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Fluorine-Induced Superhydrophilic Ti Foam with Surface Nano-Cavities for Effective Oil-in-Water Emulsion Separation Zhi-Yong Luo, Shu-Shen Lyu, Ya-Qiao Wang, and Dong-Chuan Mo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04059 • Publication Date (Web): 28 Dec 2016 Downloaded from http://pubs.acs.org on December 30, 2016

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Industrial & Engineering Chemistry Research

Fluorine-Induced Superhydrophilic Ti Foam with Surface Nano-Cavities for Effective Oil-in-Water Emulsion Separation Zhi-Yong Luo, Shu-Shen Lyu, Ya-Qiao Wang, and Dong-Chuan Mo* School of Chemical Engineering and Technology, Sun Yat-sen University, Guangzhou 510275, P. R. China KEYWORDS: Ti foam; anodization; FIS; nano-cavities; oil/water separation; superoleophobic ABSTRACT Recently, oil/water separation has attracted intensive attention due to the frequent crude oil spill accidents and the increasing amount of industrial wastewater. Ti-based materials are nontoxic and environment-friendly for oil/water separation, however, there is few attentions on this field. In the present work, we introduced, for the first time, the surface -O-Ti-F groups onto Ti foam by a simple anodization in fluorine-containing electrolyte to form superhydrophilic membrane for oil-in-water emulsion separation, which was proved to be excellent with the assist of surface nano-cavities. The water permeability of anodized Ti foam (ATiF) is elevated by about 10 times as compared to the original one, and the oil/water separation efficiency is above 99%

with

the

well

anti-corrosive

properties.

What’s

more,

this

fluorine-induced

superhydrophilicity (FIS) can be applied to metals and semi-metals for many other applications like self-cleaning, surface modification of catalysts, removal of heavy metal ions, etc.. 1 ACS Paragon Plus Environment


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INTRODUCTION Oil/water separation is a global challenge on account of the frequent crude oil spill accidents1 and the increasing amount of industrial wastewater. Traditional polymeric membranes face enormous challenge due to their energy-intensive separation process and easy to be contaminated.2 In recent years, membranes with special wettability as well as gravity-driven separation process have attracted intensive attentions since Jiang and his co-workers reported the superhydrophobic mesh decorated by polytetrafluoroethylene (PTFE) for effective oil/water separation in 2004.3 However, a water layer tends to form between oil and membrane due to the higher density of water, which goes against the separation process.4 This kinds of materials are more suitable for water-in-oil emulsion separation5,6 and oil absorption.7-10 Inspired by fish scales,11 superhydophilic and under-water superoleophobic porous materials come into sight of researchers. Nowadays, decorating metal mesh via hydrophilic components like hydrogel,12-14 surfactant,15,16 copper,17 nickel,18 Cu(OH)2,19 palygorskite,20 tungsten oxide,21 TiO2,4,22 zeolite,23 etc. is the main idea to design superhydrophilic membrane. Although excellent oil/water separation performance is achieved, it faces enormous issues in applications. For instance, the mechanical strength of mesh coated by hydrophilic inorganics is insufficient when faced scratch or friction cycles, which is mainly due to the poor adhesive force between the inorganics and mesh.24 Metal foam is an ideal matrix for oil/water separation25-27 due to its porosity and appropriate strength, among which Ti foam possesses superior advantages like non-toxic, enviromently friendly etc.. Up to now, there is few attention on Ti foam for oil/water separation. Li and coworkers reported Ti foam based on hierarchical TiO2 nanotubes for oil/water separation, flowthrough photocatalysis and self-cleaning in 2015,27 which is supported by its UV-induced 2 ACS Paragon Plus Environment

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superhydrophilicity. However, these procedures can not be proceed in the absence of UV-light. Moreover, the bottom-closed tubular structure of TiO2 nanotube is disadvantage of forming superhydrophilic surface. Fortunately, it had been reported that surfaces with halogen (F, Cl) terminal groups exhibit intrinsic hydrophilicity.28,29 In our previous work,30 we demonstated that intrinsic superhydrophilic TiO2 surface could be achieved by introducing surface -O-Ti-F groups, which is called “fluorine-induced superhydrophilicity (FIS)” and provides a new perspective to stable superhydrophilic Ti-based materials in all conditions. Meanwhile, the pore sizes of the Ti foam can be comparable with or smaller than those of the emulsified oil droplets via a suitable preparation technology. Therefore, superhydrophilic Ti foam with surface -O-Ti-F groups may be the ideal porous membrane for effective oil/water separation, especially oil-in-water emulsion separation.

Scheme 1. Schematic of the fabrication of fluorine-induced superhydrophilic Ti foam and its application for efficient oil-in-water emulsion separation. Herein, we reported the surface of anodized Ti foam (ATiF) consists of -O-Ti-F groups and nano-cavities, which is beneficial to the formation of superhydrophilic surface. Although the surface –OH or carbon species may also affect the wettability of AtiF, those were not indicated in Scheme 1 because they are the secondary factors.30 This ATiF shows 10 times water pemeability higher than the original one, and owns remarkable oil-in-water separation 3 ACS Paragon Plus Environment


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performance (separation efficiency > 99%) with the excellent anti-corrosive properties. Further, we demonstrated the role of surface -O-Ti-F groups for oil/water separation. This fluorineinduced superhydrophilic Ti foam has great potential in applications. The ATiF was synthesized by a simple anodization in fluorine-containing electrolyte (see Scheme 1 and Experimental section). The -O-Ti-F groups and nano-cavities formed on the surface during anodization can lead to superhydrophilic surface, and the thin layer of adsorded water on the surface is the keypoint for effective oil/water separation. EXPERIMENTAL SECTION Preparation of superhydrophilic Ti foam. Before anodization, Ti foam (purity ≥ 99.7%, size 3 cm × 3 cm, accuracy 20 µm, thickness 1 mm) was cleaned in deionized water, ethanol and deionized water via ultrasonic cleaner (50 kHZ), respectively, and then dried naturally.31 Anodization was carried out at 45 V for 8 h in a two-electrode electrochemical cell18 in which used Ti foam as anode and a piece of Ti foil (purity 99.7%, size 3 cm × 3 cm) as the cathode, the distance between the two electrodes is 1.5 cm. The electrolyte consists of 0.37 wt% NH4F, 18.00 wt% H2O and 81.63 wt% ethylene glycol. The bath temperature was kept at 20 °C. After anodization, the Ti foam was rinsed by using amount of deionized water to clean up the residual electrolyte, especially the ethylene glycol, and dried spontaneously. Materials characterization. The morphologies of the specimen were characterized by a scanning electron microscope (SEM, JSM-6510LV). The surface components of the specimen were analysed by an X-ray photoelectron spectrum (XPS, ESCALab250). The surface roughness was analysed by a scanning probe microscope (SPM, Dimension Fastscan), we measured three points of each specimen for statistics of surface roughness. 4 ACS Paragon Plus Environment

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The contact angle and dynamic effect of 5 µl deionized water droplet spreading out on the interfaces was carried out via a high-speed camera (Vision Research Phantom V.211 capturing at 3000 frames per second). The under-water oil contact angle and slide angle of 5 µl oil was captured via a high-speed camera and accessary adjusting bracket. The under-water adhesive test was carried out via a steel needle to manipulate the oil droplet (see Figure S1), for which the steel needle was manipulated by hand. Owing to the stronger interaction between the oil droplet and the steel needle, the oil was adhere to the steel needle, the process was recorded via a highspeed camera. Therefore, the adhesive effect between oil and ATiF was demonstrated. Oil/water separation. In this section, hexane, iso-octane, petroleum ether (three kinds of saturated oils), paraxylene (a kind of unsaturated oil) and kerosene (a kind of mineral oil), five kinds of oil models were applied for oil/water separation. The anodized Ti foam (AtiF) were placed between two quartz tubes (d = 2 cm) with flange, and fastened via screws. The oil/water emulsion (1g oil in 60 g water under 80 KHZ ultrasonic for 5 min) were separated from the upper tube to the lower tube. After separation, the original and separated water (60 ml) were acidized (pH = 1 to 2) via 1M HCl and added 2g NaCl to demulsify. Then it was extracted twice by using total 40 ml (20 ml + 20 ml) CCl4. The extractant was dried by anhydrous Na2SO4. The oil content in CCl4 was measured via an infrared oil content analyzer (OIL-8, China). Anti-corrosive experiments. The anti-corrosive property of ATiF was illustrated by using 1 M HCl, 1 M NaOH and 10 wt% NaCl solution, respectively.17,32,33 The Ti ion concentration in corrosive solution was analysed via a PE plasma atomic emission spectrometer (AES, Optima 8300), in which the solution samples were prepared by 100 mg anodized Ti foam immersed in 1 M HCl, 1 M NaOH and 10 wt% NaCl for 2 h and 8 h, respectively.

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RESULTS AND DISCUSSION Characterization of materials. As shown in Figure 1a, the Ti foam consists of irregular Ti particles with relative smooth surface (see Figure 1b), the gaps between Ti particles are ranging from several micrometers to one hundred micrometers. From Figure 1c, we can see the macrographic morphologies were almost unchanged after anodization, however, the surface of Ti particles are composed of nano-cavities (see Figure 1d), which is mainly due to the corrosion of F ions during the anodization. It is well-known that TiO2 nanotubes are generated via Ti anodization in fluorine-contained electrolyte under suitable conditions.27,34 However, compact oxides layer, nanocavities and nanopores have been also reported under specific conditions.35 In this work, the anodization conditions are also originated from the conditions of fabricating TiO2 nanotubes via anodization. However, we elevated the concentration of F- to break down the balance condition of forming TiO2 nanotubes. This is why we got nanocavities, not nanotubes. As a superhydrophilic membrane for oil/water separation, the trapped water serves as a repulsive liquid phase for oils to contact with the membrane directly, thus resulting in more oleophobic interfaces as more water is captured, this is superior to achieve a better separation performance.19 Nevertheless, the bottom-closed tubular structures of TiO2 nanotubes will trap air layer and repel the water droplet, resulting in inferior wettability. In contrast, the surface nanocavities can capture more water for the better oil/water separation performance (see Figure S2). From Figure 1e, we can see the thickness of ATiF that composed of irregular Ti particles is about 1 mm. EDS analysis indicated that ATiF consists of 25.19 at% Ti, 52.02 at% O, 11.67 at% F and 11.12 at% C, four kinds of elements. Aside from the C, which is belonged to the carbon species absorption of specimen, the O and F are originated from surface oxy-fluoridation during the anodization. What’s more, the ratio of Ti to O is close to 1:2, meaning that the top layer of Ti 6 ACS Paragon Plus Environment

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foam is TiO2, and the O atoms of TiO2 are partly replaced by F atoms to form -O-Ti-F terminal groups.30

Figure 1. The morphologies and components characterization of Ti foam. The SEM image of Ti foam (a) before and (c) after anodization. (b) and (d) are the corresponding high-magnification SEM images of (a) and (c). (e) the side-view and (f) the EDS characterization of Ti foam after anodization.



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Figure 2. The XPS characterization of Ti foam after anodization. (a) the full-spectrum of XPS analysis, the upper-left corner is the detail content of elements. (b), (c) and (d) are the high resolution XPS analysis of Ti 2p, O 1s and F 1s, respectively. It is well-known that wettability of solid interfaces mainly relies on its surface energy and roughness,36 and surface energy depends on the surface components. As shown in Figure 2a, we analysed the surface components of ATiF via XPS. It is noticed that the surface of ATiF consists of Ti, O, C and F, which is consistent with the EDS results. However, the content of F is decreased slightly, which is mainly owing to the fast migration of F versus O,37,38 thus results in the higher content of F in inner layer. the content of carbon species is increased due to the its surface absorption. From Figure 2b, the Ti 2p1/2 peak and Ti 2p3/2 peak are confirmed at 464.3 eV and 458.5 eV, respectively, which are the typical values for Ti4+.39,40 The O 1s spectrum is split into four peaks at 529.7 eV, 530.4 eV, 531.4 eV and 532.5 eV, respectively. The peak at 529.7 eV is attributed to typical Ti-O bonds,41 and the peaks at 530.4 eV, 531.4 eV and 532.5 eV are usually associated with defects,42 surface Ti-OH species and surface C-O bonds,43 respectively (see Figure 2c). Figure 2d shows the F 1s spectrum, the measured binding energy is 684 eV, a typical value for fluorinated TiO2 systems such as TiOF2 or the surface -O-Ti-F species.44 These are the further evidences that the surface of ATiF is composed of TiO2 subject and -O-Ti-F terminal groups, which benefits the formation of superhydrophilic surfaces. Ti + 2H2O → TiO2 + 4H+ + 4e-

(1)

TiO2 + 6F- + 4H+ → TiF62- + 2H2O

(2)

TiO2 + nF- + nH+ → TiO(2-n/2)Fn + (n/2)H2O

(3)

During the anodization, the chemical reactions between Ti foam and electrolyte were taken place as the equation (1) – (3). At the beginning, the surface of Ti foam were turned into TiO2 as 8 ACS Paragon Plus Environment

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equation (1), then the surface nanocavities were generated as equation (2) owing to the corrosivity of F ions. At last, the O atoms of TiO2 were partly replaced by F atoms to form surface -O-Ti-F groups as equation (3), which is mainly due to the decreasing of F ions as the processes go on. Further, we analyzed the surface roughness of ATiF by using scanning probe microscope (SPM). As we can see in Figure 3a, the surface of Ti particle is smooth relatively, while it turns into rough after anodization in fluorine-containing electrolyte (see Figure 3b). Following, the statistical data of surface roughness factors are shown in Table 1, the Rq of original and ATiF are 1.85 ± 0.04 nm and 35.4 ± 1.3 nm, respectively. Meanwhile, the surface roughness factor of ATiF is 1.19 ± 0.04, significant larger than the original one.

Figure 3. The surface roughness analysis of Ti particle via scanning probe microscope (SPM). The SPM profile analysis and 3D images of the surface of Ti particle (a) before and (b) after anodization.



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Table 1. The surface roughness parameters of Ti particle of Ti foam before and after anodization (3 µm × 3 µm)

Surface

Rq (nm)

Surface area (µm2)

Projected surface area (µm2)

Roughness factor (r)

Original Ti foam

1.85 ± 0.04

9.07 ± 0.06

9.00

1.01 ± 0.01

Anodized Ti foam

35.4 ± 1.3

10.7 ± 0.4

9.00

1.19 ± 0.04

As is mentioned in previous works30,45 that the surface wettability can be enhanced via surface roughness, which can be described by the Wenzel model46 as following formula (4): cosΘ’ = r cosΘ

(4)

where Θ’ and Θ are the contact angle on the rough surface and flat surface, respectively. r is the roughness factor, which is defined as the ratio of the surface area to the projected surface area (see Tab. 1), in which r >1, cosΘ’ > cosΘ, so Θ’ < Θ. Therefore, the wettability of ATiF is enhanced via the surface nano-cavities. Droplet tests, especially the measurement of water contact angle (WCA), underwater oil contact angle (OCA) and oil sliding angle (OSA), are significant to forecast the oil/water separation performance of membrane. As shown in Figure 4a, 5 µl water droplet spreading out on original Ti foam was recorded via a high-speed camera at 3000 frames per second. The droplet spreaded out within 30 ms and permeated through the original Ti foam within 1960 ms, the WCA is about 70 degrees. To our expectation, the ATiF is approach to superhydrophilic surface with a pimping WCA, and the permeability of ATiF is about 10 times higher than the original one (see Figure 4b). The droplet emission shown in Figure 4b is mainly due to the 10 ACS Paragon Plus Environment

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superhydrophilicity of ATiF.47 The excellent wettability of ATiF is mainly attributed to the surface -O-Ti-F groups and enhanced by the porous architectures (see Figure 1c) combining with the surface nano-cavities (see Figure 1d and Figure 3b).

Figure 4. Droplet tests of Ti foam. High-speed dynamic images of water droplet spreading out on Ti foam (a) before and (b) after anodization. (c) the underwater oil adhesion for Ti foam after anodization. (d) the underwater oil contact angle and oil sliding angle for five selected oils. The oil model is hexane, and the water droplet and oil droplet are 5 µl. Low underwater oil adhesion is beneficial to the efficient oil/water separation. In the present work, we manipulated the oil droplet via a steel needle to demonstrate the underwater oil adhesive phenomena. From Figure 4c, we can see the OCA of ATiF is up to 160°, the adhesive force is negligible (see Figure 4d), which is the fine premise of following oil/water separation.



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Then, we measured the underwater OCA and OSA of ATiF, in which five kinds of oil droplet (5 ul) are applied. As shown in Figure 4d, the ATiF shows large OCA (155° - 160°) combining with small OSA (2° - 5°). The state of the oil droplet can be described by the Cassie model,11,46 and the contact angle can be expressed as formula (5): cosΘ’OCA = f cosΘOCA + f - 1

(5)

where Θ’OCA and ΘOCA are the under-water oil contact angle on the rough surface and flat surface, respectively, f is the area fraction of the solid, which is defined as the ratio of the actual contact area by the oil droplet to the whole area of the Ti foam. A smaller area fraction means a lower chance of the oil droplet contacting the solid surface, and the larger OCA in water. The surface roughness of ATiF is significant enhanced owing to the existence of nano-cavities, resulting in a smaller f, which is in favour of the formation of membranes for oil/water separation with excellent performance.19,48 It is worth noting that the superhydrophilicity and the underwater superoleophobicity of ATiF exhibit remarkable stability under stored in normal laboratory environment for 2 months (see Figure S3). Oil/water separation. The separation of oil-in-water (O/W) emulsion is a challenge for membrane separation due to the tiny size of oil droplet.19,49-51 To separate components of an emulsion, the pore sizes of the filters need to be comparable with or smaller than those of the emulsified oil droplets.52,53 Figure 5a shows the visual performance of O/W separation, in which the white emulsion turned into transparent after separation. Then we analysed the O/W emulsion and the separated water via an optical microscope, it is noticed that there are thousands of O/W droplets in emulsion, while it disappeared after separation, resulting in a transparent solution. Further, we analysed the oil content in the separated O/W emulsion as shown in Figure 5b, the residual oil content for hexane, iso-octane, petroleum ether and kerosene is within 60 - 80 ppm, 12 ACS Paragon Plus Environment

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showing the similar separation performance. To our surprise, the separation performance of ATiF for paraxylene is excellent with the negligible residual oil content (about 6 ppm). The separation efficiency of ATiF for a selection of oils is above 99%. Specially, the separation efficiency of ATiF for paraxylene-in-water emulsion approaches to 100%, which is mainly due to its larger size of oil droplets in emulsion (see Figure S4). It is significant to the treatment of paraxylene-containing or even phenyl-containing industrial wastewater.

Figure 5. The oil-in-water emulsion separation performance and anti-corrosive properties of ATiF. (a) the visual performance and (b) oil-in-water emulsion separation performance. (c) the OCA plotted against the soak time in corrosive solutions. (d) the separation efficiency of oil-incorrosive solution separation. (e) the XPS spectrums of F 1s of ATiF before and after immersed in corrosive solution for 2 h, respectively. (f) the concentration of Ti ions in corrosive solutions after immersing for 2 h and 8 h, respectively. Anti-corrosive property is a key factor of membranes for applications. To date, many research demonstrated the well the anti-corrosive property of membranes in strong acidic, alkaline and salt solutions, in which the meshes were coated by organic,32 inorganic-organic mixture,33 13 ACS Paragon Plus Environment


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metals17,54 with nanostructures etc. to repel strong corrosive liquids. The anti-corrosive property of ATiF was illustrated by using 1 M HCl, 1 M NaOH and 10 wt% NaCl solution, respectively. As shown in Figure 5c, the OCA oscillates in a small scale for each case even immersed for 2 h. Particularly, the OCA in 1 M NaOH is smaller than other two cases, which is mainly due to the weaker interaction between the nucleophilic NaOH solution and the electron-rich surface -O-TiF groups of Ti foam according to Lewis's theory of valency, thus resulting in a more wafery solution layer between Ti foam and oil-droplet as well as a smaller OCA for 1 M NaOH solution. Fortunately, the OCAs are larger than 150° for all conditions, indicating that the well oil/water separation performance can be achieved. From Figure 5d, we can see that the separation efficiency is above 98.5% even for 1 M NaOH. Figure 5e shows the XPS spectrums of F 1s of ATiF before and after immersed for 2 h, we can see the content of surface -O-Ti-F species of Ti foam almost remains the same. The surface morphologies, especially the nano-cavities, also shows highly stability after immersing for 8 h (see Figure S5). What’s more, the concentration of Ti ions in corrosive solutions are lower than 10 ppm (see Figure 5f). In a word, the surface superhydrophilic -O-Ti-F species as well as nano-cavities keep stable in corrosive liquids, and the OCAs also almost remain the same (see Figure S6). This ATiF shows remarkable anticorrosive properties. Removal of surface F species. To further study the effects of surface -O-Ti-F groups on the oil/water separation, we annealed the ATiF at 200 °C under air atmosphere for 2 h to remove the surfaces F species. As shown in Figure 6a-b, the content of surface F species is degenerated from 9.93 at% to 2.23 at%, which may be attributed to the replacement of F atoms by O atoms at high temperature. Meanwhile, the WCA also increases to 52° with the degradation of wetting properties (see inset-photograph of Figure 6b). However, the surface polar components like


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defects etc. are elevated (see Figure S7) and the surface polar C-O species that originated from organic contaminants are decreased after annealed (see Figure S8), meaning that the wettability of ATiF can be enhanced via heat treatment, which is in accordance with the previous reports.55 This conflicting phenomenon can be described that the fluorine-induced superhydrophilicity (FIS) is superior to thermally-induced superhydrophilicity55. The degeneration of wettability of ATiF is mainly owing to the decreasing of surface -O-Ti-F groups. From Figure 6c, we can see the water permeability of ATiF also decreased after removing the surface -O-Ti-F groups. What’s more, the underwater adhesive force is significant enhanced with a 142° OCA (see Figure 6d). In a word, the wettability as well as the predictable oil/water separation performance of the ATiF is degenerated. Fortunately, the FIS of ATiF is stable at normal temperature and can endure about 100 °C under air atmosphere,30 which is significative to oil/water separation and many other applications.

Figure 6. Removal of surface F species. The XPS analysis of (a) full-spectrum and (b) F 1s of ATiF before and after annealing, respectively. (c) high-speed analysis of water droplet permeating through ATiF and (d) underwater oil adhesive effect of ATiF after annealing.



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CONCLUSIONS In summary, we introduced, for the first time, fluorine-induced superhydrophilicity (FIS) for effective oil/water separation, in which we synthesized superhydrophilic Ti foam by simple anodization in fluorine-containing electrolyte. Owing to the surface -O-Ti-F terminal groups and the assistance of the surface nano-cavities, this anodized Ti foam (ATiF) shows stable superhydrophilicity, underwater ultra-low adhesive superoleophobicity and excellent oil-in-water separation performance (separation efficiency > 99%) with the well anti-corrosive properties. The water permeability of ATiF is elevated by about 10 times as compared to the original one. After removing the surface F species by annealing at 200 °C, the wettability as well as the predictable oil/water separation performance of the ATiF is degenerated. It possesses potential applications for hydrogen evolution reaction,56 self-cleaning,57 fog-harvesting, removal of heavy metal ions,58 etc. due to the remarkable properties of ATiF such as stable superwettability, porosity, non-toxic, environment-friendly, and so on. we highlight our present work in the following five main aspects: (1) it is the first attempt to introduce FIS for oil/water separation and turned out to be efficient; (2) we synthesized the surface nano-cavities, rather than nanotubes, to benefit the formation of superhydrophilic TiO2 surfaces; (3) Ti-based porous membranes show superiority for water treatment, especially oil/water separation, due to its stability and non-toxic; (4) this stable FIS is an ideal supplement for photo-indued suerhydrophilicity of TiO2-based materials in all conditions; (5) this FIS can be applied to metals and semi-metals for many other applications. ASSOCIATED CONTENT Supporting Information


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Detail supplementary experimental materials. Figure S1: The set-up diagram for the underwater adhesive test. Figure S2: The comparison of nanotubes and nanocavities for capturing water. Figure S3: The high-speed dynamic water droplet test and underwater adhesive test of anodized Ti foam (ATiF) after stored for 2 months. Figure S4: The micrographs of oil-in-water (O/W) emulsion. Figure S5: SEM images of ATiF after immersed in HCl, NaOH and NaCl for 8 h, respectively. Figure S6: The OCAs of ATiF immersed in corrosive solutions for 2 h and 8 h, respectively. Figure S7-S8: XPS analysis of O 1s and C 1s of ATiF before and after annealed, respectively. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *Tel: +86-020-84113985. E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by Guangdong natural science foundation under Grant No.2014A030312009NSFC. ABBREVIATIONS ATiF, anodized Ti foam; FIS, fluorine-induced superhydrophilicity; WCA, water contact angle; OCA, underwater oil contact angle; OSA, underwater oil sliding angle; SEM, scanning electron microscope; TEM, transmission electron microscope ; EDS, energy dispersive spectrometer; XPS, X-ray photoelectron spectrum ; SPM, scanning probe microscope; AES: atomic emission spectrometer. 17 ACS Paragon Plus Environment


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Fluorine-Induced Superhydrophilic Ti Foam with ... - ACS Publications

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