The use of zinc <=
span
class=3DSpellE>metalloporphyrin
Tahereh Poursaberia and
Ali Akbar Miran Beigi=
b,*
Analytical
Research Group, Research Institute of Petroleum Industry, Tehran, Iran
bOil Refining Research Division,
Research Institute of Petroleum Industry, Tehran, Iran
Corresponding
autho;: Tel:
+98-21-48255042, Fax: +98-21-44739738, E-mail: amiranbeigi@yahoo.com
Abstract
This study
investigates an application of zinc metalloporphyrin
grafted Fe3O4 nanoparticles as a new adsorbent for re=
moval
of sulfate ions from wastewaters. The modification of
magnetite nanoparticles was conducted by 3-aminopropyltriethoxysilane follo=
wed
by zinc (II) porphyrin in order to
Keywords: Ma=
gnetic
nanoparticles; water samples; Sulfate
removal, Zinc (II) porphyrin;
Nanosorbent.
1. Introduction
Sulfate is a common constituent of many natural wa=
ters
and wa=
stewaters
[1], which it is present as a dissolved compound in seas and oceans or as insoluble salt (=
e.g., gypsumlayers).=
Industrial wastewaters are responsible for most
anthropogenic=
emissions
of sulfate into the environment. Domestic sewage typically contains between 20 and 500 mg L<=
sup>-1
sulfate [2] while certain industrial effluents may contain several
thousands of milligrams per liter. The main source of sulfate in the labora=
tory
wastewaters is the use of sulfuric acid in many routine chemical analyses.
Sulfur compounds are also present in wastewaters used in the research
activities such as those from the pulp and paper industry, the food process=
ing
industry, and the photographic sector, among others [3].
The damage which is caused by sulfate emissions is=
not
direct, since sulfate is a chemically inert, non-volatile, and non-toxic
compound. However, high sulfate concentrations can unbalance the natural su=
lfur
cycle [1, 2], an=
d also endang=
er human
health when excessive ingestion. The accumulation of sulfate-rich sediments=
in
lakes, rivers and sea may cause the release of toxic sulfides that can
provoke damages to the environment [4]. The World Health Organization (WHO) has established
the maximum tolerable level of sulfate in water as 500 mg L-1[5]=
. The
current U.S. EPA national Secondary Maximum
Contaminant Level for sulfate, based
on organoleptic effects, is 250 mg L-1 [6].
A number of methods are currently used to promote =
the
removal of dissolved sulfate. They include reversed osmosis, electrodialys=
is,
or nanofiltration, which are expensive, c=
an be poisoned by
impurities, and require a post-treatment of the brine [2]. In
addition, established methods for removal of sulfate from industrial
effluents include chemical precipitation, biological treatment and
adsorption technologies. Chemical precipitation, for example, to add barium=
or
calcium salts, is rapid and effective, but it may produce another kind of
pollution and secondary treatment for solid phase is necessary [1]. Removal=
of
sulfate by sulfate-reducing bacteria is another alternative; however, the e=
fficiency
of biological treatment is susceptible to environmental conditions because =
the
growth requirements of this microbial are relatively rigid [7]. Adsorption
method may be preferred for their rapid and high selectivity, and sulfur ca=
n be
recovered.
More recently, the use of NPs for sample extraction is gaining=
researchers interest [8-16]. Compared with micrometer-=
sized
particles used in the SPE, the NPs offer a multitude of benefits that
make it a better choice. They have a significantly higher surface
area-to-volume ratio and a short diffusion route, resulting in a higher
extraction capacity; rapid dynamics of extraction and its higher extraction
efficiencies [17, 18]. Also, the main advantage of magnetic
nanoparticles is their separation by application of external magnetic field=
. In
addition, combination of the molecular scale recognition and nano scale surface modification creates a powerful to=
ol for
the development of selective separation systems. Depending on the usage,
surface modification can be performed by physical / chemical sorption or
surface coating of specific ligands [19-23]. =
Supramolecular
chemistry of anions has been widely studied and created a lot of artificial=
anionophores [24, 25]
among them; in addition, metalloporphyrins (MP)
are well known for their ability as anion carriers. The coordinating site of
MPs is an acidic metal and the anion recognition is the result of specific
anion coordination with this central metal ion =
[26].
Previously, it has been reported by us that the application of magnetic
nanoparticles modified by
Zr(IV) porphyrin and oxovanadium(IV) porphyrin for removal of fluoride and nitrate respectively=
[27,
28].
Herein,
we have combined the sulfate selectivity of zinc (II) porphyrin with the
advantages of magnetic nanoparticles has been combined by us to fabricate a=
new
kind of magnetic nanosized sorbent with high af=
finity
toward sulfate ion and good magnetic separability.
The effect of pH, contact time, nanosorbent dos=
age
and some co-existing anions present in aqueous solutions on sulfate removal
efficiency were investigated.
2. Experimental procedure
2.1. Materials
Ferric chloride hexahydrate, ferrous chloride tetrahydrate, APTES, dichloromethane (DCM), N<=
span
class=3DGramE>,N-dimethylformamide (DMF),
dicyclohexylcarbodiimide (DCHC), methanol, ammo=
nia,
sodium salts of indicated anions were all analytical grade from Merck Chemi=
cal
Co. Meso-T=
etrakis
(4-carboxyphenyl) porphyrinato zinc (II) (ZnTCPP) was obtained by metallat=
ion
of the free ligand porphyrin tetrakis
(4-carboxyphenyl) porphine H2 (TCPP)
(Aldrich) according to the methods described in the literature [29]. Schematic of the Zinc (II) porphyrin is shown i=
n Fig.
1.
Fig. 1.=
Schematic representation of the Zinc (II) porphyrin use=
d in
this work.
2.2.=
Equipments
The
morphology and dimension of Fe3O4/APTES/ZnTCPP were examined by transmission electron microsc=
ope
(TEM) using Zeiss 900 TEM at a voltage of 80 kV. Size and morphology of the=
nanosorbent were investigated by Tescan
Mira LMU SEM. The phase purity was
characterized by X-ray powder diffraction (XRD) (PW-1840 diffractometer from
Philips Co) using Cu-Kα radiation (=
l=3D1.54178 Å). Ion chromato=
graphy
(IC) determinations were carried out in a S 1122=
Sykam ion chromatograph. In addition, pH
measurements were performed with a Metrohm 691 =
pH
meter. FTIR spectra were recorded on a Vertex 70 FT-IR spectrophotometer fr=
om
Bruker Co. using standard KBr pellet technique.=
2.3. Sorbent preparation
2.3.1.
Synthesis of Fe3O4 nanoparticles
The chemical co-precipitation method was used in the preparati=
on of
the Fe3O4 NPs [30]. First, for preparing a stock
solution, 10.4 g of FeCl3·6H2O, with 4.0 g of FeCl
2.3.2. Modification of Fe3O4 nanoparticles with APTES gro=
ups
Fe3O4/APTES
nanoparticles were synthesized via the reaction of APTES and hydroxyl group=
s on
the surface of magnetite. 2.3 g of Fe3O4 nanoparticles
were dispersed in 100 mL of ethanol by sonication for about 1 h. Then under
continuous mechanical stirring, 20.34 mL of APTES was added dropwise to the suspension. The reaction mixtu=
re was
kept at 40 °C for 20 h under nitrogen
atmosphere with vigorous mechanical stirring. The prepared APTES nanopartic=
les
were collected with a magnet, and washed with ethanol and deionized water.
Finally, Fe3O4/APTES nanoparticles were dried under
vacuum at 50 ◦C.
2.3.3. Grafting of Zn (TCPP)
groups at the surface of Fe
Functional=
ization
of the modified nanoparticles was carried out by suspension of Fe3O4/APTES and DCHC in DMF under nitrogen [31]. Then Zn (TCPP) =
was
dissolved in DMF and added to the suspension. The mixture was refluxed at 1=
40 ◦C for 8 h. In order to prevent the
presence of volatile dimethylamine, a product of DMF decomposition, a high =
flux
of nitrogen is recommended. After reaction, the solid Fe3O4=
/APTES/Zn
(TCPP) nanoparticles were separated magnetically and washed with DMF, CH
Fig. 2.=
A scheme of the magnetite synthesis =
and
surface modification process using APTES followed by=
metalloporphyrin insertion.
2.4. Removal of sulfate ions by Fe3O4/APTES/=
Zn
(TCPP)
Adsorption of sulfate by Fe3O4=
/APTES/ZnTCPP has been studied in batch experiments. A known
amount of nanosorbent (100 mg) was mixed with 5=
0 ml
of 50 mgL-1 aqueous sulfate solution and was shaken at room
temperature with 200 rpm for
a 30 min. The sorbent was separated before
measurement. The residual sulfate concentration of aqueous solution was
determined by ion chromatography. The sulfate removal efficiency was calcul=
ated
according to Eq. (1):
where
Co and Cr are the initial and final concentrations of=
the
sulfate ion before and after the sorption, respectively.
3. Results and discussion
3.1. Characterization of the synthesized nano=
sorbent
3.1.1. X-ray powder Diffraction (XRD)
The Joint Committee on Powder
Diffraction Standards (JCPDS) reference pattern of magnetite (No. 19-629) w=
as
used for comparison. As seen, the XRD pa=
ttern
of magnetite nanoparticles was in good agreement with that of the standard =
Fe3O4
structure. The same set of characteristic peaks w=
ere
also observed for Fe3O4/APTES and Fe3O4/A=
PTES/ZnTCPP, indicating the stability of the
crystalline phase of Fe3O4 nanoparticles during
functionalization
and revealed that the APTES coating and metalloporphyrin grafting did not
result in the phase change of Fe3O4.
Fig. 3. XRD patterns of=
Fe3O4
(a), Fe3O4/APTES (b), and Fe3O4=
/APTES/Zn(TCPP) (c).
The Single formula g=
iven
by Debye Scherre (Eq. 2) can be used to calculate the crystalline size from=
the
available XRD data. The average size of the Fe3O4
nanoparticles using Debye Scherre was about 27 nm.
<=
span
style=3D'mso-spacerun:yes'> D =3D Kλ / βcos(θ) <=
/span>(2)
<= o:p>
3.1.2. Scanning Electron Microscopy (SEM)
=
The
particle size and morphological characteristics of the magnetite nanopartic=
les,
before and after surface modification, were investigated by using SEM (Fig.=
4).
As can be seen from Fig. 4a, the bare magnetic nanoparticles show spherical
shape with some aggregates due to the lack of any repulsive force between t=
he
magnetite nanoparticles. This is mainly due to the nano-size of the Fe=
3O4,
which is about 27 nm. After APTES introduction (Fig. 4b), particles with an
approximate spherical shape and an average diameter of 30 nm were observed.
This may be considered as indirect evidence that the magnetite core of the
APTES magnetite particles consisted of a single magnetite crystallite with a
typical diameter of 27 nm; and that the difference of 3 nm corresponds the
APTES-coating. After metalloporphyrin immobilization(Fig. 4c), the dispersi=
on
of particles were improved greatly. It can easily be explained by the
electrostatic repulsion force and steric hindrance between the metaloporphy=
rin
on the surface of Fe3O4 nanoparticles. Fig. 4c shows =
that
the morphology of the functionalized magnetic nanoparticles almost maintains
the original state.
3.1.3. Transmission Electron Microscopy (TEM)
The introduction of Zn
(TCPP) into the magnetite nanoparticles was evi=
dent
from TEM results. The dark nano-Fe3O4 cores surrounde=
d by
a grey shell could be observed in Fig.5. Moreover, the particles hav=
e special
characteristics such as an approximate spherical shape and an average size of 45 nm, whi=
ch their
characteristics complement the SEM data.
=
=
Fig.
4.
Fig.
5.
TEM micrograph of Fe3O4/APTES/Zn =
(TCPP)
nanosorbents.
3.1.4. FT-IR spectrum
FT-IR is a reliable technique for the monitoring of
the variations in the functional groups. Thereofre, the
structures of the synthesized nanosorbent (Fe
Fig. 6.
3.2. Adsorption experiments
3.2.1. Optimization of the
parameters
3.2.1.1. Effect of the solutio=
n pH
It
is well known that pH is one of the most important factors which affect the
sorption process. Experiments were performed to find the optimum pH on the
sorption of sulfate ions onto proposed nanosorbents
using different pH values changing from 4.0 to 9.0.
As
presented in Figure 7, while the sulfate removal depends on the pH of the
sample, there is only a slight variation of the sulfate removal percentage =
with
the pH values in the 6.0 – 7.0 pH range. In the acidic region the sulfate
removal is decreased as a result of partial demetallat=
ion
of the metalloporphyrin complex during the cont=
act
with the low pH test solution [32, 33]. At high pH values, sulfate and OH
Fig. 7. The pH influence on the removal efficiency of sul=
fate
(amount of adsorbent:100 mg; sulfate concentration: 50 mg L−1).
3.2.1.2. Effect of the contact
time
Contact time studies were performed to obtain the optimum time with the maximum amount of sulfate removed. The adsorption of = sulfate onto nanoadsorbents was monitored for 120 min. = Sulfate was adsorbed onto nanosorbents quickly, and equilibrium was achieved within 30 min and thereafter remains constant (Fig. 8). Therefore,= the time of 30 min was chosen as optimum value for all subsequent experiments.<= o:p>
Fig. 8. Effect of
contact time on the adsorption of sulfate by modified =
nanosorbent
(pH of the solution: 6.5, amount of adsorbent: 100 mg; sulfate concentratio=
n:
50 mg L−1).
3.2.1.3. Effect of the adsorbent dosage
To find the optimum amount =
of nanosorbents which
can remove sulfate ions from aqueous solution, a batch-mode sorption study =
was
performed using various amounts (25–250 mg) of Fe
Fig. 9. Effect
of nanosorbents dosage on the sulfate removal by modifi=
ed nanosorbent (pH of the solution: 6.5, contact time: 3=
0 min,
sulfate concentration: 50 mg L−1).
3.2.2. Removal studies
3.2.2.1. Removal of sulfate from spiked sample
In order to evaluate the performance of =
the
synthesized nanosorbent for sulfate removal,
solid-phase extraction was used under optimal conditions. The deionized wat=
er
was spiked with sulfate ion to make a 50.0 mg L−1 solution. The batch adsorption experi=
ment
was carried out on 50 mL of this spiked sample under optimal conditions; i.=
e.
contact time: 30 minutes, pH=3D6.5 and sorbent dosage: 100 mg. It was found=
that
the sulfate content decreased from 50.0 mg L−1<=
span
style=3D'font-family:"Times New Roman","serif";mso-fareast-font-family:Cali=
bri;
mso-fareast-theme-font:minor-latin;mso-bidi-language:AR-SA'> to 2.75 mg L−1 (94.5 ± 2.7% removal
efficiency, (n=3D5)).
3.2.2.2. Effect of co-existing anions=
Depending on the water source, more than one anion might be present.=
By
considering the competition for the binding sites between sulfate ions and =
such
anions, they may affect the extraction efficiency of the proposed nanosorbent and might interfere with the removal effi=
ciency
of sulfate. In due course, prior to the application of proposed method on r=
eal
samples, it is essential to investigate the effect of some of the interferi=
ng
ions on the recovery percentage of sulfate; therefore, the adsorption of su=
lfate
ion is tested in the presence of spiked known amounts of interfering ions. =
The
tolerance limit was defined as the amount of the foreign ion causing a chan=
ge
of ±5% in the removal efficiency. As seen from Fig. 10, the removal percent=
age
of sulfate was remained within the tolerance limit in the presence of
fifty-fold of nitrite and nitrate and one hundred-fold of fluoride, chloride
and bromide concentrations. These experimental results indicated that the
method has a good tolerance toward matrix interferences.
Fig. 10.=
Effect of co-existing anions on removal efficiency of a 50 mg L−1<=
span
style=3D'font-size:10.0pt;font-family:"Times New Roman","serif";mso-fareast=
-font-family:
Calibri;mso-fareast-theme-font:minor-latin;mso-bidi-language:AR-SA'> sulfate
ion.
3.2.2.3. =
Regeneration
of the used sorbent
In the
evaluation of the performance of the sorbents, regeneration is an important
factor to make an economic process. Moreover, in this work, NaOH
was chosen as the stripping reagent for the recovery of sulfate ions from t=
he adsorbents.
The concentration of the NaOH solution was opti=
mized,
and the results indicated that the highest recovery was obtained by using <=
span
class=3DSpellE>NaOH 0.1 M solution (Fig. 11).
Fig. 11. The effect of NaOH=
concentration as desorbing eluent on the recovery percentage of sulfate ion=
.
Regeneration performance of Fe3O4<=
/sub>/APTES/ZnTCPP was tested for repeatedly use in practice
applications. The spent Fe3O4/APTES/ZnTCPP
was immersed in 10 ml 0.1 M NaOH solution and s=
haken
for 30 min to desorb the loaded sulphate ions. =
Then
the exchanger was separated from the NaOH solut=
ion
with aid of magnet and washed with deionized water until the eluent was up =
to a
neutral pH.
3.2.2.4. Reusability of the recycled sorbent
After the first
regeneration, nanosorbent<=
/span>
was used in the followed adsorption test to record its sulphate
adsorption efficiency again. This adsorption and desorption cycle was
repeated five times. As
seen in Fig.12, after four sorption–desorption cycles, the efficiency of
Fig. 12. The removal efficiency after five repetition usage on propose=
d nanosorbents.
3.2.2.5.
Removal of sulfate from real sample
Con=
sidering
the practical applicability of proposed nanosorbent
for removal of sulfate from real samples, it was also tested with wastewater
obtained from glass industry (Kaveh glass indus=
try
group, Saveh, Iran). The detailed characteristi=
cs of
the wastewater are presented in Table 1. As can be seen, the untreated
wastewater had sulfate concentration of 108±15 mg L−1. The=
refore,
removal experi=
ments
were performed by using 200 mg of nanosorbent a=
t pH=3D6.5
and 30 min for contact time. It was found that the sulfate content decreased to 10±2 mg L−<=
sup>1<=
span
style=3D'font-family:"Times New Roman","serif";mso-fareast-font-family:Cali=
bri;
mso-fareast-theme-font:minor-latin;mso-bidi-language:AR-SA'> (90.7 <=
span
style=3D'font-family:"Times New Roman","serif";mso-fareast-font-family:MTSY;
mso-bidi-language:AR-SA'>± 2.4% removal efficiency, (n=3D3)).
Table 1: T=
he
characteristics of glass industrial wastewater used in this study.
|
Anions |
Value (mg L-1=
) |
|
C=
hloride |
2=
28±19 |
|
F=
luoride |
35.5±1.2<= o:p> |
|
N=
itrate |
8=
.52±0.6 |
|
|
108±15 |
|
B=
romide |
0=
.06±0.004 |
|
N=
itrite |
0.12±0.006 |
4. Conclusions
In
this paper, Zinc (II) me=
talloporphyrin
grafted Fe3O4 nanoparticle as a new and powerf=
ul
sorbent for the removal of sulfate ions from aqueous media is introduced.
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