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Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method
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Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method Chuan Du, Jiadao Wang ∗ , Zhifu Chen, Darong Chen State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, PR China
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Article history: Received 22 April 2014 Received in revised form 28 May 2014 Accepted 28 May 2014 Available online xxx Keywords: Superhydrophobic Superoleophilic Polytetrafluoroethylene Filter paper Oil–water separation
a b s t r a c t A method for manufacturing durable superhydrophobic and superoleophilic filter paper for oil–water separation was developed via colloidal deposition. A porous film composed of PTFE nanoparticles was formed on filter paper, which was superhydrophobic with a water contact angle of 155.5◦ and superoleophilic with an oil contact angle of 0◦ . The obtained filter paper could separate a series of oil–water mixtures effectively with high separation efficiencies over 99%. Besides, the as-prepared filter paper kept stable superhydrophobicity and high separation efficiency even after 30 cycle times and could also work well under harsh environmental conditions like strong acidic or alkaline solutions, high temperature and ultraviolet irradiation. Compared with other approaches for fabricating oil–water materials, this approach is able to fabricate full-scale durable and practical oil–water materials easily and economically. The as-prepared filter paper is a promising candidate for oil–water separation. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Oil–water separation is becoming an important worldwide problem in the area of industrial production, environment protection and energy conservation [1–5]. Many industries such as crude oil production and refinery, petrochemical and metal finishing, textile and leather processing, and food processing and lubricant create large amount of oily wastewater inevitably which has become the most common pollutant [6–9]. Besides, frequent accidents of marine oil spill bring severe pollution and energy waste [10,11]. Except for ensuring safety of navigation to prevent the accidents, treatment of the spilled oil is much more challenging [12,13]. Actually, both of the treatment of oily wastewater and spilled oil involve in the problem of oil–water separation. A lot of technologies for the separation of oil and water mixtures have been developed during the past decades, such as ultrasonic separation, air flotation, electric field separation, biological treatment and membrane filtration, but the limitation of low separation efficiency, the generation of second pollutants, the strict requirements of oil–water mixtures, the membrane fouling problems or the high cost have always caused difficulty in practical applications [14]. In recent years, the development of superhydrophobic and superoleophilic materials for adsorption of oil from water and
∗ Corresponding author. Tel.: +86 010 62796458; fax: +86 010 62781379. E-mail address: [email protected] (J. Wang).
separation of oil and water has attracted much attention due to their high separation efficiency and wide applicability. The superhydrophobic property makes materials repel water completely, while the superoleophilic property lets oil permeate freely. Therefore, superhydrophobic and superoleophilic materials can separate oil-water efficiently [14]. A variety of methods have been developed to fabricate superhydrophobic and superoleophilic materials for separation of water and oil, including wet chemical process [15], electrochemical deposition [16], electrochemical etching [17], vapor phase deposition [18,19], sol–gel process [20,21], selfassembly process [22,23], electrospinning techniques [24,25], and others [26–30]. Generally, all these methods can be divided into two kinds: (1) chemical modification of a micro/nanostructured surface with low-surface-energy materials and (2) construction of micro/nanostructures on low-surface-energy materials. For example, Feng et al. [1] first reported a polytetrafluoroethylene (PTFE) film on a stainless steel mesh with both superhydrophobicity and superoleophilicity by a spray and dry method in 2004, which successfully separated the mixture of diesel oil and water. Zhu et al. [31] fabricated superhydrophobic and superoleophilic sponges that could effectively absorb oil from water with a simple solutionimmerse method. Zhou et al. [32] developed a robust and durable superhydrophobic cotton fabric for oil–water separation. Wang and co-workers created a thermoplastic polyurethane mat with beadon-string morphology by electrospinning, which can separate oil and water mixtures after further treated by hydrophobic nanosilica. Although many methods have been created for the fabrication
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Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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Fig. 1. Images of water wettability on the clean and entirely oil-wetted as-prepared filter paper: (a) water droplets sitting on the as-prepared filter paper, (b) a jet of water bouncing off the as-prepared filter paper, (c) the pristine filter paper immersed in water by an external force, (d) WCA measurement on the as-prepared filter paper, (e) water droplets sitting on the oil contaminated as-prepared filter paper, (f) a jet of water bouncing off the oil contaminated as-prepared filter paper, (g) the as-prepared filter paper immersed in water by an external force, and (h) the rolling state of water droplet and the measurement of SA.
of superhydrophobic and superoleophilic materials for oil–water separation, challenges still exist for easy preparation technique, full scale fabrication, recyclability and durability in mild processing environment [33]. Filter paper is widely used for adsorption of liquid and separation of solid and liquid due to its porous structure constructed by microfibers. In 2010, Wang et al. [34] created a superhydrophobic and superoleophilic filter paper with a mixture of hydrophobic silica nanoparticles (NPs) and polystyrene solution in toluene, which can successfully separate oil and water. However, the recyclability and durability in harsh processing environment were not fully tested. Herein, we report a facile preparation method for creating durable superhydrophobic and superoleophilic filter paper by colloidal deposition. The obtained filter paper has a nanoporous structure and possesses high separation efficiency (>99%) even after 30 cycle times. In addition, the as-prepared filter paper makes good performance in harsh environmental conditions such as strong acidic or alkaline solutions, high temperature and ultraviolet irradiation. All these results indicate a simple and durable way for the fabrication of oil–water separation materials.
solution for approximately 30 min, removed, and dried in an oven at 70 ◦ C for about 30 min to evaporate the solvent. Finally, the filter paper was heated at 220 ◦ C for 20 min to make the polystyrene NPs melt and then cooled naturally. The obtained filter paper was cut into pieces of different sizes for use in different experiments. 2.3. Characterization
2. Experimental
Water contact angles (WCAs) were measured with deionized water on a Dataphysics DCAT 21 (Dataphysics, Germany) instrument at room temperature. The volume of an individual droplet was 8 and each result was obtained from the average of five measurements of different points on each sample surface. The rolling state of water droplet and the oil penetrating process were recorded by a High Speed Imaging System (AcutEye, RockeTech Technology Corp., Ltd., China). The surface morphology of the filter paper was observed by a field-emission scanning electron microscope (SEM, FEI Quanta 200 FEG, Netherlands). The chemical composition was analyzed by the energy dispersive spectroscopy (EDS) equipped on the same SEM and an X-ray photoelectron spectroscopy (XPS, EscaLab 250XI, Thermo Scientific, USA) with Mg KR as the X-ray source operated at constant pass energy of 30 eV.
2.1. Materials
3. Results and discussion
Qualitative filter paper (moderate speed, nominal pore size 15∼20 m, thickness 340 ± 20 m) was purchased from Hang Zhou special paper Co., Ltd., China. The monodisperse polystyrene NP colloid solution (2.5 wt%, average particle size 200 nm) was obtained from Tianjin BaseLine ChromTech Research Centre, China. The monodisperse PTFE NP colloid solution (60 wt%, average particle size 200 nm) was bought from 3F New Material Co. Ltd., Shanghai, China.
Filter paper usually consists of wood fibers and can quickly adsorb both water and oil [34]. However, after treated by the PTFE and polystyrene NP colloidal solution, it can be seen that all droplets sitting on the as-prepared surface are ball-shaped (Fig. 1a). A jet of water from a pipet could bounce off the as-prepared filter paper without leaving anything, implying the weak interaction between water and the as-prepared filter paper (Fig. 1b). The WCA and sliding angle (SA) are shown as 155.5 ± 2◦ and 3◦ in Fig. 1d and h, definitely indicating a superhydrophobic surface. When the as-prepared filter paper was immersed into water, it showed a silver mirror-like appearance and was not wetted (Fig. 1g), while there was no such property on the pristine filter paper (Fig. 1c). This phenomenon can be attributed to the trapped air between water and the filter paper, which is consistent with the Cassie–Baxter model [35]. On the contrary, when an oil (hexane) droplet was placed onto the surface of the coated filter paper, the oil droplet was quickly absorbed within 4 ms (Fig. 2a and b),
2.2. Sample preparation The preparation of superhydrophobic filter paper was based on colloidal NP deposition. First, the PTFE colloid solution and the polystyrene colloid solution were diluted using deionized water to the mass fractions of 6 wt% and 1 wt%, respectively. Second, they were mixed with the ratio of 3:2 and ultrasonically dispersed for 15 min. After that, the filter paper was steeped in the mixed
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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Fig. 2. Images of oil wettability on the as-prepared filter paper: (a) before oil dropping, (b) after oil dropping, (c) increasing amount of oil after reaching the absorption limit, (d) oil permeating the textile.
showing superoleophilic property. When more oil was dropped, the oil quickly spread and gradually reached the uptake capacity limit of the filter paper, and then passed through (Fig. 2c and d). In addition, when the coated filter paper was fully wetted by hexane, it still showed good repellence to water as shown in Fig. 1e and f. All the results mentioned above proved stable superhydrobicity and superoleophilicity of the as-prepared filter paper. It is well known that the wettability of a solid surface is controlled by the surface chemistry and the geometrical roughness. As shown in Fig. 3a, the pristine filter paper is composed of micro fibers with different diameters between several and dozens of microns. The surface of the individual fiber is respectively smooth (Fig. 3b).
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To make up a superhydrophobic filter paper, the surface should be modified with low-surface-energy material and the roughness should also be enhanced. PTFE is a famous low-surface-energy material with a WCA of about 100◦ – 110◦ . After being treated by the way described in Section 2, the PTFE NPs with an average diameter of 200 nm nearly covered the fibers completely except for some nanoholes formed by the melted polystyrene NPs (Fig. 3c and d). The PTFE NPs not only offered low surface energy, but also provided nanoscale roughness along with the polystyrenemelted nanoholes. This nanoscale roughness complemented the microscale roughness provided by the fibers themselves, which met the requirement for the morphology of suprehydrophobicity. The combination of this multi-scale roughness and the PTFE’s low surface energy finally formed the superhydrophobic filter paper. The chemical composition of the filter paper surface was analyzed by EDS and XPS. The results of EDS showed that only peaks of C and O were detected on the pristine filter paper (Fig. 3c), while F could be observed on the superhydrophobic filter paper beside C and O (Fig. 3f). Meanwhile, XPS measurement was carried out to further investigate the surface chemical composition. As shown in Fig. 4a, only peaks corresponding to C and O were observed on the pristine filter paper. On the contrary, a new peak of F was detected after treatment (Fig. 4b). What’s more, in the C1 s high resolution spectrum (Fig. 4c), a new peak around 292 eV was found on the coated filter paper, which typically corresponded to C–F. The results of XPS measurement were identical with EDS and both of them proved the existence of PTFE on the coated filter paper. The pristine filter paper is well known for its capacity of absorption of both water and oil. When it was made superhydrophobic and superoleophilic as mentioned before, it must be a good material for removing oil from water. Fig. 5 shows the oil-absorbing process of the as-prepared filter paper. Hexane dyed with oil red was dropped onto the water surface in a beaker, and then a piece of as-prepared filter paper was taken into contact with the hexane. It can be seen the as-prepared filter paper was gradually wetted by hexane from the contact area, and just after a few seconds, all of the hexane was absorbed. As the uptake capacity of filter paper is not good, it is not suitable for the application of absorption of oil from water–oil mixtures.
Fig. 3. SEM images of the pristine (a, b) and the coated (d, e) filter paper’s surfaces. EDS spectra of the pristine (c) and the coated (f) filter paper’s surfaces.
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Fig. 4. XPS survey spectra of the pristine (a) and the coated (b) filter paper. (c) C1 s high resolution spectrum of the pristine and the coated filter paper.
The as-prepared filter paper shows good performance in the separation of oil–water mixtures by the way of filtering. In the experiment, the as-prepared filter paper (diameter = 8 cm) was folded in half two times to become a funnel and the funnel was put onto a beaker (Fig. 6a, left beaker). When the mixture of hexane (red) and water (Fig. 6a, right beaker) was poured into the as-prepared filter paper funnel, only hexane could get through and dropped into the beaker (Fig. 6b and Movie A, Supporting Information), while water was totally retained in the funnel. The whole “filter” process only lasted for about 20 s. At last, the water retained in the funnel was poured into another beaker (Fig. 6c, right beaker) which looked completely transparent. In addition, same process was done for the mixture of trichloromethane (density = 1.48 g/cm3 ) and water (Fig. 6d–f, Movie B, Supporting Information), and the result of which was as good as the mixture of hexane and water. These results indicate good separation performances of both water-on-top and oil-on-top mixtures of the as-prepared filter paper by a simple filter method. During the separation process, it could be seen that the oil was fully absorbed by the modified filter paper at first and then went down along the paper funnel to the bottom and dropped. This meant the oil could get through the modified filter paper only after it researched the limit of absorption capacity of the modified filter paper in a certain contact
area. The mechanism is quite different from the oil–water separation materials like superhydrophobic stainless steel filter mesh [1] because the superhydrophobic stainless steel filter mesh could only adsorb a little oil but not absorb. Supplementary movies S1 and S2 can be found, in the online version, at http://dx.doi.org/10.1016/j.apsusc.2014.05.207. The separation efficiency of the as-prepared filter paper for different kinds of oil–water mixtures was also investigated. The separation efficiency () was calculated by [36]:(1) = mm × 0 100where m0 is the mass of the water before separation process, m is the mass of the water after separation process. As shown in Fig. 7, the separation efficiencies of the as-prepared filter paper for a series of oil–water mixtures are all above 99%. In addition, the as-prepared filter paper has good performance on recyclability. Hexane–water mixture was adopted in the experiment for recyclability. The contaminated as-prepared filter paper after each separation experiment cycle was cleaned thoroughly by alcohol and water to remove the absorbed oil. Subsequently, the clean filter paper was dried in an oven at 70 ◦ C for 30 min. After measurement of WCA, the clean filter paper continued to be used in the next cycle. It can be seen that, after 30 cycle times, the WCA on the as-prepared filter paper slowly decreased from 155◦ to 147◦ (Fig. 8, line below), which may be caused by the residual oil absorbed by the filter paper
Fig. 5. (a–c) Images of the removal process of hexane from water using the as-prepared filter paper.
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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Fig. 6. Separation process for hexane–water mixture (a–c) and trichloromethane–water mixture (d–f) using the as-prepared filter paper. (For interpretation of the references to color in the text citation of this figure, the reader is referred to the web version of this article.).
Fig. 7. The separation efficiency of the as-prepared filter paper for a selection of oil–water mixtures.
Fig. 8. Effect of cycle times on the separation efficiency and WCA of the as-prepared filter paper.
Fig. 9. Variation of the WCA and separation efficiency of the as-prepared filter paper (a) exposed to acidic and alkaline solutions, (b) at 180 ◦ C and under ultraviolet irradiation.
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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and not cleaned up by the alcohol and water. However, the separation efficiency of the as-prepared filter paper only decreased a little and still maintained as high as the initial 99% (Fig. 8, line above). These results well demonstrated the stability of the superhydrophobicity and separation efficiency of the as-prepared filter paper in recycling. In practical use, the materials for oil–water separation always work at harsh environment such as strong acidic or alkaline solutions, high temperature and ultraviolet irradiation, thus the evaluation of environmental durability is very important. The chemical environment durability of the as-prepared filter paper was investigated by immersing them in strong acidic or alkaline solutions. As shown in Fig. 9a, the WCA still maintained above 150◦ while the separation efficiency exceeded 99% all the time after immersion in the strong acidic (pH 2) and alkaline (pH 12) solution for 72 h. Moreover, when the obtained filter paper was placed in an oven and heated at 180 ◦ C for 72 h, its WCA nearly remained unchanged within experimental error and so did the separation efficiency (Fig. 9b). It is known that many kinds of superhydrophobic surfaces fail when exposing to ultraviolet irradiation, such as hydrocarbons, fluoroalkyl and some other polymers [37–39]. Some of the superhydrophobic surfaces can even switch to superhydrophilic surfaces after exposure to ultraviolet irradiation [40,41]. Therefore, the evaluation of durability under ultraviolet irradiation is very important. In this paper, the as-prepared filter paper was put under the light of a 48 W ultraviolet lamp for 72 h. The result is shown in Fig. 9b that the superhydrophobicity and separation efficiency were still very stable, which proved good durability to ultraviolet irradiation. It is believed that all these good environmental durability can be attributed to the excellent stability of the material of PTFE. 4. Conclusion In summary, we have demonstrated a preparation approach to fabricate superhydrophobic and superoleophilic filter paper for oil–water separation by colloidal deposition. The as-prepared filter paper has a nanoporous structure and can separate a series of oil–water mixtures effectively with high separation efficiencies over 99%. The obtained filter paper can be reused for oil–water separation at least 30 times with stable superhydrophobicity and constant high separation efficiency. In addition, the as-prepared filter paper has good environmental durability as it works well under extreme environmental conditions of strong acidic or alkaline solutions, high temperature and ultraviolet irradiation. Acknowledgement This work is financially supported by the National Natural Science Foundation of China (Grants 51375253 and 51321092). References [1] L. Feng, Z. Zhang, Z. Mai, Y. Ma, B. Liu, L. Jiang, D. Zhu, A super-hydrophobic and super-oleophilic coating mesh film for the separation of oil and water, Angew. Chem. Int. Ed. Engl. 43 (2004) 2012–2014. [2] A.K. Kota, G. Kwon, W. Choi, J.M. Mabry, A. Tuteja, Hygro-responsive membranes for effective oil/water separation, Nat. Commun. 3 (2012) 1025. [3] Z. Xue, S. Wang, L. Lin, L. Chen, M. Liu, L. Feng, L. Jiang, A novel superhydrophilic and underwater superoleophobic hydrogel-coated mesh for oil/water separation, Adv. Mater. 23 (2011) 4270–4273. [4] W. Chen, Y. Su, L. Zheng, L. Wang, Z. Jiang, The improved oil/water separation performance of cellulose acetate-graft-polyacrylonitrile membranes, J. Membrane Sci. 337 (2009) 98–105. [5] C. Xue, P. Ji, P. Zhang, Y. Li, S. Jia, Fabrication of superhydrophobic and superoleophilic textiles for oil/water separation, Appl. Surf. Sci. 284 (2013) 464–471. [6] Y.J. Chan, M.F. Chong, C.L. Law, D.G. Hassell, A review on anaerobic–aerobic treatment of industrial and municipal wastewater, Chem. Eng. J. 155 (2009) 1–18.
[7] V. Singh, M.K. Purkait, C. Das, Cross-flow microfiltration of industrial oily wastewater: experimental and theoretical consideration, Sep. Sci. Technol. 46 (2011) 1213–1223. [8] M. Abbasi, A. Salahi, M. Mirfendereski, T. Mohammadi, A. Pak, Dimensional analysis of permeation flux for microfiltration of oily wastewaters using mullite ceramic membranes, Desalination 252 (2010) 113–119. [9] H. Karimnezhad, L. Rajabi, E. Salehi, A.A. Derakhshan, S. Azimi, Novel nanocomposite Kevlar fabric membranes: fabrication, characterization and performance in oil/water separation, Appl. Surf. Sci. 293 (2014) 275–286. [10] R.P. Swannell, K. Lee, M. McDonagh, Field evaluations of marine oil spill bioremediation, Microbiol. Rev. 60 (1996) 342–365. [11] A.B. Nordvik, J.L. Simmons, K.R. Bitting, A. Lewis, T. Strom-Kristiansen, Oil and water separation in marine oil spill clean-up operations, Spill Sci. Technol. B 3 (1996) 107–122. [12] M.O. Adebajo, R.L. Frost, J.T. Kloprogge, O. Carmody, S. Kokot, Porous materials for oil spill cleanup: a review of synthesis and absorbing properties, J. Porous Mater. 10 (2003) 159–170. [13] T. Arbatan, X. Fang, W. Shen, Superhydrophobic and oleophilic calcium carbonate powder as a selective oil sorbent with potential use in oil spill clean-ups, Chem. Eng. J. 166 (2011) 787–791. [14] Z. Xue, Y. Cao, N. Liu, L. Feng, L. Jiang, Special wettable materials for oil/water separation, J. Mater. Chem. A 2 (2014) 2445–2460. [15] M. Li, J. Xu, Q. Lu, Creating superhydrophobic surfaces with flowery structures on nickel substrates through a wet-chemical-process, J. Mater. Chem. 17 (2007) 4772–4776. [16] S. Wang, Y. Song, L. Jiang, Microscale and nanoscale hierarchical structured mesh films with superhydrophobic and superoleophilic properties induced by long-chain fatty acids, Nanotechnology 18 (2007) 15103. [17] D. La, T.A. Nguyen, S. Lee, J.W. Kim, Y.S. Kim, A stable superhydrophobic and superoleophilic Cu mesh based on copper hydroxide nanoneedle arrays, Appl. Surf. Sci. 257 (2011) 5705–5710. [18] J. Zhang, S. Seeger, Polyester materials with superwetting silicone nanofilaments for oil/water separation and selective oil absorption, Adv. Funct. Mater. 21 (2011) 4699–4704. [19] X. Zhou, Z. Zhang, X. Xu, X. Men, X. Zhu, Facile fabrication of superhydrophobic sponge with selective absorption and collection of oil from water, Ind. Eng. Chem. Res. 52 (2013) 9411–9416. [20] H. Yang, P. Pi, Z. Cai, X. Wen, X. Wang, J. Cheng, Z. Yang, Facile preparation of super-hydrophobic and super-oleophilic silica film on stainless steel mesh via sol-gel process, Appl. Surf. Sci. 256 (2010) 4095–4102. [21] C. Su, Y. Xu, W. Zhang, Y. Liu, J. Li, Porous ceramic membrane with superhydrophobic and superoleophilic surface for reclaiming oil from oily water, Appl. Surf. Sci. 258 (2012) 2319–2323. [22] T. Tsuruoka, S. Furukawa, Y. Takashima, K. Yoshida, S. Isoda, S. Kitagawa, Nanoporous nanorods fabricated by coordination modulation and oriented attachment growth, Angew. Chem. Int. Ed. Engl. 48 (2009) 4739–4743. [23] J. Wang, Z. Shi, J. Fan, Y. Ge, J. Yin, G. Hu, Self-assembly of graphene into threedimensional structures promoted by natural phenolic acids, J. Mater. Chem. 22 (2012) 22459–22466. [24] L. Wang, S. Yang, J. Wang, C. Wang, L. Chen, Fabrication of superhydrophobic TPU film for oil/water separation based on electrospinning route, Mater. Lett. 65 (2011) 869–872. [25] J. Lin, Y. Shang, B. Ding, J. Yang, J. Yu, S.S. Al-Deyab, Nanoporous polystyrene fibers for oil spill cleanup, Mar. Pollut. Bull. 64 (2012) 347–352. [26] D. Tian, X. Zhang, Y. Tian, Y. Wu, X. Wang, J. Zhai, L. Jiang, Photoinduced water/oil separation based on switchable superhydrophobicity/superhydrophilicity and underwater superoleophobicity of the aligned ZnO nanorod array-coated mesh films, J. Mater. Chem. 22 (2012) 19652–19657. [27] J. Li, L. Shi, Y. Chen, Y. Zhang, Z. Guo, B. Su, W. Liu, Stable superhydrophobic coatings from thiol-ligand nanocrystals and their application in oil/water separation, J. Mater. Chem. 22 (2012) 9774–9781. [28] C. Wang, T. Yao, J. Wu, C. Ma, Z. Fan, Z. Wang, Y. Cheng, Q. Lin, B. Yang, Facile approach in fabricating superhydrophobic and superoleophilic surface for water and oil mixture separation, ACS Appl. Mater. Interfaces 1 (2009) 2613–2617. [29] J. Wu, J. Chen, K. Qasim, J. Xia, W. Lei, B. Wang, A hierarchical mesh film with superhydrophobic and superoleophilic properties for oil and water separation, J. Chem. Technol. Biotechnol. 87 (2012) 427–430. [30] P. Calcagnile, D. Fragouli, I.S. Bayer, G.C. Anyfantis, L. Martiradonna, P.D. Cozzoli, R. Cingolani, A. Athanassiou, Magnetically driven floating foams for the removal of oil contaminants from water, ACS Nano 6 (2012) 5413–5419. [31] Q. Zhu, Q. Pan, F. Liu, Facile removal and collection of oils from water surfaces through superhydrophobic and superoleophilic sponges, J. Phys. Chem. C 115 (2011) 17464–17470. [32] X. Zhou, Z. Zhang, X. Xu, F. Guo, X. Zhu, X. Men, B. Ge, Robust and durable superhydrophobic cotton fabrics for oil/water separation, ACS Appl. Mater. Interfaces 5 (2013) 7208–7214. [33] X. Ding, S. Zhou, G. Gu, L. Wu, A facile and large-area fabrication method of superhydrophobic self-cleaning fluorinated polysiloxane/TiO2 nanocomposite coatings with long-term durability, J. Mater. Chem. 21 (2011) 6161–6164. [34] S. Wang, M. Li, Q. Lu, Filter paper with selective absorption and separation of liquids that differ in surface tension, ACS Appl. Mater. Interfaces 2 (2010) 677–683. [35] P. Roach, N.J. Shirtcliffe, M.I. Newton, Progress in superhydrophobic surface development, Soft Matter 4 (2008) 224–240.
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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[36] R. Gao, Q. Liu, J. Wang, J. Liu, W. Yang, Z. Gao, L. Liu, Construction of superhydrophobic and superoleophilic nickel foam for separation of water and oil mixture, Appl. Surf. Sci. 289 (2014) 417–424. [37] Y. Xiu, D.W. Hess, C.P. Wong, UV and thermally stable superhydrophobic coatings from sol–gel processing, J. Colloid Interface Sci. 326 (2008) 465–470. [38] A.V. Rao, S.D. Bhagat, H. Hirashima, G.M. Pajonk, Synthesis of flexible silica aerogels using methyltrimethoxysilane (MTMS) precursor, J. Colloid Interface Sci. 300 (2006) 279–285.
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[39] N.J. Shirtcliffe, G. McHale, M.I. Newton, C.C. Perry, Intrinsically superhydrophobic organosilica sol–gel foams, Langmuir 19 (2003) 5626–5631. [40] X. Feng, J. Zhai, L. Jiang, The fabrication and switchable superhydrophobicity of TiO2 nanorod films, Angew. Chem. Int. Ed. Engl. 44 (2005) 5115–5118. [41] H.S. Lim, D. Kwak, D.Y. Lee, S.G. Lee, K. Cho, UV-driven reversible switching of a roselike vanadium oxide film between superhydrophobicity and superhydrophilicity, J. Am. Chem. Soc. 129 (2007) 4128–4129.
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Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method Chuan Du, Jiadao Wang ∗ , Zhifu Chen, Darong Chen State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, PR China
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Article history: Received 22 April 2014 Received in revised form 28 May 2014 Accepted 28 May 2014 Available online xxx Keywords: Superhydrophobic Superoleophilic Polytetrafluoroethylene Filter paper Oil–water separation
a b s t r a c t A method for manufacturing durable superhydrophobic and superoleophilic filter paper for oil–water separation was developed via colloidal deposition. A porous film composed of PTFE nanoparticles was formed on filter paper, which was superhydrophobic with a water contact angle of 155.5◦ and superoleophilic with an oil contact angle of 0◦ . The obtained filter paper could separate a series of oil–water mixtures effectively with high separation efficiencies over 99%. Besides, the as-prepared filter paper kept stable superhydrophobicity and high separation efficiency even after 30 cycle times and could also work well under harsh environmental conditions like strong acidic or alkaline solutions, high temperature and ultraviolet irradiation. Compared with other approaches for fabricating oil–water materials, this approach is able to fabricate full-scale durable and practical oil–water materials easily and economically. The as-prepared filter paper is a promising candidate for oil–water separation. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Oil–water separation is becoming an important worldwide problem in the area of industrial production, environment protection and energy conservation [1–5]. Many industries such as crude oil production and refinery, petrochemical and metal finishing, textile and leather processing, and food processing and lubricant create large amount of oily wastewater inevitably which has become the most common pollutant [6–9]. Besides, frequent accidents of marine oil spill bring severe pollution and energy waste [10,11]. Except for ensuring safety of navigation to prevent the accidents, treatment of the spilled oil is much more challenging [12,13]. Actually, both of the treatment of oily wastewater and spilled oil involve in the problem of oil–water separation. A lot of technologies for the separation of oil and water mixtures have been developed during the past decades, such as ultrasonic separation, air flotation, electric field separation, biological treatment and membrane filtration, but the limitation of low separation efficiency, the generation of second pollutants, the strict requirements of oil–water mixtures, the membrane fouling problems or the high cost have always caused difficulty in practical applications [14]. In recent years, the development of superhydrophobic and superoleophilic materials for adsorption of oil from water and
∗ Corresponding author. Tel.: +86 010 62796458; fax: +86 010 62781379. E-mail address: [email protected] (J. Wang).
separation of oil and water has attracted much attention due to their high separation efficiency and wide applicability. The superhydrophobic property makes materials repel water completely, while the superoleophilic property lets oil permeate freely. Therefore, superhydrophobic and superoleophilic materials can separate oil-water efficiently [14]. A variety of methods have been developed to fabricate superhydrophobic and superoleophilic materials for separation of water and oil, including wet chemical process [15], electrochemical deposition [16], electrochemical etching [17], vapor phase deposition [18,19], sol–gel process [20,21], selfassembly process [22,23], electrospinning techniques [24,25], and others [26–30]. Generally, all these methods can be divided into two kinds: (1) chemical modification of a micro/nanostructured surface with low-surface-energy materials and (2) construction of micro/nanostructures on low-surface-energy materials. For example, Feng et al. [1] first reported a polytetrafluoroethylene (PTFE) film on a stainless steel mesh with both superhydrophobicity and superoleophilicity by a spray and dry method in 2004, which successfully separated the mixture of diesel oil and water. Zhu et al. [31] fabricated superhydrophobic and superoleophilic sponges that could effectively absorb oil from water with a simple solutionimmerse method. Zhou et al. [32] developed a robust and durable superhydrophobic cotton fabric for oil–water separation. Wang and co-workers created a thermoplastic polyurethane mat with beadon-string morphology by electrospinning, which can separate oil and water mixtures after further treated by hydrophobic nanosilica. Although many methods have been created for the fabrication
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Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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Fig. 1. Images of water wettability on the clean and entirely oil-wetted as-prepared filter paper: (a) water droplets sitting on the as-prepared filter paper, (b) a jet of water bouncing off the as-prepared filter paper, (c) the pristine filter paper immersed in water by an external force, (d) WCA measurement on the as-prepared filter paper, (e) water droplets sitting on the oil contaminated as-prepared filter paper, (f) a jet of water bouncing off the oil contaminated as-prepared filter paper, (g) the as-prepared filter paper immersed in water by an external force, and (h) the rolling state of water droplet and the measurement of SA.
of superhydrophobic and superoleophilic materials for oil–water separation, challenges still exist for easy preparation technique, full scale fabrication, recyclability and durability in mild processing environment [33]. Filter paper is widely used for adsorption of liquid and separation of solid and liquid due to its porous structure constructed by microfibers. In 2010, Wang et al. [34] created a superhydrophobic and superoleophilic filter paper with a mixture of hydrophobic silica nanoparticles (NPs) and polystyrene solution in toluene, which can successfully separate oil and water. However, the recyclability and durability in harsh processing environment were not fully tested. Herein, we report a facile preparation method for creating durable superhydrophobic and superoleophilic filter paper by colloidal deposition. The obtained filter paper has a nanoporous structure and possesses high separation efficiency (>99%) even after 30 cycle times. In addition, the as-prepared filter paper makes good performance in harsh environmental conditions such as strong acidic or alkaline solutions, high temperature and ultraviolet irradiation. All these results indicate a simple and durable way for the fabrication of oil–water separation materials.
solution for approximately 30 min, removed, and dried in an oven at 70 ◦ C for about 30 min to evaporate the solvent. Finally, the filter paper was heated at 220 ◦ C for 20 min to make the polystyrene NPs melt and then cooled naturally. The obtained filter paper was cut into pieces of different sizes for use in different experiments. 2.3. Characterization
2. Experimental
Water contact angles (WCAs) were measured with deionized water on a Dataphysics DCAT 21 (Dataphysics, Germany) instrument at room temperature. The volume of an individual droplet was 8 and each result was obtained from the average of five measurements of different points on each sample surface. The rolling state of water droplet and the oil penetrating process were recorded by a High Speed Imaging System (AcutEye, RockeTech Technology Corp., Ltd., China). The surface morphology of the filter paper was observed by a field-emission scanning electron microscope (SEM, FEI Quanta 200 FEG, Netherlands). The chemical composition was analyzed by the energy dispersive spectroscopy (EDS) equipped on the same SEM and an X-ray photoelectron spectroscopy (XPS, EscaLab 250XI, Thermo Scientific, USA) with Mg KR as the X-ray source operated at constant pass energy of 30 eV.
2.1. Materials
3. Results and discussion
Qualitative filter paper (moderate speed, nominal pore size 15∼20 m, thickness 340 ± 20 m) was purchased from Hang Zhou special paper Co., Ltd., China. The monodisperse polystyrene NP colloid solution (2.5 wt%, average particle size 200 nm) was obtained from Tianjin BaseLine ChromTech Research Centre, China. The monodisperse PTFE NP colloid solution (60 wt%, average particle size 200 nm) was bought from 3F New Material Co. Ltd., Shanghai, China.
Filter paper usually consists of wood fibers and can quickly adsorb both water and oil [34]. However, after treated by the PTFE and polystyrene NP colloidal solution, it can be seen that all droplets sitting on the as-prepared surface are ball-shaped (Fig. 1a). A jet of water from a pipet could bounce off the as-prepared filter paper without leaving anything, implying the weak interaction between water and the as-prepared filter paper (Fig. 1b). The WCA and sliding angle (SA) are shown as 155.5 ± 2◦ and 3◦ in Fig. 1d and h, definitely indicating a superhydrophobic surface. When the as-prepared filter paper was immersed into water, it showed a silver mirror-like appearance and was not wetted (Fig. 1g), while there was no such property on the pristine filter paper (Fig. 1c). This phenomenon can be attributed to the trapped air between water and the filter paper, which is consistent with the Cassie–Baxter model [35]. On the contrary, when an oil (hexane) droplet was placed onto the surface of the coated filter paper, the oil droplet was quickly absorbed within 4 ms (Fig. 2a and b),
2.2. Sample preparation The preparation of superhydrophobic filter paper was based on colloidal NP deposition. First, the PTFE colloid solution and the polystyrene colloid solution were diluted using deionized water to the mass fractions of 6 wt% and 1 wt%, respectively. Second, they were mixed with the ratio of 3:2 and ultrasonically dispersed for 15 min. After that, the filter paper was steeped in the mixed
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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Fig. 2. Images of oil wettability on the as-prepared filter paper: (a) before oil dropping, (b) after oil dropping, (c) increasing amount of oil after reaching the absorption limit, (d) oil permeating the textile.
showing superoleophilic property. When more oil was dropped, the oil quickly spread and gradually reached the uptake capacity limit of the filter paper, and then passed through (Fig. 2c and d). In addition, when the coated filter paper was fully wetted by hexane, it still showed good repellence to water as shown in Fig. 1e and f. All the results mentioned above proved stable superhydrobicity and superoleophilicity of the as-prepared filter paper. It is well known that the wettability of a solid surface is controlled by the surface chemistry and the geometrical roughness. As shown in Fig. 3a, the pristine filter paper is composed of micro fibers with different diameters between several and dozens of microns. The surface of the individual fiber is respectively smooth (Fig. 3b).
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To make up a superhydrophobic filter paper, the surface should be modified with low-surface-energy material and the roughness should also be enhanced. PTFE is a famous low-surface-energy material with a WCA of about 100◦ – 110◦ . After being treated by the way described in Section 2, the PTFE NPs with an average diameter of 200 nm nearly covered the fibers completely except for some nanoholes formed by the melted polystyrene NPs (Fig. 3c and d). The PTFE NPs not only offered low surface energy, but also provided nanoscale roughness along with the polystyrenemelted nanoholes. This nanoscale roughness complemented the microscale roughness provided by the fibers themselves, which met the requirement for the morphology of suprehydrophobicity. The combination of this multi-scale roughness and the PTFE’s low surface energy finally formed the superhydrophobic filter paper. The chemical composition of the filter paper surface was analyzed by EDS and XPS. The results of EDS showed that only peaks of C and O were detected on the pristine filter paper (Fig. 3c), while F could be observed on the superhydrophobic filter paper beside C and O (Fig. 3f). Meanwhile, XPS measurement was carried out to further investigate the surface chemical composition. As shown in Fig. 4a, only peaks corresponding to C and O were observed on the pristine filter paper. On the contrary, a new peak of F was detected after treatment (Fig. 4b). What’s more, in the C1 s high resolution spectrum (Fig. 4c), a new peak around 292 eV was found on the coated filter paper, which typically corresponded to C–F. The results of XPS measurement were identical with EDS and both of them proved the existence of PTFE on the coated filter paper. The pristine filter paper is well known for its capacity of absorption of both water and oil. When it was made superhydrophobic and superoleophilic as mentioned before, it must be a good material for removing oil from water. Fig. 5 shows the oil-absorbing process of the as-prepared filter paper. Hexane dyed with oil red was dropped onto the water surface in a beaker, and then a piece of as-prepared filter paper was taken into contact with the hexane. It can be seen the as-prepared filter paper was gradually wetted by hexane from the contact area, and just after a few seconds, all of the hexane was absorbed. As the uptake capacity of filter paper is not good, it is not suitable for the application of absorption of oil from water–oil mixtures.
Fig. 3. SEM images of the pristine (a, b) and the coated (d, e) filter paper’s surfaces. EDS spectra of the pristine (c) and the coated (f) filter paper’s surfaces.
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Fig. 4. XPS survey spectra of the pristine (a) and the coated (b) filter paper. (c) C1 s high resolution spectrum of the pristine and the coated filter paper.
The as-prepared filter paper shows good performance in the separation of oil–water mixtures by the way of filtering. In the experiment, the as-prepared filter paper (diameter = 8 cm) was folded in half two times to become a funnel and the funnel was put onto a beaker (Fig. 6a, left beaker). When the mixture of hexane (red) and water (Fig. 6a, right beaker) was poured into the as-prepared filter paper funnel, only hexane could get through and dropped into the beaker (Fig. 6b and Movie A, Supporting Information), while water was totally retained in the funnel. The whole “filter” process only lasted for about 20 s. At last, the water retained in the funnel was poured into another beaker (Fig. 6c, right beaker) which looked completely transparent. In addition, same process was done for the mixture of trichloromethane (density = 1.48 g/cm3 ) and water (Fig. 6d–f, Movie B, Supporting Information), and the result of which was as good as the mixture of hexane and water. These results indicate good separation performances of both water-on-top and oil-on-top mixtures of the as-prepared filter paper by a simple filter method. During the separation process, it could be seen that the oil was fully absorbed by the modified filter paper at first and then went down along the paper funnel to the bottom and dropped. This meant the oil could get through the modified filter paper only after it researched the limit of absorption capacity of the modified filter paper in a certain contact
area. The mechanism is quite different from the oil–water separation materials like superhydrophobic stainless steel filter mesh [1] because the superhydrophobic stainless steel filter mesh could only adsorb a little oil but not absorb. Supplementary movies S1 and S2 can be found, in the online version, at http://dx.doi.org/10.1016/j.apsusc.2014.05.207. The separation efficiency of the as-prepared filter paper for different kinds of oil–water mixtures was also investigated. The separation efficiency () was calculated by [36]:(1) = mm × 0 100where m0 is the mass of the water before separation process, m is the mass of the water after separation process. As shown in Fig. 7, the separation efficiencies of the as-prepared filter paper for a series of oil–water mixtures are all above 99%. In addition, the as-prepared filter paper has good performance on recyclability. Hexane–water mixture was adopted in the experiment for recyclability. The contaminated as-prepared filter paper after each separation experiment cycle was cleaned thoroughly by alcohol and water to remove the absorbed oil. Subsequently, the clean filter paper was dried in an oven at 70 ◦ C for 30 min. After measurement of WCA, the clean filter paper continued to be used in the next cycle. It can be seen that, after 30 cycle times, the WCA on the as-prepared filter paper slowly decreased from 155◦ to 147◦ (Fig. 8, line below), which may be caused by the residual oil absorbed by the filter paper
Fig. 5. (a–c) Images of the removal process of hexane from water using the as-prepared filter paper.
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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Fig. 6. Separation process for hexane–water mixture (a–c) and trichloromethane–water mixture (d–f) using the as-prepared filter paper. (For interpretation of the references to color in the text citation of this figure, the reader is referred to the web version of this article.).
Fig. 7. The separation efficiency of the as-prepared filter paper for a selection of oil–water mixtures.
Fig. 8. Effect of cycle times on the separation efficiency and WCA of the as-prepared filter paper.
Fig. 9. Variation of the WCA and separation efficiency of the as-prepared filter paper (a) exposed to acidic and alkaline solutions, (b) at 180 ◦ C and under ultraviolet irradiation.
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and not cleaned up by the alcohol and water. However, the separation efficiency of the as-prepared filter paper only decreased a little and still maintained as high as the initial 99% (Fig. 8, line above). These results well demonstrated the stability of the superhydrophobicity and separation efficiency of the as-prepared filter paper in recycling. In practical use, the materials for oil–water separation always work at harsh environment such as strong acidic or alkaline solutions, high temperature and ultraviolet irradiation, thus the evaluation of environmental durability is very important. The chemical environment durability of the as-prepared filter paper was investigated by immersing them in strong acidic or alkaline solutions. As shown in Fig. 9a, the WCA still maintained above 150◦ while the separation efficiency exceeded 99% all the time after immersion in the strong acidic (pH 2) and alkaline (pH 12) solution for 72 h. Moreover, when the obtained filter paper was placed in an oven and heated at 180 ◦ C for 72 h, its WCA nearly remained unchanged within experimental error and so did the separation efficiency (Fig. 9b). It is known that many kinds of superhydrophobic surfaces fail when exposing to ultraviolet irradiation, such as hydrocarbons, fluoroalkyl and some other polymers [37–39]. Some of the superhydrophobic surfaces can even switch to superhydrophilic surfaces after exposure to ultraviolet irradiation [40,41]. Therefore, the evaluation of durability under ultraviolet irradiation is very important. In this paper, the as-prepared filter paper was put under the light of a 48 W ultraviolet lamp for 72 h. The result is shown in Fig. 9b that the superhydrophobicity and separation efficiency were still very stable, which proved good durability to ultraviolet irradiation. It is believed that all these good environmental durability can be attributed to the excellent stability of the material of PTFE. 4. Conclusion In summary, we have demonstrated a preparation approach to fabricate superhydrophobic and superoleophilic filter paper for oil–water separation by colloidal deposition. The as-prepared filter paper has a nanoporous structure and can separate a series of oil–water mixtures effectively with high separation efficiencies over 99%. The obtained filter paper can be reused for oil–water separation at least 30 times with stable superhydrophobicity and constant high separation efficiency. In addition, the as-prepared filter paper has good environmental durability as it works well under extreme environmental conditions of strong acidic or alkaline solutions, high temperature and ultraviolet irradiation. Acknowledgement This work is financially supported by the National Natural Science Foundation of China (Grants 51375253 and 51321092). References [1] L. Feng, Z. Zhang, Z. Mai, Y. Ma, B. Liu, L. Jiang, D. Zhu, A super-hydrophobic and super-oleophilic coating mesh film for the separation of oil and water, Angew. Chem. Int. Ed. Engl. 43 (2004) 2012–2014. [2] A.K. Kota, G. Kwon, W. Choi, J.M. Mabry, A. Tuteja, Hygro-responsive membranes for effective oil/water separation, Nat. Commun. 3 (2012) 1025. [3] Z. Xue, S. Wang, L. Lin, L. Chen, M. Liu, L. Feng, L. Jiang, A novel superhydrophilic and underwater superoleophobic hydrogel-coated mesh for oil/water separation, Adv. Mater. 23 (2011) 4270–4273. [4] W. Chen, Y. Su, L. Zheng, L. Wang, Z. Jiang, The improved oil/water separation performance of cellulose acetate-graft-polyacrylonitrile membranes, J. Membrane Sci. 337 (2009) 98–105. [5] C. Xue, P. Ji, P. Zhang, Y. Li, S. Jia, Fabrication of superhydrophobic and superoleophilic textiles for oil/water separation, Appl. Surf. Sci. 284 (2013) 464–471. [6] Y.J. Chan, M.F. Chong, C.L. Law, D.G. Hassell, A review on anaerobic–aerobic treatment of industrial and municipal wastewater, Chem. Eng. J. 155 (2009) 1–18.
[7] V. Singh, M.K. Purkait, C. Das, Cross-flow microfiltration of industrial oily wastewater: experimental and theoretical consideration, Sep. Sci. Technol. 46 (2011) 1213–1223. [8] M. Abbasi, A. Salahi, M. Mirfendereski, T. Mohammadi, A. Pak, Dimensional analysis of permeation flux for microfiltration of oily wastewaters using mullite ceramic membranes, Desalination 252 (2010) 113–119. [9] H. Karimnezhad, L. Rajabi, E. Salehi, A.A. Derakhshan, S. Azimi, Novel nanocomposite Kevlar fabric membranes: fabrication, characterization and performance in oil/water separation, Appl. Surf. Sci. 293 (2014) 275–286. [10] R.P. Swannell, K. Lee, M. McDonagh, Field evaluations of marine oil spill bioremediation, Microbiol. Rev. 60 (1996) 342–365. [11] A.B. Nordvik, J.L. Simmons, K.R. Bitting, A. Lewis, T. Strom-Kristiansen, Oil and water separation in marine oil spill clean-up operations, Spill Sci. Technol. B 3 (1996) 107–122. [12] M.O. Adebajo, R.L. Frost, J.T. Kloprogge, O. Carmody, S. Kokot, Porous materials for oil spill cleanup: a review of synthesis and absorbing properties, J. Porous Mater. 10 (2003) 159–170. [13] T. Arbatan, X. Fang, W. Shen, Superhydrophobic and oleophilic calcium carbonate powder as a selective oil sorbent with potential use in oil spill clean-ups, Chem. Eng. J. 166 (2011) 787–791. [14] Z. Xue, Y. Cao, N. Liu, L. Feng, L. Jiang, Special wettable materials for oil/water separation, J. Mater. Chem. A 2 (2014) 2445–2460. [15] M. Li, J. Xu, Q. Lu, Creating superhydrophobic surfaces with flowery structures on nickel substrates through a wet-chemical-process, J. Mater. Chem. 17 (2007) 4772–4776. [16] S. Wang, Y. Song, L. Jiang, Microscale and nanoscale hierarchical structured mesh films with superhydrophobic and superoleophilic properties induced by long-chain fatty acids, Nanotechnology 18 (2007) 15103. [17] D. La, T.A. Nguyen, S. Lee, J.W. Kim, Y.S. Kim, A stable superhydrophobic and superoleophilic Cu mesh based on copper hydroxide nanoneedle arrays, Appl. Surf. Sci. 257 (2011) 5705–5710. [18] J. Zhang, S. Seeger, Polyester materials with superwetting silicone nanofilaments for oil/water separation and selective oil absorption, Adv. Funct. Mater. 21 (2011) 4699–4704. [19] X. Zhou, Z. Zhang, X. Xu, X. Men, X. Zhu, Facile fabrication of superhydrophobic sponge with selective absorption and collection of oil from water, Ind. Eng. Chem. Res. 52 (2013) 9411–9416. [20] H. Yang, P. Pi, Z. Cai, X. Wen, X. Wang, J. Cheng, Z. Yang, Facile preparation of super-hydrophobic and super-oleophilic silica film on stainless steel mesh via sol-gel process, Appl. Surf. Sci. 256 (2010) 4095–4102. [21] C. Su, Y. Xu, W. Zhang, Y. Liu, J. Li, Porous ceramic membrane with superhydrophobic and superoleophilic surface for reclaiming oil from oily water, Appl. Surf. Sci. 258 (2012) 2319–2323. [22] T. Tsuruoka, S. Furukawa, Y. Takashima, K. Yoshida, S. Isoda, S. Kitagawa, Nanoporous nanorods fabricated by coordination modulation and oriented attachment growth, Angew. Chem. Int. Ed. Engl. 48 (2009) 4739–4743. [23] J. Wang, Z. Shi, J. Fan, Y. Ge, J. Yin, G. Hu, Self-assembly of graphene into threedimensional structures promoted by natural phenolic acids, J. Mater. Chem. 22 (2012) 22459–22466. [24] L. Wang, S. Yang, J. Wang, C. Wang, L. Chen, Fabrication of superhydrophobic TPU film for oil/water separation based on electrospinning route, Mater. Lett. 65 (2011) 869–872. [25] J. Lin, Y. Shang, B. Ding, J. Yang, J. Yu, S.S. Al-Deyab, Nanoporous polystyrene fibers for oil spill cleanup, Mar. Pollut. Bull. 64 (2012) 347–352. [26] D. Tian, X. Zhang, Y. Tian, Y. Wu, X. Wang, J. Zhai, L. Jiang, Photoinduced water/oil separation based on switchable superhydrophobicity/superhydrophilicity and underwater superoleophobicity of the aligned ZnO nanorod array-coated mesh films, J. Mater. Chem. 22 (2012) 19652–19657. [27] J. Li, L. Shi, Y. Chen, Y. Zhang, Z. Guo, B. Su, W. Liu, Stable superhydrophobic coatings from thiol-ligand nanocrystals and their application in oil/water separation, J. Mater. Chem. 22 (2012) 9774–9781. [28] C. Wang, T. Yao, J. Wu, C. Ma, Z. Fan, Z. Wang, Y. Cheng, Q. Lin, B. Yang, Facile approach in fabricating superhydrophobic and superoleophilic surface for water and oil mixture separation, ACS Appl. Mater. Interfaces 1 (2009) 2613–2617. [29] J. Wu, J. Chen, K. Qasim, J. Xia, W. Lei, B. Wang, A hierarchical mesh film with superhydrophobic and superoleophilic properties for oil and water separation, J. Chem. Technol. Biotechnol. 87 (2012) 427–430. [30] P. Calcagnile, D. Fragouli, I.S. Bayer, G.C. Anyfantis, L. Martiradonna, P.D. Cozzoli, R. Cingolani, A. Athanassiou, Magnetically driven floating foams for the removal of oil contaminants from water, ACS Nano 6 (2012) 5413–5419. [31] Q. Zhu, Q. Pan, F. Liu, Facile removal and collection of oils from water surfaces through superhydrophobic and superoleophilic sponges, J. Phys. Chem. C 115 (2011) 17464–17470. [32] X. Zhou, Z. Zhang, X. Xu, F. Guo, X. Zhu, X. Men, B. Ge, Robust and durable superhydrophobic cotton fabrics for oil/water separation, ACS Appl. Mater. Interfaces 5 (2013) 7208–7214. [33] X. Ding, S. Zhou, G. Gu, L. Wu, A facile and large-area fabrication method of superhydrophobic self-cleaning fluorinated polysiloxane/TiO2 nanocomposite coatings with long-term durability, J. Mater. Chem. 21 (2011) 6161–6164. [34] S. Wang, M. Li, Q. Lu, Filter paper with selective absorption and separation of liquids that differ in surface tension, ACS Appl. Mater. Interfaces 2 (2010) 677–683. [35] P. Roach, N.J. Shirtcliffe, M.I. Newton, Progress in superhydrophobic surface development, Soft Matter 4 (2008) 224–240.
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207
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ARTICLE IN PRESS C. Du et al. / Applied Surface Science xxx (2014) xxx–xxx
[36] R. Gao, Q. Liu, J. Wang, J. Liu, W. Yang, Z. Gao, L. Liu, Construction of superhydrophobic and superoleophilic nickel foam for separation of water and oil mixture, Appl. Surf. Sci. 289 (2014) 417–424. [37] Y. Xiu, D.W. Hess, C.P. Wong, UV and thermally stable superhydrophobic coatings from sol–gel processing, J. Colloid Interface Sci. 326 (2008) 465–470. [38] A.V. Rao, S.D. Bhagat, H. Hirashima, G.M. Pajonk, Synthesis of flexible silica aerogels using methyltrimethoxysilane (MTMS) precursor, J. Colloid Interface Sci. 300 (2006) 279–285.
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[39] N.J. Shirtcliffe, G. McHale, M.I. Newton, C.C. Perry, Intrinsically superhydrophobic organosilica sol–gel foams, Langmuir 19 (2003) 5626–5631. [40] X. Feng, J. Zhai, L. Jiang, The fabrication and switchable superhydrophobicity of TiO2 nanorod films, Angew. Chem. Int. Ed. Engl. 44 (2005) 5115–5118. [41] H.S. Lim, D. Kwak, D.Y. Lee, S.G. Lee, K. Cho, UV-driven reversible switching of a roselike vanadium oxide film between superhydrophobicity and superhydrophilicity, J. Am. Chem. Soc. 129 (2007) 4128–4129.
Please cite this article in press as: C. Du, et al., Durable superhydrophobic and superoleophilic filter paper for oil–water separation prepared by a colloidal deposition method, Appl. Surf. Sci. (2014), http://dx.doi.org/10.1016/j.apsusc.2014.05.207