Supporting Information
Transport of Surface-Modified Nano Zero-Valent Iron (SM-NZVI) in
Saturated Porous Media: Effects of Surface Stabilizer Type,
Subsurface Geochemistry and Contaminant Loading
Haoran DONG1,2 and Irene M. C. LO1*
1
Department of Civil and Environmental Engineering, The Hong Kong University of
Science and Technology, Hong Kong, China
2
College of Environmental Science & Engineering, Hunan University, Changsha,
Hunan, China
*Corresponding
author:
Email:
cemclo@ust.hk;
852-23587157.
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Pages: 1-10
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Figures: Fig. S1-S8
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Table: Table S1
1
Fax:
852-23581534;
Tel:
Preparation and characterization of SM-NZVIs
Two commercial NZVIs in aqueous dispersion form were supplied by the
NANOIRON® Company (Czech Republic, EU): pristine NZVI (Nanofer 25,
produced from nanosized ferrihydrite) and surface coated by PAA (Nanofer 25S).
Nanofer 25 (referred to as CNZVI in this study) was used for further modification by
using Tween-20 or starch. Information on the three surface stabilizers is summarized
in Table S1. Deoxygenated ultrapure water was used for the preparation of
SM-NZVIs to avoid the oxidation of Fe0 during the modification process.
PAA-modified CNZVI (i.e., Nanofer 25S), Tween-20-modified CNZVI and
starch-modified CNZVI are referred to as P-CNZVI, T-CNZVI and S-CNZVI,
respectively, in the following.
T-CNZVI was prepared by dispersing CNZVI particles in aqueous Tween-20 to
result in suspensions comprising iron nanoparticles (1.0 g L-1) and Tween-20 (35
wt%), followed by sonication for 30 min. The method of preparation of S-CNZVI is
as described below. Briefly, a 0.4 wt% starch solution was prepared by mixing 0.8 g
of potato starch with 200 mL of ultrapure water and heating the mixture to 100 oC.
Once the starch solution started boiling, the heating was removed and the solution was
allowed to cool at room temperature. The cooled starch stock solution was then
introduced into CNZVI stock suspensions to result in suspensions comprising iron
nanoparticles (1.0 g L-1) and starch (0.4 wt%), followed by sonication for 30 min. The
SM-NZVI suspensions were freshly prepared before each experiment. Mössbauer
spectroscopy confirmed that ~85% were in zero-valent state in CNZVI, and no
2
obvious loss of Fe0 was observed during the surface modification.
Morphological analysis of NZVI particles was performed by TEM (JEOL 2010
TEM). The individual particles of P-CNZVI, T-CNZVI and S-CNZVI appear
spherical and have an average diameter of about 7 nm, 9 nm and 4 nm, respectively.
The hydrodynamic particle sizes of P-CNZVI, T-CNZVI and S-CNZVI (Measured at
100 mg L-1) were 183 nm, 136 nm and 361 nm, respectively, and were determined by
using dynamic light scattering (DLS) (Zetaplus, LaborScience S.A.). Aggregation of
the nanoparticles with time was monitored by measuring the time-dependent
hydrodynamic diameter via DLS.
Zeta potential measurement of porous media
The streaming potential of the porous medium (sand and soil) was measured
using an Electro Kinetic Analyzer (Anton Paar GmbH, Graz, Austria) equipped with a
cylindrical cell to house the granular porous medium. Sand or soil after saturation
with various flushing solutions was wet-packed into the cylindrical cell in a solution
as same as the flushing solution used during the corresponding column experiments.
Before the start of each measurement, the cell was equilibrated by circulating the
solution for 20 min. Streaming potentials were converted to zeta potentials using the
Helmholtz–Smoluchowski equation.
Determination of As(V) sorption on T-CNZVI
Sorption kinetics experiments were conducted using a 100 mg L-1 T-CNZVI
suspension and 1 mg L-1 As(V) in synthetic groundwater at pH 7. The final solutions
(40 mL) in 41-mL glass vials sealed with Teflon caps were shaken in an end-over-end
3
rotator at 26 rpm, at room temperature (25 ºC). At pre-determined time intervals,
suspensions were filtered using 0.2-μm pore size cellulose nitrate filters. It should be
noted that all three types of nanoparticles had particle sizes smaller than 200 nm
before the reaction and could possibly pass through the filters; thus the iron
concentration in the filtered solution was analyzed. However, the results showed that
the concentrations of iron were non-detectable, indicating that all the SM-NZVI could
be retained by the filter. This should be ascribed to the formation of larger aggregates
(d > 200 nm) after the reaction with As(V). The filtrates were acidified, diluted (if
necessary)
and
analyzed
using
a
Graphite
Furnace-Atomic
Absorption
Spectrophotometer (GF-AAS) (Hitachi, Z-8200) for total arsenic concentration. The
results are shown in Fig. S2 and the equilibrium time for As(V) adsorption by
T-CNZVI was determined to be 120 min. As(V) sorption capacity of T-CNZVI was
then evaluated. A range of As(V) (0-20 mg L-1) was reacted with T-CNZVI (100 mg
L-1) in the synthetic groundwater. After reaching the adsorption equilibrium, the
T-CNZVI suspensions were filtered and the arsenic concentration in the filtrate was
measured.
As the predominant mechanism of As(V) removal by NZVI is adsorption onto
the NZVI corrosion products (Kanel et al., 2006), the adsorption isotherm for the
As(V) adsorption on T-CNZVI was examined and the plots are shown in Fig. S3. A
Langmuir adsorption isotherm (Eq. 1), was able to describe As(V) adsorption by
T-CNZVI.
qe = qmax αCe / (1+αCe)
Eq. 1
4
where qe is the amount of As sorbed (mg g-1), α (L mg-1) is a parameter related to the
affinity of the sorbent for the sorbate, qmax (mg g-1) is the maximum As sorption
capacity, and Ce is the equilibrium As concentration in the solution (mg L-1). For
T-NZVI, the equation (R2 > 0.992) gives values of qmax (13.9 mg g-1 at pH 7).
Fig. S1 Schematic of column experiments for the transport of SM-NZVI
100
Arsenic removal (%)
80
60
40
20
0
0
100
200
300
400
500
Time (min)
Fig. S2 Kinetics of arsenic removal by T-CNZVI at pH 7 (Fe0=100 mg L-1, As(V)=1
mg L-1).
5
12
0.9
a
0.7
8
Ce/qe
qe(mg/g)
b
0.8
10
6
4
0.6
0.5
0.4
2
As(V) removal by T-CNZVI
Fit curve
0.3
0
0.2
0
2
4
6
8
10
0
2
4
Ce (mg/L)
6
8
10
Ce (mg/L)
Fig. S3 Adsorption isotherm plots (a) and Langmuir adsorption plots (b) for the
adsorption of As(V) on T-CNZVI at pH 7 (Fe0=100 mg L-1).
30
20
10
a2
a3
P-CNZVI mass ratio (%)
-1
HA=0 mg L , Sand
HA=10 mg L-1, Sand
HA=0 mg L-1, Soil
HA=10 mg L-1, Soil
P-CNZVI mass ratio (%)
a1
40
P-CNZVI mass ratio (%)
P-CNZVI mass ratio (%)
50
a4
0
9
12
15
3
6
9
12
15
b2
HA=0 mg L-1, Sand
HA=10 mg L-1, Sand
HA=0 mg L-1, Soil
HA=10 mg L-1, Soil
30
20
10
6
9
12
15
3
Column section (cm)
S-CNZVI mass ratio (%)
b1
40
3
Column section (cm)
S-CNZVI mass ratio (%)
S-CNZVI mass ratio (%)
6
Column section (cm)
b3
6
9
12
15
Column section (cm)
S-CNZVI mass ratio (%)
3
50
b4
0
9
12
15
3
HA=0 mg L-1, Sand
HA=10 mg L-1, Sand
HA=0 mg L-1, Soil
HA=10 mg L-1, Soil
30
20
10
9
12
15
3
c2
6
9
12
15
3
Column section (cm)
T-CNZVI mass ratio (%)
c1
40
6
Column section (cm)
T-CNZVI mass ratio (%)
T-CNZVI mass ratio (%)
6
Column section (cm)
c3
6
9
12
15
Column section (cm)
T-CNZVI mass ratio (%)
3
50
c4
0
3
6
9
12
Column section (cm)
15
3
6
9
12
15
Column section (cm)
3
6
9
12
Column section (cm)
15
3
6
9
12
Column section (cm)
Fig. S4 Distribution of (a) P-CNZVI; (b) S-CNZVI and (c) T-CNZVI along the length
of column at the end of injection: (1) DI water system with 100 mg L-1 of Fe0; (2)
Synthetic groundwater system with 100 mg L-1 Fe0; (3) DI water system with 1 g L-1
of Fe0 and (4) Synthetic groundwater system with 1 mg L-1 Fe0. Note: Column
sectioning is from the inlet to the outlet. In X-axis, “3” represents the column section
of “0-3 cm” and “6” represents the column section of “3-6 cm”, etc.
6
15
500
600
-1
HA=0 mg L (DI)
HA=10 mg L-1 (DI)
HA=0 mg L (GW)
HA=10 mg L-1 (GW)
Radius (nm)
400
Radius (nm)
-1
300
500
400
200
a
100
b
300
0
10
20
30
40
50
60
0
Time (min)
10
20
30
40
50
60
Time (min)
Fig. S5 Aggregation of P-CNZVI in DI water and synthetic groundwater (GW) in the
absence and presence of HA. (a) Fe0=100 mg L-1; (b) Fe0=1 g L-1
7
DI
0
HA
GW
GW+HA
GW
GW+HA
Zeta potential (mV)
-10
-20
-30
-40
X Data
-50
a
Zeta potential (mV)
0
DI
HA
-5
-10
-15
Zeta potential (mV)
0
b
-5
-10
-15
c
-20
Fig. S6 Zeta potential at pH 7 of (a) P-CNZVI, (b) T-CNZVI and (c) S-CNZVI in DI
water and synthetic groundwater (GW) in the absence and presence of HA. Error bars
represent the standard deviations of duplicate experiments
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Fig. S7 TEM images of P-CNZVI in the presence of HA (10 mg L-1): (a)
P-CNZVI=100 mg L-1; (b) P-CNZVI=1 g L-1
300
500
a
T-CNZVI (Fe0=100 mg L-1)
c
S-CNZVI (Fe0=100 mg L-1)
250
Radius (nm)
Radius (nm)
450
200
150
HA=0 mg L-1 (DI)
HA=0 mg L-1 (GW)
HA=10 mg L-1 (DI)
HA=10 mg L-1 (GW)
100
50
c
400
350
0
300
0
10
20
30
40
50
60
0
10
20
30
Time (min)
600
700
0
T-CNZVI (Fe =1 g L )
0
60
-1
S-CNZVI (Fe =1 g L )
600
Radius (nm)
500
Radius (nm)
50
d
b
-1
40
Time (min)
400
300
500
400
200
300
0
10
20
30
40
50
0
60
10
20
30
40
50
60
Time (min)
Time (min)
Fig. S8 Aggregation of (a, b) T-CNZVI and (c, d) S-CNZVI in DI water and synthetic
groundwater (GW) in the absence and presence of HA.
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Table S1 Three types of surface stabilizers for modification to NZVI
Surface-Modified
NZVI
Category of
Surface Stabilizer
Molecular
Structure of
Stabilizer
Stabilization
Mechanism
P-CNZVI
PAA
(Polyelectrolytes)1
Electrosteric
T-CNZVI
Tween-20
(Non-ionic
Surfactant)2
Steric
S-CNZVI
Starch
(Hydrophilic
biopolymers)3
Steric
1 Hydutsky
et al., 2007
Kanel et al., 2007
3 He and Zhao, 2005
2
References
(1) Hydutsky, B. W., Mack, E. J., Beckerman, B. B., Skluzacek, J. M., Mallouk, T. E.,
2007. Optimization of nano- and microiron transport through sand columns using
polyelectrolyte mixtures. Environmental Science & Technology 41, 6418–6424.
(2) Kanel, S. R., Nepal, D., Manning, B., Choi, H., 2007. Transport of
surface-modified iron nanoparticle in porous media and application to arsenic(III)
remediation. Journal of Nanoparticle Research 9, 725–735.
(3) He, F., Zhao, D., 2005. Preparation and characterization of a new class of
starch-stabilized bimetallic nanoparticles for degradation of chlorinated hydrocarbons
in water. Environmental Science & Technology 39, 3314–3320.
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