Supporting Information
Mineral-Coated Polymer Membranes with Superhydrophilicity and
Underwater Superoleophobicity for Effective Oil/Water Separation
Peng-Cheng Chen and Zhi-Kang Xu*
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of
Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, P. R. China
E-mail: [email protected]; Fax: + 86-571-87951592.
300 nm
1 m
Figure S1 SEM image of the PAA-grafted microporous polypropylene membrane. Inset is an
image with high magnification.
24000
C
Mineral-Coated
21000
18000
Ca
15000
O Na
12000
Pt
Ca
9000
PAA-Grafted
6000
3000
Pt
O
0
0
100
200
300
400
500
Energy (keV)
Figure S2 EDX spectra of the membranes before and after being mineral-coated. The results
demonstrate that the coating is mainly composed of Ca-based minerals.
1
160
Contact Angle ()
140
120
nascent
100
80
60
40
20
mineral-coated
0
0
30
60
90
120
150
180
210
240
Time (s)
Figure S3 Water contact angles of the nascent and mineral-coated membranes. The mineralcoated membranes are superhydrophilic due to the intrisic hydrophilicity of CaCO3
nanoparticles.
Figure S4 Photographs demonstrating the separation of free oil/water mixture with the
mineral-coated membrane (left image) or the nascent membrane (right image). The oil phase
(1,2-dichloroethane) is dyed with Sudan Blue II.
2
cross-section
bottom surface
14
14
12
12
12
10
10
10
8
6
4
8
6
4
2
2
0
0
0
200
400
600
800
1000
Percentage (%)
14
Percentage (%)
Percentage (%)
upper surface
8
6
4
2
0
0
Pore Size (nm)
200
400
600
800
1000
200
Pore Size (nm)
400
600
800
1000
Pore Size (nm)
Figure S5 Distribution of the pore size in the mineral-coated membranes. The pore size is
statistically obtained from SEM images. Most pores (>90%) locate in the size range of 200750 nm.
12
Intensity (%)
10
before filtration
8
6
4
2
0
10
100
1000
10000
Size (nm)
30
Intensity (%)
25
after filtration
20
15
10
5
0
1
10
100
1000
10000
Size (nm)
Figure S6 Size distribution of the oil droplets in feed emulsion (diesel-in-water, 1:10 v:v) and
corresponding filtrate. The droplet size ranges from 140 nm to 5.56 m. After filtration, no
droplets were observed in this range, suggesting high oil rejection ratio. The sharp peak (~10
nm) appearing in the data of filtrate is an unavoidable error signal during DLS testing for a
pure liquid1,2.
3
12000
2
Water Flux (L/m h)
14000
10000
O/W free mixture 1:10
O/W emulsion 1:10
O/W emulsion 1:100
O/W emulsion 1:1000
8000
6000
4000
2000
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Transmembrane Pressure (atm)
Figure S7 Dependence of water flux on trans-membrane pressure for diesel-in-water
emulsions or free diesel/water mixtures with different oil/water ratios (v/v). The oil rejection
ratio is >99%.
Calculation of the theoretical oil breakthrough pressure
For an underwater oil droplet in “Cassie-Baxter” state on the membrane surface, equation
(1) can be used to describe the critical force balance between the capillary resistance and the
pressure Pcritical on the droplet3:
Pcritical  (interfacial area)   OW  (contact line length)  cos
(1)
Here OW is the oil/water interfacial tension and  is the underwater oil contact angle on flat
mineral coating surface (Figure 3b). When the pressure is below Pcritical, oil can not penetrate
through the membrane. Since the membrane pore shape is irregular, we assume that the
interfacial area between oil and water equals to a rectangle with length L and width d (L>d). d
corresponds to the distance between two adjacent geometric peaks, which is considered as the
pore size in our work. Then the equation (1) can be described as:
Pcritical  L  d   OW  2L  cos 
Pbreakthrough  Pcritical 
2 OW cos 
d
(2)
(3)
The oil/water interfacial force OW is measured by pendant drop method4. The pore size d is
statistically obtained from SEM images. Based on equation (3), the theoretical breakthrough
pressure can be calculated (Table S1).
4
Table S1 The measured and theoretical value of breakthrough pressure for different oils
Oil/water
interfacial force
[mN/m]
Theoretical
breakthrough
pressure [kPa]
Experimental
breakthrough
pressure [kPa]
dichloroethane
27.94±0.30
71.6-269
151.7±5.8
hexadecane
51.43±0.72
129.8-487
205.0±13.2
50.44±1.63
128.3-481
210.0±10.0
gasoline
29.95±0.22
73.8-277
142.7±2.5
diesel
30.32±2.08
76.0-285
203.3±12.6
Oils
petroleum ether
Membrane pore
size range (nm)
200-750
Reference
1. Zhang, W. B. et al. Superhydrophobic and superoleophilic PVDF membranes for effective
separation of water-in-oil emulsions with high flux. Adv. Mater. 25, 2071-2076 (2013).
2. Shi, Z. et al. Ultrafast separation of emulsified oil/water mixtures by ultrathin free-Standing
single-walled carbon nanotube network films. Adv. Mater. doi:10.1002/adma.201204873
(2013).
3. Kwon, G. et al. On-demand separation of oil-water mixtures. Adv. Mater. 24, 3666-3671
(2012).
4. Morita, A. T., Carastan, D. J. & Demarquette, N. R. Influence of drop volume on surface
tension evaluated using the pendant drop method. Colloid Polym. Sci. 280, 857-864 (2002).
5