1.
INTRODUCTION
Magnetic
materials have various applications in different fields such as magnetic
storage media [1],
Ferro fluids [2],
magnetic resonance imaging (MRI) [3],
magnetically guided drug delivery [4]
magnetic bio-separation [5],
heavy metal removal [6],
and cancer therapy [7].
They have been used extensively as they have various properties such as magnetism,
catalytic features, conduction and biological acceptance [8].
The production method of nanomagnetite particles can be divided generally into
two approaches, physical and chemical methods [9].
One example of physical method is evaporating particulate materials in tube
furnace containing ultra-pure nitrogen. However, physical methods suffer from
poor size and shape. Chemical methods are simpler and more efficient [10].
Various methods such as reverse micelle, copolymer gels, solvothermal
reduction, ion exchange resin and co-precipitation are used [11].
Among these, co-precipitation method is probably the most promising one due to
its simplicity, productivity, and low cost in the production process [9].
Surface
modification and functionalization of magnetite nanoparticles are performed
using coating materials. Easy aggregation and instability of bare nanomagnetite
particles in aqueous solution, high surface energy, and susceptibility to
oxidation lead to the stabilization of iron oxide particles by surface
modification so that they can be used in various potential fields [12] [13]. Surface modification is easily performed
through the creation of few atomic layers of organic (polymer) or inorganic
(metal or oxide) surfaces [14][15].
This coating can be comprised of several materials such as organic, inorganic,
polymeric and non-polymeric ones [16].
For example, Lee and Harris (2006) attached oleic acid to the surface of
magnetite by ozonolysis and made it more lypophilic [17].
Yantasee et al. (2007) used surface modification of dimercaptosuccinic acid
(DMAS) to synthesize superparamagnetic iron oxide (Fe3O4)
and employed them as a useful sorbent material for toxic soft metals such as
Hg(II), Ag(I), Pb(II), Cd(II) and Tl(I) ions which actively bind to the DMSA
ligand and for As(III) which binds to the iron oxide lattice [18].
Zhang et al. (2011) reported that the application of starch as a stabilizer in
preparation of the Fe3O4 particles can effectively reduce
particle aggregation and lead to the formation of more effective adsorbing
sites on magnetite particle surfaces [19].
Another investigation [20]
described the formation of magnetite in the presence of 1 wt.% poly(vinyl
alcohol). Low dispersed chitosan-bound Fe3O4
nanoparticles were utilized as a unique nano-adsorbent for the removal of heavy
metal ions [21].
Rapid
industrialization and urbanization have created various pollutants particularly
those entering aquatic systems so development of efficient and cost-effective
methods for environmental treatment is critical. Nano-magnetites are ideal
candidates for pollutant removal and toxicity mitigation due to extremely small
size, high ratio of surface area to volume and more importantly the magnetism [22].
Methods of pollutants adsorption to the surface of these nanoparticles include
physical adsorption, ion-exchange, chemical bonding, hydrogen bonds, and van
der Wall forces. For example, composite of Fe3O4/ZrO2/chitosan
was synthesized and employed for the removal of amaranth and tartazine dyes [23].
Phthalates have
been used extensively as plastifying agent to make polyvinyl chloride supple
and flexible. They exist in the environment, food samples, medical devices,
perfume and cosmetics [24].
Phthalates tend to bioaccumulate in the environment and they are poorly
degradable and toxic [25];
so monitoring phthalates is of significant importance due to their wide use and
toxicity [26].
In this work, it has been tried to absorb phthalate from aqueous solution by
nanomagnetite particles. Then, absorbance and desorption conditions were
optimized.
2.
MATERIALS AND METHODS
2.1. MATERIALS
1,4-butanediol
(BD; Merck, 99%), adipic acid (ADA; Merck, 99%), terephthalic acid (TA; Merck,
98%), and titanium (IV)tetra-n-butyl orthotitanate (TBT; Merck, 98%) were
purchased and used for synthesizing polymers. FeCl3.6H2O
() and FeCl2.4H2O () along with NaOH () and HCl (Merck,
37%) were used to synthesize the nanoparticle. Dibutyl phthalate (Merck, >
99%) and dioctyl phthalate (Merck, 98%) were purchased and used as received.
All solvents were at analytical degree.
2.2. METHODS
Polymers and
nanoparticles were synthesized according to our previous work [27].
So, a brief description is given. Preparing solutions and optimization methods
will explain next.
2.2.1. POLYMER SYNTHESIS
PBA was
synthesized through two-stage melt polycondensation (first esterification and
then polycondensation) using BD and ADA with TBT as catalyst (molar ratio of
1:1:0.1, respectively). Nitrogen atmosphere and vigorous stirring were applied.
The reaction is as follows:

PBAT was also
synthesized through three-stage melt polycondensation (two stages of
esterification and then polycondensation) using BA, ADA, TA with TBT as
catalyst (molar ration of 1:1:1:0.1, respectively). Nitrogen atmosphere and
vigorous stirring were applied. The reaction is as follows:

2.2.2. BIO-NANOMAGNETITE
SYNTHESIS
Co-precipitation
method was used based on similar previous works [28][29][30].
For first nanoparticle (PBAT), PBAT (dissolved in DMSO) were added to a
round-bottom flask containing Fe.Cl3.6H2O, Fe.Cl2
(molar ratio of 10-4: 2:1, respectively), HCl 12 M (0.85 ml) and
distilled water (25 ml). After partial dissolving, NaOH 1.5 M (250 ml) was
added drop wisely while stirring vigorously and nitrogen passing. When adding
NaOH was completed, a black precipitation was obtained which was washed three
times with distilled water and dried in vacuum oven for 24h at 50oC.
Another
nanoparticle (PBA+PBAT) was also synthesized through the same procedure except
that in addition to PBAT, PBA (dissolved in CHCl3) was also added
(PBA:PBAT:FeCl3:FeCl2 à 10-4: 10-4: 2:1). This
precipitation was washed (three times) and dried at the same condition.
2.2.3. SOLUTIONS OF PHTHALATES
As
nanoparticles are used to absorb phthalates from aqueous medium, first aqueous
solution of them should be prepared. As they are insoluble in water, a 1000-ppm
stock solution of each phthalate (dibutyl phthalate (DBPh) and dioctyl
phthalate (DOPh) in methanol was prepared. Then, a 20-ppm solution was provided
in methanol from 1000-ppm stock solution of each one. Finally, 5-ppm aqueous
solution was prepared from solutions of 20 ppm. These 5 ppm solutions were used
for optimization process.
2.2.4. OPTIMIZATION PROCESS
Optimization
was performed for solution derived from absorption and desorption. First,
weight of each nanoparticle was optimized for the absorption of each phthalate.
Considered weights included 0.001 gr, 0.005 gr, 0.01 gr, and 0.02 gr. Then,
time intervals of 10 min, 20 min, 30 min, 45 min, and 60 min was used for DBPh
and 10 min, 20 min, 30 min, 45 min, 60 min, and 75 min for DOPh. Finally,
stirring speed was optimized for the absorption of each phthalate solution (250
rpm, 500 rpm, and 750 rpm).
Afterwards,
desorption was optimized. First, volume of methanol was optimized (1.5 cc, 2
cc, 2.5 cc and 3 cc). Second, time intervals of 10 min, 30 min, 20 min, and 40
min were considered. Finally, stirring speed was investigated (250 rpm, 500
rpm, and 750 rpm).
3.
RESULTS AND DISCUSSIONS
3.1. 13CNMR SPECTRA
13CNMR
spectra of polymers were taken (Browker, 400 MHz). Figs 1 and 2 show these spectra
and their corresponding tables indicate their characterizing peaks.

Figure 1: 13CNMR
spectrum of PBA

Table 1:
Leading peaks of PBA 13CNMRspectrum
Chemical shift (ppm)
|
Carbon type
|
Chemical shift (ppm)
|
Carbon type
|
76.80
|
c
|
24.26
|
f
|
173.32
|
d
|
25.24
|
b
|
180
|
g
|
33.80
|
e
|
|
|
63.80
|
a
|

Figure 2: 13CNMR
spectrum of PBAT

Table 2:
Leading peaks of PBAT 13CNMR spectrum
Chemical shift (ppm)
|
Carbon type
|
Chemical shift (ppm)
|
Carbon type
|
25.29
|
e
|
129.88
|
b
|
33.70
|
f
|
134.86
|
c
|
39.80
|
g
|
176.09
|
h
|
63.74
|
d
|
173.09
|
a
|
3.2. FTIR SPECTRUM
Fourier Transform
Infrared spectrum (FTIR) shows the characterizing peaks (Thermo Nicolet, AVATAR
370, USA). Fig. 3 shows the FTIR result of PBAT nanoparticles. Stretching Fe-O
peaks at 440.06 cm-1 and 601.11 cm-1, OOP peaks of para
substituents at 877.35 cm-1, aromatic stretching C=C at
the range of 1475-1630 cm-1,C-O stretching peaks at 1000-1300 cm-1
and broad peak at about 3395 cm-1 for stretching O-H are observed
which confirmed polymer coating
structure. Peaks at 1008.2 and 629.31 can be of esteric characteristic
peaks but they are shifted backward due to Fe bounding.

Figure 3: FTIR
spectrum of PBAT nanoparticles
Also FTIR
spectrum of PBA+PBAT nanoparticles is shown in Fig. 4 which disclosed
characteristic peaks of stretching Fe-O (432.69 cm-1 and 588.24 cm-1),
C-H chain bending (1413.39 cm-1.), and O-H stretching band (3373.06
cm-1). Peaks at 1634.05 and 1020.21 can point to ester
characteristics peaks but they are shifted backwards which can be due to the
iron bounding with the oxygen atom of esoteric group.

Figure 4: FTIR
spectrum of PBA+PBAT nanoparticles
3.3. XRD TEST
Results of
X-ray diffraction spectrum can be observed in Fig. 5. This test was performed
from 20o to 80o and CuKα was used.
According to this spectrum, crystalline structure of iron is maintained after
coating as characteristic peaks of iron can be recognized in the spectrum. In
addition, relative size of the particles based on Debye-Scherrer relation was
obtained (9.12 nm).

Figure 5: XRD
spectrum of nanoparticle
3.4. OPTIMIZATION
First,
wavelength for phthalates absorption should be determined. So, 20-ppm methanol
solutions of both DBPh and DOPh were obtained with UV-Vis spectroscopy. It was
found that the wavelength was 247nm. To determine whether the nanoparticles had
the capacity to absorb phthalates, aqueous solutions of dibutyl phthalate were
obtained and PBAT and PBAT+PBA nanoparticles were added. Then, UV spectrum of
desorption was taken while methanol was considered as blank. Results are as
follows.

Figure 6:
Desorption of DBPh by PBAT nanoparticles

Figure 7:
Desorption of DBPh by PBAT+PBA nanoparticles
As it was mentioned that time,
nanoparticle weight and stirring speed were optimized for absorption of DBPh
and DOPh from aqueous solution.
Optimum
desorption conditions were also obtained. Nanoparticles obtained from optimum
absorption were put in methanol and then UV-Vis spectrum was taken. Volume,
time and stirring speed were optimized and results are given in table 3.
Table 3:
Optimum conditions for absorption and desorption of phthalates by
bio-nanoparticles
Absorption
|
Material
|
PBAT nanoparticles
|
PBAT+PBAT nanoparticles
|
Weight (gr)
|
Time (min)
|
Stirring speed (rpm)
|
Weight (gr)
|
Time (min)
|
Stirring speed (rpm)
|
DBPh
|
0.01
|
20
|
500
|
0.01
|
45
|
500
|
DOPh
|
0.005
|
30
|
500
|
0.005
|
60
|
500
|
Desorption
|
Material
|
PBAT nanoparticles
|
PBAT+PBAT nanoparticles
|
Volume (ml)
|
Time (min)
|
Stirring speed (rpm)
|
Volume (ml)
|
Time (min)
|
Stirring speed (rpm)
|
DBPh
|
2.5
|
30
|
500
|
2.5
|
20
|
500
|
DOPh
|
2.5
|
30
|
500
|
2.5
|
20
|
500
|
3.5. CALIBRATION
Generally,
calibration is a kind of operation in which an output quantity is related to an
input quantity for a measuring system under given conditions (IUPAC). Linear
regression is used to determine the equation which best explains the linear
relationship between the response (y) and analyte level (x) (in this work, y is
the absorbance level and x is the concentration). This relation is described by
the equation of the line, i.e., y = mx + c in which m is the gradient of the
line and c is the intercept with the y-axis. The correlation coefficient, r
(and the related parameter r2) shows the strength of correlation
between the y and x values. It can take any value from +1 to -1 and the closer
it is to 1, the stronger the correlation. This correlation coefficient is
commonly used in analytical measurement. The particular value of r can indicate
a statistically significant correlation between y and x depends on the number
of data points used to calculate it (calibration curve guide).
In order to
plot calibration graphs, different aqueous concentrations of DBPh and DOPh were
prepared (0.01 ppm, 0.05 ppm, 0.1 ppm, 0.5 ppm, 1 ppm, 5 ppm, 10 ppm, and 15
ppm) and then, nanoparticles were added. In each case, four or five suitable
points were selected to plot the graphs. Results are shown in the following Figs
(8-11).

Figure 8:
Calibration graph of DBPh desorption from PBAT nanoparticles

Figure 9:
Calibration graph of DBPh desorption from PBA+PBAT nanoparticles

Figure 10:
Calibration graph of DOPh desorption from PBAT nanoparticles

Figure 11:
Calibration graph of DOPh desorption from PBA+PBAT nanoparticles
As it can be
seen from the Figs, there seems to be good correlations between absorbance and
concentration (values of R2 are close to one). In each case, the
equation may be used to estimate the amount of absorbance in any concentration.
There are some fluctuations in absorbance amount of different concentrations
which can be attributed to the instrument error tolerance and slight
differences during preparing different concentrations of the stock solution.
3.6. ISOTHERMS
Isotherms were
also plotted for these solutions at five different temperatures (15o,
20o, 25o, 30o and 35oC). Four
prepared isotherms are illustrated below.

Figure 12:
Isotherm of DBPh absorbance by PBAT nanoparticles in different temperatures

Figure 13:
Isotherm of DBPh absorbance by PBA+PBAT nanoparticles in different temperatures

Figure 14:
Isotherm of DOPh absorbance by PBAT nanoparticles in different temperatures

Figure 15:
Isotherm of DOPh absorbance by PBA+PBAT nanoparticles in different temperatures
4.
CONCLUSIONS
Bio-nanomagnetite
particles were synthesized in this work. First, two biodegradable polymers of
PBA and PBAT were produced using two- and three-stage melt polycondensation.
Their characteristics were studied using 13CNMR spectra. Next, two
different bio-nanomagnetites were synthesized using FeCl3 and FeCl2
through co-precipitation method. Nanomagnetite particles were coated with PBAT
and PBA + PBAT. FTIR and XRD spectra of bio-nanomagnetites were obtained. These
coated particles were used to absorb DOPh and DBPh from aqueous medium and
their performance were optimized regarding particle weight, absorption and
desorption duration, volume of desorption solvent, and stirring speed.
Findings show
that PBA+PBAT NP was better in absorbing phthalates from aqueous solution that
PBAT NP which may be because combined NP has more functional group and reaction
site on its surface than PBAT NP. 13CNMR spectra show peaks may be
assigned to functional groups of the polymers. In addition, FTIR spectra of
bio-nanoparticles illustrate peaks related to both polymers and iron salts.
X-ray diffraction spectrum indicates the relative size of the particles based
on Debye-Scherrer relation (9.12 nm). Calibration graphs show a good
correlation between absorbance and concentration with values of R2
approaching one. Optimum features were also obtained and summarized in table 3.
These
nanoparticles can be used to absorb phthalates from aqueous solution under
optimized conditions which multiplies their efficiency. They are biodegradable
and also reusable. Therefore, they can be used with the least trace on the
environment.
SOURCES OF FUNDING
None.
CONFLICT OF INTEREST
None.
ACKNOWLEDGMENT
Hereby the author thanks Dr. H.
Atashin for helping in analyzing XRD tests and supporting this work.
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