superoleophilic corn straw fibers as effective oil

Research Article Received: 18 August 2015

Revised: 6 October 2015

Accepted article published: 10 October 2015

Published online in Wiley Online Library:

(wileyonlinelibrary.com) DOI 10.1002/jctb.4834

Superhydrophobic/superoleophilic corn straw fibers as effective oil sorbents for the recovery of spilled oil Deli Zang, Ming Zhang, Feng Liu and Chengyu Wang* Abstract BACKGROUND: In recent years, superhydrophobic and superoleophilic materials have attracted great interest and have been applied to the removal of oil contaminants from water. The combined effect of hierarchical coarse structure and low surface free energy is essential for the acquisition of superhydrophobicity and superoleophilicity. In the present study, a facile, low-cost, fluorine-free and eco-friendly method is proposed for the development of superhydrophobic/superoleophilic corn straw fibers via conventional impregnation to realize the removal of oil from water. RESULTS: The simultaneous performances of superhydrophobicity and superoleophilicity of the product were attributed to the covalent deposition of hollow spherical zinc oxide (ZnO) particles on the surface of fibers and subsequent hydrophobic modification using hexadecyltrimethoxysilane (HDTMOS). In addition, the superhydrophobic and superoleophilic performances of as-prepared corn straw remained in complex conditions of corrosive solution and long-time storage. The absorption capacity of superhydrophobic/superoleophilic corn straw for crude oil was 20.4 g g−1 , demonstrating high uptake capacity. CONCLUSION: The superhydrophobic/superoleophilic corn straw fibers possessed excellent stability and enhanced absorption capacity. The as-prepared product could be widely used as an oil sorbent for oil/water separation. This study provided evidence for the better utilization of waste corn straw in the field of oil spills cleanup. © 2015 Society of Chemical Industry Keywords: oil absorption; corn straw; ZnO particles; superhydrophobic; superoleophilic

INTRODUCTION Along with the swift development of offshore oil exploration and maritime traffic, frequently occurring oil spills have caused serious damage to the ecological environment and great loss of natural resources.1 – 4 As awareness of the need for environmental protection has increased, many absorbent materials have been developed and applied to the cleanup of spilled oil such as chemical synthetic organic materials, activated carbon with large surface area, porous materials, oil absorption resin, etc.5 – 7 Nevertheless, these materials inevitably suffer from such defects as time-consuming, high cost, non-biodegradable, co-adsorption of water and low separation resulting from lipophilic properties.8,9 There still exists an extremely pressing need for neoteric adsorbents with both superhydrophobicity and superoleophilicity which can effectively achieve the removal of oil from water.10 Nowadays, researchers pay extensive attention to the establishment of superhydrophobic surfaces with water contact angle (WCA) larger than 150∘ and sliding angle (SA) lower than 10∘ . The superhydrophobic characteristic was attributed to combination of a construction having hierarchical rough structure and surface modification with a low surface energy substance.11 – 15 The technologies most widely used to fabricate superhydrophobic materials include chemical etching,16 template method,17 layer-by-layer self-assembly,18 physical or chemical vapor deposition,19 impregnation technology, J Chem Technol Biotechnol (2015)

sol–gel process,20 – 22 electrostatic spinning,23,24 and thermal decomposition.25 For instance, Khalil-Abad and co-workers26 developed superhydrophobic cotton textiles by introducing microsized silver particles to the woven fiber network followed by surface hydrophobization of octyltriethoxysilane. Lee et al.27 adopted an electrospinning method to achieve single-step deposition of polystyrene nanofibers onto a stainless steel mesh, and then successfully obtained superhydrophobic/superoleophilic membranes that could remove viscous oils from water. As an agricultural solid waste, corn straw was burned in situ for a long period, thus resulting in serious environmental pollution and waste of a biomass resource. Efficient utilization of corn straw resources is the key to resolving air pollution caused by straw burning. In this contribution, on account of its low density, bargain price, biodegradability and plentiful biomass, corn straw is employed to fabricate superhydrophobic/superoleophilic sorbent to extend its application to oily wastewater treatment, which is an effective way to alleviate water pollution. All raw

∗

Correspondence to: Chengyu Wang, Key Laboratory of Bio-based Material Science and Technology, Ministry of Education, Northeast Forestry University, Harbin 150040, China. E-mail: [email protected] Key Laboratory of Bio-based Material Science and Technology, Ministry of Education, Northeast Forestry University, Harbin 150040, China

www.soci.org

© 2015 Society of Chemical Industry

www.soci.org

D Zang et al.

Figure 1. (a) Chemical structure of hexadecyltrimethoxysilane (HDTMOS); (b) schematic illustration of the process for fabrication of superhydrophobic/superoleophilic corn straw and the hydrolysis of HDTMOS; (c) schematic illustration of the modification of ZnO particle with HDTMOS.

materials are commercially available and fluorine-free. The process for fabrication of superhydrophobic/superoleophilic corn straw is convenient and efficient. The deposition of abundant hollow spherical ZnO granules on the surface of fibers effectively increases surface roughness and chemical hydrophobic modification with HDTMOS reduces surface free energy, brings about simultaneous superhydrophobicity and superoleophilicity of corn straw. The product displayed good stability performance and high absorption capacity. The superhydrophobic/superoleophilic corn straw fibers could serve as oil sorbents to separate oil from oil–water mixtures.

Pretreatment of the corn straw First, corn straw was peeled and put into a pulverizer to obtain straw fibers, then sieved through 60 and 80 mesh standard screens to collect uniform graded fibers (250–425 μm). Before use, corn straw was ultrasonically rinsed with ultrapure water, anhydrous ethanol and ultrapure water, respectively. Afterwards, corn straw was immersed in a beaker containing 100 mL of 0.5 wt.% sodium hydroxide aqueous solution and 3.5 mL of 30% hydrogen peroxide and stirred for 14 h at ambient temperature. In the next process, the pH of the solution was adjusted to 6.5–7.0 with 6 mol L−1 hydrochloric acid. After washing with ultrapure water several times, the pretreated corn straw was dried at 40 ∘ C until its weight remained constant.

EXPERIMENTAL Materials Corn straw was obtained from a farm in Harbin. Anhydrous ethanol (99.7%), sodium hydroxide (96.0%), hydrogen peroxide (30.0%), hydrochloric acid (37.0%), methyl alcohol (99.7%), sodium dodecanesulphonate (SDBS, 99.0%) and acetic acid (99.5%) were purchased from Tianjin Kaitong Chemical Reagent Co., Ltd. Zinc nitrate was provided by Tianjin Hengxing Chemical Reagent Co., Ltd. Hexadecyltrimethoxysilane (HDTMOS, 99.5%) used for modifying ZnO particles was provided by Nanjing Chengong Organic Silicone Material Co., Ltd. Ultrapure water was made in-house with an Ultrapure Water System provided by Beijing Zhongyang Yongkang Environmental Protection Technology Co., Ltd. All chemical reagents were of analytical grade and were used as received without further purification. Diesel oil, gasoline, crude oil, bean oil, n-hexane, octane, toluene, chloroform used for oil contact angle (OCA) test and absorption capacity measurement were obtained from Harbin.

wileyonlinelibrary.com/jctb

Synthesis of ZnO particles First, 1.6 g of sodium hydroxide was added into a beaker of 80 mL ultrapure water and placed in a water bath under vigorous stirring for 10 min at 70 ∘ C. Then, 1.2 g of zinc nitrate was mixed with the above sodium hydroxide aqueous solution and the reaction mixture was stirred under the same conditions for another 20 h. Afterwards, the solution was placed for 6 h at room temperature, and thoroughly rinsed with ultrapure water and anhydrous ethanol to remove unreacted reagents or by-product. The resulting solution was dried at 60 ∘ C for 5 h in a vacuum oven. The white powder obtained was zinc oxide particles. Fabrication of superhydrophobic/superoleophilic corn straw In detail, 0.1 g ZnO, 0.01 g SDBS and 0.1 g pretreatment corn straw were dispersed in a solution of 10 mL methyl alcohol, 0.2 mL HDTMOS, 0.4 mL ultrapure water and 0.1 mL acetic acid under stirring at room temperature for 5 h. After washing by dipping in


J Chem Technol Biotechnol (2015)

Superhydrophobic/superoleophilic corn straw fibers

www.soci.org

(a)

(b)

(c)

(d)

Figure 2. Typical SEM images of (a, b) pristine corn straw fiber surface and (c, d) as-prepared superhydrophobic/superoleophilic corn straw fiber surface at different magnifications.

(a)

(b)

(c)

Figure 3. Images of liquid droplets on different surfaces: typical photograph of 5 μL water droplet on the surfaces of (a) raw corn straw fiber and (b) as-prepared superhydrophobic/superoleophilic corn straw fiber; (c) oil droplet on superhydrophobic/superoleophilic corn straw fiber surface.

anhydrous ethanol and ultrapure water, corn straw was dried at 40 ∘ C until no further weight loss to achieve superhydrophobic/superoleophilic corn straw fibers. As shown in Fig. 1, in our work, HDTMOS chemical agent was employed to act as a hydrophobic modifier and its modification mechanism was as follows: silicon hydroxyl groups generated from hydrolysis reaction of HDTMOS reagent reacted with hydroxyl groups on the surfaces of ZnO particles and pristine corn straw fibers, so that hydrophobic long-chain alkyl of HDTMOS was introduced onto fiber surfaces, inducing low surface energy of superhydrophobic/superoleophilic corn straw. Characterization The microstructures of pristine corn straw and the resulting superhydrophobic/superoleophilic corn straw fiber were detected using scanning electron microscopy (SEM, TM3030), with all specimens precoated with a conductive layer of sputtered gold. The chemical composition of corn straw product was characterized by Fourier transform infrared spectroscopy (FT-IR, Magna-IR 560, Nicolet) and energy-dispersive X-ray analysis (EDX). Water contact angle (WCA) and oil contact angle (OCA) measurements were carried out on a J Chem Technol Biotechnol (2015)

contact angle instrument (Hitachi, CA-A) by dropping 5 μL of ultrapure water or oil droplet onto at least five different positions of corn straw specimens. The reported values of WCA and OCA were determined by averaging the five measurements. Evaluation of absorption capability and oil removal efficiency Oil absorption capability measurement was performed in a pure oil system by dipping a nylon net bag filled with 0.5 g of corn straw into a beaker containing 150 mL of oil at room temperature. After 5 h, the nylon net bag was removed with a nipper and drained for 10 min. Finally, the oil-saturated corn straw was taken out from the nylon net bag and weighed. Oil absorption capability was defined as: ( ) q = m2 − m1 ∕m1 where q is oil absorption capability (g g−1 ); m2 is the weight of corn straw fibers after absorption (g); m1 is the initial weight of corn straw fibers before absorption (g). Similar to the oil absorption capability test, an oil removal efficiency experiment was performed in an oil–water mixture in which oil and water was layered. In detail, the nylon net bag



www.soci.org

D Zang et al.

where k is oil removal efficiency (%); w3 is the weight of corn straw fibers after absorption (g); w2 is the initial weight of corn straw fibers before absorption (g); w1 is the weight of water absorbed in the sorbents (g).

(b)

(a)

RESULTS AND DISCUSSION

Figure 4. FT-IR spectra of (a) raw corn straw fiber and (b) as-prepared superhydrophobic/superoleophilic corn straw fiber.

containing 0.5 g corn straw was added to 150 mL of different mass ratios of oil–water mixtures under stirring at room temperature. After 5 h, the nylon net bag was removed with a nipper and drained for 10 min. The saturated corn straw was removed from the nylon net bag and weighed. Oil removal efficiency was calculated by the following equation: ( ) ( ) k = w3 − w2 − w1 ∕ w3 − w2

Surface microscopy of superhydrophobic/superoleophilic corn straw Superhydrophobic behavior results from a binary surface microstructure of micro/nano construction. Therefore, surface characteristics of raw corn straw and superhydrophobic/superoleophilic corn straw were accurately surveyed using scanning electron microscopy at different magnifications, as listed in Fig. 2. The low magnification images revealed that as-prepared corn straw fiber was similar to the pristine fiber and the structure of treated corn straw was the same as that of the raw material (Fig. 2(a) and (b)). Raw corn straw fiber possessed a smooth fiber surface. After functionalizing with HDTMOS-modified ZnO particles, the surface of superhydrophobic/superoleophilic corn straw was rough because of the deposition of an insoluble layer of ZnO granules. The high magnification images (Fig. 2(c) and (d)) showed that the ZnO particles were hollow spheres with average diameter approximately 5 μm. Thus as-prepared corn straw fiber was sufficiently rough to exhibit both superhydrophobic and superoleophilic features. As can be seen, the generation of hollow spherical ZnO played a significant role during the fabrication of superhydrophobic/superoleophilic corn

(a)

(b)

Figure 5. EDX spectra of (a) pristine corn straw fiber and (b) as-prepared superhydrophobic/superoleophilic corn straw fiber.




Superhydrophobic/superoleophilic corn straw fibers

www.soci.org

(a)

(b)

Figure 8. (a) SEM image of superhydrophobic/superoleophilic corn straw sample after absorption. (b) Optical image of a water droplet on corn straw sample after absorption.

droplets dripped onto the surface of samples would contact the trapped air and bounce off without leaving residues, exhibiting a well-produced superhydrophobic property of as-obtained corn straw.

Figure 6. (a) Variation in WCA and OCA of as-prepared corn straw with different aqueous solution pH; (b) the relationship between the values of WCA and OCA of resulting corn straw and long-term exposure to ambient air.

straw fiber. In combination with the modification by HDTMOS low surface energy material, abundant air could be trapped in cavities and interspaces on the corn straw after treatment. Water

Surface wettability of superhydrophobic/superoleophilic corn straw To verify the superhydrophobicity and superoleophilicity properties of the product, we explored surface wettability of as-prepared corn straw by measuring the values of WCA and OCA on a contact angle device at room temperature as presented in Fig. 3. Because of abundant hydroxyl groups on the fiber surface, WCA of raw corn straw fiber was 0∘ (Fig. 3(a)). A water droplet on the superhydrophobic/superoleophilic corn straw fiber surface was spherical and stable, with WCA as high as 155∘ and SA less than 3∘ (Fig. 3(b)), illustrating the superhydrophobic performance of the product. In addition to water wettability, we also investigated oil wettability of as-obtained corn straw surface. An oil droplet falling onto the as-prepared sample surface immediately sank into the sample, revealing perfect oil wettability of the product. Specifically, contact angles of the resulting corn straw for diesel oil, gasoline and kerosene were near zero (Fig. 3(c)), which showed the favorable superoleophilic characteristic of the fiber.

Figure 7. Photographs of superhydrophobic/superoleophilic corn straw fibers as oil sorbents for the removal of oil from water surface: (a) the treated corn straw; (b), (c) the mixture of water and gasoline (dyed red with Sudan III for clear observation); (d) the red gasoline was absorbed by the sorbent; (e) the oil-saturated corn straw was taken out with lab spoon; (f ) the final corn straw filled with red gasoline.




www.soci.org

D Zang et al.

According to the theoretical principle of surface wettability,28 – 30 it could be concluded that the wettability of a material is controlled by its chemical composition as well as its surface morphology structure. Therefore, the combination of numerous aggregations of ZnO particles and surface decoration by low surface energy HDTMOS could prevent water from wetting the as-prepared sample surface. Chemical component analysis Fourier transform infrared (FT-IR) and energy-dispersive X-ray analysis (EDX) were conducted to detect surface chemical components of superhydrophobic/superoleophilic corn straw fiber in order to verify the presence of HDTMOS-modified ZnO particles. The typical FT-IR spectra of raw corn straw fiber and as-prepared superhydrophobic/ superoleophilic corn straw fiber over the range 700–3400 cm−1 are presented in Fig. 4. In the high frequency region, the band located at 3337 cm−1 in both spectra is due to —OH groups, which obviously decreased in the superhydrophobic/superoleophilic product compared with that of pristine corn straw fiber. In Fig. 4(b), the absorption peaks at 2920 cm−1 and 2851 cm−1 are attributed to asymmetric and symmetric stretching vibrations of —CH2 and —CH3 , confirming the existence of HDTMOS. Moreover, the characteristic absorption peak around 1100–800 cm−1 owing to the Si—O—Si stretching vibration of HDTMOS seemed to be overlapped by the C—O stretching vibration of the cellulose in corn straw fiber. Figure 5 showed EDX spectra of pristine corn straw and as-prepared superhydrophobic/superoleophilic corn straw. The oxygen (O) peak and the carbon (C) peak streamed from corn straw fiber construction were observed in both spectra. In addition, there was a new peak due to Zn, which was induced by ZnO particles in as-prepared corn straw product (Fig. 5(b)). The above results showed that ZnO particles were successfully modified by HDTMOS organic reagent during the fabrication of superhydrophobic/superoleophilic corn straw fiber. Stability evaluation Because secular stability has a significant impact on practical application, we investigated chemical stability and environmental durability of superhydrophobic/superoleophilic corn straw to determine whether it could be widely used. Chemical stability was evaluated by surveying the changes in WCA and OCA of the sample. Contact angle measurements were conducted by dropping 5 μL of aqueous solution (at various pH ranging from 0 to 14) onto a sample surface at room temperature. The relationship between the values of WCA and OCA of as-prepared corn straw and aqueous solution pH value is presented in Fig. 6(a). With increase of aqueous solution pH, the WCA on the product surface varied slightly but remained greater than 150∘ ; the measured OCA was constant at 0∘ . Thus, the superhydrophobic and superoleophilic properties of the product were retained in corrosive solutions, i.e. the as-prepared corn straw presented acid and alkali resistance. This sort of superhydrophobic/superoleophilic corn straw possessed admirable chemical stability. Also, as described in Fig. 6(b), there was no apparent change in the values of WCA and OCA of as-prepared corn straw after being exposed to ambient air for 150 days, suggesting noteworthy environmental durability of superhydrophobic/superoleophilic corn straw under atmospheric conditions.


Figure 9. (a) Maximum absorption capacity of raw corn straw and superhydrophobic/superoleophilic corn straw for different types of oils and organic solvents at room temperature. (b) Absorption efficiency of superhydrophobic/superoleophilic corn straw with different mass ratios of water to oil. (c) Reusability of superhydrophobic/superoleophilic corn straw for diesel oil, bean oil, n-hexane and chloroform.

APPLICATION TO WATER–OIL SEPARATION The water-repellency and stability of the product provided strong potential for its practical application in the field of oil spill cleanup. The high buoyancy of corn straw made it self-floating on the water surface after absorption, which was conducive to the recycling of corn straw. The superhydrophobic/superoleophilic corn straw was applied to the separation of an oil–water mixture in which oil and water was layered. Figure 7 shows the process of superhydrophobic/superoleophilic corn straw fibers as oil sorbents for the removal of oil from the water surface; the composition of mixture was 30 mL water and 5 mL gasoil. When as-prepared corn straw was dipped into water–oil mixture, the oil was absorbed quickly



Superhydrophobic/superoleophilic corn straw fibers by the sorbent and the oil-saturated corn straw floated on the surface of the water. The corn straw filled with red gasoline could be taken out with a lab spoon. As shown in Fig. 8, after absorption, the ZnO particles had not split away from the fibers and corn straw remained superhydrophobic with a WCA of 152∘ . Because of its chemical stability and environmental durability, superhydrophobic/superoleophilic corn straw could be developed and applied in the field of oily wastewater treatment. In general, oil absorption performance is measured by maximum oil absorption capacity and oil removal efficiency. Figure 9(a) shows the absorption capacity of raw corn straw and superhydrophobic/superoleophilic corn straw for gasoline, crude oil, diesel oil, engine oil, chloroform, n-hexane and toluene at ambient temperature. The maximum absorption capacity for the same oil of superhydrophobic/superoleophilic corn straw was almost three times that of raw corn straw, demonstrating that the oil absorption capacity of the product had been greatly enhanced. The oil removal efficiency of the corn straw product for diesel oil and crude oil were also investigated. From Fig. 9(b), it was observed that oil removal efficiency of superhydrophobic/superoleophilic corn straw for diesel oil–water and crude oil–water mixtures changed from 100% to 99.1% with different mass ratios of water to oil, which was mainly due to the absorption of water together with oil by the superhydrophobic/superoleophilic corn straw. Due to the fact that the recycling performance of oil sorbents plays an important role in oil–water separation, the reusability of superhydrophobic/superoleophilic corn straw for diesel oil, bean oil, n-hexane and chloroform was investigated, with results as shown in Fig. 9(c). After being rinsed in acetone and water, the product could be reused to absorb oil for many cycles, crucial for widespread use. It can be seen that at the third cycle the absorption capacity of reused corn straw for all oils and organic solvents was reduced to 77–89% of the initial maximum absorption capacity. This was mainly a result of the residual oil remaining in the fibers of the corn straw product. After the third cycle, the oil absorption capacity changed slightly with increase of cycles, showing excellent reusability.

CONCLUSIONS This study provided new insight to environment-friendly superhydrophobic/superoleophilic corn straw fibers as promising oil sorbents for oil spill cleanup. The product was prepared without using fluorine-containing organic compounds, which met the requirements of environmental protection and sustainable development. The as-prepared corn straw exhibited outstanding superhydrophobic and simultaneous superoleophilic properties with WCA of 155∘ and OCA of 0∘ . Results clearly showed that abundant hollow spherical ZnO particles on the surface of corn straw fibers were conducive to improving surface roughness, and chemical modification by HDTMOS effectively lowered the surface energy of the product. The superhydrophobic/superoleophilic corn straw possessed high absorption capacity and good reusability. The favorable stability and enhanced absorption capacity of the corn straw product suggested remarkable potential as an oil absorbent for oil–water separation.

ACKNOWLEDGEMENTS This research was supported by the National Natural Science Foundation of China (31470584) and the Fundamental Research Funds for the Central Universities (2572015 EB01). J Chem Technol Biotechnol (2015)

www.soci.org

REFERENCES 1 Nelson JR, Grubesic TH, Sim L, Rose K and Graham J, Approach for assessing coastal vulnerability to oil spills for prevention and readiness using GIS and the blowout and spill occurrence model. Ocean Coastal Manage 112:1–11 (2015). 2 Caballero-Miguez G and Fernández-González R, Institutional analysis, allocation of liabilities and third-party enforcement via courts: the case of the Prestige oil spill. Marine Policy 55:90–101 (2015). 3 Yang R, Technology research and experiment application of marine oil spill buoy. Aquatic Procedia 3:119–126 (2015). 4 Cleveland C, Hogan CM and Saundry P, Deepwater horizon oil spill. In The Encyclopedia of Earth. [Online]. (2010) Available: http://www.eoearth.org/article/Deepwater_Horizon_oil_spill [23 July 2010]. 5 Ceylan D, Dogu S, Karacik B, Yakan SD, Okay OS and Okay O, Evaluation of butyl rubber as sorbent material for the removal of oil and polycyclic aromatic hydrocarbons from seawater. Environ Sci Technol 43:3846–3852 (2009). 6 Karakasi O and Moutsatsou A, Surface modification of high calcium fly ash for its application in oil spill clean up. Fuel 89:3966–3970 (2010). 7 Zhou XM and Chuai CZ, Synthesis and characterization of a novel high – oil – absorbing resin. J Appl Polym Sci 115:3321–3325 (2010). 8 Wang J, Zheng Y and Wang A, Superhydrophobic kapok fiber oil-absorbent: preparation and high oil absorbency. Chem Eng J 213:1–7 (2012). 9 Wang B, Li J, Wang G, Liang W, Zhang Y, Shi L et al., Methodology for robust superhydrophobic fabrics and sponges from in situ growth of transition metal/metal oxide nanocrystals with thiol modification and their applications in oil/water separation. ACS Appl Mater Interfaces 5:1827–1839 (2013). 10 Wang F, Lei S, Xue M, Ou J, Li C and Li W, Superhydrophobic and superoleophilic miniature device for the collection of oils from water surfaces. J Phys Chem C 118:6344–6351 (2014). 11 Daniello R, Muralidhar P, Carron N, Greene M and Rothstein JP, Influence of slip on vortex-induced motion of a superhydrophobic cylinder. J Fluid Structures 42:358–368 (2013). 12 Gao L, Lu Y, Zhan X, Li J and Sun Q, A robust, anti-acid, and high-temperature – humidity-resistant superhydrophobic surface of wood based on a modified TiO2 film by fluoroalkyl silane. Surface Coatings Technol 262:33–39 (2015). 13 Zhang J, Song Z, Li B, Wang Q and Wang S, Fabrication and characterization of superhydrophobic poly (vinylidene fluoride) membrane for direct contact membrane distillation. Desalination 324:1–9 (2013). 14 Tang Y, Yang J, Yin L, Chen B, Tang H, Liu C et al., Fabrication of superhydrophobic polyurethane/MoS2 nanocomposite coatings with wear-resistance. Colloids Surf A: Physicochem Eng Aspects 459:261–266 (2014). 15 Crick CR, Gibbins JA and Parkin IP, Superhydrophobic polymer-coated copper-mesh; membranes for highly efficient oil–water separation. J Mater Chem A 1:5943–5948 (2013). 16 Xue C-H, Li Y-R, Zhang P, Ma J-Z and Jia S-T, Washable and wear-resistant superhydrophobic surfaces with self-cleaning property by chemical etching of fibers and hydrophobization. ACS Appl Mater Interfaces 6:10153–10161 (2014). 17 Yuan Z, Chen H, Tang J, Gong H, Liu Y, Wang Z et al., A novel preparation of polystyrene film with a superhydrophobic surface using a template method. J Phys D: Appl Phys 40:3485 (2007). 18 Zhang C, Zhang S, Gao P, Ma H and Wei Q, Superhydrophobic hybrid films prepared from silica nanoparticles and ionic liquids via layer-by-layer self-assembly. Thin Solid Films 570(Part A):27–32 (2014). 19 Wang J, Song X, Shen J, Yang G and Huang H, Fluorocarbon thin film with superhydrophobic property prepared by pyrolysis of hexafluoropropylene oxide. Appl Surf Sci 258:9782–9785 (2012). 20 Houmard M, Berthomé G, Joud JC and Langlet M, Enhanced cleanability of super-hydrophilic TiO2–SiO2 composite surfaces prepared via a sol–gel route. Surface Sci 605:456–462 (2011). 21 Yang H, Pi P, Cai Z-Q, Wen X, Wang X, Cheng J et al., Facile preparation of super-hydrophobic and super-oleophilic silica film on stainless steel mesh via sol–gel process. Appl Surface Sci 256:4095–4102 (2010). 22 Taurino R, Fabbri E, Pospiech D, Synytska A and Messori M, Preparation of scratch resistant superhydrophobic hybrid coatings by sol–gel process. Progress Organic Coatings 77:1635–1641 (2014).



www.soci.org 23 Wang X, Ding B, Yu J and Wang M, Engineering biomimetic superhydrophobic surfaces of electrospun nanomaterials. Nano Today 6:510–530 (2011). 24 Chen Z, Hao L, Chen A, Song Q and Chen C, A rapid one-step process for fabrication of superhydrophobic surface by electrodeposition method. Electrochimica Acta 59:168–171 (2012). 25 Talaeemashhadi S, Sansotera M, Gambarotti C, Famulari A, Bianchi CL, Antonio Guarda P et al., Functionalization of multi-walled carbon nanotubes with perfluoropolyether peroxide to produce superhydrophobic properties. Carbon 59:150–159 (2013). 26 Khalil-Abad MS and Yazdanshenas ME, Superhydrophobic antibacterial cotton textiles. J Colloid Interface Sci 351:293–298 (2010).


D Zang et al.

27 Lee MW, An S, Latthe SS, Lee C, Hong S and Yoon SS, Electrospun polystyrene nanofiber membrane with superhydrophobicity and superoleophilicity for selective separation of water and low viscous oil. ACS Appl Mater Interfaces 5:10597–10604 (2013). 28 Wenzel RN, Resistance of solid surfaces to wetting by water. Ind Eng Chem 28:988–994 (1936). 29 Cassie A and Baxter S, Wettability of porous surfaces. Trans Faraday Soc 40:546–551 (1944). 30 Wang C, Yao T, Wu J, Ma C, Fan Z, Wang Z et al., Facile approach in fabricating superhydrophobic and superoleophilic surface for water and oil mixture separation. ACS Appl Mater Interfaces 1:2613–2617 (2009).

