Plant Polyphenols as Multifunctional Platforms to Fabricate 3D

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Separations

Plant Polyphenols as Multifunctional Platforms to Fabricate 3D Superhydrophobic Foams for Oil/Water and Emulsion Separation Guangyan Chen, Yiran Cao, Le Ke, Xiaoxia Ye, Xin Huang, and Bi Shi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03953 • Publication Date (Web): 01 Nov 2018 Downloaded from http://pubs.acs.org on November 3, 2018

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Industrial & Engineering Chemistry Research

Plant Polyphenols as Multifunctional Platforms to Fabricate

3D

Superhydrophobic

Foams

for

Oil/Water and Emulsion Separation Guangyan Chen,a, c Yiran Cao,a Le Ke,a Xiaoxia Ye,b Xin Huang,a, b* Bi Shi a, c a

National Engineering Laboratory for Clean Technology of Leather Manufacture, Sichuan

University, Chengdu 610065, China b

Department of Biomass Chemistry and Engineering, Sichuan University, Chengdu 610065,

China c

College of Chemical Engineering, Sichuan University, Chengdu 610065, China

KEYWORDS: plant polyphenols, non-covalent decoration, superhydrophobic, oil/water separation, emulsion separation

ABSTRACT: Taking plant polyphenols as multifunctional platforms, an environmentally friendly surface decoration strategy was developed for preparing new type of 3D superhydrophobic foams. The superhydrophobic foams were fabricated by in situ growth of β-FeOOH nanoparticles on melamine foams that were pre-treated by non-covalent surface decoration of plant polyphenols-glutaraldehyde cross-linkage, followed by the Michael addition of 1-dodecanethiol to plant polyphenols. The as-prepared superhydrophobic foams had the water

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contact angle of 154.93o and 153.12o, on the external and interior surfaces, respectively. The superhydrophobic foams featured large absorption capacity, high mechanical robustness, structure stability and flame resistance. During the 100 cycles of absorption-squeezing, the loss of absorption capacity was as low as 0.14% per cycle. In a continuous separation process, organic pollutants were successfully removed from water with the separation efficiency of 98.0%. Notably, the 3D superhydrophobic foams successfully separated 6 types of oil-in-water microemulsions, with separation efficiency high up to 99.82%.

INTRODUTION Cleaning up the organic pollutants discharged by industry and daily life is essential for protecting drinking water resources.1-3 To address this issue, a variety of approaches have been developed, such as centrifugation,4 flotation technologies,5 biodegradation6 and in situ burning.7 However, these approaches have proved to be energy-intensive, relatively inefficient and even cause secondary pollution. More recently, superwetting materials with exceptional hydrophobic and oleophilic properties have been demonstrated to be efficient for selective separation of oil/water mixtures.8,9 Superhydrophobic foams could achieve a direct, ultrafast and effective collection of the target pollutants from the mixtures, which also feature lightweight and large absorption capacity. Moreover, the used foams could be recycled by simple compression. As newly emerging superwetting materials, superhydrophobic foams have shown to be the most promising candidate for removing organic pollutants from contaminated aqueous solutions.10 For the superhydrophobic foams, their surface wetting properties are governed by the surface roughness and surface energy.11,12 It has been well proved that low surface energy and high surface roughness are two indispensable conditions for obtaining superhydrophobicity.


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Generally, fabricating micro-nanostructures on materials surface is the most frequently used strategy to increase surface roughness. Unfortunately, the rough surfaces are fragile due to the weak interactions between substrate and the constructed micro-nanostructures, which are mechanical weak and readily damaged during the utilization process.13,14 To address this issue, a number of strategies have been proposed for enhancing the affinity of micro-nanostructures to the substrate surface. Zhu et al.15 prepared ZIF-8 nanocrystals onto melamine foam (MF) skeletons via in situ growth process. The high content of tertiary amine contained in MF could provide abundant binding sites for the combination between ZIF-8 nanocrystals and foam surface, which enabled 10 cycles of compression tests. Turng et al.16 grafted multidimensional nanoparticles (SiO2, GO, CNTs) on MF using hexamethylenediisocyanate (HDI) as crosslinking agent to create strong covalent bonds between the substrate and particles. However, the use of HDI and organic solvents is not preferred in view point of green chemistry. Pan et al.17 successfully immobilized a variety of nanoparticles onto the surface of MF using dopamine as binder. Nevertheless, the high cost of dopamine may be impediment for practical application. As a consequence, it is highly desirable but still challenging to realize a facile and environmentally benign fabrication of mechanical robust and high-performance superhydrophobic foams that could effectively separate diverse oil/water mixtures and emulsions with good reusability. In consideration of the safety issue during the separation of oil/water mixtures and emulsion, flame resistance is another important property that needs to be considered when designing the superhydrophobic foams.18 Plant polyphenols are natural polyphenolic compounds with a wide distribution in nature. The unique feature of plant polyphenols is their strong coordination ability towards transition metal ions.19,20 Our previous investigations have proved that plant polyphenols can play the role as


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large molecular stabilizers to provide stabilization to the nanoparticles (NPs) formed from the chelated metal species as the aromatic rings of plant polyphenols bring about steric hindrance, and the adjacent phenolic groups also contribute to the stabilization of NPs via electron donation/acception interactions.21 More interestingly, the nucleophilic centers of plant polyphenols allow themselves to react with aldehyde,22 providing the possibility to achieve a stable network that is characterized by NPs enhanced surface roughness without the necessity to chemically modify the foam substrate. Notably, the amphiphilic property of plant polyphenols enables their easy surface decoration on diverse substrate,23,24 like foam. All the properties of plant polyphenols inspired us to develop a facile and non-covalent surface decoration strategy for constructing a mechanical robust, flame resistant and superhydrophobic coating on foam. In the present investigation, we reported a facile synthesis of flame retardant 3D superhydrophobic foams that were prepared by surface decoration of MF via in situ cross-linking of bayberry tannin (BT, a typical plant polyphenols) with glutaraldehyde, followed by chelating and hydrolysis with Fe3+ and subsequent the Michael addition of 1-dodecanethiol. The hydrolysis of Fe3+ gave rise to the formation of β-FeOOH NPs, which increased the surface roughness of MF due to the enhanced micro-nanostructures. The crosslinked plant polyphenols in situ formed on MF surface was proved to significantly promote the anchoring of β-FeOOH NPs on MF. This is beneficial for obtaining stable reusability of the foams. The as-prepared 3D superhydrophobic foams had a water contact angle (WCA) of 154.93° on the external surface, which was still superhydrophobic on the interior surface with a WCA of 153.12°. The limiting oxygen index (LOI) of MF@BT-β-FeOOH was determined to be 28.0%, which passed the UL 94 V-0 rating. This 3D superhydrophobic foams exhibited high absorption capacity to diverse oils and organic solvents, which reached 65-136 times of its own weight. During the 100 cycles


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of absorption-squeezing, the 3D superhydrophobic foams showed limited loss of absorption capacity as low as 0.14% per cycle. Due to the excellent mechanical stability, the 3D superhydrophobic foams can be recycled for the separation of immiscible oil/water mixtures without significant loss of separation efficiency. A continuous separation of oil from the immiscible oil/water mixtures was also carried out. It was found that the 3D superhydrophobic foams were efficient to separate spilled oil on water with the separation efficiency high up to 98.0%. The foams were further applied for separating diverse oil-in-water microemulsions, including olive oil, pump oil and dodecane emulsified in water and the corresponding separation efficiency was high up to 99.82%, 99.58% and 99.30%, respectively. Our approach was also extended for synthesizing other superhydrophobic foams by employing Cu2O NPs to enhance the surface roughness. The as-prepared superhydrophobic foams still featured high mechanical robustness, good elasticity and high-performance separation capability to diverse immiscible oil/water mixtures. EXPERIMENTAL SECTION Materials. Bayberry tannin (BT) was purchased from Guangxi Baise Tianxing Plant Science Co, Ltd. Copper sulfate pentahydrate (CuSO4·5H2O), iron chloride hexahydrate (FeCl3·6H2O), 1-dodecanethiol (n-C12H25SH) and all the other agents were obtained from Kelong Cor. (Chengdu, China) and used without further purification. MF, kerosene, pump oil and olive oil were purchased from local market. Based on the SEM-EDX analysis, the major components of MF are C, O, and N with the total content of 97.99%. Fabrication of Superhydrophobic MF. BT (0.03 g) and glutaraldehyde (40.0 μL, 25%) were dissolved in deionized water (100 mL). The pH of the resultant mixtures was adjusted to 6.50.


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Then, a piece of MF (2.5 cm × 2.5 cm × 2.0 cm) was immersed in the above solution, followed by shaking at 150 rpm in a water bath oscillator under 50oC for 4.0 h. After this, the cross-linked plant polyphenols-coated MF was placed in FeCl3 solution (100 mL, 3.2 mmol L-1), and then shaken at 60oC for 6.0 h, followed by drying. The obtained foam was placed in ethanol solution containing 1-dodecanethiol (2.0 mg mL-1) for 24 h. The resultant foam was rinsed with ethanol and dried, and the obtained superhydrophobic foam was denoted as MF@BT-β-FeOOH. The fabrication processes of MF@BT-CuO2 were similar to those of MF@BT-β-FeOOH except that the cross-linked plant polyphenols-coated MF was placed in 100 mL of solution containing CuSO4 (1.6 mmol L-1) and glucose (2.0 mmol L-1), and then shaken at 80oC for 2.0 h. Measurement of Oil Absorption Capacity and Reusability. A piece of weighted MF@BT-β-FeOOH was fully immersed into diverse organic solvents, including dodecane, chloroform, olive oil, kerosene, pump oil, DMF, DMSO and cyclohexane, respectively. Then, the saturated foam was taken out and quickly weighed. The absorption capacity (k) of foam to above organic solvents was calculated as (W1–W0)/W0, where W0 and W1 are the weight of the foam before and after the absorption to organic solvent, respectively. The reusability of foam as oil absorbent was evaluated by repeated 100 cycles of absorption-squeezing procedures. In this procedure, the remnant organic solvents in the foam after each cycle of squeezing was calculated as (Wr–W0)/W0, where Wr is the weight of the foam after squeezing in each cycle, while the W0 is the weight of the foam itself. Oil/Water Separation. Absorption-squeezing and continuous separation approaches were carried out to remove float oils from oil/water mixtures. In absorption-squeezing procedures, the squeezed oil of each cycle was collected and measured to calculate the separation efficiency that was calculated as (V0–V1)/V0, where V0 and V1 are the initial volume of oil and the volume of


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separated oil, respectively. The continuous separation was accomplished through a self-made device that was similar to our previous work.25 MF@BT-β-FeOOH was plugged into the tube, and then the oil dyed with Sudan red was sucked up and flowed into the suction flask along the rubber tube after turning on the pump. The separation efficiency was calculated as above. The MF@BT-β-FeOOH was reused for another 4 cycles of continuous separation of immiscible dodecane/water mixture without any regeneration treatment. Table 1. The constituents of the oil-in-water microemulsions. Samples

Water (mL)

Olive oil (mL)

Pump oil (mL)

Dodecane (mL)

E1

100

2.0

0

0

E2

100

4.0

0

0

E3

100

0

2.0

0

E4

100

0

4.0

0

E5

100

0

0

2.0

E6

100

0

0

4.0

Six types of microemulsions were prepared by stirring the mixtures of water with olive oil, pump oil or dodecane with the ratio of 50:1 or 25:1 (v/v) at 3000 r min-1 for 3.0 h. The detail parameters were given in the Table 1. 0.15 g of MF@BT-β-FeOOH was cut into small pieces and put into 50 mL of microemulsion and agitated for a while, followed by filtration. Total Organic Carbon Analyzer (TOC, Elementar, Vario) was used to calculate the separation efficiency that was defined as (C0–C1)/C0, where C0 and C1 (ppm) represent the TOC value of emulsions before and after the filtration, respectively. Characterization. The surface structure of the foam was observed through a Field-emission Scanning Electron Microscopy (FESEM, S-4700, Hitachi, Japan). The chemical composition of the foam was determined by the Fourier Transform Infrared (FTIR, Thermo Scientific Nicolet


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IS10, USA) and X-ray Photoelectron Spectroscopy (XPS, Thermo Fisher, Escalab 250 Xi). WCA measurements were performed on a Contact Angle Goniometer (Krüss, DSA30) at room temperature. The WCA of each sample was obtained from the average value of three repeated measurements. The mechanical properties of the foam were measured by a compression test using an Electromechanical Universal Testing Machine (CMT6202, MTS systems Co., Ltd., China), where the samples were compressed at a rate of 50 mm min-1. The LOI was measured by a HC-2C oxygen index instrument (Jiangning, China). The UL-94 vertical burning test was carried out on a CZF-2 instrument (Jiangning, China). RESULTS AND DISCUSSION Figure 1a-d are the schematic illustrations showing the preparation of MF@BT-β-FeOOH. BT contains abundant pyrogallol groups at the B-rings, which feature high affinity to a variety of polar substrates due to the formation of multiple-hydrogen bonds that endow BT with the ability of adsorption on MF surface. The BT molecules adsorbed on MF surface were further crosslinked by using glutaraldehyde as the bridge, which can react with the nucleophilic center of C6 or C8 at the A rings of BT (Figure 1b). In this way, a cross-linkage network of plant polyphenols-glutaraldehyde was in situ formed on the surface of MF. The resultant MF@BT foams were then immersed in Fe3+ solution and kept the system under constant shaking for 6.0 h (Figure 1c). This procedure allows the chelating of Fe3+ with the pyrogallol groups of BT, and successive in situ formation of β-FeOOH NPs that are still stabilized by the phenolic hydroxyls of BT. In our experiments, the color of MF@BT changed from brown yellow to blue black when it was immersed in Fe3+ solution, indicating the formation Fe3+-BT complex. In subsequent heating process, the color of MF@BT was further changed to orange yellow, implying the formation of β-FeOOH NPs on the surface of MF@BT.


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Figure 1. Schematic illustrations showing the preparation of MF@BT-β-FeOOH (a-d), the digital photographs of water droplets on the MF (e), the external (f) and interior surface (g) of MF@BT-β-FeOOH (inset: their corresponding WCA), the digital photographs showing the sank MF and float MF@BT-β-FeOOH (h), and the MF@BT-β-FeOOH forced into water (i). For the as-prepared MF@BT-β-FeOOH, the anchored β-FeOOH NPs are aimed to significantly enhance the surface roughness of MF, while the BT-glutaraldehyde network provides high stability to the β-FeOOH NPs. Then, 1-dodecanethiol was chemical grafted onto BT to reduce the surface energy of the MF@BT-β-FeOOH (Figure 1d). In this way, we obtained 3D superhydrophobic MF@BT-β-FeOOH. As shown in Figure 1f - g, water droplets stand stably both on the external and interior surfaces of MF@BT-β-FeOOH with roughly spherical morphology, with the WCA of 154.93° and 153.12°, respectively. A layer of air bubbles were observed on the surface of MF@BT-β-FeOOH when it was forced to soak into water (Figure 1i). This observed silver mirror-like phenomena manifest that the surface of MF@BT-β-FeOOH is in Cassie-Baxter status,26 which demonstrates the excellent water-repelling property of


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MF@BT-β-FeOOH. Furthermore, the MF@BT-β-FeOOH exhibits excellent superhydrophobic stability due to the fact that the foam floated on water surface for more than one month without any infiltration by water, while the pristine MF immediately soaked into water upon the addition in water (Figure 1h).

Figure 2. FESEM images of (a, b) MF and the external surface (c, d) and fresh-cutting face (e, f) of MF@BT-β-FeOOH. The interconnected porous structure of MF was retained in the MF@BT-β-FeOOH, as shown in Figure 2. A high resolution FESEM image shows that the skeleton of MF@BT-β-FeOOH is fully covered by a dense layer of β-FeOOH NPs, and average the particle size of β-FeOOH NPs is about 210 nm. These results suggest that the morphology of pristine MF is intact during the in situ formation of BT anchored β-FeOOH NPs. The density of MF@BT-β-FeOOH was measured to be 11.01 kg m-3, which shows no obvious change to that of pristine MF (8.46 kg m-3), indicating its lightweight feature.


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Figure 3. XPS survey scans of MF and MF@BT-β-FeOOH (a) and high-resolution of C 1s (b), O 1s (c) and Fe 2p (d) spectra of MF@BT-β-FeOOH. As shown in Figure S1, the FTIR spectra of MF@BT-β-FeOOH show an absorption peak at 696 cm-1 belonging to the Fe-O stretching vibrations of β-FeOOH.27 XPS survey spectra confirms the presence of Fe and S in the MF@BT-β-FeOOH (Figure 3a), indicating the successful anchoring of β-FeOOH as well as grafting of 1-dodecanethiol on MF. The Fe 2p3/2 and Fe 2p1/2 of MF@BT-β-FeOOH are located at 711.0 and 724.7 eV, respectively (Figure 3d), and well match the characteristic peaks of β-FeOOH.28,29 The Fe 2p XPS data combined with the characteristic O 1s peaks of Fe-O and Fe-O-H at 530.6 and 531.9 eV confirm the presence of β-FeOOH in the MF@BT-β-FeOOH 30 (Figure 3c). Mechanical robustness and structure stability are essentially important for the practical application of superhydrophobic foams. Herein, cyclic compression/release tests of


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MF@BT-β-FeOOH were carried out by fixing the compressive strain of the foam to 70%. For comparison, we also performed cyclic compression/release tests of pristine MF. As shown in Figure 4a, b, the compressive stress-strain curves of MF@BT-β-FeOOH are quite similar to those of MF. Notably, the MF@BT-β-FeOOH could recover its original shape with a loss of only 3.83% in height, which suggests that the MF@BT-β-FeOOH preserved the mechanical robust nature of MF.

Figure 4. Compressive stress-strain curves of MF (a) and MF@BT-β-FeOOH (b) in the 1st and 100th compression/release cycle (inset: sequential photographs of foam during the compression/release

cycle),

FESEM

images

of

MF@BT-β-FeOOH

after

100

compression/release cycles (c, d) and ultrasonic cleaning in ethanol for 30 min (e, f). Besides, no significant detachment of β-FeOOH NPs was observed during the cyclic compression/release tests (Figure 4c, d). This indicates that the constructed roughness structure is stable enough to undergo 100 cycles of compression/release due to the anchoring effect of BT-glutaraldehyde network to the β-FeOOH NPs. To further manifest the stability of the rough


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surface structure of MF@BT-β-FeOOH, the foam composites were treated by ultrasonication in ethanol for 30 min. As shown in (Figure 4e, f), the rough surface comprised of densely packed β-FeOOH NPs was still evident for the ultrasonicated MF@BT-β-FeOOH. All these results confirm the excellent robustness and structural stability of MF@BT-β-FeOOH, which is beneficial for obtaining good recyclability during the use of oil/water and emulsion separation.

Figure 5. Digital photographs taken from the combustion process of MF (a) and MF@BT-β-FeOOH (f), digital photographs of MF and MF@BT-β-FeOOH before (b, g) and after combustion (c, h), as well as their fresh cutting face (d, e and i, k). Flame resistance is another vital factor for superhydrophobic foam to work as absorbent of flammable organic solvents because of their high risk to catch fire or explode. For the MF@BT-β-FeOOH, the substrate of MF has an outstanding flame resistance due to the abundant nitrogen content.18 To confirm the flame resistant feature of MF@BT-β-FeOOH, combustion


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experiments were carried out. As shown in Figure 5, neither the MF@BT-β-FeOOH nor the pristine MF was ignited even after 20 s ignition by the outer flame of alcohol lamb. Notably, the as-treated MF@BT-β-FeOOH still maintained its original shape and the fresh cutting face was nearly intact. In contrast, the as-treated pristine MF shrank substantially and the interior structure was seriously damaged. The LOI of MF@BT-β-FeOOH was measured as high as 28.0%, which also achieved the UL 94 V-0 rating. Figure 6a shows the saturated absorption capacity of MF@BT-β-FeOOH to a variety of oils/organic solvents, including dodecane, chloroform, olive oil, kerosene, pump oil, DMF, DMSO and cyclohexane. The absorption capacity of MF@BT-β-FeOOH is defined as (W1– W0)/W0, where, W0 and W1 are the weight of the foam before and after the absorption to oils/organic solvents. It was found that MF@BT-β-FeOOH exhibits high absorption capacity (k) to oils/organic solvents, which is 65-136 times of its own weight. We also measured the reusability of MF@BT-β-FeOOH by cyclic absorption-squeezing method. As shown in Figure 6b, the MF@BT-β-FeOOH still preserved the high absorption capacity (k), up to 60 times of its own weight, with the loss of absorption capacity as low as 0.14% per cycle during the 100 cycles of absorption-squeezing. In addition, the WCA of the recycled MF@BT-β-FeOOH was still as high as 148.1°. These results confirm that the superhydrophobic MF@BT-β-FeOOH exhibits outstanding removal ability to oils/organic solvents as well as recyclability and high stability. As shown in Figure 6d, e, we cleaned up the organic pollutants colored with Sudan red from the surface (dodecane) or bottom (chloroform) of water using MF@BT-β-FeOOH as the absorbent. The absorption process was completed within only a few seconds ascribed to the well developed porosity and superoleophilic nature of MF@BT-β-FeOOH.


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Figure 6. Absorption capacity (k) of MF@BT-β-FeOOH to different oils and organic solvents (a), reusability of MF@BT-β-FeOOH for absorption of dodecane by 100 cycles of absorption-squeezing (b) (inset: digital photographs of water droplets on the recycled MF@BT-β-FeOOH and its corresponding WCA), separation efficiency of diverse immiscible oils/water mixtures using MF@BT-β-FeOOH by absorption-squeezing approach (c), digital photographs taken from the separation of dodecane (d), chloroform (e) from water using MF@BT-β-FeOOH

and

continuous

separation

of

dodecane

from

water

using

MF@BT-β-FeOOH (f). Then MF@BT-β-FeOOH was used for separating 100 mL of immiscible mixtures of water with dodecane, pump oil, kerosene, olive oil and cyclohexane (9:1, v/v), respectively. The corresponding separation efficiencies were measured to be 96.3%, 94.8%, 91.5%, 83.5%, and 95.5% (Figure 6c). In consideration of the practical application, the continuous separation is


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highly preferred to deal with the large area contaminated water. We therefore set up a simple vacuum-assistant system for continuous separation of dodecane from 200 mL of immiscible dodecane/water mixtures (1:3, v/v) (Figure 6f). In the continuous separation process, we observed that dodecane was continuously pumped into the collecting beaker, while the water was selectively repelled by the MF@BT-β-FeOOH. After 40 seconds of separation, almost all the dodecane floated on water was removed with separation efficiency of 98.0%. Furthermore, the MF@BT-β-FeOOH was reused for continuous separation of another 4 cycles of 200 mL of immiscible dodecane/water mixtures (1:3, v/v) without any regeneration treatment. The separation efficiency were high up to 98.4%, 98.2%, 98.6% and 98.4%, respectively, during the following 4 cycles. The appreciable separation efficiency and outstanding recyclability of MF@BT-β-FeOOH indicate its promising application for treatment of float organic pollutants in large area contaminated water. Besides immiscible oil/water mixtures, the superhydrophobic MF@BT-β-FeOOH is capable of separating emulsified oil/water mixtures. Six types of oil-in-water emulsions were prepared by using different content of olive oil, pump oil and dodecane as the organic phase. The detailed components of emulsions are shown in Table 1. For the separation of olive oil-in-water microemulsion (E1), the separation process was completed within 30 min. The separated emulsion of E1 was transparent (Figure 7d), and microscope observations confirm that no emulsion droplet was found in the collected transparent residual (Figure 7f). Accordingly, the TOC of E1 was dramatically decreased from 6874.84 to 31.55 ppm, with a high separation efficiency of 99.50%. Similar high separation efficiency of E2 was also achieved with TOC decreased from 13749.68 to 24.71 ppm, and separation efficiency high up to 99.50%.


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Microscope observations also confirm the successful separation of E2. In contrast, the pristine MF is unable to separate the emulsions (Figure S2).

Figure 7. Digital photographs taken from the separation process of E1 (a-d), optical microscopic images of E1 (e, f), E2 (g, h), E3 (i, j), E4 (k, l), E5 (m, n), E6 (o, p) before and after treated with MF@BT-β-FeOOH. For the pump oil-in-water microemulsion (E3 and E4) and dodecane-in-water microemulsion (E5 and E6), the MF@BT-β-FeOOH achieved complete separation within 15 min and 10 min, respectively, with separation efficiency higher than 98.46%, along with substantial decrease of TOC (Table 2) and the disappearing of emulsion droplets in the residuals (Figure 7g-p). The difference in separation time is likely due to the fact that polarity and alkane chain length of oil phase influence emulsion stability.31 Actually, our approach is also applicable for synthesizing other superhydrophobic foams due to the universal coordination capability of BT to transition


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metal species. We prepared superhydrophobic foams by in situ formation of Cu2O NPs on MF (Figure S3), the as-prepared foams were also superhydrophobic with a WCA of 156.9o. Table 2. TOC of E1-E6 before and after the separation by the MF@BT-β-FeOOH. Before separation

After separation

Separation efficiency

(ppm)

(ppm)

(%)

31.55

99.50

E2

6874.84 (ppm) 13749.68

24.71

99.82

E3

1284.92

13.11

98.66

E4

2569.80

10.78

99.58

E5

1474.76

19.79

98.46

E6

2949.52

20.78

99.30

Emulsion E1

CONCLUSIONS In summary, we have developed an environmentally friendly and cost-effective approach to fabricate mechanical robustness and flame resistant 3D superhydrophobic foams by using plant polyphenols as multifunctional platforms. For the as-prepared superhydrophobic foams, the plant polyphenols crosslinked on MF surface is able to anchor the β-FeOOH NPs, providing mechanically robust surface roughness with highly stable superhydrophobicity. Due to the well developed porosity and superhydrophobicity, the as-prepared lightweight MF@BT-β-FeOOH is capable of separating diverse immiscible oil/water mixtures and oil-in-water microemulsions, which features high separation efficiency as well as cycling stability. Moreover, our approach could also be extended to synthesis other superhydrophobic foams.


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ASSOCIATED CONTENT Supporting Information. Figure S1. FTIR spectra of MF@BT-β-FeOOH, MF and β-FeOOH; Figure S2. The digital photographs of emulsion before (a) and after treated by the pristine MF (b); Figure S3. The digital photograph of water droplets on the MF@BT-Cu2O (a) (inset: the corresponding WCA) and FESEM images of MF@BT-Cu2O (b) (inset: high resolution FESEM image of MF@BT-Cu2O).

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (X. Huang) ORCID Xin Huang: 0000-0002-3225-2638 Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT We sincerely thank the financial supports from the National Natural Science Foundation of China (21676171, 51507107), the Fork Ying Tong Education Foundation for Young Teachers in the Higher Education Institutions of China (61099), the Science and Technology Fund for Distinguished Young Scholars of Sichuan Province (2016JQ0002), the 1000 Talents Program of Sichuan Province and Science Foundation for Distinguished Young Scholars of Sichuan University (2017SCU04A04). REFERENCES (1) Lin, X.; Lu, F.; Chen, Y.; Liu, N.; Cao, Y.; Xu, L.; Wei, Y.; Feng, L. One-Step Breaking and Separating Emulsion by Tungsten Oxide Coated Mesh. ACS Appl. Mater. Interface 2015, 7, 8108. (2) Zeng, X.; Long, Q.; Yuan, X.; Zhou, C.; Li, Z.; Jiang, C.; Xu, S.; Wang, S.; Pi, P.; Wen, X. Inspired by Stenocara Beetles: From Water Collection to High-Efficiency Water-in-Oil Emulsion Separation. ACS Nano 2017, 11, 760. (3) Si, Y.; Guo, Z. Superwetting Materials of Oil-Water Emulsion Separation. Chem. Lett. 2015, 44, 874. (4) Turano, E.; Curcio, S.; Paola, M. G. D.; Calabro, V.; Iorio, G. An Integrated Centrifugation-Ultrafiltration System in the Treatment of Olive mill Wastewater. J. Membrane Sci. 2002, 209, 519. (5) Rubio, J.; Souza, M. L.; Smith, R. W. Overview of Flotation as a Wastewater Treatment Technique. Miner. Eng. 2002, 15, 139.


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TABLE OF CONTENT GRAPHIC


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Plant Polyphenols as Multifunctional Platforms to Fabricate 3D

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