Core shell hybrid nanomaterials based on CoFe 2O4particles coated with PVP or PEG [619847]

Core –shell hybrid nanomaterials based on CoFe 2O4particles coated with PVP or PEG
biopolymers for applications in biomedicine
Cristina Ileana Covaliua,⁎, Ioana Jitarub, Gigel Paraschiva, Eugeniu Vasilec, Sorin- Ștefan Biri șa,
Lucian Diamandescud, Valentin Ionitae, Horia Iovub
aUniversity “Politehnica ”of Bucharest, Faculty of Biotechnical Systems Engineering, 313 Splaiul Independentei Street, 060042 Bucharest, Romania
bUniversity “Politehnica ”of Bucharest, Faculty of Applied Chemistry and Materials Science,1-7 Polizu Street, Bucharest 011061, Romania
cMetav, Research and Development, 31 C.A. Rosetti Street, 020011 Bucharest, Romania
dNational Institute of Materials Physics, 105 Bis Atomistilor Street, Bucharest, Romania
eUniversity “Politehnica ”of Bucharest, Faculty of Electrical Engineering, 313 Splaiul Independentei Street, Bucharest 060042, Romania
abstract article info
Article history:
Received 7 June 2012Received in revised form 10 December 2012Accepted 15 December 2012Available online 22 December 2012
Keywords:Cobalt ferrite nanoparticlesHybrid nanomaterialsPolyvinylpyrrolidone (PVP)Polyethylene glycol (PEG)Monodisperse core –shell hybrid nanoparticles based on cobalt ferrite (CoFe 2O4) particles coated with
polyvinylpyrrolidone (PVP) or polyethylene glyco l (PEG) biopolymers were obtained employing a two-
step procedure: the CoFe 2O4of 21 nm mean particle size were first synthesized by coprecipitation method
assisted by PVP soft template and then were coated by PVP or PEG biopolymers. The effect of the thermal
treatment upon the phase evolution of the obtained precursor from the coprecipitation step was monitoredby X-ray diffraction (XRD) and Fourier transform infr ared spectroscopy (FTIR) analyses. The FTIR spectra
also indicated the interaction between the cobalt fe rrite particles and the two polymers were used as bio-
compatible coatings. Transmission electron micros copy (TEM) and Selected Area Electron Diffraction
(SAED) analyses revealed the formation of approximately 22 nm CoFe
2O4-PVP and CoFe 2O4-PEG hybrid
nanoparticles. The magnetic measurements indicated that all synthesized hybrids were appropriate for applying
in biomedical field. Testing the bioeffect of the uncoated cobalt ferrite nanoparticles and corresponding hybrids
onBacillus subtilis ,Pseudomonas aeruginosa ,Escherichia coli ,Salmonella enterica serovar typhimurium bacteria
and Candida scotti yeast it was clear that no signi ficant toxic activity was obtained. Moreover, all the prepared
nanohybrids and their components possess antioxidant activity.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Finding new therapies in the field of medicine is always one of the
most important challenges. The development of new tools such as
magnetic hybrid nanomaterials consisting of cobalt ferrite
nanoparticles coated by biopolymers may have a crucial role in
their implementation in cancer therapy since bene ficial results
would lead to the improvement of public health, increase of lifetime
and decrease of mortality.
The cancer therapy applications of CoFe2O4 nanoparticles coated by
biopolymers are sustained by the numerous properties of both compo-
nents particularly by their special magnetic properties. For this reason
there have been efforts made in the synthesis and characterization ofCoFe2O4 to achieve their required features such as: narrow size distri-
bution, high magnetization values and uniform shape. These cobalt fer-
rite nanoparticles are considered to have application in some fields ofbiomedicine like magnetic resonance imagining (MRI), hyperthermia
and delivery drug consumption which implies the use of an external
magnetic field to action them from the distance [1].
Until now various synthetic routes have been studied for the
preparation of CoFe
2O4nanoparticles, such as hydrothermal [2],
coprecipitation [3], microemulsion [4], forced hydrolysis [5],a n d
reduction –oxidation routes [6]but the principal dif ficulty of these
methods is that the as-prepared nanoparticles are extremely ag-
glomerated, and have poor control of size and shape in most cases,
thus restricting their applications [7]. A way to overcome these dif fi-
culties, for the preparation of size- and shape-controlled mono-
dispersed CoFe 2O4nanoparticles is the coating of the magnetic
nanoparticles with biopolymers [8,9] . Consequently we adopted a
coprecipitation assisted with surfactant (e.g. as polymer) method
to successfully synthesized the cobalt ferrite nanoparticles.
Coating the magnetic cobalt ferrite nanoparticles with polymers
brings the following advantages: prevents their agglomeration by
forming a steric barrier between them, provides biocompatibility, offers
the possibility to link on the target zone and avoids the recognition and
elimination from the human organism by reticuloendothelial system of
the immune system [10–12]. Thus we chose two biopolymers for cobaltPowder Technology 237 (2013) 415 –426
⁎Corresponding author.
E-mail address: cristina_covaliu@yahoo.com (C.I. Covaliu).
0032-5910/$ –see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.powtec.2012.12.037
Contents lists available at SciVerse ScienceDirect
Powder Technology
journal homepage: www.elsevier.com/locate/powtec

ferrite nanoparticle biocompatibilization: polyethylene glycol (PEG)
and polyvinylpyrrolidone (PVP) ( Fig. 1 ).
Choosing PEG polymer for cobalt ferrite nanoparticle coating is based
on its following attributes: biocompatibility, low cost, nontoxicity,
non-in flammability, easy to handle and its multiple medical uses such
as: excipient in pharmaceutical, lubricant eye drops [13], basis in many
skin creams, dispersant in toothpastes and vectors in gene therapy[14], and food additive used as anti-foaming agent [15] compound in
monoclonal antibody production [16].
The second polymer PVP was selected for cobalt ferrite biocom-
patibilization taking into account the following reasons: is used as a
binder for various pharmaceutical tablets [17], disinfectant in combina-
tion with iodine used in vari ous products like Betadine [18] solutions,
ointment, pessaries, liquid soaps and surgical scrubs. It is also used in
t h ew i n ei n d u s t r ya sac l e a r i n ga g e n tf o rw h i t ew i n eo rs o m eb e e r s .
The objective of this work is the facile and low cost approach to
obtain core –shell nanostructured hybrids having suitable properties
(such as: biocompatibility, special magnetic properties, no or low tox-
icity and antioxidant activity) for applying in biomedical field. Conse-
quently, we proposed a synthesis strategy which involves two steps.
In the first step we synthesized cobalt ferrite nanoparticles by
nonconventional coprecipitation method assisted by PVP soft tem-
plate. In a second stage we used the effective PEG and PVP polymers
to coat the cobalt ferrite nanoparticles. The effects of various experi-
mental conditions on the morphology of the prepared nanohybrids
were investigated. Additionally, we report a comparison study of
the in fluence of the PVP and PEG polymers used for the coating of
the cobalt ferrite nanoparticles upon the morphology (size and ag-
glomeration tendency) hybrids finally obtained.
To justify the potential of applying them in biomedicine the two
nanohybrids and the components that form them were characterized
by magnetic measurement investigation, antioxidant activity tests and
biologic activity analyses. It is known that the lack or low levels of anti-
oxidants and the presence of reactive oxygen species (H
2O2,•OH e.g) in
human body cause oxidative stress which appears to contribute to the
occurrence of various human diseases such as cancer, Alzheimer's dis-
ease [19,20] , Parkinson's disease [21], coronary heart disease, diabetes
[22,23] , and rheumatoid arthritis [24]. Therefore, the oxidative stress
can be regarded as the cause and the consequence of some diseases.
As a conclusion the antioxidants have been investigated for the preven-tion of the diseases caused by reactive oxygen species and used in die-
tary supplements. To the best of our knowledge, till now there is noreport on the investigation of the antioxidant activity of the cobalt fer-
rite nanoparticles and their corresponding nanohybrids.
Also, from all magnetic oxide nanoparticle based hybrids with po-
tential of applying in biomedical field, much attention was paid only
to those based magnetite nanoparticles. Therefore, within present
paper, the research is directed to the synthesis, characterization and
investigation of properties useful for applying in biomedical field of
other nanosized ferrite (cobalt ferrite) and its hybrids formed by
coating it with PEG and PVP polymers.
2. Experimental section
The chemical reagents used in this study are ferric nitrate
(Fe(NO
3)3·9H 2O), cobalt nitrate (Co(NO 3)2·6H 2O), ammonia solution
28%, polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG). All re-
agents are from Sigma Aldrich and used without further puri fication.
Manipulations and reactions were carried out in air without nitrogen
or inert gas protection.
For antioxidant activity tests were used the following reagents:
1,10-phenantroline (Phen, 99%), 2,4,6-tris(2-pyridyl)-striazine (TPTZ,
99%) and neocuproine (Neo, 99%) were obtained from Sigma Aldrich,
while acetic acid, hydrochloric acid, sodium acetate, iron (III) chloride
hexahydrate (FeCl 3·6H 2O), iron (II) sulfate h eptahydrate (FeSO 4·7H 2O),
methanol (99,8%), acetone (99,5% ), and copper (II) chloride (CoCl 2·6H 2O)
were obtained from Merck. Double distillated water was used for sample
solution preparation.
The mixed solution containing 100 mL of 0.3 M Co(NO 3)2·6H 2O
and 0.6 M Fe(NO 3)3·9H 2O (with Co:Fe ratio of 1:2) was arranged in
distilled water. To this solution was added dropwise a volume of
1 M NaOH under strongly stirring till the pH value was 12. The reac-
tion was kept at room temperature for 2 h. During the procedure, the
color of solution changed from the initially brown to dark brown and
precipitation occurred. The precipitate was filtered and carefully
washed many times with distilled water and then was dried at
80 °C in air. The resulted powder was calcined at 200 and 400 °C
respectively.
The single phase cobalt ferrite power obtained by calcination at
400 °C was used for the preparation of the two hybrids by dispersing
30% of cobalt ferrite in a solution of 20% PEG or 20% PVP. Thenanohybrid powders (CoFe
2O4-PVP, CoFe 2O4-PEG) were separated
by centrifugation and dried at room temperature.
Fig. 1. The schematic representation of the core –shell hybrid materials containing the CoFe 2O4core and PEG or PVP shells proposed for investigation.416 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

The structure, composition and morphologies of the precursor
CoFe 2O4, CoFe 2O4obtained at different calcination temperatures and
corresponding nanohybrid materials with PEG and PVP were exam-
ined by Fourier transform infrared spectroscopy (FTIR) using a
model of Bruker Tensor 27 spectrometer using 32 scans at 4 cm−1
resolution in the 400 –4000 cm−1range, X-ray diffraction (XRD)
using an X'PERT PRO MPD with Cu-K αradiation ( λ=0.15418 nm),
and the transmission electron microscopy images (TEM) were
obtained on FEI Tecnai ™G2F30 S-TWIN with energy dispersive
X-ray spectrometer. The magnetic curves ( first magnetization curve
and hysteresis loop) at 24 °C (297 K), for the cobalt ferrite and the
corresponding hybrid material based samples were measured by a vi-
brating sample magnetometer (VSM 7304 LakeShore USA).
Mössbauer measurements were carried out at room temperature
on WissEL (Germany) spectrometer. A 20 mCi57Co source in Rh ma-
trix was used. The spectra were fitted in the approximation of
Lorentzian line shape.
For the determination of the antioxidant activity of the studied
products, three different methods were used. Absorbance measure-
ments were performed on a UV –Vis spectrophotometer Jasco V 530
apparatus using quartz cell of 1-cm path length. pH measurements
were made with special paper pH. The shaker SHKA 2508-ICE (Labo
Plus) and centrifuge MPW-350 (LABO-MIX) were used for sample
preparation.
2.1. FRAP I method
0.6 mL of sample acetone solution (5 mg of tested sample with
10 mL acetone), 1 mL of 0.2% FeCl 3acetone solution and 0.5 mL of ac-
etone solution of 0.5% Phen were placed into a 10 mL volumetric
flask. The obtained solution was mixed and left at room temperature
in a dark chamber. After 20 min, the absorbance of the final solution
was measured at 510 nm against a blank reagent (1 mL of FeCl 3
0.2% and 0.5 mL Phen 0.5% made up to 10 mL with acetone).
For FRAP I method the antioxidant activity was calculated using
the formula: Antioxidantactivity ¼c/C210
0:6/C2mp∞, where: c is the concentra-
tion determined after reading on the calibration curve (microgram
Fe), 10 is the sample solution volume after extraction (mL), m pis
the analyzed sample mass (g) and 0.6 is the analyzed sample solution
volume (mL).
2.2. FRAP II method
The FRAP reagent containing 2.5 mL of a 10 mmol/L TPTZ solution
in 40 mmol/L HCl of 20 mmol/L FeCl 3and 25 mL of 0.1 mol/L acetate
buffer (pH 3.6) was prepared freshly and incubated at 37 °C for
10 min. Then, 0.3 mL of acetone samples and 2 mL of FRAP reagent
were transferred into a 10 mL volumetric flask with double distillated
water. The obtained solutions were kept at room temperature for10 min and centrifuged at 15,000 rpm for 10 min in a lab centrifuge
to remove solids. The absorbance was measured at 593 nm against
a blank reagent (2 mL of FRAP reagent made up to 10 mL double
distillated water).
The antioxidant activity obtained by FRAP II method is expressed
as Antioxidantactivity ¼
c/C210
0:3/C2mp, where: c is the concentration deter-
mined after reading on the calibration curve (microgram Fe), 10 is
the sample solution volume after extraction (mL), m pis the analyzed
sample mass (g), 0.3 is the analyzed sample solution volume (mL).
2.3. CUPRAC method
1 mL of CuCl 2solution (1.0×10−2M), 1 mL of Neo alcoholic solu-
tion (7.5×10−3M) and 1 mL acetate buffer solution were added into
a test tube. To this solution 0.5 mL of sample solution (5 mg of tested
sample with 0.5 ethanol and 0.5 mL water) and water till the total vol-
ume was 4.1 mL was added and mixed for 30 min. Absorbance against ablank reagent was measured at 450 nm. Since the molar absorptivity of
trolox (Tr) in the CUPRAC method is ε=1.67×104Lmol−1cm−1and
the calibration curve for trolox is a line passing through the origin, the
trolox equivalent molar concentration of tested sample in the final solu-
tion may be found by dividing the observed absorbance to the εof
trolox. The trolox equivalent antioxidant activity may be traced back
to the original prepared sample solution considering all dilutions andthe initial mass of tested sample to find a capacity in the units of
mmol TR/g dry matter.
The antioxidant activity values obtained by CUPRAC method are
expressed as Antioxidantactivity ¼
c/C24:1/C250/C230/C210−6
X/C2mp, where: c is the con-
centration determined after reading on the calibration curve (micro-
gram TROLOX), 4.1 is the final volume of the sample to be analyzed
(mL), 50 is the sample solution volume after extraction (mL), 30 is the
reaction time (min); m pis the analyzed sample mass (g), and X is the
analyzed sample solution volume (mL).
The qualitative disk diffusion method was used to evaluate the bio-
logical activity of the uncoated cobalt ferrite nanoparticles and their
corresponding prepared hybrids on three bacterial cultures Escherichia
coliATCC 25922 (as gram negative bacteria), Pseudomonas aeruginosa
ATCC 27853 (as gram negative bacteria), Bacillus subtilis ATCC 6663
(as gram positive bacteria) and one fungal Candida scotti because
these microorganisms are used by diagnostic laboratory testing for
conducting the sterility tests of drugs and are also used in public health
tests.
Applying the disk diffusion method we used Mueller –Hinton agar
and Sabouraud agar media obtained by dissolving 20 g of agar in 1 L
of each corresponded broth media and allowed to solidify into Petri
plates (100 mm diameter).
Mueller –Hinton broth was prepared by the dissolution of 3 g of
beef extract, 17.5 g of casein acid hydrolysate and 1.5 g of starch in
1000 mL of distilled water and then was autoclaved at 116 –121 °C
for 10 –15 min. 2% sabouraud glucose broth was obtained by the dis-
solution of 10 g of mycological peptone and 20 g of glucose in
1000 mL of distilled water.
The dried surfaces of the agar Petri plates were inoculated with
fresh microorganism cultures (with the standard density correspond-
ing to 0.5 McFarland) by streaking the swab over the entire agar sur-
face. The Petri plates prepared thus were used to test 2048 μg
amounts of each hybrids and cobalt ferrite samples (added) placedin wells at equal distances (3 cm from the center of the Petri plate
and 1.5 cm from the edge of the plate). The Petri plates were placed
in an incubator at 37 °C for 18 –24 h in the case of bacteria and
24–48 h for yeast. After incubation the diameter of the inhibition
zones was measured and compared with that of the standard antibi-
otics with the following concentrations (Tobramycin 3 mg/disk,
Erythromycin 1.5 mg/disk, Cipro floxacin 5 mg/disk). Each prepared
sample was measured in three replicates.
3. Results and discussion
3.1. XRD analysis
The XRD data of the precursor directly obtained by co-precipitation
method without calcination ( Fig. 2 a) include peaks of CoFe
2O4(JCPDS
card number is 04-002-6521) and γ-Fe2O3 (JCPDS card number is
00-039-1346). After precursor calcination at 200 °C the resulted
sample presents besides well de fine crystalline peaks belonging to
CoFe 2O4phase, also peak characteristic to γ-Fe2O3(Fig. 2 b). By precur-
sor calcination at 400 °C, the sample obtained was mono-phase and it
exhibits the crystalline structure of cobalt ferrite (CoFe 2O4), with cubic
symmetry ( Fig. 2 c). The average crystallite size of CoFe 2O4obtained
by calcination at 400 °C calculated by Scherrer formula is 18 nm.
The XRD patterns of both nanohybrids based on cobalt ferrite
nanoparticles coated with PEG or PVP (CoFe 2O4-PEG and CoFe 2O4-PVP)417 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

show that the crystalline structure of CoFe 2O4is preserved after the
polymer coating procedure ( Fig. 3 a and b).
3.2. FTIR spectroscopy
The uncoated cobalt ferrite sample and their corresponded nano-
hybrids were further studied by FTIR spectroscopy for the investigation
of the formation of single phase cobalt ferrite by calcinations of the pre-
cursor resulted from coprecipitation method at different temperatures
and also for the assessment of the interaction between the CoFe 2O4parti-
cles and the two polymers used for coating them (PVP and PEG).Fig. 4 (c) shows the bonds of precursor obtained directly from
coprecipitation method which were assigned to PVP polymer used as
soft template during the synthesis. The most important bonds are
placed at 3345 cm−1for O\H group, 1638 cm−1for C_O, 1430 cm−
1for H\C\H (scissoring bending vibration), 1230 cm−1for C\H,
842 cm−1for C\C and 670 cm−1for N\C_O[30].T h eb o n d so ft h e
nitrate anion overlap with vibration bonds of C \Ha t1 2 3 0a n d
1430 cm−1.
The absence of the bands assigned to O \H, C\Oa n dC\H groups at
1000 –1300 cm−1and 2000 –3000 cm−1in the spectrum sample
obtained by precursor calcination at 400 °C con firmed the nonexistence
of the PVP soft template used during the synthesis [24] (Fig. 4 a). The20040060004008001200
10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90200400600
(440)CoFe2O4 2000C / 2h Fe2O3
*
(731)(642)(444)(533)(620)(442)(531)(511)(422)(331)(400)(222)(311)(220)*
***(111)
*Intensity (a.u.)
(442)
(731)(444)
(642)(622)(533)(620)(531)(440)(422)
(511)(400)(222)(311)(220)(111)CoFe2O4 4000C / 2h
(c)
(b)
Fe2O3*(442)
(731)(533)(442)(440)(422) * *(331)(400)(222)(311)*
(511)(220)*(111)
2θ(CuKa) )(a)
Fig. 2. XRD patterns of the precursor obtained directly by coprecipitation method (a); CoFe 2O4sample calcined at 200 °C (b) and CoFe 2O4sample calcined 400 °C (c).
20040060080010002004006008001000
(a)Intensity (a.u.)
(731)(642)(444)(622)(533)(620)(531)(440)(511)(422)(400)(222)(311)(220)(111)(b)
(731)(642)(444)(622)(533)(620)(531)(440)(511)(422)(400)(222)(311)(220)(111)
2θ(CuKa) )10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90
Fig. 3. XRD patterns of the two prepared hybrid nanomaterials: CoFe 2O4-PEG (a) and CoFe 2O4-PVP (b).418 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

presence of bands typically associated with CoFe 2O4sample appearing
at 550 and 420 cm−1[25] represents another clue of the formation of
the CoFe 2O4structure [26,27] .
In the case of PVP spectrum, the asymmetric stretching and scis-
soring bending vibrations of CH 2groups are placed at 1957 and
1465 cm−1, respectively ( Fig. 4 e). Moreover another bond attributed
to amines is observed in the region 910 –665 cm−1. This strong, broad
bond is due to N \H groups and is observed only for primary and
secondary amines and the bond assigned to N \C_O is placed at
568 cm−1.
In the case of CoFe 2O4-PVP hybrid the bond of C _O groups appears
at 1665 cm−1and the bonds at 568 cm−1and 440 cm−1are attributed
to the stretching vibration of M \O( M_Fe, Co) ( Fig. 4 d). As suggested
by previously published data a shift of the C _O groups in hybrid spectra
in comparison with that of PVP spectrum can be attributed to the
change of p- пconjugation associated with the amide group arising
from the dissociation of PVP chains due to the interaction with the
metal ions from the cobalt ferrite compound ( Fig. 4 d)[28].
Fig. 4 (b) represents the FTIR spectra of PEG and CoFe 2O4-PEG hy-
brid material. The broad bonds observed at 2860 cm−1and
1420 –1450 cm−1, respectively were assigned to the adsorbed water
characterized by to the vibration of O \H and H \O\H groups
[29,30] . These bonds were observed in CoFe 2O4-PEG as well as in
PEG spectra, but having different intensities. The PEG polymer
bonds at around 3450 cm−1and 1000 –1030 cm−1are attributed to
\OH and C \O group vibration modes. The bond of stretching vibra-
tion corresponding to esteric C \O group is placed at 1045 cm−1in
CoFe 2O4-PEG hybrid spectrum and could be a first clue of the interac-
tion between cobalt ferrite particles and PEG polymer ( Fig. 4 a). The
bonds between 2880 and 1600 cm−1correspond to the plane
deformation of C \H group vibrations. The bond at 1470 cm−1from
CoFe 2O4-PEG spectrum is attributed to the stretching vibration of
C\C group of PEG [31,32] . The bond from CoFe 2O4-PEG hybrid mate-
rial spectrum at 565 cm−1corresponds to the stretching vibration of
the bonds between the oxygen ions and the metallic ions occupying
the tetrahedral sites in cobalt ferrite crystalline structure (M tetra–O)
and the one seen at 435 cm−1is characteristic to the stretching vibra-
tion of bonds between oxygen ions and the metallic ions from the
octahedral sites of the cobalt ferrite crystalline structure (M octra–O)[33]. The second clue of interaction between cobalt ferrite parti-
cles and PEG polymer results from the shift to higher frequencies
of (M tetra–O) and (M octra–O) bonds in CoFe 2O4-PEG spectrum I
comparison with those presented in CoFe 2O4spectrum (550 and
420 cm−1).
The potential interaction between the metallic ions of the cobalt
ferrite particles and the PEG or PVP polymers is depicted in Fig. 5 .
3.3. Mössbauer spectroscopy
Room temperature Mössbauer spectra of the studied samples are
shown in Fig. 6 . The spectrum of the sample calcined at 400 °C ex-
hibits a magnetic pattern accompanied by a central quadrupole dou-
blet ( Fig. 6 a). The magnetic pattern can be deconvoluted in two
magnetic sublattices with hyper fine magnetic fields of 48.2 T and
49.9 T corresponding to iron ions in tetrahedral and octahedral posi-
tions respectively. Because no other iron structure was identi fied in
the X-ray diffractogram of the sample, the central quadrupole doublet
can be associated with iron ions in small cobalt ferrite particles being
a paramagnetic contribution to the Mössbauer spectrum. In Fig. 6 (b
and c) the Mössbauer spectra of the cobalt ferrite coated with PEG
or PVP consist of two magnetic patterns corresponding to tetrahedral
and respectively octahedral position of iron in the cobalt spinel struc-
ture. For both samples, the hyper fine magnetic fields at tetrahedral
positions are close to ~50 T and ~51 T for octahedral position, being
significantly greater than in the case of pure cobalt ferrite. This
behavior is in good agreement with magnetic measurements reveal-
ing an increase of the saturation magnetization, and hysteresis pa-
rameters, as a result of the massive agglomeration of the magnetic
nanoparticles [34,35] .
3.4. Morphological characterization
The TEM images of uncoated cobalt ferrite sample shown in
Fig. 7 a–c indicate the hexagonal shape of the particles which may
be explained by the adsorption of PVP surfactants on certain crystal
facets of the colloids which are con fined during the synthesis. This
issue was also observed by other researcher [36,37] .
Fig. 4. FTIR spectra of: CoFe 2O4(a) (obtained by calcinations at 400 °C); sample (obtained by precursor calcination at 200 °C) (b); precursor obtained by coprecipitation method
(c); CoFe 2O4-PVP (d); PVP (e); CoFe 2O4-PEG (f); and PEG (g) in the range of 450 –4000 cm−1.419 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

SAED analysis investigation of uncoated cobalt ferrite sustains the
cubic crystalline structure previous identi fied by XRD analysis with
the following Miller indices: (111), (220), (331), (222), (400),
(331), (422), (511), (440) and (533) ( Fig. 7 f).In the first step of our experimental study, the synthesis of
CoFe 2O4particles, PVP was used as a surfactant not only to prevent
primary crystals from random aggregation but also to control the for-
mation of the regular geometry of the particles. As a consequence tak-
ing account of other research in the field, we proposed a mechanism
of the formation and morphology evolution of the CoFe 2O4synthe-
sized in the presence of PVP surfactant ( Fig. 8 ).
Taking other research studies into account the mechanism could
be explained as follows: firstly, the CoFe 2O4phase is subjected to nu-
cleation and growth around the entire surface stabilized by PVP, and
secondly, because of the minimization of the total energy of the sys-
tem, the small primary CoFe 2O4nanoparticles aggregated together
and instead forming spheres, they form hexagons under the in fluence
of adsorbed PVP surfactant on a certain crystal facets PVP, in our case
(111) facets which will not develop any further. Therefore, the addi-
tion of PVP in the reaction system modi fies the kinetics of the grow-
ing process of the crystals and based on the selective adsorption
model of surfactants on different crystallographic facets [38,39]
leads to anisotropic growth of CoFe 2O4particles.
The high-resolution transmission electron microscopy shown in
Fig. 7 f, indicates the lattice spacing of 2.42 Å between adjacent lattice
planes corresponds to d-spacing of (222) planes, 2.53 Å corresponds to
(311) planes and 2.97 Å assigned to (220) planes. Also, based on TEM
investigation we can find that uncoated cobalt ferrite particles
are nearly monodisperse and the mean particle size is 21 nm.
The cobalt ferrite nanoparticles have a tendency to agglomerate
due to their magnetic properties forming honeycomb structure
(Fig. 7 e).
Fig. 9 (a) shows representative TEM images of the CoFe 2O4-PEG
nanohybrid material revealing the core/shell nanostructure with
21 nm cobalt ferrite core and 0.947 nm shell. The SAED pattern in
Fig. 9 (e) can be indexed as a cubic structure of cobalt ferrite and the
diffraction rings correspond to the different diffraction planes.
Fig. 9 f presents the nearly monodisperse CoFe 2O4-PEG nano-
hybrid material particles which tend to agglomerate forming a
honeycomb structure ( Fig. 8 b–d). Although the coverage of cobalt fer-
rite nanoparticles with polymer has a very important purpose as
mentioned in the Introduction section it has also been reported that
PEG with linear and ordered chain structure can increase the attrac-
tion among the polymer chains by coordination with the metal ions
Fig. 5. The schematic representation of the possible interaction between cobalt ferrite and PEG (a) or PVP (b).
Fig. 6. Mössbauer spectra of the studied samples: (a) CoFe 2O4calcined at 400 °C,
(b) CoFe 2O4-PEG and (c) CoFe 2O4-PVP, together with the computer fit (continuous
lines: blue lines: tetrahederal positions; red lines: octahedral positions of Fe3+
ions).420 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

of the cobalt ferrite and cause the aggregation of nanoparticles [40]
and can selectively and easily absorbed on certain crystal facets of
the as-prepared primary building blocks such as nanoparticles,nanoplates, nanorods, nanosheets, and so on [41,42] .T h u st h ep r e –
pared CoFe 2O4-PEG hybrid material pa rticles have hexagonal
shape.
Fig. 7. HRTEM images of CoFe 2O4with different scales of measurements: (a) 2 nm, (b) 5 nm, (c) 10 nm; (d) HRTEM; (e) 50 nm; (f) 100 nm; and (g) SAED.
Fig. 8. Schematic illustration of the proposed formation mechanism of CoFe 2O4particles with different morphologies.421 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

Just like CoFe 2O4-PEG nanohybrid, CoFe 2O4-PVP nanohybrid ex-
hibits a narrow size particle distribution and also a core –shell nano-
structure composed by 21 nm cobalt ferrite core and 0.951 nmpolyvinylpyrrolidone shell as it could be seen in Fig. 10 (a). The
shape of the CoFe 2O4-PVP hybrid nanoparticles is hexagonal and
their crystalline structure is sustained by high resolution-TEM and
Fig. 9. HRTEM images CoFe 2O4-PEG with different scales of measurements: (a) 2 nm, (b) 5 nm, (c) 10 nm; (d) HRTEM; (e) 100 nm; (f) 50 nm; (g) SAED.
ab
dec
Fig. 10. HRTEM images of CoFe 2O4-PVP with different scales of measurements: (a) 2 nm, (b) 100 nm, (c) 50 nm; (d) HRTEM; and (e) SAED.422 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

SAED analyses ( Fig. 10 (d) and (e)). The CoFe 2O4-PVP nanoparticle
agglomeration leads to the formation of honeycomb structure
(Fig. 10 (b) and (c)).
The morphology investigation of the two prepared hybrids shows
that coating of cobalt ferrite particles with a branched structuredpolymer as PVP comparing with coating them with a linear structured
polymer as PEG leads to obtaining hybrid nanoparticles that are less
agglomerated ( Figs. 9 (f) and 10(c)).
3.5. Dynamic light scattering analyses (DLS)
DLS analysis revealed an overall diameter of 21 nm for
CoFe
2O4particles, 23 nm for CoFe 2O4-PEG particles and 24 nmfor CoFe 2O4-PVP particles respectively and the polydispersity of
0.130. The small increase of the hybrid particles in comparison
with cobalt ferrite particles is due to the polymeric shell of the
cobalt ferrite cores.
The existence of negative charges at the surface of the cobalt fer-
rite nanoparticles is evident from the ζpotential measurement
which is −35 mV. After the coating of cobalt ferrite nanoparticles
with PVP and PEG shells the ζpotential becomes −5 mV and −4 mV.
3.6. Magnetic measurement assessment
The cobalt ferrite nanoparticles with sizes less than 10 nm have
poor magnetic response abilities considering the biomedical applica-
tions implying the use of a magnetic field[43]. Because of the small
size the low magnetization limits their usage in some biomedical
applications since they cannot be successfully manipulated by using
a moderate magnetic field[44,45] . In order to obtain a high saturation
magnetization (Ms) the preparation of larger cobalt ferrite particles
cannot be an option at all, resulting in a strong aggregation due to
the ferromagnetic attraction [46]. Great effort has focused on the syn-
thesis of large-size superparamagnetic particles with high Ms using
simple composites [47]. Lee et al. [48] reported the preparation of
highly uniform superparamagnetic spheres with sub-micrometer
scale, containing CoFe 2O4and silica having a high magnetization
value.
In our study the cobalt ferrite nanoparticles (CoFe 2O4)h a v ead i f –
ferent behavior: its combination with polyvinylpyrrolidone (PVP)
increases not only the saturation magnetization, but also the hyster-
esis parameters (coercivity and remanence) ( Fig. 12 andTable 1 ). An
explanation could be the massive agglomeration of the magnetic
nanoparticles that allows the multidomain magnetic structure
[49,50] ( Fig. 11 ).
Fig. 11. Histograms of magnetic cobalt ferrite particle (a); cobalt ferrite-PEG hybrid
material (b) and cobalt ferrite-PVP hybrid material (c).
Fig. 12. Hysteresis loops of CoFe 2O4nanoparticles (a), and CoFe 2O4-PVP nanohybrid (b).Table 1
The magnetic properties of cobalt ferrite and corresponding hybrid nanomaterials.
Material Coercivity
Hc[kA/m]Remanent
magnetizationMr[Am
2/kg]Saturation
magnetization⁎
Ms
[Am2/kg]
CoFe 2O4 16.3 15.7 54.9
CoFe 2O4+PVP 83.2 26.7 60.1
CoFe 2O4+PEG 84 28 63
⁎Hmax=955 kA/m.
3 2 1050010001500200010612
FRAP II FRAP I CUPRAC Antioxidant activity (a.u) PVP
PEG
CoFe2O4
CoFe2O4-PEG
CoFe2O4-PVP
FRAP II FRAP I CUPRACAntioxidant activity (a.u) PVP
PEG
CoFe2O4
CoFe2O4-PEG
CoFe2O4-PVP
Fig. 13. Antioxidant activity values of the prepared nanohybrids and corresponding
components obtained by CUPRAC, FRAP I and FRAP II methods.423 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

The results presented in Fig. 10 show an interesting property of
the biopolymer: it ampli fies the CoFe 2O4particle magnetic properties
as it was also reported in [51].
3.7. Antioxidant activity investigation
Radical scavenging capability of the hybrids and their compo-
nents was investigated by three different methods, FRAP I, FRAP II
and CUPRAC. From our best knowledge these methods have notbeen implemented to these hybrid nanomaterials being initiated
and used so far for soluble compound testing. Between the two poly-
mers considered for cobalt ferrite nanoparticle coating, all the three
methods used for the investigation showed that PEG has the highestantioxidant activity. This may explain the much higher antioxidant
activity of the hybrid CoFe
2O4-PEG in comparison with that of the
other obtained hybrid CoFe 2O4-PVP ( Fig. 13 ). Even if the antioxidant
activity value of cobalt ferrite powder exceeds that of the two pre-
pared hybrids we consider that for biomedical applications it is
more appropriate to have a material with many advantageous prop-
erties (like biocompatibility conferred in our case by the polymeric
component of the nanohybrids and also acceptable antioxidant ca-
pacity) than holding only one pronounced feature.
3.8. The biologic activity tests
Applying the disk diffusion it was observed that none of the hybrid
materials tested has a high inhibitory action on the four microorgan-
isms used for investigation, E. coli ATCC 25922, P. aeruginosa ATCC
27853, B. subtilis ATCC 6663 and Candida scotti .
The experiments were done in comparison with standard antibi-
otic by measuring inhibition zone diameters and the experimental
results are shown in Fig. 14 .
Between the three tested nanomaterials a minimum toxic action
was obtained for the cobalt ferrite powder and hybrid and CoFe 2O4-PVP
nanohybrid, but for CoFe 2O4-PEG nanohybrid no toxic action on tested
microorganisms was observed ( Table 2 ).
Further investigations could be carried out for a more precise
evaluation of the nanohybrid biological activities required for apply-
ing in biomedical field.
ab c d
ef g h
ij k l
mn o
Fig. 14. Pictorial diffusion spots of Bacillus subtilis CoFe 2O4-PVP (a), CoFe 2O4(b), CoFe 2O4-PEG (c); Candida scotti CoFe 2O4-PVP (d), CoFe 2O4(e), CoFe 2O4-PEG (f), Escherichia
coliCoFe 2O4-PVP (g), CoFe 2O4(h), CoFe 2O4-PEG (i); Pseudomonas aeroginosa (j) CoFe 2O4-PVP, CoFe 2O4(k), CoFe 2O4-PEG (l); and Salmonella enterica serovar typhimurium
(m) CoFe 2O4-PVP, CoFe 2O4(n), CoFe 2O4-PEG (o).
Table 2Biological activity of the prepared samples on the microorganisms tested by disk diffu-sion method.
Tested sample Microorganisms Diameter of zone of inhibition (mm)
X
2048 μgCIP
5μgE
15μgTOB
10μgCEC
30μg
CoFe
2O4-PVP Bacillus subtilis 10 38 35 20 –
Escherichia coli 04 0 0 1 8 –
Pseudomonas aeroginosa 03 2 0 1 8 –
Salmonella 04 2 0 2 0 –
Candida scotti 00 –– 0
CoFe 2O4 Bacillus subtilis 14 38 32 26 0
Escherichia coli 03 6 0 1 6 –
Pseudomonas aeroginosa 03 0 0 – 0
Salmonella 04 0 0 2 0 –
Candida scotti 00 – 00
CoFe 2O4-PEG Bacillus subtilis 03 7 3 2 2 8 –
Escherichia coli 04 2 2 2 0 –
Pseudomonas aeroginosa 02 0 0 1 8 –
Salmonella 04 0 0 1 8 –
Candida scotti 0 – 000424 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

4. Conclusions
Core –shell nanohybrids based on CoFe 2O4coated with polyethylene
glycol (PEG) and polyvinilpirolidone (PVP) biopolymers described in
this study were obtained by a facile, large scale, non-toxic and cost ef fi-
cient two step method which may be versatile for the synthesis of other
hybrid nanomaterial based ferrites coated with polymers. In the first
step nearly monodisperse CoFe 2O4hexagonal shaped nanoparticles
were synthesized by PVP biopolymer assisted coprecipitation method
which was also used besides PEG biopolymer in the second step as coat-
ings for cobalt ferrite nanoparticles obtaining two nanohybrids with
hexagonal shape particles and a mean size of 22 nm. We proposed
that the pristine CoFe 2O4particles with hexagonal shape was obtained
through oriented aggregation of primary nanocrystals facilitated by
PVP and the hexagonal shape of the final nanohybrids may result
from the absorption of the polymers on some certain crystal facets of
the cobalt ferrite. Fourier transform infrared spectroscopy results
suggested that PVP and PEG interacted with CoFe 2O4sample. The bio-
logic activity investigation results on E. coli ,P. aeruginosa ,B. subtilis
and Candida scotti outline a minimum or no toxic activity of the two
obtained core –shell nanohybrids. The existence of the antioxidant
properties of the CoFe 2O4-PEG and CoFe 2O4-PVP nanohybrids was
highlighted by three different methods. Since the main application of
the magnetic obtained nanohybrids is to address cancer therapy we
consider that besides the potential diagnose and treatment of cancer
given by their magnetic properties, the antioxidant activity con firms,
completes and enhances their therapeutic potential being considered
as multifunctional tools in cancer therapy because the antioxidants pro-
tect healthy cells from free radicals (ROS, reactive oxygen species) that
can cause the mutations of cellular DNA and consequently the appear-
ance and development of cancer.
Acknowledgments
Authors recognize the financial support from the European Social
Fund through POSDRU/89/1.5/S/54785 project: “Postdoctoral Pro-
gram for Advanced Research in the field of nanomaterials ”.
References
[1] Q.A. Pankhurst, J. Connolly, S.K. Jones, J. Dobson, Applications of magnetic
nanoparticles in biomedicine, Journal of Physics D: Applied Physics 36 (13)(2003) R167 –R181.
[2] C.C. Berry, Possible exploitation of magnetic nanoparticle —cell interaction for
biomedical applications, Journal of Materials Chemistry 15 (2005) 543 –547.
[3] J.H. Lee, Y.M. Huh, Y.W. Jun, J.W. Seo, J.T. Jang, H.T. Song, S. Kim, E.J. Cho, H.G.
Yoon, J.S. Suh, J. Cheon, Arti ficially engineered magnetic nanoparticles for
ultra-sensitive molecular imaging, Nature Medicine 13 (1) (2007) 95 –99.
[4] B. Baruwati, M.N. Nadagouda, R.S. Varma, Bulk synthesis of monodisperse ferrite
nanoparticles at water –organic interfaces under conventional and microwave
and their surface functionalization, Journal of Physical Chemistry C 112 (2008)
18399 –18404.
[ 5 ] S . Y .Z h a o ,D . K .L e e ,C . W .K i m ,H . G .C h a ,Y . H .K i m ,Y . S .K a n g ,S y n t h e s i so fm a g –
netic nanoparticles of Fe
3O4and CoFe 2O4and their surface modi fication by
surfactant adsorption, Bulletin of the Korean Chemical Society 27 (2) (2006)
237–241.
[6] Y. Lee, J. Lee, C.J. Bae, J.G. Park, H.J. Noh, J.H. Park, T. Hyeon, Large-scale synthesis
of uniform and crystalline magnetite nanoparticles using reverse micelles as
nanoreactors under re flux conditions, Advanced Functional Materials 15 (3)
(2005) 503 –509.
[ 7 ] C . I .C o v a l i u ,D .B e r g e r ,C .M a t e i ,L .D i a m a ndescu, E. Vasile, C. Cristea, V. Ionita, H.
Iovu, Magnetic nanoparticles coated with polysaccharide polymers for potential
biomedical applications, Journal of Nanoparticle Research 13 (2011)
6169 –6180.
[8] I.C. Covaliu, J. Neamtu, G. Georgescu, T. Malaeru, C. Cristea, I. Jitaru, Synthesis and
characterization of ferrites (Fe 3O4/CuFe 2O4)-calcium alginate hybrids for mag-
netic resonance imaging, Digest Journal of Nanomaterials and Biostructures 6
(2011) 245 –252.
[9] S. Bhattacharyya, J.P. Salvetat, R. Fleurier, A. Husmann, T. Cacciaguerra, M.L.
Saboungi, One step synthesis of highly crystalline and high coercive cobalt –ferrite
nanocrystals, Chemical Communications 38 (2005) 4818 –4820.
[10] A.H. Lu, E.L. Salabas, F. Schuth, Angewandte Chemie International Edition 46
(2007) 1222.[11] J. Park, S.G. Joo, Y.J. Kwon, T. Jang, J. Hyeon, Angewandte Chemie International
Edition 46 (2007) 4630.
[12] A.B. Moghaddam, Hybrid nanocomposite based on CoFe2O4 magnetic nanoparticles
and polyaniline, Iranian Journal of Chemistry and Chemical Engineering 29 (4)
(2010) 173 –179.
[13] S.C. Smolinske, in: Handbook of Food, Drug, and Cosmetic Excipients, CRC Press,
Boca Raton, 1992, p. 287.
[14] F. Kreppel, S. Kochanek, Modi fication of adenovirus gene transfer vectors with
synthetic polymers: a scienti fic review and technical guide, Molecular Therapy
16 (2007) 16 –29.
[15] A. Samantha, J. Meenach, Z. Hilt, K.W. Anderson, Poly(ethylene glycol)-based
magnetic hydrogel nanocomposites for hyperthermia cancer therapy, Acta
Biomaterialia 6 (2010) 1039 –1046.
[16] M. Licciardi, M. Grassi, M. Di Stefano, L. Feruglio, G. Giulianid, S. Valenti, A. Cappelli,
G. Giammona, PEG-benzofulvene copolymer hydrogels for antibody delivery, In-
ternational Journal of Pharmaceutics 390 (2010) 183 –190.
[17] V. Bühler, Excipients for Pharmaceuticals —Povidone, Crospovidone and Copovidone.
Springer, Berlin, Heidelberg, New York, pp. 1 –254. ISBN 978-3-540-234122005.
[18] K. Yoshida, Y. Sakurai, S. Kawahara, Anaphylaxis to polyvinylpyrrolidone in
povidone-iodine for impetigo contagiosum in a boy with atopic dermatitis, Inter-
national Archives of Allergy and Immunology 146 (2008) 169 –173.
[19] Y. Christen, Oxidative stress and Alzheimer disease, American Journal of Clinical
Nutrition 71 (2000) 21S –629S.
[20] A. Nunomura, R. Castellani, X. Zhu, P. Moreira, G. Perry, M. Smith, Involvement
of oxidative stress in Alzheimer disease, Journal of Neuropathology and Experi-mental Neurology 65 (2006) 631 –641.
[21] A. Wood-Kaczmar, S. Gandhi, N. Wood, Understanding the molecular causes of
Parkinson's disease, Trends in Molecular Medicine 12 (2006) 521 –528.
[22] G. Davì, A. Falco, C. Patrono, Lipid peroxidation in diabetes mellitus, Antioxidants
& Redox Signaling 7 (2005) 256 –268.
[23] D. Giugliano, A. Ceriello, G. Paolisso, Oxidative stress and diabetic vascular com-
plications, Diabetes Care 19 (1996) 257 –267.
[24] C. Hitchon, H. El-Gabalawy, Oxidation in rheumatoid arthritis, Arthritis Research
& Therapy 6 (2004) 265 –278.
[25] C.W. Hao, Y. Zhao, W.L. Li, Y.Z. Xu, D.J. Wang, D.F. Xu, Investigation on effect of
PVP on morphological changes and crystallization behavior of nylon 6 in
PVP/nylon 6 blends by FTIR spectroscopy, Spectroscopy and Spectral Analysis28 (2008) 2048 –2052.
[26] Y.J. Kwon, K.H. Kim, C.S. Lim, K.B. Shim, Characterization of ZnO nanopowders
synthesized by the polymerized complex method via an organochemical route,
Journal of Ceramic Processing Research 3 (2002) 146 –149.
[27] J.B. Silva, W. De Brito, S.N.D. Mohallem, In fluence of heat treatment on cobalt ferrite
ceramic powders, Materials Science and Engineering B 112 (2004) 182 –187.
[28] D. Caruntu, G. Caruntu, C.J. O'Connor, Magnetic properties of variable-sized Fe
3O4
nanoparticles synthesized from non-aqueous homogeneous solutions of polyols,Journal of Physics D: Applied Physics 40 (2007) 5801 –5809.
[29] C.I. Covaliu, G. Georgescu, J. Neam țu, T. M ălăeru, I. Jitaru, Ni0.5Zn0.5Fe
2O4spinel
nanoparticles obtained by complexation method using dimethylaminoethanol,
Journal of Optoelectronics and Advanced Materials 5 (11) (2011) 1202 –1206.
[30] M. Sangmanee, S. Maensiri, Nanostructures and magnetic properties of cobalt
ferrite (CoFe 2O4) fabricated by electrospinning, Applied Physics A 97 (2009)
167–177.
[31] M.S. Hegde, D. Larcher, L. Dupont, Synthesis and chemical reactivity of polyol
prepared monodisperse nickel powders, Solid State Ionics 93 (1 –2) (1997)
33–50.
[32] K. Sivaiah, B. Hemalatha Rudramadevi, S. Buddahudu, Structural, thermal and
optical properties of Cu2+and Co2+: PVP polymer films, Indian Journal of Pure
and Applied Physics 48 (2010) 658 –662.
[33] L.B. Newalkar, S. Komarneni, H. Katsuki, Microwave-hydrothermal synthesis and
characterization of barium titanate powders, Materials Research Bulletin 36
(2001) 2347 –2355.
[34] X. Xue, J. Wang, L. Mei, Zhigeng Wang, K. Qi, B. Yang, Recognition and enrichment
speci ficity of Fe 3O4magnetic nanoparticles surface modi fied by chitosan and
Staphylococcus aureus enterotoxins A antiserum, Colloids and Surfaces. B,
Biointerfaces 103 (2013) 107 –113.
[35] Rohan A. Hule, Darrin J. Pochan, Polymer nanocomposites for biomedical applica-
tions, MRS Bulletin 32 (2007) 354 –358.
[36] Y. Wei, L. Li, X. Yang, G. Pan, G. Yan, X. Yu, One-step UV-induced synthesis of
polypyrrole/Ag nanocomposites at the water/ionic liquid interface, Nanoscale
Research Letters 5 (2) (2010) 433 –437.
[37] Z.P. Liu, S. Li, Y. Yang, Z.K. Hu, S. Peng, J.B. Liang, Y.T. Qian, Shape-controlled syn-
thesis and growth mechanism of one-dimensional nanostructures of trigonal tel-
lurium, New Journal of Chemistry 27 (2003) 1748 –1752.
[38] W. Yu, H.Q. Xie, L.F. Chen, Y. Li, C. Zhang, Synthesis and characterization
of monodispersed copper colloids in polar solvents, Nanoscale Research Letters
4 (2009) 465 –470.
[39] H.M. Yang, J. Ouyang, A.D. Tang, Single step synthesis of high-purity CoO
nanocrystals, The Journal of Physical Chemistry. B 111 (2007) 8006 –8013.
[40] J. Dobryszycki, S. Biallozor, On some organic inhibitors of zinc corrosion in alka-
line media, Corrosion Science 43 (2001) 1309 –1319.
[41] X.H. Liu, J. Yang, L. Wang, X.J. Yang, L.D. Lu, X. Wang, An improvement on sol –gel
method for preparing ultra fine and crystallized titania powder, Materials Science
and Engineering A 289 (2000) 241 –245.
[42] Z. Chen, L. Gao, Synthesis and magnetic properties of CoFe 2O4nanoparticles by
using PEG as surfactant additive, Materials Science and Engineering B 141
(2007) 82 –86.425 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426

[43] T. Neuberger, B. Schopf, H. Hofmann, M. Hofmann, B. von Rechenberg, Super-
paramagnetic nanoparticles for biomedical applications: possibilities and limitations
of a new drug delivery system, Journal of Magnetism and Magnetic Materials 293
(2005) 483.
[44] H. Ma, X. Qi, Y. Maitani, T. Nagai, Preparation and characterization of super-
paramagnetic iron oxide nanoparticles stabilized by alginate, International
Journal of Pharmaceutics 333 (2000) 177 –186.[45] P. Tartaj, M. del Puerto Morales, S. Veintemillas-Verdaguer, T. Gonzalez-Carreno,
C.J. Serna, The preparation of magnetic nanoparticles for applications in biomed-
icine, Journal of Physics D: Applied Physics 36 (2003) 182 –197.
[46] J.H. Lee, Y.M. Huh, Y.W. Jun, J.W. Seo, J.T. Jang, H.T. Song, S. Kim, E.J. Cho, H.G.
Yoon, J.S. Suh, J. Cheon, Arti ficially engineered magnetic nanoparticles for
ultra-sensitive molecular imaging, Nature Medicine 13 (2007) 95 –99.426 C.I. Covaliu et al. / Powder Technology 237 (2013) 415 –426