Synthesis of ZnS:Mn- Fe3O4 bifunctional nanoparticles by inverse microemulsion method

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Original article

Synthesis of ZnS:Mn

eFe3

O

₄

bifunctional nanoparticles by inverse

microemulsion method

Chu Tien Dung

a,b

, Luu Manh Quynh

a

, Nguyen Phuong Linh

a

, Nguyen Hoang Nam

a,c,*

,

Nguyen Hoang Luong

c

a_{Faculty of Physics, Hanoi University of Science, Vietnam National University, Hanoi, 334 Nguyen Trai, Hanoi, Viet Nam}
b_{University of Transport and Communications, 2 Cau Giay, Hanoi, Viet Nam}

c_{Nano and Energy Center, Hanoi University of Science, Vietnam National University, Hanoi, 334 Nguyen Trai, Hanoi, Viet Nam}

a r t i c l e i n f o

Article history:
Received 31 May 2016
Accepted 10 June 2016
Available online 17 June 2016
Keywords:

ZnS:Mn
Fe3O4

Bifunctional nanoparticles
Magnetic materials
Inverse microemulsion

a b s t r a c t

ZnS:MneFe3O4 bifunctional nanoparticles were synthesized by inverse microemulsion method for
biomedicine applications. The bifunctional nanoparticles were combined from prepared ZnS:Mn and
Fe3O4nanoparticles in a SiO2cover matrix. Results show that bifunctional nanoparticles, apart from
exhibiting magnetism, have photoluminescence properties, which support the applications targeting
biomedicinefluorescent diagnostics as well as magnetic cell sorting or drug delivery.

© 2016 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi.
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1. Introduction

Multifunctional nanoparticles are of a great interest in recent
development due to the growing needs in biomedical applications.
They have potential to integrate various functionalities such as
providing contrast for labeling agent, image-guided therapies,
targeted drug delivery, thermal therapies or simultaneously serve
as magnetic separator[1e4]. At the beginning, core-shell
struc-tures were considered to improve appropriate physical as well as
chemical properties and combine them in one nanoparticle.
Advanced polymer coating such as polyethylene glycol was usually
used as functionalizing agent to make the nanoparticles have good
bio-compatibility[5e9]. Some semiconductor coatings have been
developed as photoluminescent shell to increase the luminescence

[10e12]as well as making a cover against the toxic element release
from core material, such as Se, Cd[11]. In some other applications,
metal and silica shells were coated for protecting the core
mate-rials[13,14]. However, the synthesis method of core-shell structure
referred tight conditions and expertise laboratory craftsmanship.
In this paper, a simple method of inversed microemulsion was

used to prepare new bifunctional nanoparticles ZnS:MneFe3O4

from individual Mn-doped ZnS (ZnS:Mn) semiconductor
nano-particles and Fe3O4magnetic nanoparticles in SiO2coating matrix.

ZnS:Mn semiconductor nanoparticles can be employed for
label-ing of clinical tumor tissues[15]. The magnetic nanoparticles with
superparamagnetic properties can be used as targeted delivery of
drug and/or gene, magnetic separation as well as magnetic
ther-apies [16e19]. The designed bifunctional nanoparticles can act
similar functions like core-shell structure nanoparticles, providing
simultanously photoluminescence as labeling agent in biomedical
application, biocompatible and can be also purified by magnetic
separator or can be used for drug delivery due to their magnetism,
event under the coating of SiO2matrix.

2. Experimental

2.1. Synthesis of ZnS:Mn nanoparticles

ZnS:Mn nanoparticles were synthesized by ultrasound-assisted
co-precipitation method using sodium sulphide (Na2S) as S
2ion

source. ZnCl20.5 M were mixed with surfactance sodium dodecyl

sulfate (SDS), CH3(CH2)11SO4Na) 0.25 M and Mn(CH3COO)20.5 M

to get precursor solution. The molar ratio of Mn/Zn was 1/10. This
solution was ultrasonicated with the pulse mode on:off being

2s:2s. The ultrasonic power and the frequency was 225 W and

* Corresponding author. Faculty of Physics, Hanoi University of Science, Vietnam
National University, Hanoi, 334 Nguyen Trai, Hanoi, Viet Nam.

E-mail address:(N.H. Nam).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect

Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j s a m d

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2468-2179/© 2016 The Authors. Publishing services by Elsevier B.V. on behalf of Vietnam National University, Hanoi. This is an open access article under the CC BY license
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20 kHz, respectively. During the ultrasonicating, Na2S solution was

slowly added into the precursor solution. After 2 h, the ZnS:Mn
nanoparticles were collected by washing 5 times with distilled
water before being dispersed in isopropanol.

2.2. Synthesis of Fe3O4nanoparticles

Fe3O4 nanoparticles were synthesized by co-precipitation

method[20,21]using Fe2ỵ/Fe3ỵwith 1:2 M ratios from the two
chloride salts of FeCl2and FeCl3, which were diluted to 0.01 M/

0.02 M concentration. The mixed solution was vigorously stirred
and kept at 60C before NH4OH 30% was being added to have the

black color precipitation. Thefinal solution was purified by
mag-netic separation with ethanol and distilled water several times to
decontaminate the auxiliary chemicals. Fe3O4nanoparticles, then,

were dispersed in isopropanol.

2.3. Synthesis of ZnS:MneFe3O4bifunctional nanoparticles

The bifunctional nanoparticles were combined from above two
kinds of nanoparticles by inverse microemulsion method. The
in-verse microemulsion was created by mixing hydrophobic phase of
toluene and hydrophilic phase that was made from the mixture of
ZnS:Mn solution and Fe3O4 solution in isopropanol right after

synthesis and the solution of NH4OH with distilled water. Under

sonic bath, tethraethylorthosilicate (TEOS) was added to react with

water in solution to form amorphous SiO2 matrix that covered

both types of particles.

The morphology of the ZnS:Mn, Fe3O4and the ZnS:MneFe3O4

nanoparticles was investigated by transmission electron
micro-scope (TEM, JEOL- JEM1010). The structure of nanoparticles was

studied using X-ray diffractormeter (XRD, Bruker D5005). The
average crystallite size, d, is calculated from the line broadening
using Scherrer's formula: d¼ 0.9

l

/(Bcos

q

), where B is the half

maximum line width and

l

is the wavelength of X-rays. The

chemical composition of the nanoparticles was studied by using an
energy dispersion spectroscopy (EDS) included in JEOL 5410LV
scanning electron microscope and the chemical bonding was
investigated by using Fourier Transformation Infra-Red (FTIR 6300,
Shimadzu) absorption. Magnetic properties of samples were
studied by using DMS 880 Vibrating Sample Magnetometer (VSM)

with a maximum magneticfield of 13.5 kOe at room temperature.

Optical properties of sample were investigated by using the
Flourolog FL 3-22 photoluminescence (PL) spectroscopy (Jobine
Yvone Spex, USA).

3. Results and discussion

Fig. 1shows the TEM images of the ZnS:Mn, Fe3O4, and the

ZnS:MneFe3O4nanoparticles. The TEM image of ZnS:Mn does not

show very clear shape of nanoparticles, that may be due to the
amorphous cover of synthesized nanoparticles. The TEM image of
the Fe3O4nanoparticles shows well-dispersed nanoparticles with

size of about 15 nm. The TEM image of the ZnS:MneFe3O4

nano-particles shows the colloids with the mean size of around 45 nm
and does not show small colloids of around 15 nm and 5 nm, which
are typical sizes of Fe3O4and ZnS:Mn nanoparticles, respectively.

The ZnS:MneFe3O4 nanoparticles contain ZnS:Mn and Fe3O4

nanoparticles inside. This microstructure of the ZnS:MneFe3O4

nanoparticles is supported by the results of measurements
dis-cussed below.

The XRD patterns of the Fe3O4, ZnS:Mn and ZnS:MneFe3O4

nanoparticles are shown in Fig. 2. The pattern of the

co-precipitation synthesized Fe3O4nanoparticles is characteristic of

the Fe3O4structure with diffraction peaks at 30.1, 36.0, 43.9,

53.6, 57.5va 63.1which can be assigned with (200), (311), (400),
(422), (511) va (440) reflections, respectively. Fe3O4nanoparticles

have an inverse spinel structure with oxygen forming
face-centered cubic (fcc) structure with F3dm space group. From

diffraction peaks we obtained the lattice parameter of

8.36 ± 0.04 Å. Using Scherrer's formula, the particle size was
estimated to be around 10 nm. The pattern of the synthesized

ZnS:Mn nanoparticles shows diffraction peaks at 29.1, 48.1, 57.5.

Fig. 1. TEM images of (a) ZnS:Mn, (b) Fe3O4and (c) ZnS:MneFe3O4nanoparticles.

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They can be ascribed as (111), (200), (220) reflections, respectively.
The obtained lattice parameter of 5.32± 0.02 Å for fcc structure
and the particle size was estimated to be around 4.7 nm, in
agreement with particles size observed by TEM image. The XRD

pattern of the combined ZnS:MneFe3O4 nanoparticles shows

typical amorphous structure of SiO2coated matrix with the sign of

the (311), (400), (422), (511) reflections of Fe3O4structure and the

weaker (200), (220) reflections of ZnS:Mn structure. The SiO2

cover could absorb X-ray, leading to the disappearance of some
XRD peaks of ZnS:Mn and Fe3O4nanoparticles.

The FTIR absorption spectra of the Fe3O4, ZnS:Mn and the

ZnS:MneFe3O4nanoparticles are shown inFig. 3. All the spectra

show the broad peaks at 3400 cm
1of OeH stretching vibration

[22] and the peaks at 1628, 2340, 2361 cm
1 which can be

assigned to CeO vibration of CO2[22,23]related to the air

back-ground of the measurement. These peaks are due to the presence
of CO2and H2O in all the samples. The spectrum of ZnS:MneFe3O4

shows typical absorption peaks of ZnS:Mn such as peaks at 1106,
617 and 465 cm
1of ZneS bonding or peak at 1174 cm
1 _which

appears when Mn2ỵis doped into ZnS crystal[24]. The two peaks

at 2851 and 2924 cm
1, which appear both in ZnS:Mn and

ZnS:MneFe3O4samples, are due to the microstructure formation

of ZnS:Mn nanoparticles[24]. The spectrum of ZnS:MneFe3O4also

shows typical absorption peaks of Fe3O4 nanoparticles such as

peak at 560 cm
1of FeeO vibration[25]. Furthermore, this
spec-trum has peaks of SiO2such as peaks at 797 cm
1and 960 cm
1
[26,27]. These results and the XRD results support that the
ZnS:MneFe3O4 nanoparticles were successfully combined from

ZnS:Mn and Fe3O4nanoparticles in SiO2matrix.

Fig. 4 shows the PL spectrum of ZnS:Mn and that of
ZnS:MneFe3O4nanoparticles excited at 335 nm. The spectrum of

ZnS:Mn nanoparticles have the peak at 438 nm which is originated
from defects caused by missing of some Zn ion in ZnS crystal
structure, and the peak at 595 nm which is originated from the

4_T

1/6A1 transition in 3d5electronic layer of Mn2ỵion[28e30].

The spectrum of ZnS:MneFe3O4nanoparticles also has two

pho-toluminescence peaks, one at 595 nm and the other at 425 nm,
similar to that of ZnS:Mn. However the intensity of the peak at
595 nm of ZnS:MneFe3O4 nanoparticles is lower than that of

ZnS:Mn nanoparticles. This can be explained by the presence of
Fe3O4and SiO2in ZnS:MneFe3O4nanoparticles, which reduces the

influence of Mn2ỵ _{ion on PL result. These results indicate that}

ZnS:MneFe3O4nanoparticles contain ZnS:Mn nanoparticles and

have similar PL properties with ZnS:Mn nanoparticles in visible
region, which can be used for labeling application in biomedicine.

Fig. 5shows magnetization curves measured on the ZnS:Mn,
Fe3O4and ZnS:MneFe3O4nanoparticles. It can be seen that the

magnetization of ZnS:Mn nanoparticles is very low, of 1 emu/g,
compared to those of Fe3O4 and ZnS:MneFe3O4 nanoparticles,

which reaches around 59.4 emu/g and 31.7 emu/g at 13.5 kOe,
respectively. The fact that the ZnS:MneFe3O4nanoparticles have

lower magnetization can be explained by the presence of

ZnS:Mn nanoparticles inside the sample as well as the presence

of the SiO2 cover matrix which does not exhibit magnetism.

The ZnS:MneFe3O4 nanoparticles show magnetic properties

similar to Fe3O4 nanoparticles, indicating that the synthesized

ZnS:MneFe3O4nanoparticles contain Fe3O4nanoparticles inside.

Fig. 2. X-ray patterns of ZnS:Mn, Fe3O4and ZnS:MneFe3O4nanoparticles.

Fig. 3. FTIR spectra of ZnS:Mn, Fe3O4and ZnS:MneFe3O4nanoparticles.

Fig. 4. Photoluminescence spectra of ZnS:MneFe3O4 and ZnS:Mn nanoparticles

excited at 335 nm.

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These results also support the successful combining of Fe3O4and

ZnS:Mn nanoparticles in SiO2matrix. The magnetic properties of

nanoparticles investigated also show that ZnS:MneFe3O4

nano-particles can be used for magnetic delivery, therapies or DNA
separating applications in biomedicine.

4. Conclusions

ZnS:MneFe3O4 bifunctional nanoparticles were successfully

synthesized from ZnS:Mn and Fe3O4nanoparticles in

biocompat-ible SiO2 matrix using inverse microemulsion method. The

bifunctional nanoparticles have photoluminescence similar to
ZnS:Mn photoluminescence nanoparticles and magnetic propeties
similar to Fe3O4 magnetic nanoparticles, which support their

use in both labeling and separating applications in biomedicine.
Furthermore, with the biocompartible SiO2 cover matrix, these

nanoparticles can be easily surface-modified in many
biomedicine-application purposes.

Acknowledgment

This paper is dedicated to the memory of Peter Brommer. He
was a good friend of the Vietnamese physicists during the years of
cooperation between the Hanoi and Amsterdam Universities. With
his deep knowledge of 'Magnetism of Metals' he was always ready
to assist his colleagues. We are grateful for his involvement in the
cooperation over a period as long as thirty years.

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Fig. 5. The magnetization curves of ZnS:Mn, Fe3O4and ZnS:MneFe3O4nanoparticles

at room temperature.

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