Nanocomposite Deposited Membrane for Oil-in-Water Emulsion

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Nanocomposite Deposited Membrane for Oil-in-Water Emulsion Separation with in situ Removal of Anionic Dyes and Surfactants Na Liu, Qingdong Zhang, Ruixiang Qu, Weifeng Zhang, Haifang Li, Yen Wei, and Lin Feng Langmuir, Just Accepted Manuscript • Publication Date (Web): 09 May 2017 Downloaded from http://pubs.acs.org on May 13, 2017

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Nanocomposite Deposited Membrane for Oil-inWater Emulsion Separation with in situ Removal of Anionic Dyes and Surfactants Na Liu, Qingdong Zhang, Ruixiang Qu, Weifeng Zhang, Haifang Li, Yen Wei, and Lin Feng* Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China KEYWORDS: emulsion separation, controllable dyes removal, controllable surfactants removal, high reproducibility, in situ multifunctional water purification

ABSTRACT: The decontamination of various pollutants including oils, organic dyes and surfactants from water is an unprecedented issue throughout the world. A facile filtration process for in situ multifunctional water purification by employing a low-cost and easy-made catecholPEI nanocomposite deposited membrane has been designed. In combination with the intrinsic hydrophilicity of amino-rich groups, the resultant membrane possesses superhydrophilicity and underwater superoleophobicity, which is simultaneously advantageous for capturing anionic pollutants due to the electrostatic interaction. Such membrane can be successfully used for sundry surfactant-stabilized oil-in-water emulsions separation and pH controllable removal of water-soluble dyes and the remaining surfactants at the same time. The excellent characteristics, i.e., fabrication protocol that easy to scale up, better alkaline resistance, selectively controllable

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removal ability of anionic dyes and surfactants with unaltered adsorption performance over thirty consecutive adsorption-desorption-washing cycles, will facilitate its versatility and practicability in environmental remediation and wastewater purification.

1. INTRODUCTION Water contamination, arising from the grievous effluent discharge of increasing amounts of contaminants including oil-spills, organic dyes and surfactants into water supplies by human activities, has been one leading cause of water scarcity.1-4 On one hand, these synthetic contaminants are difficult to be biodegraded because of their stable and complex chemical compositions. On the other hand, most of them are extremely toxic, mutagenic and even carcinogenic, which exacerbate mass mortality of aquatic organisms, species extinction and eventually threaten human beings due to the lack of access to portable water.5,6 As we are facing unprecedented demand for freshwater throughout the world with the rapid population growth and expansion of industrial development in the coming decades,7,8 immense interest has been sparked in developing universal methodologies to decontaminate water efficiently. Treatment of oily wastewater,9-11 especially those of surfactants-stabilized emulsified oil/water mixtures with oil droplet sizes smaller than 20 µm,12-14 has been proven pretty intractable as the majority of conventional filtration membranes are confronted with severe fouling by the accumulation of oil droplets, leading to prominent decline of permeation flux.15,16 Hence, great effort has been devoted to develop novel functionalized membranes with anti-fouling property for emulsion separation.17-22 Wherein, superwetting filtration membranes are acknowledged as an efficient and extensive technology for the effective separation of surfactant-stabilized


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emulsions.23-25 However, the obtained filtrates are still rich in remaining surfactants from the initial emulsions. Moreover, as a majority of pollutants existing in actual water environment not only contain emulsified oils but also always accompany with soluble contaminants such as dyes, pesticides, heavy metal ions, etc., which are discharged from oil spills, dyeing industries and manmade activities. It is an urgent task for the decontamination of both the stable emulsified wastewater and dye polluted water phase that are difficult to decolourise owing to their complex structures and synthetic origins.26 Currently, various approaches including adsorption,27,28 photocatalysis,29,30 microbiological method,31 etc., have been widely developed and employed for effectively disposing dyeing wastewater. Among them, adsorption is deemed as the most promising method to purify the organic dyes contaminated sewage because of its easy operation and comparably low cost.32,33 Thus many adsorbents have been prepared such as carbon-based nanomaterials,34-36 inorganic porous materials,37,38 polymeric resins,39,40 etc. Nevertheless, these adsorbents in powder forms can hardly achieve simultaneous adsorption and separation due to their suspended dispersed properties in water.41,42 Moreover, they are incapable of treating the aforementioned dye-polluted oil-in-water emulsion systems. Up to now, efficient separation of emulsified wastewater in the meanwhile removal of water soluble organic dyes and surfactants towards more realistic and sophisticated effluents is rarely reported. Herein, catechol (Cc)/polyethyleneimine (PEI) composite membrane was fabricated by a facile and low-cost co-deposition method through Michael addition and Schiff base reaction. As illustrated in Scheme 1, the intrinsic hydrophilicity and electrostatic attraction interaction with anionic molecules of amino-rich groups on the obtained membrane are advantageous in multifunctional water purification involves surfactant-stabilized oil-in-water emulsion separation as well as in situ controllable removal of dyes and the remaining surfactants. Compared with the


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reported water decontamination materials,43-48 such Cc-PEI deposited membrane showed considerably high separation capacity and excellent dye adsorption performance simultaneously in the water purification test with dye-polluted surfactant-stabilized emulsions. Meanwhile, it is for the first time to achieve the in situ successful adsorption of surfactant in this system (see details in Table S1 in the SI). Additionally, the resultant membranes exhibited better stability in a strong alkaline condition and retained constant adsorption capacity even after 30 cycles, indicating the unprecedented reproducibility. Especially, they presented the superior ability of selectively controllable removal of anionic dyes and surfactants by electrostatic interaction. Such characteristics, integrated with the fabrication protocol that is energy-efficient, low-cost and easy to scale-up, will facilitate their versatility and practicability in environmental remediation and water decontamination.


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Scheme 1. Schematic illustration of preparing Cc-PEI deposited membrane process, showing in situ multifunctional water purification combining emulsion separation and controllable removal of dyes and surfactants. 2. EXPERIMENTAL SECTION 2.1. Materials. Catechol (Cc), polyethyleneimine (PEI, Mw = 600 Da), methyl blue (MB) and rhodamine B (RD) were purchased from J&K Scientific Ltd. Tris(hydroxymethyl) aminomethane (Tris), cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were of analytical grade from Sinopharm Chemical Reagents. All other chemicals were used without further purification. 2.2. Fabrication of Cc-PEI Nanocomposite Deposited Membranes. Briefly, Cc (1.0 mg/mL) was dissolved in 100 mL of deionized water and PEI (0.01 g) was added into under magnetic stirring. A piece of mixed cellulose ester (MCE) microfiltration membrane was immersed in the mixed solution, then the solution of Tris (10 mmol/L, pH = 8.5) was dropwise added. The whole reaction cover with parafilm was kept for 24 h at ambient condition. The asobtained membrane was taken out, washed thoroughly with deionized water. The similar concentration-dependent fabrication protocols were adopted by controlling the mass ratios of CcPEI at 1: 0, 1: 0.25, 1: 0.5, and 1: 1, respectively, in which the concentration of Cc was fixed at 1.0 mg/mL. The time-dependent fabrication procedures were also adopted by controlling the immersing time for 6 h, 12 h, 18 h, and 30 h, respectively. 2.3. Preparation of Oil-in-Water Emulsions. Dye polluted surfactant-stabilized oil-in-water emulsions were prepared by mixing aqueous solution of MB (5 mg/L, pH = 4) and oil (toluene, n-octane and diesel, respectively) in 100: 1 (v/v%) with addition of 0.5 mg of SDS per mL under


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high stirring for 12 h. Typically, all the prepared emulsions were stable for more than 3 days without demulsification observed when placed at room temperature. 2.4. In situ Removal of Dye and Surfactant for Emulsified Water Purification. The resultant membrane was placed on the filtration apparatus. A certain volume of freshly prepared emulsion was poured onto the membrane. The process was carried out driven solely by gravity. The corresponding flux was calculated by measuring the needed time that collected a certain volume of filtrate. The separation efficiency was conducted by the oil rejection coefficient (R) according to the following:  Cf R (%) = 1 −  Co

  × 100% 

(1)

where Cf and Co were the oil concentration of the collected filtrate after one separation and the original oil concentration in fresh emulsion, respectively. The dye adsorption capacity (Ac, g/m3) of the Cc-PEI deposited membrane was calculated as follows:

Ac =

( Ci − Ce )V Ve

(2)

where Ci, Ce, V and Ve represented the initial concentration of dye solutions, the equilibrium concentration of dye solutions, the total volume of filtrates and the effective volume of the membrane, respectively.

2.5. Instruments and Characterization. FESEM images were obtained on a field emission scanning electron microscope (SU-8010, Hitachi Limited, Japan). FTIR spectra were recorded


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using a Fourier Infrared Spectrometer (NICOLET6700, Thermo Co-operation, USA). X-ray photoelectron spectroscopy (XPS) measurements were carried out on a Thermo escalab 250 Xi spectrometer using an Al Kα X-ray source (1486.6 eV). Contact angles were measured on a contact angle measurement machine (OCA 15 machine, Data-Physics, Germany). The variation of dye concentration was tested with Perkin Elmer Lambda-750 UV Spectrometer (United Kingdom). The mass spectra were characterized by LCMS-IT/TOF (Shimadzu, Japan). Optical microscopy images were taken on a polarizing microscope (Nikon ECLIPSE LV100POL, Japan). The oil content in the filtrate was measured with infrared spectrometer oil content analyzer (Oil480, Beijing Chinainvent Instrument Tech. Co. Ltd., China).

3. RESULTS AND DISCUSSION 3.1. Morphology and Surface Properties. It has been inferred that co-existence of catechol and amine groups are prerequisite for achieving oxidation polymerization on sundry materials,49,50 among which, catechols are well known to be capable of strongly binding to material surfaces via covalent and noncovalent interactions.51 Thus, we used a facile method that PEI was co-deposited on the microfiltration membranes with Cc, a biomimetic molecule ubiquitous in plant tissues and tenfold less costly than dopamine. The MCE microfiltration membranes we used show an interconnected porous structure with pore sizes of 0.22 µm average diameter (Figure 1a) and thickness of ca. 135 µm (Figure S1, SI), which is crucial for the further decontamination applications enabling the diffusion of effluents throughout the functionalized membranes. After being immersed in the mixed aqueous solutions of Cc and PEI with the mass ratio of 1: 0.5 for 24 h, the white MCE membrane turned brown and the color was uniform and homogeneous (Figure 1b and the insets). Interestingly, one can uncover that some nanostructured papillaes and aggregated spheres with hundreds of nanometers in size appeared on the membrane


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surface. It is caused by the accelerating deposition of Cc/PEI through Michael addition or Schiff base reaction between catechol and amine groups, which in turn endows the membrane with enhanced roughness. Besides, the composite in nanoscale wrapped thoroughly on the substrate and its thickness was about 150 nm. The effect of different Cc-PEI mass ratios on the membrane surface morphology after reacting for the same time was conducted (see detailed discussion in Figure S2 in the SI). This time-saving and low-cost preparation approach is, therefore, readily scalable for actual water treatment.

Figure 1. a) FESEM images of the nascent membrane and b) the Cc-PEI deposited membrane obtained at the mass ratio of 1: 0.5, insets: photographs of the MCE membrane before and after deposition of Cc and PEI. c) FT-IR spectra of the MCE membrane before and after Cc-PEI deposition. d) Wetting behaviors of various solvent liquids on Cc-PEI deposited membrane.


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To investigate the composite structures of the MCE membrane before and after Cc-PEI deposition, FT-IR analysis was performed under the same pressure. Wherein, attenuated total reflectance (ATR) spectroscopy was applied for testing the samples while the corresponding data was presented through transmission spectrum mode. As shown in Figure 1c, new peaks appeared on the composite deposited membrane at around 1598 cm-1, 1527 cm-1 and 1482 cm-1, which could be ascribed to the stretching vibrations of C=C in the aromatic ring on Cc. The characteristic peaks at 1644 cm-1 and 1279 cm-1 on the spectrum belonged to the stretching vibrations of aromatic C=N and C-N, indicating the Schiff base and Michael addition reaction of Cc with PEI. The adsorption bands related to PEI were well maintained and appeared at 2945 cm-1 and 2879 cm-1, which assigned to the C-H stretching vibrations. Meanwhile, the peak strength in the spectra of the Cc-PEI composite deposited membrane was much stronger than that of the nascent membrane, confirming the considerably high content of composite on the membrane surface. Furthermore, XPS was utilized to characterize the element composition on the membrane surface. Typical spectra were shown in Figure S3 (SI) and the corresponding atomic percentage of element composition was listed in the inset. The two spectra before and after deposition reaction contained C, N and O elements with similar peak shapes. Wherein, the nitrogen content rised from 8.81 % to 11.84 % after Cc-PEI deposition while the oxygen percentage declined from 49.00 % to 39.24 %. It is due to the high content of N in PEI, which is 32.56 % as calculated from its monomer. Besides, a new peak appeared around 500 eV was the Auger peak of sodium, which attributed to the contaminant that adhered onto the top surface of the membrane. High-resolution XPS spectra of C 1s, N 1s and O 1s peaks was deconvoluted and analyzed for more quantitatively clarifying the deposition formation of Cc-PEI nanocomposite (see detailed discussion in Figure S4 in the SI).


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It is noteworthy that the hierarchical structure combining micrometer scaled porous framework with nanostructured coatings as well as the presence of abundant hydrophilic amino groups, are greatly conducive to increase the hydrophilic property of the Cc-PEI deposited membrane. As expected, the membrane showed superhydrophilicity with water droplet contacting and spreading instantaneously within 1 second on the membrane surface (Figure 1d, left). Therewith, when immersing it in water, water molecules were trapped tightly via hydrogen bond interactions, forming a considerably stable hydration layer at the water/solid interface. Such layer served as a natural barrier towards oil penetration, which endowed the membrane with excellent underwater superoleophobicity for a selection of oils, such as toluene, n-octane, diesel and 1,2-dichloroethane (DCE), with all contact angles (CAs) larger than 150o (Figure 1d, right). The typical photographs of various liquid droplets on the membrane surface were also given as the insets. Moreover, the good stability of composite coatings is crucial for the practical applications of our membrane (see detailed discussion in Figure S5 in the SI). Thus, from the above analyses, it was reasonable to conclude that our membrane was formed by co-deposition of Cc and PEI onto the MCE support and was anticipated to be applied in field of emulsified wastewater treatment.

3.2. Dye Adsorption-Desorption Performance. Then a simple adsorption experiment was conducted to intuitively verify the optimal reaction ratio, wherein, anionic methyl blue (MB, chemical structure was shown in Figure S6 in the SI, left) was chosen as the indicant reagent to investigate the adsorption capacity of concentration-dependent deposited membranes. Firstly, the membranes were fixed in vacuum filtration apparatus. All initial volumes of MB (5 mg/L, pH = 4) were 100 mL and during the adsorption procedures ~ 0.1 MPa pressure was applied. As shown in Figure 2a, the peak at 630 nm ascribed to the adsorption of MB solution decreased


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gradually alongside with the increasing ratio and almost disappeared when the mass ratio is 1: 0.5, among which all of the MB was captured by the Cc-PEI nanocomposite deposited membrane due to electrostatic attraction interaction.27 The inset also clarified that the sky blue color of original solution disappeared completely within several seconds, giving a direct visual impression of the fast adsorption kinetics of MB on the deposited membranes. However, when PEI content further increased to 1: 1, the Cc concentration was too low to be polymerized into polyphenol. PEI was not able to adhere onto the MCE membrane surface efficiently because of its solubility in water. Therefore, there was no obvious morphology change or superior adsorption performance of MB than that of membrane obtained at the mass ratio of 1: 0.5. The effect of deposition time on surface morphology and adsorption capacity was also studied under the aforementioned experimental conditions (all mass ratios were controlled at 1: 0.5, see detailed discussion in Figure S7 in the SI).


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Figure 2. a) Adsorption spectra of the original MB (5 mg/L) and the decontaminated solutions with Cc-PEI deposited membranes at different mass ratios for only several seconds, inset: photographs of the corresponding solutions. b) XPS spectra of the Cc-PEI deposited membrane after adsorption and desorption of MB. c) Fluctuation curve for adsorption of MB by the same membrane after 30 consecutive adsorption-desorption-washing cycles. d) UV-vis spectra of initial MB solution, initial RD solution, the RD/MB mixed solution and the resultant filtrate, insets were the photographs of corresponding solutions. The membrane could be facilely reproduced by immersing in NaOH solution (pH = 11) for tens of seconds to desorb the blocked dyestuffs and XPS analysis was subsequently performed to confirm the successful adsorption-desorption stage (Figure 2b). Dye adsorption resulted in a new peak of S 2p at 167.5 eV, ascribed to the existence of sulfonate group from MB molecules. After desorption of MB, the S 2p peak disappeared and the tendency of XPS spectra was virtually the same as that of the fresh membrane. The recyclability of our nanocomposite Cc-PEI deposited membrane was of great importance for practical applications. As depicted in Figure 2c, even after 30 consecutive adsorption-desorption-washing cycles, the adsorption capacity of the deposited membrane was almost unchanged and retained very high. These proof-of-concept tests meant that there was no obvious deterioration in the dye removal ability of the membrane in scaled-up application range. Another advantage of the versatile Cc-PEI nanocomposite deposited membrane was that its selective adsorption capacity towards anionic dyes, which could find practical applications in the controllable separation of anionic dyestuffs from dye mixtures. Verification test was carried out by taking a mixture of MB/ rhodamine B (RD, chemical structure was shown in Figure S6 in the SI, right) with a 2: 1 mass ratio as an example. The solution concentrations of initial MB, RD,


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mixture and the filtrate were determined by UV-vis spectra (Figure 2d). It was found that the adsorption peak of MB at 550 nm disappeared in the mixed solution, which may attribute to the conjugation effect of these two dyes. After filtration, it was obvious that the crystal violet solution changed to rose red corresponding to the color of RD, whereas the adsorption peaks of MB disappeared totally with the deduction of about 98.9% in the resultant filtrate caused by electrostatic attraction interaction. Additionally, the van der Waals forces and hydrogen bonds interactions between cationic dyes and the Cc-PEI deposited membrane may account for the phenomenon that the adsorption intensity of the filtrate slightly decreased with about 17.7% compared to the original RD solution.

3.3. Surfactants Adsorption-Desorption Performance. Surfactants may infiltrate into groundwater and undergo bioaccumulation in the living organisms, which will change the structure of proteins and cause allergies. Wherein, anionic surfactants are the most toxic. An appealing protocol for remediation of anionic surfactants is the use of our Cc-PEI nanocomposite deposited membrane based on the same mechanism as that of dye removal. Proving experiments were conducted by introducing cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) as cationic surfactant and anionic surfactant, respectively (chemical structures were shown in Figure S8 in the SI). The initial concentration of these two surfactants aqueous solutions (pH = 4) we used was kept 0.5 mg/mL and mass spectra was utilized to characterized the residual amount of surfactants in the filtrate. Both the CTAB and SDS filtrates were diluted 10 times. With regard to the CTAB filtrate, the main peak of mass spectrum is located at 284.3313, which is consistent with the mass-to-charge ratio of C19H42N+ (Figure 3a and b). As for the SDS one, the main peak of 265.1478 assigned to the mass-to-charge ratio of C12H25SO4(Figure 3c and d). These results indicated that a fraction of surfactants inflowed into the filtrates.


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To quantify the residual amount of surfactants, the standard aqueous solutions of these two surfactants with the concentration of 1 ppm were prepared after being diluted 500 times, respectively. The corresponding extract ion chromatograms (EIC) of the filtrates and the standard solutions were demonstrated in Figure 3 and Figure S9 (SI). Through the calculation, 77.2 % of CTAB penetrated through the membrane while 97.9 % of SDS was absorbed on the membrane. This phenomenon could be explained by the electrostatic attraction interaction between SDS molecules and the Cc-PEI nanocomposite coatings. Considering the small molecular weight of CTAB as well as the microscale interconnected structures of as-prepared membrane, CTAB molecules were repelled and much easier to be blocked in the internal structure or flow into the filtrate. More importantly, after 30 times of filtration process for SDS aqueous solution, the removal efficiency of anionic surfactant remained above 96 % (Figure S10, SI), exhibiting excellent stability of our material.


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Figure 3. a) and b) The EIC image and mass spectrum of the filtrate with CTAB. c) and d) The EIC image and mass spectrum of the filtrate with SDS.

3.4. In situ Removal of Dye and Surfactant for Emulsified Water Purification. Given that the Cc-PEI nanocomposite deposited membrane was superoleophobic and possessed relatively larger pores (microfiltration membrane), we systematically studied its decontamination performances for dye polluted anionic surfactant-stabilized oil-in-water emulsions. Toluene was utilized as the target oil for preparing oil-in-water emulsion. Specifically, the membrane was fixed into the separation apparatus (Figure 4a). 50 mL of the freshly prepared emulsion (pH = 4) with initial concentrations of 5 mg/L MB dye and 0.5 mg/mL SDS, respectively, was poured onto the membrane and the experiment was carried out driven by gravity. Compared to the original milky blue feed emulsion, the colorless and transparent filtrate passed through the device and into the supporting flask (Figure 4b), giving a direct visual impression of the superior multifunctional capacities involving emulsion separation and in situ controllable removal of dye and surfactant. To qualitatively observe the composition difference between the feed and corresponding filtrate, optical microscopy was conducted and the results were shown in Figure S11 (SI). The whole view before filtration was flooded with densely packed oil droplets, whereas not a single droplet could be uncovered in the image of the collected filtrate, implying that toluene had been successfully removed. In addition to toluene, the composite membrane could effectively separate MB polluted SDS-stabilized emulsions composed by a range of oils such as n-octane, diesel, etc. (Figure 4c). All the separation efficiency was over 99.5 %. Meanwhile, the minimum flux reached 100 L m-2 h-1, which is acceptable since no external pressure was applied in the separation process. The feed and corresponding filtrate were also analyzed using UV-vis adsorption spectra as shown in Figure 4d. The characteristic adsorption peak at wavelength of


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630 nm which ascribed to MB dye in initial emulsion almost disappeared after one filtration, presenting the successful dye removal ability of the as-prepared membrane. At last, mass spectrum was utilized to measure the residual amount of surfactant in the filtrate and the result was shown in Figure 4e. In coincidence with the aforementioned results, 99.9 % of SDS has been absorbed by the membrane. These results indicated that, within the saturated range of adsorption, both these two anionic pollutants could be almost entirely captured by the as-obtained membrane without no competition relationship between them, confirming its superior adsorption capacities towards sundry anionic pollutants. As such, the Cc-PEI nanocomposite deposited membrane enables versatile and energy-saving purification for sophisticated wastewater that involves both the insoluble oily sewage and the water soluble effluents.


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Figure 4. a) Separation process of MB polluted SDS-stabilized toluene-in-water emulsion, in which the milky blue emulsion was demulsified as well as the colorless and transparent filtrate passed through the membrane then into the supporting flask. b) Photograph of the MB polluted SDS-stabilized toluene-in-water emulsion before and after filtration. c) Separation efficiency (red) and the corresponding permeation flux (cyan with oblique line) of the Cc- PEI deposited membrane for a range of MB polluted SDS-stabilized oil-in-water emulsions. d) UV-vis adsorption spectra of the emulsion before and after filtration. e) The EIC image of the filtrate with SDS.

3.5. Mechanism of Controllable Pollutants Removal. The above excellent adsorption capacity of dye and surfactant is attributed to the vast specific surface area of the as-obtained membrane with 3D porous structures. In addition, the residual abundance of amino groups in PEI could be reinforced protonated at a lower pH value, and thus strengthen the electrostatic interaction between the resultant membranes and anionic molecules. As a proof of concept, the effect of pH value on the adsorption capacity of MB molecules was conducted and shown in Figure S12 (see detailed discussion in the SI). As depicted in Figure 5a, the surface of Cc-PEI coatings with positive charge under the acidic condition could quickly capture negatively charged pollutants via electrostatic attraction in adsorption stage, while achieved almost total desorption in the elution stage under alkaline solution. It was confirmed in Figure 5b that MB dye was all captured by the Cc-PEI nanocomposite deposited membrane in adsorption stage, whereas the color of membrane after desorption was nearly identical to the freshly as-prepared membrane, signifying the thorough dye elution process under alkaline condition. Significantly, the whole continuous adsorption-desorption test could be accomplished in only several minutes,


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which endowed the resultant membrane with high reproducibility for wastewater treatment in real conditions.

Figure 5. a) Schematic illustration for controllable dyes and surfactants adsorption-desorption cyclic test through the Cc-PEI deposited membrane by alternative filtration of acidic dye solution and sequential regeneration in alkali aqueous solution. b) Color variation of the Cc-PEI deposited membrane after cyclic test of MB adsorption-desorption stage.

4. CONCLUSIONS In summary, we report that the multifunctional microfiltration membranes can be facilely fabricated by one-step co-depositing biomimetic adhesive catechol and PEI on the support membrane under mild conditions. The incorporation of PEI during the self-polymerization process of polyphenol endowed the resultant membranes with distinctive advantages of hydrophilicity and amino-rich surfaces. Based on the combination of the support membrane with micrometer-scaled interconnected porous structure, such nanocomposite deposited membranes


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with superhydrophilicity and underwater superoleophobicity are advantageous in multifunctional water purification towards emulsion separation and in situ removal of dyes and surfactants. As a proof of concept, they exhibited simultaneously high separation capacity and excellent adsorption performance in the water purification test with dye-polluted surfactant-stabilized emulsions. Besides, the deposited membranes presented better stability in a strong alkaline condition and retained high adsorption capacity even after 30 cycles, indicating the unprecedented reproducibility. More importantly, they showed the superior property of controllable removal of anionic dyes and surfactants by electrostatic attraction interactions. Such characteristics, integrated with the fabrication protocol that is energy-efficient, low-cost and easy to scale-up, may provide prospects for facilitating their versatility and practicability in environmental remediation and wastewater purification.

ASSOCIATED CONTENT Supporting Information Comparison of the properties between the Cc-PEI composite membrane and the reported water decontamination materials, cross-section image of the nascent MCE membrane, morphologies of the Cc-PEI deposited membranes obtained in different mass ratios, XPS spectra, high-resolution XPS spectra, alkaline resistance measurement, molecular structures of dyes, morphologies of the Cc-PEI deposited membranes obtained in different deposition time and the corresponding adsorption spectra of MB solutions, molecular structures of surfactants, EIC images and mass spectra of the surfactant standard solutions, recyclability test of SDS adsorption, optical microscopy images of the emulsion before and after filtration, and effect of pH value on the


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adsorption capacity. The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * E-mail: [email protected]. Phone: +86-010-62792698.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors are grateful for financial support from the National Natural Science Foundation (51173099, 21134004).

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Table of Contents: Catechol-PEI nanocomposite deposited membrane is facilely designed through low-cost method on microfiltration membrane surface, which is advantageous in emulsion separation and in situ water-soluble pollutants removal with superior separation capacity and controllable adsorption performance simultaneously. Especially, such energyefficient membrane presents selective removal ability of anionic molecules and better alkaline resistance with high reproducibility.


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Nanocomposite Deposited Membrane for Oil-in-Water Emulsion

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