Design of Recyclable Superhydrophobic PU@Fe3O4@PS Sponge for

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Design of Recyclable Superhydrophobic PU@FeO@PS Sponge for Removing Oily Contaminants from Water Yu Zhou, Ning Zhang, Xiang Zhou, Yubing Hu, Gazi Hao, Xiaodong Li, and Wei Jiang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b04642 • Publication Date (Web): 22 Jan 2019 Downloaded from http://pubs.acs.org on January 27, 2019

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Industrial & Engineering Chemistry Research

Design of Recyclable Superhydrophobic PU@Fe3O4@PS Sponge for Removing Oily Contaminants from Water Yu Zhou†, Ning Zhang†, Xiang Zhou†, Yubing Hu†, Gazi Hao†, Xiaodong Li‡, Wei Jiang*,† †National Special Superfine Powder Engineering Research Center, Nanjing University of Science and Technology, Nanjing 210094, PR China ‡Jiangsu Lianrui New Material Company, Lianyungang 222346, PR China

Abstract: With the increase of oil spill accidents and discharge of oily wastewater, a novel oil adsorption material with superhydrophobicity and reusability is desired. To our knowledge, low surface energy and surface roughness are two key factors for superhydrophobic materials. Thus, a recyclable superhydrophobic PU@Fe3O4@PS sponge was fabricated through ultrasonic dip-coating and self-initiated photografting and photopolymerization (SIPGP) to attach Fe3O4 nanoparticles and polystyrene (PS) brushes onto the skeleton surface of the polyurethane (PU) sponge, constructing superhydrophobic micro-nano hierarchical surface. The preparation process was facile and simple, which was accomplished without initiator under simple UV irradiation. This as-prepared sponge selectively removed various oily contaminants from water with high adsorption capacity, and its magnetic property and elasticity endowed it with good reusability. When it was connected with a negative pressure system, continuous oil-water separation was achieved. Therefore, it is really a potential adsorbent for practical application in oil-polluted water treatment.

Keywords: Dip-coating; Photopolymerization; PU@Fe3O4@PS sponge; Oil-water separation; Reusability; Magnetic response 1

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1. INTRODUCTION The rapid development of modern transportation and industry has brought a great convenience to our lives. However, it has also caused a series of environmental pollution, such as the oil spill accidents and discharge of oily wastewater1-4. These problems not only limit the further development of society, but also directly result in the rapid deterioration of the ecological environment and threaten our health. However, the most common oil-water separation methods are still the traditional techniques including in-situ controlled ignition, physical collection, chemical dispersions, and biodegradation5-7. Among them, the physical adsorbents are convenient and environmentally friendly, which are recognized as the most appropriate way for oily wastewater treatment. An ideal adsorbent should possess the following characteristics: high adsorption capacity, excellent oil/water selectivity, low cost and outstanding recyclability8-10. In recent years, a series of new three-dimensional porous materials with superhydrophobic and superoleophilic properties have been synthesized successfully, including high oil-adsorbing resins11-14, graphene-based aerogels15-19 and modified composite sponges20-24, etc., to realize oil-water separation instead of natural porous minerals and carbon materials25-27. However, most of these materials are of tedious synthesis procedure and fragile during application, which thus increases the cost and limits the practical application in oil-water separation. Compared with the above-mentioned materials, polyurethane (PU) sponge is commercially available and displays outstanding properties including low density, excellent elasticity and easy large-scale fabrication28-30. However, pure PU sponge does 2


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not have enough oil-water selectivity and requires further interfacial modification. Material interfaces play a particularly central role in functional composites, which provide a special treatment of the surface of the material to achieve the desired function31, 32. Recently, engineering interfaces of materials have drawn the attention of many researchers and a variety of interface modification methods have been developed to obtain superhydrophobic/superoleophilic PU sponge for the removal of oils and organic solvent pollutants in water treatment 33-39. For example, Zhang et al.34 reported a bioinspired multifunctional polyurethane sponge in a multi-step process including etching with chromic acid solution to increase surface roughness and then dip-coating in ethanol solution of fluoroalkylsilane to reduce surface energy. In the first step, etching with acid solution increases surface roughness of sponge and brings in active groups simultaneously, which makes it easy for the following modification. However, compared with the original sponge, the acid solution definitely sacrifices its mechanical properties. In addition, this step produces acidic wastes which will cause secondary pollution during the application process. Zhou et al.36 prepared a graphene/polyurethane sponge via one-pot synthesis by solvothermal technique. The synthetic process requires high temperature and high pressure. Wang et al.38 fabricated a carbon nanotubes reinforced superhydrophobic/superoleophilic polyurethane sponge with the assistance of oxidative self-polymerization of dopamine. However, it still needs to pretreat with chromic acid solution, and multi-step reactions are followed to anchor carbon nanotubes and graft hydrophobic octadecylamine onto the skeleton of sponge, which limits the large-scale manufacture. Therefore, it is urgent to find a facile and 3



environmentally

friendly

technology

for

preparing

superhydrophobic

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and

superoleophilic PU sponge, which not only endows sponge with outstanding chemical and mechanical stability but also can be easy to scale up. The photopolymerization is a facile method which can be employed for surface modification with polymer40-42. It causes no damage to the original material and can be accomplished without any initiator under simple illumination. However, it is rarely reported in the preparation of oil adsorption materials. Based on this inspiration, here we reported a two-step process to fabricate a superhydrophobic PU@Fe3O4@PS sponge. The PU sponge was firstly functionalized with Fe3O4 nanoparticles by ultrasonic dip-coating to obtain magnetic property and active surface for further modification. Then polystyrene (PS) brushes were grafted onto the skeleton surface of PU@Fe3O4 sponge through self-initiated photografting and photopolymerization (SIPGP)43-45 under UV irradiation. As expected, the prepared PU@Fe3O4@PS sponge possessed of superhydrophobicity, high adsorption capacity and excellent reusability. Thus, it was applied to selectively adsorb various oils and organic solvents from water, and it realized continuous and efficient oil-water separation in conjunction with a peristaltic pump. Additionally, the magnetic property of PU@Fe3O4@PS sponge made it convenient for recovery by a magnet after oil adsorption. Above all, this sponge was regenerated simply and can be used for oil adsorption multiple times, which will have huge potential application to deal with spill accidents and oily wastewater.

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2. EXPERIMENTAL SECTION 2.1. Materials. Iron (III) chloride hexahydrate (FeCl3•6H2O), sodium acetate anhydrous (NaAc), sodium hydroxide (NaOH), phenylethylene and ethyl acetate were obtained from Sinopharm Chemical Reagent Co. Ltd., Shanghai, China. Polyvinyl pyrrolidone (PVP) and divinylbenzene were bought from Aladdin Reagent Co., Ltd., Shanghai, China. Acetone and toluene were purchased from Shanghai Linfeng Chemical Reagent Co. Ltd., Shanghai, China. Ethylene glycol and ethanol were purchased from Nanjing Chemical Reagent Co. Ltd., Nanjing, China. PU sponge was provided by a local store. All reagents were analytically pure and used as received without further purification. Deionized water was employed in all the experiments.

2.2. Preparation of PU@Fe3O4@PS sponge. Magnetic Fe3O4 nanoparticles were synthesized via an improved solvothermal route from previous report46. Typically, 1.5 g of FeCl3•6H2O, 1 g of PVP, and 2 g of NaAc were completely dissolved in 30 mL of ethylene glycol under sonication for 30 min. Then the solution was sealed in a hydrothermal reaction vessel and heated for 8 h at 200 °C. The obtained Fe3O4 nanoparticles were repeatedly washed with ethanol and deionized water for five times. Pristine PU sponges (1×1×3 cm3) were stirred in deionized water and acetone aqueous solution at 60 °C for 2 h, respectively, and then dried at 60 °C for 2 h. After drying, a few pieces of PU sponges were immersed into a 5mg/mL alcoholic suspension solution of Fe3O4 nanoparticles and sonicated at room temperature for 10 min to obtain 5



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PU@Fe3O4 sponge, followed by drying in oven. Then a piece of sponge was immersed in a quartz tube containing 6 mL of phenylethylene and 0.3 mL of divinylbenzene, and irradiated with 100 W Hg lamp under nitrogen atmosphere for 10 h. After SIPGP was performed, the obtained PU@Fe3O4@PS sponge was successively washed with toluene, ethyl acetate and ethanol, and finally dried in oven at 60 °C for 2 h. For a comparative study, PU@PS sponge was prepared without magnetic Fe3O4 nanoparticles via the same photopolymerization process.

2.3. Characterization. The microscopic morphology of samples was observed at 15 kV by Model S-4800 field

emission

scanning

electron

microscope

(SEM)

(Hitachi,

Japan).

Thermogravimetric analysis (TGA) was conducted by TA 2100 Thermogravimetric Analyzer (TA Instruments, USA) from 50 °C to 600 °C under a nitrogen atmosphere at the heating rate of 10 °C/min. The water contact angles (WCAs) at room temperature were measured by a contact angle measuring instrument (XG-CAME, China) to study hydrophobic property of sponges. X-ray diffraction (XRD) spectrum of Fe3O4 nanoparticles was recorded by Bruker-AXS D8 Advance (Bruker, Germany) with Cu Kα radiation. Fourier transform infrared (FT-IR) spectrum was collected by a Thermo Scientific Nicolet iS10 FT-IR spectrometer (Nicolet, USA) within the wave number of 1000-4000 cm-1. The magnetic property of PU@Fe3O4@PS sponge was tested by a vibrating sample magnetometer (VSM) (Lake Shore 735) at 300 K in a field of 10000 Oe to -10000 Oe.

2.4. Oil adsorption experiments. 6


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The adsorption capacity of PU@Fe3O4@PS sponge for different oils and organic solvents was determined by a weighing method. The sponge was placed into a beaker containing 30 mL of oil or organic solvent at room temperature for 30 min and weighed before and after adsorption. During the above oil adsorption test, various oils were employed and each oil was measured for three times. The adsorption capacity can be calculated according to the following formula: 𝑄=

𝑚𝑠 ― 𝑚0 𝑚0

Where, Q is the adsorption capacity of PU@Fe3O4@PS sponge. 𝑚0 and 𝑚𝑠 are the mass of sponge before and after adsorption. The reusability of PU@Fe3O4@PS sponge was investigated by the following procedure. The sponge was placed in oil surface at room temperature for 5 min and weighed before and after adsorption. Then the oil saturated sponge was squeezed by a simple mechanical compression to release the adsorbed oil, followed by washing with anhydrous ethanol and drying at 60 °C for 2 h. This process was repeated 20 times to confirm the recyclability of PU@Fe3O4@PS sponge. The removal of oil from water surface was performed by a self-made device composed of a peristaltic pump, pipe and PU@Fe3O4@PS sponge. Under the drive of peristaltic pump, oil was continuously adsorbed through sponge and pump and finally collected into the beaker.

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3. RESULTS AND DISCUSSION 3.1. Preparation of PU@Fe3O4@PS sponge. The preparation schematic of recyclable superhydrophobic PU@Fe3O4@PS sponge was illustrated in Figure 1a, and mainly contained two procedures. Firstly, the cleaned PU sponge was sonicated into a Fe3O4 homogeneous dispersion solution in ethanol to attach magnetic Fe3O4 nanoparticles onto the skeleton surface of PU sponge, and the PU@Fe3O4 sponge was obtained. The micron-sized skeleton of sponge associated with the Fe3O4 nanoparticles constructed a micro-nano hierarchical structure that increased the roughness of the surface of sponge. In addition, Fe3O4 nanoparticles synthesized in the aqueous phase are covered with a lot of –OH groups47, 48. Under UV irradiation, these groups on the surface of sponge can be initiated to grow polymer brushes as photoactive sites without additional initiator40,

49.

Thus, the SIPGP was

performed as the second procedure to endow PU@Fe3O4 sponge with hydrophobicity. To improve the stability of the PU@Fe3O4@PS sponge, the divinylbenzene was used to enhance cross-linking effect between PS brushes, making PS cover the sponge skeleton like a mesh. The PS brushes imparted superhydrophobic property to the PU@Fe3O4@PS sponge, and bound the Fe3O4 nanoparticles tightly on the skeleton surface of sponge simultaneously. To study whether there was a successful attachment of PS onto the skeleton surface of PU@Fe3O4 sponge, the water contact angle (WCA) was measured to research the change of surface wettability before and after the SIPGP process. As shown in Figure 1b, the WCA of pristine sponge was 118.1°. After sonication in Fe3O4 homogeneous 8


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dispersion solution, the WCA of PU@Fe3O4 sponge decreased to 106.7° (Figure 1c), because of the presence of –OH groups on the surface of Fe3O4 nanoparticles. However, the value of WCA increased by more than 40 degrees and reached up to 151.3° (Figure 1d) after UV irradiation, indicating the superhydrophobicity of the sponge surface. As a result, it can be concluded that a layer of PS was successfully grafted onto the skeleton surface of PU@Fe3O4 sponge and the PU@Fe3O4@PS sponge was generated. Abovementioned two procedures endowed sponge with a superhydrophobic micro-nano hierarchical structure.

Figure 1. (a) The schematic illustration for preparation of PU@Fe3O4@PS sponge; The WCA of (b) PU sponge, (c) PU@Fe3O4 sponge and (d) PU@Fe3O4@PS sponge.

3.2. Surface morphology and chemical composition of PU@Fe3O4@PS sponge. The surface morphology of pristine PU sponge, PU@Fe3O4@PS sponge, PU@Fe3O4 sponge and PU@PS sponge was investigated by scanning electron microscope (SEM) at different magnifications. The pristine PU sponge had an inherent 9



three-dimensional porous network structure with pore sizes of 200-600 μm (Figure 2a), which is important for storing the adsorbed oil. Figure 2b and Figure 2c showed that the skeleton surface of pristine sponge was quite smooth, which is bad for improving hydrophobicity. After dip-coating in magnetic Fe3O4 nanoparticles dispersion solution, the skeleton surface was covered with a layer of spherical nanoparticles and became very rough (Figure 2d, e, f), indicating that Fe3O4 has been successfully attached onto the skeleton surface of sponge. After SIPGP process, the PU@Fe3O4@PS sponge still maintained the same three-dimensional skeleton structure like the pristine sponge (Figure 2g). Figure 2h and Figure 2i were high-magnification SEM images of the skeleton surface of PU@Fe3O4@PS sponge. Compared with the PU@Fe3O4 sponge, the density of nanoparticles increased on the skeleton surface of sponge, resulting in a micro-nano scale rough hierarchical structure, which was of benefit to form superhydrophobic surface. Furthermore, we also synthesized PU@PS sponge without Fe3O4 nanoparticles via the same photopolymerization process. However, only a few PS randomly scattered on the skeleton surface of the sponge (Figure S1), which demonstrates it is difficult for the pristine sponge to grow PS. Therefore, we can infer that Fe3O4 nanoparticles play a role in activating the surface of sponge, which is conducive to the growth of PS brushes in SIPGP process.

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Figure 2. SEM image of (a-c) PU sponge, (d-f) PU@Fe3O4 sponge, and (g-i) PU@Fe3O4@PS sponge at different magnifications.

To investigate the surface chemical composition of sponges, XRD and FT-IR characterizations were performed. Figure 3 showed the XRD pattern of Fe3O4 nanoparticles. The characteristic diffraction peaks appeared at 30.17°, 35.53°, 43.12°, 53.56°, 56.99° and 62.54° that corresponded to (220), (311), (400), (422), (511) and (440) crystal planes of cubic Fe3O4 (JCPDS card no. 19-0629), respectively. The fourier transform infrared (FT-IR) spectra of pristine PU sponge and PU@Fe3O4@PS sponge were displayed in Figure 4 to confirm the existence of PS brushes and Fe3O4 nanoparticles. The typical absorption peaks of PU sponge appeared in the ranges of 1000-1800 cm-1 and 2700-3500cm-136.The curve of PU@Fe3O4@PS sponge was similar to that of the pristine sponge. After careful examination, two new peaks were observed at 3026 cm-1 and 1492 cm-1, which were contributed by -CH- stretching 11



vibration and -C=C- flexural vibration of the benzene ring50-53. Additionally, another strong absorption peak at 564 cm-1 can be ascribed to the Fe-O stretching vibration54. These results indicate that PS and Fe3O4 nanoparticles was grafted on the skeleton surface of sponge successfully by means of dip-coating and photopolymerization.

Figure 3. XRD pattern of Fe3O4 nanoparticles.

Figure 4. FT-IR spectra of sponge before and after modification.

3.3. Properties of PU@Fe3O4@PS sponge. The thermal stability of Fe3O4 nanoparticles and sponges was investigated by thermogravimetric analysis, as shown in Figure 5. As expected, Fe3O4 nanoparticles exhibited no obvious weight change with the increase of temperature, and the weight 12


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loss was only 3.9% at 600 °C. On the contrary, the pristine PU sponge showed a significant weight loss in the range of 250-400 °C, which was attributed to the decomposition of polyurethane36, 38. And there was little residue at last, suggesting that the polyurethane almost decomposed completely at 600 °C. The TGA curve of PU@Fe3O4 sponge was similar to that of pristine sponge but had 12.5% residual mass at 600 °C, which was considered to be the amount of Fe3O4 nanoparticles attached onto the sponge surface. However, compared with pure sponge and PU@Fe3O4 sponge, the decomposition temperature of PU@Fe3O4@PS sponge was higher, mainly ascribed to the presence of PS. In addition, it was noted that there was no weight loss before 200 °C, indicating that the PU@Fe3O4@PS sponge possess satisfactory thermal stability when it is applied in the situations under 200 °C.

Figure 5. TGA curves of Fe3O4, PU sponge, PU@Fe3O4 sponge and PU@Fe3O4@PS sponge.

The magnetic property of Fe3O4 nanoparticles and sponges was examined from 10000 Oe to -10000 Oe by a vibrating sample magnetometer (VSM) at room temperature. As shown in Figure 6, the pure Fe3O4 nanoparticles displayed good magnetic property with a high saturation magnetization of 82.6 emu/g. After 13



functionalization by above Fe3O4, the PU@Fe3O4 sponge was equipped with magnetic property with the saturation magnetization of 23.1 emu/g. By comparison, the value of PU@Fe3O4@PS sponge decreased to 13.4 emu/g after further SIPGP process, which was a normal change55. This result indicates that the introduction of Fe3O4 endowed sponge with magnetic response. Thus, the PU@Fe3O4 sponge can be recovered by a magnet after oil adsorption during practical application56-58.

Figure 6. Magnetic curves of Fe3O4, PU@Fe3O4 sponge and PU@Fe3O4@PS sponge.

The surface wettability of the PU@Fe3O4@PS sponge was also investigated during the experiments. As shown in Figure 7a, when a drop of water (dyed with methylene blue) was dropped on the surface of sponge, it kept a spherical shape as expected while diesel drop completely penetrated into the sponge immediately. It implies that the as-prepared PU@Fe3O4@PS sponge possessed good hydrophobicity and lipophilicity. In addition, the sponge was floating in water surface stably when it was put into a baker with water (Figure 7b), because of the low density and water repellency of the sponge. Another typical experiment30, 59 was also carried out to prove the superhydrophobicity of the PU@Fe3O4@PS sponge, as shown in Figure 7c. When 14


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the sponge was pressed into the water, a silver mirror-like plane was observed due to air layer between the sponge and water. After unloading the external force, the sponge returned to the water surface at once, indicating that the PS brushes have been grafted and uniformly dispersed onto the sponge surface.

Figure 7. (a) Water drop and oil drop on the surface of PU@Fe3O4@PS sponge; PU@Fe3O4@PS sponge (b) floating in the water surface and (c) immersing into water.

3.4. Oil Adsorbency and oil-water separation. The PU@Fe3O4@PS sponge exhibited superhydrophobicity, superoleophilicity, high porosity structure and outstanding elasticity, making it an ideal adsorbent for oily contaminants. Figure 8a showed the adsorption process of methylbenzene (dyed with stain Sultan IV) in the water surface with prepared sponge. When the sponge touched the organic solvent layer, it adsorbed methylbenzene at once, and it completed the adsorption process in a few seconds. More importantly, the PU@Fe3O4@PS sponge can be freely magnetically driven to other contaminated areas with a magnet because of its magnetic property. After completing removal of methylbenzene from water surface, the used sponge can be magnetically recovered, which provided a convenient recycling method. The PU@Fe3O4@PS sponge can also be employed to selectively adsorb heavy organic solvent under water, such as chloroform. As shown in Figure 8b, when the sponge contacted with the chloroform droplet (dyed with stain Sultan IV) 15



under water through external forces, the chloroform was immediately sucked into the sponge immediately. Furthermore, there was no adsorbed chloroform falling down during the process out of water, indicating excellent holding capacity of PU@Fe3O4@PS sponge.

Figure 8. Adsorption processes of (a) methylbenzene in water surface and (b) chloroform under water.

In order to evaluate the adsorption capacity of PU@Fe3O4@PS sponge, various types of frequently encountered oils and organic solvents were used for oil adsorption experiment, such as diesel, lubricating oil, paroline, castor oil, hexadecane, hexane, cyclohexane, toluene, chloroform and carbon tetrachloride. In general, the adsorption capacity for these oils and organic solvents was 24-105 times of its self-weight depending on their viscosity and density, as shown in Figure 9. This PU@Fe3O4@PS sponge showed a relatively high adsorption capacity compared with other reported superhydrophobic sponges in Table S1. Most importantly, the sponge can be used for oil adsorption directly and be squeezed to release adsorbed oil for regeneration. Thus, diesel, castor oil, toluene and chloroform were utilized to explore the reusability of 16


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PU@Fe3O4@PS sponge according to the method described in experimental section. It was noted that the adsorption capacity still remained above 90% of initial value while the weight of sponge decreased only 5% after 20 cycles, as presented in Figure 10. For diesel, the WCA of sponge decreased from 151° to 143.6° after 20 cycles (Figure S2). The PU@Fe3O4@PS sponge showed excellent reusability, suggesting it is a low cost and environmentally friendly adsorbent for removing oily contaminants from water.

Figure 9. Adsorption capacity of PU@Fe3O4@PS sponge for different oils and organic solvents.

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Figure 10. Adsorption capacity of PU@Fe3O4@PS sponge for (a) diesel, (b) castor oil, (c) toluene and (d) chloroform during 20 cycles.

The PU@Fe3O4@PS sponge had micron-sized pore structure and superior elasticity. And the approach for realizing continuous and efficient oil-water separation with as-prepared sponge was further studied. Figure 11 showed the oil-water separation process with self-made device composed of a peristaltic pump, pipe and as-prepared PU@Fe3O4@PS sponge (detailed separation process can be seen in Movie S1). Once the sponge touched the diesel oil layer (dyed with stain Sultan IV) on the water, it quickly adsorbed diesel and reached to adsorption equilibrium (Figure 11a). After pumping, the diesel was continuously adsorbed with the assistance of the sponge, and 18


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finally led to oil collection apparatus through pipe and peristaltic pump (Figure 11b). It was clear that the level of diesel declined rapidly, and there was no residual diesel floating in the water surface after a while (Figure 11c). At the same time, almost no water was in the collected diesel and the separation efficiency was as high as 99.4%, exhibiting high selectivity of PU@Fe3O4@PS sponge for continuous oil-water separation.

Figure 11. Continuous separation of diesel from water with a peristaltic pump.

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4. CONCLUSION In summary, a recyclable superhydrophobic PU@Fe3O4@PS sponge was designed and successfully fabricated via a facile and simple two-step synthetic route. The Fe3O4 nanoparticles and PS brushes were firmly anchored on the skeleton surface of commercial PU sponge by means of ultrasonic dip-coating and SIPGP. The obtained PU@Fe3O4@PS sponge exhibited adsorption capacity up to 105 times towards of its own weight and remained above 90% after 20 cycles, indicating its high oil adsorption capacity, outstanding stability and reusability. Furthermore, the sponge can be driven to the oil-bearing zone and recovered by an external magnetic field. Simple mechanical compression was adopted to release the adsorbed oil and regenerate the sponge. When connected to a peristaltic pump, the sponge could achieve continuous and efficient insitu oil collection from water surface. Therefore, the PU@Fe3O4@PS sponge associated with the functionalization technology of SIPGP has great potential in the field of oilwater separation.

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ASSOCIATED CONTENT Supporting Information SEM images of PU@PS sponge. The change of WCA of PU@Fe3O4@PS sponge before and after 20 adsorption-desorptions. Comparison of the sorption capability with other reported sponges (PDF) Continuous separation of diesel from water with a peristaltic pump (AVI)

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected].

Tel: +86-25-84315042, Fax: +86-25-84315042.

ORCID Wei Jiang: 0000-0001-5663-9119 Notes The authors declare no competing financial interest.

Acknowledgements We acknowledge the funding support from the Natural Science Foundation of China (50972060), Environmental Protection Scientific Research Project of Jiangsu Province (2016056), National Key R&D Program of China (2016YFB0302800), Qing Lan Project, the Weapon Research Support Fund (62201070804), the Priority Academic Program Development of Jiangsu Higher Education Institutions, and Basic Product Innovation Technology Research Project of Explosives.

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Abstract Graphics

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Figure 1. (a) The schematic illustration for preparation of PU@Fe3O4@PS sponge; The WCA of (b) PU sponge, (c) PU@Fe3O4 sponge and (d) PU@Fe3O4@PS sponge.



Figure 2. SEM image of (a-c) PU sponge, (d-f) PU@Fe3O4 sponge, and (g-i) PU@Fe3O4@PS sponge at different magnifications.


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Figure 3. XRD pattern of Fe3O4 nanoparticles.



Figure 4. FT-IR spectra of sponge before and after modification.


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Figure 5. TGA curves of Fe3O4, PU sponge, PU@Fe3O4 sponge and PU@Fe3O4@PS sponge.



Figure 6. Magnetic curves of Fe3O4, PU@Fe3O4 sponge and PU@Fe3O4@PS sponge.


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Figure 7. (a) Water drop and oil drop on the surface of PU@Fe3O4@PS sponge; PU@Fe3O4@PS sponge (b) floating in the water surface and (c) immersing into water.



Figure 8. Adsorption processes of (a) methylbenzene in water surface and (b) chloroform under water.


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Figure 9. Adsorption capacity of PU@Fe3O4@PS sponge for different oils and organic solvents.



Figure 10. Adsorption capacity of PU@Fe3O4@PS sponge for (a) diesel, (b) castor oil, (c) toluene and (d) chloroform during 20 cycles.


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Figure 11. Continuous separation of diesel from water with a peristaltic pump.




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Design of Recyclable Superhydrophobic PU@Fe3O4@PS Sponge for

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