Chemical Engineering Journal 213 (2012) 1–7
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Superhydrophobic kapok ﬁber oil-absorbent: Preparation and high oil absorbency Jintao Wang a,b, Yian Zheng a,b, Aiqin Wang a,⇑ a b
Center of Eco-Material and Green Chemistry, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China Graduate University of the Chinese Academy of Sciences, Beijing 100049, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
" Superhydrophobic kapok ﬁber was
prepared via sol–gel method and used for oil sorption. " The modiﬁed kapok ﬁber is covered by silica nanoparticles and surface become rough. " The modiﬁed kapok ﬁber have high oil sorption capacity and oil–water separation selectivity. " The modiﬁed kapok ﬁber have the capability of removing oil in oil/ water mixture.
a r t i c l e
i n f o
Article history: Received 9 August 2012 Received in revised form 20 September 2012 Accepted 21 September 2012 Available online 11 October 2012 Keywords: Superhydrophobic Silica nanoparticles Kapok ﬁber Oil sorption capacity Reusability
a b s t r a c t Superhydrophobic and oleophilic oil sorbent was successfully prepared by the incorporation of silica nanoparticles onto kapok ﬁber via sol–gel method and subsequent hydrophobic modiﬁcation using hydrolyzed dodecyltrimethoxysilane (DTMS). The formation of silica nanoparticles was conﬁrmed by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and investigation of the wetting behavior of water and oil on ﬁber surface. The coated ﬁber exhibited excellent oil/water selectivity in the cleanup of oil over water. The as-prepared ﬁber can quickly absorb diesel and soybean oil up to above 46.9 and 58.8 g/g, with the improvement in oil sorption capacity to be 46.6% and 20.2% compared with raw ﬁber, respectively. Owing to high oil sorption capacity, excellent hydrophobic property and reusability, and good environmental friendliness, the as-prepared oil sorbent can be considered as promising alternative for organic synthetic ﬁber to clean up the spilled oil. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction In recent years, water pollution caused by the oil spillage has become increasingly serious with the acceleration of urbanization and industrialization process . Commonly used methods of solving these oil-leakage problems include mechanical extraction, combustion and chemical degradation. Owing to the economy and efﬁciency for oil spill cleanup, mechanical extraction by sorption materials is regarded as one of the most desirable choices for the recovery of oil. Although many sorption materials such as inor⇑ Corresponding author. Tel.: +86 931 4968118; fax: +86 931 8277088. E-mail address: [email protected]
(A. Wang). 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.09.116
ganic mineral materials , synthetic materials,  and natural materials  have been widely studied for the removal of spilled oil, these materials still have some limitations such as low oil sorption capacity, inadequate buoyancy, high cost, and poor reusability. Especially, most of materials studied have poor hydrophobicity, resulting in low oil–water separation selectivity and efﬁciency [5,6]. Hence, the exploitation of new oil sorption materials with high sorption capacity, low cost, low water pickup, excellent environmental beneﬁt and reusability is rather important for oil pollution treatment. Superhydrophobic surface with water contact angles higher than 150° has attracted extensive interest [7,8]. Previous studies have revealed that superhydrophobicity depends on not only the
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low surface energy of the substrate but also the hierarchical microand nanostructures of the surface. So far, various methods such as phase separation , laser etching , sol–gel method , and chemical vapor deposition  have been used to prepare superhydrophobic surface. Therein, nano-structured surface generated by sol–gel method followed by further hydrophobic modiﬁcation, is taken as a simple and effective technique for fabricating superhydrophobic coatings onto the surface of materials , by which the resulting materials will exhibit excellent afﬁnity to oil and water repellency in water–oil surroundings, and accordingly, these superhydrophobic materials can be applied in the ﬁeld of oil spill clean-up. A variety of materials, such as carbon nanotube sponges , nanowire membranes , superhydrophobic and superoleophilic sponges , superhydrophobic, and oleophilic calcium carbonate powder  have been developed for separating oil from water. Even so, the drawbacks of these materials with complicated preparation process and high cost still limit their application scale in practice. Kapok is a kind of natural plant ﬁber that has low density, good buoyancy, huge hollowness and excellent hydrophobicity. These unique characteristics endow kapok ﬁber with higher oil sorption capability compared with common natural ﬁbers and commercial oil absorbent [18,19]. However, the smooth ﬁber surface due to the coverage of a small amount of waxy coating makes it difﬁcult to effectively retain oil to ﬁber assembly. If the oil sorption capacity and hydrophobicity of kapok ﬁber can be further enhanced by surface modiﬁcation, it would be more valuable for the oil spill cleanup. The silica coating shows excellent adhesion on cellulosic materials by the condensation between the hydroxyl groups of the hydrolyzed silanes and those existing on the surface of cellulose . Hence, it is feasible to turn the surface of kapok ﬁber from hydrophobicity into superhydrophobicity. To the best of our knowledge, there is no report on the use of superhydrophobic kapok ﬁber for oil sorption. Herein, the oil sorbent based on superhydrophobic kapok ﬁber was prepared through a facile sol–gel technique. The sorption capacity and hydrophobicity of modiﬁed ﬁber were evaluated. The results of this study provide ideas for the application of other superhydrophobic modiﬁed cellulosic materials in oil spill cleanup. 2. Experimental 2.1. Materials Kapok was purchased from Shanghai Pan-Da Co. Ltd., China. NaClO2 (chemically pure) was provided by Beijin Hua-Wei Chemical Reagent Co., China. Acetic acid (analytical grade), sodium dodecyl benzene sulfonate (SDBS, chemically pure), and CHCl3 (analytical grade) were received from Shanghai Chemical Reagent Factory, China. Tetraethylorthosilicate (TEOS, chemically pure) were supplied by Tianjin Chemical Reagent Factory, China. Dodecyltrimethoxysilane (DTMS, chemically pure) was provided by Sinopharm Chemical Reagent Co., Ltd., China. NH3H2O (analytical grade) was obtained Baiyin Chemical Reagent Factory, China. Ethanol, toluene, n-hexane (analytical grade) were supplied by Tianjin Li-An Chemical Reagent Co. Ltd., China. Gasoline, diesel and soybean oil came from the local market, Lanzhou, China. 2.2. Preparation process of superhydrophobic kapok ﬁber Raw ﬁber was treated with NaClO2 according to the reported process . Raw ﬁber was placed into 400 mL of NaClO2 solution (0.5 wt.%), while a certain amount of acetic acid was added to adjust pH 4.5. Afterwards, the treatment was kept at 80 °C for 1 h at 700 rpm. The treated ﬁber was washed several times with distilled
water until the pH level of ﬁltrate reached neutrality, then dried in an oven at 70 °C to constant weight and used in all the later modiﬁcation. TEOS (4 wt.%) and SDBS (1.2 mmol/L) were added to a certain amount of distilled water, stirred at room temperature for 1 h, then NaClO2-treated kapok ﬁber was added into the mixture and stirred for 20 min followed by a gradual addition of NH3H2O (1.8 wt.%). The reaction was maintained at room temperature for 4 h. The resulting ﬁber was washed several times with methanol, and dried in vacuum oven at 60 °C to constant weight. Then, the coated ﬁber was added into ethanol solution of DTMS (2 wt.%) and hydrolyzed for 1 h. Finally, the obtained sample was ﬁltered, dried at room temperature and cured at 120 °C for 1 h. 2.3. Measurements of oil sorption capacity In oil medium without water: The dried sample (0.1 g) was put into a stainless-steel mesh weighed beforehand and immersed in oil at room temperature. The sample and the mesh were taken out from the oil together after a certain time, drained for 10 s, and wiped with ﬁlter paper to remove excess oil from the bottom of the mesh. The oil absorbency of the sample was determined by weighing the samples before and after the absorption, and calculated by the following formula:
Q ¼ ðM t M i M w Þ=M i where Q is the oil sorption capacity of the sorbents calculated as grams of oil per gram of sample, Mt the weight of the wet sorbents after draining (g), Mi the initial weight of sorbents (g) and Mw is the weight of water absorbed in the sorbents (g). In pure oil medium without any water, Mw is equal to zero. In oil/water mixture: The diesel or soybean oil was mixed with 60 mL of artiﬁcial seawater (3.5 wt.% NaCl) in a 100 mL conical ﬂask for 10 min at 150 rpm over an orbital shaker. The agitation can make the oil ﬂoat to the surface of the artiﬁcial seawater and form the oil layer. Then, 0.1 g sorbent was added to the oil/water mixture. The concentrations of diesel and soybean oil used varied from 0.01 to 0.14 g/mL of water. The sorbent was left in the oil/ water mixture and shaken for 60 min at 30 °C. After that, the sample was removed from the ﬂask using mesh screen, drained for 1 min, and weighed. Water content was determined by the method of extraction separation using n-hexane as the solvent. 2.4. Reusability Kapok ﬁber of absorbing oil from the water surface was removed with the aid of a mesh screen, which was then placed on a sand core funnel and drained under vacuum for 10 min before weighing. Oil will be recovered without severe disruption of the appearance of the ﬁber. The sorption/desorption cycle was repeated for eight cycles to evaluate the recyclability of the ﬁber. 2.5. Characterizations Fourier transform infrared (FTIR) spectra were recorded on a Nicolet NEXUS FTIR spectrometer using KBr pellets. The micrographs of samples were examined using SEM (JSM-5600LV, JEOL). Before SEM observation, all samples were ﬁxed on aluminum stubs and coated with gold. The surface wettability of water and oil on the surface of kapok ﬁber was observed with a digital SLR camera after the water or oil dyed with coloring matter was dripped on the surface of ﬁber from a syringe (1 mL). Contact angle measurements were carried out using a Krüss DSA 100 (Krüss Company, Ltd., Germany) apparatus at ambient temperature, and the volumes of probing liquids in the measurements were approximately 5 lL. Prior to observation, kapok ﬁber assembly was ﬂattened with tablet machine.
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3. Results and discussion 3.1. Fabrication of superhydrophobic and oleophilic surface The superhydrophobic modiﬁcation process for raw kapok ﬁber is shown in Fig. 1. The hydroxyl groups on the cellulosic materials play a vital role for the formation of superhydrophobic surface [20,21]. The surface of raw kapok ﬁber is covered by natural plant wax, which makes silica nanoparticles more difﬁcult to attach to the surface of the ﬁber. Therefore, it is necessary to remove the surface plant wax of kapok ﬁber. In this study, kapok ﬁber was treated with NaClO2, and the hollow structure of the ﬁber was still intact after the treatment . Moreover, the treatment will result in the generation of interspaces and increase the hydroxyl concentration of the ﬁber surface, making the hydrolyzed silanol easily penetrate into the interspaces of the ﬁber to form silica nanoparticles . Thereinto, partial silica nanoparticles present on the surface of the ﬁber by means of the hydrogen bond interaction between the Si–OH group of the hydrolyzed silane and the hydroxyl groups of the ﬁber, while some silica nanoparticles can ﬁrmly adhere to the ﬁber surface in the form of physical conglutination. In order to reveal the hydrophobic and lipophilic effect of the modiﬁed ﬁber surface, the surface wettability of water and oil on the surface of raw, treated, and modiﬁed ﬁber was observed, as shown in Fig. 2. The blue-colored water drop shows a large contact angle on raw kapok ﬁber (h = 116°), while the water drop sinks rapidly into the ﬁber treated with NaClO2 to form a large spreading radius on the surface. The kapok ﬁber coated by the silica hydrosol with subsequent hydrolyzation in DTMS has water contact angle of 151°, which is much higher than raw ﬁber, indicating that the treatment effectively improves the hydrophobic property of raw ﬁber. When the red-colored oil drop is applied on the surface of three kinds of ﬁber, the drop sinks completely into the ﬁber in a very short time, suggesting that the oil drop is a wetting liquid for all three ﬁbers. Owning to its light density and superhydrophobic nature, the modiﬁed ﬁber may ﬂoat on the surface of water more steadily before and after collecting all of oils from water, a predominant characteristic for practical use of oil spills cleanup. 3.2. FTIR spectra The FTIR spectra of raw, treated, and superhydrophobic kapok ﬁbers are displayed in Fig. 3. Comparing the spectra of raw, treated and superhydrophobic ﬁbers, the following ﬁndings will be obtained. In Fig. 3c, the intensity of the peak at 3411 cm1 (stretching
Fig. 1. Schematic representation of transition from raw kapok ﬁber to superhydrophobic kapok ﬁber.
vibration peak of surface –OH) decreases obviously as compared with that of treated ﬁber; a absorption peak (symmetric stretching vibration of Si–O–Si) is observed at 467 cm1 ; strong absorption bands corresponding to asymmetric and symmetric stretching vibration of CH2 and CH3 in DTMS appear at 2923 and 2856 cm1 . In addition, the characteristic absorption peaks around 1100–1000 cm1 attributed to Si–O–Si of silica nano-particles and DTMS seem to be overlapped by the C–O stretching vibration of cellulose in ﬁber. These changes indicate that the total numbers of –OH was reduced and hydrophobic silica nano-particles were formed on the surface of kapok ﬁber. 3.3. Morphology analyses The surface appearances of raw, treated and superhydrophobic kapok ﬁbers are shown in Fig. 4. It is obvious that raw kapok ﬁber shows a smooth surface owning to the coverage of inherent plant wax (Fig. 4a), while the treatment makes the ﬁber surface become rough with subtle textures and wrinkles, implying that waxy coating has been removed from the ﬁber surface and the ﬁber changes from hydrophobic to hydrophilic due to the exposition of more cellulose hydroxyl groups . Different from raw and treated ﬁber, the modiﬁed ﬁber is covered by dense silica nanoparticles without any interstices, which renders the surface rougher. In addition, even though the external surface of the ﬁber is covered by silica nanoparticles, the internal hollow lumen is not blocked by the silica nanoparticles, ensuring that the intrinsic oil sorption capacity is not reduced for raw kapok ﬁber as an oil sorbent. 3.4. Oil sorption capacity of raw and superhydrophobic ﬁber for various oils The superhydrophobic modiﬁcation of kapok ﬁber not only fabricates a rough structure on the surface but also decreases the surface energy, which in turn affects its oil afﬁnity. To study the maximum oil sorption capacity of superhydrophobic ﬁber for various common oils, the sorption experiment was carried out in pure oil without any water. For comparison, the oil sorption capability of raw kapok ﬁber was also investigated. As shown in Fig. 5, the oil sorption capacity of raw kapok ﬁber for n-hexane, toluene, chloroform, gasoline, diesel, and soybean oil is 22.8, 30.4, 41.9, 34.1, 38.1, and 49.1 g/g, respectively, while the oil sorption capacity of modiﬁed ﬁber for these oils can reach about 41.8, 56, 85.5, 50.5, 54.2, and 59.8 g/g, respectively. This means that superhydrophobic modiﬁcation is very useful for preparing a kind of oil sorbent with excellent oil sorption performance. In addition, it can be observed that the modiﬁed ﬁber exhibits high oil sorption capacity for chloroform and vegetable oil. The high oil sorption capacity for chloroform is due to its high relative density , for vegetable oil, this is mainly attributed to its high viscosity [18,23]. The oil with high viscosity is easier to adhere to the ﬁber surface and be kept in the ﬁber assembly. Generally, for kapok ﬁber, the parameters such as the amount of surface wax, hollow lumen, surface roughness, twist, crimp and ﬁneness etc. play an important role in the retention of oil [26,27]. The oil that is retained in the ﬁber assembly can be divided into two kinds of types: the oil stored in an internal lumen and the oil retained in the voids among ﬁbers [18,22,28]. After the modiﬁcation of kapok ﬁber, the oil absorbed in the voids of the ﬁbers is difﬁcult to escape from the surface of ﬁber during the dripping of the oil-loaded ﬁber assembly due to more stable capillary bridging between ﬁber bundles. According to Wenzel model and the Cassie– Baxter model [29,30], the fabrication of a proper microsturcture can make a smooth oleophilic surface to be more oleophilic or even superoleophilic due to the capillary effect. Consequently, the oil afﬁnity of raw kapok ﬁber was markedly improved by roughening the surface and lowering the surface energy. By contrast, more oil
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Fig. 2. Pictures of water droplet (dyed with methylene blue) on (a) raw, (b) treated, and (c) superhydrophobic kapok ﬁber surface; oil droplet (dyed with oil red O) on (a1) raw, (b1) treated, and (c1) superhydrophobic kapok ﬁber surface. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)
3.5. Effect of amount of oil on water
Fig. 3. FTIR spectra of (a) raw, (b) treated, and (c) superhydrophobic kapok ﬁber.
can escape from raw kapok ﬁber assembly as a result of the smooth surface. The ﬁndings in this study imply that the surface roughness and surface energy of kapok ﬁber are two important factors that inﬂuence the oil sorption capability. Besides, the oil sorption capacities of modiﬁed ﬁber in this study and other recently reported oilabsorbing ﬁber also are compared and shown in Table 1, and the results are encouraging. Although the oil sorption capacity of polyvinyl chloride/polystyrene ﬁber is close to that of raw kapok ﬁber , this type of synthetic organic material as oil sorbent is difﬁcult to be used on a large scale due to its high cost and nonbiodegradability. Compared with this type of synthetic sorbents, superhydrophobic kapok ﬁber is much easier to prepare for practical use, demonstrating its great potentials in the removal of toxic organic solvents or oil spills from water. The application of oil sorbent based on natural ﬁber may offer an opportunity to alleviate the current environmental crisis especially for the global scale of serious water contamination arising from oil spills and industrial organic contaminants.
It is very important to know exact sorption capacity of oil sorbent on water surface for effective use of one kind of sorbent in practical oil spill cleanup. The oil and water sorption capacities of raw and superhydrophobic ﬁber in the oil on the water containing various amount of oil (diesel and soybean oil) are shown in Fig. 6. The investigation of amounts of water pickup will reﬂect the hydrophobic characteristic of sorbent and its oil afﬁnity. It is observed that the oil sorption capacities of both raw and modiﬁed ﬁbers increase with increasing the initial concentration of oil until they reach a plateau. When the concentrations of diesel and soybean oil used are below the values of 3.6 and 4.8 g/mL respectively, both raw ﬁber and superhydrophobic ﬁbers are capable of removing all of ﬂoating oils on water, giving an indication that similar oil sorption capacities for raw and superhydrophobic ﬁbers can be obtained within this range of oil concentration. Afterwards, superhydrophobic ﬁber always exhibits higher sorption capacities compared with raw ﬁber. As such, a certain amount of oil ﬂoating on water can be completely picked up in a shorter time by the superhydrophobic ﬁber, which is useful for preventing the dispersion of spilled oil on water. Such high oil sorption capacity should be mainly attributed to the surface roughness within nanometer size magnitude. Therefore, as-prepared ﬁber can better hold the oil to the ﬁber assembly. In oil/water mixture systems, the maximum oil sorption capacities of raw ﬁber are about 32 and 48.9 g/g for diesel and soybean oil, while the oil capacities of modiﬁed ﬁber are 46.9 and 58.8 g/g for the two oils, respectively. This indicates that the oil sorption capacity of raw ﬁber can be improved signiﬁcantly by the surface modiﬁcation. In addition, the water pickup of superhydrophobic ﬁber is obviously lower than that of raw ﬁber, showing its good oil/water selectivity. Excellent selectivity for oil on water surface and high oil sorption capacity demonstrate that modiﬁed ﬁber is full of application potential in the large-scale removal of oils from water. 3.6. Removal of oil ﬁlm by raw and superhydrophobic ﬁber In order to exhibit the oil sorption characteristics of modiﬁed ﬁber on artiﬁcial sea water, optical images for the cleanup of soy-
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Fig. 4. SEM micrographs of (a, a1) raw, (b, b1) treated, and (c, c1) superhydrophobic kapok ﬁber.
Fig. 5. Maximum sorption capacities of raw and superhydrophobic kapok ﬁber for different oils.
Table 1 Comparison of oil sorption capacities from this study and other oil-absorbing ﬁbers. Absorbing ﬁber
Type of oil
Sorption capacity (g/g)
Raw cotton ﬁber
Vegetable oil Diesel
Polyvinyl chloride/ polystyrene ﬁber Commercial polypropylene Methacrylate–lauryl methacrylate ﬁber Wool ﬁber-based nonwoven
Raw kapok ﬁber Superhydrophobic kapok ﬁber
Diesel Toluene Chloroform Diesel Vegetable oil Diesel Soybean oil Diesel Soybean oil
8 15 34.7 10.6 14.5 38.1 49.1 54.2 59.8
bean oil from the water surface by raw and as-prepared ﬁber are displayed in Fig. 7. It can be seen that the superhydrophobic ﬁber is easier to separate oil from the water surface compared with raw
ﬁber. When the superhydrophobic ﬁber is immersed in oil/water mixture, the oil is quickly absorbed by the ﬁber within several seconds. After that, the oil can removed easily from the oil/water mixture by taking away the oil-loaded modiﬁed ﬁber from the water surface. Interestingly, almost no dripping of the oil appears in the process of moving the ﬁber from the water surface, and there is also no obvious residual oil can be observed in the container. On the contrary, for raw ﬁber, 6 g of oil is difﬁcult to be completely cleanup from the oil/water mixture, and the dripping of oil is very serious when picking up the oil-loaded ﬁber. The sorption of oil by ﬁber is mainly regulated by surface sorption and capillary action, thus the factors such as surface wax, ﬁneness, pore structure, and surface roughness will affect the oil sorption capacity of ﬁber assembly. For this study, the surface roughness plays an important role in the retention of oil, and the improvement of surface roughness after coating with silica nanoparticle hinders the escape of absorbed oil from the ﬁber assembly, while the absorbed oil is easier to escape from the assembly of raw ﬁber due to smooth lumen surface.
3.7. Reusability To recover absorbed oil and reuse the superhydrophobic ﬁber, oil-loaded ﬁber assembly is squeezed with the aid of vacuum pump, and the ﬁber of removing oil is used for the next sorption of oil on the water surface. The reusability change in oil sorption capacity of superhydrophobic kapok ﬁber for diesel and soybean oil after eight sorption and desorption cycles is shown in Fig. 8. It can be seen that the oil sorption capacities decrease slightly throughout the whole cycles and the decrease of oil sorption capacity does not exceed 20% after 8 cycles of sorption/desorption. The decreases of oil-absorption capacity are mainly attributed to the residual oils in the voids of ﬁber assembly. Importantly, about more than 90% volume of absorbed oil can be removed by the vacuum ﬁltration. Once the vacuum is generated in the oil recovery system, the absorbed oil is immediately released and delivered into ﬁlter container from the funnel. The recovering of oil from ﬁbers via strong mechanical pressure can cause the severe loss of intrinsic sorption capability of porous sorbent due to the occurrence of
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Fig. 6. Removal of oil as a function of oil concentration by raw and superhydrophobic kapok ﬁber.
Fig. 7. Pictures for the cleanup of soybean oil (colored with oil red O) from water. (a) Soybean oil was ﬂoating on water; (b) the oil was absorbed by superhydrophobic ﬁber; (c) the oil-loaded superhydrophobic ﬁber was picked up; (d) the oil was absorbed by raw ﬁber; and (e) the oil-loaded raw ﬁber was picked up. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)
by the hydrophobization of DTMS. After the surface modiﬁcation of kapok ﬁber, the existence of uniform nanoscale roughness protuberances with low surface energy imparted the ﬁber better oil/water selectivity and higher oil sorption capability. The absorbed oil can be easily recovered with the aid of simple mechanical squeezing, with no severe loss of sorption properties after reusing several times. The results also suggest that superhydrophobic modiﬁcation for cellulosic materials is an effective method to improve the oil sorption capability. Owning to the advantages of high oil sorption capacity, low density, easily scalable fabrication, and excellent hydrophobic property and reusability, the as-prepared ﬁber is promising as a candidate for the replacement of organic oil sorbent and applied in the large-scale removal of spilled oil on water surface. Acknowledgments
Fig. 8. Reusability of raw and superhydrophobic kapok ﬁber.
irreversible deformation and the contraction [18,22]. As a result, the sorbents can only be utilized for limited times. In this study, oil is recovered by a large margin from oil-loaded ﬁbers by milder procedure without severe disruption of the ﬁber hollow lumen. This also implies that removing oil from porous materials with vacuum pump may be an effective method in practical oil recovery. The excellent reusability makes superhydrophobic ﬁber be more attractive than traditional oil sorbents like polypropylene and active carbons in the cleanup of spilled oil. 4. Conclusions A superhydrophobic surface was fabricated on kapok ﬁber through the sol–gel method using TEOS as the precursor followed
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