Supplementary Data - Springer Static Content Server

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Journal of Nanoparticle Research
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Supplementary Material
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Facilitated transport of titanium dioxide nanoparticles by humic
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substances in saturated porous media under acidic conditions
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Ruichang Zhang a, c, Haibo Zhang b, Chen Tu b, Xuefeng Hu b, Lianzhen Li b,
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Yongming Luo a, b, *
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10
a
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Science, Chinese Academy of Sciences, Nanjing 210008, China
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b
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Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai
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264003, China
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c
Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil
Key Laboratory of Coastal Environmental Processes and Ecological Remediation,
University of Chinese Academy of Sciences
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17
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*Corresponding author. Tel./fax: +86-535-2109 007. E-mail: [email protected] (Luo
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YM).
1
1500
Intensity (Counts)
Anatase
1000
500
0
10
20
30
40
60
70
80
2 
21
22
50
Fig. S1 XRD pattern of TiO2 NPS in the present study
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2
60
TiO2 NPs
Zeta Potential (mV)
40
HS
Quartz
20
0
-20
-40
-60
2
3
4
5
7
8
pH
24
25
6
Fig. S2 Zeta potentials of bare TiO2 NPs, HS and quartz in deionized water
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2937
937
1106
1036
1387
1631
2874
3455
4000
3500
3000
2500
2000
1500
1000
500
-1
26
27
Wave number (cm )
Fig. S3 FTIR spectrum of HS in this study
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28
Table S1 The assignmen of absorption bands in FTIR spectrum of HS
Wavenumber (cm-1)
Assignment
3455
2937
2874
1631
1387
1106
1036
937
OH stretching vibration
Aliphatic CH2 stretching vibration
CH2 symmetric stretching vibration
Aromatic C=C stretching vibration
COO symmetric stretching vibration
Aliphatic C-OH stretching vibration
C-O-C stretching
Aliphatic C-C vibration
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5
1.0
y=0.039x+0.006
2
R =0.999
0.8
Abs
0.6
y=0.011x+0.003
2
R =0.999
0.4
TiO2 NPs at 343 nm
0.2
HS at 228 nm
0.0
0
20
40
60
80
-1
30
31
Concentration (mg L )
Fig. S4 Calibration curves for UV light absorbance of TiO2 NPs and HS
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Table S2 Physiochemical parameters of transport experiments of TiO2 NPs.
Background condition
pH
Na+
(mmol L-1)
0 mg L-1 HS
0.5 mg L-1 HS
1 mg L-1 HS
5 mg L-1 HS
10 mg L-1 HS
pH 4.0
pH 5.0
pH 6.0
1 mmol L-1 NaCl
10 mmol L-1 NaCl
100 mmol L-1 NaCl
250 mmol L-1 NaCl
0.5 mmol L-1 CaCl2
1 mmol L-1 CaCl2
2 mmol L-1 CaCl2
5 mmol L-1 CaCl2
4.0
4.0
4.0
4.0
4.0
4.0
5.0
6.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
1
10
100
250
Ca2+
(mmol L-1)
HS
(mg L-1)
Porosity
Flow velocity
(cm min-1)
0.5
1
2
5
0
0.5
1
5
10
0.5
0.5
0.5
5
5
5
5
5
5
5
5
0.45
0.42
0.47
0.46
0.45
0.42
0.45
0.43
0.43
0.45
0.43
0.42
0.44
0.42
0.42
0.46
0.36
0.36
0.36
0.38
0.37
0.36
0.36
0.36
0.36
0.37
0.35
0.37
0.37
0.37
0.36
0.36
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Adsorption of HS onto TiO2 NPs
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To quantitatively evaluate the effects of HS on the stability and transport behavior of
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TiO2 NPs observed in column experiments, adsorption studies were conducted to
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determine the amount of HS adsorbed onto TiO2 NPs in conditions identical to those
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used in transport experiments. The suspended particles in TiO2 NPs suspension
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prepared above were pelleted by sequential centrifugation (Chen et al. 2012). Briefly,
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10 mL suspensions were added to Teflon centrifuge tubes and centrifuged for 20
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minutes at 9,400  g (3K 15, Sigma Laborzentrifugen). Then 8 mL of supernatant
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were carefully withdrawn from each tube and transferred into another clean centrifuge
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tube for centrifugation. This procedure was repeated until the TiO2 NPs was
43
completely removed from the solution. The HS concentration in the supernatant was
44
determined using a spectrophotometer (GENESYS 10S UV-Vis, Thermo Scientific)
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at 228 nm. The adsorbed HS were then determined by the difference between the
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initial and final HS concentrations in the aqueous phase. Control experiments with
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TiO2 NPs-free solutions showed no variations in HS concentrations before and after
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the centrifugation processes in the range of HS concentrations tested.
8
pH 4.0
pH 5.0
pH 6.0
a
2
Adsorbed amount (mg/m )
0.8
0.6
0.4
0.2
0.0
1
10
-1
HS (mg L )
b
2
Adsorbed amount (mg/m )
0.35
0.30
0.25
0.20
0.15
0.10
1
10
100
-1
NaCl (mmol L )
49
50
Fig. S5 Amounts of HS a dsorbedonto the TiO2 NPs surface as a function of pH and
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HS concentration (0.1 mmol L-1 NaCl) (a), and NaCl concentration (5 mg L-1 HS and
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pH 5.0) (b) in the TiO2 suspension
9
3413
2928
1625
1042
1389 1118
514
HS coated TiO2 NPs
TiO2 NPs
4000
3500
3000
2500
2000
1500
1000
500
-1
53
Wave number (cm )
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Fig. S6 FTIR spectra of TiO2 NPs and HS coated TiO2 NPs. Peaks at 2928 cm-1 for
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aliphatic CH2, 1118 cm-1 for aliphatic C-OH, and 1042 cm-1 for C-O-C in FTIR
56
spectra of HS coated TiO2 NPs could reasonably inferred the adsorption of HS onto
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the surface of TiO2 NPs.
10
58
Particles attachment efficiency
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Using the single collector efficiency model, a dimensionless contact efficiency η0
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could be calculated as follows (Tufenkji and Elimelech 2004),
0  D  I  G
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(S1)
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Where ηD, ηI, and ηG are collector efficiency components for particles transported to
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the collector due to diffusion, interception, and gravity, respectively. Diffusion is
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associated with smaller particles when they undergo Brownian motion due to random
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bombardment by molecules of the suspending medium and as a result come in contact
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with the collector surface. Interception occurs when the moving particles contact with
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the collector grain while traveling along a streamline. Gravitational sedimentation is
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related to the settling of particles on collector grains by the combined effects of the
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buoyant weight of the particle and the fluid drag on the particles (Rahman et al. 2013;
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Yao et al. 1971).
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Single collector contact efficiency can also be calculated using the following equation
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in detail (Tufenkji and Elimelech 2004):
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0  2.4 As1/3 N R 0.081 N Pe 0.715 NvdW 0.052  0.55N R1.675 N A0.125  0.22 N R 0.24 NG1.11 NvdW 0.053
(S2)
Where As is the porosity-dependent parameter of Happel’s model:
2(1  p 5 )
As 
2  3 p  3 p5  2 p6
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(S3)
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Here p is determined according to p  (1   )1/3 , where ε is the porosity of a porous
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medium.
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NR is the aspect radio, which is defined as:
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NR 
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dp
(S4)
dc
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Where dp and dc are the diameter of TiO2 NPs aggregate and quartz packed in column
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respectively.
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NPe is Peclet number, which is described as:
N Pe 
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Ud c
D
(S5)
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Where U is the approach (superficial) velocity of the TiO2 NPs suspension, and D∞ is
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the diffusion coefficient in an infinite medium, which is calculated using:
D 
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kT
6 a p
(S6)
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Here, k is the Boltzmann constant, 1.3805×10-23, T is the temperature in degree of
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Kelvin, 293 K, μ is the absolute viscosity of fluid, and ap is the radius of TiO2 NPs.
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NvdW is the van der Waals number, which is defined as:
A
kT
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N vdW 
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Where A is the Hamaker constant for the interacting system of TiO2 NPs -water-quartz,
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and was assumed to be 1.0×10-20.
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NG is the gravity number obtained by the following equation:
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NG 
2a p 2 (  p   f ) g
9U
(S7)
(S8)
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Where ρp and ρf is the density of TiO2 NPs and fluid respectively, and g is the
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gravitational acceleration, 9.81 m s-2.
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NA is the attraction number, which is calculated using:
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NA 
A
12 a p 2U
12
(S9)
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Essentially, η0 is the probability that a particle will collide with the collector grain
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through one of the three modes of transport (diffusion, interception, and transport),
101
depending on system hydrodynamics, particle size, density, and van der Waal’s forces
102
(Saleh et al. 2008).
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Under conditions relevant to most aquatic systems, the single collector removal
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efficiency η is lower than the single collector contact efficiency η0 due to repulsive
105
colloidal interactions between particles and collector grains (Tufenkji and Elimelech
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2004). The actual single collector removal efficiency is often expressed using eq. S10,
 
107
2d c
ln(Ci / C0 )
3(1   ) L
(S10)
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Here, dc is the average diameter of the collector particles, ε is packed bed porosity, L
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is the length of the column, and C0 and Ci are influent and effluent particle
110
concentration, respectively.
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The attachment efficiency or “sticking coefficient” α in eq. S11 represents the fraction
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of collisions between particles and collectors that result in attachment, i.e., describes
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the ratio between the experimental single collector removal efficiency η and the
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predicted single collector contact efficiency η0.
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
116
13

0
(S11)
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Derjaguin–Landau–Verwey–Overbeek (DLVO) theory
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DLVO theory was applied to evaluate the role of electrostatic and van der Waals
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interactions on the interaction between the nanoparticles and the nanoparticle-quartz
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surfaces.
Total (h)  vdW (h)   dl (h)
121
(S12)
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DLVO interaction energies between TiO2 NPs were calculated assuming
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sphere-sphere geometry by utilizing the following equations (Gregory 1981):
vdW (h)  
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A101a p
12h(1  14h /  )
(S13)
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dl (h)  2 0 r a p p 2 ln 1  exp( h)
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Interaction profiles for nanoparticles and quartz sand particles were developed
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assuming sphere-plate geometry and the following equations were used for
128
calculation (Gregory 1981):
vdW (h)  
129
A102 a p
6h(1  14h /  )
(S14)
(S15)
130


1  exp( h) 
 dl (h)   0 r a p 2 p c ln 
  p 2  c 2  ln 1  exp(2 h) (S16)

1  exp( h) 


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In DLVO interaction energy profiles, positive interaction energy values represent
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repulsive condition whereas negative interaction energy values correspond to
133
attraction.
134
When DLVO interaction energy between TiO2 NPs is calculated, ap is the radius of
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the initial TiO2 NPs, 30 nm, and in the case of the energy between TiO2 NPs and
136
quartz surface, the radius of an equivalent sphere for the nanoparticle aggregates
137
which were measured by DLS has been used as the nanoparticle radius (ap). h denotes
14
138
the (minimum) surface-to-surface separation distance between the spheres (for
139
sphere–sphere geometry) or between a sphere and a plate (for sphere–plate geometry).
140
A characteristic wavelength (λ) of 100 nm was assumed in the calculations.
141
Permittivity of free space (ε0) and dielectric constant (εr) of water are 8.854×10-12 C
142
V-1 m-1 and 81.5 respectively, κ is the inverse Debye length (m-1) which was estimated
143
for each electrolyte solution using eq. S17, and ψp and ψc are the surface potentials of
144
TiO2 NPs and quartz collector (V), respectively. For the calculation of interaction
145
profiles, zeta potentials of TiO2 NPs and quartz were measured under different
146
chemical conditions and these values were used instead of surface potentials. The
147
Hamaker constant for TiO2 NPs–water–TiO2 NPs interaction system (A101) used was
148
3.7×10-20 J (Shih et al. 2012) and for TiO2 NPs–water–quartz system (A102) 1.0×10-20 J
149
was used (Chowdhury et al. 2011).
103 e 2 N A (2 I ) 
 

  0 r kT 
150
1/ 2
?
151
(S17)
152
Where e is the electron charge, 1.60×10-19 C, NA is Avogadro’s constant, 6.02×1023
153
mol-1, and I is the ionic strength of the solution.
15
Interaction Energy (kT)
20
-1
0 mg L
-1
0.5 mg L
-1
1 mg L
-1
5 mg L
-1
10 mg L
a
15
10
5
0
-5
-10
0
10
20
30
40
Separation Distance (nm)
Interaction Energy (kT)
10
5
0
-5
-10
154
pH 4.0
pH 5.0
pH 6.0
b
0
10
20
30
40
Separation Distance (nm)
155
Fig. S7 Calculated DLVO interaction energy between TiO2 NPs (based on primary
156
size) under varying HS concentrations (pH 4.0 and 0.1 mmol L-1 NaCl) (a), and under
157
varying pH (5 mg L-1 HS and 0.1 mmol L-1 NaCl) (b)
16
1.0
0.8
C/C0
0.6
0.4
0.2
0.0
0
1
2
3
158
159
160
4
5
PV
Fig. S8 Breakthrough curve of conservative Br-tracer (0.1 mmol L-1, pH 4.0 and 0.1
mmol L-1 NaCl) in quartz sands.
17
1.0
-1
a
0 mg L
-1
1 mg L
-1
5 mg L
-1
10 mg L
0.8
C/C0
0.6
0.4
0.2
0.0
0
1
2
3
5
PV
1.0
-1
b
0 mg L
-1
1 mg L
-1
5 mg L
-1
10 mg L
0.8
0.6
C/C0
4
0.4
0.2
0.0
0
161
162
163
1
2
3
4
5
PV
Fig. S9 Breakthrough curves for TiO2 NPs under different HS concentrations at pH
5.0 (a) and pH 6.0(b)
18
Interaction Energy (kT)
600
-1
a
0 mg L
-1
0.5 mg L
-1
1 mg L
-1
5 mg L
-1
10 mg L
400
200
0
-200
-400
0
10
20
30
40
Interaction Energy (kT)
Separation Distance (nm)
400
b
pH 4.0
pH 5.0
pH 6.0
200
0
-200
0
164
165
166
167
10
20
30
40
Separation Distance (nm)
Fig. S10 Calculated DLVO interaction energy between TiO2 NPs (based on
aggregated size) and quartz under varying HS concentrations (pH 4.0 and 0.1 mmol
L-1 NaCl) (a), and under varying pH (0.5 mg L-1 HS and 0.1 mmol L-1 NaCl) (b)
19
30
pH 5.0
-1
1 mg L HS
-1
2 mmol L CaCl2
Number (%)
25
20
15
10
5
0
100
168
169
170
171
1000
10000
Hydrodynamic Diameter (nm)
Fig. S11 Representative number-weighted hydrodynamic diameter distribution of the
TiO2 NPs in the influent samples at 0.5 mg L-1 HS, 1 mg L-1 HS and 2 mmol L-1
CaCl2. The solid lines are drawn to provide visual guides
20
172
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173
Chen GX, Liu XY, Su CM (2012) Distinct effects of humic acid on transport and
174
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Chowdhury I, Hong Y, Honda RJ, Walker SL (2011) Mechanisms of TiO2 nanoparticle
177
transport in porous media: Role of solution chemistry, nanoparticle
178
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10.1016/j.jcis.2011.04.111
180
Gregory J (1981) Approximate expressions for retarded Vanderwaals interaction. J
181
Colloid Interf Sci 83:138-145 doi:Doi 10.1016/0021-9797(81)90018-7
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Rahman T, George J, Shipley HJ (2013) Transport of aluminum oxide nanoparticles in
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21
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