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Chemical and equipment-free strategy to fabricate water/ oil separating materials for emergent oil-spill accidents Guannan Ju, Jing Liu, Donglin Li, Mengjiao Cheng, and Feng Shi Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b04548 • Publication Date (Web): 19 Feb 2017 Downloaded from http://pubs.acs.org on February 20, 2017
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Chemical and equipment-free strategy to fabricate water/oil separating materials for emergent oil-spill accidents Guannan Ju, Jing Liu, Donglin Li, Mengjiao Cheng,* and Feng Shi State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, 15 Beisanhuan East Road, Chaoyang District, Beijing, 100029 (P. R. China) KEYWORDS: Water/oil separation, superhydrophobicity/superoleophilicity, candle soot, onestep fabrication
ABSTRACT: Oil spill accidents normally have two important features when considering practical clean-up strategies: (1) unexpected occurrence in any situations possibly without specific equipment and chemicals; (2) emergency to be cleaned to minimize the influences on ecosystems. To address these two practical problems regarding removal of spilt oil, we have proposed an in situ, rapid and facile candle-soot strategy to fabricate water/oil separating materials based on superhydrophobicity/superoleophilicity. The one-step fabrication method is independent on any chemicals or equipment and can be ready for use through short smoking processes within 5 min by using raw materials available in daily life such as textiles. The as-
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prepared materials perform good durability for repeated separation test and high recovery rate of various oils from water/oil mixtures. This strategy provides possibility of rapid response to sudden oil spill accidents, especially in cases without any equipment or chemicals and in poor countries/areas those could hardly afford transportation and storage of expensive separating materials.
INTRODUCTION With increasing oil transportation demands, accidents of oil spill occurred frequently and caused serious damage on ecosystems, animals and even human beings through water systems.1,2 To
handle
the
oil-polluted
water,
superhydrophobic/superoleophilic3-10
or
materials
with
extreme
wettability
such
as
superhydrophilic/underwater-superoleophobic11-20
properties have been proposed to clean oily water through permeating one component of the oil/water mixtures and meanwhile blocking the other.21-24 However, there are two challenges in practical uses with such kinds of materials with extreme wetting properties: (1) the fabrication normally requires suitable surface roughness with hierarchical micro/nano structures, which risks mechanical damage in storage and transportation procedures; (2) multi-steps (two or more) and specific equipment or chemicals are necessary in fabrication process, which makes it almost impossible to prepare those special materials in situ for instant use towards emergent accidents. To realize wide applications of these materials regarding oil/water separation, we should consider the demands in practical situations: most oil spilt accidents emergent to be dealt with are unexpected to occur under many possible occasions at harbors, in pipe or ship transportation etc.; many poor countries/areas could hardly afford special chemicals/equipment or transportation/storage of prepared materials. Therefore, it is meaningful to develop in situ, rapid
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and facile fabrication strategies that are independent on specific chemicals or equipment for oil/water separation based on materials with extreme wettability. It is a common phenomenon that incomplete combustion of carbon materials such as candle, wood, coal etc. could produce soot,25,26 whose deposition on substrates could result both rough structures composed of irregular carbon particles and low-surface-energy coating at the same time to realize superhydrophobic properties. Inspired by this fact, in this article we have proposed a facile and rapid (within 5 min) candle-soot strategy to in situ fabricate superhydrophobic coatings on porous materials of copper foam and various textile fabrics, which were used for efficient oil/water separation by selectively permeating the oil while blocking the water because of the superhydrophobic/superoleophilic properties. Through further integrating these materials into devices, we realized continuous collection of oil from water, whose recovery rate reached as high as 98.8%. Since the preparation process was independent on specific equipment and chemicals, we have established a facile in situ fabrication methodology of superhydrophobic materials versatile for a wide range of porous structures available in normal life and thus addressed the practical difficulty in emergent demands towards unexpected oil spill accidents and situations short of chemicals and equipment. EXPERIMENTAL SECTION Materials: Copper foam was obtained from Anping Xinlong Wire Mesh Manufacture Co., Ltd., Anping, China. Solvent Blue 78, toluene, n-hexane, silicone oil, isobutanol, dichloromethane and ethanol were purchased from Sinopharm Chemical Reagent Beijing Co., Ltd., Beijing, China. Deionized water was used for all the tests and experiments. All chemicals were used as received without further purification.
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Instruments and Characterization: Scanning electron microscope (SEM) images and Energy Dispersive X-ray Spectrum (EDX) were obtained from an EVO MA25 instrument (Carl Zeiss, Wetzlar, Germany) at 20.0 kV. X-ray photoelectron spectroscopy were carried out on a ESCALAB 250 instrument (ThermoFisher Scientific, USA). Photographic images were taken by a camera (HDR-PJ790, SONY, Tokyo, Japan). The peristaltic pump (BT300-2J) with a pressure difference of 0.05 MPa was from Baoding Longer Precision Pump Co., Ltd., Hebei, China. Fabrication of the water/oil separating device. The water/oil separating device was designed and fabricated by a candle-soot strategy. Firstly a piece of cubic copper foam (5.5 × 6 cm2) was manually folded in to a box without cover (3 × 2.5 × 1.5 mm3) following the schematic procedure in Scheme S1. Secondly the box was cleaned under ultra-sonication in ethanol and subsequent deionized water for three times each, followed by drying in an oven. Thirdly a commercially available candle was lighted for 3 min until the flame was stable. The flame height was about 3 cm, which could be divided into three parts in the sequence of near to far from the wick: innermost zone with unburnt wax vapors, middle zone with partially burnt wax and outermost zone with completely burnt wax and hottest portion of flame. We held the copper foam or fabrics with tweezers to the position of about 1 cm away from the wick, approximately in the middle zone, and the flame was pressed down to this height without passing through the copper foam or fabrics. In the subsequent candle soot deposition process, we waved the copper foam or fabrics back and forth at this height for 2.5 min to obtain a homogeneous layer. Each side of the copper foam box was treated on the candle flame for 2.5 min in this way. Another smaller box with a dimension of (2.7 × 2.2 × 1.5 mm3) was punched with a hole (diameter: 5 mm) in the bottom center intended to be connected with a pump pipe and subsequently treated with
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the same candle soot strategy. The small box without cover was turned over to cover the asprepared large box, thus forming a locked close device with superhydrophobicity. For the fabrics, we used the textiles such as towel, bed sheet etc. as purchased and cut into pieces of cloth with a size of 3 × 3 cm2. Except that the cloth was not washed, the candle soot treatment was identical compared with that for the copper foam. Namely the cut cloth was held in the middle of the candle flame (about 1 cm away from the wick) and waved back and forth for 2.5 min on each side to deposit the candle soot homogeneously and avoid burning. Test of superhydrophobicity/superoleophilicity in air. Water or oil droplets were positioned onto the surface of the as-prepared device and different type of superhydrophobic textiles using a plastic dropper. Water contact angle (WCA) and oil contact angle (OCA) measurements on the as-prepared materials were carried out with 4-µL droplets on a OCA 20 instrument (DataPhysics Instruments Gmbh, Filderstadt, Germany). The surface wettability before and after mechanical abrasion was shown in Figure S1 of Supporting Information. Water/oil separating tests. With the above as-prepared superhydrophobic/superoleophilic open box without cover, we further checked its water/oil separating performance with model water/oil mixtures. Firstly, the water/oil mixtures were prepared by adding 15 mL of red-dyed water into 30 mL of blue-dyed toluene. Then the water/oil mixtures were poured into the interior of the box. Driven by gravity, the blue oil permeated through the bottom surface into the collecting vessel while water remained in the interior of the box. After abrasion, the permeation difference between water and oil was re-checked through this method as shown in Figure S1. Continuous water/oil separation. In order to realize continuous separation and in situ collection of oil, we joined the as-prepared device with a peristaltic pump through inserting the pump pipe
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into the created central hole of the covering box, thus forming a continuous oil separating/collecting apparatus. Water/oil mixtures (40 mL of toluene and 450 mL of water) were applied in all of our experiments for demonstration. We dyed the oil layer with Solvent Blue 78 to distinguish the water/oil mixtures. One end of a pump pipe was connected with the asprepared device and the other end was placed into a collecting vessel; the device was then placed on the oil spill spot. The dyed-blue oil could be absorbed upon contacting the device and further pumped away from the interior of the device to be collected, thus leading to a continuous working mode. With the two locked boxes, the device has four double-layered walls with superhydrophobic properties, which could hold air layer and connect the inner space. When the pressure difference created by the pump is too large or there is little oil to be pumped away, this air layer helps to avoid pumping water into the box to pollute collected oil. The residual oil amount in water after water/oil separation was measured with a TOC-V CPH instrument (SHIMADZU), which is used for analyses of organic carbon in petroleum industry. For each device, at least six rounds of water/oil separation tests were carried out. To check the versatility to various oil types, five kinds of oil (toluene, n-hexane, silicone oil, isobutanol and dichloromethane) were used for evaluation. RESULTS AND DISCUSSION
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Scheme 1. Schematic illustration of the candle-soot strategy to obtain superhydrophobic coatings and the integration of the as-prepared superhydrophobic materials into a locked device.
Since the combustion produces both carbon particles and heat, we tried to exclude the influence of heat on substrate by taking a model substrate of porous copper foam to demonstrate the proposed candle-soot strategy. As shown in Scheme 1, after the candle was lighted for 3 min, we place the bottom surface of a folded open box at a distance of 1 cm from the wick and kept the smoking process for 2.5 min for each side surface. To clarify the deposition of carbon particles on the substrate, we used SEM, EDX patterns and XPS to characterize the surface morphology (Figure 1) and composition (Figure S2-4) of the copper foam before and after the deposition of candle soot, respectively. From Figure 1a, we can observe that the bare copper foam exhibits a porous structure consisting of staggered meshes forming irregular pores with an averaged diameter of about 500 µm. The mesh surfaces in Figure 1b-c are relatively smooth except some slightly cracked patterns. After the candle soot treatment, the porous structure of the copper foam is still maintained (Figure 1d), which ensures the infiltration of oil driven by both
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gravity and capillary forces (Scheme S2 of Supporting Information).27-29 From the magnified image in Figure 1e, the meshes seemed to be wrapped in a 20 µm-thick layer of carbon as indicated from the EDX patterns and XPS results in Figure S2-4. The nanoscale/sub-microscale carbon particles aggregated randomly to form irregular 3D network (Figure 1f). The deposition of carbon particles should be caused by placing the copper foam in the position of the candle flame where soot gathered after incomplete combustion, which is reproducible with similar surface morphologies in repeated experiments (Figure S5). The hierarchical micro-/nanostructures constructed by the randomly aggregated carbon particles contributed to high surface roughness necessary for superhydrophobicity. Furthermore, these carbon particles themselves act as a low-surface-energy coating for the realization of superhydrophobicity, thus avoiding extra surface modification as required in most reports. In this way, the fast and simple smoking way could ideally realize the two essential factors to obtain superhydrophobicity.
Figure 1. SEM images of the copper foam (a-c) before and (d-f) after the deposition of candle soot with different magnifications.
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To confirm the superhydrophobicity of the as-modified copper foam, we investigated the wettability of the copper foam before and after smoking process with observable liquid tests and water contact angle (WCA) measurements in Figure 2. For the bare copper foam before candle soot deposition, the macroscopic water droplet could slowly spread on the copper foam and the WCA value is about 0° with a 4-µL water droplet (Figure 2a and 2d), which is attributed to the hydrophilic nature of metal and porous structures to induce capillary force for the absorption of wettable liquid.30-33 After deposited with candle soot, the copper foam turned from its originally orange-red appearance to totally dark black as displayed in Figure 2b. Water rolled off the surface upon dropping it and the corresponding WCA value was 155° (Figure 2e), which confirmed the superhydrophobicity of the as-prepared copper foam with candle soot. On the contrary, when the oil droplet of toluene dyed with Solvent Blue 78 was applied onto the same as-prepared surface, it quickly spread over the surface completely within 0.5 s, indicating the superoleophilic property of the surface as confirmed by the oil contact angle (OCA) of 0° (Figure 2c and 2f). The remarkable difference of wettability towards water and oil on the copper foam surface has provided possibility for oil/water separation through blocking water while absorbing oil at the same time.
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Figure 2. Photos of water droplets placed on the copper foam (a) before and (b) after the candle soot strategy. (c) Dropping toluene droplet dyed blue onto the copper foam deposited with candle soot. (d-f) Schemes of the observable wettability corresponding to (a-c) and the insets are (d-e) WCA and (f) OCA results.
With the porous copper foam as a model substrate, we have demonstrated the feasibility of the proposed method to obtain selective permeability between oil and water. However, copper foam is not available in many situations of normal life. To clarify the versatility of this method, we wondered whether textiles available in daily life were suitable to be used as the substrates. Therefore, we have systematically investigated the fabrication and the wettability towards water/oil of various textiles woven by ceramic fiber, glass fiber, 20% chinlon and 80% terylene (synthetic mixture), thin cotton (bed sheet), 60% cotton and 40% terylene (cotton mixture) and thick cotton (towel) as shown in Figure 3a-f, correspondingly, which are commercially available and quite common for daily use. The above six kinds of cloth were cut into a size of 3 × 3 cm2
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and subsequently treated with the candle-soot strategy in Scheme 1. Note that the cloth should be moved rapidly to avoid concentrated heat at a fixed point to reach the kindling point of the cloth. After this short smoking process, the cloth was not damaged or burned and displayed a black or grey color due to the deposited carbon particles. The microscale surface morphology of the above textiles before and after candle soot deposition were compared in Figures S6-11, which present homogeneous coverage of fine particles. The as-prepared textiles showed a good superhydrophobicity as shown in Figure 3a’-f’; when we dropped the dyed toluene onto these as-prepared cloth, we observed that the oil droplet rapidly wetted the surface, indicating their superoleophilicity (Figure 3a’’-f’’) (oil collection from water surface by the smoked cloth was shown in Figure S12). These results have demonstrated that these textiles available in life could also be used following this facile and rapid candle-soot strategy without any pre-treatment to fabricate materials with selective permeability towards water and oil.
Figure 3. Photographs of cloth woven by (a) ceramic fiber, (b) glass fiber, (c) synthetic mixture containing 20% chinlon and 80% terylene, (d) thin cotton (bed sheet), (e) woven mixture containing 60% cotton and 40% terylene and (f) thick cotton (towel). Corresponding cloth treated with candle soot shows superhydrophobicity in (a’-f’) and superoleophilicity in (a’’-f’’).
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After we confirmed the superhydrophobicity/superoleophilicity of the as-prepared materials with the candle-soot strategy, we tried to clarify their performance in water/oil separation. In Figure 4a, we folded the copper foam into a rectangular box without cover, followed by deposition of candle soot of every side. To create a model system of water/oil mixtures, we added 15 mL red-dyed water into 30 mL blue-dyed toluene. Upon pouring the water/oil mixtures into the device, we could observe that the red-dyed oil was immediately absorbed within 0.5 s and infiltrated through the device into the beaker as a result of superoleophilicity of the device (Figure 4b) and gravity. At the same time, the red water was thoroughly blocked within the device because of its superhydrophobicity, leading to complete separation of the water/oil mixtures (Figure 4c-d). To this end, we have demonstrated the device prepared by the candlesoot strategy could be used for efficient and low-energy-cost water/oil separation independent on special
equipment.
Additionally,
the
as-prepared
device
maintained
its
superhydrophobicity/superoleophilicity even after 24 h of immersion in acidic and alkaline solutions, demonstrating the stability of the extreme surface wettability towards harsh conditions (Figure S13). After mechanical abrasion, the copper foam still present water/oil separation performance even though the WCA reduced slightly (Figure S2c&d).
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Figure 4. Photographs of (a) the superhydrophobic copper foam box (left) and the water/oil mixtures dyed red/blue (right), (b) oil collection, and (c-d) water blocking within the device.
To promote the established methodology for practical use regarding the demand in cleaning large amount of spilt oil, we considered an in situ continuous separation way by integrating the as-prepared device into a system as schematically illustrated with the apparatus model in Figure 5a. The device was connected to a peristaltic pump with a rubber pipe from the hole created on the top surface of the copper foam box; the pressure difference between the device side and the collection vessel side is about 0.05 MPa. With the design of two locked copper foam boxes without cover, the device has four double-layered walls with superhydrophobic properties, which could hold air layer and connect the inner space. In this way, when the pressure difference created by the pump is too large or there is little oil in the box, the air layer could help to avoid
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pumping water into the box to pollute the collected oil. We took the water/oil mixtures of 450 mL water and 40 mL toluene dyed with Solvent Blue 78 as a model system, and used the copper foam device for demonstration. Upon placing the device on the spilt oil and starting the pump at 50 rpm, we could observe that the blue oil could be rapidly absorbed into the device, transported through the pipe and gathered in the collection vessel (Figure 5b-d). When most oil was pumped away, the pipe started to pump into continuous air instead of water even if the peristaltic pump kept running. This is because the applied pressure difference of 0.05 MPa is small and the locked structure of two copper foam boxes with trapped air in four walls further reduces pressure difference, thus avoiding secondary pollution by water/oil mixture even when the collected oil amount was very low (Figure S14). The recovery rate was calculated by comparing the gathered amount of oil and the original poured amount. In this case, we have collected 39.5 mL of toluene out of the original 40 mL and the recycled rate reached 98.8%, which should be higher because there was residual oil in the porous device walls and pump pipes. The residual oil amount in water after water/oil separation was 25 µg/mL (averaged result) measured with a TOC-V CPH instrument (SHIMADZU).
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Figure 5. (a) Schematic illustration of the apparatus for continuous water/oil separation. Snapshots in the water/oil sepration process: (b) the model system of water/oil mixture with originally 40 mL of toluene dyed blue; (c) start of oil collection (the pump not is shown); (d) continuous working mode of oil removal; (e) end of separation with 39.5 mL collected oil. Considering the complex composition of spilt oil, we checked the performance of the device in separating five kinds of water/oil mixtures containing water and model oil types such as toluene, n-hexane, silicone oil, isobutanol and dichloromethane, respectively. With the apparatus for continuous water/oil separation in Figure 5, we carried out water/oil separation of the above five mixtures separately and calculated the corresponding “recycled rates”, i. e. the volume ratio of the collected oil amount and the original oil amount in the mixture. As summarized in Figure 6a, all the recycled rates were over 95% for each type of oil. The solvents with densities of either lower or higher than that of water could be efficiently separated from the water/oil mixture by using the device with two inter-locked copper foam boxes. Furthermore, we considered practical situations of cleaning spilt oil at different spots; therefore, the durability of the device and
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reproducibility of the recycled rates in each water/oil separation should be evaluated. Taking the mixture of water/toluene as an example, we prepared six identical 450 mL-water/ 40 mL-toluene mixtures and conducted six times of water/oil separation process of these mixtures one-by-one with the same device in the apparatus of Figure 5. In each separation process, the recycled rate was calculated and summarized in Figure 6b. All the other five types of oil were also used following the same procedure. The results demonstrated that the device shows a steady recycled rate level higher than 95% in six identical repeated water/oil separation processes regardless of the oil types, thus ensuring good durability and reproducibility in practical use with the continuous working mode.
Figure 6. Recycled rates of five oil types: toluene, n-hexane, silicone oil, isobutanol and dichloromethane in (a) one round of water/oil separation; (b) six sequential oil clean-up processes.
CONCLUSIONS
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In summary, we have demonstrated an in situ, facile and rapid candle-soot strategy to prepare materials for water/oil separation without requirements of any special equipment or chemicals. Many porous materials available in daily life such as textiles woven by ceramic fiber, glass fiber, 20% chinlon and 80% terylene (synthetic mixture), thin cotton (bed sheet), 60% cotton and 40% terylene (mixture) and thick cotton (towel) could be used as the raw materials and the water/oil separating materials could be ready for use within 5 min through a facile one-step process of candle soot deposition. The mechanism of the water/oil separation was attributed to the remarkably different wettability of the as-prepared materials with superhydrophobicity and superoleophilicity. By further integrating these materials into devices, we realized continuous oil collection from water, whose recycled rate reached as high as 98.8%. Besides, this method is suitable for the clean-up of a wide range of oil categories with recycled rates over 95%. Therefore, we believe the proposed strategy has provided a chemical and equipment-free strategy for practical use in emergent oil spilt accidents or poor countries/areas.
ASSOCIATED CONTENT Supporting Information. Folding of the device, EDX and XPS analyses, chemical and mechanical stability of deposited candle soot, pore size effect, SEM and WCA of textiles before and after candle soot treatment, oil removal by the textiles and continuous water/oil separation in situations of small oil amount. AUTHOR INFORMATION Corresponding Author
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*E-mail:
[email protected]; Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This research was supported by NSFC (21674009; 21604002), the Fundamental Research Funds for the Central Universities (ZY1610), Open Project of State Key Laboratory for Supramolecular Structure and Materials (SKLSSM 201617) and Beijing Nova Program Interdisciplinary Studies Cooperative Projects.
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(10) Zhang, X. Y.; Li, Z.; Liu, K. S.; Jiang, L. Bioinspired multifunctional foam with self‐ cleaning and oil/water separation. Adv. Funct. Mater. 2013, 23, 2881-2886. (11) Zhang, L. B.; Zhong, Y. J.; Cha, D. Y.; Wang, P. A self-cleaning underwater superoleophobic mesh for oil-water separation. Sci. Rep. 2013, 3, 2326. (12) Xu, L. P.; Zhao, J.; Su, B.; Liu, X. L.; Peng, J. T.; Liu, Y. B.; Liu, H. L.; Yang, G.; Jiang, L.; Wen, Y. Q.; Zhang, X. J.; Wang, S. T. An ion-induced low-oil-adhesion organic/inorganic hybrid film for stable superoleophobicity in seawater. Adv. Mater. 2013, 25, 606-611. (13) Liu, X. L.; Zhou, J.; Xue, Z. X.; Gao, J.; Meng, J. X.; Wang, S. T.; Jiang, L. Clam’s shell inspired high-energy inorganic coatings with underwater low adhesive superoleophobicity. Adv. Mater. 2012, 24, 3401-3405. (14) Xue, Z. X.; Wang, S. T.; Lin, L.; Chen, L.; Liu, M. J.; Feng, L.; Jiang, L. A novel superhydrophilic and underwater superoleophobic hydrogel-coated mesh for oil/water separation. Adv. Mater. 2011, 23, 4270-4273. (15) Liu, M. J.; Wang, S. T.; Wei, Z. X.; Song, Y. L.; Jiang, L. Bioinspired design of a superoleophobic and low adhesive water/solid interface. Adv. Mater. 2009, 21, 665-669. (16) Cai, Y.; Lin, L.; Xue, Z. X.; Liu, M. J.; Wang, S. T.; Jiang, L. Filefish-inspired surface design for anisotropic underwater oleophobicity. Adv. Funct. Mater. 2014, 24, 809-816. (17) Fan, J. B.; Song, Y. Y.; Wang, S. T.; Meng, J. X.; Yang, G.; Guo, X. L.; Feng, L.; Jiang, L. Directly coating hydrogel on filter paper for effective oil–water separation in highly acidic, alkaline, and salty environment. Adv. Funct. Mater. 2015, 25, 5368-5375.
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(18) 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. (19) Gao, X. F.; Xu, L. P.; Xue, Z. X.; Feng, L.; Peng, J. T.; Wen, Y. Q.; Wang, S. T.; Zhang, X. J. Dual-scaled porous nitrocellulose membranes with underwater superoleophobicity for highly efficient oil/water separation. Adv. Mater. 2014, 26, 1771-1775. (20) Xu, L. P.; Peng, J. T.; Liu, Y. B.; Wen, Y. Q.; Zhang, X. J.; Jiang, L.; Wang, S. T. Nacreinspired design of mechanical stable coating with underwater superoleophobicity. ACS Nano 2013, 7, 5077-5083. (21) Sai, H. Z.; Fu, R.; Xing, L.; Xiang, J. H.; Li, Z. Y.; Li, F.; Zhang, T. Surface modification of bacterial cellulose aerogels’ web-like skeleton for oil/water separation. ACS Appl. Mater. Interfaces 2015, 7, 7373-7381. (22) Cheng, M. J.; Gao, Y. F.; Guo, X. P.; Shi, Z. Y.; Chen, J. F.; Shi, F. A functionally integrated device for effective and facile oil spill cleanup. Langmuir 2011, 27, 7371-7375. (23) Ju, G. N.; Cheng, M. J.; Shi, F. A pH-responsive smart surface for the continuous separation of oil/water/oil ternary mixtures. NPG Asia Mater. 2014, 6, e111. (24) Zhu, Q.; Pan, Q. M. Mussel-inspired direct immobilization of nanoparticles and application for oil–water separation. ACS Nano, 2014, 8, 1402-1409. (25) Deng, X.; Mammen, L.; Butt, H. J.; Vollmer, D. Candle soot as a template for a transparent robust superamphiphobic coating. Science 2012, 335, 67-70.
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(26) Liu, X. J.; Xu, Y.; Chen, Z.; Ben, K. Y.; Guan, Z. S. Robust and antireflective superhydrophobic surfaces prepared by CVD of cured polydimethylsiloxane with candle soot as a template. RSC Adv. 2015, 5, 1315-1318. (27) Song, B. T.; Xu, Q. Highly hydrophobic and superoleophilic nanofibrous Mats with controllable pore sizes for efficient oil/water separation. Langmuir 2016, 32, 9960-9966. (28) Li, J.; Kang, R. M.; Tang, X. H.; She, H. D.; Yang, Y. X.; Zha, F. Superhydrophobic meshes that can repel hot water and strong corrosive liquids used for efficient gravity-driven oil/water separation. Nanoscale, 2016, 8, 7638-7645. (29) Wang, Q.; Meng, Q; Wang, P.; Liu, H.; Jiang, L. Bio-inspired direct patterning functional nanothin microlines: controllable liquid transfer, ACS Nano 2015, 9, 4362-4370. (30) Cassie, A. B. D.; Baxter, S. Wettability of porous surfaces. Trans. Faraday Soc. 1944, 40, 546-551. (31) Wang, S. T.; Liu, K. S.; Yao, X.; Jiang, L. Bioinspired surfaces with superwettability: new insight on theory, design, and applications. Chem. Rev. 2015, 115, 8230-8293. (32) Liu, K. S.; Cao, M. Y.; Fujishima, A.; Jiang, L. Bio-inspired titanium dioxide materials with special wettability and their applications. Chem. Rev. 2014, 114, 10044-10094. (33) Su, B.; Tian, Y.; Jiang, L. Bioinspired interfaces with superwettability: From materials to chemistry. J. Am. Chem. Soc. 2016, 138, 1727-1748.
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Table of Contents Graphic
We have demonstrated an in situ, facile and rapid candle-soot strategy to prepare materials for water/oil separation without requirements in any special equipment or chemicals. By further integrating these materials into devices, we realized continuous collection of oil from water.
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Figure 1. SEM images of the copper foam (a-c) before and (d-f) after the deposition of candle soot with different magnifications. 38x17mm (300 x 300 DPI)
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Figure 2. Photos of water droplets placed on the copper foam (a) before and (b) after the candle soot strategy. (c) Dropping toluene droplet dyed blue onto the copper foam deposited with candle soot. (d-f) Schemes of the observable wettability corresponding to (a-c) and the insets are (d-e) WCA and (f) OCA results. 25x17mm (300 x 300 DPI)
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Figure 3. Photographs of cloth woven by (a) ceramic fiber, (b) glass fiber, (c) synthetic mixture containing 20% chinlon and 80% terylene, (d) thin cotton (bed sheet), (e) woven mixture containing 60% cotton and 40% terylene and (f) thick cotton (towel). Corresponding cloth treated with candle soot shows superhydrophobicity in (a’-f’) and superoleophilicity in (a’’-f’’). 18x8mm (300 x 300 DPI)
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Figure 4. Photographs of (a) the superhydrophobic copper foam box (left) and the water/oil mixtures dyed red/blue (right), (b) oil collection, and (c-d) water blocking within the device. 35x40mm (300 x 300 DPI)
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Figure 5. (a) Schematic illustration of the apparatus for continuous water/oil separation. Snapshots in the water/oil sepration process: (b) the model system of water/oil mixture with originally 40 mL of toluene dyed blue; (c) start of oil collection (the pump not is shown); (d) continuous working mode of oil removal; (e) end of separation with 39.5 mL collected oil. 47x38mm (300 x 300 DPI)
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Figure 6. Recycled rates of five oil types: toluene, n-hexane, silicone oil, isobutanol and dichloromethane in (a) one round of water/oil separation; (b) six sequential oil clean-up processes. 24x9mm (300 x 300 DPI)
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Scheme 1. Schematic illustration of the candle-soot strategy to obtain superhydrophobic coatings and the integration of the as-prepared superhydrophobic materials into a locked device. 26x20mm (300 x 300 DPI)
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Table of contents graphic 22x13mm (300 x 300 DPI)
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