One-step Surface Grafting Method for Preparing Zwitterionic

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One-step Surface Grafting Method for Preparing Zwitterionic Nanofiltation Membrane via In-situ Introduction of Initiator in Interfacial Polymerization Yao-Shen Guo, Yi-Fang Mi, Yan-Li Ji, Quanfu An, and Congjie Gao ACS Appl. Polym. Mater., Just Accepted Manuscript • DOI: 10.1021/acsapm.9b00059 • Publication Date (Web): 01 Apr 2019 Downloaded from http://pubs.acs.org on April 3, 2019

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ACS Applied Polymer Materials

One-step Surface Grafting Method for Preparing Zwitterionic Nanofiltation Membrane via In-situ Introduction of Initiator in Interfacial Polymerization Yao-Shen Guoa, Yi-Fang Mia, Yan-Li Jic, Quan-Fu Ana,b*, Cong-Jie Gaoc a

MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of

Polymer Science & Engineering, Zhejiang University, Hangzhou 310027, China b

Beijing Key Laboratory for Green Catalysis and Separation, College of Environmental and

Energy Engineering, Beijing University of Technology, Beijing 100124, China c

Center for Membrane and Water Science &Technology, Ocean College, Zhejiang University of

Technology, Hangzhou 310014, China

ABSTRACT In this work, polyamide membrane was first prepared via in-situ introduction of surface-initiated atom transfer radical polymerization (SI-ATRP) initiator in interfacial polymerization. Then, zwitterionic membrane was obtained by SI-ATRP grafting of sulfobetaine methacrylate on polyamide membrane. The prepared membranes were characterized by Fourier Transform Infrared Spectroscopy, X-ray Photoelectron Spectroscopy and Atomic Force Microscopy, indicating the successful grafting of zwitterions on polyamide membrane. Pure water permeability of optimized zwitterionic membrane was up to 16.8 L m−2 h−1 bar−1, 2.9 times as high as polyamide membrane with similar Na2SO4 rejection. The NaCl rejection of membrane after grafting for 1 h was only 17.2%, much lower than polyamide membrane, which was sought for separation of monovalent salts/neutral organics. The membrane also showed excellent anti-fouling property when three categories of usual pollutants were chosen as feed solution. The one-step SI-ATRP method for preparing zwitterionic membranes with high permeability was facile and convenient, which had promising applications in desalination and food separation processes.

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KEYWORDS: surface grafting, zwitterionic membrane, high permeability, efficient separation of NaCl/raffinose, anti-fouling property

1. Introduction Technologies for water treatment, which can solve the problem of global water crisis, have been widely concerned in recent years

1–3.

Membrane technology has

attracted numerous attentions because of its environmental-friendly and energy-saving characterization 4–7. In the field of membrane technologies, nanofiltration membranes (NFMs), which possess appropriate rejection of different salts and neutral organics, has been widely applied in desalination, food and biology separation

8–10.

Current

studies about NFMs have focused on the construction of membranes with high permeability as well as functionality like anti-fouling property11,12. In order to realize this requirement, amounts of hydrophilic substances were incorporated into membrane matrix

13,14.

The addition of hydrophilic substances can

enhance the hydrophilicity of membrane and thus increase membrane permeability 15– 17.

Meanwhile, hydrophilic membrane surfaces can decrease the interaction between

membrane and hydrophobic pollutions, which are beneficial to constructing anti-fouling layers

18,19.

Among hydrophilic substances, zwitterions, containing both

anionic and cationic groups in the same unit, were widely used in the preparation of membrane

20–22.

For instance, Mi et al. firstly prepared nanofiltration membrane

containing tertiary amine via the reaction of 3,3’-diamino-N-methyldipropylamine and 1,3,5-benzenetricarboxylic chloride. Then, the prepared membrane reacted with 1,3-propanesultone via ring-opening reaction to fabricate zwitterionic membrane. The resulted membrane exhibited higher flux and better anti-fouling property compared with pristine membrane

23.

Duong et al. prepared zwitterion via quaternization and

ring-opening reaction. The zwitterion was added into polyamide matrix via interfacial polymerization to prepare zwitterionic membrane. The obtained loose nanofiltration membrane showed high permeability and anti-fouling property

24.

It was found that,

compared with other hydrophilic substances like polyethylene glycol (PEG),


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zwitterionic surfaces could combine more “free water” and form hydration layer because of the intra- and inter-ether proximity between the oppositely charged groups, resulting high permeability and anti-fouling property

25–28.

In addition, zwitterionic

membrane can promote the permeation of NaCl through membrane via the formation of ion selective channels. This is beneficial to the high-efficiency separation of NaCl/ neutral organic, which is widely demanded in practical separation process29. Various methods can be used to incorporate zwitterions into membranes, such as surface grafting, phase inversion, solution coating and interfacial polymerization 30,31. The method of surface grafting has been widely researched, which can construct a large amount of zwitterions on membrane surface to achieve higher permeability and better anti-fouling ability compared with other methods

32,33.

Among the methods of

surface grafting, surface-initiated atom transfer radical polymerization (SI-ATRP) is a “living” radical polymerization process34,35. Meanwhile, SI-ATRP process can reduce chain transfer and inhibit cross-linking of surface modification layers, which is beneficial to permeability 36. Saeki et al. prepared membrane with SI-ATRP initiator on surface via the reaction of polyamide, diethanolamine and 2-bromopropionyl bromide, sequentially. Then, zwitterion, 2-methacryloyloxyethyl phosphorylcholine, was incorporated into membrane via SI-ATRP. The obtained membrane showed anti-biofouling property 37. Zhao et al. obtained polypropylene membrane containing poly (sulfobetaine methacrylate) (PSBMA) via SI-ATRP method. Initiator sites were introduced on membrane surface by grafting 2-hydroxyethyl methacrylate on polypropylene membrane and then reacting with 2-bromopropionyl bromide. The resulted membrane exhibited good anti-protein-fouling performance

38.

However,

although the above methods could introduce initiators homogenously, those approaches of introducing initiators were complicated and not easy to operate. Thus, exploring a new method of immobilizing initiators in membrane matrix easily and uniformly is needed to be solved. In this work, 2-bromopropioyl bromide was mixed with 1,3,5-benzenetricarboxylic



chloride in hexane phase and then reacted with piperazine in water phase to obtain membrane with initiators in membrane matrix. This in-situ introduction of initiators in polyamide matrix was easy to operate. Furthermore, this method could control the structure of obtained membrane and make initiators distribute uniformly. Subsequently, PSBMA was grafted via SI-ATRP method. As we know, it was the first time to introduce initiators in polyamide matrix by interfacial polymerization. The membrane grafted with PSBMA exhibited high water permeability, anti-fouling property, low rejection of NaCl and high rejection of raffinose. This work also provided a universal way to prepare zwitterionic membrane with high grafting length of zwitterions, which possessed application prospect in membrane separation and anti-fouling field.

2. EXPERIMENTAL SECTION 2.1. Materials 1,3,5-Benzenetricarboxylic chloride (TMC, J&K) and piperazine (PIP, TCI) were both used without further purification. Sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), calcium chloride (CaCl2), sodium chloride (NaCl), bovine serum albumin (BSA), lysozyme (LYZ), sodium alginate (NaAlg), humic acid (HA), sodium hydroxide (NaOH), PEG (molecular weight 200, 300, 400, 600 and 800 Da), raffinose, hexane and methanol were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Sulfobetaine methacrylate (SBMA), 2-bromopropioyl bromide (BpBr), 2, 2'-bipyridyl (BPY), copper (II) bromide (CuBr2) and copper (I) bromide (CuBr) were obtained from Sigma-Aldrich Co., Ltd. Deionized (DI) water (resistance of 18 MΩcm) was used for experiments and tests. Polysulfone ultrafiltration supporting membranes (molecular weight cut-off 20kDa) were obtained from Development Center of Water Treatment Technology, Hangzhou, China. 2.2. Preparation of polyamide membranes incorporated with 2-bromopropioyl bromide


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As shown in Figure 1, the polyamide membranes were prepared via incorporating different concentration of BpBr (0.025, 0.05, 0.10, 0.15, 0.20 wt%) in hexane phase of interfacial polymerization. These membranes were named as PA-ini-0.025, PA-ini-0.05, PA-ini-0.10, PA-ini-0.15 and PA-ini-0.20, respectively (PA-ini-x, ini was the abbreviation of initiator). To be specific, PSF supporting membrane was immersed in an aqueous solution containing 0.35 wt% PIP (pH=12.0) for 2 min and the excess solution was removed from the membrane surface. Membrane was then immersed in hexane solution containing 0.20 wt% TMC and various concentration of BpBr for 1 min. After pouring the excess organic solution, membrane was dried at 50 ℃ for 15 min for subsequent polymerization. Finally, the prepared membrane was washed thoroughly with water and preserved in 50 vol% methanol-water solution to prevent bacteria breeding7. Meanwhile, the pristine PIP/TMC membrane (named as PA-ini-0) was also fabricated with PIP and TMC by the same procedure. As the chemical structure of polyamide membrane shown in Figure 1, the cross-linking extent, linear extent and end extent of membrane were denoted as x, y and z, respectively.



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Figure 1. Synthetic scheme for preparing PA-ini-x via interfacial polymerization and subsequently surface-initiated atom transfer radical polymerization. 2.3. Preparation of PSBMA grafted nanofiltration membranes As depicted in Figure 1, zwitterionic nanofiltration membranes with different grafting length of SBMA were prepared by SI-ATRP of monomer on PA-ini-0.15, named as PA-zwi-X (X meant SI-ATRP time and zwi meant zwitterions). Firstly, PA-ini-0.15 was placed into a flask under nitrogen protection. At the same time, 40 mmol SBMA, 12 mmol BPY, 1 mmol CuBr2 and 5 mmol CuBr were dissolved in 125 mL 50 vol% methanol-water and the solution was transferred into the flask after being purged with nitrogen for 30 min. Then, the mixture solution in the flask was stirred at room temperature for a scheduled SI-ATRP time (0.1, 0.2, 0.4, 1 and 3 h) and the reaction was terminated by exposing the solution to air39,40. Finally, the obtained membranes were cleaned thoroughly with methanol and water, sequentially. The membranes were stored in a cool, dark place in 50 vol% methanol-water. In SI-ATRP process, degree of polymerization (DP) was used to characterize grafting length of zwitterions, which represented the average length of PSBMA in membrane matrix. DP was calculated by the content of S(mol%) and Br(mol%) from X-ray photoelectron spectroscopy (XPS) result. The specific calculation way was listed in Eq. (1): DP= S(mol%)/ Br(mol%)

(1)

2.4. Membrane characterization All the membrane samples were cleaned with water and cured at 25 ℃ under vacuum for 24 h for further characterization. Composition of NFMs were measured by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR, Nicolet6700, Thermo Fisher Scientific, USA) with ZnSe inner reflection element (angle of incidence of 45°) and XPS (Escalab 250Xi, Thermo Fisher Scientific, USA). The ATR-FTIR and XPS results were replicated for three times. Zeta potential was measured by an electrokinetic analyzer (SurPass, Anton Paar GmbH, Austria). The


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dry membrane was pasted on sample stage and slit width was adjusted to 100 nm. Then, zeta potential test was represented with 1.0 mmol L-1 KCl aqueous solutions at 25 °C and pH changing from 3.0 to 10.0. 0.1 mol L-1 HCl and NaOH were used to tune pH. The results were the average values of four tests. Surface hydrophilicity of membranes was characterized by a water contact angle measurements (OCA 20, Data Physics Instruments GmbH, Germany). The contact angles were tested five times and the averages were recorded. Morphologies of membranes were evaluated by field emission scanning electron microscopy (FESEM, S4800, HITACHI, Japan). Membranes were fractured in liquid nitrogen before characterizing the cross-section images. Membrane samples for SEM were sputter-coated with platinum and visualized at a voltage of 3 kV. Membrane surface roughness was characterized by a multimode atomic force microscopy (AFM, MultiMode 8,BRUKER) in ScanAsyst at room temperature with a cantilever (Model: NCHV, BRUKER, spring constant k=42 Nm−1, resonance frequency f0 = 320 kHz). The scan rate was 0.977Hz. Samples used for dry test were dried at 25 ℃ under vacuum until the weight was constant and those used for wet test were immersed in water for 30 min before analysing. The surface roughness was calculated according to the measured root mean square (RMS) roughness. The morphology characterization was repeated for three times. 2.5. Nanofiltration performance Water permeability and rejection of membrane were investigated with a cross-flow flat apparatus. Membrane was pre-filtrated with water at 25 ℃ and 6 bar to acquire a steady state before further testing. Solute rejection was measured with 1000 ppm Na2SO4, MgSO4, CaCl2, NaCl, PEG and raffinose aqueous solution, respectively. The water flux (J) and solute rejection (R) were obtained by the following Eq. (2) and Eq. (3): J= V/ (A×Δt)

(2)

R=(1- cP/ cF) ×100%

(3)

where V (L) is the volume of water over a period of time Δt (h), A is the effective



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area of the membrane (7.84 cm2), cP and cF (ppm) are the solution concentrations of the permeate and feed, respectively 41,42. Solution concentrations were measured by a conductivity meter (FE30, Mettler-Toledo, Switzerland) for inorganic salts and total organic carbon analysis (TOC-L, Shimadzu, Japan) for organics. The calculations of mean pore size and pore size distribution were based on the assumption of no steric and hydrodynamic interactions between the organic solutes and the membrane material. The specific calculation method was described in Supporting Information23. In addition, NaCl/raffinose solution with specific concentrations was used to investigate separation ability of monovalent salts/ organics. In all the experiments, membrane was examined at least three times and the average was recorded as the result. In addition, three categories of usual pollutants (protein, saccharide and humic acid) were used to evaluate antifouling property. Firstly, membrane was operated for 2 h with water and steady flux (J0) was recorded. Then, 100 ppm BSA aqueous solution was filtered continuously through the membrane for 5 h and the flux (Jt) was recorded over the whole time. After that, membrane was filtered by pure water for another 2 h in order to wash away the pollutants. In fouling experiment, 2 h filtration for pure water and 5 h filtration for pollutant solution was defined as a cycle. After 2.5 cycles, the water flux (Jr) was measured again. Other pollutants (LYZ, NaAlg and HA) were conducted same operation. In fouling experiments, membranes were tested for three times and the average was calculated as the result. The flux recovery ratio (FRR) was obtained by the following Eq. (4): FRR=(Jr/J0)×100%

(4)

Reversible (Fr) and irreversible (Fir) resistances of membranes were calculated in Eq. (5) and Eq. (6), respectively: Fr=(Jr-Jt)/J0×100%

(5)

Fir=(J0-Jr)/J0×100%

(6)

3. Results and discussion


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3.1. Characterization of PA-ini-x From FTIR spectra of PA-ini-x (Figure 2a), the peak at 1106 and 1242 cm-1 represented groups of O=S=O on PSF supporting membrane. Meanwhile, the peak at 1621 cm-1 represented CONH on polyamide membrane, which indicated polyamide separation layer was successfully incorporated on PSF membrane

44.

Peak at 1621

cm-1 decreased with increasing amount of BpBr, indicating that cross-linking degree decreased when more BpBr molecules were added into hexane solution. XPS results (Table S1) exhibited that the content of BpBr in polyamide membrane increased when increasing the concentration of initiator. What’s more, SEM surface images (Figure 2b and c) showed that PA-ini-0 and PA-ini-0.15 all possessed nodular structures, which were widely existed in NFMs prepared via interfacial polymerization

45,46.

It

should be noted that nodular structure became looser when single functional BpBr was incorporated. SEM cross-section images (Figure 2d and e) exhibited that thickness of membrane decreased when initiator was added, due to the formation of end extent structure during interfacial polymerization (Figure 1). In addition, EDS was used to characterize the uniformity of initiators in PA-ini-0.15. Br only existed in initiators and thus, the distribution of Br could represent the dispersion of initiators in membrane matrix. As shown in Figure S2a, initiators were uniformly dispersed in membrane matrix. Furthermore, combining the phenomena of FTIR, XPS and surface images, the density of interfacial network decreased when more initiators was introduced in polyamide matrix. Water permeability of PA-ini-x (Figure 2f) first increased and then decreased when increasing the concentration of initiator, which was due to the balance of thickness and hydrophobicity. On one hand, thickness of membrane decreased when more initiator was added, which was beneficial to water permeability (Table S1). On the other hand, membrane became more hydrophobic due to the introduction of C-Br on membrane as shown in Figure 2g and Figure S3 and thus, permeability decreased. In addition, rejection of Na2SO4 maintained over 90% when concentration of initiator



was not higher than 0.15 wt% (Figure 2g). From the above discussion, PA-ini-0.15, with high content of initiator and water permeability, was chosen to conduct SI-ATRP, which had potential to achieve high performance after grafting SBMA. PA-ini-0

Transmittance (%)

a Polysulfone

-CONH-

b

d

O=S=O

PA-ini-0

PA-ini-0.05

200nm

400nm

PA-ini-0.10 PA-ini-0.15

c

PA-ini-0.15

PA-ini-0.20

2000

1600

1242

1200

-1

800

100

-2

80 60 6 40

4

20

2 0

5 i-0 15 .20 .05 -0.10 02 -0 . i-0 -in i-0 i -0 . ini -in -in A-in ini PA A A A P P P P PA

0

g Water contact angle ()

8

e

200nm

400nm

Na2SO4 rejection (%)

-1 -1

12 10

PA-ini-0.15 142±8nm

1106

Wavenumber (cm )

f

PA-ini-0 233±12nm

PA-ini-0.025

1621

Permeability (L.m .h . bar )

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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PSF PA-ini-0.025 PA-ini-0.10 PA-ini-0.20

100

PA-ini-0 PA-ini-0.05 PA-ini-0.15

80

60

40 0

20

40

60

80

Time (h)

100

120

Figure 2. Characterizations of PA-ini-x: (a) FTIR spectra, (b-e) SEM surface and cross-section images, (f) Permeability and Na2SO4 rejection (25℃, pH=6.5), (g) water contact angle. 3.2. Characterization of PA-zwi-X Compared with PA-ini-0.15, the ATR-FTIR spectra of PA-zwi-X appeared two peaks at 1726 and 1040 cm-1, which represented COO and SO3- on PSBMA, respectively (Figure 3a) 38. Meanwhile, peak intensity of the two new peaks increased with increasing SI-ATRP time, indicating that grafting length of SBMA monomer on PA-ini-0.15 increased. In XPS results, there were two peaks with bonding energy at 402.1 eV and 399.5 eV in N 1s core-level spectra of PA-zwi-X, corresponding to N+ and CON, respectively (Figure 3b) 47,48. The peak intensity of N+ increased and that of


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CON decreased with grafting time, consistent with the increasing SBMA content and DP in polyamide membrane (Table S2). This phenomenon indicated that grafting length increased when SI-ATPR time was longer, which further proved the results of ATR-FTIR. a PA-ini-0

b

-

-COO- -CONH-

-SO3

-CON-

PA-ini-0.15

4000

PA-zwi-3h PA-zwi-1h PA-zwi-0.4h PA-zwi-0.2h PA-zwi-0.1h PA-ini-0.15 PA-ini-0

PA-zwi-0.1h PA-zwi-0.2h

+

Counts (s)

Transmittance (%)

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


PA-zwi-0.4h PA-zwi-1h PA-zwi-3h

-N (CH3)2-

3000

2000

1040

1726 1621

1000

2000

1600

1200

-1

Wavenumber (cm )

800

408

404

400

396

392

Binding energy (eV)

Figure 3. (a) FTIR spectra and (b) N 1s spectra of membranes after grafting PSBMA. PA-zwi-0.1h meant grafting PSBMA on PA-ini-0.15 for 0.1h and other labels were named in the same way. 3.3. Morphologies of PA-zwi-X As shown in Figure 4a-c, morphologies of PA-zwi-X were characterized by SEM. It was obvious that PA-zwi-X was covered by PSBMA polymer instead of nodular structure and amount of PSBMA was higher when SI-ATRP time was longer. Meanwhile, thickness of PA-zwi-X increased with grafting time because of the incorporation of more PSBMA (Figure 4d-f and Table S2). In addition, EDS was used to investigate the distribution of PSBMA (element S) in PA-zwi-1h (polyacrylonitrile supporting membrane). As shown in Figure S2b, zwitterions layer (element S) was uniformly covered on membrane surface. AFM images in air phase were also explored (Figure 5a-d). PA-ini-0 possessed RMS of 16.1 nm, RMS of PA-zwi-X gradually decreased with increasing SI-ATRP time due to the coverage of uniform PSBMA. RMS of PA-zwi-1h was only 8.6 nm, which was beneficial to antifouling property of membrane in practical application. What’s more, AFM images in water



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phase were also discussed (Figure 5e-h). Compared with RMS in air phase, RMS in water phase were higher because of swelling phenomenon of polymer. PA-zwi-3h had most PSBMA on membrane surface among all the membranes and the swelling degree was the highest. Therefore, the RMS change of PA-zwi-3h was the biggest. PA-zwi-0.2h

a

PA-zwi-1h

400nm

PA-zwi-0.2h 170±9nm

d

200nm

b

400nm

PA-zwi-1h 188±11nm

e

c

PA-zwi-3h

400nm

f

PA-zwi-3h 204±13nm

200nm

200nm

Figure 4. SEM surface (a-c) and cross-section images (d-f) of membranes after grafting PSBMA. a PA-ini-0 RMS=16.1nm

b PA-zwi-0.2h RMS=13.1nm c PA-zwi-1h RMS=8.6nm

e PA-ini-0 RMS=19.7nm

f PA-zwi-0.2h RMS=19.2nm g PA-zwi-1h RMS=18.3nm

d PA-zwi-3h RMS=5.9nm

h PA-zwi-3h RMS=17.8nm

Figure 5. AFM images of membranes grafting PSBMA: (a-d) air phase, (e-h) water phase.


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3.4. Effect of grafting time on NFMs performance In this work, five different SI-ATRP times (0.1 h, 0.2 h, 0.4 h, 1 h, 3 h) were chosen to investigate the effect of grafting time on NFMs performance (Figure 6a). Membrane permeability was associated with not only surface hydrophilicity but membrane thickness

49.

PA-zwi-X became more hydrophilic with the increasing

grafting time due to the more hydrophilic SO3- groups on membrane surface (Figure 6b and Figure S4), thus, higher permeability

44.

Meanwhile, the thickness of

membrane increased when grafting time increased, which lengthened water pathway and enhanced membrane resistance, endowing low permeability 50. Thus, permeability first increased and then decreased with increasing grafting time under the balance of hydrophilicity and membrane thickness (Figure 6a). Surprisingly, optimal permeability was up to 16.8 L m-2 h-1.bar-1when grafting time was 0.2 h, higher than PA-ini-0 (5.7 L m-2 h-1.bar-1) and PA-ini-0.15 (10.4 L m-2 h-1.bar-1). In addition, Na2SO4 rejection of PA-zwi-X was still at high level, which was more than 97.0% (Figure 6a), indicating the uniform coverage of PSBMA layer. Furthermore, PA-ini-0 and PA-ini-0.15 showed negative charge at pH=6.5, zeta potential of PA-zwi-X was enhanced with increasing grafting time (Figure 7a). This was because the incorporation of zwitterion PSBMA, which reduced negative charges in membrane matrix 51. 3.5. Nanofiltration performance of NFMs Rejection of different salts and neutral molecules were also explored, which was affected by Donnan effect and steric effect 52,53. Membranes were negatively charged, thus, had high Na2SO4 and MgSO4 rejection and low CaCl2 rejection (Figure 7b) 54,55. CaCl2 rejection increased with grafting time due to the decrease of negative charge and molecular weight cut-off (MWCO). However, rejection of NaCl decreased with increasing grafting time although MWCO of membranes was decreased. This was since ion-selective channels were formed by grafting PSBMA on polyamide surface, which could selectively permeate NaCl, via the formation of (-N(CH3)2·Cl−) and



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(-SO3·Na+) through strong electrostatic attractions29. Thus, rejection of NaCl decreased to less than 20% when grafting time was 1 h. Consequently, PA-zwi-1h with high permeability and low NaCl rejection can be applied for separation of NaCl and neutral organics, which has application prospects in food and biological separation processes. MWCO of membranes were investigated by total organic carbon analysis (Figure 7c). Compared with PA-ini-0, PA-ini-0.15 with high flux and low rejection had higher MWCO of 730 Da. MWCO of PA-zwi-X decreased with increasing grafting time. Furthermore, mean effective pore radius of membranes were also characterized. As shown in Figure 7d, PA-ini-0.15 showed larger mean effective pore radius of 0.345 nm compared with that of PA-ini-0 (0.317 nm). PA-zwi-0.2h, PA-zwi-1h and PA-zwi-3h had mean effective pore radius of 0.322, 0.312 and 0.309 nm, respectively. The result of mean effective pore radius was in accordance with MWCO of membranes. Meanwhile, membrane covered by PSBMA showed high rejection of raffinose (Figure 7b). Salt permeability (1000 ppm) of membranes were also discussed (Figure 7e). In salt solution, osmotic pressure was generated and thus driving force of membrane decreased, salt permeability was lower than pure water permeability

56.

NaCl

permeability was the highest of all test salts because of its lowest osmotic pressure 57. We also characterized stability of membranes. In 7 days’ test, PA-ini-0, PA-zwi-0.2h and PA-zwi-1h all possessed stable flux and Na2SO4 rejection (Figure 7f). This result indicated that PA-zwi-X was stable and long-term useful. Effect of NaCl and Na2SO4 concentration on membrane performance was further tested (Figure S5a and b). When salt concentration increased from 500 to 4000 ppm, salt permeability and rejection decreased. When concentration of NaCl and Na2SO4 increased, driving force of membranes decreased owing to the increase of osmotic pressure as discussed above, which caused lower permeability. Furthermore, electrostatic shield effect was strengthened when salt concentration was enhanced and thus, salt rejection decreased 58.

From the above discussion, compared with other membranes, PA-zwi-1h


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simultaneously possessed moderate water permeability, low NaCl rejection and high raffinose rejection, which could efficiently separate NaCl/raffinose. Meanwhile, PA-zwi-1h with high content of PSBMA might have better anti-fouling property. Thus, PA-zwi-1h was chosen for further discussion. The prepared membrane in this work was also compared with several membranes in the reported literature (Table 1). Compared with the reported membranes, PA-zwi-0.2h exhibited perfect property with high flux and Na2SO4 rejection. What’s more, fabrication process of PA-zwi-X was easy to operate and could control the structure of obtained membranes. It was also the first time to introduce initiator in polyamide matrix through interfacial polymerization. PA-zwi-X with high permeability might have potential applications in membrane fouling field. b

a 20

PA-ini-0.15 PA-zwi-0.2h PA-zwi-1h

80

12

60

8

40

4

20

0

0


100

16

-2

-1

Water contact angle ()

100

-1

Water permeability (L.m .h . bar )

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


80

PA-zwi-0.1h PA-zwi-0.4h PA-zwi-3h

60 40 20

h h .15 .2h .4h .1h i-1 i-3 i-0 i-0 i-0 i-0 zw zw -in - zw - zw AA- zw P P A A A PA P P P

0

20

40

60

Time (s)

80

100

120

Figure 6. (a) Effect of SI-ATRP time on water permeability and Na2SO4 rejection (25℃, pH=6.5) and (b) water contact angles of membranes after grafting PSBMA.



Page 16 of 41

Table 1 Materials and preparation method of zwitterionic membranes and their performance Membrane PA-zwi-0.2h PA-zwi-1h NFM4 100/0 ZCP/MPD

RO/MPC Zwi-GO-PES TFC-zwi-50

AEPPS-TMC

Materials

Preparation

PWP

R(Na2SO4)

R(NaCl)

c(salt)

Ref.

method

(L.m

(%)

(%)

PIP/TMC/

Surface grafting

16.8

97.2

24.4

1000ppm

This work

PSBMA

(SI-ATRP)

PIP/TMC/

Surface grafting

13.5

98.1

17.2

1000ppm

This work

PSBMA

(SI-ATRP)

DNMA/TMC

Surface grafting

12.0

15.0

36.0

1000ppm

23

/1,3-PS

(ring-opening)

MPD/TMC/

Dispersion and

135.0

5.0

2000ppm

24

Zwitterionic

interfacial

copolymer

polymerization

MPD/TMC/

Surface grafting

0.5

90

5000ppm

37

MPC

(SI-ATRP)

PES/DMAc/

Dispersion and

Zwi-GO

phase inversion

PIP/TMC/

Dispersion and

Zwitterionic

interfacial

copolymer

polymerization

AEPPS/TMC

Interfacial

-2

.h .bar -1

)

-1

11.98

10.0

3.0

1000ppm

60

8.5

93.0

50.0

1000ppm

61

14.4

1000ppm

54

8.4

polymerization

NF-90 NF-270

phenylene

Interfacial

diamine/TMC

polymerization

PIP/TMC

Interfacial

5.2

95.0

92.0

0.05mol/L

59

8.5

96.0

59.0

0.05mol/L

59

6.1

98.0

94.0

0.05mol/L

59

polymerization

BW30XLE

phenylene

Interfacial

diamine/TMC

polymerization


Page 17 of 41

b 140 PA-ini-0 PA-ini-0.15 PA-zwi-0.1h PA-zwi-0.2h PA-zwi-0.4h PA-zwi-1h PA-zwi-3h

20 0 -20 -40

Na2SO4 MgSO4

120

NaCl CaCl2 Raffinose

100 80 60 40 20

-60 3

4

5

6

pH

7

8

9

10

0

11

c

d 5

i-0 .15 i-0.1h i-0.2h i-0.4h wi-1h wi-3h -in i-0 -in A-zw A-zw A-zw PA-z PA-z PA PA P P P

PA-ini-0.15 PA-ini-0 PA-zwi-0.2h PA-zwi-1h PA-zwi-3h

80

PA-ini-0 PA-ini-0.15 PA-zwi-0.1h PA-zwi-0.2h PA-zwi-0.4h PA-zwi-1h PA-zwi-3h

60

40 200

400

500

600

700

-1

15

3 2 1 0 0.0

0.2

f

0.4 0.6 Pore radius, rp (nm)

0.8

1.0

100

-1

)

-1

18

4

800

PEG molecular weight (Da)

e

20

12 9 Na2SO4

6 3 0

NaCl CaCl2 MgSO4

80 60

12

4

-2

-1

PA-ini-0 PA-zwi-0.2h PA-zwi-1h

16

40

8

20

4

2

-2

300

Na SO permeability (L.m .h .bar

Retention (%)

-1

100

Probability density function (nm )

2


Zeta potential (mV)

40

Rejection (%)

a

Salt permeability (L.m .h . bar )

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


i-0 .15 i-0.1h i-0.2h i-0.4h wi-1h wi-3h -in i-0 PA A-in A-zw A-zw A-zw PA-z PA-z P P P P

0

0

20

40

60

80

100

120

140

160

0

Time (h)

Figure 7. (a) Zeta potential of membranes, (b) rejection of membranes, (c-d) MWCO and pore radius of membranes, (e) Salt permeability of membranes and (f) stability of membranes (1000 ppm feed solution, 25℃ pH=6.5). 3.6. Separation property of monovalent salts/neutral organics Given the exceptional water permeability and low NaCl rejection, PA-zwi-X has promising application in the separation of monovalent salts/neutral organics, which has been widely used in food and biological field

59,62.

So, a labscale concentration

test was carried out to explore separation and concentration performance of



membrane. Mixture solution of 5000 ppm NaCl and 1000 ppm raffinose was selected as model solution. In Figure 8a and c, column represented the concentration of raffinose versus testing time and line represented the concentration of NaCl versus testing time. In Figure 8b and d, the middle line meant flux versus testing time and other lines meant corresponding rejection (circle line was rejection of raffinose and triangle one meant NaCl rejection). After concentrating for 30 h, concentration of raffinose in feed solution changed from 1000 ppm to 5186 ppm and concentration of NaCl in feed solution only increased a little when PA-zwi-1h was used (Figure 8a). Meanwhile, rejection of raffinose maintained over 95.0% and rejection of NaCl decreased from 9.8% to 3.7% over the concentration time (Figure 8b). This phenomenon indicated that PA-zwi-1h with high solution permeability could reject major raffinose and permeate nearly all NaCl, which could realize efficient separation of NaCl and raffinose. However, when PA-ini-0 was used, raffinose concentration only changed from 1000 ppm to 1984 ppm after the same concentration time due to low permeability (Figure 8c). At the same time, NaCl rejection of PA-ini-0 (31.3% to 28.3%) was much higher than that of PA-zwi-1h (9.8% to 3.7%) as described in Figure 8d. So, PA-ini-0 with low permeability and high NaCl rejection was not suitable for effective separation of raffinose and NaCl. The successful concentration process of PA-zwi-1h was attributed to the much higher permeability and markedly decreased NaCl rejection via introducing high grafting length of PSBMA.


Page 18 of 41

5000

4000

4000

3000

3000

2000

2000

1000

1000

b

-1 -2

CNaCl (ppm)

Craffinose (ppm)

-1

5000

100 14 80

12 10

60 8 40

6 4

Rejection (%)

a

20 2

c

0

5

10

15

20

25

30

0

0

Time (h)

d

2500

0

4

8

6

12 16 Time (h)

20

24

28

100

3000

1000

2000

500 0

1000

0

4

8

12

16

20

24

28

0

Time (h)

-1

5 80

4

-1

1500

-2

CNaCl (ppm)

4000

Flux (L.m .h . bar )

5000 2000

0

3

60

2 40

Rejection (%)

0

Craffinose (ppm)

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


Flux (L.m .h . bar )

Page 19 of 41

1 0

0

4

8

12 16 Time (h)

20

24

28

20

Figure 8. Concentration change of mixture feed solution and nanofiltration property of membranes during concentration process (25 ℃, pH=6.5, 1000 ppm raffinose and 5000 ppm NaCl): (a) and (b) PA-zwi-1h, (c) and (d) PA-ini-0. 3.7. Antifouling performance of NFMs As we all know, membrane fouling is an inevitable problem during operation process, which is mainly due to the hydrophobic interaction between the membrane surface and pollutants. Therefore, to solve this problem, hydrophilic membrane surface was developed as discussed previously. Membrane fouling experiment was carried out to explore anti-fouling performance of membranes. Usually, pollutants were classified as proteins, saccharide and humic acid. BSA, LYZ, NaAlg and HA were typical pollutants among the three categories, which were widespread foulants in the industrial application. Thus, these foulants were chosen to evaluate fouling property of nanofiltration membrane in laboratory. In Figure 9, flux recovery coefficient was defined as the ratio of flux at certain time to initial flux. It represented the normalized flux at every record time. Flux decline ratio represented fouling degree of membrane, which consisted of reversible fouling (foulants could be completely removed by water cleaning) and irreversible fouling (foulants could not be removed by water cleaning). Flux decline ratio caused by reversible and irreversible fouling was named as Fr and



Page 20 of 41

Fir, respectively, which were defined in Section 2.5. Firstly, two kinds of proteins (BSA and LYZ) were used. When 100 ppm BSA was used as feed solution, PA-zwi-1h showed lowest flux decline compared with PA-ini-0 and PA-ini-0.15 (Figure 9a and b). After washing by water, PA-zwi-1h exhibited highest FRR of 95.5% and lowest Fir of 4.5%. This phenomenon was attributed to high grafting length of zwitterion PSBMA on membrane surface. Zwitterions enhance hydrophilicity of membrane and thus, hydrophobic interactions between BSA and membrane surface reduced. Therefore, the amount of protein adsorbed on membrane surface decreased 23.

In addition, high grafting length of PSBMA can construct tight hydration layer on

membrane surface, thus, enhance anti-fouling property. What’s more, negatively charged NFMs has electrostatic repulsion toward negatively charged BSA (pH=6.5), which is beneficial to membrane antifouling. When LYZ was chosen as feed solution, membrane was polluted severely than BSA because of its positive charge (Figure 9c and d). At pH=6.5, electrostatic force was existed between membrane surface and LYZ. However, PA-zwi-1h also showed high FRR, indicating that fouling layer on PA-zwi-1h was easy to be cleaned. As discussed above, high grafting length of zwitterions can fully combine water molecules via electrostatic interactions and form hydration layer, which make pollutants layer loose and easy to be washed away 23. Thus, PA-zwi-1h exhibited high FRR when it was fouled by LYZ. Furthermore, humic acid (HA) and saccharide (NaAlg) were also selected as feed solution to investigate antifouling property (Figure 9e-h). PA-zwi-1h showed better antifouling performance toward these two pollutions compared with PA-ini-0 and PA-ini-0.15. Incorporation of hydrophilic zwitterion PSBMA made PA-zwi-1h possess exceptional antifouling performance. Hydration layer constructed by high grafting length of PSBMA made pollutants could not easily adhere to membrane surface and easy to be cleaned, thus, PA-zwi-1h showed highest FRR

63.

From the

above results, high grafting length of zwitterions, which can strongly combine water molecules, is of vital importance to membrane antifouling performance. In short, the improvement of hydrophilicity, which is attributed to the introduction of PSBMA, can


Page 21 of 41

efficiently enhance anti-fouling property of membrane. a

b

0.9

Flux decline ratio (%)

Flux recovery coefficient

1.0

0.8 PA-ini-0 PA-ini-0.15 PA-zwi-1h

0.7 0.6 0.5

0

2

4

6

8

10

12

14

d


0.7 0.6 0.5

0

2

4

6

8

10

Time (h)

12

14

f

0.9 0.8 PA-ini-0 PA-ini-0.15 PA-zwi-1h

0.7 0.6 0.5

0

2

4

6

8

10

Time (h)

g

12

14

10

5

PA-ini-0

PA-ini-0.15

PA-zwi-1h

25 Fr Fir

20 15 10 5

PA-ini-0

PA-ini-0.15

PA-zwi-1h

Fr Fir 15

10

5

0

16

h

1.0

PA-ini-0

PA-ini-0.15

PA-zwi-1h

20


0.7 0.6 0.5

15

20


1.0

Fr Fir

0

16



e



1.0 0.9

20

0

16

Time (h)

c


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


0

2

4

6

8

10

12

14

16

Fr Fir 15

10

5

0

PA-ini-0

PA-ini-0.15

PA-zwi-1h

Time (h)

Figure 9. Flux recovery coefficient (the ratio of flux at certain time to initial flux) and flux decline ratio (Fr and Fir defined in Section 2.5) of membranes: (a) and (b) 100



ppm BSA solution, (c) and (d) 100 ppm LYZ solution, (e) and (f) 100 ppm HA solution, (g) and (h) 100 ppm NaAlg solution.

4. Conclusion 2-Bromopropioyl bromide was incorporated into polyamide matrix and hydrophilic PSBMA was grafted in membrane matrix via SI-ATRP method. The obtained zwitterionic membrane exhibited exceptional water permeability of 16.8 L m−2h−1bar−1 and high rejection of Na2SO4 and MgSO4. The optimised grafting length of PSBMA endowed the zwitterionic membrane with high permeability. Meanwhile, the zwitterionic membrane showed low rejection of NaCl because of the incorporation of high grafting length of PSBMA, which exhibited superior separation ability of monovalent salts/neutral organics. Membranes after grafting PSBMA also showed good stability and antifouling property. Therefore, this study presented a facile method to prepare zwitterions grafted polyamide nanofiltration membranes with high permeability, stability, anti-fouling property and separation ability of monovalent salts/neutral organics.

ASSOCIATED CONTENT Supporting Information XPS results of PA-ini-x and PA-zwi-X Optical image of zwitterionic membrane EDS of membranes Water contact of PA-ini-x and PA-zwi-X Pore size distribution of membranes Na2SO4 and NaCl concentration change on membranes performance SEM images of membranes after fouling and cleaning

AUTHOR INFORMATION Corresponding Author


Page 22 of 41

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


*E-mail: [email protected]

Notes The authors declare no competing financial interest. Acknowledgements This research was financially supported by National Natural Science Foundation of China (No. 21676233, 21788004), National Basic Research Program of China (No. 2015CB655303), The Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions (CIT&TCD20170305) and Scientific Research Program of Beijing Education Commission (KZ201910005001). Reference (1) Madaeni, S. S.; Zinadini, S.; Vatanpour, V. Preparation of Superhydrophobic Nanofiltration Membrane by Embedding Multiwalled Carbon Nanotube and Polydimethylsiloxane in Pores of Microfiltration Membrane. Separation and Purification Technology 2013, 111, 98–107. (2) Gin, D. L.; Noble, R. D. Designing the Next Generation of Chemical Separation Membranes. Science 2011, 332 (6030), 674–676. (3) Laakso, T.; Pihlajamäki, A.; Mänttäri, M. Effect of Polycation Structure on the Fabrication of Polyelectrolyte Multilayer Hollow Fiber Membranes for Loose Nanofiltration Applications. Separation and Purification Technology 2018, 194, 141– 148. (4) Wang, Z.; Zhang, P.; Hu, F.; Zhao, Y.; Zhu, L. A Crosslinked β-Cyclodextrin Polymer Used for Rapid Removal of a Broad-Spectrum of Organic Micropollutants from Water. Carbohydrate Polymers 2017, 177, 224–231. (5) Xu, Z.; Li, X.; Teng, K.; Zhou, B.; Ma, M.; Shan, M.; Jiao, K.; Qian, X.; Fan, J. High Flux and Rejection of Hierarchical Composite Membranes Based on Carbon Nanotube Network and Ultrathin Electrospun Nanofibrous Layer for Dye Removal. Journal of Membrane Science 2017, 535, 94–102. (6) Ye, C.C.; Zhao, F.Y.; Wu, J.K.; Weng, X.D.; Zheng, P.Y.; Mi, Y.F.; An, Q.F.; Gao, C.J. Sulfated Polyelectrolyte Complex Nanoparticles Structured Nanoflitration Membrane for Dye Desalination. Chem. Eng. J. 2017, 307, 526–536.



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(38) Zhao, Y.H.; Wee, K.H.; Bai, R. Highly Hydrophilic and Low-Protein-Fouling Polypropylene Membrane Prepared by Surface Modification with Sulfobetaine-Based Zwitterionic Polymer through a Combined Surface Polymerization Method. Journal of Membrane Science 2010, 362 (1), 326–333. (39) Liu, P.S.; Chen, Q.; Wu, S.S.; Shen, J.; Lin, S.C. Surface Modification of Cellulose Membranes with Zwitterionic Polymers for Resistance to Protein Adsorption and Platelet Adhesion. Journal of Membrane Science 2010, 350 (1), 387– 394. (40) Liu, P.S.; Chen, Q.; Liu, X.; Yuan, B.; Wu, S.S.; Shen, J.; Lin, S.C. Grafting of Zwitterion from Cellulose Membranes via ATRP for Improving Blood Compatibility. Biomacromolecules 2009, 10 (10), 2809–2816. (41) Tang, Y.; Tang, B.; Wu, P. Preparation of a Positively Charged Nanofiltration Membrane Based on Hydrophilic–Hydrophobic Transformation of a Poly(Ionic Liquid). Journal of Materials Chemistry A 2015, 3 (23), 12367–12376. (42) Ji, Y.L.; An, Q.F.; Zhao, F.Y.; Gao, C.J. Fabrication of Chitosan/PDMCHEA Blend Positively Charged Membranes with Improved Mechanical Properties and High Nanofiltration Performances. Desalination 2015, 357, 8–15. (43) Peng, F.; Huang, X.; Jawor, A.; Hoek, E. M. V. Transport, Structural, and Interfacial Properties of Poly(Vinyl Alcohol)–Polysulfone Composite Nanofiltration Membranes. Journal of Membrane Science 2010, 353 (1), 169–176. (44) An, Q.F.; Sun, W.D.; Zhao, Q.; Ji, Y.L.; Gao, C.J. Study on a Novel Nanofiltration Membrane Prepared by Interfacial Polymerization with Zwitterionic Amine Monomers. Journal of Membrane Science 2013, 431, 171–179. (45) Tian, Y.; Cao, Y.; Wang, Y.; Yang, W.; Feng, J. Realizing Ultrahigh Modulus and High Strength of Macroscopic Graphene Oxide Papers Through Crosslinking of Mussel-Inspired Polymers. Advanced Materials 25 (21), 2980–2983. (46) Tiraferri, A.; Vecitis, C. D.; Elimelech, M. Covalent Binding of Single-Walled Carbon Nanotubes to Polyamide Membranes for Antimicrobial Surface Properties. ACS Appl. Mater. Interfaces 2011, 3 (8), 2869–2877. (47) Yang, H.C.; Liao, K.J.; Huang, H.; Wu, Q.Y.; Wan, L.S.; Xu, Z.K. Mussel-Inspired Modification of a Polymer Membrane for Ultra-High Water Permeability and Oil-in-Water Emulsion Separation. Journal of Materials Chemistry A 2014, 2 (26), 10225–10230. (48) Venault, A.; Wei, T.C.; Shih, H.L.; Yeh, C.C.; Chinnathambi, A.; Alharbi, S. A.; Carretier, S.; Aimar, P.; Lai, J.-Y.; Chang, Y. Antifouling Pseudo-Zwitterionic Poly(Vinylidene Fluoride) Membranes with Efficient Mixed-Charge Surface Grafting



via Glow Dielectric Barrier Discharge Plasma-Induced Copolymerization. Journal of Membrane Science 2016, 516, 13–25. (49) Wu, C.; Liu, S.; Wang, Z.; Zhang, J.; Wang, X.; Lu, X.; Jia, Y.; Hung, W.-S.; Lee, K.-R. Nanofiltration Membranes with Dually Charged Composite Layer Exhibiting Super-High Multivalent-Salt Rejection. Journal of Membrane Science 2016, 517, 64–72. (50) Li, H.; Shi, W.; Zhang, Y.; Du, Q.; Qin, X.; Su, Y. Improved Performance of Poly(Piperazine Amide) Composite Nanofiltration Membranes by Adding Aluminum Hydroxide Nanospheres. Separation and Purification Technology 2016, 166, 240– 251. (51) Xue, S.M.; Xu, Z.L.; Tang, Y.J.; Ji, C.H. Polypiperazine-Amide Nanofiltration Membrane Modified by Different Functionalized Multiwalled Carbon Nanotubes (MWCNTs). ACS Appl. Mater. Interfaces 2016, 8 (29), 19135–19144. (52) Wang, X.L.; Tsuru, T.; Nakao, S.; Kimura, S. The Electrostatic and Steric-Hindrance Model for the Transport of Charged Solutes through Nanofiltration Membranes. Journal of Membrane Science 1997, 135 (1), 19–32. (53) Bellona, C.; Drewes, J. E.; Xu, P.; Amy, G. Factors Affecting the Rejection of Organic Solutes during NF/RO Treatment—a Literature Review. Water Research 2004, 38 (12), 2795–2809. (54) Weng, X.D.; Ji, Y.L.; Ma, R.; Zhao, F.Y.; An, Q.F.; Gao, C.J. Superhydrophilic and Antibacterial Zwitterionic Polyamide Nanofiltration Membranes for Antibiotics Separation. Journal of Membrane Science 2016, 510, 122–130. (55) Ji, Y.L.; An, Q.F.; Weng, X.D.; Hung, W.S.; Lee, K.R.; Gao, C.J. Microstructure and Performance of Zwitterionic Polymeric Nanoparticle/Polyamide Thin-Film Nanocomposite Membranes for Salts/Organics Separation. Journal of Membrane Science 2018, 548, 559–571. (56) Cath, T. Y.; Childress, A. E.; Elimelech, M. Forward Osmosis: Principles, Applications, and Recent Developments. Journal of Membrane Science 2006, 281 (1), 70–87. (57) Ozaki, H.; Sharma, K.; Saktaywin, W. Performance of an Ultra-Low-Pressure Reverse Osmosis Membrane (ULPROM) for Separating Heavy Metal: Effects of Interference Parameters. Desalination 2002, 144 (1), 287–294. (58) Zhao, F.Y.; Ji, Y.L.; Weng, X.D.; Mi, Y.F.; Ye, C.C.; An, Q.F.; Gao, C.J. High-Flux Positively Charged Nanocomposite Nanofiltration Membranes Filled with


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Poly(Dopamine) Modified Multiwall Carbon Nanotubes. ACS Appl. Mater. Interfaces 2016, 8 (10), 6693–6700. (59) Guo, Y.S.; Mi, Y.F.; Zhao, F.Y.; Ji, Y.L.; An, Q.F.; Gao, C.J. Zwitterions Functionalized Multi-Walled Carbon Nanotubes/Polyamide Hybrid Nanofiltration Membranes for Monovalent/Divalent Salts Separation. Separation and Purification Technology 2018, 206, 59–68. (60) Zhu, J.; Tian, M.; Hou, J.; Wang, J.; Lin, J.; Zhang, Y.; Liu, J.; Bruggen, B. V. der. Surface Zwitterionic Functionalized Graphene Oxide for a Novel Loose Nanofiltration Membrane. J. Mater. Chem. A 2016, 4 (5), 1980–1990. (61) He, Y.; Liu, J.; Han, G.; Chung, T.-S. Novel Thin-Film Composite Nanofiltration Membranes Consisting of a Zwitterionic Co-Polymer for Selenium and Arsenic Removal. Journal of Membrane Science 2018, 555, 299–306. (62) Ji, Y.L.; Gu, B.X.; An, Q.F.; Gao, C.J. Recent Advances in the Fabrication of Membranes Containing “Ion Pairs” for Nanofiltration Processes. Polymers 2017, 9 (12), 715. (63) Ji, Y.L.; Zhao, Q.; An, Q.F.; Shao, L.L.; Lee, K.R.; Xu, Z.K.; Gao, C.J. Novel Separation Membranes Based on Zwitterionic Colloid Particles: Tunable Selectivity and Enhanced Antifouling Property. Journal of Materials Chemistry A 2013, 1 (39), 12213–12220.



TOC 16.8 L.m-2 .h-1 .bar-1 16

16

12

12

2.9 times

-2 -1

2.9 times 8

-1

4

4 0

PA-zwi-0.2 PA-ini-0 0

PA-ini-0

PA-zwi-X

PA-zwi-0.2

PA-ini-x pollutants

-1

-1

8

-2

5.7 L.m-2 .h-1 .bar-1

anti-fouling L.m .h .bar

2.9 times

L.m .h .bar

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

Page 30 of 41

zwitterions


hydration layer

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


Figure 1. Synthetic scheme for preparing PA-ini-x via interfacial polymerization and subsequently surface-initiated atom transfer radical polymerization. Figure 2. Characterizations of PA-ini-x: (a) FTIR spectra, (b-e) SEM surface and cross-section images, (f) Permeability and Na2 SO4 rejection (25℃, pH=6.5), (g) water contact angle. Figure 3. (a) FTIR spectra and (b) N 1s spectra of membranes after grafting PSBMA. PA-zwi-0.1h meant grafting PSBMA on PA-ini-0.15 for 0.1h and other labels were named in the same way. Figure 4. SEM surface (a-c) and cross-section images (d-f) of membranes after grafting PSBMA. Figure 5. AFM images of membranes grafting PSBMA: (a-d) air phase, (e-h) water phase. Figure 6. (a) Effect of SI-ATRP time on water permeability and Na2 SO4 rejection (25℃, pH=6.5) and (b) water contact angles of membranes after grafting PSBMA. Figure 7. (a) Zeta potential of membranes, (b) rejection of membranes, (c-d) MWCO and pore radius of membranes, (e) Salt permeability of membranes and (f) stability of membranes (1000 ppm feed solution, 25℃ pH=6.5). Figure 8. Concentration change of mixture feed solution and nanofiltration property of membranes during concentration process (25 ℃, pH=6.5, 1000 ppm raffinose and 5000 ppm NaCl): (a) and (b) PA-zwi-1h, (c) and (d) PA-ini-0. Figure 9. Flux recovery coefficient (the ratio of flux at certain time to initial flux) and flux decline ratio (Fr and Fir defined in Section 2.5) of membranes: (a) and (b) 100 ppm BSA solution, (c) and (d) 100 ppm LYZ solution, (e) and (f) 100 ppm HA solution, (g) and (h) 100 ppm NaAlg solution. Table 1 Materials and preparation method of zwitterionic membranes and their performance



Figure 1. Synthetic scheme for preparing PA-ini-x via interfacial polymerization and subsequently surface-initiated atom transfer radical polymerization.


Page 32 of 41

Page 33 of 41

PA-ini-0 Polysulfone

-CONH-

d


200nm

400nm

PA-ini-0.10 PA-ini-0.15

PA-ini-0.15

c

PA-ini-0.20

2000

1600

1242

1200

Wavenumber (cm-1)

800

12

e

100 80

8 60 6 40

4

20

2 25 i-0 .05 .10 .15 i-0.20 -in -0.0 -ini-0 ini-0 i-0 PA A-ini -in PA-in A A A P P P P

0

200nm

400nm

10

0

PA-ini-0.15 142±8nm

1106

g Water contact angle (°)

1621

f

PA-ini-0 233±12nm

b

O=S=O


Transmittance (%)

a

Permeability (L.m-2.h-1. bar-1)

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


PSF PA-ini-0.025 PA-ini-0.10 PA-ini-0.20

100


80

60

40 0

20

40

60

80

100

120

Time (h)

Figure 2. Characterizations of PA-ini-x: (a) FTIR spectra, (b-e) SEM surface and cross-section images, (f) Permeability and Na2 SO4 rejection (25℃, pH=6.5), (g) water contact angle.



a PA-ini-0 PA-ini-0.15

b

-SO3-

-COO- -CONH-

-CON-

4000

PA-zwi-3h PA-zwi-1h PA-zwi-0.4h PA-zwi-0.2h PA-zwi-0.1h PA-ini-0.15 PA-ini-0

PA-zwi-0.1h PA-zwi-0.2h

Counts (s)

Transmittance (%)

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

Page 34 of 41

PA-zwi-0.4h PA-zwi-1h PA-zwi-3h

-N+(CH3)2-

3000

2000

1040

1726 1621

1000

2000

1600

1200

Wavenumber (cm-1)

800

408

404

400

396

392

Binding energy (eV)

Figure 3. (a) FTIR spectra and (b) N 1s spectra of membranes after grafting PSBMA. PA-zwi-0.1h meant grafting PSBMA on PA-ini-0.15 for 0.1h and other labels were named in the same way.


Page 35 of 41 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


PA-zwi-0.2h

a

PA-zwi-1h

400nm

PA-zwi-0.2h 170±9nm

d

200nm

b

PA-zwi-3h

400nm

PA-zwi-1h 188±11nm

e

200nm

c

400nm

PA-zwi-3h 204±13nm

f

200nm

Figure 4. SEM surface (a-c) and cross-section images (d-f) of membranes after grafting PSBMA.



a PA-ini-0 RMS=16.1nm

b PA-zwi-0.2h RMS=13.1nm c PA-zwi-1h RMS=8.6nm

e PA-ini-0 RMS=19.7nm

f PA-zwi-0.2h RMS=19.2nm g PA-zwi-1h RMS=18.3nm

Page 36 of 41

d PA-zwi-3h RMS=5.9nm

h PA-zwi-3h RMS=17.8nm

Figure 5. AFM images of membranes grafting PSBMA: (a-d) air phase, (e-h) water phase.


Page 37 of 41

a

b 20

Water contact angle (°)

100 PA-ini-0.15 PA-zwi-0.2h PA-zwi-1h

100

16

80

12

60

8

40

4

20


Water permeability (L.m-2.h-1. bar-1)

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


80

PA-zwi-0.1h PA-zwi-0.4h PA-zwi-3h

60 40 20

0

h h h h .15 -0.1h i-1 i-3 0.2 0.4 i-0 wi- -zwi- A-zw A-zw wi -in z z A P P P PA PA PA

0

0

20

40

60

80

100

120

Time (s)

Figure 6. (a) Effect of SI-ATRP time on water permeability and Na2 SO4 rejection (25℃, pH=6.5) and (b) water contact angles of membranes after grafting PSBMA.



b 140 PA-ini-0 PA-ini-0.15 PA-zwi-0.1h PA-zwi-0.2h PA-zwi-0.4h PA-zwi-1h PA-zwi-3h

20 0 -20 -40

CaCl2 NaCl Raffinose

100 80 60 40 20

-60 2

3

4

5

6

7

8

9

10

0

11

pH c

PA-ini-0 PA-ini-0.15 PA-zwi-0.1h PA-zwi-0.2h PA-zwi-0.4h PA-zwi-1h PA-zwi-3h

60

40 200

300

400

500

600

700

Probability density function (nm-1)

80

PA-ini-0.15 PA-ini-0 PA-zwi-0.2h PA-zwi-1h PA-zwi-3h

4 3 2 1 0 0.0

800

PEG molecular weight (Da)

e

i-0 -0.15 -0.1h i-0.2h -0.4h i-1h i-3h w i -in w i i PA A-in A-zw A-zw A-zw PA-z PA-z P P P P

d 5

100

0.2

f

0.4 0.6 Pore radius, rp (nm)

0.8

1.0

18 -1

)

100

Na2SO4 permeability (L.m .h .bar

Retention (%)

Na2SO4 MgSO4

120

20

-2

12

3 0

16

80 60

12

9 6

PA-ini-0 PA-zwi-0.2h PA-zwi-1h

-1

15

Na2SO4 NaCl CaCl2 MgSO4

3h i-0 -0.15 -0.1h i-0.2h -0.4h i-1h w -in i wii i PA A-in A-zw A-zw A-zw PA-z PA-z P P P P

8

40

4

20

0

0

20

40

60

80

100

120

140

160


Zeta potential (mV)

40

Rejection (%)

a

Salt permeability (L.m-2.h-1. bar-1)

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

Page 38 of 41

0

Time (h)

Figure 7. (a) Zeta potential of membranes, (b) rejection of membranes, (c-d) MWCO and pore radius of membranes, (e) Salt permeability of membranes and (f) stability of membranes (1000 ppm feed solution, 25℃ pH=6.5).


5000

4000

4000

CNaCl (ppm)

Craffinose (ppm)

5000

3000

3000

2000

2000

1000

1000

b

100 14 80

12 10

60 8 40

6

Rejection (%)

a

4 20 2

0

c

0

5

10

15

20

25

30

0

0

Time (h)

0

4

8

d 6

2500

12 16 20 Time (h)

24

28

0

100

CNaCl (ppm)

4000 1500

3000

1000

2000

500 0

1000

0

4

8

12

16

20

Time (h)

24

28

0

5 80 4 3

60

2 40

Rejection (%)

2000

Flux (L.m-2.h-1. bar-1)

5000

Craffinose (ppm)

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


Flux (L.m-2.h-1. bar-1)

Page 39 of 41

1 0

0

4

8

12 16 Time (h)

20

24

28

20

Figure 8. Concentration change of mixture feed solution and nanofiltration property of membranes during concentration process (25 ℃, pH=6.5, 1000 ppm raffinose and 5000 ppm NaCl): (a) and (b) PA-zwi-1h, (c) and (d) PA-ini-0.



a

b

0.9



1.0


0.7 0.6 0.5

0

2

4

6

8

10

12

14

20 Fr Fir 15

10

5

0

16

PA-ini-0

Time (h)

c

d Flux decline ratio (%)


1.0 0.9 0.8 PA-ini-0 PA-ini-0.15 PA-zwi-1h

0.7 0.6 0.5

0

2

4

6

8

10

12

14

15 10 5


0.7 0.6 0.5

0

2

4

g

6

8

10

Time (h)

12

14

PA-zwi-1h

Fr Fir 15

10

5

0

16

h

1.0

PA-ini-0

PA-ini-0.15

PA-zwi-1h

20


0.7 0.6 0.5

PA-ini-0.15

20


0.9

Fr Fir

20

PA-ini-0

f

1.0

PA-zwi-1h

0

16



e

PA-ini-0.15

25

Time (h)


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

Page 40 of 41

Fr Fir 15

10

5

0

0

2

4

6

8

10

12

14

16

PA-ini-0

PA-ini-0.15

PA-zwi-1h

Time (h) Figure 9. Flux recovery coefficient (the ratio of flux at certain time to initial flux) and flux decline ratio (Fr and Fir defined in Section 2.5) of membranes: (a) and (b) 100 ppm BSA solution, (c) and (d) 100 ppm LYZ solution, (e) and (f) 100 ppm HA solution, (g) and (h) 100 ppm NaAlg solution.


Page 41 of 41 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


Table 1 Materials and preparation method of zwitterionic membranes and their performance Membrane PA-zwi-0.2h PA-zwi-1h NFM4 100/0 ZCP/MPD

RO/MPC Zwi-GO-PES TFC-zwi-50

AEPPS-TMC

Materials

Preparation

PWP

R(Na2SO4)

R(NaCl)

c(salt)

Ref.

method

(L.m -2 .h-1 .bar-1 )

(% )

(% )

PIP/TMC/

Surface grafting

16.8

97.2

PSBMA

(SI-AT RP)

24.4

1000ppm

This work

PIP/TMC/

Surface grafting

13.5

98.1

17.2

1000ppm

This work

PSBMA

(SI-AT RP)

DNMA/TMC

Surface grafting

12.0

15.0

36.0

1000ppm

23

/1,3-PS

(ring-opening)

MPD/T MC/

Dispersion and

135.0

5.0

2000ppm

24

Zwitterionic

interfacial

copolymer

polymerization

MPD/TMC/

Surface grafting

0.5

90

5000ppm

37

MPC

(SI-AT RP)

PES/DMAc/

Dispersion and

Zwi-GO

phase inversion

PIP/TMC/

Dispersion and

Zwitterionic

interfacial

copolymer

polymerization

AEPPS/T MC

Interfacial

11.98

10.0

3.0

1000ppm

60

8.5

93.0

50.0

1000ppm

61

14.4

1000ppm

54

8.4

polymerization

NF-90 NF-270

phenylene

Interfacial

diamine/TMC

polymerization

PIP/TMC

Interfacial

5.2

95.0

92.0

0.05mol/L

59

8.5

96.0

59.0

0.05mol/L

59

6.1

98.0

94.0

0.05mol/L

59

polymerization

BW30XLE

phenylene

Interfacial

diamine/TMC

polymerization


One-step Surface Grafting Method for Preparing Zwitterionic

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