Electronic Supplementary Material (ESI) for RSC Advances.
This journal is © The Royal Society of Chemistry 2015
Electronic Supplementary Information
Polyethylenimine/grapefruit peel hybrid biosorbent for
removal of toxic CdTe quantum dots from water
Ying Zhang, Baozhu Hu, Yuming Huang*
The Key Laboratory of Eco-environments in Three Gorges Reservoir Region,
Ministry of Education, College of Chemistry and Chemical Engineering, Southwest
University, Chongqing 400715, China.
1
Adsorption kinetics
Two kinetic models, namely pseudo-first-order (eq 1)1 and pseudo-second-order
(eq 2)2, were used to describe the adsorption behavior.
ln(qeqt) = lnqe  kt
(1)
t/qt = 1/v0 + t/qe
(2)
where qe (mg/g) and qt (mg/g) represent the adsorption capacity at equilibrium and at
time t, k is the pseudo-first-order adsorption rate constant, and v0 is the initial
adsorption rate (mg g1 h1). The regression coefficient values (R2) and related
parameters obtained from pseudo-first-order and pseudo-second-order models are
shown in Table S2.
Adsorption isotherms
The isotherm data were fitted by the Langmuir (eq 3)3 and Freundlich (eq 4)4
isotherms according equations as follows:
1/qe = 1/qmax + (1/qmaxb) (1/Ce)
(3)
log qe = log k + (1/n) log Ce
(4)
where qe (mg/g) and qmax (mg/g) are the equilibrium adsorption capacity and the
maximum adsorption capacity, Ce (mg/L) is the concentration of solution at
equilibrium, b is the constant related to energy of adsorption, k and n are the constants
of Freundlich adsorption. The parameters of the Langmuir and Freundlich models
calculated from the adsorption isotherms are listed in Table S3.
References
1.
M. Najafi, Y. Yousefi, A. A. Rafati, Sep. Purif. Technol., 2012, 85, 193205.
2
2.
L. Wang,; X. L. Wu, W. H. Xu, X. J. Huang, J. H. Liu, A. W. Xu, ACS App. Mater.
3.
Interfaces, 2012, 4, 26862692.
Z. Yu, X. Zhang, Y. Huang, Ind. Eng. Chem. Res., 2013, 52, 11956–11966.
4.
J. Wang, L. Zhao, W. Duan, L. Han, Y. Chen, Ind. Eng. Chem. Res., 2012, 51, 1365513662.
Table S1. Nitrogen content of GP and PEI-GP by the XPS analysis
Biosorbent
Nitrogen content (at. %)
GP
4.29
PEI-GP-0.8
7.13
Table S2. The relevant parameters of the pseudo-first-order and the pseudo-secondorder kinetics
Adsorbents
qe,exp
Pseudo-first-order
Pseudo-second-order
(mg g-1)
qe,cal
k
(mg g-1)
(h-1)
R2
qe,cal
v0
(mg g-1)
(mg g-1 h-1)
R2
PEI-GP-0.2
173.24
85.51
0.2234
0.8714
177.31
234.19
0.9991
PEI-GP-0.4
280.83
121.58
0.1634
0.8973
288.18
336.70
0.9996
PEI-GP-0.6
377.07
271.66
0.2632
0.8578
400.00
275.48
0.9971
PEI-GP-0.8
431.84
392.06
0.2338
0.9844
478.47
195.70
0.9961
PEI-GP-1.0
356.03
251.72
0.2448
0.9766
383.14
243.31
0.9970
3
Table S3. Freundlich isotherm and langmuir isotherm parameters for adsorption of
CdTe DQs onto PEI-GP
Adsorbents
Langmuir
b
Freundlich
qmax (mg/g)
R2
n
k
R2
(L/mg)
PEI-GP-0.2
-0.0023
-62.933
0.3998
0.552
0.006
0.9542
PEI-GP-0.4
-0.0004
-342.466
0.3409
0.707
0.104
0.9555
PEI-GP-0.6
-0.0001
-1080.66
0.1722
0.806
0.374
0.9396
PEI-GP-0.8
-0.0001
-1078.76
0.2388
0.790
0.403
0.9434
PEI-GP-1.0
-0.00009
-1546.42
0.2138
0.835
0.600
0.9713
Table S4. Concentrations of K+, Na+, Ca2+ and Mg2+ in the tested water samples
K+
Na+
Ca2+
Mg2+
(mg/L)
(mg/L)
(mg/L)
(mg/L)
ultra pure water
not detected
not detected
not detected
not detected
tap water
2.30
11.9
56.0
12.2
wastewater
12.2
59.0
74.7
13.1
Water sample
4
GP
PEI-GP-0.2
PEI-GP-0.4
PEI-GP-0.6
PEI-GP-0.8
PEI-GP-1.0
Figure S1. SEM images of GP and PEI-GP with different PEI content
5
20
CdTe QDs
PEI-GP-0.8
Zeta potential (mV)
10
0
-10
-20
-30
-40
2
4
6
8
10
pH
Figure S2. The effect of solution pH on the zeta potential of CdTe QDs and PEI-GP0.8 adsorbent
Figure S3. Images of CdTe QDs under different solution pH ranging from 2 to 11
(from left to right: 2, 3, 4, 5, 6, 7, 8, 8.4, 9, 10, and 11)
6
Statistics Graph (1 measurements)
Statistics Graph (1 measurements)
40
30
Volume (%)
Volume (%)
15
10
5
20
10
0
0
1
10
100
1000
10000
1
10
Size (d.nm)
Mean withpH=2
Max-Min error bar
Mean withpH=3
Max-Min error bar
40
20
30
20
10000
1000
10000
1000
10000
15
10
10
5
0
0
1
10
100
1000
10000
1
10
100
Size (d.nm)
Size (d.nm)
pH=4
Mean with
Max-Min error bar
Mean withpH=5
Max-Min error bar
Statistics Graph (1 measurements)
Statistics Graph (1 measurements)
40
40
30
30
Volume (%)
Volume (%)
1000
Statistics Graph (1 measurements)
25
Volume (%)
Volume (%)
Statistics Graph (1 measurements)
50
20
10
20
10
0
0
1
10
100
1000
10000
1
10
Size (d.nm)
Mean withpH=6
Max-Min error bar
Mean withpH=7
Max-Min error bar
Statistics Graph (1 measurements)
40
30
30
Volume (%)
40
20
10
0
20
10
0
1
10
100
1000
10000
1
10
100
Size (d.nm)
Size (d.nm)
Mean withpH=8
Max-Min error bar
pH=8.4
Mean with
Max-Min error bar
Statistics Graph (1 measurements)
1000
10000
1000
10000
Statistics Graph (1 measurements)
40
25
30
Volume (%)
Volume (%)
100
Size (d.nm)
Statistics Graph (1 measurements)
Volume (%)
100
Size (d.nm)
20
10
20
15
10
5
0
0
1
10
100
1000
10000
1
10
100
Size (d.nm)
Size (d.nm)
pH=9
Mean with
Max-Min error bar
Mean withpH=10
Max-Min error bar
7
Statistics Graph (1 measurements)
Volume (%)
50
40
30
20
10
0
1
10
100
1000
10000
Size (d.nm)
pH=11
Mean with
Max-Min error bar
Figure S4. Hydrodynamic diameter distributions of CdTe QDs under different solution pH
ranging from 2 to 11.
8
1.5
2.4
0.5
-1.0
1.0
0.8
1.0
1.2
LogCe
1.4
1.6
1.8
2.8
PEI-GP-0.6
1.6
1.8
2.0
2.2
LogCe
2.4
2.6
2.8
2.4
Logqe
2.0
1.8
1.6
1.6
1.8
2.0
2.2
LogCe
Stage 2
y=0.31694 x+1.91792
R2=0.99728
2.2
2.0
1.8
Stage 1
y=1.53375 x-0.9862
R2=0.99572
1.4
PEI-GP-0.8
2.6
Stage 2
y=0.26768 x+1.96298
R2=0.99069
2.2
Logqe
Stage 1
y=1.8407 x-1.78694
R2=0.99876
3.0
2.4
1.2
1.4
1.6
1.2
2.8
2.6
1.8
1.4
Stage 1
y=2.37529 x-2.03148
R2=0.99969
0.6
Stage 2
y=0.51672 x+1.23115
R2=0.99414
2.0
0.0
-0.5
PEI-GP-0.4
2.2
Stage 2
y=0.61893 x+0.4045
R2=0.99838
Logqe
Logqe
1.0
2.6
PEI-GP-0.2
Stage 1
y=1.48421 x-0.81979
R2=0.99107
1.6
1.4
2.4
2.6
2.8
1.4
1.6
1.8
2.0
2.2
LogCe
2.4
2.6
2.8
3.0
2.8
PEI-GP-1.0
2.6
Logqe
2.4
Stage 2
y=0.6623 x+1.06653
R2=0.99022
2.2
2.0
Stage 1
y=1.5348 x-0.83786
R2=0.99944
1.8
1.6
1.4
1.4
1.6
1.8
2.0
2.2
LogCe
2.4
2.6
2.8
Figure S5. The absorption isotherm model of CdTe QDs onto PEI-GP adsorbents by
Freundlich model fitting
9
Adsorption capacity (mg/g)
PEI-GP-0.2
PEI-GP-0.4
PEI-GP-0.6
PEI-GP-0.8
PEI-GP-1.0
800
600
400
200
0
20
40
60
80
100
NaCl concentration (mM)
Figure S6. Effect of NaCl concentration on the adsorption of CdTe QDs onto PEI-GP
IRLS (a.u.)
2000
without NaCl
10 mMNaCl
30 mMNaCl
100 mMNaCl
1500
1000
500
450
500
550
Wavelength (nm)
600
Figure S7. RLS spectra of CdTe QDs in the presence of various concentrations of
NaCl.
10
QDs (A)
Statistics Graph (1 measurements)
Volume (%)
40
30
20
10
0
1
10
100
1000
10000
Size (d.nm)
100 mM NaCl (B)
Statistics
Graph
(1Max-Min
measurements)
Mean
with
error bar
Volume (%)
40
30
20
10
0
1
10
100
1000
10000
Size (d.nm)
1 mM CaCl2 (C)
Statistics
Graph
(1 measurements)
Mean
with Max-Min
error bar
Volume (%)
50
40
30
20
10
0
1
10
100
1000
10000
Size (d.nm)
Mean with Max-Min error bar
Figure S8. Hydrodynamic diameter distribution of CdTe QDs (A) in the presence of
100
mM
NaCl
(B)
and
11
1
mM
CaCl2
(C).
Adsorption capacity (mg/g)
600
PEI-GP-0.2
PEI-GP-0.4
PEI-GP-0.6
PEI-GP-0.8
PEI-GP-1.0
500
400
300
200
0
5
10
15
HA concentration (mg/L)
20
Figure S9. Effect of HA concentration on the adsorption of CdTe QDs onto PEI-GP.
1.0
Pure water
Tap water
Wastewater
0.8
C/C0
0.6
0.4
0.2
0.0
0
500
1000 1500 2000 2500 3000 3500
BV
Figure S10. Breakthrough curves for PEI-GP mini-column for biosorption of CdTe
QDs in pure water, tap water and wastewater.
12