PEO macromolecules on the surface of the Fe3O4/Ag nanoparticles
of the nanocomposite system comes dominantly from the core
Fe3O4(0.125)/Ag(0.375) nanoparticles after purification [18-23]. In
ingredient in the Fe3O4/Ag core–shell nanoparticles which is in
Fig. 3 (b), the pure PEO-PPO-PEO polymer molecules display
turn protected by Ag and PEO-PPO-PEO from oxidation. Fig. 4
one strong characteristic band at the position of approximately
shows the hysteresis curves of the Fe3O4 and Fe3O4/Ag
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the pure PEO-PPO-PEO polymer and the polymer-capped
−1
1,110.92 cm due to the C-O-C stretching vibration of the ether bonding which usually ranges between 1,250 cm −1
−1
and 1,000
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cm , and one sharp characteristic band at the position of −1
core–shell nanoparticles at 300 K. It is clear from the curves that
Fe3O4/Ag
core–shell
nanoparticles
behave
superparamagnetically at room temperature with a lower
approximately 1,466.71 cm due to the C-H bending vibration.
magnetization of 14.1 emu/g, while the Fe3O4 nanoparticles
As given in Fig. 3 (a), these characteristic vibration and bending
show soft ferromagnetic or near superparamagnetic properties
features
the
with magnetization of 75.8 emu/g and coercivity of 10.6 Oe.
PEO-PPO-PEO-capped Fe3O4(0.125)/Ag(0.375) nanoparticles, but
Compared to the Fe3O4 nanoparticles, the Fe3O4/Ag core–shell
reappear
in
the
FTIR
spectrum
of
blue-shifting to the positions of approximately 1,124.54 cm
−1
for the C-O-C stretching vibration and approximately 1,633.12 −1
cm
for the C-H bending vibration [18,27] respectively.
Evidently, the vibration and bending shapes and absorption intensities vary between the pure PEO-PPO-PEO molecules and the PEO-PPO-PEO-capped Fe3O4(0.125)/Ag(0.375) nanoparticles. Both blue-shifting and shape change in the C-O-C stretching and C-H bending modes may be attributed to the interactive coordination of the oxygen atoms in the PEO-PPO-PEO main
nanoparticles are easier to saturate, which could be partly owing to proximity effects and unique spatial configurations [28].
ACCEPTED MANUSCRIPT absorption band in the visible region arising from the surface plasmon resonance (SPR). As shown in Fig. 6 (a), Ag nanoparticles exhibit the SPR absorption band at 430 nm. Fe3O4(0.125)/Ag(0.375) (Fig. 6 (b)), Fe3O4(0.25)/Ag(0.25) (Fig. 6 (c)) and Fe3O4(0.375)/Ag(0.125) (Fig. 6 (d)) nanoparticles show the absorption band from the SPR of the nanostructured Ag at about 450 nm, 490 nm and 530 nm respectively. As anticipated, the spectrum of the Fe3O4 nanocrystals(Fig. 6 (e)) grants no signature absorption. There is distinct red-shifting and
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broadening of the SPR of the Fe3O4/Ag core–shell nanoparticles relative to that of the Ag nanoparticles. Meanwhile, the SPR absorption peaks move to longer wavelength with decreasing in
nanoparticles at room temperature.
the thickness of Ag nanolayer. It is well established that the SPR
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Fig. 4. Hysteresis curves of the Fe3O4 (a) and Fe3O4/Ag (b)
band of metal nanoparticles strongly depends on the size, shape, composition, and dielectric property of the nanoparticles and the
properties as visually revealed in Fig. 5 for the separation and
local environment [29-31]. The as-synthesized Fe3O4/Ag
redispersion process of the nanoparticles in water and hexane.
nanoparticles with SPR absorption band in the visible light
Under the influence of an external magnetic field, the
region could be treated as a promising photocatalyst candidate.
homogeneous dispersion (Fig. 5 (c)) to a clear, transparent
(Fig.
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solution, with the nanoparticles collected by a piece of magnet
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nanoparticles in water rapidly change from a grey black,
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The Fe3O4/Ag core-shell nanoparticles possess amphiphilic
5 (d)). The collected nanoparticles can be easily and
reversibly dispersed by shaking-up after removal of the magnetic field and the above process can be repeated as many
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times as desired. A similar process happens to the nanoparticles
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in hexane, as shown in Fig. 5 (a) and (b). The amphiphility of the nanoparticles is accredited to the presence of the amphiphilic PEO-PPO-PEO macromolecules on the particle
Fig. 6. UV-visible absorbance spectra of Ag (a), Fe3O4(0.125)/Ag(0.375) (b),
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surface.
Fe3O4(0.25)/Ag(0.25) (c), and Fe3O4(0.375)/Ag(0.125) (d), respectively, in
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addition to Fe3O4 nanoparticles (e) dispersed in hexane.
In summary, we have succeeded in the facile synthesis of the PEO-PPO-PEO-capped bi-phase dispersible Fe3O4/Ag
Fig. 5. Photo images of solvent dispersion-collection processes of the
core–shell nanoparticles by the modifid nanoemulsion method
PEO-PPO-PEO-capped Fe3O4/Ag nanoparticles. (a) Dispersion in
using the triblock copolymer PEO-PPO-PEO as the surfactant.
hexane and corresponding magnetic collection (b), and (c) dispersion in
The morphology and structural analyses reveal the narrow
water and corresponding magnetic collection (d).
particle size distribution with an average diameter ~15.9 nm and high crystallinity of the nanoparticles. The FTIR assessment
The optical properties of the PEO-PPO-PEO-capped Fe3O4/Ag
core–shell
nanoparticles
were
appraised
substantiates the lacing of the PEO-PPO-PEO macromolecules
by
onto the surface of the nanoparticles. The optical measurements
UV-visible absorption spectroscopy. Fig. 6 shows the UV-vis
present a well-defined absorption band of the nanoparticles
spectra of (a) Ag, (b) Fe3O4(0.125)/Ag(0.375), (c) Fe3O4(0.25)/Ag(0.25),
which manifests the surface plasmon resonance (SPR) of the
(d) Fe3O4(0.375)/Ag(0.125), and (e) Fe3O4 nanoparticles dispersed in
nanostructured Ag. The magnetic characterization shows the
hexane. It is well recognized that Ag nanoparticles reveal an
excellent magnetic performance of the Fe3O4/Ag nanoparticle
ACCEPTED MANUSCRIPT system. Moreover, the Fe3O4/Ag nanoparticles could be directly
cyclodextrin modified Fe3O4 nanospheres, Chem. Res. 3 (2016)
dispersed in both hydrophilic and hydrophobic solvent, in which
364-368.
the dispersion-collection processes of the nanoparticles were demonstrated
for
application
readiness.
Hence,
[7]
the
J. Sun, S.B. Zhou, P. Hou, Y. Yang, J. Weng, X.H. Li, M.Y. Li, Synthesis
PEO-PPO-PEO-capped Fe3O4/Ag core–shell nanoparticles are
and
characterization
of
biocompatible
Fe3O4
nanoparticles, J. biomed. Mater. Res. Part A. 80 (2007) 333-341.
promising for applications such as photocatalyst, optical
[8]
detection, magnetic separation and biological detection.
J. Wang, D.Q. Song, H. Zhang, J. Zhang, Y. Jin, H.Q. Zhang, H. Zhou, Y. Sun, Studies of Fe3O4/Ag/Au composites for immunoassay based on surface plasmon resonance biosensor,
Acknowledgements
Colloids. Surf. B. 102 (2013) 165-170.
This work was supported in part by the National Natural
[9]
M. Ma, J. Xie, Y. Zhang, Z.P. Chen, N. Gu, Fe3O4@Pt nanoparticles with enhanced peroxidase-like catalytic activity,
and the Key Scientific Research Projects of Henan Province
Mater. Lett. 105 (2013) 36-39.
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Science Foundation of China (nos. 51172064 and 21671055)
Colleges and Universities, Foundation of Education Department
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[10] D.P. Tang, R. Yuan, Y.Q. Chai, Magnetic core−shell Fe3O4@Ag
of Henan Province, China (no. 16A150002).
nanoparticles coated carbon paste interface for studies of
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carcinoembryonic antigen in clinical immunoassay, J. Phys. Chem. B. 110 (2006) 11640-11646.
[11] J.H. Shen, Y.H. Zhu, X.L. Yang, J. Zong, C.Z. Li,
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Multifunctional Fe3O4@Ag/SiO2/Au core–shell microspheres as a novel sers-activity label via long-range plasmon coupling,
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Non-aqueous synthesis of water-dispersible Fe3O4–Ca3(PO4)2 core–shell nanoparticles, Nanotechnol. 22 (2010) 055701. [28] H.L. Liu, J.H. Wu, J.H. Min, J.H. Lee, Y.K. Kim, Monosized core–shell Fe3O4(Fe)/Au multifunctional nanocrystals, J. nanosci. Nanotechnol. 9 (2009) 754-758. [29] P. Pawinrat, O. Mekasuwandumrong, J. Panpranot, Synthesis of Au–ZnO and Pt–ZnO nanocomposites by one-step flame spray pyrolysis and its application for photocatalytic degradation of dyes, Cata. Commun. 10 (2009) 1380-1385. [30] D.Z. Qin, G.R. Yang, G.X. He, L. Zhang, Q.X. Zhang, L.Y. Li, The investigation on synthesis and optical properties of ag-doped ZnS nanocrystals by hydrothermal method, Chalcogenide Lett. 9 (2012) 441-446.
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mice, Biomaterials. 30 (2009) 6748-6756.
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Graphical abstract
Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles were successfully synthesized via non-aqueous nanoemulsion process. The
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nanoparticles had been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible light absorbance spectrometry (UV-vis). The nanoparticles show
high crystallinity, excellent magnetic and optical performance. Moreover, the Fe3O4/Ag nanoparticles
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could be directly dispersed in both hydrophilic and hydrophobic solvent.
ACCEPTED MANUSCRIPT Highlights The Fe3O4/Ag nanoparticles were synthesized via non-aqueous nanoemulsion process.
The nanoparticles could be dispersed in both aqueous and organic media.
The nanoparticles show high crystallinity, good magnetic and optical performance.
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nanoparticles:
Chunyan Li, Zheng Guan, Chenguang Ma, Ning Fang, Hongling Liu, Mingxue Li PII: DOI: Reference:
S1387-7003(17)30508-7 doi: 10.1016/j.inoche.2017.08.019 INOCHE 6742
To appear in:
Inorganic Chemistry Communications
Received date: Revised date: Accepted date:
12 June 2017 7 August 2017 16 August 2017
Please cite this article as: Chunyan Li, Zheng Guan, Chenguang Ma, Ning Fang, Hongling Liu, Mingxue Li , Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles: Synthesis, characterization and properties, Inorganic Chemistry Communications (2017), doi: 10.1016/j.inoche.2017.08.019
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles: synthesis, characterization and properties Chunyan Lia, Zheng Guanb, Chenguang Maa, Ning Fanga, Hongling Liua,* and Mingxue Lia,*
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Henan Key Laboratory of Polyoxometalates, Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical
Engineering, Henan University, Kaifeng 475004, PR China
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Henan Chemical Technician College, Kaifeng 475004, Henan China
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*Corresponding author. Fax: +86-371-23881589. E-mail address: [email protected] (H.L. Liu)
ACCEPTED MANUSCRIPT ABSTRACT
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Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles were successfully synthesized via non-aqueous nanoemulsion process using the triblock copolymer poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as the surfactant. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses confirm the structure and morphology of the polymer-capped Fe3O4/Ag nanoparticles. The measurements obtained using ultraviolet-visible light absorbance spectrometry (UV-vis), vibrating sample magnetometry (VSM) demonstrate that the nanoparticles exhibit a surface plasmon resonance (SPR) absorption band around 430 nm from nanostructured Ag and a unique magnetic nature at room temperature. This kind of bifunctional optical-magnetic core–shell nanoparticles could be of interest in interfacial proximity effects due to the unique spatial nanostructure configuration and have potential applications in various areas. Keywords: Core–shell; Nanoparticles; Nanoemulsion; Polymer; Bi-phase dispersible
ACCEPTED MANUSCRIPT Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles: synthesis, characterization and properties Chunyan Lia, Zheng Guanb, Chenguang Maa, Ning Fanga, Hongling Liua,* and Mingxue Lia,* a
Henan Key Laboratory of Polyoxometalates, Institute of Molecular and Crystal Engineering, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, PR China b Henan Chemical Technician College, Kaifeng 475004, Henan China ____________________________________________________________________________________________________________ ABSTRACT: Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles were successfully synthesized via nanoemulsion
process
using
the
triblock
copolymer
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non-aqueous
poly(ethylene
glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) as the surfactant. X-ray
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diffraction (XRD) and transmission electron microscopy (TEM) analyses confirm the structure and morphology of the polymer-capped Fe3O4/Ag nanoparticles. The measurements obtained using ultraviolet-visible light absorbance spectrometry (UV-vis), vibrating sample magnetometry (VSM)
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Aritcle history: Received xx xx 2017 Received in revised form xx xx 2017 Accepted xx xx 2017 Available online xx xx 2017 Keywords: Core–shell Nanoparticles Nanoemulsion Polymer Bi-phase dispersible
demonstrate that the nanoparticles exhibit a surface plasmon resonance (SPR) absorption band around 430 nm from nanostructured Ag and a unique magnetic nature at room temperature. This kind of bifunctional optical-magnetic core–shell nanoparticles could be of interest in interfacial
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ARTICLEINFO
proximity effects due to the unique spatial nanostructure configuration and have potential applications in various areas.
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synthesis of Fe3O4/Ag core–shell nanoparticles with narrow size distribution and bi-phase dispersibility remains a one of the
and good biocompatibility [1–7]. However, the applications of
most challenging issue.
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The preparation of Fe3O4 magnetic nanoparticles has been
extensively studied because of their unique magnetic properties
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Fe3O4 have been limited due to its inherent properties. For
In this work, we report a simple and efficient method for the synthesis of polymer-capped Fe3O4/Ag nanoparticles using
aggregate, easily oxidized or dissolved in an acid medium and
triblock
have fewer activating groups [8]. In order to overcome these
PEO-PPO-PEO
problems, numerous studies are available with respect to the
non-charging trait, biocompatibility, non-toxicity, and aqueous
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example, pure magnetic nanoparticles are likely to form a large
copolymer
PEO-PPO-PEO
demonstrates
as
distinct
the
surfactant.
advantages
of
solubility and has been employed in a variety of field [19-23].
well-known composite system that have shown enhanced
In nanoemulsion process, the PEO-PPO-PEO molecules not
optical, magnetic, and catalytic properties compared to their
only participate as a surfactant, but also play a role in stabilizing
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addition of noble metals [9-14]. Core-shell nanostructures are a
individual single-component materials [15]. An outer noble
the nanoparticles formed, as attested in our reports on long-term
metallic shell on the surface of iron oxide nanoparticle, not only
stable,
provides the stability to the nanoparticle in solution but also
Fe3O4/ZnO, Fe3O4/Au, and FeAu nanoparticles [24-27]. The
help binding various biological ligands at the nanoparticle
PEO-PPO-PEO-capped Fe3O4/Ag core-shell nanoparticles as
surface for various biomedical applications [16]. Silver is a kind
prepared herein show high crystallinity, monodispersity,
of well studied material, possessing localized surface plasmon
excellent magnetic and optical performance. In particular, the
resonance, surface-enhanced Raman scattering, and is applied in
resulting nanoparticles could be directly dispersed in both
chemical and biological sensing [17]. The combination of
aqueous
magnetic nanoparticles with silver can retain the optical and
modification.
highly
and
crystalline,
organic
monosized
media
without
Fe3O4/Ca3(PO4)2,
further
surface
magnetic properties of the respective components and provide
The Fe3O4/Ag nanoparticles were prepared by the
synergistically enhanced performance and functionalities which
controlled sequential synthesis of the Ag capping onto the
could go beyond those of the individual components. In
surface of the Fe3O4 seeds. The reactions were completed in a
addition, the binary system can be removed from the medium
250 mL flask in a heating mantle, equipped with a cooling
by means of an external magnetic field [18]. However, the
condenser and a thermocouple. In a typical experiment, the
ACCEPTED MANUSCRIPT Fe3O4 seeds were first produced by the reduction of Fe(acac)3
Fe3O4(0.375)/Ag(0.125) nanoparticles (thin shell) and Fe3O4
by 1,2-hexadecanediol (2.5 mmol) at high-temperature in the
nanoparticles are shown in Fig. 1. As shown in Fig. 1,
presence of the polymer surfactant molecules of PEO-PPO-PEO
Fe3O4(0.125)/Ag(0.375) (thick
(0.1358 mmol) dissolved in dioctyl ether (10 mL). The reaction
nanoparticles (thin shell) exhibit diffraction peaks at 38.2 ○ ,
mixture was first heated to 125 ℃ in 1 h and maintained for 1 h
44.4○ , 64.59○ , 77.59○ and 81.75 ○ , which can be indexed to
at 125 ℃, then rapidly raised to 280 ℃ in 15 min and refluxed at
(111), (200), (220), (311) and (222) planes of silver, respectively.
the temperature for 1 h. After cooling down to room
In the thicker Ag-shell sample (Fig. 1 (a)), only silver peaks,
temperature, Ag(acac) with 2 mL dioctyl ether was added to the
possibly overlapped with iron peaks for they are very near to
solution for coating Ag nanolayers. At this stage, the reaction
each other in some positions, are visible. In contrast, the thinner
mixture started with heating to 80 ℃ in 1 h, maintained for 2 h
Ag-shell sample (Fig. 1 (b)) demonstrates two weak peaks (311)
at 80 ℃, then rapidly heated to 215 ℃ and refluxing for 2 h at
and (440) of Fe3O4 nanoparticles (Fig. 1 (c)), in addition to the
215 ℃. After the completion of the reaction, a pale brown
normal silver. It implies that X-ray can penetrate to the core of
product was separated from the supernatant by centrifugation,
Fe3O4 if the silver shell is not sufficiently thick, otherwise the
which was washed with ethanol–hexane in a volume ratio of 1 :
signal from the core is shielded to become visible in the XRD
2 several times, and re-dispersed in ethanol for further use.
pattern. The absence of any diffraction peaks for magnetite is
Three compositions in the ratios of Fe(acac)3 to Ag(acac) 1:3,
most likely due to the heavy atom effect from silver as a result
1:1 and 3:1 were prepared and named Fe3O4(0.125)/Ag(0.375),
of the formation of Ag-coated Fe3O4 nanocrystals.
Fe(acac)3 are 0.125 mmol, 0.25 mmol and 0.375 mmol, respectively, corresponding to the amounts of Ag(acac) are
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Fe3O4(0.375)/Ag(0.125)
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0.375 mmol, 0.25 mmol and 0.125 mmol, respectively. For
and
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Fe3O4(0.25)/Ag(0.25) and Fe3O4(0.375)/Ag(0.125). The amounts of
shell)
comparison, Fe3O4 and Ag nanoparticles were synthesized
similarly using only Fe(acac)3 and Ag(acac) respectively as the precursor.
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In the paper, the microstructure and grain size of the
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Fe3O4/Ag core-shell nanoparticles were acquired by X-ray diffraction (XRD, Philips X'Pert Pro, Philips, Amsterdam, Netherlands;
λ=1.54056Å)
using
Cu
Kα radiation
Fig. 1. XRD patterns for the respective Fe3O4/Ag and Fe3O4
transmission electron microscopy (TEM, JEM-2010) including
nanoparticles. (a) Fe3O4(0.125)/Ag(0.375) nanoparticles (thick shell), (b)
the mode of high resolution (HRTEM). The UV-vis spectra
Fe3O4(0.375)/Ag(0.125) nanoparticles (thin shell), (c) Fe3O4 nanoparticles.
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and
were measured by a UV-vis spectrometer (UV-vis near IR
Bar diagram for the JCPDS of Fe3O4 (in square) and Ag (in circle).
spectrophotometer, Hitachi U4100), revealing the band edge
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and surface plasmon resonance features of the nanostructured
The morphology and particle size of the prepared
Fe3O4 and Ag materials in the composite nanoparticles. In the
Fe3O4(0.125)/Ag(0.375) nanoparticles were recorded by TEM. As
Fourier transform infrared spectroscopy (FTIR) studies, the
shown in Fig. 2 (a), the nanoparticles apparently are highly
washed PEO-PPO-PEO capped Fe3O4/Ag nanoparticles and the
crystalline, virtually uniform and nearly spherical or polyhedral
pure PEO-PPO-PEO polymer were separately crushed with a
in shape. The size distribution of the nanoparticles acquired
pestle in anagate mortar. The individually crushed material was
from Fig. 2 (a) is presented in Fig. 2 (b), in which the histogram
mixed with KBr in about 1 : 100 proportion. The mixture was
has a tight size distribution and gives an average particle size of
then compressed into a 2 mm semi-transparent disk by applying
~15.9 nm in diameter. The size distribution is described quite
a force of 10 T for 2 min. The FTIR spectra were recorded in
satisfactorily by the Gaussian function. Fig. 2 (c) represents the
-1
the wavenumber range of 4000–400 cm using an Avatar 360
high-resolution TEM image of a single Fe3O4(0.125)/Ag(0.375)
FTIR spectrometer (Nicolet Company, USA). The magnetic
core–shell nanoparticle with highly regular lattices running over
properties were subsequently studied by VSM (Lakeshore
the nanocrystal. As labeled, the spacing of 2.75 Å is assigned to
7300).
the projection of the (311) Fe3O4 plane, whereas the spacing of
XRD patterns for Fe3O4(0.125)/Ag(0.375) (thick shell),
1.44 Å is originated from the (220) Ag plane. Nevertheless, the
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chains to the metal atoms in the hybrid nanostructure [18]. As
substance of Ag in high resolution imaging are in essence
the extra PEO-PPO-PEO molecules were removed by the
consistent with the XRD observation as analyzed above.
purification process, the outcome overtly draws to the conclusion of covering of the PEO-PPO-PEO molecules onto the surface of the Fe3O4/Ag nanoparticles, which can be further corroborated by the other relevant absorption bands in the
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spectra.
nanoparticles. (a) Bright-field image, (b) particle size histogram with
nanoparticle.
Fig. 3. FTIR spectra of (a) the PEO-PPO-PEO- capped Fe3O4(0.125)/Ag(0.375) nanoparticles and (b) the pure PEO-PPO-PEO
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Gaussian fit, (c) HRTEM of an individual Fe3O4(0.125)/Ag(0.375)
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Fig. 2. TEM analyses of the PEO-PPO-PEO-capped Fe3O4(0.125)/Ag(0.375)
+
polymer.
The magnetic properties of the Fe3O4/Ag nanoparticles were studied against the Fe3O4 nanoparticles at room temperature, as presented in Fig. 4. Ag and the PEO-PPO-PEO
was undertaken by comparatively assessing the FTIR spectra of
macromolecules are nonmagnetic in nature, thus the magnetism
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The determination of existence of the PEO-PPO-PEO macromolecules on the surface of the Fe3O4/Ag nanoparticles
of the nanocomposite system comes dominantly from the core
Fe3O4(0.125)/Ag(0.375) nanoparticles after purification [18-23]. In
ingredient in the Fe3O4/Ag core–shell nanoparticles which is in
Fig. 3 (b), the pure PEO-PPO-PEO polymer molecules display
turn protected by Ag and PEO-PPO-PEO from oxidation. Fig. 4
one strong characteristic band at the position of approximately
shows the hysteresis curves of the Fe3O4 and Fe3O4/Ag
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the pure PEO-PPO-PEO polymer and the polymer-capped
−1
1,110.92 cm due to the C-O-C stretching vibration of the ether bonding which usually ranges between 1,250 cm −1
−1
and 1,000
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cm , and one sharp characteristic band at the position of −1
core–shell nanoparticles at 300 K. It is clear from the curves that
Fe3O4/Ag
core–shell
nanoparticles
behave
superparamagnetically at room temperature with a lower
approximately 1,466.71 cm due to the C-H bending vibration.
magnetization of 14.1 emu/g, while the Fe3O4 nanoparticles
As given in Fig. 3 (a), these characteristic vibration and bending
show soft ferromagnetic or near superparamagnetic properties
features
the
with magnetization of 75.8 emu/g and coercivity of 10.6 Oe.
PEO-PPO-PEO-capped Fe3O4(0.125)/Ag(0.375) nanoparticles, but
Compared to the Fe3O4 nanoparticles, the Fe3O4/Ag core–shell
reappear
in
the
FTIR
spectrum
of
blue-shifting to the positions of approximately 1,124.54 cm
−1
for the C-O-C stretching vibration and approximately 1,633.12 −1
cm
for the C-H bending vibration [18,27] respectively.
Evidently, the vibration and bending shapes and absorption intensities vary between the pure PEO-PPO-PEO molecules and the PEO-PPO-PEO-capped Fe3O4(0.125)/Ag(0.375) nanoparticles. Both blue-shifting and shape change in the C-O-C stretching and C-H bending modes may be attributed to the interactive coordination of the oxygen atoms in the PEO-PPO-PEO main
nanoparticles are easier to saturate, which could be partly owing to proximity effects and unique spatial configurations [28].
ACCEPTED MANUSCRIPT absorption band in the visible region arising from the surface plasmon resonance (SPR). As shown in Fig. 6 (a), Ag nanoparticles exhibit the SPR absorption band at 430 nm. Fe3O4(0.125)/Ag(0.375) (Fig. 6 (b)), Fe3O4(0.25)/Ag(0.25) (Fig. 6 (c)) and Fe3O4(0.375)/Ag(0.125) (Fig. 6 (d)) nanoparticles show the absorption band from the SPR of the nanostructured Ag at about 450 nm, 490 nm and 530 nm respectively. As anticipated, the spectrum of the Fe3O4 nanocrystals(Fig. 6 (e)) grants no signature absorption. There is distinct red-shifting and
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broadening of the SPR of the Fe3O4/Ag core–shell nanoparticles relative to that of the Ag nanoparticles. Meanwhile, the SPR absorption peaks move to longer wavelength with decreasing in
nanoparticles at room temperature.
the thickness of Ag nanolayer. It is well established that the SPR
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Fig. 4. Hysteresis curves of the Fe3O4 (a) and Fe3O4/Ag (b)
band of metal nanoparticles strongly depends on the size, shape, composition, and dielectric property of the nanoparticles and the
properties as visually revealed in Fig. 5 for the separation and
local environment [29-31]. The as-synthesized Fe3O4/Ag
redispersion process of the nanoparticles in water and hexane.
nanoparticles with SPR absorption band in the visible light
Under the influence of an external magnetic field, the
region could be treated as a promising photocatalyst candidate.
homogeneous dispersion (Fig. 5 (c)) to a clear, transparent
(Fig.
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solution, with the nanoparticles collected by a piece of magnet
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nanoparticles in water rapidly change from a grey black,
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The Fe3O4/Ag core-shell nanoparticles possess amphiphilic
5 (d)). The collected nanoparticles can be easily and
reversibly dispersed by shaking-up after removal of the magnetic field and the above process can be repeated as many
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times as desired. A similar process happens to the nanoparticles
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in hexane, as shown in Fig. 5 (a) and (b). The amphiphility of the nanoparticles is accredited to the presence of the amphiphilic PEO-PPO-PEO macromolecules on the particle
Fig. 6. UV-visible absorbance spectra of Ag (a), Fe3O4(0.125)/Ag(0.375) (b),
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surface.
Fe3O4(0.25)/Ag(0.25) (c), and Fe3O4(0.375)/Ag(0.125) (d), respectively, in
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addition to Fe3O4 nanoparticles (e) dispersed in hexane.
In summary, we have succeeded in the facile synthesis of the PEO-PPO-PEO-capped bi-phase dispersible Fe3O4/Ag
Fig. 5. Photo images of solvent dispersion-collection processes of the
core–shell nanoparticles by the modifid nanoemulsion method
PEO-PPO-PEO-capped Fe3O4/Ag nanoparticles. (a) Dispersion in
using the triblock copolymer PEO-PPO-PEO as the surfactant.
hexane and corresponding magnetic collection (b), and (c) dispersion in
The morphology and structural analyses reveal the narrow
water and corresponding magnetic collection (d).
particle size distribution with an average diameter ~15.9 nm and high crystallinity of the nanoparticles. The FTIR assessment
The optical properties of the PEO-PPO-PEO-capped Fe3O4/Ag
core–shell
nanoparticles
were
appraised
substantiates the lacing of the PEO-PPO-PEO macromolecules
by
onto the surface of the nanoparticles. The optical measurements
UV-visible absorption spectroscopy. Fig. 6 shows the UV-vis
present a well-defined absorption band of the nanoparticles
spectra of (a) Ag, (b) Fe3O4(0.125)/Ag(0.375), (c) Fe3O4(0.25)/Ag(0.25),
which manifests the surface plasmon resonance (SPR) of the
(d) Fe3O4(0.375)/Ag(0.125), and (e) Fe3O4 nanoparticles dispersed in
nanostructured Ag. The magnetic characterization shows the
hexane. It is well recognized that Ag nanoparticles reveal an
excellent magnetic performance of the Fe3O4/Ag nanoparticle
ACCEPTED MANUSCRIPT system. Moreover, the Fe3O4/Ag nanoparticles could be directly
cyclodextrin modified Fe3O4 nanospheres, Chem. Res. 3 (2016)
dispersed in both hydrophilic and hydrophobic solvent, in which
364-368.
the dispersion-collection processes of the nanoparticles were demonstrated
for
application
readiness.
Hence,
[7]
the
J. Sun, S.B. Zhou, P. Hou, Y. Yang, J. Weng, X.H. Li, M.Y. Li, Synthesis
PEO-PPO-PEO-capped Fe3O4/Ag core–shell nanoparticles are
and
characterization
of
biocompatible
Fe3O4
nanoparticles, J. biomed. Mater. Res. Part A. 80 (2007) 333-341.
promising for applications such as photocatalyst, optical
[8]
detection, magnetic separation and biological detection.
J. Wang, D.Q. Song, H. Zhang, J. Zhang, Y. Jin, H.Q. Zhang, H. Zhou, Y. Sun, Studies of Fe3O4/Ag/Au composites for immunoassay based on surface plasmon resonance biosensor,
Acknowledgements
Colloids. Surf. B. 102 (2013) 165-170.
This work was supported in part by the National Natural
[9]
M. Ma, J. Xie, Y. Zhang, Z.P. Chen, N. Gu, Fe3O4@Pt nanoparticles with enhanced peroxidase-like catalytic activity,
and the Key Scientific Research Projects of Henan Province
Mater. Lett. 105 (2013) 36-39.
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Science Foundation of China (nos. 51172064 and 21671055)
Colleges and Universities, Foundation of Education Department
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[10] D.P. Tang, R. Yuan, Y.Q. Chai, Magnetic core−shell Fe3O4@Ag
of Henan Province, China (no. 16A150002).
nanoparticles coated carbon paste interface for studies of
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carcinoembryonic antigen in clinical immunoassay, J. Phys. Chem. B. 110 (2006) 11640-11646.
[11] J.H. Shen, Y.H. Zhu, X.L. Yang, J. Zong, C.Z. Li,
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Multifunctional Fe3O4@Ag/SiO2/Au core–shell microspheres as a novel sers-activity label via long-range plasmon coupling,
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Langmuir. 29 (2012) 690-695.
[1]
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Graphical abstract
Bi-phase dispersible Fe3O4/Ag core–shell nanoparticles were successfully synthesized via non-aqueous nanoemulsion process. The
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nanoparticles had been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible light absorbance spectrometry (UV-vis). The nanoparticles show
high crystallinity, excellent magnetic and optical performance. Moreover, the Fe3O4/Ag nanoparticles
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could be directly dispersed in both hydrophilic and hydrophobic solvent.
ACCEPTED MANUSCRIPT Highlights The Fe3O4/Ag nanoparticles were synthesized via non-aqueous nanoemulsion process.
The nanoparticles could be dispersed in both aqueous and organic media.
The nanoparticles show high crystallinity, good magnetic and optical performance.
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