Facile preparation of grass-like hierarchical structured γ-AlOOH coated stainless steel mesh with superhydrophobic and superoleophilic for highly efficient oil-water separation

Accepted Manuscript Facile preparation of grass-like hierarchical structured γ-AlOOH coated stainless steel mesh with superhydrophobic and superoleophilic for highly efficient oil-water separation Ming Zhang, Zhilun Wu, Fancheng Meng, Huixing Lin PII: DOI: Reference:

S1383-5866(18)31955-5 https://doi.org/10.1016/j.seppur.2018.08.069 SEPPUR 14890

To appear in:

Separation and Purification Technology

Received Date: Revised Date: Accepted Date:

4 June 2018 13 August 2018 29 August 2018

Please cite this article as: M. Zhang, Z. Wu, F. Meng, H. Lin, Facile preparation of grass-like hierarchical structured γ-AlOOH coated stainless steel mesh with superhydrophobic and superoleophilic for highly efficient oil-water separation, Separation and Purification Technology (2018), doi: https://doi.org/10.1016/j.seppur.2018.08.069

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Facile preparation of grass-like hierarchical structured γ-AlOOH coated stainless steel mesh with superhydrophobic and superoleophilic for highly efficient oil-water separation Ming Zhang1, Zhilun Wu1, Fancheng Meng1, 2*, Huixing Lin2* (1.College of Materials Science and Engineering, Chongqing University of Technology, Chongqing, 400054, P.R. China;2.Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences,Shanghai,201800, P.R. China) Abstract: a superhydrophobic and superoleophilic γ-AlOOH membrane on stainless steel mesh was fabricated by an inexpensive, template-free hydrothermal method using Al(NO3)3·9H2O and Na2C2O4 as starting materials. A novel γ-AlOOH film with a grass-like structure was synthesized and grass-like grains were tightly connected to form a hierarchical microstructure, which created a rougher stainless steel mesh surface. The influences of the additive amount of Na2C2O4 and Al(NO3)3·9H2O on morphology and water contact angle of products were discussed. The prepared film is superhydrophobic not only for pure water but also for corrosive water under acidic or alkaline conditions. The obtained superhydrophobic and superlipophilic coated mesh exhibited high efficient oil/water separation. Besides the maximum diesel-water separation efficiency reach 99.6%, a high water intrusion pressure value of 2.2 kPa is also calculated, which make it promising application in large-scale, high-efficient and reusable oil/water separation filed. Keywords: superhydrophobic; hierarchical; separation; hydrothermal 1. Introduction 

Corresponding author. Tel./fax: +86 23 62408527 E-mail address: [email protected] (F.C. Meng)  Corresponding author. Tel./fax: +86 21 69906356 E-mail address: [email protected] (H.X. Lin) 1

Oily wastewater has attracted great attentions due to its potential destroy in environmental and ecological system [1-3]. The effective separation of oily wastewater has become a worldwide issue [4, 5]. Various convention approaches have been used in oil-water separation field, such as chemical and filtration treatments [6], the use of oil-absorbing materials [7], as well as gravity separation [8]. However, these methods still have distinct drawbacks of low separation efficiency, energy-cost or complex separation instruments. Thus, there is an imperative demand of developing effective technologies or new functional materials for oil-water separation. Recently, the membranes with superhydrophobic and superoleophilic properties have been fabricated and exhibited to be most promising materials for oil-water separation [9-11]. In these studies, the superhydrophobicity can cause water to run off completely, while superoleophilicity can allow oils to be spreads and pass through the mesh surface quickly [12]. So far, many researchers have tried to construct superhydrophobic and superoleophilic surface on porous materials, such as metal mesh, fabrics, sponge, filter papers, etc [13-16]. Many methods, such as lay-by-lay or layer-by-layer grafting method [17-19], electrospinning method [20-22], the polymer or polymer composite coating method [23-25], the spray-coating of the polymer method [26-28], sol-gel method [29-31], the electrochemical deposition method [32-34], the wet chemical approach [35-37], etc, have been utilized to obtain superhydrophobic surfaces. However, among of all these methods and materials, parts of used reagents are harmful and expensive, and the fabrication process and equipment is also time-consuming and complicated. Up to now, various materials with superhydrophobic property, such as TiO2, cellulose, polymer membrane, silica, ZnO, zeolite, hydrogel, graphene oxide, etc [3,23,24,29,38-41], have been developed for oil-water separation by appropriate surface energy as well as construction of

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hierarchal rough surface. On the whole, the current approaches for surface superhydrophobicity modification can be divided into two types: organic polymer-based grafting and inorganic material coating. Among these materials, inorganic coating material is one particularly good choice because of its high durability and mechanical strength. The polymeric material usually has poor stability and becomes unstable under harsh conditions during the separation process. However, the reports concerning high oil-water separation efficiency inorganic membrane with novel morphologies are still very rare. In fact, many superhydrophobic inorganic surfaces have been successfully fabricated, in which micro/nano hierarchical architectures are usually used to create suitable roughness [38, 42, 43]. Among them, aluminum oxide hydroxide (γ-AlOOH) is a good candidate material due to its non-toxicity, cheapness, chemical inertness, high mechanical thermal stability as well as easily controlled morphology. Until now, different superhydrophobic γ-AlOOH coatings have been fabricated on different substrate with different hierarchical structure [44-46]. For example, Zhang et al [47] made a superhydrophobic boehmite membrane on austenitic stainless steels by soaking boehmite gel film in boiling water (CA ~152°). A superhyrophobic AlO (OH) film from anodic alumina oxide (AAO) surface with a copper catalyst was fabricated by a simple two-phase thermal method, and the water CA of 152.8° was obtained [48]. In addition, Wang et al [49] prepared a superhydrophobic γ-AlOOH nanosheets film on a glass substrate by a hydrothermal method and the water CA reached 160°±3°. However, there reports are only study the superhydrophobic property of γ-AlOOH membranes on glass or quartz substrate, and few reports focus on oil-water separation property of porous substrate. Undoubtedly, the investigation of fabricating γ-AlOOH superhydrophobic surfaces for oil-water separation is helpful for many branches of academic and industrial research.

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In this article, grass-like hierarchical γ-AlOOH membrane with highly efficient oil/water separation was fabricated by a simple template-free hydrothermal route using Al (NO 3)3·9H2O as an aluminum source and Na2C2O4 as precipitating agent. The stainless steel mesh is chosen as the substrate, which is widely used as engineering material. The advantage is low-cost starting materials, facile, template-free, and this grass-like structure film exhibits high water contact angle of 165° and oil-water separation efficiency reach 99.6%, which make it promising highly efficient separation materials for environmental applications. 2. Experimental 2.1 Materials High purity aluminum nitrate (Al(NO3)3·9H2O, 99.99%), sodiumoxalate (Na2C2O4, 99.99%), stearic acid (C18H36O2) were used as starting materials. All chemicals (Sinopharm Chemical Reagent Co.Ltd,China)were used as received, without further purification. The original stainless steel meshes with pore diameter of 250 mesh were cleaned sequentially with detergent, deionized water, acetone, deionized water. After being dried at 75℃ for 10min, they were disposed in piranha solution ( VH2SO4 : VH2O2  6 : 4 ) for 2h before being used. A series of experiments were performed by controlling the starting Al/C (Al (NO 3)3·9H2O/Na2C2O4) ratio. In a typical experiment, Al (NO3)3·9H2O and Na2C2O4 were dissolved in 80 mL of distilled water (Al/C mol ratio=1:0.1, 1:0.025, 1:0.01, Al (NO3)3·9H2O = 0.2 mmol). Contrast experiments were also done using 1 mmol, 3 mmol, 6 mmol of Al (NO3)3·9H2O, while the concentration of Na2C2O4 remained at a constant of 0.2 mmol. After being stirred at room temperature for 0.5h, the mixed Al(NO3)3·9H2O and Na2C2O4 solution was transferred into a 100 mL Teflon-lined stainless autoclave and stainless steel meshes were immediately inserted before the autoclave was sealed. Experiment conditions were controlled at 190℃ for 10h, with autogenous pressure in an electric 4

oven, and then cooled to room temperature naturally. The γ-AlOOH films on the substrates were obtained. The dried γ-AlOOH film was immersed in a stearic acid solution (0.05 M in 30ml ETOH) at room temperature for 1h, and then dried at 70℃ for 15min. The oil-water separation rests were done by using the mixture of 20 ml of oil (or organic solvent) and 20 ml of water. In order to estimate the separation efficiency of the as-prepared coated mesh versus the recycle number during oil/water separation, recycled experiment of diesel/water mixture was also carried out after oil/water separation experiment. 2.2 Instruments and characterization Morphological analysis was performed via a Zeiss Sigma HD scanning electron microscope and atomic force microscopy (AFM, Park NX10, and Korea). Crystal Structure of the product was identified by X-ray diffraction (XRD, DX-2500, and Empyrean) analysis using Cu Ka radiation. Surface chemical composition was investigated by X-ray photoelectron spectrometer (XPS, Model ESCALAB 250, and America). The contact angle (CA) of water and water droplets with different pH value (ranging from 2~12) were measured for 10uL droplets using an FDSA MagicDroplet-100 contact angle goniometer [50]. All reported contact angles represented an average value of six measurements of different positions on each sample surface. The separation efficiency of oil-water can be calculated by oil rejection coefficient (R %) as follows:

 C  R(%)  1  P   100  C0  Where C0 is the oil concentration of the original oil-water mixture and Cp is the oil concentration of collected water after separation. Two kinds of oil (cooking oil and diesel) were used in the experiment of oil-water separation. 5

3. Results and discussion

Fig.1. The XRD patterns of the 190℃ for 10h with 0.2 mmol Na2C2O4 and 2mmol Al(NO3)3·9H2O Fig.1 shows the XRD patterns of the Na 2C2O4 with 0.2mmol and Al(NO3)3·9H2O with 2mmol at 190℃ for 10h. The three strong peaks 43.58°、50.79° and 74.70° correspond to the (111)、(200) and (220) crystal planes of stainless steel mesh. The peaks at 29.04°、38.96° and 49.60° are indexed to orthorhombic γ-AlOOH (JCPDS 21-1307) (120)、(031) and (200) planes.

Fig.2. FESEM images of original stainless steel mesh: (a) low magnification, (b) high magnification

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d

1200

1000

Heigh(nm)

800

600

400

200

0

1

2

3

4

5

Length(μm)

g

Au

Fe O Au Fe Ni 0

1

Al

Cr Au 2

Au 3

4

5

6

Au Ni 7

8

9

E n ergy(K ev)

Fig.3. (a) low magnification FESEM images of γ-AlOOH film prepared at 190℃ for 10h with Na2C2O4 concentration of 0.2 mmol; (b)two-dimensional (2-D) AFM image of the area bounded by the black square in panel (a);(c) three-dimensional (3-D) AFM image of the area bounded by the black square in panel (a); (d) fluctuation of the height for the red line shown in panel (b); FESEM images of γ-AlOOH film prepared at 190℃ for 10h with Na2C2O4 concentration of 0.2 mmol: (e) high magnification; (f) cross sectional; (g) EDS spectrum of the (Al/O) coated mesh.

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The inserts in (g) show the SEM-EDS elemental mapping of Al and O; Figure 2a shows the original mesh has a pore size of about 600μm, and high magnification image shows that mesh wires have smooth surface. After hydrothermal treatment, it finds that a dense and uniform γ-AlOOH coat is grown on the original meshes (Figure 3a). Fig 3e-f shows the SEM image of the cross section of the product at high magnification. As shown in Fig 3e, allium mongolicum-like nano-grasses are grown on the surface of stainless steel mesh. The grass-like γ-AlOOH architectures distribute uniformly and have almost of the same shape and size. It can be observe that grass-like architectures film vertically grow on the surface of stainless steel mesh. The size of grass-like nanoarchitectures is about 0.6 to 1.5μm, and the width of their petals is about 0.07 to 0.4μm. The three-dimensional (3-D) morphology and roughness of the grass-like nanoarchitectures were further characterized by AFM (Atomic Foce Microscope). Figures 3b and 3c are two-dimensional (2-D) and three-dimensional (3-D) AFM images in the square region of Figure 3a, respectively. The height of the grass-like nanoarchitectures is concentrated in the range of 0~1200 nm and consistent with the SEM image of the cross-section of the product height. The surface roughness is measured of 142nm. As shown in Fig 3g, because the samples need to be sprayed gold before making FESEM, so except the main elements of the substrate(such as Fe、Cr and Ni), the Au also appears. The Energy Dispersive Spectrometer (EDS) results show that both Al and O exist on the surface of coated mesh. The inserts of Fig 3g shows the FESEM-EDS elemental mapping results, indicating a uniform distribution of the Al and O on the surface of the coated mesh.

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Fig.4. (a) XPS spectra of γ-AlOOH coated mesh prepared at 190℃ for 10h with Na2C2O4 concentration of 0.2 mmol; (b) O 1s XPS spectra of γ-AlOOH coated mesh Fig 4a shows XPS spectra of the γ-AlOOH coated stainless steel mesh. Elements of Fe, Al, C and O are found on treated stainless steel surfaces. The Fe 2p peak is made of stainless steel mesh. The binding energy data of C 1s at 284.9 eV are attributed to the ambient hydrocarbons (C−H and C−C) [51]. The Al 2p peaks at 74.3 eV show that the chemical state of aluminum atoms in the γ-AlOOH is Al (III). It has been proven that O 1s (531.58ev, Figure 4b) peaks could be

fitted into three peaks located at ≈530.1–530.3, ≈531.5–532.0, and ≈532.8–533.4 eV, which were designated as surface O2− and OH− groups and as free H2O, respectively [52]. This result further conform that the surface composition of coated stainless steel mesh is γ-AlOOH.

Fig.5. FESEM images of the products prepared at 190℃ for 10h with different concentrations of Na2C2O4: (a) 0.05 mmol; (b) 0.02 mmol In order to investigate the effect of concentration of Na2C2O4 on morphology, a series of

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concentration-related experiments were performed. When the concentration of Al(NO3)3·9H2O keep at 2mmol but the concentration value of Na2C2O4 being decrease to 0.05, grass-like γ-AlOOH architectures start to coexist with a small quantity of γ-AlOOH microspheres (Fig 5a). When the concentration of Na2C2O4 is changed to lower values (0.02), large quantities of γ-AlOOH microspheres appear and grass-like architectures almost disappear (Fig 5b).

160

157.1

158.2

165

C o n ta c t a n g le ( )

140 120 100 80 60 40 20 0 0.02

0.05

0.2

Na 2 C 2 O 4 (m m ol)

Fig.6. Relationship between different Na2C2O4 concentrations and water contact angle of the films obtained at 190℃ for 10h As shown in Fig 6, it shows the relationship between different Na 2C2O4 concentrations and contact angle of water of the as-prepared meshes at 190℃ for 10 h. It can be observed that the water contact angles of the prepared membranes at all concentrations are greater than 150°, which proved that the membrane has the property of superhydrophobic. When the concentration of Na2C2O4 is 0.02mmol and 0.05mmol, the water contact angle of the film is 157.1° and 158.2°, respectively. And when the concentration of Na 2C2O4 reaches 0.2mmol, the contact angle of water is the highest, reaching 165°. The formation of grass-like γ-AlOOH hierarchical superstructure can be explained as follows: firstly, the Na2C2O4 will hydrolyze and gives rise to OH- ions (Eqn. (1)) Al3+ will react with OHand form colloids Al (OH) 3. With subsequent increase in reaction time, sphere-like γ-AlOOH is 10

obtained from the early formed Al (OH) 3 colloids (Eqn. (3)). Secondly, under high temperature and pressure, the sphere-like γ-AlOOH will be transferred to layered γ-AlOOH under an acid condition. Meanwhile, C2O42- anions can be adsorbed on the positive surface of boehmithe because of the electrostatic attraction [45]. The weak hydrogen bonds between γ-AlOOH layered structures will break and curl under acid conditions and C2O42- adsorption, which will lead to the formation of γ-AlOOH 1-D narrowed nanosheets via a rolling mechanism [45, 53-55]. Thirdly, owing to the existing of OH- groups on the nanosheets surface, nanosheets can self-assemble into the grass-like 3D superstructures via oriented-attachment process [45, 56]. This process involves the following reactions: Na2C2O4+2H2O==2Na++2OH-+ H2C2O4

(1)

Al3++3OH- =Al(OH)3

(2)

Al(OH) 3=AlOOH+H2O

(3)

Decreases of the C2O42- anion concentration will result in reduction of hydrolyze and adsorption, which has not benefit for the transformation from sphere-like γ-AlOOH to layered

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Fig.7. FESEM images of the products prepared at 190℃ for 10h with different concentrations of Al(NO3)3·9H2O: (a) 1 mmol; (b) 3 mmol; (d) 6 mmol Figure 7 shows SEM images of the samples obtained by varying Al(NO3)3·9H2O concentration from 1 to 6 mmo1. As can be seen from Fig 7a, the boehmite membrane prepared with 1 mmol Al (NO3)3·9H2O exhibit dense and uniform surface with nanoflake-like structure architectures. When the concentration of Al (NO3)3·9H2O is increased to 3 mmo1, the morphology change to sheaf-like architectures assemblies. A further increase of the Al (NO 3)3·9H2O concentration to 6 mmo1 result in a loosened surface composing of large nanflakes with length of 4~6 um and width of 100 nm, accompanied with occasional microsphere-like particles (Figure 7c). The convention of morphology and structures may be closely related to the concentrations variation of Al3+. As the concentration of Al3+ decrease to 1mmol, the pH of the solution increases (initial pH=3.2, 10 h, pH=1.4), which lead to the formation of nanosheets of the γ-AlOOH. Further decreasing PH of the precipitation reduces the interfacial tension of the system, which will also decrease the internanoflake repulsion and favors the formation of sheaf-like hierarchical structure (Figure 7b). Strongly acidic conditions will form with Al 3+concentration of 6 mmol, which result in a weak hydrolysis of aluminium species. Under such condition, Al (OH) 2+ becomes the only significant hydrolysis product. It had been proven by ref [57] from the stability plots that such environment was not favorable for synthesis of AlOOH. So the loosened surface composing of large nanoflakes are formed (Figure 7c).

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Fig.8. Relationship between different Al(NO3)3·9H2O concentrations and water contact angle of the films obtained at 190℃ for 10h As shown in Fig 8, it shows the relationship between different Al(NO3)3·9H2O concentrations and contact angle of water of the as-prepared meshes at 190℃ for 10 h. When the concentration of Al(NO3)3·9H2O is 1mmol, 3mmol and 6mmol, the water contact angle of the film is 159.2°, 163.9° and 148.2°, respectively. Dense hierarchical structure amplifies surface roughness and improves superhydrophobic wettability.

Fig.9. (a) photograph of water droplet dropped on original stainless steel mesh, (b) photograph of water droplet on superhydrophobic γ-AlOOH coated stainless steel mesh surface, (c) Wetting of water and oil on γ-AlOOH coated stainless steel mesh ,(d) Cassie model

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The water contact angle (WCA) of the original mesh and as-prepared mesh were tested by a contact angle meter. Fig 9(a) shows that the initial mesh has a WCA of about 120°±1°, and the grass-like γ-AlOOH coated mesh has a WCA of about 165°±1°(Figure 8b). These results indicate the wetting states transition is controlled by changing surface morphology of mesh. Such a grass-like hierarchical structure amplifies surface roughness and result in superhydrophobic wettability. Figure 8c shows that the OCA (Oil contact angle) and WCA of the prepared superhydrophobic stainless steel mesh are 0° and 165°, respectively. The relationship between surface roughness and contact angle can be described by Cassie equation: cosθ* = f1cosθ-f2

(4)

Where f1 is the fraction of solid-water interface area and f2 (=1-f1) is the fraction of air-water interface area. In addition, θ* is the CA of hydrophobic surface and θ is the CA of primitive smooth surface. In our experiment, the WCA (θ) of primitive mesh is 125° and the WCA (θ*) of the superhydrophobic γ-AlOOH coated mesh is 165°. According to eq4, the values of f1 and f2 (8.00％ and 92.00％) can be calculated. That indicate that ~92％ of contact area are covered with the air between the water droplet and rough surface and only ~8％ of surface area is in contact with the water. This novel structure captures much more air in the surface of the product, which lead to a transformation from the liquid-solid two-phase contact into liquid solid three phase. The liquid-solid contact area is decreases and water contact angle increases, which increases the superhydrophobic property of the surface [52].

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Fig.10. (a) separation efficiency of oils or organic solvents and their separation time; (b) γ-AlOOH coated stainless steel mesh can withstand the height of hydraulic pressure; (c) recycled experiments for separating diesel from water; (d) The relationship between pH and the CA on the γ-AlOOH coated In order to investigate the oil-water separation properties of the superhydrophobic γ-AlOOH coated stainless steel mesh, the cooking oil and diesel were selected as representative for oil-water separation experiments. Fig 10 (a) indicates oil-water separation efficiency and time of γ-AlOOH coated mesh. The separation efficiency of cooking oil, diesel, edible oil, engine oil, hexane, petroleum ether and benzene reach 99.1%, 99.6%, 97.7%, 98.2%, 97.0%, 93.8% and 98.4%, respectively. Various oil-water mixtures can be separated well in a short time (no more than 2.5 minutes). During oil-water separation process, the intrusion pressure of water is also important factor for the evaluation of separation efficiency, and the experimental intrusion pressure value can be calculated by following Eq (5): Pexp = ρghmax(5) 15

Where ρ is the density of water, g is the gravitational acceleration, h max is γ-AlOOH coated mesh can support the maximum height of water, and Pexp is the experimental water intrusion pressure. When the water phase is above the Pexp, the water will penetrate through the rough mesh. In figure 10(b), the maximum bearable height achieved is 22.4 cm, and the water intrusion pressure is 2.20 kPa, which indicates water can pass through the mesh above this pressure. The oil or organic solvents intrusion pressures are all 0. This means that the prepared nanostructures exhibit favorable pressure resistance.

Recycled test exhibit that the as-prepared γ-AlOOH coated

mesh maintain high separation efficiency after 40 recycles of oil-water separation (diesel and water) (figure 10(c)).

The dashed line in Figure 10d shows the relationship between PH and

superhydrophobicity, and increasing PH has little or no effect on the film’s CA. The CA is vary slightly from 162.9±2.0° to 164 ± 0.1°. Consequently, above results show that the as-prepared mesh has good stability and ability for separating a large amount of oil-water mixtures. 4. Conclusions In summary, we fabricated the hierarchical γ-AlOOH membrane with a grass-like morphology on stainless steel mesh via a simple template-free hydrothermal method. Meanwhile, the

obtained grass-like

γ-AlOOH

membrane

has

excellent

superhydrophobicity and

superlipophilicity property; the water contact angle is 165°±1°, the oil contact angle is 0°. The separating efficiency of diesel reaches 99.6% and maintains high separation efficiency after 40 cycles of separation. The cassie model was used to explain the effect of roughness on wetting behavior. The contact area between droplets and micro/nano structures is only 8%, which increase the superhydrophobic character of the surface. The prepared stainless steel mesh has an oil intrusion pressure of 0 Pa and a high water pressure intrusion pressure of 2.2 kPa. Furthermore,

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the film remains stable even in a wide range of pH environments, which makes it promising application in large-scale and high-efficient oil/water separation filed. Acknowledgements This work was financially supported by the Open Project Program of Key Laboratory of Inorganic Functional Materials and Devices, Chinese Academy of Sciences (Grant No.: KLIFMD-2015-06). References [1] M.A. Shannon, P.W. Bohn, M. Elimelech, J.G. Georgiadis, B.J. Mariñas, A.M. Mayes. Science and technology for water purification in the coming decades, Nature. 452 (2008), pp. 301-10 [2] J. Ju, K. Xiao, X. Yao,H. Bai , L. Jiang, Bioinspired conical copper wire with gradient wettability for continuous and efficient fog collection, Adv. Mater. 25 (2013), pp. 5937-5942 [3] H. Shi, Y. He, Y. Pan, H. Di, G. Zeng , L. Zhang, C. Zhang, (2016) A modified mussel-inspired method to fabricate TiO2 decorated superhydrophilic PVDF membrane for oil/water separation,J. Menbrane. Sci. 506 (2016), pp. 60-70 [4] Q. Ma, H. Cheng, A.G. Fane, R. Wang, H. Zhang, Recent development of advanced Materials with special wettability for selective oil/water separation, Small. 12 (2016), pp. 2186-2202 [5] J. Li, R. Kang, X. Tang, H. She, Y. Yang, F. Zha, Superhydrophobic meshes that can repel hot water and strong corrosive liquids used for efficient gravity-driven oil/water separation, Nanoscale. 8 (2016), pp. 7638 [6] X. Zeng, L. Qian, X. Yuan, C. Zhou, Z. Li, J. Cheng, S. Xu, S. Wang, P. Pi, X. Wen, Inspired by stenocara beetles: from water collection to high-efficiency water-in-oil emulsion separation, Acs. Nano. 11 (2017), pp. 760 17

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Highlights ►A novel glass-like superhydrophobic and superoleophilic boehmite(γ-AlOOH) coated stainless mesh was fabricated by a simple template-free hydrothermal method . ►The coated mesh exhibited an extremely water contact angle of 165°±1°,and the oil contact angle is 0°. ►The wettability mechanism relies on micro-nano scale hierarchical structure ►The obtained film could be used to separate oil-water mixtures and high efficient diesel-water separation of 99.6%. ►The prepared stainless steel mesh has a high water pressure intrusion pressure of 2.2 kPa.

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Graphical Abstract Ming Zhang1, Zhilun Wu1, Fancheng Meng1, 2*, Huixing Lin2* (1.College of Materials Science and Engineering, Chongqing University of Technology, Chongqing, 400054, P.R. China;2.Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences,Shanghai,201800, P.R. China)

The grass-like γ-AlOOH architectures distribute uniformly and have almost of the same shape and size. It can be observe that grass-like architectures film vertically grow on the surface of stainless steel mesh.

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Corresponding author. Tel./fax: +86 23 62408527 E-mail address: [email protected] (F.C. Meng)  Corresponding author. Tel./fax: +86 21 69906356 E-mail address: [email protected] (H.X. Lin) 26