Polymer Decorated Filter Material for Wastewater Treatment: In-situ

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Polymer Decorated Filter Material for Wastewater Treatment: Insitu Ultrafast Oil/water Emulsion Separation and Azo Dye Adsorption Weifeng Zhang, Na Liu, Liangxin Xu, Ruixiang Qu, Yuning Chen, Qingdong Zhang, Yanan Liu, Yen Wei, and Lin Feng Langmuir, Just Accepted Manuscript • Publication Date (Web): 19 Oct 2018 Downloaded from http://pubs.acs.org on October 19, 2018

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Polymer Decorated Filter Material for Wastewater Treatment: In-situ Ultrafast Oil/water Emulsion Separation and Azo Dye Adsorption Weifeng Zhang †, Na Liu ‡, Liangxin Xu †, Ruixiang Qu †, Yuning Chen †, Qingdong Zhang †, Yanan Liu †, Yen Wei† and Lin Feng* † †Department

of Chemistry, Tsinghua University, Beijing 100084, P. R. China

E-mail: [email protected] ‡Institute

of Materials for Energy and Environment, School of Materials Science and

Engineering, Qingdao University, Qingdao 266071, P. R. China KEYWORDS: Environmental problem; Material science; Special wettability; Wastewater treatment; In-situ separation and adsorption

Abstract: Aiming to realize the wastewater treatment of various pollutants simultaneously, a dual-functional Poly (ether amine)-Polydopamine (PEA-PDA) modified filter material was fabricated in this work for in-situ separation of stable oil-in-water emulsion and adsorption of anionic azo dyes. PEA and PDA could be copolymerized via Michael addition reaction on polyurethane sponge substrate firmly. The as-prepared filter shows superhydrophilic and underwater superoleophobic wettability. After being squeezed in glass tube, the material could separate different kinds of stabilized oil-in-water emulsions with high flux and efficiency.

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Besides, PEA-PDA copolymer endows the material with the ability to adsorb large amount of anionic azo dyes during the separation of emulsions with good adsorption capacity. Moreover, adsorbed dyes in the filter material could be easily desorbed in base aqueous solution and the whole process is conducted under gravity without external aid. This dual-functional material shows great potential for the application in industrial field because of its ability for the complex wastewater treatment. INTRODUCTION With rapid developments of global industries, the quality of human life has improved significantly in recent years. However, these progresses also led to serious environmental problems including air pollution, water pollution and soil pollution which require people to deal with. Water pollution, as one of the major pollution derived from increasing discharged wastewater in our daily life and industrial process, have not only resulted in the loss of valuable resources, but also caused threats to the human health and environment.[1-7] There are various pollutants dispersed in wastewater including water insoluble and soluble pollutants. Among them, oily wastewater and dyeing wastewater are two typical types which have aroused great attention to deal with.[8-11] For the separation of oily wastewater, superwetting materials have aroused great attention and been utilized in this field.[12-20] Compared with traditional methods such as gravity sedimentation, centrifugation separation and so on, materials with special wettability are able to separate immiscible oil/water mixtures and stabilized waterin-oil or oil-in-water emulsions with droplet size below 20 μm. Up to now, numerous superwetting materials including porous nitrocellulose membrane,[21] PMAPS-g-PVDF membrane,[22] inorganic nanowire hair copper mesh,[23] multifunctional biomimetic PVDF membrane and oil-unidirectional membrane have been fabricated successfully.[24-27] While for


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the purification of water soluble dyes, taking the most common harmful azo dyes as an example, the traditional methods such as active sludge biochemical process are inefficient, sometimes even produce hazardous aromatic amines under anaerobic conditions. The photodegradation has proved to be an useful way to deal with dyeing wastewater and lots of works including TiO2 and ZnO nanosized materials have also been reported.[2,28] But the degradation time of these materials are relatively long. Besides, the whole process must be conducted under conditions of light. Another facile way for the removal of dyes is adsorption, which has been regarded as one of the most attractive method because of its low cost, high capacity and efficiency.[29-37] Through the interactions between dyes and materials including host-guest interaction, hydrogen bonding, ionic bonding and so on, water soluble dyes could be adsorbed on the surface rapidly, achieving the whole separation process. However, whether the treatment of oily wastewater or dyeing wastewater, the aforementioned materials only focused on the separation of one type water pollutants, few works reported the treatment of the aforementioned pollutants simultaneously. In real situations, oil and dyes often coexist in wastewater. For example, industrial discharged dyeing wastewater contains both soluble dyes as well as insoluble oil, forming stable dyed oil/water emulsions. Thus, there is still a huge challenge for scientists to fabricate new multifunctional filter materials for the complex wastewater treatment. Poly (ether amine) (PEA) is a hydrophilic polymer which has been proved to be an ideal candidate for the adsorption of some specific dyes with high capacity.[38.39] Herein, based on the adsorption ability of PEA, we synthesized a dual-functional Poly (ether amine)-Polydopamine (PEA-PDA) modified filter material for in-situ separation of emulsion and adsorption of anionic azo dyes as demonstrated in Scheme 1. Polyurethane (PU) sponge is chosen as the substrate since this low cost material owns inherently three dimensional porous structures, which could


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amplify the wettability of the coating polymer.[40] Taking advantage of self-polymerization and adhesion property of dopamine, PEA and PDA could be copolymerized via Michael addition reaction on substrate firmly, forming hierarchical structures. The as-prepared material exhibits superhydrophilic and underwater superoleophobic wettability. After being squeezed in glass tube, the material is able to separate different kinds of stabilized oil-in-water emulsions with ultrahigh flux. Besides, PEA-PDA copolymer endows the material with the ability to adsorb anionic azo dyes during the separation of dyed oil-in-water emulsions with high flux, separation efficiency and adsorption capacity. The possible mechanism has also been explained in the scheme: after copolymerization process, polymer networks could be formed on substrate, the PEA polymer could capture the molecules of azo dyes through host-guest interaction while the amino groups of the copolymer could adsorb the captured anionic azo dyes via ionic bonding. Thus, by the synergistic effect of host-guest and ionic bonding interactions, azo dye molecules could be captured rapidly by the as-prepared material. More importantly, the adsorbed dyes in sponge could be easily desorbed in weak base aqueous solution and the whole process is conducted under gravity without external aid. This dual-functional material shows great potential for the application in industrial field because of its ability for complex wastewater treatment.


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Scheme 1. The fabrication of the PEA-PDA coated sponge and the possible mechanism of the dye adsorption and emulsion separation.

EXPERIMENTAL SECTION Materials and Instruments. Poly (ether amine) (Mn~230, 400 and 2000, Aladdin Industrial Inc., Shanghai, China) and dopamine hydrochloride (Sangon Biotech Co. Ltd., Shanghai, China) were of analytical grade and used directly. Tris(hydroxymethyl)aminomethane, orange II, acid black and direct red from Sinopharm Chemical Reagent Beijing Co., Ltd., Beijing, P. R. China were used as purchased without further purification. Polyurethane (PU) sponge were purchased


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from a commercial store. For the characterization, Scanning electron microscopy (SEM) images of the sponge morphology were observed by field emission scanning electron microscope (SU8010, Hitachi Limited, Japan). The X-ray photoelectron spectra (XPS) of the materials was obtained by a Thermo escalab 250Xi spectrometer with an Al Kα X-ray source (1486.6 eV). Water contact angles (WCAs) and underwater oil contact angles (OCAs) were measured on an OCA20 machine (Data-Physics, Germany) at ambient temperature, each contact angle was the average of measuring five different positions on one sample. For oil-in-water emulsion separation, the oil content in the filtrates was extracted by CCl4 and tested by an infrared spectrometer oil content analyzer (CY2000, China). The adsorption capacity of the sponge towards different azo dyes was characterized by a Perkin Elmer Lambda-750 UV spectrometer.. Fabrication of PEA-PDA Coated Sponge. For PEA-PDA modified sponge, first, the PU sponge were cut into 9×9×2 cm3, then it was immersed in a beaker containing 500 mL deionized water and 1.0 g DOPA. After that, 20 ml PEA and 5 ml Tirs were added to the solution drop by drop. The beaker was sealed and the solution was stirred for 72 hours at ambient temperature. Finally, the as-prepared sponge was cleaned by water further characterization. Preparation of Azo Dyed Water, Surfactant Oil-in-water Emulsions and Azo Dyed Surfactant Oil-in-water Emulsions. For the preparation of azo dyed water, different types of azo dyes including orange II, acid black and direct red were added directly to deionized water, the concentration was 5 mg/L. While for the emulsions, three types of highly stabilized oil-inwater emulsions were prepared, including toluene-in-water emulsion, gasoline-in-water emulsion and n-octane in water emulsion. Tween 20 was chosen as the surfactant. For each type of emulsion, oil and water was mixed in 1:100 (v/v) with the adding of 3 mg/mL Tween 20. The whole solution was stirred for 24 hours. While for the preparation of azo dyed surfactant oil-in-


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water emulsions, the whole processes were similar, after the corresponding emulsions were stirred for 24 hours, azo dyes were added to the emulsions and the concentration was 5 mg/L. Dye Adsorption and Emulsion Separation Experiments for PEA-PDA Modified Sponge. The as-prepared sponge was squeezed into a glass tube, which was implemented for adsorption and demulsification process. Then the azo dyed water or oil-in-water emulsions were poured onto the sponge. The whole process was carried out under gravity. For the test of adsorption capacity, the samples before and after adsorption were characterized by UV-vis spectra. While for the characterization of efficiency, three samples were prepared for one separation cycle and each sample was also measured three times. The oil content was measured by an infrared spectrometer oil content analyzer and the solvent used in test was carbon tetrachloride (CCl4). Since water insoluable oil could be extracted by CCl4 from water while water soluable dyes could not, the measurement is independent with the adding of dyes. The separation efficiency was calculated by the rejection coefficient (R (%)). According to the equation:  Cp  R(%)  1   100%  Co 

(1)

Here, Co and Cp are the oil content in water before and after separation, respectively. RESULTS AND DISCUSSION Surface Morphology and Wetting Behavior. The morphology and contact angles of the asprepared filter material were illustrated in Figure 1. Figure 1a and 1b are the low-magnification field emission scanning electron microscopy (FESEM) images of original PU sponge and PEAPDA coated material, respectively (The molecular weight of the PEA is about 2000 Da). From the SEM images, it is obvious that both substrate and as-prepared material display porous


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structures with numerous tiny pores. But compared with the smooth substrate, layers of polymer have been decorated on the as-prepared filter material and form rough structures. Figure 1c and 1d are the high-magnification SEM images of the corresponding materials. In order to make the conclusion more accurate, different areas of the substrate and coated sponge were captured and displayed in Figure S1. As shown in SEM images, the PU sponge exhibits relatively smooth surface while the modified sponge exhibits rough structures. From the enlarged SEM images, numerous papillae can be observed and dispersed uniformly on the surface of the material compared with the substrate, demonstrating that the copolymer is expected to be modified on the sponge successfully. Moreover, influences of PEA molecular weight on the adsorption ability of the as-prepared material were discussed. PEA-PDA copolymer coated filter with the PEA molecular weight of about 230 Da, 400 Da and 2000 Da were fabricated and named as 230-PEAPDA filter, 400-PEA-PDA filter and 2000-PEA-PDA filter, respectively. Acid black dyed aqueous solution was used to test the adsorption ability of each sponge. As shown in Figure S2ad, although both the sponges exhibit porous rough structures, the copolymer papillae are less than that of 2000-PEA-PDA filter from SEM images. Figure S2e and S2f are digital photos of the dye adsorption capacity of the corresponding sponges, the filtrates of the 230 and 400-PEAPDA sponges are still blue from digital photos. Besides, UV-vis spectra before and after adsorption were also measured as shown in Figure S2g and S2h. Since PEA with larger molecular weight has longer polymer chain and more functional groups, it is easier to react with polydopamine, form co-polymer networks and exhibit better adsorption ability. So the adsorption capacities of 230-PEA-PDA and 400-PEA-PDA are only 32.6% and 50.1%, respectively, indicating that the ability of these filter materials is insufficient. The aforementioned results demonstrate that PEA with larger molecular weight owns better adsorption ability. Figure 1e is


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the digital photo of the pristine sponge and PEA-PDA material, respectively. The color of the material coated with copolymer is much deeper, proving that the polymer was decorated on the surface. It is worth noting that because the substrate used in this work is cut by a scissor from a large piece of sponge, some cracks can be observed. Although these cracks exist on the surface of the sponge, they have no influences on the inner porous structures. Thus, as long as the substrate is decorated for sufficient time, plenty of polymer can be modified successfully. For comparison, the material decorated with PDA only was also prepared as a control. Dye

Figure 1. a) and b) FESEM images of the substrate and PEA-PDA filter material, respectively. c) and d) High-magnification SEM images of the substrate and as-prepared sponge. e) The digital images of the pristine sponge and PEA-PDA filter material. f) The water contact angle (WCA) and underwater oil contact angle (OCAs) of the as-prepared material.


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adsorption capacity of the PDA sponge was insufficient and the color of the filtrate was not transparent (Figure S3), demonstrating the important role of PEA. For the wetting behavior of the PEA-PDA filter, the water contact angle (WCA) and underwater oil contact angle (UOCA) of PU substrate were first measured as a control (Figure S4), the substrate exhibits hydrophobicity with WCA about 130.3° and underwater superoleophilicity with UOCA about 0°. While after the substrate is modified with hydrophilic PEA-PDA polymer and form rough structures, the material owns superhydrophilic and underwater superoleophobic wettability. Besides, the filter exhibits underwater superoleophobicity towards different types of oils such as toluene, gasoline, n-octane and petroleum ether as shown in Figure 1f. It is clear that the underwater OCAs are all above 150°. More importantly, the material shows great anti-corrosive property in a wide range of pH value from 3 to 10, the underwater OCAs in acid or base solutions were all above 150°, demonstrating the excellent stability of the sponge. Surface Characterization of the Filter Material. The chemical reaction of the copolymerization process was illustrated in Scheme 1. Through the Michael addition reaction, PEA could react with PDA and form copolymer networks. X-ray photoelectron spectra (XPS) was conducted for the characterization of the surface composition to verify the polymerization as shown in Figure 2. From the high-resolution C 1s narrow scan of the PU sponge and PEA-PDA filter material (Figure 2c and 2d), it is obvious that the peaks of C-C at 284.7 ev, C-O at 285.4 ev and C-N at 286.1 ev appear on both of the spectra. While after copolymerization process, a new peak at 284.1 eV appears on the spectrum of PEA-PDA material, which represents π-π satellite. The appearance of the π-π satellite peak demonstrates that PDA exists in the copolymer. Figure 2e and 2f are the high resolution of N 1s spectra of the substrate and PEA-PDA filter,


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Figure 2. XPS analysis of the PU sponge and PEA-PDA sponge, respectively. a), c) and e) The survey scans, high-resolution XPS C 1s and N 1s of the PU sponge. b), d) and f) The survey scans, high-resolution XPS C 1s and N 1s of the PEA-PDA sponge. respectively. After the coating process, the peak at 398.2 eV is labelled as the group -CH-NH2, which is ascribed to the characteristic peak of PEA. Besides, the FTIR spectrum of PEA-PDA filter material was alsomeasured as shown in Figure S5, the characteristic peak at 1286 cm-1 is ascribed to the stretching vibrations of aromatic C-N group, indicating the Michael addition reaction of PEA with PDA. All the results aforementioned prove that the PEA-PDA copolymer has been decorated on the PU sponge successfully.


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The Mechanism of Emulsion Separation and Experiments of Ultrafast Oil-in-Water Emulsion Separation. Since the as-prepared filter material combines superhydrophilic/underwater superoleophobic special wettability with tiny pore size, when the material is squeezed into glass tube and oil-in-water emulsion is poured onto the surface, water will pass though the surface quickly and form a water layer immediately. The water layer is able to block micro sized oil droplets dispersed in emulsion, achieving the separation process. Before the separation of PEA-PDA material, emulsion separation performance of the sponge substrate was first tested as illustrated in Figure S6, it is obvious that the substrate is not able to achieve the separation process. In the experiments of PEA-PDA sponge, three types of oil-in-water emulsions were prepared and the corresponding oil droplet size distribution was displayed in Figure S7. All the emulsions are stable with average droplet size below 15 μm. The separation performance was illustrated in Figure 3. From the digital photos of aforementioned emulsions (Figure 3a-3c), it is obvious that after the separation process, all the milky stabilized emulsions become transparent water without dispersed oil droplets, demonstrating that the filter is able to separate various oil-in-water emulsions. To further characterize the separation capacity, oil content after separation was also tested as shown in Figure 3d. The separation efficiencies towards all kinds of emulsions are above 99.3%, which proves the excellent separation ability of the sponge. Besides, the flux of the material towards the aforementioned emulsions were also measured and displayed in Figure 3e, the flux of the sponge was above 1800 L/m2h. Since the oil-in-water emulsions is highly stable, the speed of the separation is high. More importantly, compared with other excellent works, [41-47] the separation efficiency and flux of this work are much higher as displayed in Figure 3f.


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Figure 3. a)-c) The digital photos of the filter material towards gasoline in water emulsion, noctane in water emulsion and toluene in water emulsion, respectively. d) The separation efficiency of the aforementioned stabilized emulsions. e) The separation flux of the sponge for various oil-in-water emulsions. f) The comparison of this work with other excellent materials about the flux and separation efficiency. Adsorption of Dyed Aqueous Solution and the Mechanism. The as-prepared PEA-PDA filter material was first used for the adsorption of azo dyed aqueous solution. The possible mechanism has been illustrated in Scheme 1. Since PEA-PDA polymer networks could be formed on the substrate after copolymerization, during the adsorption process of specific anionic azo dyes, PEA polymer is able to capture the molecules via host-guest interaction while the amino groups of PDA, PEA and substrate could adsorb the captured dye molecules through ionic bonding. As a result, anionic azo dyes could be adsorbed rapidly by the synergistic effect of PEA and PDA copolymer. Moreover, in order to prove that the host-guest interaction of the PEA plays an important role in the whole adsorption process, adsorption experiment of methy blue was conducted as a control (Figure S8). From the photographs and UV-vis spectrum before and after adsorption, the PEA-PDA was not able to remove the methyl blue molecules from aqueous solution. If the adsorption mechanism was explained only by the ionic bonding of the amino groups, methyl blue molecules should also be adsorbed since it is a type of anionic dyes. Thus,


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the results demonstrate that the host-guest interaction of the PEA to specific azo dye molecules is of great significance during the whole adsorption process. In the experiment, three kinds of azo dyes including orange II, acid black and direct red were chosen as the samples as shown in Figure 4a, 4d and 4g. The concentration of the dyed solution was 5 mg/L. Before the adsorption, the material was squeezed into the glass tube. Then 500 ml of the dyed aqueous solution was poured continuously onto the material and the whole process was conducted under gravity. Figure 4 also shows the digital photos and UV-vis spectra of the three kinds of original dyed solutions and the filtrates. It is obvious that after adsorption process, the filtrates all become transparent with no color compared to the original dyed solutions (Figure 4b, 4e and 4h). While from the UV-vis spectra of these dyed solutions (Figure 4c, 4f and 4i), the peaks of orange II at 485 nm, acid black at 623 nm and direct red at 500 nm all disappear after adsorption, which further demonstrates that the as-prepared filter material has the ability to adsorb different kinds of azo dyes. In order to calculate the concentration of the filtrates and the adsorption capacity, a series of standard dyed solution were prepared and the absorbance was also measured through UV-vis spectra. It turned out that the concentration of the solution is linear with the absorbance of the spectra and the relationship was listed in Figure S9. After calculation, the azo dye adsorption capacity of the PEA-PDA sponge is at least 15400 mg/m3 for orange II, 14500 mg/m3 for acid black and 14400mg/m3 for direct red, which is relatively high for the filtrating adsorption under gravity. More importantly, the adsorbed azo dyes in the material could be easily desorbed in base solution as shown in Figure S10, orange II was chosen as the sample. After the PEA-PDA sponge was immersed in the solution (pH=10) for several minutes, the transparent solution became orange which demonstrates that the azo dyes were desorbed from the surface and the material could be recycled. In addition, the kinetic adsorption


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behavior was characterized as shown in Figure S11. Figure S11a is the effect of contact time on the adsorption of orange II, it demonstrates that the adsorption rate is fast at first and adsorption equilibrium can be achieve within 80 minutes. From Figure S11b, it is obvious that t/qt is proportional to t, so the pseudo second order model can be used to describe the adsorption behavior. The anticrrosive property of PEA-PDA filter was also tested as illustrated in Figure S12. The as-prepared sponges were immersed in acid or alkali at different pH values and taken pictures. It is obvious after 3 days, solutions with pH values 1 and 2 turned brown while the other solutions were still transparent, indicating that the sponge is stable in a wide range of pH value from 3 to 10. Figure S13a-d are the WCAs and UOCAs of the material after it was immersed in acid and alkali for 3 days, the material still exhibits superhydrophilic and underwater superoleophobic wettability. Besides, the PEA-PDA sponge can still separate stabilized oil-inwater emulsions as shown in Figure S13e and S13f. Talking about the adsorption ability, Figure S14a and S14b demonstrate the corresponding UV-Vis spectra for adsorption of orange II after the immersion in acid and alkali for 3 days, the adsorption efficiencies are all above 90%. Moreover, the sponge maintains its good adsorption performance even after it is stored in water for 6 months as shown in Figure S14c, the efficiency is still above 98%, demonstrating the excellent stability and long lifetime of this material.


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Figure 4. a), d) and g) Molecules of orange II, acid black and direct red, respectively. b), e) and h) Digital pictures of the large amount adsorption experiments of the as-prepared sponge towards azo dyes including orange II, acid black and direct red. c), f) and i) The UV-Vis spectra of the azo dyes adsorption, respectively. In-situ Separation and Adsorption of Azo Dyed Stable Oil-in-water Emulsions. The superhydrophilic/underwater superoleophobic wettability in combination with small pore size provide the material with the possibility for the in-situ separation and adsorption of stable dyed emulsions. In the in-situ separation experiments, three types of oil-in-water emulsions including gasoline in water emulsion, n-octane in water emulsion and toluene in water emulsion were prepared. Tween 20 was chosen as the surfactant. In each type of emulsion, three kinds of azo dyes were added with the concentration of 5 mg/L including orange II dyed oil-in-water emulsion, acid black dyed oil-in-water emulsion and direct red dyed oil-in-water emulsion. The in-situ separation and adsorption performance of the PEA-PDA filter material towards orange II


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dyed gasoline in water emulsion, acid black dyed n-octane in water emulsion and direct red dyed toluene in water emulsion under gravity are shown in Figure 5. From the photographs, the emulsions are in the left vials and the filtrates after the separation are in the right vials, it is obvious that the dyed milky emulsions all become transparent without color after the whole filtration process. Besides, the optical images of the corresponding feed emulsions and filtrates were also captured. As shown in the images, numerous tiny oil droplets are dispersed in the feed emulsions, but after the in-situ separation and adsorption, there are no droplets in the filtrates. The UV-vis absorbance of the filtrate also becomes flat with no peaks compared with that of original solutions. The performance of the filter towards other six kinds of dyed oil-in-water emulsions were also tested in Figure S15-S17. Moreover, in order to characterize the variation of oil absorption peaks, UV-vis spectra of orange II dyed gasoline-in-water feed emulsion, direct red dyed toluene-in-water feed emulsion and the corresponding filtrates were tested as illustrated in Figure S18 (n-octane in water emulsion was not tested since we could not detect the oil peak in ultraviolet range). It is worth noting that because the scattering effect of oil droplets dispersed in emulsion, oil peaks cannot be measured directly. So the dyed emulsions and filtrates were first dissolved in absolute ethanol before test. From the images, it is clear that both oil peaks (below 300 nm) and dye peaks appear in the spectra of feed emulsions, while after in-situ separation and adsorption, there is no peak in the spectra of filtrates. In addition, talking about the dyed emulsion adsorption behavior, because water layer is formed on the surface of the material during the separation, oil droplets dispersed in emulsion can be blocked by the sponge, so there is almost no influence on the adsorption of dyes and the azo dye adsorption capacity is similar to that of solutions without oil (15234 mg/m3 for orange II, 14368 mg/m3 for acid black and 14210mg/m3 for direct red). All the results indicate that the as-prepared material is able to


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Figure 5. The in-situ emulsion separation and azo dye adsorption performance of the PEA-PDA filter material towards Orange II dyed gasoline in water emulsion, acid black dyed n-octane in water emulsion and direct red dyed toluene in water emulsion.a), e) and i) The optical images of the corresponding feed emulsions. b), f) and j) The photographs of the corresponding azo dyed emulsions before and after in-situ separation and adsorption. c), g) and k) The optical images of the corresponding filtrate emulsions. d), h) and l) UV-Vis spectra before and after the adsorption of azo dyes for the corresponding solutions. achieve the in-situ separation and adsorption of azo dyed stable emulsions. As for the in-situ separation capacity of the filter material, separation efficiency has been measured to characterize the ability as shown in Figure 6. Figure 6a-6c describe the separation efficiencies of the material towards nine kinds of oil-in-water emulsions. It is clear that the PEAPDA modified filter is able to separate various azo dyed emulsions with high efficiency over 99 %. Besides, the stability of the material is tested as illustrated in Figure 6d and 6e, the separation efficiency is still above 99% after 25 times of separation and the adsorption efficiency is still above 90 % after 25 cycles, indicating that the material owns excellent emulsion separation and dye adsorption ability. In order to test the stability of the emulsions used in this work, three types


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Figure 6. a)-c) The separation efficiency of the different oil-in-water emulsions dyed with azo dyes. d) and e) Separation and adsorption recyclability of the PEA-PDA material, after 25 cycles, the sponge still owns excellent separation efficiency and adsorption ability. f) and g) Stability tests of the ado dyed emulsions. After 3 days, the emulsions were still stable without demulsification. of the aforementioned dyed oil-in-water emulsions were prepared and stored without turbulence as shown in Figure 6f and 6g. All the emulsions were highly stable and could be stored for at least 3 days without demulsification. Compared to our previous works as shown in supplementary information (Table S1),[48-55] the prepared PEA-PDA filter material has the advantage of facile fabrication methods, high efficiency and flux. More importantly, the material can achieve in-situ emulsion separation and adsorption of different azo dyes. Besides, it is able to separate emulsions under gravity instead of vacuum filtration, which will reduce the cost and


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difficulty of operation greatly. This dual-functional material overcomes the weaknesses and shows great potential for the application in industrial field. CONCLUSIONS In summary, a dual-functional PEA-PDA filter material was fabricated for in-situ separation of stable oil-in-water emulsions and adsorption of anionic azo dyes. By utilizing the selfpolymerization and adhesion property of dopamine, PEA and PDA could be copolymerized via Michael addition reaction on substrate firmly. The as-prepared filter exhibits micro-nano rough structures, which provides the material with superhydrophilic and underwater superoleophobic wettability. After being squeezed in glass tube, the filter could separate different kinds of stabilized oil-in-water emulsions. Besides, PEA-PDA copolymer endows the material with the ability to adsorb anionic azo dyes during the separation of dyed stabilized oil-in-water emulsions with high flux, separation efficiency and adsorption capacity. Moreover, the adsorbed dyes in sponge could be easily desorbed in weak base aqueous solution and the whole process is conducted under gravity without external aid. This dual-functional material shows great potential for the application in industrial field because of its ability for complex wastewater treatment. ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. Additional data and figures including SEM images of substrate and as-prepared material, digital photos and UV-vis spectra of the adsorption capacity of other PEA-PDA filters and PDAsponge, water contact angle and underwater oil contact angle for PU substrate, FTIR spectrum of PEA-PDA filter, oil droplet size distribution for water-in-oil emulsions, adsorption performance


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of methy blue, relationship between UV-vis absorbance and concentration of azo dyes, desorption ability, anti-crossive property test, in-situ separation and adsorption experiments for other 6 types of azo dyed emulsions, comparison of the PEA-PDA filter material with other previous filtration materials. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. The authors declare no competing financial interest. ACKNOWLEDGMENT The authors are grateful for financial support from the National Natural Science Foundation (51173099).


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Table of Contents:


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Scheme 1. The fabrication of the PEA-PDA coated sponge and the possible mechanism of the dye adsorption and emulsion separation. 90x85mm (300 x 300 DPI)


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Figure 1. a) and b) FESEM images of the substrate and PEA-PDA filter material, respectively. c) and d) Highmagnification SEM images of the substrate and as-prepared sponge. e) The digital images of the pristine sponge and PEA-PDA filter material. f) The water contact angle (WCA) and underwater oil contact angle (OCAs) of the as-prepared material. 99x104mm (300 x 300 DPI)


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Figure 2. XPS analysis of the PU sponge and PEA-PDA sponge, respectively. a), c) and e) The survey scans, high-resolution XPS C 1s and N 1s of the PU sponge. b), d) and f) The survey scans, high-resolution XPS C 1s and N 1s of the PEA-PDA sponge. 149x156mm (300 x 300 DPI)


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Figure 3. a)-c) The digital photos of the filter material towards gasoline in water emulsion, n-octane in water emulsion and toluene in water emulsion, respectively. d) The separation efficiency of the aforementioned stabilized emulsions. e) The separation flux of the sponge for various oil-in-water emulsions. f) The comparison of this work with other excellent materials about the flux and separation efficiency. 188x91mm (300 x 300 DPI)


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Figure 4. a), d) and g) Molecules of orange II, acid black and direct red, respectively. b), e) and h) Digital pictures of the large amount adsorption experiments of the as-prepared sponge towards azo dyes including orange II, acid black and direct red. c), f) and i) The UV-Vis spectra of the azo dyes adsorption, respectively. 199x137mm (300 x 300 DPI)


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Figure 5. The in-situ emulsion separation and azo dye adsorption performance of the PEA-PDA filter material towards Orange II dyed gasoline in water emulsion, acid black dyed n-octane in water emulsion and direct red dyed toluene in water emulsion.a), e) and i) The optical images of the corresponding feed emulsions. b), f) and j) The photographs of the corresponding azo dyed emulsions before and after in-situ separation and adsorption. c), g) and k) The optical images of the corresponding filtrate emulsions. d), h) and l) UV-Vis spectra before and after the adsorption of azo dyes for the corresponding emulsions. 199x113mm (300 x 300 DPI)


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Figure 6. a)-c) The separation efficiency of the different oil-in-water emulsions dyed with azo dyes. d) and e) Separation and adsorption recyclability of the PEA-PDA material, after 25 cycles, the sponge still owns excellent separation efficiency and adsorption ability. f) and g) Stability tests of the ado dyed emulsions. After 3 days, the emulsions were still stable without demulsification. 224x199mm (300 x 300 DPI)


Polymer Decorated Filter Material for Wastewater Treatment: In-situ

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