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Hydrogel-coated basalt fibre with superhydrophilic and underwater superoleophobic performance for oil-water separation
Composites Communications 14 (2019) 1–6
Contents lists available at ScienceDirect
Composites Communications journal homepage: www.elsevier.com/locate/coco
Short Communication
Hydrogel-coated basalt fibre with superhydrophilic and underwater superoleophobic performance for oil-water separation
T
Deng-Liang Caia,b, Peng-Cheng Maa,b,∗ a Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi, 830011, China b Center of Material and Opto-electronic Research, University of Chinese Academy of Sciences, Beijing, 100049, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Basalt fibre Hydrogel Superhydrophilicity Oil-water separation
Materials with controlled surface properties show great potential for various applications. In this paper, we reported a method to prepare a superhydrophilic fabric consisting of basalt fibre (BF) and konjac glucomannan (KGM). Different techniques were employed to study the morphology and surface information of the developed materials. The results showed that the KGM was deacetylated to form a hydrogel when processed in an alkali condition, and the excellent film-forming performance of the hydrogel led to the formation of a coating layer on BF fabric. The coating endowed the developed fabric with enhanced mechanical performance and superhydrophilicity in air condition. Interestingly, the material, subjected to a water condition, exhibited a stable superoleophobicity as confirmed by the extremely low adhesion to oil and remarkable resistance to the corrosive liquids, thus holding the promise to be a suitable candidate for separating various oil-water mixtures.
1. Introduction
is that when contacting with water, the liquid spreads quickly to form a flat film on the surface of material rather than in the state of droplet, and the oily contaminants on the material can be easily cleaned by the super-spreading water film. Many techniques have been adopted to prepare superhydrophilic materials through a combination of surface chemistry and construction of rough structure, such as vapor deposition [7], etching [8], hydrothermal treatment [9], and so on. Among these methods, surface coating has more advantages over the others as the process does not take a prolonged chemical reaction time. In addition, the coating method can be applied to polymeric or assembled structures by static or dynamic absorption without changing the structures of the substrates. As a matured technique, this process does not require complicated or expensive equipment, thus providing a possibility for the scale-up production of materials. As for the substrate materials, metallic meshes (stainless steel, copper, nickel) are mainly used as a suitable substrate for oil-water separation, the biggest problem of these substrates is the high cost and marginal resistance to the chemical corrosion [10]. Sponge is a cheap and commercially available material with huge space for oil absorption and storage, which is used to remove oils from the water after a purposeful construction with low surface energy coating [11], but it brings complex post-treatment as it has to be squeezed to get oils from the pores in the material for cyclic operation. Carbon-based aerogels have
With ever-increasing production and usage of petroleum products, oil spillage and chemical leakage occur frequently worldwide every year. Pollution arising from these accidents has led to severe environmental problems. For example, the Deepwater Horizon oil spill occurred in 2010 led to the severe damage to the coral community in the Gulf of Mexico [1]. Besides the leakages arising from industrial oily compounds and chemicals, the discharge of sewage containing waste cooking oil also causes negative impact on surrounding ecosystems [2]. Therefore, materials that can effectively separate oils and chemicals from water are in urgently needed. Inspired by some natural species (lotus leaf, water fly, etc), superhydrophobic and superoleophilic sponges/aerogels/meshes modified by nanoparticles and polymers [3–5] were designed to achieve such objective. These composites are also called “oil-removing” materials, which realize the absorption or filtration of various oils from water selectively and effectively. However, the problems associated with the high cost of nanoparticles, pore plugging and contamination by viscous oily compounds, have limited the practical applications of these materials. As an alternative, great attention was focused on developing materials with superhydrophilic performance [6], namely “water removing” performance. One of the unique advantages of such materials
∗ Corresponding author. Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi, 830011, China. E-mail address: [email protected] (P.-C. Ma).
https://doi.org/10.1016/j.coco.2019.05.002 Received 16 February 2019; Received in revised form 8 May 2019; Accepted 9 May 2019 Available online 11 May 2019 2452-2139/ © 2019 Elsevier Ltd. All rights reserved.
Composites Communications 14 (2019) 1–6
D.-L. Cai and P.-C. Ma
Where C0 (vol%) and Cp (vol%) are the oil concentration of the original oil/water mixture and the collected water, respectively. The water flux J was calculated according to Equation (2):
intrigued huge attention due to the low density, high porosity and large surface area [12], the materials usually contained carbon nanotubes or graphene that are not cheap. Therefore, a suitable substrate with an excellent cost-performance property is highly desirable. Herein, we reported a low-cost and facile method to fabricate superhydrophilic basalt fibre (BF) with a surface modifier originated from konjac glucomannan (KGM), aiming at developing a green and inexhaustible composite material with remarkable sustainability. Different techniques were employed to characterize the morphology, surface states and wetting behavior of the material. The applicability of the developed fabric for separating oil-water mixture was studied, and the mechanism behind the superoleophobicity of material was illustrated.
J=V/AT
(2)
Here, V is the volume of filtering water (L), A is the effective area of fabric (m2) and T is the filtration time (h). For each test, three batch experiments were performed and an average value on water flux with standard deviation was reported. For the study on the stability of fabric in harsh environment, the coated BF was immersed into various liquids, including dimethyl formamide (DMF), saturated NaCl (26.5%), H2SO4 (20.0%) and NaOH (5 M), for 24 h. Then the sample was taken out and washed by water before testing its surface property and oil-water separation performance.
2. Experimental 2.1. Materials
2.4. Characterization
KGM powder was obtained from a local market. BF fabric was purchased from Guizhou Shixin Basalt Technology Co., China. Commercially available oil products (gasoline, sunflower oil), crude oil (Karamay Oilfield, China), and organic liquids (1, 2-dichloroethane, nhexane) were used as probing liquids for oil-absorption and oil-water separation studies. Sodium hydroxide (NaOH) was used to adjust the alkality of solution. All chemicals were in analytical grade and used as received without further purification. Ultrapure water (Millipore, resistivity > 18.5MΩ·cm) was used in experiment.
The deacetylation process of KGM was studied by Fourier-transform infrared spectrometer (FT-IR, FTS-165, Biorad, US). The morphology of fabric was characterized by a scanning electronic microscope (SEM, Supra 55VP, Zeiss, Germany). The chemical state of element on fibre surface was evaluated by X-ray photoelectron spectroscopy (XPS, EscaLab 250Xi, Thermo Scientific, US). The wetting behavior of sample against water and oil was analyzed by measuring the contact angle on a goniometer (XG-CAMA, Shanghai Xuanyichuangxi, China). Interactions (Adhesion force, oil-fouling) between the BF and liquid were studied on a high-sensitivity microelectromechanical balance system (DCAT 25, Data-Physics, Germany). The content of oil after separation was determined using an oil content analyzer (JLBG-126, Jilin Jiguang, China). The tensile strength of single BF was measured on a fibre tensile tester (XQ-1A, Shanghai Xinxian, China). The test was performed according to the ASTM C1557-14 standard. The gauge length of sample and the loading speed were fixed at 25.0 mm and 2.0 mm/min, respectively. At least 30 specimens of each fibre were tested and a mean value with a standard deviation was reported. The thermal stability of the BF was evaluated on a thermogravimetric analyzer (TGA, STA 449F3, Netzsch, Germany) with a hating rate of 10 °C/min from 25 to 600 °C in air condition.
2.2. Fabrication of DA-KGM coated BF For the preparation of coated BF fabric, KGM powder (0.50 g) was dissolved in water (100 mL) and stirred for 5 h to get a homogeneous solution at room temperature. Then the pH of solution was adjusted to 9.5 by NaOH (0.10 M) and magnetically stirred for another 1 h, yielding the deacetylated KGM (DA-KGM) solution. A piece of BF (20.0 × 20.0 cm) pre-cleaned by acetone and ethanol was put into the above solution for 10 min to ensure a complete wetting, and then the fabric was drawn from the mixture and put onto a Teflon plate. The excessive solution was removed manually using a glass rod. The final product was obtained by putting the fabric into an oven at 90 °C for 3 h.
3. Results and discussion
2.3. Experimental setups for oil/water separation
3.1. Morphology and physical properties of the sample
The hydrogel-coated BF was cut into 5.0 × 5.0 cm sample, and then fixed between two glass tubes. The fabric was wetted by water at first, and during the separation process, the mixture of hexane and water (20%, v/v) were poured into the upper glass tube. The whole process was driven by the gravity without other force. The separation efficiency was calculated by oil rejection coefficient R (%) according to Equation (1) [13]: R = (1-Cp/C0)×100%
The preparation and application of the hydrogel-coated BF for oil/ water separation are schematically showed in Fig. 1. KGM, a watersoluble natural compound stored in the tubers of amorphophallus konjac, is constructed by a linear polymer consisting of glucose and mannose units connected through the β-1,4 glycosidic linkages with acetyl groups [14]. When this material was subjected to an alkali condition, a deacetylation happened, resulting in the formation of
(1)
Fig. 1. Schematic showing the preparation of DA-KGM coated BF fabric and its application for oil-water separation. 2
Composites Communications 14 (2019) 1–6
D.-L. Cai and P.-C. Ma
Fig. 2. SEM images showing the morphology of BF before and after hydrogel coating (A: Raw-BF; B: Coated-BF; C: Cross section of Coated-BF).
thermally irreversible hydrogel with excellent film-forming properties [15]. Consequently, a thin layer of hydrogel was coated onto the BF fabric. The introduction of hydrogel did not change the weight of fabric significantly, as the measured average density of fabric was increased by less than 1.5% from 192.1 to 194.5 g/m2. Different techniques were employed to examine the variations on BF before and after hydrogel coating. SEM images were acquired to compare the surface morphology of samples (Fig. 2). As observed in Fig. 2A, a lot of fibres were aligned horizontally and vertically in the Raw BF, and these fibres were arranged in a woven manner without roving. A SEM image with a higher magnification shows that the fibres were contacted loosely, the diameter of individual filament was around 11 μm, and the surface of the fibre was smooth (Inset in Fig. 2A). The Coated-BF exhibited a similar morphology with that of Raw-BF under a mild magnification (Fig. 2B), suggesting the coating process did not sacrifice the woven structure of fabrics. However, a thin layer of amorphous material was noticed among the fibres, resulting in the bonding of individual fibres in the Coated-BF (Inset in Fig. 2B). This observation was mainly due to the penetration of hydrogel between two adjacent fibres during the coating process. The excellent film-former performance of the hydrogel resulted in a uniform layer of coating on fibre surface, as confirmed by viewing the cross-sectional area of the fractured fibres (Fig. 2C). When acetyl group in KGM was removed, a thermally stable hydrogel was expected due to the strengthening effect of hydrogen bond in the material at elevated temperature [16]. This process was
confirmed by comparing the FT-IR spectrum of KGM and DA-KGM. As shown in Fig. 3A, the KGM exhibited some peaks at 2883 cm−1 (stretching vibration of –CH2-), 1635 cm−1 (in-plane deformation of bound water), 1374 and 1008 cm−1 (in-plane and out-of-plane bending vibration of –CH2-). A broad band assigned to the stretching vibration of hydroxyl group (-OH) shifts to a lower wavenumber from 3359 to 3343 cm−1 after the alkali treatment, which was attributed to the enhancement of hydrogen bonding due to the gelation [16]. A peak at 1730 cm−1 was found in KGM sample, which is ascribed to the stretching vibration of –C]O in the acetyl group [17], and this peak was almost absence in the DA-KGM. The removal of acetyl groups in the backbone of KGM triggered the gelation of long polymer chain in the material [17], thus forming a coating layer on BF surface. The surface chemistry of BF was further studied using XPS. Fig. 3B shows the full XPS spectra and elemental composition of samples. Carbon (C) and oxygen (O) are the two major constituent elements on BF surface. During the spinning of BF from basalt melt, the brittle fibre is usually processed with sizing containing organic polymer and silane coupling agent to protect the filament from mechanical damage [18], and this resulted in the presence of C, O and Si on fibre surface. The atomic ratio of O/Si in the Raw BF is 6.2, and this value increased to 10.4 in the Coated BF due to the introduction of DA-KGM hydrogel, as the coating contained a higher amount of oxygen and covered the fibre surface. Compared with the Raw BF, an extra element Na (Binding energies at 497.4 and 1072.0 eV) was noticed in the Coated BF because NaOH was used to adjust the pH value of KGM solution during the
Fig. 3. Chemical information of hydrogel and BF samples (A: FT-IR spectrum of hydrogel before and after deacetylation; B: XPS spectrum of BF samples; C and D: C 1s spectra of Raw and Coated BF). 3
Composites Communications 14 (2019) 1–6
D.-L. Cai and P.-C. Ma
Fig. 4. Thermal properties of BF before and after hydrogel coating.
deacetylation. Fig. 3C exhibits the deconvoluted C1s spectra of Raw BF, two peaks are noticed at 284.5 and 286.4 eV, corresponding to the sp2 Cg and C–O functionalities in the material [19]. These results further confirmed the existence of sizing (organic film former and silane) on fiber surface. Interestingly, besides the binding energies at 284.5 and 286.4 eV, the C1s spectra of Coated BF shows a new one with marginal intensity at 287.8 eV (C]O bond, Fig. 3D), suggesting the presence of functional groups in the hydrogel originated from the DA-KGM. The hydrogel coating is expected to rectify the mechanical properties of BF sample. To verify this, single fibre was separated from the fabrics and tested. The results showed that the Coated BF had a higher tensile strength (1826 ± 371 MPa) than the Raw BF (1684 ± 259 MPa), this positive effect is due to the fact that the coating fills the cracks on fibre surface, functioning as a healing agent to repair the defects in the material [20]. The weight content of hydrogel on BF was quantitatively measured by studying the weight loss of material under the elevated temperature. Fig. 4 presented the TGA and derivative TG (DTG) curves of Raw and
Fig. 6. Practical application of the developed material for oil-water separation (A: Experimental setups; B: Collected water after separation using Raw and Coated BF; C and D: Anti-oil adhesion performance of Raw and Coated BF; E: Mechanism behind the underwater superoleophobicity of Coated BF).
Fig. 5. Wetting behavior of BF samples under different conditions (A and B: Water wettability of the Raw and Coated BF in air; C and D: Underwater wettability of the samples against oil; E: Superoleophobic and low oil-adhesion properties of Coated BF for various oils; F: Adhesive force curve of Coated BF against dichloroethane). 4
Composites Communications 14 (2019) 1–6
D.-L. Cai and P.-C. Ma
Fig. 7. Underwater oil contact angles of Coated BF unprocessed and those processed in different corrosive liquids.
suggesting the poor performance of the sample for oil-water separation. The red oil was absence in the liquid separated by the Coated BF, and the measured oil content in water was 0.057 mg/mL, revealing a high separation efficiency of 99.96% along with a water permeate flux of 8137.9 L/(m2·h). This exciting result was much better than the one separated by glass fiber fabric modified with silane coupling agent [21,22]. Besides the excellent capability to separate the oil-water mixture, the Coated BF also showed anti-fouling performance for oil. For example, when the Raw BF was put into the water with a floating layer of sunflower oil (dyed by oil red), the oil adhered to the fabric and was stretched to the bottom of the container (Fig. 6C). However, when the Coated BF was processed in the same way, the oil was remained in the floating layer, and the surface of fabric was clean (Fig. 6D), indicating the excellent anti-oil fouling performance of the developed material. Such interesting property originated from the hydroxyl groups in the Coated BF, which interacted with water molecules to form a thin layer of water on sample surface, and the inherent immiscibility between water and oil resulted in the repellence to oil compounds during the filtration process, which was schematically shown in Fig. 6E. The stability of the material for oil-water separation is important because the liquid to be processed may contain corrosive compounds. In such case, we immersed the Coated BF sample into different liquids (DMF, saturated NaCl, 20% H2SO4, 5 M NaOH) for 24 h. After that, the sample was collected and then the underwater contact angles of the fabric against hexane were measured, and the data were compared with the one without corrosive processing (Fig. 7). The results showed that the hexane droplet formed quasi-spherical shape on the Coated BF surface with underwater oil contact angles above 150° for all samples, indicating the superoleophobic performance of the Coated BF was not sacrificed under the corrosive conditions. It is expected that the developed fabrics can be applied for oil-water separation in harsh environment.
Coated BF in air condition, showing the thermal stability of samples. From these curves, it can be seen that Raw BF was a good material to resist the high temperature, as the weight loss of the sample was less than 0.3%. In sharp contrast, the Coated BF showed a continuous weight loss starting from 206.8 °C with a peak temperature at 286.8 °C (Obtained from DTG curve), suggesting the decomposition of coating in air flow. The percentage of the residual weight for the sample was lower than that of the Raw BF (98.6% vs. 99.8%), confirming the content of coating on BF was 1.2%, and this result was in good agreement with the density change (1.3%) of the sample. The studies on thermal stability demonstrated that the Coated BF can be used below 200 °C. 3.2. Wetting behavior and oil-water separation performance of composites The hydroxyl groups in the coating may change the surface wettability of BF sample. This can be evaluated by measuring the contact angles of the samples against water. When a water droplet was applied on the surface of Raw BF in air, the liquid formed a hemispherical shape with a contact angle of 87.5° (Fig. 5A), the droplet was absorbed by the sample after 4 min because of capillary effect. On the contrary, the water droplet was absorbed instantaneously by the Coated BF (Fig. 5B), making it impossible to get a reliable contact angle. Such different behavior indicated that the coating enhanced the hydrophilic property of BF due to the presence of hydroxyl groups in the material. Such hydrophilic performance was further confirmed by studying the contact angle of sample against oil in water. For example, an oil drop (1,2dichloroethane, density=1.24 g/mL) was formed in water on the Raw BF sample with a contact angle of 80.1° (Fig. 5C), which was much lower than that observed on the Coated BF under the same condition (153.5°, Fig. 5D). These evidences also demonstrated that the coating endowed the BF with underwater superoleophobicity, thus providing a possibility for the material to separate oil-water mixture, which will be discussed in the following section. In addition, the underwater superoleophobic performance of Coated BF was independent of the types of oil. As shown in Fig. 5E, the contact angles of the sample against various oils were all above 150° with the highest value of 156.4° for sunflower oil. Fig. 5F displays the adhesive force curve when 1,2-dichloroethane droplet is forced to contact with the Coated BF and detached with a constant speed of 0.001 mm/s (Insets in Fig. 5F). Marginal deformation was observed in the receding curve and the measured value of adhesion force between the sample and oil was 1.67 μN, and the adhesion forces for other oils were all less than 5.0 μN (Fig. 5E). These results demonstrated that the Coated BF had not only an underwater superoleophobic property, but also processed ultralow adhesion to the oil, which, in other words, indicated that the sample had the excellent anti-fouling performance for oil. The capability of the developed fabric for oil-water separation was demonstrated as well. During the experiment, BF fabrics were cut into square piece with a length of 5.0 cm and pre-wetted by water in advance, then the sample was fixed between two glass tubes. A mixture consisting of n-hexane and water (20.0 vol%, hexane was dyed by oil red) was poured into the upper glass tube. It was observed that water passed through the fabric quickly and dropped into the lower tube by using a single-unit gravimetric filtration (Fig. 6A), whereas the nhexane was retained in the upper glass tube. Fig. 6B shows the filtrate obtained by using Raw and Coated BF as a separation membrane. A thin layer of red oil was found when Raw BF was employed for separation,
4. Conclusions In summary, a composite fabric with superhydrophilic and underwater superoleophobic properties was prepared, and the developed material showed an excellent performance to separate oil-water mixture with high efficiency. More importantly, the fabric with hydrogel coating exhibited an ultralow underwater oil-adhesion force, which endowed the material with an excellent anti-oil fouling performance. Furthermore, the superhydrophilicity and underwater superoleophobicity of material arising from the coating were not sacrificed when the fabric was subjected to the alkali, acid and organic solutions, thus holding the promise to be used in harsh environment. We expect that the material developed in this study is a good candidate for the fences dealing the oil spill accidents and separating various oil-water mixtures. Acknowledgements This project was supported by the Major Science and Technology Program of Xinjiang Uygur Autonomous Region (Project No.: 2018A02002-3), the Director Foundation of XTIPC-CAS (Grant No.: 2016PY005), and the Science and Technology Program of Liupanshui City, China (Grant No.: 52020-2018-01-05). 5
Composites Communications 14 (2019) 1–6
D.-L. Cai and P.-C. Ma
References
[11] N. Cao, B. Yang, A. Barras, S. Szunerits, R. Boukherroub, Polyurethane sponge functionalized with superhydrophobic nanodiamond particles for efficient oil/ water separation, Chem. Eng. J. 307 (2017) 319–325. [12] C. Wang, S. Yang, Q. Ma, X. Jia, P.-C. Ma, Preparation of carbon nanotubes/graphene hybrid aerogel and its application for the adsorption of organic compounds, Carbon 118 (2017) 765–771. [13] Z. Xue, S. Wang, L. Lin, L. Chen, M. Liu, L. Feng, L. Jiang, A novel superhydrophilic and underwater superoleophobic hydrogel-coated mesh for oil/water separation, Adv. Mater. 23 (2011) 4270–4273. [14] Y. Yuan, L. Wang, J. Pang, X. Hong, R.-J. Mu, W.-H. Wang, B.-Q. Xie, A Review of the development of properties and structures based on konjac glucomannan as functional materials, Chin. J. Struct. Chem. 36 (2017) 346–360. [15] C. Zhang, J.-D. Chen, F.-Q. Yang, Konjac glucomannan, a promising polysaccharide for OCDDS, Carbohydr. Polym. 104 (2014) 175–181. [16] L. Huang, R. Takahashi, S. Kobayashi, T. Kawase, K. Nishinari, Gelation behavior of native and acetylated konjac glucomannan, Biomacromolecules 3 (2002) 1296–1303. [17] H. Zhang, M. Yoshimura, K. Nishinari, M.A.K. Williams, T.J. Foster, I.T. Norton, Gelation behaviour of konjac glucomannan with different molecular weights, Biopolymers 59 (2001) 38–50. [18] E.A. Ivashchenko, Sizing and finishing agents for basalt and glass fibers, Theor. Found. Chem. Eng. 43 (2009) 511–516. [19] P.C. Ma, J.K. Kim JK, B.Z. Tang, Functionalization of carbon nanotubes using a silane coupling agent, Carbon 44 (2006) 3232–3238. [20] K.L. Kuzmin, I.A. Timoshkin, S.I. Gutnikov, E.S. Zhukovskaya, Y.V. Lipatov, B.I. Lazoryak, Effect of silane/nano-silica on the mechanical properties of basalt fiber reinforced epoxy composites, Compos. Interfac. 24 (2017) 13–34. [21] D. Zang, F. Liu, M. Zhang, X. Niu, Z. Gao, C. Wang, Superhydrophobic coating on fiberglass cloth for selective removal of oil from water, Chem. Eng. J. 262 (2015) 210–216. [22] I. Phiri, K.Y. Eum, J.W. Kim, W.S. Choi, S.H. Kim, J.M. Ko, H. Jung, Simultaneous complementary oil-water separation and water desalination using functionalized woven glass fiber membranes, J. Ind. Eng. Chem. 73 (2019) 78–86.
[1] H.K. White, P.-Y. Hsing, W. Cho, T.M. Shank, E.E. Cordes, A.M. Quattrini, R.K. Nelson, R. Camilli, A.W.J. Demopoulos, C.R. German, J.M. Brooks, H.H. Roberts, W. Shedd, C.M. Reddy, C.R. Fisher, Impact of the Deepwater Horizon oil spill on a deep-water coral community in the Gulf of Mexico, P. Natl. Acad. Sci. 109 (2012) 20303–20308. [2] H. Zhang, Z. Xu, D. Zhou, J. Cao, Waste cooking oil-to-energy under incomplete information: identifying policy options through an evolutionary game, Appl. Energy 185 (2017) 547–555. [3] J. Chen, H. You, L. Xu, T. Li, X. Jiang, C.M. Li, Facile synthesis of a two-tier hierarchical structured superhydrophobic-superoleophilic melamine sponge for rapid and efficient oil/water separation, J. Colloid Interface Sci. 506 (2017) 659–668. [4] Z. Li, L. Shao, W. Hu, T. Zheng, L. Lu, Y. Cao, Y. Chen, Excellent reusable chitosan/ cellulose aerogel as an oil and organic solvent absorbent, Carbohydr. Polym. 191 (2018) 183–190. [5] J. Song, S. Li, C. Zhao, Y. Lu, D. Zhao, J. Sun, T. Roy, C.J. Carmalt, X. Deng, I.P. Parkin, A superhydrophilic cement-coated mesh: an acid, alkali, and organic reagent-free material for oil/water separation, Nanoscale 10 (2018) 1920–1929. [6] S. Gao, J. Sun, P. Liu, F. Zhang, W. Zhang, S. Yuan, J. Li, J. Jin, A robust polyionized hydrogel with an unprecedented underwater anti-crude-oil-adhesion property, Adv. Mater. 28 (2016) 5307–5314. [7] M.M. Machado, A.O. Lobo, F.R. Marciano, E.J. Corat, M.A.F. Corat, Analysis of cellular adhesion on superhydrophobic and superhydrophilic vertically aligned carbon nanotube scaffolds, Mater. Sci. Eng. C 48 (2015) 365–371. [8] Y. Cheng, T. Zhu, S. Li, J. Huang, J. Mao, H. Yang, S. Gao, Z. Chen, Y. Lai, A novel strategy for fabricating robust superhydrophobic fabrics by environmentallyfriendly enzyme etching, Chem. Eng. J. 355 (2019) 290–298. [9] W. Lv, Q. Mei, J. Xiao, M. Du, Q. Zheng, 3D multiscale superhydrophilic sponges with delicately designed pore size for ultrafast oil/water separation, Adv. Funct. Mater. 27 (2017) 1704293. [10] Z.M. Siddiqi, M.M. Amin, Effect of south China sea water on corrosion behaviour of copper alloy and mild steel, Asian J. Water Environ. Pollut. 14 (1) (2017) 1–8.
6
Contents lists available at ScienceDirect
Composites Communications journal homepage: www.elsevier.com/locate/coco
Short Communication
Hydrogel-coated basalt fibre with superhydrophilic and underwater superoleophobic performance for oil-water separation
T
Deng-Liang Caia,b, Peng-Cheng Maa,b,∗ a Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi, 830011, China b Center of Material and Opto-electronic Research, University of Chinese Academy of Sciences, Beijing, 100049, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Basalt fibre Hydrogel Superhydrophilicity Oil-water separation
Materials with controlled surface properties show great potential for various applications. In this paper, we reported a method to prepare a superhydrophilic fabric consisting of basalt fibre (BF) and konjac glucomannan (KGM). Different techniques were employed to study the morphology and surface information of the developed materials. The results showed that the KGM was deacetylated to form a hydrogel when processed in an alkali condition, and the excellent film-forming performance of the hydrogel led to the formation of a coating layer on BF fabric. The coating endowed the developed fabric with enhanced mechanical performance and superhydrophilicity in air condition. Interestingly, the material, subjected to a water condition, exhibited a stable superoleophobicity as confirmed by the extremely low adhesion to oil and remarkable resistance to the corrosive liquids, thus holding the promise to be a suitable candidate for separating various oil-water mixtures.
1. Introduction
is that when contacting with water, the liquid spreads quickly to form a flat film on the surface of material rather than in the state of droplet, and the oily contaminants on the material can be easily cleaned by the super-spreading water film. Many techniques have been adopted to prepare superhydrophilic materials through a combination of surface chemistry and construction of rough structure, such as vapor deposition [7], etching [8], hydrothermal treatment [9], and so on. Among these methods, surface coating has more advantages over the others as the process does not take a prolonged chemical reaction time. In addition, the coating method can be applied to polymeric or assembled structures by static or dynamic absorption without changing the structures of the substrates. As a matured technique, this process does not require complicated or expensive equipment, thus providing a possibility for the scale-up production of materials. As for the substrate materials, metallic meshes (stainless steel, copper, nickel) are mainly used as a suitable substrate for oil-water separation, the biggest problem of these substrates is the high cost and marginal resistance to the chemical corrosion [10]. Sponge is a cheap and commercially available material with huge space for oil absorption and storage, which is used to remove oils from the water after a purposeful construction with low surface energy coating [11], but it brings complex post-treatment as it has to be squeezed to get oils from the pores in the material for cyclic operation. Carbon-based aerogels have
With ever-increasing production and usage of petroleum products, oil spillage and chemical leakage occur frequently worldwide every year. Pollution arising from these accidents has led to severe environmental problems. For example, the Deepwater Horizon oil spill occurred in 2010 led to the severe damage to the coral community in the Gulf of Mexico [1]. Besides the leakages arising from industrial oily compounds and chemicals, the discharge of sewage containing waste cooking oil also causes negative impact on surrounding ecosystems [2]. Therefore, materials that can effectively separate oils and chemicals from water are in urgently needed. Inspired by some natural species (lotus leaf, water fly, etc), superhydrophobic and superoleophilic sponges/aerogels/meshes modified by nanoparticles and polymers [3–5] were designed to achieve such objective. These composites are also called “oil-removing” materials, which realize the absorption or filtration of various oils from water selectively and effectively. However, the problems associated with the high cost of nanoparticles, pore plugging and contamination by viscous oily compounds, have limited the practical applications of these materials. As an alternative, great attention was focused on developing materials with superhydrophilic performance [6], namely “water removing” performance. One of the unique advantages of such materials
∗ Corresponding author. Laboratory of Environmental Science and Technology, The Xinjiang Technical Institute of Physics and Chemistry, Key Laboratory of Functional Materials and Devices for Special Environments, Chinese Academy of Sciences, Urumqi, 830011, China. E-mail address: [email protected] (P.-C. Ma).
https://doi.org/10.1016/j.coco.2019.05.002 Received 16 February 2019; Received in revised form 8 May 2019; Accepted 9 May 2019 Available online 11 May 2019 2452-2139/ © 2019 Elsevier Ltd. All rights reserved.
Composites Communications 14 (2019) 1–6
D.-L. Cai and P.-C. Ma
Where C0 (vol%) and Cp (vol%) are the oil concentration of the original oil/water mixture and the collected water, respectively. The water flux J was calculated according to Equation (2):
intrigued huge attention due to the low density, high porosity and large surface area [12], the materials usually contained carbon nanotubes or graphene that are not cheap. Therefore, a suitable substrate with an excellent cost-performance property is highly desirable. Herein, we reported a low-cost and facile method to fabricate superhydrophilic basalt fibre (BF) with a surface modifier originated from konjac glucomannan (KGM), aiming at developing a green and inexhaustible composite material with remarkable sustainability. Different techniques were employed to characterize the morphology, surface states and wetting behavior of the material. The applicability of the developed fabric for separating oil-water mixture was studied, and the mechanism behind the superoleophobicity of material was illustrated.
J=V/AT
(2)
Here, V is the volume of filtering water (L), A is the effective area of fabric (m2) and T is the filtration time (h). For each test, three batch experiments were performed and an average value on water flux with standard deviation was reported. For the study on the stability of fabric in harsh environment, the coated BF was immersed into various liquids, including dimethyl formamide (DMF), saturated NaCl (26.5%), H2SO4 (20.0%) and NaOH (5 M), for 24 h. Then the sample was taken out and washed by water before testing its surface property and oil-water separation performance.
2. Experimental 2.1. Materials
2.4. Characterization
KGM powder was obtained from a local market. BF fabric was purchased from Guizhou Shixin Basalt Technology Co., China. Commercially available oil products (gasoline, sunflower oil), crude oil (Karamay Oilfield, China), and organic liquids (1, 2-dichloroethane, nhexane) were used as probing liquids for oil-absorption and oil-water separation studies. Sodium hydroxide (NaOH) was used to adjust the alkality of solution. All chemicals were in analytical grade and used as received without further purification. Ultrapure water (Millipore, resistivity > 18.5MΩ·cm) was used in experiment.
The deacetylation process of KGM was studied by Fourier-transform infrared spectrometer (FT-IR, FTS-165, Biorad, US). The morphology of fabric was characterized by a scanning electronic microscope (SEM, Supra 55VP, Zeiss, Germany). The chemical state of element on fibre surface was evaluated by X-ray photoelectron spectroscopy (XPS, EscaLab 250Xi, Thermo Scientific, US). The wetting behavior of sample against water and oil was analyzed by measuring the contact angle on a goniometer (XG-CAMA, Shanghai Xuanyichuangxi, China). Interactions (Adhesion force, oil-fouling) between the BF and liquid were studied on a high-sensitivity microelectromechanical balance system (DCAT 25, Data-Physics, Germany). The content of oil after separation was determined using an oil content analyzer (JLBG-126, Jilin Jiguang, China). The tensile strength of single BF was measured on a fibre tensile tester (XQ-1A, Shanghai Xinxian, China). The test was performed according to the ASTM C1557-14 standard. The gauge length of sample and the loading speed were fixed at 25.0 mm and 2.0 mm/min, respectively. At least 30 specimens of each fibre were tested and a mean value with a standard deviation was reported. The thermal stability of the BF was evaluated on a thermogravimetric analyzer (TGA, STA 449F3, Netzsch, Germany) with a hating rate of 10 °C/min from 25 to 600 °C in air condition.
2.2. Fabrication of DA-KGM coated BF For the preparation of coated BF fabric, KGM powder (0.50 g) was dissolved in water (100 mL) and stirred for 5 h to get a homogeneous solution at room temperature. Then the pH of solution was adjusted to 9.5 by NaOH (0.10 M) and magnetically stirred for another 1 h, yielding the deacetylated KGM (DA-KGM) solution. A piece of BF (20.0 × 20.0 cm) pre-cleaned by acetone and ethanol was put into the above solution for 10 min to ensure a complete wetting, and then the fabric was drawn from the mixture and put onto a Teflon plate. The excessive solution was removed manually using a glass rod. The final product was obtained by putting the fabric into an oven at 90 °C for 3 h.
3. Results and discussion
2.3. Experimental setups for oil/water separation
3.1. Morphology and physical properties of the sample
The hydrogel-coated BF was cut into 5.0 × 5.0 cm sample, and then fixed between two glass tubes. The fabric was wetted by water at first, and during the separation process, the mixture of hexane and water (20%, v/v) were poured into the upper glass tube. The whole process was driven by the gravity without other force. The separation efficiency was calculated by oil rejection coefficient R (%) according to Equation (1) [13]: R = (1-Cp/C0)×100%
The preparation and application of the hydrogel-coated BF for oil/ water separation are schematically showed in Fig. 1. KGM, a watersoluble natural compound stored in the tubers of amorphophallus konjac, is constructed by a linear polymer consisting of glucose and mannose units connected through the β-1,4 glycosidic linkages with acetyl groups [14]. When this material was subjected to an alkali condition, a deacetylation happened, resulting in the formation of
(1)
Fig. 1. Schematic showing the preparation of DA-KGM coated BF fabric and its application for oil-water separation. 2
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Fig. 2. SEM images showing the morphology of BF before and after hydrogel coating (A: Raw-BF; B: Coated-BF; C: Cross section of Coated-BF).
thermally irreversible hydrogel with excellent film-forming properties [15]. Consequently, a thin layer of hydrogel was coated onto the BF fabric. The introduction of hydrogel did not change the weight of fabric significantly, as the measured average density of fabric was increased by less than 1.5% from 192.1 to 194.5 g/m2. Different techniques were employed to examine the variations on BF before and after hydrogel coating. SEM images were acquired to compare the surface morphology of samples (Fig. 2). As observed in Fig. 2A, a lot of fibres were aligned horizontally and vertically in the Raw BF, and these fibres were arranged in a woven manner without roving. A SEM image with a higher magnification shows that the fibres were contacted loosely, the diameter of individual filament was around 11 μm, and the surface of the fibre was smooth (Inset in Fig. 2A). The Coated-BF exhibited a similar morphology with that of Raw-BF under a mild magnification (Fig. 2B), suggesting the coating process did not sacrifice the woven structure of fabrics. However, a thin layer of amorphous material was noticed among the fibres, resulting in the bonding of individual fibres in the Coated-BF (Inset in Fig. 2B). This observation was mainly due to the penetration of hydrogel between two adjacent fibres during the coating process. The excellent film-former performance of the hydrogel resulted in a uniform layer of coating on fibre surface, as confirmed by viewing the cross-sectional area of the fractured fibres (Fig. 2C). When acetyl group in KGM was removed, a thermally stable hydrogel was expected due to the strengthening effect of hydrogen bond in the material at elevated temperature [16]. This process was
confirmed by comparing the FT-IR spectrum of KGM and DA-KGM. As shown in Fig. 3A, the KGM exhibited some peaks at 2883 cm−1 (stretching vibration of –CH2-), 1635 cm−1 (in-plane deformation of bound water), 1374 and 1008 cm−1 (in-plane and out-of-plane bending vibration of –CH2-). A broad band assigned to the stretching vibration of hydroxyl group (-OH) shifts to a lower wavenumber from 3359 to 3343 cm−1 after the alkali treatment, which was attributed to the enhancement of hydrogen bonding due to the gelation [16]. A peak at 1730 cm−1 was found in KGM sample, which is ascribed to the stretching vibration of –C]O in the acetyl group [17], and this peak was almost absence in the DA-KGM. The removal of acetyl groups in the backbone of KGM triggered the gelation of long polymer chain in the material [17], thus forming a coating layer on BF surface. The surface chemistry of BF was further studied using XPS. Fig. 3B shows the full XPS spectra and elemental composition of samples. Carbon (C) and oxygen (O) are the two major constituent elements on BF surface. During the spinning of BF from basalt melt, the brittle fibre is usually processed with sizing containing organic polymer and silane coupling agent to protect the filament from mechanical damage [18], and this resulted in the presence of C, O and Si on fibre surface. The atomic ratio of O/Si in the Raw BF is 6.2, and this value increased to 10.4 in the Coated BF due to the introduction of DA-KGM hydrogel, as the coating contained a higher amount of oxygen and covered the fibre surface. Compared with the Raw BF, an extra element Na (Binding energies at 497.4 and 1072.0 eV) was noticed in the Coated BF because NaOH was used to adjust the pH value of KGM solution during the
Fig. 3. Chemical information of hydrogel and BF samples (A: FT-IR spectrum of hydrogel before and after deacetylation; B: XPS spectrum of BF samples; C and D: C 1s spectra of Raw and Coated BF). 3
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Fig. 4. Thermal properties of BF before and after hydrogel coating.
deacetylation. Fig. 3C exhibits the deconvoluted C1s spectra of Raw BF, two peaks are noticed at 284.5 and 286.4 eV, corresponding to the sp2 Cg and C–O functionalities in the material [19]. These results further confirmed the existence of sizing (organic film former and silane) on fiber surface. Interestingly, besides the binding energies at 284.5 and 286.4 eV, the C1s spectra of Coated BF shows a new one with marginal intensity at 287.8 eV (C]O bond, Fig. 3D), suggesting the presence of functional groups in the hydrogel originated from the DA-KGM. The hydrogel coating is expected to rectify the mechanical properties of BF sample. To verify this, single fibre was separated from the fabrics and tested. The results showed that the Coated BF had a higher tensile strength (1826 ± 371 MPa) than the Raw BF (1684 ± 259 MPa), this positive effect is due to the fact that the coating fills the cracks on fibre surface, functioning as a healing agent to repair the defects in the material [20]. The weight content of hydrogel on BF was quantitatively measured by studying the weight loss of material under the elevated temperature. Fig. 4 presented the TGA and derivative TG (DTG) curves of Raw and
Fig. 6. Practical application of the developed material for oil-water separation (A: Experimental setups; B: Collected water after separation using Raw and Coated BF; C and D: Anti-oil adhesion performance of Raw and Coated BF; E: Mechanism behind the underwater superoleophobicity of Coated BF).
Fig. 5. Wetting behavior of BF samples under different conditions (A and B: Water wettability of the Raw and Coated BF in air; C and D: Underwater wettability of the samples against oil; E: Superoleophobic and low oil-adhesion properties of Coated BF for various oils; F: Adhesive force curve of Coated BF against dichloroethane). 4
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Fig. 7. Underwater oil contact angles of Coated BF unprocessed and those processed in different corrosive liquids.
suggesting the poor performance of the sample for oil-water separation. The red oil was absence in the liquid separated by the Coated BF, and the measured oil content in water was 0.057 mg/mL, revealing a high separation efficiency of 99.96% along with a water permeate flux of 8137.9 L/(m2·h). This exciting result was much better than the one separated by glass fiber fabric modified with silane coupling agent [21,22]. Besides the excellent capability to separate the oil-water mixture, the Coated BF also showed anti-fouling performance for oil. For example, when the Raw BF was put into the water with a floating layer of sunflower oil (dyed by oil red), the oil adhered to the fabric and was stretched to the bottom of the container (Fig. 6C). However, when the Coated BF was processed in the same way, the oil was remained in the floating layer, and the surface of fabric was clean (Fig. 6D), indicating the excellent anti-oil fouling performance of the developed material. Such interesting property originated from the hydroxyl groups in the Coated BF, which interacted with water molecules to form a thin layer of water on sample surface, and the inherent immiscibility between water and oil resulted in the repellence to oil compounds during the filtration process, which was schematically shown in Fig. 6E. The stability of the material for oil-water separation is important because the liquid to be processed may contain corrosive compounds. In such case, we immersed the Coated BF sample into different liquids (DMF, saturated NaCl, 20% H2SO4, 5 M NaOH) for 24 h. After that, the sample was collected and then the underwater contact angles of the fabric against hexane were measured, and the data were compared with the one without corrosive processing (Fig. 7). The results showed that the hexane droplet formed quasi-spherical shape on the Coated BF surface with underwater oil contact angles above 150° for all samples, indicating the superoleophobic performance of the Coated BF was not sacrificed under the corrosive conditions. It is expected that the developed fabrics can be applied for oil-water separation in harsh environment.
Coated BF in air condition, showing the thermal stability of samples. From these curves, it can be seen that Raw BF was a good material to resist the high temperature, as the weight loss of the sample was less than 0.3%. In sharp contrast, the Coated BF showed a continuous weight loss starting from 206.8 °C with a peak temperature at 286.8 °C (Obtained from DTG curve), suggesting the decomposition of coating in air flow. The percentage of the residual weight for the sample was lower than that of the Raw BF (98.6% vs. 99.8%), confirming the content of coating on BF was 1.2%, and this result was in good agreement with the density change (1.3%) of the sample. The studies on thermal stability demonstrated that the Coated BF can be used below 200 °C. 3.2. Wetting behavior and oil-water separation performance of composites The hydroxyl groups in the coating may change the surface wettability of BF sample. This can be evaluated by measuring the contact angles of the samples against water. When a water droplet was applied on the surface of Raw BF in air, the liquid formed a hemispherical shape with a contact angle of 87.5° (Fig. 5A), the droplet was absorbed by the sample after 4 min because of capillary effect. On the contrary, the water droplet was absorbed instantaneously by the Coated BF (Fig. 5B), making it impossible to get a reliable contact angle. Such different behavior indicated that the coating enhanced the hydrophilic property of BF due to the presence of hydroxyl groups in the material. Such hydrophilic performance was further confirmed by studying the contact angle of sample against oil in water. For example, an oil drop (1,2dichloroethane, density=1.24 g/mL) was formed in water on the Raw BF sample with a contact angle of 80.1° (Fig. 5C), which was much lower than that observed on the Coated BF under the same condition (153.5°, Fig. 5D). These evidences also demonstrated that the coating endowed the BF with underwater superoleophobicity, thus providing a possibility for the material to separate oil-water mixture, which will be discussed in the following section. In addition, the underwater superoleophobic performance of Coated BF was independent of the types of oil. As shown in Fig. 5E, the contact angles of the sample against various oils were all above 150° with the highest value of 156.4° for sunflower oil. Fig. 5F displays the adhesive force curve when 1,2-dichloroethane droplet is forced to contact with the Coated BF and detached with a constant speed of 0.001 mm/s (Insets in Fig. 5F). Marginal deformation was observed in the receding curve and the measured value of adhesion force between the sample and oil was 1.67 μN, and the adhesion forces for other oils were all less than 5.0 μN (Fig. 5E). These results demonstrated that the Coated BF had not only an underwater superoleophobic property, but also processed ultralow adhesion to the oil, which, in other words, indicated that the sample had the excellent anti-fouling performance for oil. The capability of the developed fabric for oil-water separation was demonstrated as well. During the experiment, BF fabrics were cut into square piece with a length of 5.0 cm and pre-wetted by water in advance, then the sample was fixed between two glass tubes. A mixture consisting of n-hexane and water (20.0 vol%, hexane was dyed by oil red) was poured into the upper glass tube. It was observed that water passed through the fabric quickly and dropped into the lower tube by using a single-unit gravimetric filtration (Fig. 6A), whereas the nhexane was retained in the upper glass tube. Fig. 6B shows the filtrate obtained by using Raw and Coated BF as a separation membrane. A thin layer of red oil was found when Raw BF was employed for separation,
4. Conclusions In summary, a composite fabric with superhydrophilic and underwater superoleophobic properties was prepared, and the developed material showed an excellent performance to separate oil-water mixture with high efficiency. More importantly, the fabric with hydrogel coating exhibited an ultralow underwater oil-adhesion force, which endowed the material with an excellent anti-oil fouling performance. Furthermore, the superhydrophilicity and underwater superoleophobicity of material arising from the coating were not sacrificed when the fabric was subjected to the alkali, acid and organic solutions, thus holding the promise to be used in harsh environment. We expect that the material developed in this study is a good candidate for the fences dealing the oil spill accidents and separating various oil-water mixtures. Acknowledgements This project was supported by the Major Science and Technology Program of Xinjiang Uygur Autonomous Region (Project No.: 2018A02002-3), the Director Foundation of XTIPC-CAS (Grant No.: 2016PY005), and the Science and Technology Program of Liupanshui City, China (Grant No.: 52020-2018-01-05). 5
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References
[11] N. Cao, B. Yang, A. Barras, S. Szunerits, R. Boukherroub, Polyurethane sponge functionalized with superhydrophobic nanodiamond particles for efficient oil/ water separation, Chem. Eng. J. 307 (2017) 319–325. [12] C. Wang, S. Yang, Q. Ma, X. Jia, P.-C. Ma, Preparation of carbon nanotubes/graphene hybrid aerogel and its application for the adsorption of organic compounds, Carbon 118 (2017) 765–771. [13] Z. Xue, S. Wang, L. Lin, L. Chen, M. Liu, L. Feng, L. Jiang, A novel superhydrophilic and underwater superoleophobic hydrogel-coated mesh for oil/water separation, Adv. Mater. 23 (2011) 4270–4273. [14] Y. Yuan, L. Wang, J. Pang, X. Hong, R.-J. Mu, W.-H. Wang, B.-Q. Xie, A Review of the development of properties and structures based on konjac glucomannan as functional materials, Chin. J. Struct. Chem. 36 (2017) 346–360. [15] C. Zhang, J.-D. Chen, F.-Q. Yang, Konjac glucomannan, a promising polysaccharide for OCDDS, Carbohydr. Polym. 104 (2014) 175–181. [16] L. Huang, R. Takahashi, S. Kobayashi, T. Kawase, K. Nishinari, Gelation behavior of native and acetylated konjac glucomannan, Biomacromolecules 3 (2002) 1296–1303. [17] H. Zhang, M. Yoshimura, K. Nishinari, M.A.K. Williams, T.J. Foster, I.T. Norton, Gelation behaviour of konjac glucomannan with different molecular weights, Biopolymers 59 (2001) 38–50. [18] E.A. Ivashchenko, Sizing and finishing agents for basalt and glass fibers, Theor. Found. Chem. Eng. 43 (2009) 511–516. [19] P.C. Ma, J.K. Kim JK, B.Z. Tang, Functionalization of carbon nanotubes using a silane coupling agent, Carbon 44 (2006) 3232–3238. [20] K.L. Kuzmin, I.A. Timoshkin, S.I. Gutnikov, E.S. Zhukovskaya, Y.V. Lipatov, B.I. Lazoryak, Effect of silane/nano-silica on the mechanical properties of basalt fiber reinforced epoxy composites, Compos. Interfac. 24 (2017) 13–34. [21] D. Zang, F. Liu, M. Zhang, X. Niu, Z. Gao, C. Wang, Superhydrophobic coating on fiberglass cloth for selective removal of oil from water, Chem. Eng. J. 262 (2015) 210–216. [22] I. Phiri, K.Y. Eum, J.W. Kim, W.S. Choi, S.H. Kim, J.M. Ko, H. Jung, Simultaneous complementary oil-water separation and water desalination using functionalized woven glass fiber membranes, J. Ind. Eng. Chem. 73 (2019) 78–86.
[1] H.K. White, P.-Y. Hsing, W. Cho, T.M. Shank, E.E. Cordes, A.M. Quattrini, R.K. Nelson, R. Camilli, A.W.J. Demopoulos, C.R. German, J.M. Brooks, H.H. Roberts, W. Shedd, C.M. Reddy, C.R. Fisher, Impact of the Deepwater Horizon oil spill on a deep-water coral community in the Gulf of Mexico, P. Natl. Acad. Sci. 109 (2012) 20303–20308. [2] H. Zhang, Z. Xu, D. Zhou, J. Cao, Waste cooking oil-to-energy under incomplete information: identifying policy options through an evolutionary game, Appl. Energy 185 (2017) 547–555. [3] J. Chen, H. You, L. Xu, T. Li, X. Jiang, C.M. Li, Facile synthesis of a two-tier hierarchical structured superhydrophobic-superoleophilic melamine sponge for rapid and efficient oil/water separation, J. Colloid Interface Sci. 506 (2017) 659–668. [4] Z. Li, L. Shao, W. Hu, T. Zheng, L. Lu, Y. Cao, Y. Chen, Excellent reusable chitosan/ cellulose aerogel as an oil and organic solvent absorbent, Carbohydr. Polym. 191 (2018) 183–190. [5] J. Song, S. Li, C. Zhao, Y. Lu, D. Zhao, J. Sun, T. Roy, C.J. Carmalt, X. Deng, I.P. Parkin, A superhydrophilic cement-coated mesh: an acid, alkali, and organic reagent-free material for oil/water separation, Nanoscale 10 (2018) 1920–1929. [6] S. Gao, J. Sun, P. Liu, F. Zhang, W. Zhang, S. Yuan, J. Li, J. Jin, A robust polyionized hydrogel with an unprecedented underwater anti-crude-oil-adhesion property, Adv. Mater. 28 (2016) 5307–5314. [7] M.M. Machado, A.O. Lobo, F.R. Marciano, E.J. Corat, M.A.F. Corat, Analysis of cellular adhesion on superhydrophobic and superhydrophilic vertically aligned carbon nanotube scaffolds, Mater. Sci. Eng. C 48 (2015) 365–371. [8] Y. Cheng, T. Zhu, S. Li, J. Huang, J. Mao, H. Yang, S. Gao, Z. Chen, Y. Lai, A novel strategy for fabricating robust superhydrophobic fabrics by environmentallyfriendly enzyme etching, Chem. Eng. J. 355 (2019) 290–298. [9] W. Lv, Q. Mei, J. Xiao, M. Du, Q. Zheng, 3D multiscale superhydrophilic sponges with delicately designed pore size for ultrafast oil/water separation, Adv. Funct. Mater. 27 (2017) 1704293. [10] Z.M. Siddiqi, M.M. Amin, Effect of south China sea water on corrosion behaviour of copper alloy and mild steel, Asian J. Water Environ. Pollut. 14 (1) (2017) 1–8.
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