Multifunctional Core-Shell Zwitterionic Nanoparticles to Build Robust

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Surfaces, Interfaces, and Applications

Multifunctional Core-Shell Zwitterionic Nanoparticles to Build Robust, Stable Antifouling Membranes via Magnetic-Controlled Surface Segregation Hongguang Sun, Yanqiu Zhang, Songwei Li, Yongping Bai, Jun Ma, and Lu Shao ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b13862 • Publication Date (Web): 04 Sep 2019 Downloaded from pubs.acs.org on September 4, 2019

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ACS Applied Materials & Interfaces

Multifunctional Core-Shell Zwitterionic Nanoparticles to Build Robust, Stable Antifouling Membranes via MagneticControlled Surface Segregation Hongguang Sun,† Yanqiu Zhang,† Songwei Li,† Yongping Bai,†,⊥ Jun Ma,‡ Lu Shao*†

†

MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion

and Storage, State Key Laboratory of Urban Water Resource and Environment, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, PR China.

‡

State Key Laboratory of Urban Water Resource and Environment, School of

Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, PR China.

⊥

Wuxi HIT New Material Research Institute Co. Ltd., Wuxi 214183, PR China.

KEYWORDS: Zwitterionic nanoparticles, membrane separation, magnetic-controlled surface segregation, antifouling, long-term stability

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Abstract Novel multifunctional core-shell nanoparticles (Fe3O4@PSBMA NPs) with magnetic and zwitterionic properties were firstly synthesized and efficiently incorporated into the poly (vinylidene fluoride) (PVDF) membranes via magnetically-controlled surface segregation towards the better water-energy-food nextus. The combination of zwitterionic polymers (PSBMA) and Fe3O4 particles can improve the compatibility of additives with PVDF matrix, and significantly improve the migration of Fe3O4@PSBMA NPs onto membrane surfaces under magnetic fields during nonsolvent induced phase separations (NIPS). The modified membrane with surfaceenriched multifunctional zwitterionic nanoparticles had an enhanced water flux (168%, ~630.5 L m-2 h-1), excellent fouling resistance (~93.8%), and increased rejection to BSA (94.1 %). Most importantly, the PVDF/M-Fe3O4@PSBMA membrane had an excellent stability under the long-term filtration test for practical water-treatment applications.

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1. Introduction Membrane technology is a green alternative to traditional separation unit operations， in which polymer membranes are widely applied in diverse processes due to the unique characteristics of convenience and efficiency.1-4 However, for typical polymeric membranes, it is hard to avoid fouling on surfaces and inside pores. These undesirable adsorption and accumulation of foulants/pollutants are harmful for membrane performance, stability, and life span.5-7 In general, the most direct method for reducing fouling is to construct a compact hydrophilic surface with antifouling materials, such as zwitterionic and peptidomimetic polymers.8-12 Comparatively, zwitterionic materials are the overwhelmingly preferred choice for the formation of hydration shell via electrostatic interactions, as it exhibits a stronger force for adsorbing water which alleviates membrane fouling.13-14 According to previous studies, zwitterionic segments can be adhered to membrane surfaces through diverse strategies such as surface grafting15-16 or coating.17-19 However, these methods generally require multi-step processing, resulting in increased costs or a possible decrease in water flux.3, 9 As a unique approach for membrane fabrication, surface segregation has been incorporated into conventional non-solvent induced phase separation (NIPS) process to achieve in situ and three-dimensional hydrophilic modification without additional processing steps.20-22 During the immersion-precipitation process, a diffusive exchange of solvents and non-solvents trigger the precipitation of polymeric membrane materials, forming a robust antifouling surface with spontaneous “free surface segregation” and “forced surface segregation” of hydrophilic segments from the surface segregation modifier (SSM) onto membrane surfaces and pore faces. Recently, sulfobetaine methacrylate (SBMA), a kind of zwitterionic monomer, has attracted extensive attention in membrane modification.13 The effective antifouling properties of PSBMA and polymer-based PSBMA have been demonstrated in many kinds of membranes. Kaner et al. manufactured fouling-resistance PVDF UF membranes with two zwitterion-containing polymer additives (PMMA-r-SBMA and PMMA-r-SB2VP).9 Li 3



et al. fabricated a high antifouling PVDF membrane with PVDF-g-PSBMA additive by an immersion precipitation process.23 Chen et al. synthesized antifouling membrane surface mixed with zwitterionic polymer (CA-g-PHFBM) via “forced surface segregation” approach.24 However, the surface segregation efficiency could be further improved in order to optimize membrane structure and achieve high performance and long-term usage. Recently, magnetic nanoparticles, with their inherent magnetic properties, have been used for organic pollutants removal, and in biomedical and cancer nanotheranostics fields.25-27 Surface modified membranes have been successfully prepared with magnetic Fe3O4 or Fe3O4/GO materials via assistance from the external magnetic field during the phase inversion process, improving the fouling-resistance property.28-32 In theory, the combination of polymeric SSM with inorganic magnetic particles to engineer antifouling surfaces should be the preferred choice for magneticcontrolled surface segregation. This is due to the fact that more compatible organic polymers ensure the simplicity of the process and the integration of the structure as to be stable and highly efficient. However, it is still challenging to combine conjugate magnetic particles and zwitterionic polymers to construct a stable antifouling membrane via magnetic-controlled surface segregation.

Scheme 1. Schematic diagrams of the preparation of Fe3O4@PSBMA particles.

Herein, the composite zwitterionic nanoparticles (Fe3O4@PSBMA) were synthesized for the first time to engineer antifouling membrane via magnetic-controlled 4


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surface segregation. The structure and synthetic procedure of Fe3O4@PSBMA NPs are illustrated in Scheme 1 and Figure S1. SEM and EDS mapping of the membrane crosssections could verify such magnetic-induced forced surface segregation behavior. The comprehensive performances of water permeation and fouling-resistance were thoroughly investigated and discussed. Most importantly, the long-term stability of Fe3O4@PSBMA NPs in the membrane matrix was evaluated.

2. Experimental 2.1. Materials PVDF (FR904) powder was purchased from Shanghai 3F New Material Co., Ltd. 1Methyl-2-pyrrolidinone (NMP), Polyvinylpyrrolidone (PVP, K30), and Bovine serum albumin (BSA) were provided by Aladdin. FeCl3 · 6H2O, FeCl2 · 4H2O, sulfobetaine methacrylate (SBMA), vinyltrimethoxysilane (VTES), and azobisisobutyronitrile (AIBN) were obtained from Sigma-Aldrich. All reagents were used as received without further purification. 2.2. Synthesis of Fe3O4 and Fe3O4@PSBMA NPs Fe3O4 magnetic nanoparticles were synthesized according to the previous reports.33-35 Briefly, FeCl3 ·6H2O and FeCl2 ·4H2O (2: 1 molar ratio) were dissolved into ultrapure water under stirring at 85 oC with an air-free system to produce a mixture solution. Subsequently, NH3 ·H2O (28-30 %) was added dropwise into the solution above until the pH reached a value of 10. The coprecipitation reaction was carried out for 30 min, after which the product was separated using a magnet and washed for several times with water and ethanol. Finally, the product was dried in a vacuum oven at 80 oC until it reached a constant weight. To enable grafting of poly (sulfobetaine methacrylate) onto the Fe3O4 nanoparticles surface, the silane coupling agent was first immobilized onto the Fe3O4 nanoparticles based on the previous protocol.36 In short, 0.5 g Fe3O4 nanoparticles were dispersed via ultrasound into a mixture solution of ultrapure water and ethanol. Afterwards, the 5



mixture was whisked for half an hour after the addition of VTES. The temperature of system was raised to 75 oC after adjusting to a weak acid with glacial acetic acid. The precipitants were collected with a magnet, and then washed with ethanol. Finally, this product was dried in an oven and named Fe3O4@VTES. Subsequently, Fe3O4@VTES NPs, SBMA and AIBN were dispersed into the THF solution. The polymerization proceeded at 75 oC for 8 hours with an air-free atmosphere. The precipitants were collected with a magnet and washed with THF. The products were dried and called as Fe3O4@PSBMA NPs. The synthesis process of Fe3O4@PSBMA NPs was presented in Scheme 1 with the information of the structure. The morphology, magnetism, composition, and particle size were characterized by transmission electron microscopy (TEM, Hitachi H7650), vibrating sample magnetometry (VSM, MPMS3, Quantum) and Fourier transform infrared (FTIR, Nicolet iS50). 2.3. Membrane fabrication and characterizations In this study, magnetic field was utilized to fabricate ultrafiltration membranes with or without magnetic NPs during the membrane formation process (Figure 1 and Figure S2)37. Typically, a homogeneous casting solution (PVDF, magnetic NPs, PVP and NMP) could be formed at 75 oC for 10 hours. Then, the cool and bubble-free solution was casted onto a glass plate with the thickness of 150 μm in a magnetic field (0.15± 0.01T) at a distance of 4.2 cm. After 60 s delay, the glass was immersed into a water bath for 24 hours to promote the inversion process (Figure S3 and Figure S4). Then, the membrane was soaked in water before usage. The composition of casting solutions was illustrated in Table 1.

Figure 1. Schematic for the fabrication of PVDF/M-Fe3O4@PSBMA membrane.

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Scanning electron microscopy (SEM, Quanta 200F) and Atomic Force Microscopy (AFM, Solver P47) were utilized to explore the morphology and roughness of the membranes38. Chemical elements of membrane surface were detected by the X-ray photoelectron spectroscopy (XPS, SHIMASZU). The hydrophilicity of the membrane was investigated based on the sessile-drop method, using a German G 10 Kruss instrument with the contact angle (CA) as parameter. Table 1. Composition of various membranes. PVDF (wt.%)

PVP (wt.%)

Nanoparticle (wt.%)

NMP (wt.%)

Magnetic field

PVDF

15.0

0.5

--

84.5

No

PVDF/Fe3O4@VTES

15.0

0.5

1.0

83.5

No

PVDF/Fe3O4@SBMA

15.0

0.5

1.0

83.5

No

PVDF/M-Fe3O4@VTES

15.0

0.5

1.0

83.5

Yes

PVDF/M-Fe3O4@SBMA

15.0

0.5

1.0

83.5

Yes

Membrane

2.4. Water flux and fouling experiments The performances of membranes were detected with a self-made filtration device (Figure S5). The effective area of the membrane was 38.48 cm2 with an operating pressure of 0.1 MPa. The permeation of water flux can be calculated by the Eq. (1). 𝑉

𝐽 = 𝐴×𝑇

(1)

where J represents the flux (L m-2 h-1), V stands for the volume of permeated (L), A and T represent the membrane area (m2) and operation time (h), respectively. Bovine serum albumin (BSA) was selected as the model protein to simulate the wastewater with a concentration of 1g L-1 in the feed solution. The concentration of BSA solution in the permeation was detected with the ultraviolet-visible spectrophotometer (UV-752, China) at a wavelength of 280 nm. The BSA rejection was calculated with the Eq. (2). 7



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𝐶𝑝

(2)

𝑅 = 1 ― 𝐶𝑓 × 100%

where R represents the rejection to BSA (%), Cp and Cf stand for the concentration of BSA in the permeation and feed solutions (g L-1), respectively. The fouling-resistance of membranes was evaluated by filtration cycles consisting of the following steps: water permeation, BSA solution permeation, and water permeation again after washing with distilled water and so on. Then, the parameter of flux recovery ratio (FRR) was calculated with Eq. (3). 𝐽𝑤2

(3)

𝐹𝑅𝑅 = 𝐽𝑤1 × 100%

where Jw1 and Jw2 represent the water flux before and after the filtration of BSA solution, respectively. In order to investigate the membrane fouling process in detail, three main parameters were calculated in Eq. (4) - (6).

( 𝑅 =( 𝑅 =(

𝐽𝑝

)

(4)

𝑅𝑡 = 1 ― 𝐽𝑤1 × 100%

) × 100% ) × 100% = 𝑅 ― 𝑅

𝐽𝑤2 ― 𝐽𝑝

𝑟

𝑖𝑟

𝐽𝑤1

(5)

𝐽𝑤1 ― 𝐽𝑤2 𝐽𝑤1

𝑡

𝑟

(6)

Where Rr and Rir represent the reversible and irreversible fouling ratio, respectively. The total fouling ratio (Rt) is defined as the sum of Rr and Rir. 2.5. Stability and durability of the membranes To detect the stability of Fe3O4@PSBMA NPs, the modified membrane was filtrated with water for 24 hours, in which the permeated water (15 ml) was sampled every 2 hours. Afterwards, iron concentrations were detected in the samples with an inductively coupled plasma optical emission spectroscopy (ICP-OES).

3. Results and discussion 3.1. Characterization of Fe3O4@PSBMA NPs. Fe3O4@PSBMA NPs were synthesized by free radical polymerization and their physicochemical properties are illustrated in Figure 2 and Figure S6. The average 8


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diameter of a bare Fe3O4 NPs is about 28.0 nm, and it increases to 112.2 nm after the grafting of PSBMA on the particle surface, which is followed by the appearance of cluster.39 Meanwhile, a new absorption band at 1730 cm-1 appeared for Fe3O4@PSBMA NPs assigning to the stretching vibration of -SO32- from PSBMA (Figure S7).

Figure 2. Morphologies and characteristics of the bare Fe3O4 and Fe3O4@PSBMA NPs. (A) TEM images of bare Fe3O4 (a) and Fe3O4@PSBMA NPS (b). (B) TGA and (C) Magnetization hysteresis loops of prepared NPs.

The disappearance of the Fe element and the emergence of Si and S elements on the Fe3O4@PSBMA NPs indicated that Fe3O4 NPs were progressively being wrapped by the VTES and PSBMA polymers (Figure S8). To determine the content of graftingpolymers on particle surfaces, thermogravimetric analysis (TGA) is a reliable technique (Figure 2B). As such, for Fe3O4@VTES, the weight loss at temperature of (< 200 oC) and (> 450 oC) are associated with the desorption water and structure water, respectively.40 Due to the decomposition of PSBMA polymers grafted onto the silica surface, the TGA curve of Fe3O4@PSBMA showed a weight loss of 21.6 wt.% apart from two water loss events. The magnetic properties of prepared particles were investigated with a VSM and the obtained hysteresis loops were presented in Figure 2C. No hysteresis was spotted, implying typical superparamagnetic behaviors for the three specimens. The saturated magnetization for pristine Fe3O4, Fe3O4@VTES and Fe3O4@PSBMA NPs were 53.11, 9



29.75 and 17.93 emu g-1, respectively, this normal phenomenon appeared in previous works.41-43 By calculating from the decrease of saturation magnetization, the content of zwitterionic PSBMA polymers grafting on the surface of Fe3O4 NPs were ca. 22.3 wt.% (close to the data of TGA).44 In addition, it was noted that the magnetism of Fe3O4@PSBMA NPs were still strong enough to migrate in the direction of magnetic field within seconds.

3.2. Segregation behavior and stability of Fe3O4@PSBMA NPs The elemental distribution in the cross-section of PVDF/Fe3O4@PSBMA and PVDF/M-Fe3O4@PSBMA membranes (with or without magnetic field) were detected by the SEM-EDS, which can visualize the segregation behavior of Fe3O4@PSBMA NPs. According to Figure 3, the typical elements of sulfur and iron could be visibly observed in the cross-section of both membranes. Compared with the approximate uniformity of elements on the PVDF/Fe3O4@PSBMA membrane, a significant element gradient appeared on the cross-section of the PVDF/M-Fe3O4@PSBMA membrane, with an enrichment of S and Fe elements on the near-surface area.

Figure 3. SEM-EDS images on the cross-section of PVDF/Fe3O4@PSBMA and PVDF/MFe3O4@PSBMA membranes.

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In addition, the difference in surface elements composition of PVDF/MFe3O4@PSBMA membrane (top and bottom side) was detected in detail by XPS (Figure 4A and Table S1). Sulfur, the dominating element, emerged on both sides of the PVDF/M-Fe3O4@PSBMA membrane, with a higher content on the top surface than that on the bottom surface (~4.6 times). Furthermore, the atomic ratios of S/F and S/N increased from 0.007 and 0.135, respectively, for the bottom surface of the membrane to 0.034 and 1.214, respectively, for the top surface. This suggests the enrichment of Fe3O4@PSBMA NPs on the membrane top surface. Thus, it is proven that magnetic field induced casting could promote the migration of Fe3O4@PSBMA NPs onto the membrane surface, which is beneficial to improving the hydrophilicity and antifouling properties of the membrane.

Figure 4. (A) XPS spectra, (B) concentration of iron in the permeate solution, (C) contact angle of PVDF/M-Fe3O4@PSBMA membrane after different filtration times and (D-F) SEM and AFM images of prepared membranes.

The stability of additives in the membrane matrix is critical for the durable hydrophilicity of membrane. Hence, the ICP-OES instrument was utilized to directly detect concentration of Fe3O4@PSBMA NPs leaching within the membrane filtration (Figure 4B). The iron concentration in the permeate flux was only 0.027 mg L-1 in the first 30 min filtration. After continuous filtration for 3 hours, it decreased to 0.006 mg 11



L-1. This result suggests that the Fe3O4@PSBMA NPs could retain in the membrane matrix during a great majority of membrane filtration. In addition, the variations in contact angle of PVDF/M-Fe3O4@PSBMA membrane were investigated for different filtration tests (Figure 4C). A slight increase in contact angle (~2.3o) was observed after 24 h filtration, implying the stability of PVDF/M-Fe3O4@PSBMA membrane surface.

3.3. Morphology and structure of membranes The SEM and AFM images of the samples were detected and illustrated in Figure 4D-4F and Figure S9. A type of asymmetric structure could be observed on the crosssection of membranes. However, when Fe3O4@VTES and Fe3O4@PSBMA were incorporated into the polymer matrix, wider pore channels emerged due to the instantaneous liquid-liquid phase demixing. In contrast, the PVDF/M-Fe3O4@PSBMA membrane showed more inner-pores and enlarged macrovoids than that of the PVDF/Fe3O4@VTES membrane. Furthermore, both the porosity and mean pore size of membranes increased with the addition of Fe3O4@VTES or Fe3O4@PSBMA NPs (Table S2). As expected, the PVDF/M-Fe3O4@PSBMA membrane showed the largest porosity and mean pore size, indicating potential advantages in water permeability. In addition, the roughness of PVDF/M-Fe3O4@VTES or PVDF/M-Fe3O4@PSBMA membrane was higher than that of the pure PVDF membrane. The increased roughness might be the outcome of surface enrichment of additives, which could enhance the hydrophilicity and antifouling properties of membranes.

3.4. Hydrophilicity and filtration properties It is undoubtable that the filtration property of membrane can be altered by the surface hydrophilicity, which can be determined by measuring contact angle.45-46 Normally, a lower contact angle suggests a more hydrophilic membrane surface.47-48 Compared to the PVDF membrane, which had a highest contact angle of 79.3o, the contact angle of membranes modified with Fe3O4@VTES or Fe3O4@PSBMA NPs evidently decreased, suggesting its superior hydrophilicity (Figure 5A). During the 12


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phase inversion process, hydrophilic NPs will spontaneously migrate toward the membrane/water interface to decrease the interface energy.49 It was noted that PVDF/M-Fe3O4@VTES and PVDF/M-Fe3O4@PSBMA membranes have smaller contact angles that those of PVDF/Fe3O4@VTES and PVDF/Fe3O4@PSBMA membranes. This behavior is caused by the magnetically forced surface segregation, resulting in the enrichment and migration of magnetic NPs onto the membrane surface.28 Therefore, it is certain that this improved hydrophilicity will be beneficial to the permeability and antifouling properties.

Figure 5. Contact angle (A), water flux and BSA rejection (B), normalized flux (C) and fouling resistance ratio (D) of prepared membranes.

The filtration results (in Figure 5B) showed that an increasing trend can be observed for water flux and BSA rejections for all membranes supplemented with nanoparticles. Specially, the water flux of PVDF/M-Fe3O4@PSBMA membrane was as high as 630.5 L m-2 h-1, which is 168%, 97% and 26% higher than that of PVDF, PVDF/Fe3O4@VTES and PVDF/Fe3O4@PSBMA membranes, respectively. Two possible reasons for this behavior: (1) a more hydrophilic membrane surface was 13



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formed by the violent migration of Fe3O4@PSBMA NPs under a magnetic field. (2) improved pore size and porosity of PVDF/M-Fe3O4@PSBMA membrane. In addition, it was noted that the rejections of all membranes exceeded 90%, particularly, the PVDF/M-Fe3O4@PSBMA membrane expressed an increased BSA rejection of 94.1 %. This implies that more zwitterionic polymers were enriched and retained onto the membrane surface and inner pores to minimize interfacial free energy,

24which

is a

spontaneous process enhanced by the magnetic field force.

3.5. Antifouling performance of membranes. Membrane fouling is mainly induced by multiple interactions between membrane matrix and protein, including electrostatic interaction, hydrogen bonding and hydrophobic impact et al. An optimum membrane surface should be immune to protein fouling and have characteristics of good hydrophilicity, sufficient hydrogen bond receptor/donors and overall electric neutrality.50 Consequently, a versatile particle, containing phosphatidylcholine and a magnetic response, was synthesized by grafting the zwitterionic polymer (PSBMA) onto the Fe3O4 surfaces. It was proven that Fe3O4@PSBMA NPs migrated onto and enriched the membrane surface; this implied that sufficient PSBMA polymers appeared on the membrane/water interface. The permeation fluxes of membranes within a three-cycle filtration were illustrated in Figure 5C. Briefly, the membranes were successively filtrated with pure water, BSA solution, and then pure water again after simple flushing. However, while the BSA solution was being filtrated, a noticeable decline of permeation flux could be observed. This indicated that membrane fouling was gradually formed by concentration polarization. Subsequently, the permeation flux recovered to varying degrees after the membranes were flushed with deionized water. After the cyclic test, four parameters were calculated to evaluate the fouling resistance of the membranes, and the corresponding results are illustrated in Figure 5D. Evidently, raw PVDF membrane showed the lowest FRR (40.6 %) and highest Rt (85.8%). Normally, membranes with a higher FRR and lower Rt possesses excellent antifouling properties.51 With the 14


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incorporation of Fe3O4@PSBMA NPs into the membrane matrix, the overall FRR increased up to 86.2% and Rt also decreased. Additionally, the FRR further improved to 93.8% when the magnetic field was used to assist the preparation of PVDF/MFe3O4@PSBMA membrane, and the irreversible fouling ratio (Rir) was reduced extensively, from 59.5% to 6.2%. This means that during the phase inversion process, an excellent antifouling membrane was engineered with Fe3O4@PSBMA NPs under magnetism. Finally, an overall comparison was made between PVDF/M-Fe3O4@PSBMA membrane and zwitterionic polymer modified membranes of previous studies, and the data is presented in Table 2. Note that the PVDF/M-Fe3O4@PSBMA membrane presented a superior performance compared with other modified membranes, indicating that this high-performance membrane has the potential to be utilized in other separation systems.

Table 2. Performance comparisons of this work against previous works. Membrane PVDF-gPSBMA/PVDF PVDF/HPE-gMPEG PVDF/SPANI PVDF/PVDF-gPMABS PVDF/TiO2PMMA-PSBMA PVDF/MFe3O4@PSBMA

Contact angle (degree)

Water flux (L m-2 h-1)

BSA rejection (%)

Water flux recovery (%)

Ref.

67

239.13

--

81.2

52

49

507

92

82

53

29

160

~92

~95

54

67.4

136.3

98.6

95.3

55

74.8

~227

--

94

56

58.7

630.5

94.1

93.8

This work

4. Conclusions In summary, magnetic and zwitterionic Fe3O4@PSBMA NPs were synthesized and utilized to prepare PVDF/M-Fe3O4@PSBMA membrane during phase inversion process via magnetic field induced casting. It was proven that Fe3O4@PSBMA NPs 15



migrated onto and enriched the membrane surface with long-term stability. In addition, the PVDF/M-Fe3O4@PSBMA membrane exhibited upgraded water flux (168%, ~630.5 L m-2 h-1), increased protein rejection (94.1%) and excellent fouling-resistance (FRR~93.8%). Thus, this method can improve the overall performance of the membrane by manipulating the segregation of additives onto the membrane surface rather than using a simple blending strategy.

Associated Content Supporting Information. The structure of nanoparticles, Scheme of preparation process of membrane, Schematic of magnetic field forced surface segregation, Nonsolvent induced phase separation process, Ultrafiltration system, The particle size, FTIR spectra, XPS spectra of particles, Morphology of membranes, Composition of PVDF/M-Fe3O4@PSBMA membrane with top and bottom sides, Porosity and mean pore size of membranes. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]; Notes The authors declare no competing financial interest.

Acknowledgements This work was supported by the National Natural Science Foundation of China (21878062) and Open Project of State Key Laboratory of Urban Water Resource and Environment (Harbin Institute Technology) (No. QA201922). The authors wish to acknowledge Keyi Kang Yao (Johns Hopkins University, Department of Environmental Health and Engineering), for her help in polishing the language in this 16


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work.

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Multifunctional Core-Shell Zwitterionic Nanoparticles to Build Robust

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