Polyacrylamide-Polydivinylbenzene Decorated Membrane for Sundry

Aug 5, 2016 - Aiming to solve the worldwide challenge of stabilized oil-in-water emulsion separation, a PAM-PDVB decorated nylon membrane is fabricate...
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Polyacrylamide-Polydivinylbenzene Decorated Membrane for Sundry Ionic Stabilized Emulsions Separation via a Facile Solvothermal Method Weifeng Zhang, Na Liu, Yingze Cao, Yuning Chen, Qingdong Zhang, Xin Lin, Ruixiang Qu, Haifang Li, and Lin Feng* Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China S Supporting Information *

ABSTRACT: Aiming to solve the worldwide challenge of stabilized oil-in-water emulsion separation, a PAM-PDVB decorated nylon membrane is fabricated via a facile solvothermal route in our group. The main composition is PAM, while the PDVB plays a role as cross-linker in order to improve the interaction between the polymer and the substrate. By the combination of the superhydrophilic and underwater superoleophobic wettability of the PAM polymer with the micropore size of the substrate, the as-prepared material is able to achieve the separation of various stabilized oil-in-water emulsions including cationic type, nonionic type, and anionic type. Compared with previous works, the emulsions used in this case are more stable and can stay for several days. Besides, the solvothermal method is facile, cost saving, and relatively environmentally friendly in this experiment. Moreover, the PAM-PDVB modified membrane exhibits excellent pH stability, recyclability, and high separation efficiency (above 99%), which can be scaled up and used in the practical industrial field. KEYWORDS: polyacrylamide, polydivinylbenzene, solvothermal method, special wettability, stabilized emulsion separation methacrylate (PDMAEMA) hydrogel coated mesh,22 porous nitrocellulose membranes,23 inorganic nanowire hair copper mesh,24 PMAPS-g-PVDF membrane, and so on.25 These materials can realize the separation of immiscible oil/water mixtures, even the oil-in-water emulsions. However, most of the materials are unable to meet the stringent environmental circumstances such as high concentration of acid and alkali conditions during the separation process. For the emulsion separation process, the emulsions used in the experiments are unstable and can only stay for a while. Thus, how to overcome these difficulties is of great significance when applying the “water-removing” materials in the practical oil/water separation situation. Polyacrylamide (PAM) is a hydrophilic polymer which can be utilized in tissue engineering,26,27 waste treatment,28,29 dye adsorption,30 drug delivery, and so on.31,32 Our group reported previously to synthesize and modify the PAM hydrogel on the stainless steel mesh through in situ radical polymerization, realizing the separation of oil/water mixtures.20 However, this hydrogel coated mesh can only separate immiscible oil/water mixtures. Besides, the interaction between PAM and substrate is not firm enough since the hydrogel is coated on the mesh from the pre-gel solution during polymerization, which will

1. INTRODUCTION Global industrial developments and huge demand for petroleum resources lead to a rapid progress of science and technology; on the contrary, they also caused serious environmental polutions.1−5 Numerous oil spill accidents and large quantities of oily wastewater discharged from various fields not only result in the loss of precious resources but also threaten both the human health and the environment.6−8 Therefore, how to achieve the efficient separation of oil/water mixtures, especially the emulsions with the droplet size below 20 μm, is a worldwide challenge to overcome.9 Since the separation process is related to interfacial issues, materials with special wettability have gained considerable interests in recent years because of the higher efficiency compared with other methods.10−16 Among them, “oil-removing” materials with superhydrophobicity/superoleophilicity and “water-removing” materials with superhydrophilicity/underwater superoleophobicity are the two typical examples and have been paid much attention.17,18 Compared with two kinds of materials, “oilremoving” materials are easily fouled and blocked by oils due to the superoleophilic wettability, causing the difficulty for recycling. “Water-removing” material can overcome this drawback because of its intrinsic hydrophilicity, so water can form a layer on the surface and protect the material from oil fouling. Thus, “water-removing” materials show great potential in the real oil/water separation and has been fabricated successfully,19−21 for instance, poly(dimethyl amino)ethyl © 2016 American Chemical Society

Received: June 11, 2016 Accepted: August 5, 2016 Published: August 5, 2016 21816

DOI: 10.1021/acsami.6b07018 ACS Appl. Mater. Interfaces 2016, 8, 21816−21823

Research Article

ACS Applied Materials & Interfaces

four kinds of oil-in-water emulsions including toluene in water, gasoline in water, n-hexane in water, and n-octane in water have been prepared. For each type of emulsion, oil and water was mixed in 1:100 (v/v) with the adding of 4 mg/mL of the corresponding surfactant. The whole solution was stirred for 24 h. Typically, all the emulsions are stable for 4 days. 2.4. Emulsion Separation Experiments for PAM-PDVB Modified Membrane. The as-prepared membrane was fixed in the filtration device, which was implemented for the demulsification process. Then, the oil-in-water emulsions were poured onto the surface. The whole process was carried out under gravity. The membrane could separate various types of emulsions with high efficiency. For the test of efficiency, three samples were prepared and each sample was also measured three times for one separation cycle. The oil content in water after the separation was measured and calculated by the rejection coefficient (R (%)). According to the equation

affect the recyclability of the material. Therefore, it is necessary to find an effective way to fabricate PAM coated material to meet the oil/water separation in complex situations. Herein, by changing the synthetic method and proper substrates, we fabricate a PAM decorated nylon membrane and develop the function of the material from the separation of immiscible oil/water separation to stabilized oil-in-water emulsion. Moreover, polydivinylbenzene (PDVB) was used as a cross-linker aiming to improve the affinity to the substrates. As shown in Scheme 1, the PAM-PDVB polymer can be Scheme 1. Fabrication of the PAM-PDVB Decorated Membrane and the Mechanism of the Emulsion Separation

⎛ Cp ⎞ R(%) = ⎜1 − ⎟ × 100% Co ⎠ ⎝

(1)

This equation could be used in many situations including the oil/water separation and emulsion separation. When it is applied to characterize the capacity of emulsion separation, the rejection coefficient could also be called separation efficiency. Here, Co and Cp are the oil contents in water before and after separation, respectively. 2.5. Instruments and Characterization. A field emission scanning electron microscope (SU-8010, Hitachi Limited, Japan) was used to observe the surface morphology of the membrane. The Xray photoelectron spectra (XPS) of the materials were obtained by a Thermo escalab 250Xi spectrometer with an Al Kα X-ray source (1486.6 eV). A HORIBAJY HR-800 machine with an Ar laser source (514 nm) was utilized to get the Raman spectrum. Water contact angles (WCAs) and underwater oil contact angles (OCAs) were tested using an OCA20 machine (Data-Physics, Germany). The final contact angle of each sample was calculated by measuring five contact angles of different positions and taking the average. For oil content in water in emulsion and filtrates, the whole process was tested by an infrared spectrometer oil content analyzer (CY2000, China). Optical microscope images of the emulsion and filtrates were captured via a Nikon ECLIPSE LV100POL polarizing optical microscope. For the droplet size distribution, dynamic light scattering (DLS) measurements were carried out by a Zeta Plus apparatus (Zeta Plus, Brookhaven Instruments, Holtsville, NY). The mass spectra were characterized by LCMS-IT/TOF (Shimadzu, Japan).

decorated on a nylon microfiltration membrane successfully via a facile solvothermal route. With the combination of the superhydrophilic PAM polymer with the appropriate pore size of the membrane, the as-prepared material is able to realize the separation of various types of highly stabilized oil-in-water emulsions including cationic type, nonionic type, and anionic type driven solely by gravity. More importantly, the PAMPDVB modified membrane shows excellent recyclability and high separation efficiency, which can be scaled up and used in the real industry application field.

3. RESULTS AND DISCUSSION 3.1. Surface Morphology and Characterization. Structure characterization of the substrate and the PAMPDVB decorated membrane is demonstrated in Figure 1. Figure 1a is the field emission scanning electron microscopy (FESEM) image of the original nylon membrane with the pore size of 0.8 μm. As shown in the image, the membrane exhibits a hierarchical structure with a 3D network. Figure 1b is the FESEM image of the PAM-PDVB decorated membrane. Obviously, the surface morphology has changed compared with the original substrate. There is a layer of polymer wrapped on the membrane, indicating the successful polymerization of the monomers. From the high-magnification image and the enlarged inset image of the membrane as shown in Figure 1c, many wrinkles and some papillae can be observed, which are mostly dispersed at the edges of the surface. This kind of hierarchical micro/nanostructure is able to amplify the wetting property of the as-prepared membrane.33 The thickness of the polymer layer was also studied. Figure S1a,b shows the crosssectional SEM images of the original nylon membrane and the PAM-PDVB membrane, respectively. Compared with the

2. EXPERIMENTAL SECTION 2.1. Materials. Acrylamide (J&K Co. Ltd., Beijing, China), divinylbenzene (m- and p- mixture, J&K Co. Ltd., Beijing, China), 2,2′-azoisobutyronitrile (J&K Co. Ltd., Beijing, China), and ethyl acetate (Dongfanglongshun Co. Ltd., Beijing, China) were of analytical grade and used derectly. Other reagents from Sinopharm Chemical Reagent Beijing Co., Ltd., Beijing, P. R. China, were used as purchased without further purification. 2.2. Fabrication of PAM-PDVB Modified Membrane. For the PAM-PDVB modified membrane, first, the acrylamide (AM) and divinylbenzene (DVB) monomers were dissolved in 45 mL of ethyl acetate with the mole ratio of 30:1; then, 0.05g of initiator 2,2′azoisobutyronitrile (AIBN) was added into the solution and stirred for 5 h at ambient temperature. After that, it was transferred into a Teflon autoclave. Then, a clean nylon microfiltration membrane with an average pore size of 0.8 μm was immersed in the solution. The autoclave was heated at 100 °C for 24 h. The as-prepared membrane was washed with deionized water and acetone carefully and dried out. 2.3. Preparation of Surfactant Oil-in-Water Emulsions. According to different surfactants, three types of stabilized oil-inwater emulsions were prepared, including a cationic emulsion with CTAB surfactant, a nonionic emulsion with Tween 20 surfactant, and an anionic emulsion with SDS surfactant. For each type of emulsion, 21817

DOI: 10.1021/acsami.6b07018 ACS Appl. Mater. Interfaces 2016, 8, 21816−21823

Research Article

ACS Applied Materials & Interfaces

Figure 1. Structure characterization of the substrate and the PAM-PDVB decorated membrane. (a) FESEM image of the nylon membrane as a substrate. (b) FESEM image of the PAM-PDVB modified membrane. (c) High-magnification image of the as-prepared material and the enlarged SEM image of the surface. (d) XPS high-resolution C 1s narrow scans of the nylon membrane. (e) XPS high-resolution C 1s narrow scans of the PAM-PDVB modified membrane. (f) Raman spectra of the nylon substrate and the PAM-PDVB coated membrane.

smooth nylon wires, a layer of the PAM-PDVB polymer has been wrapped on the surface of the wires successfully, forming the rough structures. From the high-magnification SEM image of the as-prepared material (Figure S1c), the thickness of the polymer layer is several hundreds of nanometers. For the characterization of the surface composition, XPS analysis was carried out. The chemical structure of the nylon membrane and the chemical reaction are displayed in Scheme 2 for better comprehension. The cross-link network was formed after the polymerization. Panels (d) and (e) in Figure 1 are the highresolution C 1s narrow scans of the nylon membrane and the PAM-PDVB coated membrane, respectively. After the modification process, the peak at 284.7 eV was labeled, representing the CC and π−π satellite since the shape of the peak is different with that which appeared in the substrate. Because the π−π satellite peak is the characteristic peak of PDVB, the results indicated that the PDVB polymer was decorated on the surface of the membrane. Moreover, Raman spectra were also conducted to analyze the functional groups of the as-prepared material as shown in Figure 1f. After the polymerization, the peaks of the as-prepared membrane become much more intensive than that of the original substrate since the modification of more polymer on the membrane could enhance the intensity of the peaks greatly. The peaks at 1600 and 1720 cm−1 have become more intensive compared with that of the original substrates. These peaks are ascribed to the benzene ring and −CONH2, which are the characteristic peaks of PDVB

Scheme 2. (a) Chemical Structure of Nylon Membrane. (b) Chemical Reaction of the AM and DVB Polymerization

and PAM, respectively. All the results above demonstrate that the PAM and PDVB polymer has been decorated on the nylon membrane successfully. 21818

DOI: 10.1021/acsami.6b07018 ACS Appl. Mater. Interfaces 2016, 8, 21816−21823

Research Article

ACS Applied Materials & Interfaces

Figure 2. (a, b) Photographs of the water contact angles (WCA) and underwater oil contact angles (OCA) of the as-prepared membrane, respectively. Oil sample dichloroethane was dyed with Rhodamine B. The insets are the corresponding images of WCA and OCA. (c) The underwater OCAs of toluene, gasoline, n-hexane, and n-octane. (d) The underwater OCAs for the membrane in acid, water, and alkali.

3.2. Wetting Behaviors and pH Stability Test. The wettability and pH stability of the PAM-PDVB membrane were characterized via testing water contact angles (WCAs) and underwater oil contact angles (OCAs) as shown in Figure 2. In the experiments, after measuring five different positions of each sample and taking the average, the final contact angle was obtained. Panels (a) and (b) in Figure 2 are the photographs of the WCAs and underwater OCAs, respectively. The oil sample 1,2-dichloroethane was dyed with Rhodamine B. It is clear that the water droplets spread and wetted the membrane rapidly once touching the surface. When the material was immersed in water, the oil droplets could stay on the membrane and exhibit a quasi-spherical shape. The insets are the images of WCA and OCA of the material. The oil samples used in these experiments contain both the light oils (whose density is smaller than that of water) and heavy oils (whose density is larger than that of water). During the measurement, the membrane is above the light oils while below the heavy oils. From the Figure 2a,b, the WCA is almost 0° and the underwater OCA is above 150°, indicating that the membrane possesses superhydrophilic/ underwater superoleophobic wettability. According to the previous literatures, the special wettability of the PAM-PDVB coated membrane can be explained by the combination of the intrinsic hydrophilicity of the PAM polymer with the hierarchical morphology.4 Except for 1,2-dichloroethane, the as-prepared material shows underwater superoleophobicity for various types of oils including toluene, gasoline, n-hexane, and n-octane, which is illustrated in Figure 2c. Obviously, the underwater OCAs are all above 150°. More importantly, the PAM-PDVB modified membrane exhibits excellent pH stability. Figure 2d is the underwater OCAs of the material in acid, water, and alkali; 1,2-dichloroethane was chosen as the oil sample. As demonstrated in the chart, the membrane shows underwater superoleophobicity in a wide pH range from 0 to 14, which is of great significance in the practical separation circumstances. 3.3. The Emulsion Separation Mechanism of the PAMPDVB Membrane. The PAM-PDVB decorated membrane is

able to achieve the separation of various stabilized oil-in-water emulsions including cationic type, nonionic type, and anionic type. The mechanism is explained in Scheme 1. Since the asprepared membrane combines the micropore size with the inherently superhydrophilic and underwater superoleophobic wettability of the PAM polymer, when the oil-in-water emulsion is poured onto the surface, the membrane is able to capture the micro-oil droplets dispersed in the emulsion while permitting the water to penetrate through the membrane, realizing the emulsion separation process. More importantly, during the separation process, the water will form a protection layer on the membrane surface, which can block the micro- and nano-sized oil droplets completely. This layer will also endow the membrane with the antifouling property that is important for the recyclability of the material. Compared with the previous PAM hydrogel coated mesh obtained by UV irradiation polymerization,20 the enhanced separation ability is attributed to the adding of cross-linker PDVB, membrane substrate with smaller pore size and different synthetic method. Through the solvothermal method, the polymer could be modified on the membrane directly during the polymerization process instead of the UV treatment of the flowing pre-gel solution. Besides, the PDVB acts as the cross-linker to make the PAM a cross-linking network, which could be modifed on the nylon membrane firmly. To further demonstrate the stability of the material, the PAM-PDVB membranes were immersed in strong acid and alkali solutions for 48 h, respectively, as shown in Figure S2. From the digital images and SEM images, the morphology and microstructures remained almost the same as those of the original membrane no matter in acid or alkali solutions. The results proved the stability of the membrane. Aiming to prove the function of the PDVB, a PAM modified membrane without PDVB was also synthesized as a control. Panels (a) and (b) in Figure S3 are the oil-in-water emulsion separation performance of the substrate and PAM coated membrane, respectively. It is clear that the filtrate of the nylon membrane in the right vial is almost the same as that of the original emulsion, indicating that the substrate cannot separate 21819

DOI: 10.1021/acsami.6b07018 ACS Appl. Mater. Interfaces 2016, 8, 21816−21823

Research Article

ACS Applied Materials & Interfaces

Figure 3. Separation performance of the material toward the nonionic toluene in water emulsion, the cationic n-octane in water emulsion, and the anionic gasoline in water emulsion. (a−c) The optical images of the corresponding feed emulsions. (d−f) The photographs of the corresponding emulsions before and after separation. (g−i) The optical images of the corresponding filtrate emulsions. (j−l) The droplet size analysis of the corresponding emulsions.

the emulsion. For the PAM coated membrane, the color of the solution after separation becomes a little lighter, but still opaque, because the interaction of the PAM and substrate is not firm enough. The results demonstrate that the PDVB plays an important role as cross-linker and is able to improve the affinity of the PAM to the nylon membrane, thus achieving the whole demulsification process. 3.4. Separation Performance of the PAM-PDVB Membrane. In the emulsion separation experiment, three types of stabilized oil-in-water emulsions were prepared: a nonionic emulsion with Tween 20 as the surfactant, a cationic emulsion with hexadecyltrimethylammonium bromide (CTAB) as the surfactant, and an anionic emulsion with sodium dodecyl sulfate (SDS) as the surfactant. According to the difference of oils, for each type of emulsion, four kinds of emulsions including toluene in water, gasoline in water, n-hexane in water, and n-octane in water have been prepared with the ratio of oil to water of 1:100 (v/v). Figure 3 is the separation performance of the material toward the nonionic toluene in water emulsion, cationic n-octane in water emulsion, and anionic gasoline in water emulsion. For each separation, the PAM-PDVB decorated membrane was fixed in the filtration device, and then the emulsion was poured onto the surface. The whole process was conducted under gravity. As the photographs show in Figure 3d−f, the milky emulsions became transparent after the separation process. Besides, optical images of the emulsions before and after separation were also captured, aiming to observe the emulsions clearly. In the feed emulsions (Figure 3a−c), numerous micro-oil droplets are dispersed in water uniformly, whereas, after separation, almost no oil droplets can be observed in the filtrate (Figure 3g−i). All the results indicate that the PAM-PDVB modified membrane is able to separate all of these three types of emulsions. Moreover, dynamic light scattering (DLS) measurements were carried out to analyze the droplet size distribution, as shown in Figure 3j−l. In the

combination with the optical images and the DLS measurements, all of these three types of emulsions contain both microsized oil droplets and nano-sized oil droplets. For the toluene in water emulsion, the droplet size is even much smaller since the toluene is much easier to be dispersed in water than other oil samples. The DLS analyses of the filtrates are not given because there is almost no oil droplets existing in water, which further illustrates the purity of the filtrate. Actually, both the microsized and nano-sized oil droplets were removed completely after the separation process as shown in the optical images of the filtrate and the DLS measurements, indicating the excellent separation ability of the as-prepared membrane. The separation performance for the other nine types of emulsions was all conducted and tested, as shown in Figures S4−S6. It is clear that the PAM-PDVB membrane is able to realize the separation of sundry stabilized oil-in-water emulsions. The flux of the as-prepared membrane was measured and is displayed in Figure S7. Nonionic, cationic, and anionic toluene in water emulsions were chosen as the samples. The flux of the membrane was all below 12 L/m2 h since the emulsions are very stable due to the existence of relatively more surfactant. If the membrane was used over time, the flux decreased slowly since the surfactants blocked the pores of the material. However, after simply washing the membrane with deionized water and acetone, the flux returned to the original state, indicating the good recyclability of the material. Besides, the intruding pressure experiment was also conducted as illustrated in Figure S8, where the maximum height of the toluene in water emulsions in the separation device was 8.2 cm, which means that the intruding pressure of the material is 0.823 kPa. For the highly stabilized emulsion separation, since the separation amount and speed are lower than those of the immiscible oil/water mixture, the intruding pressure of this membrane is acceptable. 21820

DOI: 10.1021/acsami.6b07018 ACS Appl. Mater. Interfaces 2016, 8, 21816−21823

Research Article

ACS Applied Materials & Interfaces

Figure 4. Separation efficiency and stability test of the PAM-PDVB decorated membrane. (a−c) Separation efficiency of the membrane toward nonionic, cationic, and anionic stabilized oil-in-water emulsions, respectively. (d) The stability and recyclability tests of the as-prepared material. (e, f) Stability tests of the cationic, nonionic, and anionic toluene in water emulsions.

It is necessary to investigate where the surfactant went after the emulsion separation process since the concentration of the surfactant we used is as high as 4 mg/mL. The mass spectra were utilized to characterize the types and amount of the surfactant in the filtrate as shown in Figures S9−S11. The Tween 20 filtrate was diluted 30 times while the CTAB and SDS filtrates were diluted 100 times. For the Tween 20 filtrate, the differences between the peaks of 371.2196 and 327.1995, 437.2371 and 393.2098, 567.3191 and 525.2902, 611.3442 and 567.3191, and 655.3690 and 611.3442 are all about 44. The value is equal to the mass of C2H4O, which is the repeated unit of Tween 20. As for the CTAB filtrate, the main peak of the mass spectrum is 284.3314, which is coincident with the massto-charge ratio of C19H42N+. When it comes to the SDS filtrate, 265.1477 is the main peak in the mass spectrum; it is the massto-charge ratio of C12H25SO4−. All the aforementioned results have proved that a part of the surfactant is in the filtrate after the emulsion separation. To identify the amount of the surfactant in the filtrate, the standard solutions of the three types of surfactant with the concentration of 12 ppm were prepared. The corresponding total ion chromatograms (TIC) and extract ion chromatograms (EIC) of the filtrate and standard solution were measured and are illustrated in Figures S9−S11. After the calculation, we could deduce that, after the emulsion separation process, 68.6% of the CTAB and 73.75% of the Tween 20 was blocked on the membrane while almost all the SDS was penetrated through the membrane. This could be explained by the difference of the solubility and molecular structure. The CTAB and Tween 20 have larger molecular weight and more complex molecular structure than the SDS, so the membrane could block most of the surfactant. For SDS, it is

easier to be dispersed in water, so most of the SDS was in the filtrate. 3.5. Separation Efficiency and Stability Tests. In order to characterize the separation efficiency of the material, the oil content in water after the separation was measured and calculated by the rejection coefficient (R (%)).The results are illustrated in Figure 4a−c. From the charts, the PAM-PDVB coated membrane exhibits excellent separation ability with the oil content between 70 mg/L and separation efficiency above 99% no matter for the nonionic, cationic, or anionic oil-in-water emulsion. Besides, the recyclability of the material was also tested as shown in Figure 4d. After 30 times of separation, the efficiency is still above 99%, which demonstrates the stability of the membrane. These properties are of great importance to be applied in the real emulsion separation situation. More importantly, the stability of the emulsions is another criterion to examine the performance of the as-prepared membrane. Panels (e) and (f) in Figure 4 are the stability tests of cationic, nonionic, and anionic toluene in water emulsions. It is clear that, after 4 days, the emulsions are still stable without demulsification. Besides, the separation ability of the membrane under strong acid and alkali solutions was also characterized. The separation performance and efficiency of nonionic, cationic, and anionic toluene in water emulsions with the pH values of 0 and 14 was conducted and tested. Figure S12 is the digital photos of the corresponding emulsions before and after separation; the filtrate all becomes transparent compared with the milky emulsions, indicating the excellent separation capacity of the membrane under strong acid and alkali conditions. The separation efficiency is slightly less than that of the emulsions under neutral condition, but still above 98.8% as shown in Figure S13. 21821

DOI: 10.1021/acsami.6b07018 ACS Appl. Mater. Interfaces 2016, 8, 21816−21823

Research Article

ACS Applied Materials & Interfaces

and Selective Oil Adsorption. ACS Appl. Mater. Interfaces 2015, 7, 791−800. (9) Kota, A. K.; Kwon, G.; Choi, W.; Mabry, J. M.; Tuteja, A. HygroResponsive Membranes for Effective Oil−Water Separation. Nat. Commun. 2012, 3, 1025. (10) Cao, Y.; Liu, N.; Zhang, W.; Feng, L.; Wei, Y. One-Step Coating toward Multifunctional Applications: Oil/Water Mixtures and Emulsions Separation and Contaminants Adsorption. ACS Appl. Mater. Interfaces 2016, 8, 3333−3339. (11) Feng, X.; Jiang, L. Design and Creation of Superwetting/ Antiwetting Surfaces. Adv. Mater. 2006, 18, 3063−3078. (12) Liu, M.; Wang, S.; Wei, Z.; Song, Y.; Jiang, L. Bioinspired Design of a Superoleophobic and Low Adhesive Water/Solid Interface. Adv. Mater. 2009, 21, 665−669. (13) Sun, T.; Feng, L.; Gao, X.; Jiang, L. Bioinspired Surfaces with Special Wettability. Acc. Chem. Res. 2005, 38, 644−652. (14) Feng, L.; Li, S.; Li, Y.; Li, H.; Zhang, L.; Zhai, J.; Song, Y.; Liu, B.; Jiang, L.; Zhu, D. Super-Hydrophobic Surfaces: From Natural to Artificial. Adv. Mater. 2002, 14, 1857−1860. (15) Li, X.; Wang, M.; Wang, C.; Cheng, C.; Wang, X. Facile Immobilization of Ag Nanocluster on Nanofibrous Membrane for Oil/ Water Separation. ACS Appl. Mater. Interfaces 2014, 6, 15272−15282. (16) Xue, Z.; Liu, M.; Jiang, L. Recent Developments in Polymeric Superoleophobic Surfaces. J. Polym. Sci., Part B: Polym. Phys. 2012, 50, 1209−1224. (17) Feng, L.; Zhang, Z.; Mai, Z.; Ma, Y.; Liu, B.; Jiang, L.; Zhu, D. A Super-Hydrophobic and Super-Oleophilic Coating Mesh Film for the Separation of Oil and Water. Angew. Chem., Int. Ed. 2004, 43, 2012− 2014. (18) Zhang, W.; Liu, N.; Cao, Y.; Chen, Y.; Xu, L.; Lin, X.; Feng, L. A Solvothermal Route Decorated on Different Substrates: Controllable Separation of an Oil/Water Mixture to a Stabilized Nanoscale Emulsion. Adv. Mater. 2015, 27, 7349−7355. (19) Liu, Y.-Q.; Zhang, Y.-L.; Fu, X.-Y.; Sun, H.-B. Bioinspired Underwater Superoleophobic Membrane Based on a Graphene Oxide Coated Wire Mesh for Efficient Oil/Water Separation. ACS Appl. Mater. Interfaces 2015, 7, 20930−20936. (20) Xue, Z.; Wang, S.; Lin, L.; Chen, L.; Liu, M.; Feng, L.; Jiang, L. A Novel Superhydrophilic and Underwater Superoleophobic Hydrogel-Coated Mesh for Oil/Water Separation. Adv. Mater. 2011, 23, 4270−4273. (21) Gondal, M. A.; Sadullah, M. S.; Dastageer, M. A.; McKinley, G. H.; Panchanathan, D.; Varanasi, K. K. Study of Factors Governing Oil−Water Separation Process Using TiO2 Films Prepared by Spray Deposition of Nanoparticle Dispersions. ACS Appl. Mater. Interfaces 2014, 6, 13422−13429. (22) Cao, Y.; Liu, N.; Fu, C.; Li, K.; Tao, L.; Feng, L.; Wei, Y. Thermo and pH Dual-Responsive Materials for Controllable Oil/ Water Separation. ACS Appl. Mater. Interfaces 2014, 6, 2026−2030. (23) Gao, X.; Xu, L.-P.; Xue, Z.; Feng, L.; Peng, J.; Wen, Y.; Wang, S.; Zhang, X. Dual-Scaled Porous Nitrocellulose Membranes with Underwater Superoleophobicity for Highly Efficient Oil/Water Separation. Adv. Mater. 2014, 26, 1771−1775. (24) Zhang, F.; Zhang, W. B.; Shi, Z.; Wang, D.; Jin, J.; Jiang, L. Nanowire-Haired Inorganic Membranes with Superhydrophilicity and Underwater Ultralow Adhesive Superoleophobicity for High-Efficiency Oil/Water Separation. Adv. Mater. 2013, 25, 4192−4198. (25) Zhu, Y.; Zhang, F.; Wang, D.; Pei, X. F.; Zhang, W.; Jin, J. A novel zwitterionic polyelectrolyte grafted PVDF membrane for thoroughly separating oil from water with ultrahigh efficiency. J. Mater. Chem. A 2013, 1, 5758−5765. (26) Calvert, P. Hydrogels for Soft Machines. Adv. Mater. 2009, 21, 743−756. (27) Drury, J. L.; Mooney, D. J. Hydrogels for Tissue Engineering: Scaffold Design Variables and Applications. Biomaterials 2003, 24, 4337−4351. (28) Chauhan, G. S.; Chauhan, S.; Kumar, S.; Kumari, A. A Study in the Adsorption of Fe2+ and on Pine Needles Based Hydrogels. Bioresour. Technol. 2008, 99, 6464−6470.

4. CONCLUSIONS In summary, a PAM-PDVB decorated nylon membrane is synthesized through a facile solvothermal route in our group. The PDVB acts as cross-linker aiming to improve the interaction between the polymer and the substrate. By the combination of the inherently superhydrophilic and underwater superoleophobic wettability of the PAM polymer with the micropore size of the substrate, the as-prepared membrane is able to separate various stabilized oil-in-water emulsions including cationic type, nonionic type, and anionic type. Besides, the emulsions used in this case were more stable and could stay for several days compared with the emulsions of the previous works. The solvothermal method is facile and environmentally friendly in this experiment. Moreover, the PAM-PDVB modified membrane exhibits excellent pH stability, recyclability, and high separation efficiency, which can be scaled up and used in the real industry application field.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.6b07018. Digital images of the demulsification of the nylon membrane and the PAM coated membrane, and the emulsion separation performances of the material toward nonionic, cationic, and anionic oil-in-water emulsions (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: fl@mail.tsinghua.edu.cn. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful for financial support from the National Natural Science Foundation (51173099, 21134004). REFERENCES

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DOI: 10.1021/acsami.6b07018 ACS Appl. Mater. Interfaces 2016, 8, 21816−21823