ph-controllable on-demand oil/water separation on the switchable superhydrophobic/superhydrophilic and underwater low adhesive

Transcription

1 ph-controllable on-demand oil/water separation on the switchable superhydrophobic/superhydrophilic and underwater low adhesive superoleophobic copper mesh film Zhongjun Cheng, Jingwen Wang, *, Hua Lai, Ying Du, Rui Hou, Chong Li, Naiqing Zhang and Kening Sun*, Natural Science Research Center, Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin, Heilongjiang , P. R. China. Heilongjiang Science and Technology Information Research Institute, Harbin, Heilongjiang ,P.R. China. XRD X-ray diffraction (XRD) was carried out using a D8 Advance (Bruker) X-ray diffractometer with Cu Ka radiation (λ = nm), the test range of 2θ is from 10 to 70. * * Theta (degree)

2 Figure S1. XRD of the copper mesh substrate after immersion in the NaOH and (NH 4 ) 2 S 2 O 8 solution. From Figure S1, it can be seen that all the indexed diffraction peaks except those marked with stars (attributed to the copper substrate) can be indexed to the orthorhombic phase of Cu(OH) 2. a) b) 1.5 µm 5 µm Figure S2. (a) SEM image of the Cu(OH) 2 nanorods at high magnification; (b) cross-sectional view of Cu(OH) 2 nanorods. a) b) c) t = 60 s 50 µm t = 120 s 50 µm t = 180 s 50 µm d) e) f) t = 240 s 50 µm t = 300 s 100 µm t = 600 s 100 µm g) h) i) t = 900 s 100 µm t = 1200 s 100 µm t = 1800 s 50 µm

3 Figure S3. SEM images of copper mesh substrates after immersion in the NaOH and (NH 4 ) 2 S 2 O 8 solution for different times. From these images, it can be seen that as the immersion time is increased, the length of the Cu(OH) 2 nanorods is increased and the mesh pore size is decreased. 160 Contact angle ( o ) Time (s) Figure S4. Dependence of water contact angle on the immersion time for the fabrication of Cu(OH) 2 nanorods on the copper substrate (all the substrates were modified with HS(CH 2 ) 9 CH 3 ). Form the figure, it can be seen that when the immersion time is larger than 3 min, the obtained film would has the superhydrophobicity. Thus, the time 3 min was chosen for the fabrication of nanostructures on the substrates

4 Au4f a) b) Intensity (a. u.) Cu2p O1s C1s S2p Intensity (a. u.) Binding energy (ev) Binding energy (ev) Figure S5. (a)xps survey of the surface, (b) high-solution C1s XPS spectra of the surface (prepared with X COOH = 0.6). The peak at ev is ascribed to C-C/C-H, the peak at about ev is ascribed to COOH, the peak at about ev is ascribed to C-O. Ratio (I C-O /I C-C/C-H ) 0.10 Experimental result Theoretical result X COOH Figure S6. The relationship between the ratio of the C1s intensity of the carboxylic acid groups to that of alkyl carbons and the X COOH in the modified solutions. From Figure S6, it can be seen that the C1s peak intensity of carboxylic acid groups comparing with that of the alkyl carbons is increased as the X COOH is increased (X COOH is the mole fraction of HS(CH 2 ) 10 COOH the in the modified solution),

5 meanwhile, the experimental results approximate the theoretical results, indicating that the modification method used in the paper is effective and the surface composition can be controlled by changing the composition of the modified solution Contact angle ( O ) on flat copper mesh with ph = 7 on flat copper mesh with ph = 12 on rough copper mesh with ph = 7 on rough copper mesh with ph = X COOH Figure S7. Dependence of the contact angles on the X COOH (mole fraction of HS(CH 2 ) 10 COOH in the modified solution). It can be seen that the transition from the superhydrophobicity to the superhydrophilicity can be realized on the film prepared with X COOH = 0.6. From Figure S7, it can be see that a solution of X COOH = 0.6 provides the best wettability transition. In this case, the film can transit from the super-hydrophobicity to the super-hydrophilicity. Compared with the rough copper mesh film, the changes of the contact angles responsive to water ph are limited on the flat copper mesh films prepared with different X COOH, further confirming the enhanced effect of the Cu(OH) 2 nanostructures. Because the surface prepared with X COOH = 0.6 has the best ph-responsivity, it was chosen for the following research about the oil/water separation.

6 Figure S8. A 4 µl water droplet (ph = 7) can roll on the film with a sliding angle of about 3, indicating that the film is low adhesive to water. Add water Figure S9. After wetting by basic water, water would permeate the film as more water is added on the film. 160 ph = 7 Water contact angle ( o ) ph = Cycle Figure S10. The water contact angles in air can be repeated by changing the water ph alternately. After being rinsed with pure water and dried with N 2, the basic-exposed film would return to its initial superhydrophobic state for neutral water, indicating that the film remains the ph-responsivity. The reversible transition between the two states can be repeated several times without any loss of the reversibility. Moreover, such

7 responsivity can be remained after at least one month without special protection, indicating that the film has a good chemical stability water in air Contact angle ( o ) ph Figure S11. Dependence of water contact angle on water ph. In addition to the reversibility, we also investigated the relationship between the contact angles and the water ph. It can be seen that for acidic water and neutral water, the film shows superhydrophobicity. When the water ph is further increased, the contact angles would be decreased, and when the ph is about 12, the film shows superhydrophilicity. a) Oil in air b) Oil in water Figure S12. (a) Shape of an oil droplet on the as-prepared copper mesh film, it can be the film is superoleophilic in air. (b) Shape of an oil droplet on the as-prepared copper mesh film in water (ph =7), it can be the film is superoleophilic in neutral water.

8 160 ph = 12 Oil contact angle ( o ) ph = Cycle Figure S13. The oil contact angles in water can be repeated by changing the water ph alternately. Similar as the variation of water contact angles in air, the oil contact angle in water can also be reversible changed by changing the water ph. As shown in Figure S13, after being rinsed with pure water and dried with N 2, the basic-exposed film would return to the superoleophilic state in neutral water. The reversible transition between the superoleophilic and superoleophobic states can be repeated several times without any loss of the reversibility.

9 oil in water Contact angle ( o ) ph Figure S14. Dependence of oil contact angle on the water ph. We also investigated the dependence of oil contact angles on the water ph. Because the film in highly acidic water is unstable, here, solutions with ph from 4 to 14 were used. From Figure S14, we can find that in acidic and neutral water, the film shows underwater superoleophilicity. As the water ph is further increased, the oil contact angled would be increased, and the water ph is higher than 11, the film would show superphobicity. Diesel oil Silicon oil Hexane Gasoline Petroleum ether Figure S 15. Shapes of oil droplet contact with the film in water with ph 12.

10 a) b) Figure S16. Photographs of hexane-in-water emulsion prepared with surfactant before (b) and after separation (c), respectively. Herein, the emulsion prepared with surfactant was also used to test the separating ability of the as-prepared film. Take the toluene-in-water as an example, tween 80 (HLB = 15, an emulsifier of the oil-in-water type; 0.15 g) was added into 30 ml of water, and then 1 ml of toluene was added. The mixture was stirred for 3 h. From the two images, it can be seen that after separation, the milky white emulsion becomes clear, indicating that the emulsion prepared with surfactant can also be separated with the as-prepared film. a) b) CA = 93 CA = 130 Figure S17. (a) Shape of a water droplet on the flat copper surface in ari (prepared with X COOH = 0.6); (b) shape of an oil droplet (1, 2-dichloroethane) on the flat copper surface in basic water (ph = 12).

11 60 50 Contact angle ( o ) ph Figure S18. Dependence of contact angles on water ph on the flat surface modified by single HS(CH 2 ) 10 COOH molecule.