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CuSO/HO Triggered Polydopamine/Poly(sulfobetaine methacrylate) Coatings for Antifouling Membrane Surfaces Chao Zhang, Hao-Nan Li, Yong Du, Meng-Qi Ma, and Zhi-Kang Xu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b03948 • Publication Date (Web): 16 Jan 2017 Downloaded from http://pubs.acs.org on January 19, 2017

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[Revised as an article for publication in Langmuir]

CuSO4/H2O2 Triggered Polydopamine/Poly(sulfobetaine methacrylate) Coatings for Antifouling Membrane Surfaces Chao Zhanga,b,, Hao-Nan Lia,b, Yong Dua,b, Meng-Qi Maa,b, and Zhi-Kang Xua,b∗ a

MOE Key Laboratory of Macromolecular Synthesis and Functionalization, bKey Laboratory of

Adsorption and Separation Materials & Technologies of Zhejiang Province, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China

KEYWORDS. mussel-inspired coating; polydopamine; zwitterionic polymer; antifouling; membrane surface.

Abstract The mussel-inspired polydopamine (PDA) coatings have been broadly exploited for constructing functional membrane surfaces. One-step co-deposition of PDA with antifouling polymers, especially zwitterionic polymer, has been regarded as a promising strategy for fabricating antifouling membrane surfaces. However, one challenge is that the co-deposition is usually a slow process with ten hours or even several days. Herein, we report that CuSO4/H2O2 is able to notably accelerate the co-deposition process of PDA with poly(sulfobetaine methacrylate) (PSBMA). In our case, PSBMA is facilely anchored on the polypropylene microporous membranes (PPMMs) surfaces within 1 h with the assistance of PDA due to its strong interfacial adhesion. The PDA/PSBMA-coated PPMMs show excellent surface hydrophilicity, high water permeation flux (7506 ± 528 L/m2⋅h at 0.1 MPa), and outstanding antifouling property. Moreover, the antifouling property is still

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maintained after the membranes were treated with acid and alkali solutions as well as organic solvents. To recap, it provides a facile, universal and time-saving strategy to exploit high-efficiency and durable antifouling membrane surfaces.

1. INTRODUCTION Water scarcity and pollutions have been regarded as one of the biggest threats to the sustainable development of industrial and social activities. To address these issues, a series of technologies have been proposed for water treatment and reuse, including flocculation,1 adsorption,2 biological treatment3 and photocatalysis.4 In the last decades, membrane separation has been developed into the most promising candidate for water purification due to its easy scale-up, high efficiency, low cost and energy-saving characteristics.5-6 However, membrane fouling is usually a ubiquitous phenomenon during practical applications. It resulted from strong interactions between the membrane surfaces with proteins, colloidal particles or natural organic matters, especially hydrophobic membranes surfaces.7 The membrane fouling phenomenon will in turn lead to an increase of transmembrane pressure, a decline of water permeation flux, and a decrease of membrane life-span. Numerous strategies have been investigated to alleviate the membrane fouling phenomenon. In general, they can be divided into two types: improvement of the membrane matrix and modification of the membrane surface.8-11 Among them, surface modification has been considered as the most common and effective method because it can delicately and facilely tune the surface properties without influencing the structures of the membrane matrix. Up to now, various materials and fabrication approaches have been developed for the surface modification. For example, water-soluble polymers, such as poly(ethylene glycol) (PEG),12-13 poly(vinyl pyrrolidone) (PVP)14 and zwitterionic polymers,15-19 have been found as useful antifouling agents due to their capability of forming a bonded water layer on the membrane surfaces to


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effectively resist the fouling. These polymers are usually anchored on the membrane surfaces through covalent bindings via UV20 or plasma grafting21 and physical interactions via dip-coating or layer-by-layer (LBL).22-23 However, these fabrication methods go far from desirable for the practical requirements of great facility, high efficiency and low cost. Therefore, it still remains a challenge to design an easy, efficient and universal method for constructing membrane surfaces with antifouling characteristic. In 2007, Messersmith et al. proposed that the mussel-inspired plydopamine (PDA) coatings can be fabricated on various organic and inorganic material surfaces because of strong and universal interfacial adhesive forces.24 Apart from the material-independent property, these coatings contain some functional/reactive groups (catechol, amine, and imine) for providing the capability of post-functionalization.25, 26 Therefore, they can be used as the intermediate layer to fabricate antifouling surfaces by attaching those amine- or thiol-ended polymers via the “grafting-to” method.27 Similarly, the “grafting-from” method can also be used for the same purpose via surface-initiated polymerization.28 For example, a bromoalkyl initiator was anchored on the PDA-coated membrane surface and subsequently initiated atom transfer radical polymerization (ATRP) for fabricating zwitterionic poly(sulfobetaine methacrylate) (PSBMA) brushes.28 However, the processes require multiple steps or complex operations such as water-free or oxygen-free conditions. In our previous work, a one-step method was developed to construct antifouling membrane surfaces via the co-deposition of PDA and PSBMA by their non-covalent interactions.29 This method was also be utilized by Emrick et al. to fabricate biocompatible, hydrophilic and

fouling-resistant

surfaces

via

the

co-deposition

of

PDA

and

poly(methacryloyloxyethylphosphorylcholine) (PMPC).30 The one-step co-deposition greatly simplifies the fabrication process, but it generally costs ten hours or even several days. To date, the majority of mussel-inspired modification approaches for antifouling


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surfaces are faced with the same issue,31-35 shown in Table 1. The co-deposition rate is highly dependent on the oxidation of dopamine and formation of PDA. However, it is very slow for the typical air-oxidization of dopamine and the formation of PDA coatings. Fortunately, numerous oxidants have been proposed to tremendously enhance the formation rate of PDA.36, 37 In previous work, we utilized CuSO4/H2O2 as a trigger to produce a great deal of reactive oxygen free radicals, which can rapidly initiate the polymerization of dopamine and greatly improve the deposition rate of PDA.38 Therefore, CuSO4/H2O2 can similarly accelerate any other co-deposition systems based on PDA. In addition, compared with conventional oxidation methods, CuSO4/H2O2-triggered PDA coatings exhibit high uniformity and stability apart from the high deposition rate, which provides new perspectives for fabricating desirable PDA-based coatings. Herein, we report a rapid, facile and universal approach to fabricate antifouling membrane surfaces via the CuSO4/H2O2-triggered co-deposition of PDA and PSBMA. The PDA/PSBMA coatings are successfully constructed on the polypropylene microfiltration membranes (PPMMs) surfaces due to the assisted-deposition of PDA, and the co-deposition time is tremendously shortened from 18 h to 1 h. The modified PPMMs were characterized in detail by field emission scanning electron microscopy (FESEM), attenuated total reflectance fourier transform infrared (ATR/FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The surface wettability, water permeation flux and protein resistance are immensely enhanced after the co-deposition of PDA/PSBMA coatings. Moreover, the PDA/PSBMA-coated PPMMs show excellent stability under various conditions, including salt, acid and alkali solutions and organic solvents. To the best of our knowledge, this method makes a great progress on the fabrication of antifouling membrane surfaces.

2. EXPERIMENTAL SECTION


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2.1 Materials Polypropylene microfiltration membrane (PPMM, mean pore size ∼ 0.2 μm) was purchased from Membrana GmbH (Germany). The samples with a diameter of 2.5 cm were washed by acetone for 2 h to remove adsorbed impurities and then dried in a vacuum oven at 60 °C. Dopamine hydrochloride, tris(hydroxymethyl) aminomenthane and N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethyl

ammonium

betaine

(sulfobetaine

methacrylate, SBMA, 97%) were obtained from Sigma-Aldrich (USA). Bovine serum albumin (BSA, pI = 4.8, 67 kDa), lysozyme (Lys, pI = 10.8, 14.4 kDa), hemoglobin (Hgb, pI = 7.0, 65 kDa) and fluorescent-labeled BSA (FL-BSA, pI = 6.0, 6672 kDa) were acquired from Sinopharm Chemical Reagent (China) and Shanghai Jiahe Biotechnology Co. Ltd. (China), respectively. Escherichia coil (E.coil, strain ATCC 29213) was purchased from VWR International, LLC (China). Other reagents such as sodium dihydrogen phosphate, disodium hydrogen phosphate, copper(II) sulfate pentahydrate, hydrogen peroxide, ethanol, hydrochloric acid, potassium persulfate and acetone were purchased from Sinopharm Chemical Reagent Co., Ltd (China). All the reagents were used without further purification. Experimental water was deionized and ultrafiltrated to18.2 ΩM with an ELGA LabWater system (France). 2.2 Synthesis of PSBMA PSBMA was synthesized by typical free radical polymerization. Firstly, SBMA aqueous solution (0.1 g/mL) in a flask was degassed by bubbling N2 for 30 min and then placed in oil bath at 70 °C. Subsequently, potassium persulfate (4 %, wt %) was quickly added into the flask as initiator to initiate the polymerization for 10 h. Finally, the polymerization mixture was dialyzed against water for 3 days to remove residual monomers and oligomers, and lyophilized to obtain the product. H1 NMR showed the chemical structure of PSBMA (Fig. S1 in Supporting Information). The synthesized polymer had number-average


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molecular weight of 1.189 × 104 Da, which was characterized by GPC (Table S1 in Supporting Information). 2.3 Co-deposition of PDA/PSBMA triggered by CuSO4/H2O2 Dopamine, PSBMA, CuSO4 (5 mM) and H2O2 (19.6 mM) were all dissolved in Tris buffer (pH = 8.5, 50 mM) to prepare the deposition solutions. The concentration of dopamine was kept at 2 g/L and the mass ratio of dopamine/PSBMA was varied from 1:0 to 1:5, 1:10, 1:20 and 1:50. PPMM samples were first pre-wetted by ethanol and then immersed in the deposition solutions shaken in an air oscillator at 25 °C for 1 h. Subsequently, the samples were washed by ultrapure water overnight and dried in a vacuum oven at 60 °C for 4 h. 2.4 Characterization Field emission scanning electron microscope (FESEM, Hitachi S4800, Japan) was used to characterize the surface morphologies of the membranes. X-ray photoelectron spectra were employed to measure the chemical composition of the membrane surfaces using a spectrometer (XPS, Perkin Elmer, USA) with Al Kα excitation radiation (1486.6 eV). FT-IR/ATR spectra were also acquired the chemical structures of the membrane surfaces by using an infrared spectrophotometer (Nicolet 6700, USA) equipped with an ATR accessory (ZnSe crystal, 45°). The charge property of the membrane surfaces was detected by a streaming potential method using the electrokinetic analyzer (SurPASS Anton Paar, GmbH, Austria) with KCl (1 mmol/L) solution as electrolyte solution. The surface wettability of the membrane was evaluated by the detection of water contact angles using a DropMeter A-200 contact angle system (MAIST VisionInspection & Measurement Co. Ltd., China). Pure water flux of the membranes was measured by a dead-end stirred-cell filtration system (Millipore 6700P05, USA). UV-vis absorbance of proteins was determined by a UV–vis spectrophotometer (UV-2450, Shimadzu Inc, Japan). Fluorescence microscope


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(Nikon ECLIPES Ti-U, Japan) was used to observe the FL-BSA adsorption on the membrane surfaces. 2.5 Co-deposition density of PDA/PSBMA The deposition density (DD, mg/cm2) was measured by the weighing method and calculated by the following equation (1): DD =

𝑀1 −𝑀0 𝑆

(1)

where M1, M0 and S are the weight (mg) of the modified membrane, the weight (mg) of the nascent membrane and the area (4.91 cm2) of the membrane, respectively. Each result is an average of at least three parallel experiments. 2.6 Protein resistance performances The protein resistance of the membranes was evaluated by static protein adsorption and dynamic protein filtration. For static protein adsorption, BSA, Hgb and Lys were chosen as model proteins, and their adsorption capacities were obtained by calculating the concentration difference of protein solution after the immersion of membranes for 4 h. The related operations are according to previous report,29 and the protein adsorption capacity of the membranes (Q, mg/g) was calculated using the following equation (2): Q=

𝐶0 −𝐶1 𝑊

× 𝑉 × 1000

(2)

where C0 and C1 are the concentration (mg/mL) of protein solution before and after adsorption, respectively. V is the volume (mL) of protein solution and W is the weight (mg) of the membranes. Dynamic protein filtration was performed by a dead-end stirred-cell filtration system (Millipore 6700P05, USA). Firstly, the membranes were compacted at 0.3 MPa for 30 min, and then the water flux (Jw, L/m2⋅h) was measured at 0.1 MPa after operating under this pressure for 10 min to reach a stable value. Similarly, the permeation flux (JP, L/m2⋅h) of protein solution was detected by filtrating the BSA or Lys solution with concentration of


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1.0 g/L. To investigate the flux recovery property, PBS solution was used to clean the membrane for another 30 min at 0.10 MPa, and the according water flux (JR, L/m2⋅h) was measured again. The relative flux reduction (RFR) and the flux recovery ratio (FRR) were calculated by the following equation (3) and (4): 𝐽𝑝

RFR (%) = �1 − 𝐽 � × 100

FRR (%) =

2.7 Bacterial Adhesion

𝐽𝑅

𝐽𝑊

𝑤

× 100

(3) (4)

E.coil was selected as the model bacteria to evaluate the bacterial adhesion property of the membranes, and according operation is similar to previous reports.30 All samples were divided into two groups, and their incubation time was 2 h and 24 h, respectively. After incubation, the bacteria adhered on the membranes were anchored by cross-linking using glutaraldehyde, and then the membranes were immersed into ethanol for 6 h to totally exchange water and dried in vacuum at 60 °C for 4 h. Finally, FESEM was used to analyze the bacterial adhesion on the membrane surfaces, and then the statistical analysis method was utilized to quantitatively assess the bacterial adhesion property. 2.8 Stability of PDA/PSBMA coatings To evaluate the stability of PDA/PSBMA coatings, the changes in antifouling performance were characterized after the membranes were treated with different solutions such as potassium chloride solution (0.1 M), sodium hydroxide solution (pH = 11), hydrochloric acid solution (pH = 3) and some typical organic solvents. Firstly, the membranes were treated by the aforementioned solutions in a shaken bath at room temperature under 100 rpm for 12 h, and then RFR and FRR were measured again. Finally, these RFR and FRR were compared with those of the untreated membranes.

3. RESULTS AND DISCUSSION


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3.1 Surface morphology and chemistry of the PDA/PSBMA-coated membranes It is well known that the surface modification by PDA deposition is highly related to a series of factors, including dopamine concentrations, temperature, deposition time, and oxidants.39 In our cases, the deposition temperature and the dopamine concentration were fixed at 25 °C and 2 mg/mL, respectively, and the influence of deposition time using CuSO4/H2O2 as a trigger was investigated in detail (Fig. S2 in Supporting Information). The deposition density gradually increased with the increase of deposition time and then kept a steady value after 1 h. It is possible that numerous PDA aggregates begin to precipitate from the deposition solutions after 1 h, and these large particles cannot be adhesively deposited on the membrane surface to form coatings. Thus, 1 h was selected as the optimal time for the co-deposition of PDA with PSBMA. In co-deposition case, the mass ratio of dopamine/PSBMA will influence the deposition density. Fig. 1 showed that it had a slight rise with the decrease of the mass ratio from 1:5 to 1:50. Compared with the deposition of PDA, the deposition density of PDA/PSBMA had an obvious decline, which collaborated with previous report.30 A possible reason is that PSBMA can slow down the polymerization rate of dopamine because of some non-covalent interactions between PSBMA and PDA.29 However, it is worth noting that the deposition density can reach 0.305 mg/cm2 after 1 h when the mass ratio of dopamine/PSBMA is 1:50. As a contrast, the deposition density of 0.325 mg/cm2 can be obtained after 12 h co-deposition under air condition.29 It is obvious that the rapid co-deposition method using CuSO4/H2O2 as a trigger is more time-saving. ATR/FT-IR and XPS spectra were used to analyze the chemical structures and compositions of the co-deposited coatings with different mass ratios of dopamine/PSBMA on PPMM surfaces. Fig. 2A showed that, compared with the nascent PPMM, a weak absorption peak at 1610 cm-1 was attributed to the C=C stretching vibration of aromatic


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ring, indicating the formation of PDA on the membrane surfaces. By contrast, several characteristic peaks appeared obviously after the co-deposition of PDA/PSBMA. The peaks at 1725 cm-1, 1160 cm-1 and 1031 cm-1 were ascribed to the vibrations of O-C=O stretching, S=O asymmetric stretching and symmetric stretching, respectively,28 which demonstrates that PSBMA is successfully deposited on the PPMM surfaces with the assistance of PDA. Besides, the intensity of the aforementioned peaks gradually enhanced with the increase of mass ratio of PSBMA, qualitatively exhibiting the content of PSBMA is gradually raised in the coatings. Fig. 2B indicated that the nascent PPMM only had a major peak at 284.6 eV, which was attributed to the binding energy of C1s. Two signals of O1s and N1s appeared on the PDA-coated membrane surface. Apart from these two peaks, a signal of S2p3 can also be detected on the PDA/PSBMA-coated PPMMs. This peak was used to calculate the percentage of sulfur element, and it reached 2.07 % for the membrane co-deposited with a mass ratio of 1:50 for 1 h. Both ATR/FT-IR and XPS results confirm that PSBMA is able to be successfully fabricated on the PPMM surfaces via the rapid co-deposition method. It is well known that PDA coatings oxidized by air are not smooth, and there are some large PDA particles in the coatings surface,37 which will cause the membrane pores to be blocked to some extent. The PDA/PSBMA coating oxidized by air is also faced with the same problem. However, Fig. 3 indicated that there were no obvious changes on the membrane surfaces modified by our rapid co-deposition method. It means that CuSO4/H2O2 can trigger the fast oxidation polymerization of dopamine followed by the homogenous deposition of PDA/PSBMA on the membrane surfaces,38 indicating that rapid co-deposition method possesses good conformal function. 3.2 Surface wettability and permeation property of the PDA/PSBMA-coated membranes The surface wettability and permeation property of the PDA/PSBMA-coated membranes


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were evaluated by water contact angle (WCA), and the results were exhibited in Fig. 4a. For the nascent PPMM, the WCA was near 150°. WCA of the modified membranes dramatically declined to even less than 20°, and finally the water drop permeated through the membranes in a short time, which was attributed to the intrinsic hydrophilicity of zwitterionic polymers. To further investigate the permeation property, we quantitatively analyzed the time for a water drop to permeate through the membrane from its top surface to the opposite side. Fig. 4b showed that the permeation time gradually decreased with the increase of PSBMA content and required only 0.4 s when the mass ratio of dopamine/PSBMA is 1:50. This permeation property was unparalleled and hardly obtained by other modification methods such as UV-induced graft polymerization10 and air-oxidized PDA deposition.29 Pure water permeation fluxes were also measured to further evaluate the hydrophilicity of as-prepared membranes (Fig. S3 in Supporting Information). The permeation flux of PPMMs had an immense improvement after the rapid co-deposition of PDA/PSBMA. It is worth noting that the PDA/PSBMA-coated PPMMs can reach 7506± 528 L/m2⋅h under 0.1 MPa, which is 19 times higher than that of the nascent PPMM (382 ± 46 L/m2⋅h) and also much higher than that of PDA/PSBMA-coated PPMMs oxidized by air (6000 ± 120 L/m2⋅h).29 The results were ascribed to the modified PPMMs with unparalleled hydrophilicity and permeation property. On the other hand, the rapid co-deposition method showed conformal function and had little influence on the membrane morphology without the phenomena of the membrane pore blockage. 3.3 Antifouling performance of the PDA/PSBMA-coated membranes BSA protein was selected as a model protein to evaluate the antifouling performance of as-prepared membranes by dynamic protein filtration experiment. Fig. 5a showed that RFR for the nascent PPMM was nearly 92%, which indicated that the membrane pores were easily blocked by the proteins. Besides, this protein adsorption was irreversible and hard to


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be washed away, resulting in a low FRR (24%). RFR gradually declined and FRR accordingly increased with the increasing amount of PSBMA in the co-deposited PDA/PSBMA coatings, which were ascribed to aforementioned enhanced hydrophilicity and in consistent with above results. The possible reason is that PSBMA contains both positively and negatively charged moieties and can be strongly hydrated through ionic solvation, which is useful to fabricate a robust water molecule layer on the membrane surface to resist protein adsorption. In order to further evaluate the antifouling performance, BSA, Hgb and Lys were used as model proteins to carry out static protein adsorption experiment, as exhibited in Fig. 5b. It can be seen that the nascent and modified PPMMs all adsorbed a certain amount of proteins, especially for Lys with positive charges in PBS (pH = 7.0). All the PPMMs were negatively charged in PBS (pH = 7.0), which was confirmed by their zeta potentials (Fig. S4 in Supporting Information). Therefore, the PPMM surfaces will

adsorb

more

Lys

via

strong

electrostatic

interactions.

In

addition,

the

PDA/PSBMA-coated PPMMs showed better fouling resistance performance for three proteins than those of the nascent and PDA-coated PPMMs. In order to intuitively reveal protein resistance property, fluorescence microscopy was used to observe the FL-BSA adsorption on the as-prepared membrane surfaces. Fig. 6 illustrated that the fluorescence for the PDA/PSBMA-coated PPMMs was barely observed, but the nascent PPMM showed extremely strong fluorescence. All results indicate the introduction of PSBMA dramatically enhances the protein resistance property of the membrane surfaces. Apart from proteins, bacteria can also adhere on the membrane surfaces, resulting in severe biofouling, especially for some biomedical applications.40 Sim9ilarly, we chose E. coil as typical bacteria to study the anti-adhesion property of as-prepared membranes. Fig. 7 showed that there were a large number of bacteria attaching on the nascent PPMM surfaces after 2 h incubation. As a contrast, the adhesion of bacteria was significantly


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suppressed on the PDA-coated surfaces, and the amount of its bacterial adhesion was only 10% of nascent surfaces (Fig. S5 in Supporting Information). For the PDA/PSBMA-coated surfaces, the bacteria couldn’t be observed, and the adhesion was inhibited almost completely. To investigate its long-term resistance against E. coli adhesion, FESEM images were observed from those samples incubated in E. coli suspensions for 24 h (Fig. S6 in Supporting Information). It was apparent that the PDA/PSBMA-coated surfaces still had no bacteria adhesion and exhibited durable resistance to bacterial fouling. In addition, we roundly compared the antifouling performance of our approach with other mussel-inspired methods (Table 1). It can be seen that our method possesses the shortest coating time as well as exhibits relatively excellent antifouling properties. PSBMA brushes has been regarded an ideal antifouling material and similarly used as reference. The RFR and FRR of PSBMA brushes on the PPMMs surfaces via UV-induced grafting are 35% and 95%, respectively,10 which is better than our method. But its fabrication method is too complicate and lack of universality. To recap, the greatest advantage of our method is that the fabrication strategy is enough simple as well as possesses acceptably high-efficiency antifouling performance. 3.4 Stability of the PDA/PSBMA-coated membranes The service stability plays a crucial role for membranes in practical applications. It is well known that PDA coatings are formed through covalent polymerization and non-covalent self-assembly,41 and the non-covalent parts are unstable under harsh condition.42-43 The interactions are also non-covalent between PSBMA and PDA during their co-deposition.29 Therefore, the coating stability has to be enhanced by subsequent oxidization treatment to increase the cross-linking structure of coating.30 To our delight, CuSO4/H2O2-triggered coatings exhibit high stability due to more covalent parts and cross-linking sites than that of air oxidation.38 Therefore, we studied the coating stability by


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systematically analyzing the change of antifouling properties under different conditions. Fig. 8a showed that RFR and FRR for the PDA/PSBMA-coated PPMMs had little change after the treatment by pH = 11 and pH = 3. Similarly, the antifouling property of the as-prepared membranes was maintained after the treatment by common organic solvents (Fig. 8b). In addition, we investigated their antifouling property under long-term operation in 0.1 M NaCl (Fig. 9a). Although the value of FRR had slight fluctuation, it was still near 80%, indicating that the antifouling performance of the modified membranes exhibits long-term stability. These all demonstrate that the structure of CuSO4/H2O2-triggered PDA/PSBMA coatings exhibits outstanding stability and durability, which is unmatched by other methods. In view of rapid co-deposition using CuSO4/H2O2 as a trigger, residual copper ions in the coatings are potential risk for water treatment. These copper ions might be eluted and lead to secondary pollution. Thus, we detected the concentration of copper ions in the filtrate (Fig. S7 in Supporting Information). The concentration of copper ions was only 1.5 µg/L, which is far less than the maximum concentration for drinking water (2 mg/L). It endows PDA/PSBMA-coated membranes with tremendous potential for practical application.

4. CONCLUSION In summary, we propose a facile, universal and efficient method to construct antifouling membrane surfaces via the rapid co-deposition of PDA and PSBMA triggered by CuSO4/H2O2. Compared with conventional processes, the co-deposition time is immensely shortened to 1 hour by our method. The PDA/PSBMA-coated membranes show unparalleled surface hydrophilicity and water permeation property. In addition, these membranes have low water flux reduction, high water flux recovery, as well as low protein adsorption and bacterial adhesion. Furthermore, the PDA/PSBMA-coated membranes also


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exhibit outstanding stability under some harsh conditions. In one word, it is the first time for fabricating the high-efficiency and durable antifouling membrane surfaces via rapid co-deposition of PDA and zwitterionic polymer, which can be similarly applied in other co-deposition systems and broaden the applications of PDA-based coatings.

ASSOCIATED CONTENT Supporting Information. Details of 1H NMR and GPC data of PSBMA, deposition density of PDA, XPS and zeta potential data of the nascent, PDA-coated and PDA/PSBMA-coated PPMMs, FESEM images of the surfaces of PDA/PSBMA-coated PPMMs after the E. coil adhesion. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] Notes The authors declare no competing financial interest.

Acknowledgements Financial support is acknowledged to the Zhejiang Provincial Natural Science Foundation of China (Grant no. LZ15E030001), and the National Natural Science Foundation of China (Grant no. 21534009).

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Figure Captions: Fig. 1. Effect of dopamine/PSBMA mass ratio on the deposition density of PDA/PSBMA. Fig. 2. (A) ATR/FT-IR spectra of (a) nascent PPMMs, (b) PDA-coated PPMMs and (c-e) PDA/PSBMA-coated PPMMs with different dopamine/PSBMA mass ratios: (c) 1:10, (d) 1:20 and (e) 1:50. (B) XPS spectra of (a) nascent, (b) PDA-coated and (c) PDA/PSBMA-coated PPMMs (dopamine/PSBMA mass ratio, 1:50). Fig. 3. FESEM images of the membrane surface for (a) nascent, (b) PDA-coated and (c, d) PDA/PSBMA-coated PPMMs with different dopamine/PSBMA mass ratios: (c) 1:10 and (d) 1:50. The scale bar is 5 µm. Fig. 4. (a) Dynamic water contact angle and (b) water droplet permeation time of the PDA/PSBMA-coated PPMMs. Fig. 5. (a) Dynamic BSA filtration and (b) protein (BSA, Hgb and Lys) adsorption quantity of the nascent and PDA/PSBMA-coated PPMMs. Fig. 6. Fluorescence microscopic images of FL-BSA adsorption on various PPMM surfaces: (a) nascent, (b) PDA-coated and (c) PDA/PSBMA-coated. The scale bar is 100 µm. Fig. 7. FESEM images of the membrane surfaces. (a) Nascent, (b) PDA-coated and (c) PDA/PSBMA-coated PPMMs after incubated in E. coil suspension. The bacterial incubation time and scale bar are 2 h and 5 µm, respectively. Fig. 8. Relative flux reduction (RFR) and flux recovery ratio (FRR) of the PDA/PSBMA-coated PPMMs after immersed in different conditions for 12 h: (a) acid and alkali solutions (b) organic solvents. Fig. 9. Relative flux reduction (RFR) and flux recovery ratio (FRR) of the PDA/PSBMA-coated PPMMs after immersed in 0.1 M NaCl for different times.


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0.4

DD (mg/cm2)

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0.3

0.2

0.1

0.0 1:0

1:5

1:10

1:20

1:50

DA:PSBMA (mg:mg) Fig. 1. Effect of dopamine/PSBMA mass ratio on the deposition density of PDA/ PSBMA.


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1160 1031

1725 1610

(A)

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O 1s

(B)

C 1s

(e)

(c)

N 1s

(d)

(b)

(c) (b)

S 2s S 2p3

(a)

(a) 1800

1600

1400

1200

1000

-1

Wavenumbers (cm )

800

600

500

400

300

200

100

Binding energy (eV)

Fig. 2. (A) ATR/FT-IR spectra of (a) nascent PPMMs, (b) PDA-coated PPMMs and (c-e) PDA/PSBMA- coated PPMMs with different dopamine/PSBMA mass ratios: (c) 1:10, (d) 1:20 and (e) 1:50. (B) XPS spectra of (a) nascent, (b) PDA-coated and (c) PDA/PSBMAcoated PPMMs (dopamine/PSBMA mass ratio, 1:50).


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Fig. 3. FESEM images of the membrane surface for (a) nascent, (b) PDA-coated and (c, d) PDA/PSBMA-coated PPMMs with different dopamine/PSBMA mass ratios: (c) 1:10 and (d) 1:50. The scale bar is 5 µm.


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180

1.2

(a)

160 140 Nascent PPMM

120

PDA-coated PPMM (1:0)

100

PDA/PSBMA-coated PPMM (1:10)

80


60


40 20 0

Permeation time (s)

Water contact angle (°)

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

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(b)

1.0 0.8 0.6 0.4 0.2 0.0

0.0

0.5

1.0

1.5

Time (s)

2.0

1:0

1:10

1:20

1:50

Dopamine:PSBMA (g:g)

Fig. 4. (a) Dynamic water contact angle and (b) water droplet permeation time of the PDA/PSBMA-coated PPMMs.


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(a) 100

RFR FRR

(b)

100 80

60

40 20

0

Nascent PDA-coated

80

Q (mg/g)

RFR and FRR(%)

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

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PDA/PSBMA-coated

60 40 20

0:0

1:0

1:10

1:20

1:50

0

Dopamine:PSBMA (g/g)

BSA

Hgb

Lys

Fig. 5. (a) Dynamic BSA filtration and (b) protein (BSA, Hgb and Lys) adsorption quantity of the nascent and PDA/PSBMA-coated PPMMs.


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Fig. 6. Fluorescence microscopic images of FL-BSA adsorption on various PPMM surfaces: (a) nascent, (b) PDA-coated and (c) PDA/PSBMA-coated. The scale bar is 100 µm.


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Fig. 7. FESEM images of the membrane surfaces. (a) Nascent, (b) PDA-coated and (c) PDA/PSBMA-coated PPMMs after incubated in E. coil suspension. The bacterial incubation time and scale bar are 2 h and 5 µm, respectively.


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100

100

RFR FRR

80 60

40 20

RFR FRR

80 60

40 20

0

d ate e r t Un

(b) RFR and FRR(%)

(a) RFR and FRR(%)

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

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0

pH

=3

pH

1 =1

e l d e ate hano eton ptan e t tre c H n E A U

Fig. 8. Relative flux reduction (RFR) and flux recovery ratio (FRR) of the PDA/PSBMA-coated PPMMs after immersed in different conditions for 12 h: (a) acid and alkali solutions (b) organic solvents.


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100

RFR and FRR(%)

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

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RFR FRR 80 60

40 20

0 0

6

12

18

24

Treated time (h) Fig. 9. Relative flux reduction (RFR) and flux recovery ratio (FRR) of the PDA/PSBMAcoated PPMMs after immersed in 0.1 M NaCl for different times.


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Table 1. The deposition conditions and antifouling properties via mussel-inspired modification approaches. antifouling PDA-based coatings

Coating time (h)

Relative flux reduction (%)

Flux recovery ratio (%)

Bacterial attachment (%)

Ref.

PDA/PSBMA coatings

18

37.2

83.5

/

[29]

PDA/PEI coatings

4

55.2

64.6

/

[31]

PDA/PMPC coatings

4

/

/

15

[30]

PDA coatings followed by ATRP

6

58

81.7

/

[32]

PDA coating followed by zwitterionic brush grafting

12

62.8

76.5

/

[33]

PDA/PVP coatings

6

60.8

60

/

[34]

PDA coatings followed by mineralization

6

47.6

84

/

[35]

PDA/PSBMA coatings triggered by CuSO4/H2O2

1

45.7

77.8

0.2

This work

* Relative flux reduction and flux recovery ratio were assessed via the filtration of BSA solutions. * Bacterial attachment experiment used E. coil as the model bacterial.


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Table of Contents Graphic


Poly(sulfobetaine

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