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Colloids and Surfaces A: Physicochem. Eng. Aspects 457 (2014) 433–440

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Colloids and Surfaces A: Physicochemical and
Engineering Aspects
journal homepage: www.elsevier.com/locate/colsurfa

Removal of phosphate from aqueous solution using nanoscale
zerovalent iron (nZVI)
Zhipan Wen a , Yalei Zhang a,∗ , Chaomeng Dai b,∗
a
b

State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai 200092, China
College of Civil Engineering, Tongji University, Shanghai 200092, China

h i g h l i g h t s

g r a p h i c a l

a b s t r a c t

• nZVI is a suitable and effective material for phosphate removal.

• pH affected the removal efficiency of
phosphate significantly.

• Ionic strength did not affect phosphate removal.

• Coexisting anions (except carbonate anion) did not affect phosphate

removal.
• Phosphate is mainly sequestrated
within nZVI by adsorption and coprecipitation.

a r t i c l e

i n f o

Article history:
Received 9 March 2014
Received in revised form 6 June 2014
Accepted 11 June 2014
Available online 18 June 2014
Keywords:
Phosphate removal
Adsorption
Nanoscale zerovalent iron (nZVI)
Eutrophication

a b s t r a c t
Nanoscale zerovalent iron (nZVI) was used to remove phosphate from aqueous solution, and the influence of pH, ionic strength and coexisting anions on phosphate removal was investigated. The results agree
well with both Langmuir model and Freundlich model, and the calculated maximum adsorption capacity of phosphate was 245.65 mg/g, suggesting significantly higher and excellent uptake of phosphate
by nZVI. The removal of phosphate obviously decreased with an increasing pH due to the isoelectric
point (IEP) of nZVI, but exhibited no change with ionic strength and coexisting anions (except carbonate
anion). The microstructure of fresh and reacted nZVI was characterized by FT-IR, XRD and XPS and these
results indicated that no redox reaction occurred to the P(V). These observations shed light on the mechanisms of phosphate removal were mainly adsorption and coprecipitation processes. The higher uptake
of phosphate indicates that nZVI was a suitable and effective material for phosphate removal.
© 2014 Elsevier B.V. All rights reserved.

1. Introduction

In recent years, nanoscale zerovalent iron (nZVI) has been
widely investigated for treatment of environmental contaminants.

∗ Corresponding authors at: Tongji University, State Key Laboratory of Pollution
Control and Resource Reuse, 1239 Siping Road, Shanghai 200092, China.
Tel.: +86 0 21 65985811/+86 0 21 65980624;
fax: +86 0 21 65986960/+86 0 21 65989961.
E-mail addresses: ,
(Y. Zhang), (C. Dai).
/>0927-7757/© 2014 Elsevier B.V. All rights reserved.

In previous studies, nZVI has been used for the removal of chlorinated organic compounds, polychlorinated biphenyls (PCBs) [1–3],
heavy metals [4–7], and certain inorganic compounds [8,9] from
wastewater or groundwater. Compared to other bulk materials,
nZVI has a larger specific surface area and high reactivity. This nZVI
can also overcome the narrow limitations of gravitational force and
advance Brownian motion movement and dispersion [4]. In addition, nZVI is a non-toxic material. It is known that when iron reacts
with water, it forms a thin oxide layer, which is expressed as oxyhydroxide (FeOOH) and hydrogen gas [10]. As a result, nZVI has a
core–shell structure with a zerovalent iron core and iron hydroxides as the shell. Due to this characteristic core–shell structure,


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nZVI presents unique properties and also a dual redox chemistry
capability [6].
As a major nutrient in aquatic ecology, phosphate has been
regarded as the limiting factor responsible for water eutrophication, which depletes oxygen, affects aquatic life forms and
jeopardizes water quality [11]. Phosphate pollution includes

municipal and industrial wastewater, agricultural drainage,
stormwater runoff and household sources. Therefore, most of the
extra phosphate in wastewater should be removed before being
discharged into water bodies, such as rivers or lakes.
At present, several methods have been widely applied to phosphate removal from wastewater, such as chemical precipitation,
bacterial activity and adsorption by materials. Chemical precipitation of phosphate with metal cations, such as Ca2+ , Al3+ and Fe3+ ,
is an effective method of phosphate removal from wastewater but
not suitable for wastewater with high phosphate because of the
large consumption of chemicals. Phosphate removal by phosphateaccumulating bacteria (PCB) in activated sludge is also widely used
in conventional sewage treatment plants, but phosphate removal is
limited by biological conditions and wastewater composition [12].
Furthermore, this approach will produce excess sludge containing high concentrations of phosphate and other pollutants, such
as heavy metals, which are notably difficult and costly to treat.
Among these methods, adsorption seems considered to be one of
the most promising technologies for phosphate removal because
it is simple to operate, cost-effective, high removal efficiency and
versatile for different water streams. So numerous adsorbents, such
as fly ash, red mud [13–16], steel slag [17,18], iron-based components [11,19–22] and zirconium [23,24] have been widely used
to remove phosphate from aqueous solutions. However, the serious drawback for those adsorbents was low adsorption capacity of
phosphate, which limited the usage of these adsorbents. Moreover,
certain adsorbents such as natural mineral that contained organic
pollutants and heavy metals could release into water during the
process of water treatment and cause secondary pollution.
Despite the widespread use of nZVI in treatment of organic contaminants and heavy metals, to our best knowledge, few paper
discuss phosphate removal by nZVI [25]. In the present study, nZVI
was used to remove phosphate from aqueous solutions, and the
influence of certain relevant factors including pH, ionic strength
and coexisting anions were investigated. The microstructure of the
fresh and reacted nZVI was characterized by Fourier transform
infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and X-ray

photoelectron spectroscopy (XPS) to reveal the detailed mechanisms of phosphate removal by nZVI, with the goal of providing
a more effective and environmentally friendly method to remove
phosphate from water, especially water with high phosphate concentrations.
2. Materials and methods
2.1. Materials
All reagents were analytical grade and were used without further purification. Nanoscale zerovalent iron (nZVI) was synthesized
by reduction of ferric iron (FeCl3 ·6H2 O) (Sigma-Aldrich, USA) by
sodium borohydride (NaBH4 ) (Sigma-Aldrich, USA) as reported previously [10,26] according to the following reaction:
4Fe3+ + 3BH4 − + 9H2 O → 4Fe0 ↓ + 3H2 BO3 − + 12H+ + 6H2 ↑
Briefly, a 1:1 (v/v) mixture of FeCl3 ·6H2 O (0.05 M) and NaBH4
(0.2 M) was vigorously stirred in flask for 30 min. The nZVI precipitate was collected with vacuum filtration and washed with
deionized water. The iron nanoparticles were refrigerated in a
sealed container under ethanol at 4 ◦ C to minimize any reaction

with water. The BET surface area of this obtained nZVI was approximately 27.65 m2 /g, which was consistent with the previous report
(30 m2 /g) [5].
Standard phosphate stock solution was prepared by dissolving
anhydrous potassium orthophosphate (KH2 PO4 ) (Sigma-Aldrich,
USA) in appropriate amounts of deionized water, and stored at 4 ◦ C.
2.2. Batch phosphate removal and equilibrium experiments
The adsorption kinetics experiments were performed in glass
bottles (35 mL) containing 30 mL of phosphate solution at 10 mg/L.
Upon adding a certain amount of adsorbent (30 mg), the bottles
were sealed with screw caps and placed in the thermostatic shaker
(200 rpm) at 25 ◦ C. Individual bottles were sacrificed after certain
time intervals (5, 10, 15, 30, 60, 90, 120, 150, 180 min) and immediately filtered by a 0.45 ␮m membrane, and the residual phosphate
concentrations of the filtrate were determined.
Equilibrium experiments were carried out by adding 30 mg
adsorbent into a series of 35 mL bottles filled with 30 mL phosphate solutions at different concentrations (10, 20, 50, 100, 200,
400, 600, 800, 1000 mg/L); the bottles were sealed with screw caps

and placed in the thermostatic shaker (200 rpm) at 25 ◦ C for 2 h to
ensure equilibrium.
2.3. Effect of pH
The phosphate solutions (30 mL, 100 mg/L) and adsorbent
(30 mg) were mixed in the batch bottles, then the pH of the mixed
solutions was adjusted to the desired values ranging from 3.0 to
12.0 by adding HCl or NaOH solution. The sealed bottles were placed
in the thermostatic shaker (200 rpm) at 25 ◦ C for 2 h to ensure equilibrium.
2.4. Effect of ionic strength
The effects of ionic strength on phosphate removal were performed in the same fashion as pH measurement. nZVI (30 mg) was
added to 30 mL (100 mg/L) sample phosphate solutions containing a known concentration of NaCl (0.005–0.1 M), and mixed in the
batch bottles. The sealed bottles were placed in the thermostatic
shaker (200 rpm) at 25 ◦ C for 2 h to ensure equilibrium.
2.5. Coexisting anions
The amount of phosphate adsorbed was measured to evaluate
the effect of coexisting anions, including chloride, nitrate, sulfate
and carbonate, which were often present in the surface water and
wastewater. Solutions of sodium chloride, sodium nitrate, sodium
sulfate and sodium carbonate at a concentration of 0.1 M were
added to the phosphate solutions (100 mg/L, 30 mL), and 30 mg
adsorbent was later added. After 2 h balancing in the thermostatic
shaker (200 rpm) at 25 ◦ C, the equilibrium concentration of phosphate was determined.
2.6. Analytical methods
Samples were filtered through a 0.45 ␮m membrane, and the
residual phosphate concentrations were analyzed according to
a standard method (ascorbic acid molybdate blue method). The
soluble total Fe concentration in the samples at a predetermined
reaction time was measured after filtration through a 0.45 ␮m
membrane, in which 5 mL filtrate was added to 5 mL deionized
water (containing 10% ultrahigh purity HNO3 ) and measured

by inductively coupled plasma spectrometry Optical Emission


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435

Spectrometry (ICP-OES, Agilent 720ES, USA). The samples’ pH was
determined by a glass potential meter.
2.7. Characterization of nZVI
Fourier transform infrared (FT-IR) spectroscopy spectra of samples were recorded to monitor changes in the functional group of
the ZVI before and after the adsorption tests on a Nicolet 5700
spectrometer using KBr pellets in the range of 4000–400 cm−1 .
The nZVI before and after adsorption were placed in a glass
holder and scanned from 10◦ to 90◦ , with the scanning speed set
of 1o min−1 and a step size of 0.02◦ . The results were recorded by a
Bruker D8 Advance Powder X-ray Diffractometer (XRD, Germany)
˚ radiation source, while the operation
using a Cu K␣ ( = 1.54178 A)
voltage and current were kept at 40 kV and 40 mA, respectively.
Fresh and P-loaded nZVI samples were vacuum-dried, sealed
under nitrogen and characterized using XPS performed on a Perkin
Elmer PHI 5000 ESCA System spectrometer equipped with a rotating Al anode generating Al K␣ X-ray radiation at 1486.7 eV. The
X-ray beam was monochromatized using seven crystals mounted
on three Rowland circles. Samples were analyzed in the C 1s, O 1s,
Fe 2p and P 2p regions, which accounted for the major elements
present at the surface of samples.
Fig. 2. Phosphate removal (mgP/g) and percentage phosphate removal.

3. Results and discussion

3.1. Batch phosphate removal and equilibrium experiments
The phosphate removal batch study plays an important role for
adsorption studies because it can predict the equilibrium time and
removal rate of phosphate from aqueous solution by an adsorbent.
Fig. 1 presents the phosphate removal and the soluble total iron
concentration in aqueous solution as a function of contact time.
With an initial concentration of 10 mg/L, the phosphate removal
efficiency was more than 99% within 5 min and remained constant
over 180 min, which agrees with the study published by Chouyyok
[11], who used Fe(III)-EDA-SAMMS to remove phosphate, with
adsorption equilibrium achieved at just 1 min. Due to its high

surface area, nZVI offered more active binding sites, and phosphate
could be adsorbed rapidly and easily. The soluble total iron concentration increased in the first 15 min and later decreased from
2.64 mg/L to 1.35 mg/L by the end of the reaction. Although the
surface of the nZVI formed a layer of oxyhydroxide (FeOOH) due to
the reaction of iron with water [4,10], part of the Fe2+ and/or Fe3+
was still released from nZVI and formed Fe(OH)2 and/or Fe(OH)3 ,
which were beneficial to the phosphate removal as a result of a
subsequent coagulation/precipitation process [21].
Fig. 2 shows phosphate removal and percentage phosphate
removal versus phosphate equilibrium concentration. The results
were fitted with the Langmuir model (1) and Freundlich model (2),
respectively:
Ce
Ce
1
=
+
qe

qmax
KL qmax
ln qe = ln KF +

(1)

1
ln Ce
n

(2)

where Ce is the equilibrium concentration of phosphate (mg/L); qe is
the equilibrium adsorption capacity (mg/g); qmax is the maximum
adsorption capacity (mg/g); KL is the adsorption constant (L/mg);
KF and 1/n are Freundlich isotherm constants related to adsorption
capacity and intensity of adsorption, respectively.
The calculated isotherms parameters of the Langmuir and
Freundlich models for phosphate are summarized in Table 1. The
adsorption data of phosphate was better fitted by the Freundlich
model (R2 = 0.9818) than by the Langmuir model (R2 = 0.9369) from
the correlation coefficients (R2 ), suggesting that phosphate experienced multilayer adsorption on the surface of nZVI. The maximum
adsorption capacity was 245.65 mg/g, which indicated that nZVI
has more potential and was more effective than other reported
related adsorbents [21–24,27]. The constant KF of Freunlich model,
which defined as adsorption capacity which described the arsenic
Table 1
Estimated isotherm parameters for phosphate adsorption by nZVI.
Langmuir isotherm model

Fig. 1. The adsorption kinetics of phosphate and the total iron concentration. Error
bars represent standard error of the mean.

Freundlich isotherm model

KL (L/mg)

qmax (mg/g)

R2

n

KF

R2

0.0145

245.65

0.9369

3.61

38.11

0.9818

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Z. Wen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 457 (2014) 433–440

Fig. 3. Effect of pH on phosphate removal. Error bars represent standard error of
the mean.

adsorbed on the adsorbent for the unit equilibrium concentration
were 38.11, indicating nZVI exhibited higher adsorption capacity
for phosphate, which was consistent with the experimental results.
Moreover, the values of n in Freundlich model for phosphate was
greater than 1, suggesting this isotherm is nonlinear, which can be
attributed to adsorption site heterogeneity, electrostatic attraction
and other sorbent–sorbate interactions.
The percentage phosphate removal reached nearly 99% at a
low initial phosphate concentration (10–50 mg/L) and decreased
as the initial phosphate concentration increased to 1000 mg/L.
Søvik and Kløve [28] reported that chemical precipitation played
an important role at a higher initial phosphate concentration;
therefore, the phosphate removal mechanism at the high initial
phosphate concentrations (100–1000 mg/L) may include adsorption and coprecipitation processes.
3.2. Effect of pH
The pH of the aqueous solution was an important parameter in
the adsorption of cations and anions at the solid–liquid interface
[29]. The phosphate species present mainly depended on the pH of
the aqueous solution. H3 PO4 was the predominant species when
the pH was lower than 2.1, between 2.1 and 7.2 H2 PO4 − predominated, between 7.2 and 12.3 HPO4 2− predominated, and the main
species was PO4 3− when pH was higher than 12.3 [30].
The effect of pH on the removal of phosphate from aqueous
solution is depicted in Fig. 3. The phosphate removal efficiency

decreased with increasing pH and dropped sharply between 7.0 and
8.0. This trend agreed with a previous study, which reported that
strong phosphate adsorption depended on the solution pH [22].
This effect was most likely observed because the isoelectric point
(IEP) of the nZVI was approximately 8.0 [31,32]; the surface of the
nZVI carries a positive charge when the pH of the solution was lower
than the IEP and thus would adsorb the negatively charged phosphate species. However, if the pH of the solution was higher than
the IEP, the phosphate removal decreased because the nZVI surface carried more negative charges and had a lower affinity toward
phosphate species. At the same time, there were more OH− ions at
high pH, which competed with the phosphate ions for the adsorption sites [27]. One notable finding was that even when the pH

Fig. 4. Effect of ionic strength on phosphate removal. Error bars represent standard
error of the mean.

of the solution ranged from 10.0 to 12.0, phosphate removal still
reached 35%. It was proposed that in this pH range, electrostatic
attraction mechanisms may not be predominant, while the coagulation/precipitation process most likely exerted an important role.
Conversely, the equilibrium pH had an opposite trend compared to
the phosphate removal.
3.3. Effect of ionic strength
Fig. 4 demonstrates that the phosphate removal was slightly
dependent on the ionic strength, even when the NaCl concentration ranged from 0.005 M to 0.1 M. A strong dependence on ionic
strength was typical for outer-sphere complexes through electrostatic forces [24], but this result indicated the phosphate most
likely formed inner-sphere complexes, which involves appreciable covalent bonding along with ionic bonding at the solid–liquid
interface. Furthermore, inner-sphere complexes (chemical bonds)
were more stable than outer-sphere complexes (ion pairs).
3.4. Coexisting anions
Several common anions, which could potentially interfere in the
removal of phosphate, often coexisted in the surface water and
wastewater. Therefore, it was notably important to estimate their

influence on removal efficiency during the process of phosphate
removal from surface water or wastewater. The results in Table 2
indicated that the presence of 0.1 M chloride, nitrate or sulfate (a

Table 2
Effect of coexisting anions on phosphate removal by nZVI.
Matrix

Initial pH

Final pH

% Phosphate
removal

Phosphate
Phosphate + 0.1 M sodium chloride
Phosphate + 0.1 M sodium nitrate
Phosphate + 0.1 M sodium sulfate
Phosphate + 0.1 M sodium carbonate

5.14
4.97
4.95
5.06
11.29

9.25
9.09
9.18

9.13
11.11

78.49
76.36
77.97
81.56
14.70


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437

Fig. 6. XRD analysis of fresh nZVI and reacted nZVI.
Fig. 5. The FT-IR spectra of fresh nZVI (a), P (10 mg/L)-loaded nZVI (b) and P
(100 mg/L)-loaded nZVI (c).

concentration in approximately 30-fold molar excess of the phosphate) had only a small effect on phosphate adsorption. However,
carbonate strongly influenced phosphate adsorption, and the percentage of phosphate removal in this case was only 14.70%. This
phenomenon was due to the initial pH of the solutions. The initial pH of the solution containing 100 mg/L phosphate and 0.1 M
sodium carbonate was 11.29, phosphate removal decreased sharply
due to OH− ions at high pH, which competed with the phosphate
ions for adsorption sites [27], and electrostatic repulsion between
the phosphate and the nZVI, the surface of which carried more
negative charges at this pH value, which result in the decrease of
phosphate removal. This result indicated that common anions in
surface water and wastewater did not affect the phosphate removal
by nZVI.
3.5. Characterization of nZVI

Fig. 5a is the FT-IR spectrum of fresh nZVI, and b and c represent the FT-IR spectra between 4000 and 400 cm−1 , of the nZVI
that adsorbed 10 mg/L and 100 mg/L phosphate, respectively. Broad
and strong peaks at ∼3400 cm−1 (O H stretching vibration) and
peaks at ∼1640 cm−1 (O H bending vibration) indicated the presence of physisorbed interstitial water molecules on the surface of
the nZVI [33]. The peak at 1327 cm−1 (O H bending vibration) indicated the presence of surface hydroxyls on nZVI. After adsorption, a
portion of hydroxyl groups were replaced by PO4 3− , and this peak
was shifted to a higher wavenumber (1384 cm−1 ) and weakened
[24]. New peaks at 1090 cm−1 and 1060 cm−1 appeared on the spectra of P-loaded nZVI (In Fig. 5b and c) compared to the fresh nZVI,
which were attributed to the bending vibration of adsorbed phosphate P O, revealing some phosphate ions had been adsorbed the
surface of nZVI. It was worth noting that some extra peaks were
also observed at 496, 543 and 568 cm−1 , which may be attributed
to the lattice vibrations of Fe O Fe and Fe O iron–oxygen bonds
[34,35].
Fig. 6 compares the XRD patterns of fresh nZVI and reacted nZVI
in the 2Â range of 10–90◦ . For fresh nZVI, the three characteristic
peaks that appeared at 44.6◦ , 65.2◦ and 82.3◦ could be indexed to

(1 1 0), (2 0 0), and (2 1 1) (JCPDS No. 06-0696), in which the crystal structure was a regular ␣-Fe crystalline state [36,37]. The same
peaks for Fe(0) also appeared on the reacted nZVI but the related
peaks weaken; however, the reacted sample also contained additional P mineral phases, such as vivianite (Fe3 (PO4 )2 ·8H2 O) (JCPDS
No. 30-0662), which indicated phosphate was adsorbed on the surface of nZVI. Vivianite was also formed while the nZVI was exposed
to the HPO4 2− anions 6 month [38] and appeared as a secondary
mineralization product from the bioreduction of lepidocrocite (␥FeOOH) [39]. In this present study, vivianite was the predominant
mineral product.
X-ray photoelectron spectroscopy (XPS) is a versatile analysis
technique that was used to investigate the composition and chemical state of nZVI before and after phosphate adsorption. Fig. 7
presents the full-range survey spectra of fresh nZVI and P-loaded
nZVI. Based on photoelectron peaks, the major elements of fresh
nZVI were consisted mainly of iron (Fe), oxygen (O) and carbon (C).
The small amounts of carbon appearing on the spectra was due to

exposure to air and water during the sample preparation and reaction [4]. The P 2p spectra on the full-range survey of P-loaded nZVI
indicated that the phosphate species present in aqueous solution
had been adsorbed on the surface of nZVI, and the photoelectron
peaks were more obvious if the phosphate initial concentration was
higher.
The O 1s narrow scans in fresh nZVI and P-loaded nZVI can be
deconvoluted into three overlapped peaks corresponding to oxide
oxygen (O2− ), hydroxyl groups (OH− ) and adsorbed water (H2 O).
From Fig. 7a–c and Table 3, it was found that the O 1s spectra were
quite different before and after adsorption. M O (where M represents a metal oxide substrate) increased from 37.41% to 40.53% and
44.56%, this increase may be attributed to the new oxygen which
from P O after phosphate was adsorbed on the surface of nZVI.
Moreover, P (100 mg/L)-loaded nZVI has relative high percentage of
M O due to the more phosphate on the surface of nZVI. In contrast,
OH− decreased from 45.90% to 43.27% and 40.93%, respectively. It
was known that high concentration of Fe–OH was proposed as the
main reason for the high phosphate adsorption capacity of nZVI.
However, by increasing the phosphate adsorbed on the surface of
nZVI, some OH− would be replaced by phosphate, so the percentage


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Z. Wen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 457 (2014) 433–440

Fig. 7. Full-range XPS spectra of Fresh nZVI and P-loaded nZVI, O 1s spectra with three deconvolutions of Fresh nZVI (a), P (10 mg/L)-loaded nZVI (b) and P (100 mg/L)-loaded
nZVI (c).

of OH− decreased after P-loaded nZVI. More than 2% percentage of
OH− decreased compared P (100 mg/L)-loaded nZVI to P (10 mg/L)loaded nZVI, suggesting more phosphate had been adsorbed on the

surface of nZVI. Detailed XPS surveys on the Fe 2p and P 2p of nZVI
are shown in Fig. 8a and b. The binding energies at 711.4 eV and
725.0 eV were assigned to Fe 2p3/2 and Fe 2p1/2 in Fig. 5, and the
separation of the Fe 2p3/2 and Fe 2p1/2 spin–orbit levels was 13.6 eV,
which was attributed to Fe(III) ions. However, the binding energies of 2p3/2 and 2p1/2 for fresh nZVI were 711.0 eV and 724.5 eV,
Table 3
Relative contents of O 1s in various chemical states.
Samples

Fresh nZVI

P (10 mg/L)-loaded nZVI

P (100 mg/L)-loaded nZVI

Chemical
states

Binding
energy (eV)

Percent (%)

O2−
OH−
H2 O
O2−
OH−
H2 O
O2−

OH−
H2 O

529.99
531.32
532.71
530.06
531.29
532.36
529.86
531.24
532.69

37.41
45.90
16.69
40.53
43.27
16.20
44.56
40.93
14.51

respectively. It was found that the binding energies of Fe were
shifted to the higher binding energy after phosphate had been
adsorbed on the surface of nZVI, suggesting the possibility that
Fe atoms was involved in the adsorption. In addition, the fresh
nZVI yielded a small peak at 707.0 eV compared to the P-loaded
nZVI, suggesting the presence of zerovalent iron (Fe(0) 2p3/2 ) [4].
The missing metallic iron peaks in the P-loaded nZVI implied that

surface corrosion occurred [40]; the nZVI core shrank, and the concomitantly thickness of the iron oxide shell increased after reaction
[41]. At the same time, a relatively small amount of zerovalent iron
indicated that the surface of nZVI was nearly all iron oxyhydroxide, which could be expressed as FeOOH [10]. High-resolution P
2p deconvoluted spectra are shown in Fig. 8b. Only one P 2p peak
appeared at 133.4 eV, attributable to the P(V) O bonding, after
phosphate adsorption, suggesting the phosphate ions present in
aqueous solutions had been adsorbed on the surface of nZVI and
no occurrence of redox reaction between phosphate ions and nZVI,
although the latter always was realized to a strong reducing agent. It
was also obvious that the photoelectron peak at an initial phosphate
concentration of 100 mgP/L was much greater than at 10 mgP/L,
which was consistent with high-resolution O 1s deconvoluted spectra analysis that was discussed before.


Z. Wen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 457 (2014) 433–440

439

Fig. 8. XPS survey on the Fe 2p (a) and P 2p (b) of nZVI.

4. Conclusions
Nanoscale zreovalent iron (nZVI) was synthesized and characterized for removal of phosphate. The adsorption results agree well
with the Langmuir model and Freundlich model, and the phosphate
removal is highly pH-dependent but only slightly dependent on
the ionic strength. The coexisting anions chloride, nitrate and sulfate did not affect phosphate removal, but removal efficiency was
significantly impacted by the carbonate anion due to its initial pH
value in solution. The results of FT-IR, XRD and XPS indicate that the
mainly mechanism of phosphate removal includes adsorption and
coprecipitation and no occurrence redox reaction between adsorbates and adsorbent. The higher uptake of phosphate indicates that
this obtained nZVI material has great potential in the removal of

phosphate from contaminated water, especially water with high
phosphate concentrations.
Acknowledgments
This work was financially supported, in part, by the National
Natural Science Foundation of China (Nos. 41172210, 51278356,
41372240), Industry-university-research Program of Shanghai
Municipal Education Commission (14cxy07), and the National
Key Technologies R&D Program of China (Nos. 2012BAJ25B02,
2012BAJ25B04).
References
[1] B. Schrick, J.L. Blough, A.D. Jones, T.E. Mallouk, Hydrodechlorination of
trichloroethylene to hydrocarbons using bimetallic nickel–iron nanoparticles,
Chem. Mater. 14 (2002) 5140–5147.
[2] C.B. Wang, W.X. Zhang, Synthesizing nanoscale iron particles for rapid and
complete dechlorination of TCE and PCBs, Environ. Sci. Technol. 31 (1997)
2154–2156.
[3] G.V. Lowry, K.M. Johnson, Congener-specific dechlorination of dissolved PCBs
by microscale and nanoscale zerovalent iron in a water/methanol solution,
Environ. Sci. Technol. 38 (2004) 5208–5216.
[4] X.Q. Li, W.X. Zhang, Sequestration of metal cations with zerovalent iron
nanoparticles—a study with high resolution X-ray photoelectron spectroscopy
(HR-XPS), J. Phys. Chem. C 111 (2007) 6939–6946.
[5] M.A.V. Ramos, W. Yan, X.Q. Li, B.E. Koel, W.X. Zhang, Simultaneous oxidation and reduction of arsenic by zero-valent iron nanoparticles: understanding
the significance of the core–shell structure, J. Phys. Chem. C 113 (2009)
14591–14594.

[6] W. Yan, M.A.V. Ramos, B.E. Koel, W.X. Zhang, As(III) sequestration by iron
nanoparticles: study of solid-phase redox transformations with X-ray photoelectron spectroscopy, J. Phys. Chem. C 116 (2012) 5303–5311.
[7] W. Yan, R. Vasic, A.I. Frenkel, B.E. Koel, Intraparticle reduction of arsenite
(As(III)) by nanoscale zerovalent iron (nZVI) investigated with in situ X-ray

absorption spectroscopy, Environ. Sci. Technol. 46 (2012) 7018–7026.
[8] J.S. Cao, D. Elliott, W.X. Zhang, Perchlorate reduction by nanoscale iron particles,
J. Nanopart. Res. 7 (2005) 499–506.
[9] X.Q. Li, D.W. Elliott, W.X. Zhang, Zero-valent iron nanoparticles for abatement
of environmental pollutants: materials and engineering aspects, Crit. Rev. Solid
State Mater. Sci. 31 (2006) 111–122.
[10] X.Q. Li, W.X. Zhang, Iron nanoparticles: the core–shell structure and unique
properties for Ni(II) sequestration, Langmuir 22 (2006) 4638–4642.
[11] W. Chouyyok, R.J. Wiacek, K. Pattamakomsan, T. Sangvanich, R.M. Grudzien,
G.E. Fryxell, W. Yantasee, Phosphate removal by anion binding on
functionalized nanoporous sorbents, Environ. Sci. Technol. 44 (2010)
3073–3078.
[12] W. Xiong, J. Peng, Development and characterization of ferrihydritemodified diatomite as a phosphorus adsorbent, Water Res. 42 (2008)
4869–4877.
[13] K.C. Cheung, T.H. Venkitachalam, Improving phosphate removal of sand infiltration system using alkaline fly ash, Chemosphere 41 (2000) 243–249.
[14] Q. Guan, X. Hu, D. Wu, X. Shang, C. Ye, H. Kong, Phosphate removal in marine
electrolytes by zeolite synthesized from coal fly ash, Fuel 88 (2009) 1643–1649.
[15] P. Pengthamkeerati, T. Satapanajaru, P. Chularuengoaksorn, Chemical modification of coal fly ash for the removal of phosphate from aqueous solution, Fuel
87 (2008) 2469–2476.
[16] G. Akay, B. Keskinler, A. C¸akici, U. Danis, Phosphate removal from water by red
mud using crossflow microfiltration, Water Res. 32 (1998) 717–726.
[17] L.I. Bowden, A.P. Jarvis, P.L. Younger, K.L. Johnson, Phosphorus removal from
waste waters using basic oxygen steel slag, Environ. Sci. Technol. 43 (2009)
2476–2481.
[18] C. Barca, C. Gérente, D. Meyer, F. Chazarenc, Y. Andrès, Phosphate removal from
synthetic and real wastewater using steel slags produced in Europe, Water Res.
46 (2012) 2376–2384.
[19] C. Namasivayam, K. Prathap, Recycling Fe(III)/Cr(III) hydroxide, an industrial
solid waste for the removal of phosphate from water, J. Hazard. Mater. 123
(2005) 127–134.

[20] G.S. Zhang, H.J. Liu, R.P. Liu, J.H. Qu, Removal of phosphate from water by a
Fe–Mn binary oxide adsorbent, J. Colloid Interface Sci. 335 (2009) 168–174.
[21] Y. Lee, S.G. Zimmermann, A.T. Kieu, U. von Gunten, Ferrate (Fe(VI)) application
for municipal wastewater treatment: a novel process for simultaneous micropollutant oxidation and phosphate removal, Environ. Sci. Technol. 43 (2009)
3831–3838.
[22] H. Zeng, B. Fisher, D.E. Giammar, Individual, Competitive adsorption of arsenate
and phosphate to a high-surface-area iron oxide-based sorbent, Environ. Sci.
Technol. 42 (2007) 147–152.
[23] B.K. Biswas, K. Inoue, K.N. Ghimire, H. Harada, K. Ohto, H. Kawakita, Removal
and recovery of phosphorus from water by means of adsorption onto orange
waste gel loaded with zirconium, Bioresour. Technol. 99 (2008) 8685–8690.
[24] H. Liu, X. Sun, C. Yin, C. Hu, Removal of phosphate by mesoporous ZrO2 , J. Hazard.
Mater. 151 (2008) 616–622.
[25] T. Almeelbi, A. Bezbaruah, Aqueous phosphate removal using nanoscale zerovalent iron, J. Nanopart. Res. 14 (2012) 1–14.


440

Z. Wen et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 457 (2014) 433–440

[26] J.E. Martin, A.A. Herzing, W. Yan, X.Q. Li, B.E. Koel, C.J. Kiely, W.X. Zhang,
Determination of the oxide layer thickness in core–shell zerovalent iron
nanoparticles, Langmuir 24 (2008) 4329–4334.
[27] T.S. Anirudhan, B.F. Noeline, D.M. Manohar, Phosphate removal from wastewaters using a weak anion exchanger prepared from a lignocellulosic residue,
Environ. Sci. Technol. 40 (2006) 2740–2745.
[28] A.K. Søvik, B. Kløve, Phosphorus retention processes in shell sand filter systems
treating municipal wastewater, Ecol. Eng. 25 (2005) 168–182.
[29] L. Zeng, X. Li, J. Liu, Adsorptive removal of phosphate from aqueous solutions
using iron oxide tailings, Water Res. 38 (2004) 1318–1326.
[30] B.J. Pan, J. Wu, B.C. Pan, L. Lv, W.M. Zhang, L.L. Xiao, X.S. Wang, X.C. Tao,

S.R. Zheng, Development of polymer-based nanosized hydrated ferric oxides
(HFOs) for enhanced phosphate removal from waste effluents, Water Res. 43
(2009) 4421–4429.
[31] Y.P. Sun, X.Q. Li, W.X. Zhang, H.P. Wang, A method for the preparation of stable
dispersion of zero-valent iron nanoparticles, Colloids Surf., A: Physicochem.
Eng. Aspects 308 (2007) 60–66.
[32] Y.P. Sun, X.Q. Li, J. Cao, W.X. Zhang, H.P. Wang, Characterization of zero-valent
iron nanoparticles, Adv. Colloid Interface Sci. 120 (2006) 47–56.
[33] J. Zhou, S. Yang, J. Yu, Z. Shu, Novel hollow microspheres of hierarchical
zinc–aluminum layered double hydroxides and their enhanced adsorption
capacity for phosphate in water, J. Hazard. Mater. 192 (2011) 1114–1121.
[34] H. Fu, X. Quan, Complexes of fulvic acid on the surface of hematite, goethite,
and akaganeite: FTIR observation, Chemosphere 63 (2006) 403–410.

[35] Z. Ai, Y. Cheng, L. Zhang, J. Qiu, Efficient removal of Cr(VI) from aqueous solution with Fe@Fe2 O3 core–shell nanowires, Environ. Sci. Technol. 42 (2008)
6955–6960.
[36] Q. Wang, S. Lee, H. Choi, Aging study on the structure of Fe0 -nanoparticles:
stabilization, characterization, and reactivity, J. Phys. Chem. C 114 (2010)
2027–2033.
[37] X. Wang, C. Chen, Y. Chang, H. Liu, Dechlorination of chlorinated methanes by
Pd/Fe bimetallic nanoparticles, J. Hazard. Mater. 161 (2009) 815–823.
[38] B.C. Reinsch, B. Forsberg, R.L. Penn, C.S. Kim, G.V. Lowry, Chemical transformations during aging of zerovalent iron nanoparticles in the presence of
common groundwater dissolved constituents, Environ. Sci. Technol. 44 (2010)
3455–3461.
[39] E.J. O’Loughlin, C.A. Gorski, M.M. Scherer, M.I. Boyanov, K.M. Kemner, Effects of
oxyanions, natural organic matter, and bacterial cell numbers on the bioreduction of lepidocrocite (␥-FeOOH) and the formation of secondary mineralization
products, Environ. Sci. Technol. 44 (2010) 4570–4576.
[40] W. Yan, A.A. Herzing, X.Q. Li, C.J. Kiely, W.X. Zhang, Structural evolution of
Pd-doped nanoscale zero-valent iron (nZVI) in aqueous media and implications for particle aging and reactivity, Environ. Sci. Technol. 44 (2010) 4288–
4294.

[41] B.W. Zhu, T.T. Lim, Catalytic reduction of chlorobenzenes with Pd/Fe nanoparticles: reactive sites, catalyst stability, particle aging, and regeneration, Environ.
Sci. Technol. 41 (2007) 7523–7529.