Superhydrophobic Metal-Organic Framework Membrane with Self

Subscriber access provided by University of Winnipeg Library

Article

Superhydrophobic Metal-Organic Framework Membrane with SelfRepairing Ability for High-Efficiency Oil/Water Emulsion Separation Yahui Cai, Dongyun Chen, Na-Jun Li, Qing-Feng Xu, Hua Li, Jing-Hui He, and Jian-Mei Lu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05793 • Publication Date (Web): 21 Dec 2018 Downloaded from http://pubs.acs.org on December 25, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Superhydrophobic Metal-Organic Framework Membrane with Self-repairing for HighEfficiency Oil/Water Emulsion Separation Yahui Cai, Dongyun Chen,* Najun Li, Qingfeng Xu, Hua Li, Jinghui He and Jianmei Lu* College of Chemistry, Chemical Engineering and Materials Science, Collaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University, NO. 199, Ren’ai Road, Suzhou, 215123, China. E-mail address: [email protected], [email protected].

1 Environment ACS Paragon Plus

ACS Sustainable Chemistry & Engineering 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: Special wetting characteristic surfaces typically combine low surface energy micro/nanoscale structures; and special wetting coating material applications are wide-ranging, including self-cleaning and drag-reducing surfaces to anti-adhesives. However, the poor durability of these special wetting surfaces greatly limits their practical application, and external conditions such as illumination, friction and corrosion can damage and destroy the low-surfaceenergy surface of the superhydrophobic coatings. These low-surface-energy materials must then be redeposited to restore the superhydrophobic coatings, which is cost and time prohibitive. Endowing superhydrophobic coatings with a self-repairing performance could effectively solve these durability problems. Here we report a robust, superhydrophobic metal organic frameworklayer membrane with a repair ability. This composite membrane was prepared by a simple wet-chemistry coating technique consisting of fluorinated alkyl silane, a fluorocarbon surfactant, and a hydrophobic ZIF-90 membrane. This study represents a durable superhydrophobic membrane for sewage treatment application.

KEYWORDS: Self-repairing, zeolitic imidazolate framework (ZIF-90) membrane, oil-water emulsions separation, superhydrophobicity, surface chemistry


Page 2 of 27

Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Super-lyophobic surfaces have attracted widespread attention in environment fields.1-4 The superhydrophobic or superoleophobic surface depending on the liquid-repelled, which usually has a liquid contact angle higher than 150°. Super-lyophobic materials great advantage in selfcleaning, anti-pollution and anti-corrosion. The practical applications mainly involve separation of oil/water mixture,5-10 microfluidic devices,11-12 and separation of stabilized oil/water emulsions.13-14 As we all know, the oily wastewater consists of an immiscible mixture and a stabilized emulsion in most cases. As we all know, the stabilized water/oil emulsions in the oily wastewater possesses a droplet size < 20 μm, and thus the separation of these stabilized emulsions from oily wastewater remains a worldwide challenge.15-16 Recently, these superrepellent materials have also been used to separate the stabilized emulsions, such as reported for an inorganic nanowire-coated mesh,17 a plasma membrane-associated PMAPS-g-PVDF membrane,18 and graphene-oxide-coated membrane.19 Though numerous oil/water emulsionseparating super-repellent materials have been successfully prepared, most exhibit poor durability and mechanical robustness.20-21 For example, exposure to chemical oxidation in air, illumination or friction can lead to permanently lose super-repellent property of these materials. Therefore, it is necessary to improve their durability in practical applications.22-24 Plants maintain their superhydrophobicity by repairing the surface after destroyed, this is the self-repairing performance.25-26 Therefore, the superhydrophobic materials with a self-repairing performance could effectively solve the above problems. Self-repairing performance is extremely effective for improving durability because of its regenerating ability suffer damage from external conditions. Self-repairing materials have been previously reported, as have great advantages in practical applications, such as that reported by Li et al., comprising chemical vapor 3 Environment ACS Paragon Plus


deposition of a fluorinated carbon chain on a porous surface to achieve a self-repairing surface.27 Lin et al. have also reported that, by applying a coating of fluorinated-decylpolyhedral oligomeric silsequioxane and fluoroalkyl silane onto the fabric, they could produce a selfrepairing superamphiphobic surface. Herein we report a self-repairing superhydrophobic ZIF-90 membrane for the first time, using an improved hydrophobic zeolitic imidazolate framework (ZIF-90), via the wet-chemistry coating technique shown in Scheme 1. Zeolite imidazole frameworks are very robust porous coordination polymers (MOFs) exhibiting excellent chemical stability and flexibility. We selected the hydrophobic ZIF-90 layer because of its cheap and easy preparation and its wellestablished micro/nanoscale surface on various substrates. The coating herein consisted of a frequentlyused, easily available fluoro-containing polymer, also called FAS, a hydrophobic ZIF-90 layer and Zonyl®321 (a fluorinated co-polymer comprising fluoropolymer core and polyurethane shell) as the hydrophobic parts and fluorocarbon surfactant, respectively. The micro/nanoscaled hierarchical structures preparation was the critical step. The principle of selfrepairing is that a lot of fluoroalkylsilane moieties preserve in coarse porous structure as healing agents.28-29 Once the fluoroalkylsilane on the surface is destroyed and disappeared, the preserved fluoroalkylsilane could again migrate to the surface under heat treatment conditions to re-acquire superhydrophobicity of the composite membrane.30


Page 4 of 27

Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. Schematic illustration of the procedure for preparation of a durable self-repairing superhydrophobic ZIF-90 membrane via a wet-chemistry coating technique on a polydopaminemodified nonwoven polypropylene. EXPERIMETAL SECTION Materials. All chemicals and solvents were used without further purification. Imidazolate-2carboxyaldehyde (C4H4N2O, >99%) were purchased from Adamas Reagent Co., Ltd, Zn(NO3)2•6H2O (>99%) supplied by macklin, sodium formate (HCOONa, 99.998% metals basis, Aladdin), methanol (CH3OH, 99.99%, aladdin), 2,3,4,5,6-Pentafluorobenzonitrile (>99%, Sigma-Aldrich), BH3•THF (1.0 M, J&K), THF (>99.9%) were purchased from Sigma-Aldrich, diethyl ether (C4H10O, >99.7, Sinopharm Chemical Reagent Co. Ltd), NaOH (>97%, Aladdin), HCl (>99%, Aladdin), Na2SO4 (>99%, Aladdin), dopamine (C8H11O2N, >97%, Ark),



tris(hydroxymethyl) aminomethane (C4H11NO3, 99.5%, sigma-aldrich), 1H, 1H, 2H, 2Hperfluorodecyltriethoxysilane(C16H19F17O3Si, >97%, j&k), Zonyl321 was provided by DuPont, polypropylene nonwoven fabric was purchased from the local supermarket. Preparation of dopamine-based surface. Dopamine (2mg/mL) was completely dissolved in 10 mM Tris-HCl (pH 8.5) solution in a beaker. And then a PP nonwoven was treated with the above solution at 25 °C for 24h, which could lead to the polydopamine layer de-positing on the nonwoven surface. The PD-modified nonwoven was washed with water several times, dried at 60 °C overnight. Synthesis of semi-continuous hydrophobic ZIF-90 layer on PD-modified nonwoven. A ZIF-90 membrane was prepared by solvothermal method in a Teflon-lined autoclave. Normally, 0.44g Zn(NO3)2•6H2O, 0.568g imidazole-2-formaldehyde and 0.101g sodium formate were dissolved in 30ml methanol and then ultrasonic treatment. The PD-modified nonwoven was placed in a Teflon-lined autoclave with above solution, and heated in an oven at 85 °C for 24 h. The ZIF-90 layer nonwoven was washed with methanol three times to remove the impurities after cooling to room temperature, and then dried at room temperature. The hydrophobic ZIF-90 membrane was prepared according to the reported elsewhere.31 The as-synthesized ZIF-90 membrane was put into 30 mL methanol solution contained 0.347 g pentalfluorobenzylamine, and heated to 100 °C for 24h. And then the hydrophobic ZIF-90 layer was washed with fresh methanol several times. Finally, the as-prepared hydrophobic ZIF-90 membrane was dried under vacuum for 24 h. Preparation of self-repairing superhydrophobic ZIF-90 membrane. Briefly, FAS (2 mL) and Zonyl321 (2.5 g) were mixed, and vigorously stirring for 2 h, and then 150 mL water was


Page 6 of 27

Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


added and vigorously stirred for 30 min to form homogeneous suspension. For soft substrates, dip coating was used. Normally, the hydrophobic ZIF-90 membrane was immersed into the above suspension for 30 min. The improved hydrophobic ZIF-90 membrane was dried for 30 min at room temperature and finally cured for 2 h at 135 °C. Washing and brushing durability and self-repairing performance test. The washing and brushing test were conducted with tube brush. Briefly, the prepared nonwoven sample (size, 30 mm × 40 mm) was scrubbed under water flow. During washing, temperature remains the same. After 30 min of washing, the composite membrane sample was dried at ambient temperature. The surface wettability of the as-prepared composite membrane sample was then measured and water contact angle is slightly reduced. The entire scrub process is equivalent to several cycles. To test self-repairing performance, the as-prepared ZIF-90 composite membrane was damaged via O2 plasma treatment to verify self-repair performance. The prepared composite membrane completely changed into hydrophilic and oleophilic after plasma treatment, and then heated for 5 min at 135 °C. After that, the surface wettability of the composite membrane recover its original state. RESULTS AND DISCUSSION Morphologies of the Prepared Superhydrophobic ZIF-90 Composite Membrane. The self-repairing superhydrophobic ZIF-90 membrane was used herein for oil/water emulsion separation. In order to observe the surface structure, a scanning electron microscope (SEM) and optical picture were used, whose images are given in Figure 1 and Figure S1. The semicontinuous ZIF-90 layer grows well on dopamine-modified membrane (as shown in Figure S2), which exhibits an uneven surface with a high roughness that enhances liquid repellency, as seen



in the images of the surface of the semi-continuous ZIF-90 layer (Figures 1a and 1b) and the hydrophobic ZIF-90 layer (Figures 1c and 1d) corresponds to the pure ZIF-90 layer and pentafluorobenzylamine modified hydrophobic ZIF-90 layer in Schematic, respectively. We can see that the surface of the ZIF-90 layer and the hydrophobic ZIF-90 layer are rough but regular, which indicated that ZIF-90 surface hydrophobicity modified did not change the surface morphology. The hydrophobic ZIF-90 membrane was then immersed into the coating liquid and was cured to obtain the self-repairing MOF membrane. The modified layer could be clearly observed on the surface of the composite membrane and between the semi-continuous ZIF-90 crystals (shown in Figures 1e and 1f and Figure S3). And all the gaps between the hydrophobic ZIF-90 crystals are completely sealed by Zonyl®321/FAS/water coating liquid due to the strong interaction among Zonyl®321, FAS and hydrophobic ZIF-90, thus forming a stabilized selfrepairing MOF membrane (high-magnification SEM image Figure S4).


Page 8 of 27

Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. SEM images of the (a, b) semi-continuous ZIF-90 layer on the polydopamine-modified PP membrane, (c, d) hydrophobic ZIF-90-layer modified membrane, and (e, f) self-repairing ZIF-90 composite membrane.



Page 10 of 27

Structures of the Prepared Superhydrophobic ZIF-90 Composite Membrane. Using Xray photoelectron spectroscopy (XPS) we analyzed the elementary composition and interactions within the composites. Figure 2 shows the full survey spectrum and the single elementary spectra of the composite membrane to analyze the elementary components. The single elementary XPS spectra of the Si 2p, C 1s, and F 1s peaks from the composite membrane are shown in Figures 2b, 2c and 2d, respectively. The Si 2p peak appears at 102.0 eV is consistent with the Siliconcarbon single bond group in the FAS. The C 1s peaks at 284.8, 286.0, and 289.0 eV are consistent with the carbon-oxygen and carbon-carbon single bond and carbon-oxygen double bond in the Zonyl®321. The peaks appear at 687.1 and 689.0 eV are attributed to the F 1s in −CF2 and −CF3 groups in the FAS and the Zonyl®321. An examination of Figure S5 suggests that the pentalfluorobenzylamine has been successfully modified in the ZIF-90 layer, wherein the emergence of the F 1s signal peak is solid evidence. The existence of fluorinated alkyls and the ZIF-90 layer on the composite membrane surface induces a low surface energy, and thus the excellent superhydrophobic surface of the coating can be caused by both the low free energy and high roughness of its surface. The elemental content of the different ZIF-90 layers was examined by XPS and energy dispersive spectra (EDS) (Figure S6 and Figure S7). It is found that no F is present on the ZIF-90 layer, 4.02 (at.%) is present on the hydrophobic ZIF-90 layer and 24.79 (at.%) on the self-repairing ZIF-90 layer. The hydrophobicity of the ZIF-90 membrane was prepared by modifying with pentafluorobenzylamine (pentafluorobenzylamine was successfully synthesized by FT-IR Figure S8). As shown in Figure S9, the C=O band is replaced by the C=N bond.

The

emergence

of

the

1510,

1030,

1125,

and

1235

cm−1

proves

that

pentafluorobenzylamine has been modified on the ZIF-90 membrane. To verify that the modified ZIF-90 layer remains unchanged after treatment, we acquired energy dispersive spectra (EDS)


Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


elemental mapping images (Figure 3 and Figure S10) and X-ray diffraction (XRD) images (Figure S11). A comparison of Figure 3 and Figure S9 indicates that the multi-fluorine coating has been uniformly modified on the ZIF-90 layer. In addition, the powder XRD pattern of the different ZIF-90 layers reveal that all of the major crystallographic planes can be indexed to pristine ZIF-90. Based on these observations it is concluded that after the various treatments the ZIF-90 layers were not damaged.

Figure 2. (a) XPS survey spectrum of the coated ZIF-90 layer, and (b–d) single elementary XPS spectra of the (b) F 1s, (c) Si 2p and (d) C 1s.



Figure 3. Energy dispersive spectra (EDS) elemental mapping images of a coated ZIF-90 membrane showing the spatial distribution of (a) all individual elemental maps combined, (b) C, (c) O, (d) N, (e) F and (f) Si. Wettability behavior of the Prepared Superhydrophobic ZIF-90 Composite Membrane. To test the wettability of the coated ZIF-90 layers, we employed contact angle measurements. In Figure 4a, a slice of pristine ZIF-90 layer exhibits a water contact angle of about 94° (blue 10 μL drop in optical photograph in Figure 4a) while the oil contact angle is 0° (red 10 μL hexane spot in optical photograph in Figure 4a). In Figure 4b, the fluorinated ZIF-90 layer exhibits a WCA of about 148° and the OCA is zero. In Figure 4c, the fluorinated silanes-coated ZIF-90-layer composite exhibits a remarkably large CA of 170° with the water droplet, indicating the superhydrophobic performance of the composite. Water sliding angle (WSA) tests were carried out to measure the contact angle hysteresis, which was found to be 2°. Further, to verify the stability of the repelling water, the water droplet was stayed on the modified ZIF-90 membrane for 10 min. As depicted in Figure S12, the water droplet con-tact angle does not reduce during this time. 12 Environment ACS Paragon Plus

Page 12 of 27

Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Measurement of the contact angle for the water drop (left) and oil drop (right) on the (a) ZIF-90 layer, (b) hydrophobic ZIF-90 layer, and (c) coated fluorinated silanes ZIF-90 layer. The photographs at right in a, b and c show the corresponding drops from above. Self-repairing performance and stability test of the prepared ZIF-90 membrane. The selfrepairing performance of the superhydrophobic modified ZIF-90 membrane was tested via artificially destroying the surface of composite membrane with O2 plasma treatment, which likely introduced hydrophilic groups on the membrane surface.32 Following an oxygen plasma treatment of 3 min, the O2 plasma-treated modified ZIF-90 membrane exhibits amphipathicity



with a CA of 0° (Figure 5a, left image, and Figure 5b). This result reinforces the hypothesis that the very rough structure combined with the lyophilic groups produces the superhydrophilicity and superoleophilicity of the O2 plasma-damaged modified ZIF-90 membrane. Interestingly, when the O2 plasma-damaged ZIF-90 membrane was subsequently treated by heating at 135° for 3 min, its superhydrophobicity was restored with a contact angle of 170° (Figure 5a, right image, and Figure 5c). Further verifying the self-repairing of the ZIF-90 membrane surface wettability, a water droplet impinging the modified membrane surface exhibited high water repellence and low water adhesion, leading the water droplet to bounce on the surface. A contact angle instrument video was obtained to observe the interaction of the water droplet with the surface of the modified ZIF-90 membrane, where selected frames of this video are shown in Figure 5d, which could be seen that a water droplet impinged on the modofied ZIF-90 membrane, whereupon the drop bounced before resting on the surface. In addition, the self-repairing was repeatable many times after O2 plasma damage/heat-treatment cycles. Figure 5e shows the change of the WCA after 10 damage/treatment cycles, where the WCA is seen to reduce slightly but still maintain its superhydrophobic properties.


Page 14 of 27

Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) Photographs of colored water (blue) and oil (red) on the modified ZIF-90 membrane after the first O2 plasma damage (left) and after subsequent heat treatment (right). (b) WCA after O2 plasma treatment, (c, d) after heating treatment showing the water droplet (c) resting on the surface and (d) bouncing on the coated membrane surface. (e) WCA of the modified membrane after 10 damage/treatment cycles. We also note that the superhydrophobic modified ZIF-90 membrane exhibited an admirable durability to external damage. For instance, the modified ZIF-90 membranes were durable against 100 cycles of O2 plasma damage/heat-treatment (Figure 6a). Figure 6b shows the WCA and WSA changes as a function of damage/treatment cycles, where it can be seen that the WCA slightly reduced while the WSA increased with increasing number of O2 plasma damage/heat



treatment

cycles.

However,

the

treated

coated

ZIF-90

Page 16 of 27

membrane

maintained

its

superhydrophobicity (WCA=168°) even after 100 damage/treatment cycles while the WSA remained very low after this number of cycles (WSA=4°). The SEM images of the surface of the coated ZIF-90 layer after 100 cycles remains essentially unchanged from its appearance before plasma treatment (Figure 6c). In addition to the O2 plasma damage treatment, coated membranes must also exhibit washing durability because of the requirement of regular cleaning. The results of our washing treatments showed that the coated ZIF-90 membrane maintained its superhydrophobicity even after 200 washing cycles (Figure 6d), where the WCA=168° and the WSA=3° (Figure 6e). After washing, the surface morphology of the coated ZIF-90 layer observed via SEM was found to be unchanged from its appearance before washing treatment (Figure 6f). The coating durability arises from the common interaction among FAS, the Zonyl®321 and the fluorinated ZIF-90. As is known, Zonyl®321 has strong adhesion to most substrates, as the same time, FAS acts as crosslinking agent between the Zonyl®321 and fluorinated ZIF-90 membrane. The self-repairing performance of the composite membrane herein, therefore, is owing to reappear on the membrane surface of the small-molecule FAS under heat treatment. With heating, fluoroalkyl groups migrate to the surface of the membrane and surface energy to be restored to a minimum, which is the key to self-repairing performance. Which was achieved via analyzing the distribution of fluorine on the surface of the membrane (as shown in Figure S13). In addition, In order to explore the role of all components in the composite membrane, we conducted a series of comparative experiments, the result is as (Table 1, Supporting information). The experimental results show that the superhydrophobicity of the composite membrane is due to the interaction of hydrophobic ZIF-90, Zonyl®321 and FAS. The hydrophobic ZIF-90 forms a rough and porous surface, while the addition of FAS and


Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Zonyl®321 further reduces the surface free energy of the membrane and acts as a crosslinking agent to make the system more stable, and FAS also is the self-repairing agent.

Figure 6. (a-c) Results of the coated ZIF-90 membrane after 100 cycles of plasma/heat treatments, showing (a) before-and-after photographs of water and oil on the coated membrane, (b) WCA and WSA change with the plasma/heat treatment cycles, (c) SEM image after 100 cycles. (d-f) Results of the membrane after 200 washing cycles, showing (d) before-and-after photographs of water and oil on the coated membrane, (e) WCA and WSA change with washing cycles, (f) SEM image of coated fabric after 200 wash cycles. Application of the Prepared Superhydrophobic ZIF-90 Membrane for Separation of Surfactant Stabilized Oil/Water Emulsions. Based on these results, the self-repairing ZIF-90 membrane is a very promising material for use in oil/water separation. Therefore, we designed an experiment using the self-repairing ZIF-90 membrane as a separation membrane, thus exhibiting



its superwetting characteristic, micro-roughness and porous structure. As shown Figure 7, the functionalized ZIF-90 membrane was fixed between two glass containers and an emulsifierstabilized water-in-hexane emulsion was poured into the upper glass container (Movie S1 in the Supporting Information). Because of the superhydrophobicity of the modified ZIF-90 membrane, as the water/oil emulsion contacts the composite membrane the oil phase immediately permeated the superhydrophobic layer and formed an oil phase layer, which led to the water droplets being rejected while the oil selectively permeated through the membrane. Before separation, the stabilized water-in-oil emulsion was a milky-colored liquid, but following separation the collected filtrate was transparent (Figure 7a). To test the efficiency of the separation (reaches 99.98%), the oil purity after separation was measured, as shown in Figures 7b, 7c and 7d. The self-repairing ZIF-90 membrane exhibits extreme efficiency and flux for various water-in-oil emulsions. Including water-in-toluene, Water-in-hexane, water-in-chlorobenzene and water-ingasoline emulsions. And the photographs and microscope images of the oil/water emulsions have been tested one-to-one (as shown Figure S14). More importantly, the membrane maintains a high separation efficiency (99.96%) and flux for the water-in-hexane emulsion after 30 cycles. Meanwhile, compared the performance of the state-of-the-art materials in the literature, which could be seen that our materials exhibit excellent performance as shown in Table 1.


Page 18 of 27

Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. (a) The filtration system for oil/water emulsion separation process. (b, c) using various oil/water emulsions, the (b) separation efficiency and (c) flux of the self-repairing ZIF-90 membrane. (d) The stability experiments of the self-repairing ZIF-90 membrane for the hexane/water emulsion. Table 1. Comparison of the flux and efficiency of some state-of-the-art materials



Page 20 of 27

CONCLUSIONS In summary, for the first time we demonstrated a fabricated self-repairing ZIF-90 membrane with

superhydrophobic

characteristics

using

preserving

healing

agents,

including

fluoroalkylsilane, that are incorporated into the rough micro-porous structure. The robust superhydrophobic ZIF-90 membrane exhibited self-repairing performance against various external destruction (such as chemical and physical damages), where the damage cycles were repeated many times without decreasing the superhydrophobicity. This introduction of a selfrepairing function into a robust superhydrophobic coating is quite promising, and will greatly extend the lifespan of superhydrophobic coatings in practical applications. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: XXXXXXXX. Surface structure of the ZIF-90 membrane and modified ZIF-90 membrane; X-ray photoelectron spectroscopy (XPS) analysis of the ZIF-90 membrane and modified ZIF-90 membrnae; FT-IR datas of pentafluorobenzylamine, ZIF-90 and hydrophobic ZIF-90; Energy dispersive spectra (EDS) elemental mapping images and X-ray diffraction (XRD) analysis; Stability test of the water repellency; Analysis of self-healing ability; Studying the role of each coating component. AUTHOR INFORMATION Corresponding Authors


Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


*E-mail: [email protected]. *E-mail: [email protected]. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS We gratefully acknowledge the financial support provided by the National Key R&D Program of China (2017YFC0210901, 2017YFC0210906), National Natural Science Foundation of China (51573122, 21722607, 21776190), Natural Science Foundation of the Jiangsu Higher Education Institutions of China (17KJA430014, 17KJA150009), the Science and Technology Program for Social Development of Jiangsu (BE2015637) and the project supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). REFERENCES (1) Shannon, M. A.; Bohn, P. W.; Elimelech, M.; Georgiadis, J. G.; Mariñas, B. J.; Mayes, A. M., Science and technology for water purification in the coming decades. Nature 2008, 452, 301-310. DOI: 10.1038/nature06599. (2) Gao, X.; Xu, L. P.; Xue, Z.; Feng, L.; Peng, J.; Wen, Y.; Wang, S.; Zhang, X., Dual-scaled porous nitrocellulose membranes with un-derwater superoleophobicity for highly efficient oil/water separation. Adv. Mater. 2014, 26, 1771-1775. DOI: 10.1002/adma.201304487. (3) Shi, Z.; Zhang, W.; Zhang, F.; Liu, X.; Wang, D.; Jin, J.; Jiang, L., Ultrafast separation of emulsified oil/water mixtures by ultrathin free-standing single-walled carbon nanotube network films. Adv. Mater. 2013, 25, 2422-2427. DOI: 10.1002/adma.201204873



(4) Zhang, W.; Shi, Z.; Zhang, F.; Liu, X.; Jin, J.; Jiang, L. Superhydrophobic and Superoleophilic PVDF Membranes for Effective Separation of Waterin-Oil-Emulsions with High Flux. Adv. Mater. 2013, 25, 2071-2076. DOI: 10.1002/adma.201204520. (5) Li, A.; Sun, H. X.; Tan, D. Z.; Fan, W. J.; Wen, S. H.; Qing, X. J.; Li, G. X.; Li, S. Y.; Deng, W. Q., Superhydrophobic conjugated microporous polymers for separation and adsorption. Energ. Environ. Sci. 2011, 4, 2062-2065. DOI: 10.1039/C1EE01092A. (6) Yuan, J.; Liu, X.; Akbulut, O.; Hu, J.; Suib, S. L.; Jing, K.; Stellacci, F., Superwetting nanowire membranes for selective absorption. Nat. Nanotechnol. 2008, 3, 332-336. DOI: 10.1038/nnano.2008.136. (7) Zhang, Y.; Wei, S.; Liu, F.; Du, Y.; Liu, S.; Ji, Y.; Yokoi, T.; Tatsumi, T.; Xiao, F. S., Superhydrophobic nanoporous polymers as efficient adsorbents for organic compounds. Nano Today 2009, 4, 135-142. DOI: 10.1016/j.nantod.2009.02.010. (8) Gui, X.; Wei, J.; Wang, K.; Cao, A.; Zhu, H.; Jia, Y.; Shu, Q.; Wu, D., Carbon nanotube sponges. Adv. Mater. 2010, 22, 617-621. DOI: 10.1002/adma.200902986. (9) Feng, L.; Zhang, Y.; Xi, J.; Zhu, Y.; Wang, N.; Xia, F.; Jiang, L., Petal effect: a superhydrophobic state with high adhesive force. Langmuir 2008, 24, 4114-4119. DOI: 10.1021/la703821h. (10) Xue, Z.; Liu, M.; Jiang, L., Recent developments in polymeric superoleophobic surfaces. J. Polym. Sci. Pol. Phys. 2012, 50, 1209-1224. DOI: 10.1002/polb.23115. (11) Thorsen, T.; Maerkl, S. J.; Quake, S. R., Microfluidic Large-Scale Integration. Science 2002, 298, 580-584. DOI: 10.1126/science.1076996.


Page 22 of 27

Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(12) Beebe, D. J.; Moore, J. S.; Bauer, J. M.; Yu, Q.; Liu, R. H.; Devadoss, C.; Jo, B. H., Functional hydrogel structures for autonomous flow control inside microfluidic channels. Nature 2000, 404, 588-590. DOI: 10.1038/35007047. (13) Zhang, W.; Liu, N.; Cao, Y.; Chen, Y.; Xu, L.; Lin, X.; Feng, L., A Solvothermal Route Decorated on Different Substrates: Controllable Separation of an Oil/Water Mixture to a Stabilized

Nanoscale

Emul-sion.

Adv.

Mater.

2015,

27,

7349-7355.

DOI:

10.1002/adma.201502695. (14) Kwon, G.; Kota, A. K.; Li, Y.; Sohani, A.; Mabry, J. M.; Tuteja, A., On-demand separation of oil-water mixtures. Adv. Mater. 2012, 24, 3666-3671. DOI: 10.1002/adma.201502695. (15)

Yin, X.; Cheng, H.; Wang, X.; Yao, Y., Morphology and properties of hollow-fiber

membrane made by PAN mixing with small amount of PVDF, J. Membrane Sci. 1998, 146, 179184. DOI: 10.1016/S0376-7388(98)00107-0. (16)

Chu,

Z.;

Feng,

Y.;

Seeger,

S.,

Oil/Water

Separation

with

Selective

Superantiwetting/Superwetting Surface Materials. Angew. Chem. Int. Ed. 2015, 54, 2328-2338. DOI: 10.1002/anie.201405785. (17)

Zhang, F.; Zhang, W. B.; Shi, Z.; Wang, D.; Jin, J.; Jiang, L., Nanowire-Haired Inorganic

Membranes with Superhydrophilici-ty and Underwater Ultralow Adhesive Superoleophobicity for High-Efficiency Oil/Water Separation. Adv. Mater. 2013, 25, 4192-4198. DOI: 10.1002/adma.201301480 (18)

Chang, Y.; Shih, Y. J.; Ruaan, R. C.; Higuchi, A.; Chen, W. Y.; Lai, J. Y., Preparation of

poly(vinylidene fluoride) microfiltration membrane with uniform surface-copolymerized poly(ethylene gly-col) methacrylate and improvement of blood compatibility. J. Membrane Sci. 2008, 309, 165-174. DOI: 10.1016/j.memsci.2007.10.024.



(19)

Lin, X.; Chen, Y.; Liu, N.; Cao, Y.; Xu, L.; Zhang, W.; Feng, L., In situ ultrafast

separation and purification of oil/water emulsions by superwetting TiO2 nanocluster-based mesh. Nanoscale 2016, 8, 8525-8529. DOI: 10.1039/C6NR01119E. (20)

Quéré, D., Wetting and Roughness. Annu. Rev. Mater. Res. 2008, 38, 71-99. DOI:

10.1146/annurev.matsci.38.060407.132434. (21)

Spaeth, M.; Barthlott, W., Lotus-Effect®: Biomimetic Super-Hydrophobic Surfaces and

their Application. Adv. Sci. Tech. 2008, 60, 38-46. DOI: 10.4028/www.scientific.net/AST.60.38. (22)

Han, J. T.; Zheng, Y.; Cho, J. H.; Xu, X.; Cho, K., Stable superhydrophobic organic-

inorganic hybrid films by electrostatic self-assembly. J. Phys. Chem. B 2005, 109, 20773-20778. DOI: 10.1021/jp052691x. (23)

Zimmermann, J.; Reifler, F. A.; Fortunato, G.; Gerhardt, L. C.; Seeger, S., A Simple, One

‐Step Approach to Durable and Ro-bust Superhydrophobic Textiles. Adv. Funct. Mater. 2010, 18, 3662-3669. DOI: 10.1002/adfm.200800755. (24)

Zhao, Y.; Xu, Z.; Wang, X.; Lin, T., Photoreactive azido-containing silica

nanoparticle/polycation multilayers: durable super-hydrophobic coating on cotton fabrics. Langmuir 2012, 28, 6328-6335. DOI: 10.1021/la300281q. (25)

Neinhuis, C.; Koch, K.; Barthlott, W., Movement and re-generation of epicuticular waxes

through plant cuticles. Planta 2001, 213, 427-434. DOI: 10.1007/s004250100. (26)

Koch, K.; Bhushan, B.; Ensikat, H. J.; Barthlott, W., Self-healing of voids in the wax

coating on plant surfaces. Phil. Trans. R. Soc. A 2009, 367, 1673-1688. DOI: 10.1098/rsta.2009.0015. (27)

Zhou, H.; Wang, H.; Niu, H.; Gestos, A.; Lin, T., Robust, Self ‐ Healing

Superamphiphobic Fabrics Prepared by Two ‐ Step Coating of Fluoro ‐ Containing Polymer,


Page 24 of 27

Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fluoroalkyl Silane, and Modified Silica Nanoparticles. Adv. Funct. Mater. 2013, 23, 1664-1670. DOI: 10.1002/adfm.201202030. (28)

Zhai, L.; Berg, M. C.; Cebeci, F. Ç.; Kim, Y.; Milwid, J. M.; Michael F Rubner, A.;

Cohen, R. E., Patterned Superhydrophobic Surfaces: Toward a Synthetic Mimic of the Namib Desert Beetle. Nano Lett. 2015, 6, 1213-1217. DOI: 10.1021/nl060644q. (29)

Wang, H.; Fang, J.; Cheng, T.; Ding, J.; Qu, L.; Dai, L.; Wang, X.; Lin, T., One-step

coating of fluoro-containing silica na-noparticles for universal generation of surface superhydrophobicity. Chem. Commun. 2008, 7, 877-879. DOI:10.1039/B714352D. (30)

Li, Y.; Li, L.; Sun, J., Bioinspired self-healing superhydrophobic coatings. Angew. Chem.

Int. Ed. Edit. 2010, 49, 6129-6133. DOI; 10.1002/ange.201001258. (31)

Liu, C. Y.; Liu, Q.; Huang, A. S., A superhydrophobic zeolitic imidazolate framework

(ZIF-90) with high steam stability for efficient recovery of bioalcohols, Chem. Commun. 2016, 52, 3400-3402. DOI: 10.1039/C5CC10171A. (32)

JunweiLi; KyunghuiOh; HyukYu, Surface rearrangements of oxygen plasma treated

polystyrene: Surface dynamics and humidity effect. Chin. J. Polym. Sci. 2005, 23, 187-196. DOI: 10.1142/S0256767905000321. (33)

Huang, M. L.; Si, Y.; Tang, X. M.; Zhu, Z. G.; Ding, B.; Liu, L. F.; Zheng, G.; Yu, W. J

Luo J. Y., Gravity driven separation of emulsified oil-water mixtures utilizing in situ polymerized superhydrophobic and superoleophilic nanofibrous membranes, J. Mater. Chem. A 2013, 1, 14071-14074. DOI: 10.1039/C3TA13385K. (34)

Kota1, A. K.; Kwon, G.; Choi, W.; Tuteja, J. M. Mabry A., Hygro-responsive

membranes for effective oil-water separation, Nat. Commun. 2012, 3, 1025. DOI: 10.1038/ncomms2027.



(35)

Kukizaki, M.; Goto, M., Demulsification of water-in-oil emulsions by permeation

through Shirasu-porous-glass (SPG) membranes, J. Membrane Sci. 2008, 322, 196-203. DOI: 10.1016/j.memsci.2008.05.029. (36)

Zhou, Y. B.; Chen, L.; Hu, X. M.; Lu, J., Modified Resin Coalescer for Oil-in-Water

Emulsion Treatment: Effect of Operating Conditions on Oil Removal Performance, Ind. Eng. Chem. Res. 2009, 48, 1660-1664. DOI: 10.1021/ie8012242. (37)

Jiang, G. M.; Li, J. X.; Nie, Y. L.; Zhang, S.; Dong, F.; Guan, B. H.; Lv, X. S.,

Immobilizing Water into Crystal Lattice of Calcium Sulfate for its Separation from Water-in-Oil Emulsion, Environ. Sci. Technol. 2016, 50, 7650-7657. DOI: 10.1021/acs.est.6b01152. (38)

Kocherginsky, N. M.; Tana, C. L.; Lu, W. F., Demulsification of water-in-oil emulsions

via filtration through a hydrophilic polymer membrane, J. Membrane Sci. 2003, 220, 117-128. DOI: 10.1016/S0376-7388(03)00223-0.


Page 26 of 27

Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC

We report a robust, superhydrophobic MOF-membrane with a novel self-repairing ability. This membrane was prepared by a simple wet-chemistry surface modification technique consisting of fluorinated alkyl silane and hydrophobic ZIF90-layer. This study represents a key step towards fabricating self-healing superhydrophobic membrane with self-repairing ability for practical applications. Moreover, the prepared superhydrophobic ZIF-90 membrane showed high separation of efficiency to oil/water emulsion (99.98%).


Superhydrophobic Metal-Organic Framework Membrane with Self

Recommend Documents