Article pubs.acs.org/IECR
Continuous Oil−Water Separation Using PolydimethylsiloxaneFunctionalized Melamine Sponge Xuemei Chen, Justin A. Weibel, and Suresh V. Garimella* School of Mechanical Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907-2088, United States S Supporting Information *
ABSTRACT: The development of absorbent materials with high selectivity for oils and organic solvents is of great ecological importance for removing pollutants from contaminated water sources. We have developed a facile solution-immersion process for creating polydimethylsiloxane (PDMS)-functionalized sponges for oil−water separation. Sponge materials with densities ranging from 8 to 26 mg/cm3 were investigated as candidate skeletons. After functionalization, the lowest-density melamine sponge exhibits superior superhydrophobic and superoleophilic properties, absorption capacity, oil−water selectivity, and absorption recyclability. Via suction through such a functionalized sponge, we have experimentally demonstrated that various kinds of oils can be continuously separated from immiscible liquid mixtures without any water uptake. The widely available raw materials (melamine sponge and PDMS solution) and simple synthesis steps yield a cost-effective and scalable process for fabrication of absorbent materials that can be readily adopted for the cleanup of oil spills and industrial chemical leakage of low-surface-tension solvents that are immiscible with water.
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INTRODUCTION Oil spillage and discharge of organic chemicals from industrial sources have caused severe ecological and environmental damage. The conventional methods used to clean oils and organic pollutants include mechanical extraction by oil skimmers,1 chemical dispersion,2 and in situ burning.3 These methods are slow, energy-intensive, or can cause secondary pollution. In recent years, the use of porous materials with combined superhydrophobic and superoleophilic wetting properties have come to be recognized as one of the more effective approaches for removing oils from water surfaces without such drawbacks. Superhydrophobic and superoleophilic-functionalized filtration materials, such as meshes,4−6 membranes,7−9 fabrics,10−12 and filter paper,13,14 have attracted attention over the past decade because of their ability to directly separate oils from water. However, to use this type of material to remove oil from water, the polluted water must be collected and then filtered, which is impractical for application to large bodies of water. Absorbent materials can separate oils from water by manual uptake by absorption and subsequent wringing, or for large-scale cleanup, the oil can be captured continuously via absorption and simultaneously pumped out of the material. An ideal absorbent material should have high absorption capacity and excellent recyclability. Studies on continuous in situ separation techniques have focused on the development of exotic three-dimensional functional porous materials, including carbon aerogels,15,16 carbon-nanofiber aerogels,17 hierarchical cellular structured aerogels,18 graphene frameworks or aerogels, 19,20 carbon nanotube (CNT) sponges,21 and magnetic foams.22 The complicated preparation processes, high costs, and challenges to scalability inherent to © XXXX American Chemical Society
these approaches severely limit their practicality. Over the past few years, commercially available polymer sponges, such as polyurethane and melamine sponges, have received attention for their potential as oil-absorbent materials because of their open-celled structure, high porosity, and favorable elasticity. While such polymer sponges are naturally wetting, they have been rendered superhydrophobic and superoleophilic by modification with nanostructured materials (such as CNTs, graphene, SiO2, Fe3O4, or Ag),23−29 chemical etching,30,31 or polymer grafting32−36 for improving oil selectivity and oilabsorbent capacity. However, these functionalized sponges require the introduction of an additional adhesion medium (PDMS or polydopamine) to bind the nanostructured materials onto the sponge skeletons,23−29 use strong and corrosive etchants (such as chromic acid),21,22 or have limited absorption recyclability.32−34 Despite the progress in enhancing the capabilities of superhydrophobic and superoleophilic sponges, cleanup of large-scale water contamination still suffers from a lack of processes for facile fabrication of robust and scalable absorption materials. In this paper, we present a simple solution-immersion method for the fabrication of superhydrophobic and superoleophilic PDMS-functionalized sponges. To demonstrate this solution-immersion process, commercial melamine and polyether sponges with different densities are treated. These are ideal skeleton materials because of their ultralow density, high Received: January 18, 2016 Revised: March 6, 2016 Accepted: March 14, 2016
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DOI: 10.1021/acs.iecr.6b00234 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 1. SEM images of PDMS-functionalized melamine sponges with densities of (a) 8 mg/cm3 (M8) and (b) 9.6 mg/cm3 (M9.6) and polyether sponges with densities of (c) 14 mg/cm3 (P14), (d) 19 mg/cm3 (P19), (e) 23 mg/cm3 (P23), and (f) 26 mg/cm3 (P26). The right-hand side of each panel shows the magnified morphologies of corresponding sponges.
porosity, and excellent elasticity, all of which are ideal characteristics for increasing absorption capacity. PDMS is used as the coating material because of its hydrophobic nature, mechanical flexibility, and stable properties, and because it can be irreversibly bound to polymer sponge materials without the use of adhesives. PDMS was utilized as the functional material in a single very recent study by Jin et al.,37 who explored the effect of PDMS concentration on the wetting characteristic of cotton. The current work instead investigates the effect of sponge density (8−26 mg/cm3) on the wetting properties, absorption capacities, and oil−water separation efficiency. Sponges with a low density exhibit superior superhydrophobic and superoleophilic properties, absorption capacity, absorption recyclability, oil−water selectivity, and oil−water separation efficiency.
angle values are reported. Oils with different surface tensions (hexane, toluene, octadecene, silicone oil, and motor oil) were used as test fluids to demonstrate the superoleophilicity of the as-fabricated sponges. The degree of hydrophobicity of the sponges was also demonstrated by measuring the intrusion pressure (Pint), which indicates the maximum water pressure that the sponge interface can support before it penetrates the surface. The sponge (∼2 cm thick) was clamped between two flanges at the base of a vertical tube that was filled with water. The intrusion pressure, Pint, is equal to ρghmax, where ρ is the density of water and g is the gravitational constant; hmax is the maximum height of water the sponge can support. Oil Absorption Capacity and Absorption Recyclability. The absorption capacity was determined by immersing sponges into pools of various oils until they were saturated with liquid. The weight of the saturated sponges was measured immediately after taking out of the liquid pool to minimize the influence of evaporation of the organic solvents. The gravimetric absorption capacity (k) of the sponges was calculated as [(m1 − m0)/m0], where m0 is the weight of the unladen PDMS-coated sponge and m1 is the weight of the saturated PDMS-coated sponge. To assess absorption recyclability, the sponges were then manually squeezed out and immersed back into the oil until the sponge became saturated with the liquids again; this process was repeated 20 times. To ensure repeatability of the results, both oil absorption capacity and absorption recyclability tests were repeated three times. Continuous in Situ Oil−Water Separation. A vacuumpump system was used to demonstrate continuous removal of oils from the surface of water. One end of a tube was inserted into the core of the functionalized sponge; the other end was attached to the top of a Büchner flask. The sponge was dipped into the water and immediately absorbed floating oils (dyed with oil red O, which does not affect the surface tension of the oils). The pump attached to the vacuum flask was turned on and the absorbed oils flow through the tube into the flask. For samples that did not have any visible water uptake, the moisture content of the collected oils was measured using a coulometer (Karl Fischer 831 KF Coulometer).
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EXPERIMENTAL METHODS Surface Fabrication. Melamine sponges with densities of 8 and 9.6 mg/cm3 and polyether sponges with densities of 14, 19, 23, and 26 are denoted as M8, M9.6, P14, P19, P23, and P26 based on the sponge material and density. PDMS prepolymer (Sylgard 184A; 5 g) and thermal curing agent (Sylgard 184B; 0.5 g) were added to hexane (150 mL). The mixture was stirred for 40 min to form a homogeneous solution. The sponges were first cleaned with isopropanol and deionized water and then dried in an oven at 100 °C for 2 h. The clean sponges were immersed in the hexane solution for 1 h, squeezed after removal to express the absorbed solution, and dried in an oven at 170 °C for 4 h. Characterization. The surface morphologies of the PDMSfunctionalized sponges were observed by scanning electron microscopy (SEM, Hitachi S4800). The elemental composition of the surface of the sponges was determined by X-ray photoelectron spectroscopy (XPS). The XPS results were obtained at the Surface Analysis Facility in the Birck Nanotechnology Center at Purdue University. Static water contact angles on the functionalized sponges were measured using a Ramé-Hart goniometer (model 590). Droplets of ∼5 μL volume were gently deposited on the samples with a pipet, and the contact angle was measured using the goniometer optics. The measurements were repeated three times at different locations on each sample, and the mean contact B
DOI: 10.1021/acs.iecr.6b00234 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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RESULTS AND DISCUSSION Figure 1 shows SEM images of six PDMS-functionalized sponges: (a, b) melamine and (c−f) polyether sponges. The magnified sponge morphologies show that the sponges are conformally coated with a smooth film of PDMS; there is no roughness formed on the sponge skeletons as a result of the coating. The pore sizes of sponges M8 and M9.6 (characterized from analysis of a larger set of SEM images for each sample) are in the range of 80−140 μm and 50−100 μm, respectively, and the sponge ligaments are ∼6 μm in diameter. The pore and ligament dimensions of the polyether sponges are much larger, with pore size ranges of 250−970, 230−900, 220−830, and 210−810 μm and ligament diameters of ∼56, ∼80, ∼85, and ∼96 μm for sponges P14, P19, P23, and P26, respectively. The smaller pore size and ligament diameter of melamine sponges yield a larger porosity (≥99.4%) compared to the polyether sponges (∼97%−98%) (see section S1 in Supporting Information). The chemical composition before and after PDMS functionalization of sponge M8 was analyzed by XPS; Figure 2 shows these representative XPS spectra. For the unfunction-
confirmed by the small roll-off angle (less than10°) for functionalized sponges M8 and M9.6. Water droplets placed on the polyether sponges (P14, P19, P23, and P26) appear as slightly flattened spheres, and trace amounts of water are left after touching the water droplets with tissue paper (see the dashed circles in Figure 3c−f). The trends in wetting behavior for sponges with different densities are characterized by the water contact angle and shown in Figure 3g. The contact angles on sponges M8 and M9.6 are larger than 150°, indicating their superhydrophobic nature. The water contact angle is decreased (but still hydrophobic) for the higher-density polyether sponges and is on the order of only ∼135° or less. The superhydrophobic nature of sponges M8 and M9.6 is further indicated by the mirrorlike sheen surface of the sponges that appears when they are submerged in water (Figure 3h). This appearance of the surfaces is attributed to a layer of air that is trapped between the water and the sponge. When oil droplets are placed on the melamine and polyether sponges, they are permanently absorbed into the surfaces, indicating that the sponges are superoleophilic (Figure 3a−f). Figure 4a shows a schematic drawing of the setup used to measure the intrusion pressure (Pint). As shown in Figure 4b, sponge M8 has the largest intrusion pressure (∼3 kPa); further increases in the sponge density decrease the intrusion pressure. The trend of intrusion pressure for sponges with different densities mirrors that of the static contact angle with water; the surface wettability increases with density for these sponge samples. The wettability of surfaces is governed by both the surface roughness and the surface energy.38,39 All sponges characterized here are coated with the same low-surface-energy material (PDMS); the superior hydrophobicity of the melamine sponges can be attributed to their larger porosity (≥99.4%) compared with polyether sponges (∼97−98%), which results in a smaller fraction of solid−liquid contact area and lower waterdroplet adhesion area, rendering the surface superhydrophobic (based on the Cassie equation40). The high porosity and superoleophilicity of the functionalized sponges allows them to absorb a wide range of oils. Figure 5a shows the absorption capacity of the functionalized sponges for various oils, including hexane, toluene, octadecene, silicone oil, and motor oil. Note that the functionalized sponges become saturated with hexane, toluene, octadecene, and silicone oil within ∼5 s. The saturation time with the highviscosity motor oil is comparatively longer; the sponges take >2 min to saturate. Compared to the unfunctionalized sponges (see Figure S2), the absorption capacity of functionalized ones (on a gravimetric basis) is lowered because the PDMS density (965 mg/cm3) is much larger than the density of the sponges themselves (8−26 mg/cm3). The thin PDMS coating (required to impart selectivity) on the sponge skeletons can markedly increase their weight, even though the open volume that holds oil in the sponges does not change significantly after PDMS coating. As can be seen in Figure 5a, the absorption capacity of PDMS-functionalized sponges decreases with increasing sponge density (i.e., reducing porosity). Sponge M8 exhibits the highest absorption capacity, ranging from 45 to 75 times its own weight, depending on the density of the oils. The highest absorption capacity of sponge M8 is directly ascribed to its highest porosity, which provides the greatest percentage open volume in the sponge to hold the oils (see Section S1 in Supporting Information; in general, all of the sponges become completely saturated with these liquids). The absorption capacity of our functionalized sponge M8 is comparable to
Figure 2. XPS spectra of sponge M8 before and after PDMS coating, as well as for the PDMS-coated sponge after 200 compression cycles.
alized sponge, the three peaks detected at 283, 421, and 531 eV are attributed to the bonding energies of C 1s, N 1s, and O 1s, which are chemical components in melamine. After PDMS functionalization, the peak intensity associated with N 1s disappears, and that of C 1s and O 1s are strengthened; two new peaks appear at 101 and 152 eV, which are attributed to Si 2p and Si 2s. The primary elemental components of PDMS include Si, C, and O; hence, the presence of Si peaks and the strengthened C and O peaks indicate that the sponge skeletons were successfully modified by PDMS coating. To evaluate the coating adhesion robustness, the functionalized sponge sample was manually compressed flat and released for 200 cycles. The peak intensities of the XPS spectra are unaltered, suggesting PDMS remains strongly adhered to the sponge after the compression cycles. The surface wetting characteristics of the functionalized sponges are evaluated with sessile droplet experiments. Figure 3a−f shows images of water and oil droplets placed on sponges M8, M9.6, P14, P19, P23, and P26, respectively. On the melamine sponges (M8 and M9.6), water droplets sit atop the surfaces in a spherical shape; when touched with tissue paper, the droplets are immediately absorbed by the paper and removed from the sponge surfaces without leaving any residual water (see the dashed circles in Figure 3a,b), indicating the negligible adhesion of water to these surfaces, which is further C
DOI: 10.1021/acs.iecr.6b00234 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 3. Wetting characteristics of the functionalized sponges: (a−f) magnified contact angle images of water droplets (left), photographs of water droplets (colored with green dye) and oil droplets (dyed with oil red O) (middle), and photographs of the same surfaces after touching water droplets with tissue paper (right) where the dashed circles indicate the locations where the water droplets were initially deposited (sponges M8, M9.6, P14, P19, P23, and P26, respectively); (g) measured water contact angles for the different density sponges (error bars are obtained from measuring contact angles at different locations across the corresponding samples); and (h) photographs of sponges M8 (left) and M9.8 (right) being submerged in water.
absorption recyclability). We evaluate the absorption recyclability of sponge M8 via cyclic absorption−squeezing operations. As shown in Figure 5b, for the organic liquids (hexane and toluene), the absorption capacity remains unchanged over 20 absorption-squeezing cycles. However, when absorbing viscous oils (octadecene, silicone oil, and motor oil), some residual oil is retained in the open pore structures after squeezing out the sponge, which would dramatically decrease the absorption capacity after the first cycle. Therefore, in order to remove residual oil between absorption−squeezing cycles for purposes of evaluating potential degradation of the sponge/coating itself, the sponge is immersed into hexane for a few seconds after each absorption−squeezing cycle. It can be seen from Figure 5b that the absorption capacity of sponges with viscous oils remains undiminished over 20 cycles. This indicates the reusability of sponge M8 for the uptake of oils.
Figure 4. (a) Schematic drawing of a sponge sample supporting a column of water (colored with green dye) in the setup used to measure (b) the intrusion pressures of the functionalized sponges.
the reported values for polymer sponges with different functionalizations, as shown in Table 1; the functionalization process developed herein is, however, more cost-effective and scalable. For practical applications, the sponge should not only exhibit a high absorption capacity but also be reusable (i.e.,
Figure 5. (a) Absorption capacities of the functionalized sponges for hexane, toluene, octadecene, silicone oil, and motor oil and (b) absorption recyclability of functionalized sponge M8. D
DOI: 10.1021/acs.iecr.6b00234 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Industrial & Engineering Chemistry Research Table 1. Comparison of Absorption Capacity for Sponges with Different Functionalities sponge type CNT/dopamine/Octadecylamine-modified polyurethane (PU) sponge CNT/PDMS-coated PU sponge graphene/PDMS-coated melamine sponge Fe3O4/dopamine-coated PU sponge Ag/polydopamine-coated melamine sponge
FeCl3/1H,1H,2H,2H-perfluorooctyltriethoxysilane(PTES)/Pyrrole-coated PU sponge 1,3-oxazolidine/1,4-dioxane/stearoyl chloride/NaHCO3-grafted PU sponge octadecyltrichlorosilane-coated melamine sponge polydopamine/1H,1H,2H,2H-perfluorodecanethiol-coated melamine sponge PDMS-functionalized melamine sponge M8
oil type
absorption capacity (g/g)
hexane silicone oil hexane hexane motor oil hexane hexane toluene octadecene silicone oil Motor oil hexane toluene toluene motor oil hexane toluene hexane toluene octadecene silicone oil motor oil
34.9 29 ∼15 ∼55 ∼90 ∼10 ∼60 ∼95 ∼65 ∼31 ∼24 17.2 34.0 96.2 94.0 ∼80 ∼112 45.4 71.5 55.4 61.4 46.3
ref 23 24 25 28 29
32 34 35 36 current work
water mixture, unlike the unfunctionalized sponge M8 (see Figure S3), the oil layer is quickly absorbed by the sponge within a few seconds and the oil-saturated sponge continues to float on the water surface (see Movie S1). After the sponge is swept over the surface to absorb all the oil, only clean water is left in the glass Petri dish. This rapid separation demonstrates the potential of such melamine sponges for oil pollutant cleanup and oil−water separation. Because of the selective absorption behavior of the PDMSfunctionalized sponges, we use a vacuum pump system to remove oils from water in a continuous manner. Figure 7 shows the separation of a silicone oil (dyed with oil red O)−water mixture using sponge M8 (see Movie S2). When the sponge is placed onto the surface of the mixture, it saturates with oil within the first 15 s. The absorbed oil flows through the tube to the flask. Oil in the vicinity of the sponge is concurrently absorbed to achieve continuous separation from the water. The silicone oil is eventually completely removed from the water surface, leaving only transparent and clean water in the beaker. From qualitative observation, no uptake of water by the sponge appears in the collection flask of oil (if water were extracted, it
The simultaneous superhydrophobic and superoleophilic nature of the PDMS-functionalized melamine sponges is critical for selective separation of oil pollutants from water. Figure 6
Figure 6. Photographs of the selective absorption of silicone oil (dyed with oil red O) from water (functionalized sponge M8).
demonstrates the highly selective absorption behavior of sponge M8; silicone oil (dyed with oil red O) is used as the oil target in water. After the sponge is introduced into the oil−
Figure 7. Photographs showing the continuous absorption and removal of silicon oil (dyed with oil red O) from water using functionalized sponge M8. The images inset in panel (f) show the collected oil (top) and clear water (bottom) after separation. E
DOI: 10.1021/acs.iecr.6b00234 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
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Figure 8. Photographs showing the collected (a) hexane and (b) silicone oil separated from water using all of the functionalized sponges considered; the arrows indicate water drops observable within the collected liquid in the case of the polyether sponges.
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would be clearly visible as immiscible water droplets in the flask). The experiment was repeated with both functionalized melamine sponges (M8 and M9.6) for all of the additional oils investigated in the current study (hexane, toluene, octadecene, and motor oil; Movies S3−S6 in the Supporting Information). The same separation behavior is observed. The water content in the collected oils is measured; the purity of the collected samples (see Figure S4) is greater than 99.98% (the same purity as the unused liquids as purchased). This result indicates nearly 100% oil−water separation efficiency, owing to the excellent selectivity of the functionalized melamine sponges. For comparison, the functionalized polyether sponges are assessed in the continuous separation facility and a limited amount of water is drawn into the collected oils in the case of the polyether sponges. Panels a and b in Figure 8 show sets of photographs of the collected flasks of hexane and silicone oil, respectively. There are no water drops in the collected hexane or silicone oil when separating with the melamine sponges, whereas water drops are clearly observed (called out with white arrows) when using polyether sponges. These results demonstrate that only the melamine sponges provide high oil−water separation efficiency. The simple solution-immersion method developed here to impart superhydrophobicity to melamine sponges is versatile and can be readily applied to materials with fine porous structures, such as fabrics, fibrous cotton, and nanowires. Figure S5 shows photographs of water droplets placed on PDMSfunctionalized polyether fabric, cotton fabric, a cotton ball, and CuO nanowires (all initially superhydrophilic). The spherical water droplets are seen to easily roll off the surfaces without leaving any traces of water, indicating the superhydrophobic nature of the functionalized materials.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.6b00234. Estimated sponge porosity, absorption capacities of unfunctionalized sponges, purity of oils separated using the functionalized melamine sponges, and photographs of water droplets (PDF) Movie S1: absorption and removal of silicone oil from a water surface using sponge M8 (AVI) Movie S2: continuous absorption and removal of silicone oil from the water surface (AVI) Movie S3: continuous absorption and removal of hexane from the water surface (AVI) Movie S4: continuous absorption and removal of toluene from the water surface (AVI) Movie S5: continuous absorption and removal of octadecene from the water surface (AVI) Movie S6: continuous absorption and removal of motor oil from the water surface (AVI)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We gratefully thank Adam Green from UFP Technologies for providing the polyether sponges and Dr. Daniel T. Smith from Department of Industrial and Physical Pharmacy, Purdue University for the use of their coulometer.
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CONCLUSIONS We have demonstrated a simple, inexpensive, versatile, and scalable process to prepare superhydrophobic and superoleophilic sponges for oil−water separation. The PDMSfunctionalized melamine sponge with the lowest density (8 mg/cm3) absorbs a wide range of oils with absorption capacities of 45−75 times its weight and exhibits reusability through multiple absorption−squeezing cycles. Applying suction to the sponge allows continuous separation of low-surface-tension oils (demonstrated for hexane, toluene, octadecene, silicone oil, and motor oil) from the surface of an immiscible liquid mixture without any unwanted water uptake. These promising results demonstrate that our facile fabrication process, and the highperformance absorbent material produced, has excellent potential for large-scale cleanup of oil spills and chemical leaks.
REFERENCES
(1) Broje, V.; Keller, A. A. Improved Mechanical Oil Spill Recovery Using an Optimized Geometry for the Skimmer Surface. Environ. Sci. Technol. 2006, 40, 7914. (2) Kujawinski, E. B.; Kido Soule, M. C.; Valentine, D. L.; Boysen, A. K.; Longnecker, K.; Redmond, M. C. Fate of Dispersants Associated with the Deepwater Horizon Oil Spill. Environ. Sci. Technol. 2011, 45, 1298. (3) Buist, I.; Potter, S.; Nedwed, T.; Mullin, J. Herding surfactants to contract and thicken oil spills in pack ice for in situ burning. Cold Reg. Sci. Technol. 2011, 67, 3. (4) 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. (5) Song, J.; Huang, S.; Lu, Y.; Bu, X.; Mates, J. E.; Ghosh, A.; Ganguly, R.; Carmalt, C. J.; Parkin, I. P.; Xu, W.; Megaridis, C. M. Self-
F
DOI: 10.1021/acs.iecr.6b00234 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research Driven One-Step Oil Removal from Oil Spill on Water via SelectiveWettability Steel Mesh. ACS Appl. Mater. Interfaces 2014, 6, 19858. (6) Wang, F.; Lei, S.; Xu, Y.; Ou, J. Green Approach to the Fabrication of Superhydrophobic Mesh Surface for Oil/Water Separation. ChemPhysChem 2015, 16, 2237. (7) Zhang, W.; Shi, Z.; Zhang, F.; Liu, X.; Jin, J.; Jiang, L. Superhydrophobic and superoleophilic PVDF membranes for effective separation of water-in-oil emulsions with high flux. Adv. Mater. 2013, 25, 2071. (8) Zhang, L.; Wang, P. Grafted membranes and substrates having surfaces with switchable superoleophilicity and superoleophobicity and applications thereof. U.S. Patent 20130264287, 2012. (9) Solomon, B. R.; Varanasi, K. K.; Hyder, M. N. Devices and methods using porous membranes for oil-water emulsion separation. U.S. Patent 20150075989, 2014. (10) Zhou, X.; Zhang, Z.; Xu, X.; Guo, F.; Zhu, X.; Men, X.; Ge, B. Robust and durable superhydrophobic cotton fabrics for oil/water separation. ACS Appl. Mater. Interfaces 2013, 5, 7208. (11) Zhu, T.; Cai, C.; Duan, C.; Zhai, S.; Liang, S.; Jin, Y.; Zhao, N.; Xu, J. Robust polypropylene fabrics super-repelling various liquids: a simple, rapid and scalable fabrication method by solvent swelling. ACS Appl. Mater. Interfaces 2015, 7, 13996. (12) Huang, J. Y.; Li, S. H.; Ge, M. Z.; Wang, L. N.; Xing, T. L.; Chen, G. Q.; Liu, X. F.; Al-Deyab, S. S.; Zhang, K.-Q.; Chen, T.; Lai, Y. K. Robust superhydrophobic TiO 2@ fabrics for UV shielding, selfcleaning and oil−water separation. J. Mater. Chem. A 2015, 3, 2825. (13) Wang, S.; Li, M.; Lu, Q. Filter Paper with Selective Absorption and Separation of Liquids that Differ in Surface Tension. ACS Appl. Mater. Interfaces 2010, 2, 677. (14) Feng, X.; Shi, Y.; Liu, J.; Yang, W. Fabrication of filter paper with tunable wettability and its application in oil−water separation. J. Sol-Gel Sci. Technol. 2015, 76, 129. (15) Sun, H.; Xu, Z.; Gao, C. Multifunctional, ultra-flyweight, synergistically assembled carbon aerogels. Adv. Mater. 2013, 25, 2554. (16) Chen, L.; Du, R.; Zhang, J.; Yi, T. Density controlled oil uptake and beyond: from carbon nanotubes to graphene nanoribbon aerogels. J. Mater. Chem. A 2015, 3, 20547. (17) Wu, Z.-Y.; Li, C.; Liang, H.-W.; Zhang, Y.-N.; Wang, X.; Chen, J.-F.; Yu, S.-H. Carbon nanofiber aerogels for emergent cleanup of oil spillage and chemical leakage under harsh conditions. Sci. Rep. 2014, 4, 4079. (18) Si, Y.; Fu, Q.; Wang, X.; Zhu, J.; Yu, J.; Sun, G.; Ding, B. Superelastic and Superhydrophobic Nanofiber-Assembled Cellular Aerogels for Effective Separation of Oil/Water Emulsions. ACS Nano 2015, 9, 3791. (19) Zhao, Y.; Hu, C.; Hu, Y.; Cheng, H.; Shi, G.; Qu, L. A Versatile, Ultralight, Nitrogen-Doped Graphene Framework. Angew. Chem. 2012, 124, 11533. (20) Xu, L.; Xiao, G.; Chen, C.; Li, R.; Mai, Y.; Sun, G.; Yan, D. Superhydrophobic and superoleophilic graphene aerogel prepared by facile chemical reduction. J. Mater. Chem. A 2015, 3, 7498. (21) Gui, X.; Zeng, Z.; Lin, Z.; Gan, Q.; Xiang, R.; Zhu, Y.; Cao, A.; Tang, Z. Magnetic and Highly Recyclable Macroporous Carbon Nanotubes for Spilled Oil Sorption and Separation. ACS Appl. Mater. Interfaces 2013, 5, 5845. (22) Chen, N.; Pan, Q. Versatile Fabrication of Ultralight Magnetic Foams and Application for Oil−Water Separation. ACS Nano 2013, 7, 6875. (23) Wang, H.; Wang, E.; Liu, Z.; Gao, D.; Yuan, R.; Sun, L.; Zhu, Y. A novel carbon nanotubes reinforced superhydrophobic and superoleophilic polyurethane sponge for selective oil-water separation through a chemical fabrication. J. Mater. Chem. A 2015, 3, 266. (24) Wang, C.-F.; Lin, S.-J. Robust superhydrophobic/superoleophilic sponge for effective continuous absorption and expulsion of oil pollutants from water. ACS Appl. Mater. Interfaces 2013, 5, 8861. (25) Nguyen, D. D.; Tai, N.-H.; Lee, S.-B.; Kuo, W.-S. Superhydrophobic and superoleophilic properties of graphene-based sponges fabricated using a facile dip coating method. Energy Environ. Sci. 2012, 5, 7908.
(26) Tai, N.-H. Superhydrophobic and superoleophilic composite. U.S. Patent 20140057782, 2014. (27) Ge, J.; Ye, Y. D.; Yao, H. B.; Zhu, X.; Wang, X.; Wu, L.; Wang, J. L.; Ding, H.; Yong, N.; He, L. H.; Yu, S.-H. Pumping through porous hydrophobic/oleophilic materials: an alternative technology for oil spill remediation. Angew. Chem. 2014, 126, 3686. (28) Liu, S.; Xu, Q.; Latthe, S. S.; Gurav, A. B.; Xing, R. Superhydrophobic/superoleophilic magnetic polyurethane sponge for oil/water separation. RSC Adv. 2015, 5, 68293. (29) Xu, Z.; Miyazaki, K.; Hori, T. Dopamine-Induced Superhydrophobic Melamine Foam for Oil/Water Separation. Adv. Mater. Interfaces 2015, 2, 1500255. (30) Zhang, X.; Li, Z.; Liu, K.; Jiang, L. Bioinspired Multifunctional Foam with Self-Cleaning and Oil/Water Separation. Adv. Funct. Mater. 2013, 23, 2881. (31) Seok, S.; Shin, S.; Lee, T. J.; Jeong, J.-M.; Yang, M.; Kim, D. H.; Park, J. Y.; Lee, S. J.; Choi, B. G.; Lee, K. G. Multifunctional Polyurethane Sponge for Polymerase Chain Reaction Enhancement. ACS Appl. Mater. Interfaces 2015, 7, 4699. (32) Zhou, X.; Zhang, Z.; Xu, X.; Men, X.; Zhu, X. Facile fabrication of superhydrophobic sponge with selective absorption and collection of oil from water. Ind. Eng. Chem. Res. 2013, 52, 9411. (33) Zhu, Q.; Chu, Y.; Wang, Z.; Chen, N.; Lin, L.; Liu, F.; Pan, Q. Robust superhydrophobic polyurethane sponge as a highly reusable oil-absorption material. J. Mater. Chem. A 2013, 1, 5386. (34) Wang, G.; Zeng, Z.; Wu, X.; Ren, T.; Han, J.; Xue, Q. Threedimensional structured sponge with high oil wettability for the cleanup of oil contaminations and separation of oil-water mixtures. Polym. Chem. 2014, 5, 5942. (35) Pham, V. H.; Dickerson, J. H. Superhydrophobic silanized melamine sponges as high efficiency oil absorbent materials. ACS Appl. Mater. Interfaces 2014, 6, 14181. (36) Ruan, C.; Ai, K.; Li, X.; Lu, L. A superhydrophobic sponge with excellent absorbency and flame retardancy. Angew. Chem., Int. Ed. 2014, 53, 5556. (37) Jin, Y.; Jiang, P.; Ke, Q.; Cheng, F.; Zhu, Y.; Zhang, Y. Superhydrophobic and superoleophilic polydimethylsiloxane-coated cotton for oil−water separation process: An evidence of the relationship between its loading capacity and oil absorption ability. J. Hazard. Mater. 2015, 300, 175. (38) Blossey, R. Self-cleaning surfacesvirtual realities. Nat. Mater. 2003, 2, 301. (39) Yao, X.; Xu, L.; Jiang, L. Fabrication and characterization of superhydrophobic surfaces with dynamic stability. Adv. Funct. Mater. 2010, 20, 3343. (40) Cassie, A. B. D.; Baxter, S. Wettability of porous surfaces. Trans. Faraday Soc. 1944, 40, 546.
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DOI: 10.1021/acs.iecr.6b00234 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
