LETTER pubs.acs.org/Langmuir
A Functionally Integrated Device for Effective and Facile Oil Spill Cleanup Mengjiao Cheng, Yongfeng Gao, Xianpeng Guo, Zhaoyuan Shi, Jian-feng Chen, and Feng Shi* State Key Laboratory of Chemical Resource Engineering & State Key Laboratory of Organic Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, P. R. China ABSTRACT: In this Letter, we have fabricated a multifunctional device for highly efficient and inexpensive oil spill cleanup by combining electroless metal deposition with self-assembled monolayers, which has integrated the functions of oil containment booms, oil-sorption materials, oil skimmers, and wateroil separating devices. This functionally integrated device has a lower density than that of water, which leads to a potential application as oil containment booms; it can take up oil that is 3.5 times its own weight, which shows excellent oil-sorption properties, with the wateroil separating yield of the as-prepared device being up to 92%. The device has the advantages of high efficiency, capacity of antiwave, and reproducibility, which is suitable for many types of organic solvents or oils, even for emulsion of petroleum and water, and thus is a proof-of-principle idea to be applied in marine spilt oil cleanup and other wateroil separating systems.
1. INTRODUCTION With the development of offshore oil production, more and more oil spill accidents happened, among which the Gulf of Mexico oil spill in 2010 caused great concern and worry.1,2 When oil spill accidents occurred, oil containment booms would be used to prevent the spilt oil from dispersing and subsequent measures had been employed to clean up the oil, such as physical absorption by oil-sorption materials, in situ burning,3 mechanical recovery,46 physics diffusion, dispersants,7 enhanced bioremediation,8,9 oil skimmer,10 porous sorbent materials,1113 and so on. However, all of the above methods needed their own specific equipment and should be operated independently, which might increase the cost and decrease the efficiency of the cleanup process. Therefore, we wonder whether it is possible to prepare a novel multifunctional device to integrate the functions of oil containment booms, oil-sorption materials, oil skimmers, and wateroil separating devices, leading to highly efficient and inexpensive oil cleanup equipment in the future. Recently, superhydrophobic materials1416 have extended applications to the research area of oil spill cleanup, for their specific surface properties of superoleophilicity and superhydrophobicity. Jiang and co-workers prepared a superhydrophobic and superoleophilic coating on stainless steel mesh substrates by spraying polytetrafluoroethylene onto the mesh, which could be used for separating oil from water.17 This film could only bear a water pressure no higher than 426 mm water column,18,19 which provided a potential opportunity to prepare closed oil skimmers but only if its ability to bear water pressure could be enhanced. Kong et al. constructed thermally stable, freestanding nanowire membranes of cryptomelane with superhydrophobic property by a self-assembly method, which could selectively absorb oils up to 20 times the material’s weight and might be used in the field of oil spill cleanup.20 The absorbed oil was removed by heating the r 2011 American Chemical Society
nanowire membrane to elevated temperatures (390 °C). We have previously demonstrated that a closed cube made of superhydrophobic nickel foam could float on the water surface and this as-prepared nickel foam could be possibly used to create oil containment booms.21 Although superhydrophobic coated films are promising to be used as oil-sorption materials, oil water separating materials, and oil containment booms, there still remains a challenge to integrate these three functions into one device. In this Letter, we will demonstrate a multifunctional device for highly efficient and inexpensive oil spill cleanup by combining electroless metal deposition2225 with self-assembled monolayers2629 (SAMs), which integrates the functions of oil containment booms, oil-sorption materials, oil skimmers, and wateroil separating devices.
2. EXPERIMENTAL SECTION 2.1. Materials and Instruments. HF (40%), AgNO3, toluene, and Solvent Blue 78 (Sinopharm Chemical Reagent Beijing Co., Ltd., Beijing, China) were used as received. Nickel foam (Anping Xinlong Wire Mesh Manufacture Co., Ltd., China) was cleaned by alternate ultrasonication in ethanol and deionized water for three times and then dried in an oven. P-silicon (111) wafer (GRINM Semiconductor Materials Co., Ltd., Beijing, China) was cleaned by immersing into a H2SO4/H2O2 = 7:3 (v/v) solution for a few minutes followed by washing with deionized water and drying with N2 gas stream. nDodecanethiol (SH(CH2)11CH3) was purchased from Aldrich and used as received. Scanning electron microscopy (SEM) measurements were carried out on an EVO MA 25 instrument at 20.0 kV. Photographic images were Received: March 29, 2011 Revised: May 12, 2011 Published: May 17, 2011 7371
dx.doi.org/10.1021/la201168j | Langmuir 2011, 27, 7371–7375
Langmuir
LETTER
taken with a Nikon camera (D5000). The contact angle was characterized on the OCA20 instrument (DataPhysics Instruments Gmbh, Filderstadt). A high-speed disperse mixer (FJ200) was used to disperse the oil and water mixture solution.
2.2. Fabrication of the Superhydrophobic and Superoleophilic Nickel Foam. The superhydrophobic and superoleophilic surface was fabricated by combining electroless metal deposition with SAMs. A nickel foam box (obtained by folding method) and a silicon wafer were attached tightly by a clamp and immersed into a mixture aqueous solution of AgNO3 (20 mM) and HF (5 M) at 70 °C for 15 min. Afterward, the box was taken out of the mixture solution and dried in an oven. The as-prepared box was modified by immersing it in the ethanol solution of n-dodecanethiol (1 mM) overnight. Then the nickel foam box was washed with ethanol and deionized water and dried in an oven. 2.3. Separating Toluene from Water. In order to distinguish toluene from water, we dyed toluene to a blue color with a solvent dye named Solvent Blue 78, which is widely used to dye resin, polyester, and other oil systems. The labeled toluene (50 mL) and 150 mL of water were added into a beaker forming the oil and water mixture solution. After the as-prepared nickel foam box was put on the surface of the solution, dyed toluene infiltrated in rapidly. Then we collected the toluene in the box with a dropper and measured its volume. 2.4. Separating PetroleumWater Emulsion. The petroleum water mixture was obtained through dispersing petroleum and water for 10 min with an emulsifying machine at a rotating speed of 12 000 rpm. Then the device modified with dendritic silver aggregates and SAMs of ndodecanethiol was put into the beaker, and the petroleum diffused through the box walls, infiltrated into the box, and was collected, following a similar process as that for toluenewater separation.
Figure 1. Scheme for the fabrication process of the superhydrophobic and superoleophilic nickel foam.
2.5. Oil Spill Cleanup under the Condition of Simulated Seawater. The simulated seawater was prepared by adding 5.3 g of sodium chloride into 150 mL of water, forming the salt solution with a percentage of 3.5% (w/w), then adding 10 mL of oil which floated on the water. The mixture was dispersed by using a high-speed dispersing mixer at 12 000 rpm for 10 min in a beaker. After the as-prepared nickel foam vessel was put on the surface of the solution, oil infiltrated in rapidly. Then we collected the oil in the vessel by using a straw.
2.6. The Recycled Experiments of WaterOil Separation. The recycled experiments were carried out by the following process. After separating the oilwater mixture, the superhydrophobic box was taken out from the beaker and washed with ethanol carefully and dried in the oven at 60 °C (it could also be dried at room temperature with a longer time than that when dried in an oven). After the above treatment, the nickel foam box was put into the beaker with the oilwater mixture to repeat the separating process.
3. RESULTS AND DISCUSSION The functionally integrated device was fabricated as the following process, shown in Figure 1. First, the nickel foam was folded to a rectangular box without top roof with a designed edge length. In this experiment, the size of the box was about 4.0 cm 4.0 cm 2.0 cm. One thing should that be pointed out is that the nickel foam was very soft and easy to fold into any shape with any size. Second, the nickel foam and a silicon wafer (approximately 0.5 cm2) were attached tightly by a clamp and immersed into a mixture of aqueous solution of AgNO3 (20 mM) and HF (5 M) at 70 °C for 15 min, which would deposit a layer of dendritic silver aggregates by electroless metal deposition.21,23 Afterward, the box was taken out of the mixture solution, washed with deionized water, and dried in an oven. Finally, the as-prepared device was immersed in the ethanol solution of n-dodecanethiol (1 mM) overnight. After washing with ethanol
Figure 2. Optical images of nickel foam before (a) and after (b) immersing in the HF/AgNO3 mixture solution; the insets are their corresponding SEM images. (c) Photograph of a water droplet on the superhydrophobic box, and the inset shows the contact angle of water on the surface of the box. (d) Contact angle measurement with toluene droplets.
and drying in an oven, SAMs of n-dodecanethiol formed on the surface of the box. The surface morphologies of nickel foam before and after electroless metal deposition were characterized by using a digital camera and SEM. The untreated nickel foam was a porous film (Figure 2a) formed by continuous meshes, which contained staggered holes with a diameter of around 500 μm. Figure 2b shows that silver aggregates covered the surface of meshes homogeneously and bridged the holes, after electroless metal deposition process in the HF/AgNO3 mixture solution. From the inset of Figure 2b, we can observe that the silver aggregates 7372
dx.doi.org/10.1021/la201168j |Langmuir 2011, 27, 7371–7375
Langmuir were dendritic with micrometer-scale coral-like structures bearing nanometer-scale branches. The millimeter-, micrometer-, and nanometer-scale hierarchical structures present should provide enough roughness to display superhydrophobicity after surface modification with SAMs of n-dodecanethiol. In order to clarify the superhydrophobicity and superoleophilicity of the as-prepared box, static contact angle measurements were carried out with water droplets and toluene droplets (the droplet volume is 4 μL). As shown in Figure 2c, a water droplet formed a ball-like shape in the modified nickel box and the contact angle of water droplets was about 155° (inset of Figure 2c), which demonstrated the superhydrophobic property of the surface. When measured with toluene droplets, the droplet diffused into the film immediately as the droplets touched the surface as presented in Figure 2d. This phenomenon proved the superoleophilicity, which suggested this treated nickel foam could be used as an oil-sorption material.
Figure 3. Photographs of the oil uptake process. (a) A toluene droplet labeled with Solvent Blue 78 dye was dropped onto the middle of the water surface; (b) a piece of nickel foam with a size of 1.5 cm 2.5 cm was held to approach the toluene droplet; (c) the toluene droplet was taken up as soon as it made contact with the nickel foam; (d) almost no toluene remains after absorption.
LETTER
In an attempt to investigate the uptake capacities of the asprepared nickel foam, the following experiment was carried out as shown in Figure 3. A toluene droplet labeled with Solvent Blue 78 dye was dropped onto the middle of the water surface, and then a piece of nickel foam with a size of 1.5 cm 2.5 cm was held to approach the toluene droplet. The toluene droplet was taken up as soon as it made contact with the nickel foam, without any residual toluene as presented in Figure 3d, which was due to the difference of surface energy between water and toluene. Moreover, taking toluene as an example, the nickel foam could take up 3.5 times its own weight. This uptake experiment suggested that the modified nickel foam was a good choice for oil-sorption materials. However, only absorbing oil from water was not enough for solutions to oil spill accidents; it was still necessary to separate wateroil mixtures toward preparing the oil skimmer and separating device. In order to understand the separating yield of the functional device, as illustrated in Figure 4, we took a watertoluene system as an example to separate toluene from water. A total of 50 mL of toluene labeled with Solvent Blue 78 dye (Figure 4a, a0 ) was added to a beaker containing 150 mL of water. Since the density of toluene is lower than that of water, the added toluene finally floated on the water surface (Figure 4b). When we put the superhydrophobic box with the size of 4.0 cm 4.0 cm 2.0 cm on the water surface, toluene was soon taken up by the superoleophilic box (Figure 4c), infiltrated through the walls, and finally gathered into the box due to gravitational effects (Figure 4d). The collected toluene in the box had been transferred to the original measuring cylinder by using a dropper (Figure 4e), and the collected amount of toluene was 46 mL. We came to the conclusion that the separating yield of the asprepared device was up to 92%, and the residual amount should be absorbed within the box walls until reaching a saturated value. Hence, if the separation proceeded continuously, the separating yield should increase. Besides, the controlled experiments showed that the prepared device could be used even at 70 °C or in the salt water. After we successfully carried out the separation of the toluene water system, we wondered whether our device could be applied to oil spill cleanup, which meant separating petroleum from water, especially the chocolate-like emulsion formed under deep
Figure 4. Separating yield of the toluene and water mixture solution via the as-prepared device. (ae) Process of separating toluene (labeled with Solvent Blue 78 dye) from water; (a0 ) the total adding volume of toluene was 50 mL; (e0 ) the recovered volume of toluene was 46 mL. 7373
dx.doi.org/10.1021/la201168j |Langmuir 2011, 27, 7371–7375
Langmuir
LETTER
Figure 5. Process of separating petroleum from chocolate-like emulsion. (a) Petroleumwater emulsion after dispersion with an emulsifying machine; (b) emulsion after separating for 30 min; (c) mixture after standing overnight; (df) top views of the beaker in the separating process corresponding to (ac).
Figure 6. Separating experiments for different types of oil and the recycled experiments. (a) Separating experiments between water and different kinds of oil or organic solvents; the original volume was 30 mL for each. (b) Recycled experiments for separating oil from water by using the as-prepared device.
ocean and execrable oceanic weather. To study the oil spill cleanup behavior of the as-prepared device, we had imitated the petroleumwater mixture process under natural extreme conditions through dispersing petroleum and water for 10 min with an emulsifying machine at a rotating speed of 12 000 r/min. The resultant mixture is presented in Figure 5a (top view, Figure 5d), which was a homogeneous chocolate-like emulsion with a brown color. When we put the device modified with dendritic silver aggregates and SAMs of n-dodecanethiol into the beaker, the petroleum diffused through the box walls, infiltrated into the box, and was collected, following a similar process as that for toluenewater separation. After handling with the emulsion for around 30 min, we could observe that the color of the emulsion changed from brown to light orange as shown in Figure 5b (top view, Figure 5e), which indicated that most of the petroleum had been recovered from the system. Standing overnight, the water phase finally got clean and transparent as shown in Figure 5c. Although from Figure 5f (the top view of Figure 5c) there still remained a thin layer of petroleum, our device had already shown a good wateroil separating property, which could be used as the multifunctional oil skimmer with wateroil separating function.
Under the condition of simulated seawater, the separating results showed that simulated seawaterpetroleum mixtures could be separated well, which were the same as the water petroleum system. Besides, the as-prepared device was different from the traditional oil skimmer with an open system that could not be well used in storms, meaning that our device could separate oil from water under closed conditions and thus its ability to function in storm conditions should be improved. Moreover, this wateroil separating system could be extended to other organic solvents or industrial oils, which are shown in Figure 6a. We had tried different types of oils such as gasoline, motor oil, kerosene, diesel oil, and olive oil to obtain their separating yields. For each kind of oil, the original amount was 30 mL, and after separation more than 90% of their primary additive amount could be recovered. Another important issue for the oil spill cleanup is that the device should be recycled (Figure 6b). The asprepared device could be used for more than 10 times with persistent high separating yields, which demonstrated its reproducibility. 7374
dx.doi.org/10.1021/la201168j |Langmuir 2011, 27, 7371–7375
Langmuir
4. CONCLUSION In summary, we have developed an efficient multifunctional device for oil spill cleanup. The device has integrated the functions of oil containment booms, oil-sorption materials, oil skimmers, and wateroil separating devices, and it has the advantages of high efficiency, capacity of antiwave, and reproducibility, which is suitable for many types of organic solvents or oils, even for emulsion of petroleum and water. We believe that the as-prepared device is a proof-of-principle idea to be applied in marine spilt oil cleanup and other wateroil separating systems. Moreover, this work will open a new avenue to the application of superhydrophobic or self-cleaning materials. ’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected].
LETTER
(20) Yuan, J. K.; Liu, X. G.; Akbulut, O.; Hu, J. Q.; Suib, S. L.; Kong, J.; Stellacci, F. Nat. Nanotechnol. 2008, 3, 332–336. (21) Gao, Y. F.; Cheng, M. J.; Wang, B. L.; Feng, Z. G.; Shi, F. Adv. Mater. 2010, 22, 5125–5128. (22) Xia, X. H.; Ashruf, C. M. A.; French, P. J.; Kelly, J. J. Chem. Mater. 2000, 12, 1671–1678. (23) Shi, F.; Song, Y. Y.; Niu, H.; Xia, X. H.; Wang, Z. Q.; Zhang, X. Chem. Mater. 2006, 18, 1365–1368. (24) Pesika, N. S.; Radisic, A.; Stebe, K. J.; Searson, P. C. Nano Lett. 2006, 6, 1023–1026. (25) Peng, K. Q.; Lee, S. T. Adv. Mater. 2010, 23, 198–215. (26) Kobayashi, S.; Nishikawa, T.; Takenobu, T.; Mori, S.; Shimoda, T.; Mitani, T.; Shimotani, H.; Yoshimoto, N.; Ogawa, S.; Iwasa, Y. Nat. Mater. 2004, 3, 317–322. (27) Shi, F.; Wang, Z. Q.; Zhang, X. Adv. Mater. 2005, 17, 1005–1009. (28) Yu, X.; Wang, Z. Q.; Jiang, Y. G.; Shi, F.; Zhang, X. Adv. Mater. 2005, 17, 1289–1293. (29) Shi, F.; Niu, J.; Liu, J. L.; Liu, F.; Wang, Z. Q.; Feng, X. Q.; Zhang, X. Adv. Mater. 2007, 19, 2257–2261.
’ ACKNOWLEDGMENT This work was supported by National Natural Science Foundation of China (Grant No. 20821004), Beijing Nova Program of China (Grant No. 2009B011), the Key Project of Chinese Ministry of Education (Grant No. 109012), Open Project of State Key Laboratory of Supramolecular Structure and Materials (Grant No. SKLSSM201101). The first two authors, M. J. Cheng and Y. F. Gao, equally contributed to this work. ’ REFERENCES (1) Li, H. L.; Boufadel, M. C. Nat. Geosci. 2010, 3, 96–99. (2) Editorial. Nature 2010, 465, 9. (3) George, C.; Francis, F.; Jay, M. Combust. Flame 1992, 90, 295–304. (4) Howarter, J. A.; Youngblood, J. P. Adv. Mater. 2007, 19, 3838–3843. (5) Ono, T.; Sugimoto, T.; Shinkai, S.; Sada, K. Nat. Mater. 2007, 6, 429–433. (6) Konishi, M.; Kishimoto, M.; Tamesui, N.; Omasa, T.; Shioya, S.; Ohtake, H. Biochem. Eng. J. 2005, 24, 49–54. (7) Fingas, M. F.; Fieldhouse, B.; Bier, I.; Conrod, D.; Tennyson, E. In The Use of Chemicals in Oil Spill Response, ASTM STP 1252; Lane, P., Ed.; American Society for Testing and Materials: Philadelphia, PA, 1994. (8) Hoff, R. Z. Mar. Pollut. Bull. 1993, 26, 476–481. (9) Atlas, R. M. J. Chem. Technol. Biotechnol. 2007, 52, 149–156. (10) Fingas, M. Chem. Ind. 1995, 24, 1005–1008. (11) Adebajo, M. O.; Frost, R. L.; Kloprogge, J. T.; Carmody, O.; Kokot, S. J. Porous Mater. 2003, 10, 159–170. (12) Howarter, J. A.; Youngblood, J. P. J. Colloid Interface Sci. 2009, 329, 127–132. (13) Ji, F.; Li, C. L.; Dong, X. Q.; Li, Y.; Wang, D. D. J. Hazard. Mater. 2009, 164, 1346–1351. (14) Zhao, N.; Shi, F.; Wang, Z. Q.; Zhang, X. Langmuir 2005, 21, 4713–4716. (15) Jiang, Y. G.; Wang, Z. Q.; Yu, X.; Shi, F.; Xu, H. P.; Zhang, X. Langmuir 2005, 21, 1986–1990. (16) Zhang, L.; Zheng, M.; Liu, X. K.; Sun, J. Q. Langmuir 2011, 27, 1346–1352. (17) Feng, L.; Zhang, Z. Y.; Mai, Z. H.; Ma, Y. M.; Liu, B. Q.; Jiang, L.; Zhu, D. B. Angew. Chem., Int. Ed. 2004, 43, 2012–2014. (18) Qin, F. T.; Yu, Z. J.; Fang, X. H.; Liu, X. H.; Sun, X. Y. Front. Chem. Eng. China 2009, 3, 112–118. (19) Qin, F. T.; Yu, Z. J.; Fang, X. H.; Liu, X. H.; Sun, X. Y. A novel composite coating mesh film for oil/water separation, Proceedings of the 12th Asian Pacific Confederation of Chemical Engineering Congress, Dalian, China, 2008. 7375
dx.doi.org/10.1021/la201168j |Langmuir 2011, 27, 7371–7375
