Effects of Particle Morphology on the Antibiofouling Performance of

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Effects of Particle Morphology on the Antibiofouling Performance of Silver Embedded Polysulfone Membranes and Rate of Silver Leaching Meng Hu, Kai Zhong, Yujia Liang, Sheryl H. Ehrman, and Baoxia Mi Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04934 • Publication Date (Web): 08 Feb 2017 Downloaded from http://pubs.acs.org on February 10, 2017

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Industrial & Engineering Chemistry Research

Manuscript

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Effects of Particle Morphology on the Antibiofouling

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Performance of Silver Embedded Polysulfone Membranes

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and Rate of Silver Leaching

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Meng Hua,*,1, Kai Zhongb, Yujia Liangb, Sheryl H. Ehrmanb, and Baoxia Mia,2

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a

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MD

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b

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Department of Civil and Environmental Engineering, University of Maryland, College Park,

Department of Chemical and Biomolecular Engineering, University of Maryland, College Park,

MD

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In preparation as an invited paper to

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14

2016

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*

The author to whom correspondence should be addressed. e-mail: [email protected]; tel.: +1-410-516-5151; fax: +1-410-516-8996

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1

Current address: Department of Environmental Health and Engineering, Johns Hopkins University, Baltimore, MD 2 Current address: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 1 ACS Paragon Plus Environment


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ABSTRACT

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Herein we report the effects of particle morphology on the antibiofouling performance and silver

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leaching of silver embedded polysulfone (PSf) membranes. Composite PSf membranes were

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incorporated with three silver particles with different size and shape: microparticle (mAg),

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nanoparticle (npAg), and nanowire (nwAg). Biofouling of a control and Ag-embedded PSf

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membranes were monitored in a direct observation system, and bacterial antiadhesive property

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was observed only with membranes incorporated with nanoscale Ag particles, i.e., npAg and

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nwAg. Ag leaching experiments indicate that Ag release from composite membrane during

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filtration did not corroborate with Ag dissolution, suggesting liberation of whole Ag particles.

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mAg-PSf registered the highest Ag release despite the slowest dissolution kinetics of mAg,

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which accounted for its lack of antiadhesion property despite similar antimicrobial activities.

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Overall, the study highlights the role of particle morphology in regulating Ag leaching and thus

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in controlling antibiofouling performance for Ag-embedded membranes.

2 ACS Paragon Plus Environment

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1. Introduction

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Low-pressure membrane filtration has seen growing applications in water and wastewater

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treatment owing to their treatment reliability, low capital and operating cost, and small

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footprint.1-3 Low-pressure membrane technologies include microfiltration (MF) and

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ultrafiltration (UF) processes. However, biofouling of MF/UF membranes represents a serious

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challenge to the increasing implementation of low-pressure membrane systems.4-6 Biofouling is

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the result of the deposition of microorganisms on membrane surface, their permanent attachment

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onto the surface, and the associated bacterial processes that lead to the formation of a biofilm on

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the membrane surface. These events negatively impact membrane performance by reducing

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membrane flux and water quality, increasing overall energy cost, and shortening membrane life.4,

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5, 7

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To control biofouling, various efforts have been made to increase biofouling resistance of

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MF/UF membranes by embedding antimicrobial nanomaterials.8, 9 Notably, silver nanoparticles

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(npAg) have been widely employed for this purpose. For example, npAg-incorporated composite

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membranes exhibited strong antimicrobial activities,10-13 decreased bacterial attachment,13-16 and

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even inhibited biofilm formation.11, 13 Liu et al. monitored the deposition rate and subsequent

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detachment of Escherichia coli (E. coli) using a direct observation system, and found much

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improved bacterial detachment for npAg-embedded polysulfone (PSf) membrane (75% bacterial

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removal) upon physical cleaning in comparison to npAg-free PSf membrane (18% bacterial

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removal).15 The antiadhesive property was attributed to the antimicrobial activities of npAg on

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the membrane surface, which inactivated deposited bacteria, prevented permanent bacterial

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attachment, and suppressed biofilm formation.11, 13-15



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Silver has excellent antimicrobial properties in both metallic (Ag) and ionic (Ag+) forms.17,

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18

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bacteria such as bacterial protein damage, electron transport chain interruption, and DNA

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dimerization.19-21 While the toxicity mechanisms for Ag+ ions are well understood, the origin of

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the antimicrobial properties of npAg is under debate.22, 23 In addition to the release of Ag+ ions,

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direct contact between nanoscale npAg and bacteria has been reported to cause cell wall pitting

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and disrupt cell membrane permeability.18, 24, 25 Therefore, antibacterial effect of npAg depends

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on npAg particle morphology (e.g., size and shape).14, 26 For example, triangular silver

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nanoplates with a lattice plane were observed to show stronger antimicrobial activities

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compared to spherical and rod-shaped nanoparticles in the same size range of 1-10 nm.26

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Ag+ ions interact with thiol groups in bacteria, and can cause catastrophic consequences to

Particle morphology not only influences the bacterial toxicity of npAg but also greatly

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affects the depletion rate of npAg due to dissolution and release from membranes. The

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dissolution of metallic silver takes place with the oxidation of surface Ag atoms by dissolved

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oxygen and the formation of atomic layer thick silver (I) oxide, followed by the release of

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soluble Ag+ ions upon protonation.27, 28 The surface area dependent dissolution has been

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explored to control Ag+ ion release by controlling particle size and shape.29 The release rate of

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npAg increased inversely when the particle size decreased,27, 29 and a silver foil released

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significantly slower than did a npAg with an equal area.29 In the same token, it is anticipated that

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one can control the particle morphology of silver particles to engineer a silver composite

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membrane with long-lasting biofouling resistance.

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In the present study, we investigate the effects of the particle morphology of silver

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particles on the antibiofouling performance and the rate of silver leaching for Ag-incorporated

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composite membranes. Specifically, the composite membranes were synthesized by embedding


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in polysulfone npAg (average diameter = 80 nm), silver nanowire (nwAg, average diameter = 90

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nm, average length = 20 µm), and silver microparticle (mAg, average diameter = 1 µm),

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respectively. Bacterial deposition and detachment were monitored in a direct observation system

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to assess the biofouling performance of Ag-incorporated composite membranes. Silver leaching

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was evaluated under both static storage and filtration conditions.

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2. Materials and methods

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2.1.

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Polysulfone (PSf, Udel P3500) was provided by Solvay Specialty Polymers USA (Douglasville,

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GA). N-methyl-2-pyrrolidone (NMP, 99.5%), silver nanoparticles (npAg) (cat# 576832, < 100

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nm), and poly(ethylene oxide) (average MW 100,000) were purchased from Sigma-Aldrich (St.

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Louis, MO). Silver nanowire (nwAg, average diameter = 90 nm, average length = 20 µm) was

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obtained in ethanol solution (SLV-NW-90, Blue Nano Inc., Charlotte, NC). Silver microparticles

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(mAg) were produced by a co-solvent spray pyrolysis method30, and had an average diameter of

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1 µm. mAg and nwAg were imaged with an SU-70 scanning electron microscope (SEM, Hitachi,

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Japan); npAg particles were imaged with a transmission electron microscope (TEM, JEOL JEM

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2100 LaB6, Japan).

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2.2.

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Ag-free and Ag-embedded composite membranes were synthesized via phase separation. To

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prepare solutions for Ag-embedded composite membranes, a 12 wt% PSf solution was first

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prepared in NMP and degassed in a vacuum desiccator for over two days. mAg, npAg, and

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nwAg were dispersed in NMP with via sonication (Sonicator 4000, Qsonica, LLC., Newtown,

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Materials

Membrane synthesis

CT). mAg and npAg were in powder form and used as received. Ethanol in nwAg stock was



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evaporated before dispersing nwAg in NMP. The well-dispersed silver organosols were then

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added to PSf/NMP solutions, and the mixtures were stirred vigorously. The final solution

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compositions were 11% PSf, 0.1% Ag (mAg, npAg, or nwAg), and 88.9% NMP by weight. A

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solution for the control membrane (i.e., pure PSf membrane) consisted of 11 wt% PSf and 89 wt%

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NMP. Membranes were obtained by casting each solution onto a glass plate using a custom-

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made casting knife with an application depth of 254 µm, and immediately transferring the glass

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plate with the cast film to a 3 wt% NMP coagulation bath for phase separation for 10 min. The

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cast membranes were then soaked in a deionized (DI) water bath for at least two days while still

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on glass plates. Subsequently, the membranes were stored in DI water at 4 °C for further

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experiments. For simplicity, membranes with no Ag, mAg, npAg, and nwAg are designated as

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PSf, mAg-PSf, npAg-PSf, and nwAg-PSf, respectively.

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2.3.

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Pure water flux of the membranes was determined using a dead-end filtration cell (Amicon 8400,

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Millipore Corp., Billerica, MA) with DI water at room temperature over a pressure range of

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68.95-275.8 kPa (10-40 psi). Membranes were compacted at 344.75 kPa (50 psi) for 6 hrs before

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flux tests. Water contact angle (WCA) was measured by the sessile drop method with a Kruss

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goniometer (Model G10, Kruss USA, Charlotte, NC). Ten measurements were performed on

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each type of membranes that had dried overnight.

Membrane characterization

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Membrane morphology was observed with an SU-70 scanning electron microscope (SEM,

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Hitachi, Japan) equipped with an X-ray energy dispersive spectroscopy (X-EDS) system. X-EDS

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was used to characterize the elemental compositions of membrane surfaces. Membrane samples

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were dried overnight and sputter-coated with gold before imaging. Samples were cracked in

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liquid nitrogen for cross-section imaging. Surface pore size (diameter) and finger-like structure


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(channel size) in the cross-section were analyzed for the micrographs using ImageJ® (NIH, MD).

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For each type of membranes, 50 surface pores and 20 channels on each layer of the cross-section

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were selected. Membrane topography was observed with an atomic force microscope

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(Multimode, Veeco, Plainview, NY) in tapping mode.

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2.4.

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2.4.1. Bacterial preparation

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Green-fluorescently labeled Escherichia coli (E. coli) K12 MG1655 was selected as the model

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bacterium in the study. A single E. coli colony was introduced into 50 mL Luria-Bertani (LB)

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medium containing 0.05 g/L Kanamycin, which was incubated at 37 ºC overnight (~16 h, the E.

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coli population reached death phase). 0.1 mL of such cultured E. coli stock was transferred into

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another 50 mL Luria-Bertani (LB) medium containing 0.05 g/L Kanamycin and incubated at 37

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ºC until the optical density of the media reached approx. 0.3 (i.e., mid-log phase) at a wavelength

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of 600 nm. E. coli cells were washed for three times and re-suspended in isotonic solution (154

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mM NaCl) for use within 8 h.

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2.4.2. Membrane antimicrobial property

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To evaluate the antimicrobial property of the membranes, 1 mL of 5000 CFU/mL E. coli

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suspension was filtered onto pure PSf and Ag-embedded PSf membranes using a vacuum

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filtration cell. The E. coli suspension was obtained by serially diluting the aforementioned stock

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(5 × 108 CFU/mL). Membrane samples were cut into disks of a diameter of 45 mm, and were

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autoclaved along with the filtration cell a priori. After filtration, the membrane samples were

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placed on LB agar plates and incubated at 37 ºC overnight. Viable cells after incubation were

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counted in colony forming units (CFU).

Antimicrobial and biofouling experiments

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2.4.3. Biofouling experiments

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To test membrane biofouling performance, adhesion and detachment of E. coli were monitored

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in a custom-made direct observation system. The direct observation system consisted of a

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window-cell membrane filtration unit and a fluorescence microscope. A membrane sample of 20

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cm2 was first stabilized in the filtration unit with 2 L of 100 mM NaCl in feed vessel. The feed

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vessel was applied with a pressure range of 69-103 kPa, depending on the membrane, for a

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constant permeate flux of 43 µm/s. A peristaltic pump was used to regulate the cross-flow rate at

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4 cm/s. After 30-min stabilization, E. coli suspension was spiked into the feed vessel to reach 5 ×

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105 CFU/mL and bacterial deposition commenced. The deposition experiment lasted 60 min, and

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images of the membrane sample in the window-cell were taken throughout each experiment with

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a camera mounted to the fluorescence microscope. After bacterial deposition, the permeate flux

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was terminated and the membrane was rinsed at an elevated cross-flow rate of 64 cm/s for 30

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min. Again the detachment of E. coli was monitored by imaging the membrane surface during

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rinsing. All images were analyzed in ImageJ® (NIH, MD).

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2.5.

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2.5.1. Ag dissolution

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To assess the dissolution kinetics for silver particles of different morphologies, 0.1 g silver

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particles were mixed in 1 L of DI water under constant magnetic stirring for 24 h. Periodical

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samples of 1 mL each were taken and measured in a Perkin-Elmer (Waltham, MA) 5100 ZL

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GFAAS atomic absorption spectrometer (AAS) for Ag+ concentration. All water samples and

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standards were acidified with 0.5% trace metal grade HNO3. The detection limit of Ag for the

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AAS was 0.05 ppb using a graphite furnace.

Silver dissolution and leaching from composite membranes

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2.5.2. Static Ag leaching

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For each type of Ag-embedded composite membranes, two membrane coupons with an area of

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43 cm2 were cut. Each membrane coupon was soaked in 50 mL DI water in a tightly capped

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centrifuge tube at room temperature. 1 mL water sample was taken periodically throughout a

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duration of 28 days to monitor the release of Ag+ under static conditions. Sample treatment and

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Ag+ measurement followed the same protocols described above.

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2.5.3. Ag leaching during filtration

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To assess the release of Ag during filtration, DI water was filtered through non-compacted Ag-

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embedded composite membranes using a vacuum filtration cell with an effective membrane area

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of 41.8 cm2. Permeate samples were collected per filtration of 1 L DI water, and a total of 6 L

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was filtered. Concentration of released Ag in the permeate was analyzed in the AAS as described

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above.

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3. Results and discussion

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3.1. Silver particle and membrane characterization

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Characterization of silver particles. Silver with different particle morphology, namely

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microparticle (mAg), nanoparticle (npAg), and nanowire (nwAg), were used in this study to

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prepare Ag-embedded composite PSf membranes. Spherical mAg was synthesized via co-solvent

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spray pyrolysiss,30 and had an average diameter of 1 µm (Figure 1a). Although the as-received

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npAg particles were largely aggregated, individual particles could still be identified (Figure 1b).

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We estimated the average diameter of npAg to be 80 nm from 20 such particles. Figure 1c shows

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the morphology of nwAg, which matched the size provided by the supplier (average diameter =

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90 nm, average length = 30 µm). Based on the dimensional data, we calculated the specific



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surface area (SSA) of the silver particles, which follow the order npAg (75 µm-1) > nwAg (45

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µm-1) > mAg (6 µm-1).

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[ Figure 1 ]

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Membrane characterization. Pure PSf and Ag-embedded membranes were prepared by phase

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separation. This process led to the formation of asymmetric membranes with a dense active layer

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and a porous support layer.31 Figure 2 shows the surface of the active layer and the cross section

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of the PSf and Ag-embedded membranes. The membranes incorporated with different silver

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particles had similar surface and cross section structure to the pure PSf membrane. All

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membranes feature typical ultrafiltration membrane properties with nanometer scale pores on the

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dense surface layer and micron-sized macrovoids spanning across the membrane matrix. Also

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presented in Figure 2 is the surface topography of the PSf and Ag-embedded membranes, which

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showed similar surface roughness in the range of 5—11 nm. The addition of different silver

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particles did not noticeably change the hydrophilicity of the PSf membrane, as evidenced by

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water contact angle measurements in Figure 3a. Figure 3b presents the loading of silver on the

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surface of Ag-embedded membranes measured by X-EDS, and no significant difference was

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observed statistically (single factor anova analysis, p = 0.05).

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[ Figure 2 ]

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[ Figure 3 ]

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3.2. Effect of silver particle morphology on membrane filtration performance

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Both PSf and Ag-embedded membranes were tested for their pure water permeability and

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rejection of PEO (MW 100 K) after 6 h compaction. The performance data were listed in Table 1.

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Generally, the Ag-embedded composite membranes had higher pure water permeability and

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lower rejection of PEO-100K. This is corroborated with the diameter of the pores on the


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membrane surface determined by image analysis; enlargement of pores was observed after

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embedding silver particles. The incorporation of npAg slightly changed the filtration

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performance, increasing the pure water permeability from 149 L/m2-h-bar for the PSf to 199

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L/m2-h-bar while decreasing rejection of PEO-100K from 97.4% to 92.1%. Similar results were

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reported in previous studies.15, 32 It is interesting to note that among the three silver particles,

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nwAg, also a nanomaterial, had the most impact on membrane performance with a 7-fold

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enhancement of pure water permeability. Overall, the performance of the PSf and Ag composite

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membranes fall in the range of typical ultrafiltration, and the pore size of the membranes ensured

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the deposition of bacteria (approx. 4-5 µm) on the membrane surface rather than in the

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membrane matrix.

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Table 1 Filtration performance and surface pore size of PSf and Ag-embedded membranes. Pure water permeability, Rejection of PEO-100K Surface pore L/m2-h-bar diameter, nm PSf 97.4% 23.2 ± 6.8 149 ± 12 mAg-PSf 93.2% 30.6 ± 8.5 374 ± 51 npAg-PSf 92.1% 35.2 ± 8.8 199 ± 23 nwAg-PSf 90.7% 37.5 ± 9.8 1138 ± 40

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3.3. Effect of silver particle morphology on membrane biofouling

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To investigate biofouling on PSf and Ag-embedded composite membranes, we monitored the

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deposition and detachment of bacteria on the membrane surface in a direct observation system

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used in our previous study.15 Figure 4a presents the number of bacteria cells on the membrane

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surface of a unit area (cell density on membrane surface) as a function of time. There was no

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significant difference in the cell deposition rate for the PSf and Ag-embedded composite

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membranes, as indicated by the slope in the initial linear range of the deposition profile (initial

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20 min). The cell density of bacteria deposited on the membrane surface was similar for the PSf 11 ACS Paragon Plus Environment


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membrane and the composite membranes containing nano silver, i.e., npAg and nwAg. The

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mAg-embedded membrane observed a slightly higher cell density on its surface, likely due to its

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slightly higher surface roughness (rms 10.9 nm) than the other membranes (rms 5.2—6.8 nm)33,

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. [ Figure 4 ] The deposited bacteria were immediately cleaned with an elevated cross-flow rate (64 cm/s)

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for 30 min. The cell density was recorded during the cleaning process, and the normalized cell

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density was plotted against time in Figure 4b. Approximately 40% of the deposited bacteria were

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removed from the surfaces of the npAg- and nwAg-PSf membranes, whereas the PSf membrane

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only registered 20% bacterial removal. Previous studies have reported similar anti-adhesive

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property for npAg-incorporated membranes, and attributed the enhanced removal of bacteria to

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silver ions released from the membrane14 and direct contact between silver nanoparticles on

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membrane surfaces and the attached bacteria cells15. Both mechanisms led to the inactivation of

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the deposited bacteria and thus higher detachment rate. The seemingly identical bacterial

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removal rate with npAg-PSf and nwAg-PSf indicates that such anti-adhesive property also

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applied to nwAg, another nanoscale silver. The impregnation of mAg, however, did not have any

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effect on the detachment of deposited bacteria on the membrane surface during membrane

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cleaning. The absence of the anti-adhesive property could be due to the lack of either sufficient

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bioavailable silver or the antimicrobial property due to direct contact with nanomaterials, both of

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which were possible with the silver nanomaterials. Additional antimicrobial experiments

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demonstrate that similar to npAg- and nwAg-PSf membranes, mAg-PSf membrane also showed

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up to 2-log of reduction in E. coli grown on membrane surfaces (Figure 4c). The result indicates


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that contact with mAg also caused E. coli inactivation, and insufficient bioavailable silver from

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mAg-PSf membrane may be the reason for the lack of anti-adhesive property.

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3.4. Effect of silver particle morphology on its release from composite membranes

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One challenge for engineering Ag-embedded membrane for biofouling control is the loss of the

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anti-adhesion property with the release of silver due to dissolution. Ag leaching/release occurs

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during membrane storage and filtration, and slower Ag release is desirable to prolong the

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biofouling resistance of Ag-embedded membranes. Ag dissolution is the result of Ag oxidation

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by dissolved oxygen and the formation of atomic thick layer of silver oxide, which is followed

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by the release of Ag+ upon protonation. The mechanism suggests that Ag dissolution depends

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upon the specific surface area (SSA) of silver particles, with faster dissolution kinetics for

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particles of higher SSA.29 We monitored the dissolution of the Ag particles in DI water, and

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modeled the concentration of dissolved Ag+ with first-order kinetics27, 29 (Figure 5a). Ag

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dissolution kinetics followed the order of npAg > nwAg > mAg, with first-order rate constants at

272

0.233 h-1 for npAg (r2 = 0.943), 0.222 h-1 for nwAg (r2 = 0.998), and 0.126 h-1 for mAg (r2 =

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0.949). The data suggest that dissolution of the Ag particles used in this study show the SSA

274

dependence observed previously.

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[ Figure 5 ]

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To mimic Ag leaching during membrane storage, membrane samples were stored in closed

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tubes filled with DI water. Cumulative Ag release under the static conditions was monitored, and

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plotted in Figure 5b as a function of time. No discernable difference of Ag leaching was

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observed for the Ag-embedded membranes after 21 days. This was expected as Ag dissolution

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ceased when dissolved oxygen was consumed during closed storage. The results indicate that the

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morphology of Ag particles did not have any obvious effect on Ag leaching during membrane



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storage as long as dissolved oxygen is limited during storage (e.g., closed storage and not

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replacing storage water).

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During membrane filtration, however, Ag leaching is expedited as there is a continuous

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supply of dissolved oxygen from the water to be filtered. Figure 5c shows Ag release during

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filtration of DI water through the Ag-embedded membranes. Surprisingly, the mAg-PSf

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membrane released markedly more silver than npAg- and nwAg-embedded membranes, despite

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the slowest dissolution rate for mAg particles. After filtering 6 L of DI water (i.e., total volume

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of 0.14 L/cm2) through the membranes, 2.77 µg/cm2 silver leached out of the mAg-PSf

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membrane, almost four times that released from npAg-PSf (0.76 µg/cm2) and nwAg-PSf (0.79

291

µg/cm2) membranes. The dissolution independent Ag leaching indicates that other routes of Ag

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release also contributed to the higher leaching for the mAg-PSf membrane. For example, release

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of whole mAg particles from the membrane matrix might be possible, which was observed for

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npAg particles released from nanocomposites.35-38 It is proposed that engineered nanomaterials

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can release from nanocomposites by dissolution, desorption, passive diffusion, and degradation

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of polymer matrix.38 Polymer degradation and diffusion are unlikely mechanisms considering the

297

unfavorable experimental condition (i.e., filtering DI water in dead-end cell) for biofilm

298

formation and that diffusion within polymer composite is believed to be possible when the

299

diameter of embedded silver particles is smaller than 1.33 nm38, 39. Desorption might contribute

300

to the higher release of mAg in two ways. First, the distribution of mAg particles may favor their

301

liberation at the membrane-water interface, both on the surface and the macrovoid channel, by

302

the shear stress caused by water flow. With the same mass loading, the number of mAg particles

303

was significantly lower than that of both npAg and nwAg particles, resulting in a lower viscosity

304

for the polymer solution. Faster demixing has been reported for polymer/nanomaterial mixture


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305

with lower viscosity during phase separation, which led to concentrated particle distribution at

306

the polymer-nonsolvent (water) interface.32, 40 Additionally, each released microscale mAg

307

particle contains considerably more mass of silver than single npAg and nwAg particles. We did

308

not rule out the possibility of the release of npAg and nwAg from their respective composite

309

membranes due to desorption; yet their significantly smaller dimensions suggest reduced loss of

310

silver with the release of whole particles. This could also explain the higher Ag release from the

311

mAg-PSf membrane caused its absence of anti-adhesive property during filtration, even though it

312

had similar antibacterial properties to npAg- and nwAg-embedded membranes shown in the

313

antimicrobial experiments. Further research is warranted on the release mechanisms for Ag-

314

embedded composite membranes, which will inform better designs of biofouling-resistant

315

membranes with prolonged effects.

316 317

4. Conclusions

318

Using mAg, npAg, and nwAg, the present work investigates the effect of particle morphology of silver on

319

the antibiofouling performance and silver leaching of the Ag-embedded PSf membranes. Incorporation of

320

all particles did not significantly change membrane surface properties and performance with the exception

321

of nwAg, which improved pure water flux by seven fold. As expected, both npAg- and nwAg-embedded

322

membranes observed enhanced antibiofouling performance, which was attributed to the antiadhesive

323

property endowed by silver. The improved biofouling resistance was absent for mAg-PSf membranes

324

during biofouling experiment, despite similar antimicrobial activities for Ag-embedded membranes

325

irrespective of silver particle morphology. The results indicate that the lack of bioavailable Ag was the

326

reason for the lack of antiadhesive feature for mAg-PSf membranes. Leaching experiments show that

327

minimum Ag was lost during static storage for 21 days, presumably due to the consumption of dissolved

328

oxygen. Although mAg had the slowest dissolution kinetics among the silver particles investigated, its

329

release from the composite membrane was considerably higher than that of npAg and nwAg. The 15 ACS Paragon Plus Environment


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

330

dissolution independent release suggests desorption of whole mAg particles, which may be responsible

331

for the low biofouling performance of mAg-PSf membranes.

332 333

Acknowledgements

334

This work was supported by the National Science Foundation (Grants No. CBET-1154572 and CBET-

335

1336581). We also acknowledge the support of the Maryland NanoCenter and its NispLab. The NispLab

336

is supported in part by the National Science Foundation as a Materials Research Science and Engineering

337

Center Shared Experimental Facility. We would also like to thank Drs. Yaolin Liu, Yan Kang, Liangbing

338

Hu, and Hongli Zhu, and Marya Orf Anderson for their assistance during the experiments. The opinions

339

expressed herein are those of the authors and do not necessarily reflect those of the sponsors. This

340

contribution was identified by Francois Perreault (Arizona State University) and Santiago Romero-Vargas

341

Castrillon (University of Minnesota) as the Best Presentation in the session “Elucidating the Molecular-

342

Level Interactions between Biological Membranes & Engineered Nanomaterials” of the 2016 ACS Fall

343

National Meeting in Philadelphia, PA.

344


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445



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

446

(a) mAg

(c) nwAg

(b) npAg

447 448

Figure 1 Electron micrographs of Ag particles: (a) microparticles (mAg), (b) nanoparticles (npAg), and (c) nanowires (nwAg). mAg and nwAg

449

were imaged with SEM, and npAg particles were imaged with TEM.


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450

PSf

rms = 6.40 nm

mAg-PSf

npAg-PSf

nwAg-PSf

rms = 6.77 nm

rms = 10.91 nm

rms = 5.21 nm

451 452

Figure 2 SEM images of the surface (top row) and cross section (middle row), and surface topography

453

(bottom row) of pure polysulfone (PSf) membrane, silver microparticle embedded polysulfone (mAg-PSf)

454

membrane, silver nanoparticle embedded polysulfone (npAg-PSf) membrane, and silver nanowire

455

embedded polysulfone (nwAg-PSf) membrane.



100 (a)

Ag to S ratio by weight

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

80

60

40

PSf

mAg

npAg

Page 22 of 25

(b) 0.12

0.06

0.00

nwAg

mAg

npAg

nwAg

Membrane type

Membrane type

456 457

Figure 3 Surface properties of control polysulfone (PSf) and Ag-embedded PSf membranes: (a)

458

membrane hydrophilicity indicated by water contact angle measurements, and (b) surface Ag coverage

459

indicated by the weight ratio of Ag to sulfur determined by SEM X-EDS.


Page 23 of 25

8000 PSf mAg-PSf npAg-PSf nwAg-PSf

4000 0

0

10

20

30

40

Time (min)

50

60

PSf mAg-PSf npAg-PSf nwAg-PSf

0.9

160

E. coli (CFU)

2

460

12000

Normalized cell density

1.0

16000 (a) Bacterial deposition

Cell density (#/mm )

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


0.8 0.7 0.6

(c) Antimicrobial property

120 80 40

(b) Membrane cleaning 0.5

0

5

10

15

20

25

0

30

Time (min)

PSf

mAg

npAg

nwAg

Membrane type

461

Figure 4 Biofouling performance and antimicrobial property of control polysulfone (PSf) and Ag-embedded PSf membranes: (a) deposition of E.

462

coli on membrane surface and (b) bacterial detachment from membrane surface during membrane cleaning monitored in a direct observation

463

system, and (c) inhibition of E. coli growth on membrane surface.



npAg, k = 0.233 h

1.5

-1

nwAg, k = 0.222 h

1.0 0.5

-1

+

mAg, k = 0.126 h

464

0.0 0

5

10

15

20

Time (h)

25

0.6

2

2

-1

4

(b) Static Ag leaching mAg-PSf npAg-PSf nwAg-PSf

0.4 0.2 0.0

0

5

10

15

Cumulative silver (∝g/cm )

2.0

0.8

(a) Dissolution of Ag

Cumulative silver ( ∝g/cm )

2.5

Ag concentration (mg/L)

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

Page 24 of 25

20

25

(c) Ag release during filtration mAg-PSf 3 npAg-PSf nwAg-PSf 2 1 0 0.00

0.04

0.08

0.12

0.16 2

Time (day)

Total volume filtered (L/cm )

465

Figure 5 (a) Dissolution of Ag particles (open symbols) modelling with first-order kinetics (solid lines). Ag release during (a) static storage and (b)

466

filtration of DI water. Concentration of Ag in all liquid samples were acidified with 0.5% trace metal grade HNO3, and measured in an atomic

467

absorption spectrometer (AAS).


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468


TOC

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Effects of Particle Morphology on the Antibiofouling Performance of

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