Polysulfone Membranes Modified with Bioinspired Polydopamine and

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Letter

Polysulfone Membranes Modified with Bioinspired Polydopamine and Silver Nanoparticles Formed in situ to Mitigate Biofouling Li Tang, Kenneth John T. Livi, and Kai Loon Chen Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.5b00008 • Publication Date (Web): 16 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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Environmental Science & Technology Letters

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Polysulfone Membranes Modified with Bioinspired Polydopamine and Silver Nanoparticles Formed in situ to Mitigate Biofouling

Environmental Science & Technology Letters Revised: February 9, 2015

Li Tang,† Kenneth J. T. Livi,‡ and Kai Loon Chen †,*

†

Department of Geography and Environmental Engineering, Johns Hopkins University, Baltimore, Maryland 21218-2686

‡

High-Resolution Analytical Electron Microbeam Facility at The Integrated Imaging Center, Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218-2686

* Corresponding author: Kai Loon Chen, E-mail: [email protected], Phone: (410) 516-7095, Fax: (410) 516-8996

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ACS Paragon Plus Environment


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Abstract

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The surface of a polysulfone (PSU) membrane was modified with a bioinspired polydopamine

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(PDA) film followed by the in situ formation of silver nanoparticles (AgNPs) to mitigate

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membrane biofouling. The PDA modification enhanced the membrane’s bacterial anti-adhesive

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properties by increasing the surface hydrophilicity while AgNPs imparted strong antimicrobial

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properties to the membrane. The AgNPs could be generated on the membrane surface by simply

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exposing the membrane to AgNO3 solutions; Ag+ ions were reduced by the catechol groups in

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PDA, the AgNP mass loading increased with exposure time, and the AgNPs were firmly

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immobilized on the membrane through metal coordination. During leaching tests, the Ag+ ions

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released were 2–3 orders of magnitude lower in concentration than the established contaminant

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limit for drinking water, thereby providing a safe antimicrobial technology.

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membrane surface modification technique paves a way to mitigating biofouling by enhancing the

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membrane’s anti-adhesive and antimicrobial properties, simultaneously.

This novel

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Introduction

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Membrane filtration has become one of the most popular technologies for water

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purification and wastewater reuse due to its efficiency and effectiveness.1-4 However, biofouling,

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or the formation of biofilms on membranes, has been a major obstacle that hinders their

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widespread application in water treatment.5-8 Current efforts to mitigate biofouling have been

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placed on modifying membrane surfaces by enhancing their hydrophilicity.9-13

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Polydopamine (PDA) is a bioinspired polymer with a molecular structure similar to the

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adhesive proteins of mussels.14 PDA is highly hydrophilic due to the presence of catechol,

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quinone, and amine groups in its structure.15 In addition, PDA can adhere firmly to a wide

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variety of materials in the wet environment through covalent bonding, hydrogen binding, π-π

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stacking, metal coordination or chelation, and/or charge-transfer complexing.15 These unique

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features of PDA have been leveraged to enhance membrane hydrophilicity for use in membrane

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filtration.14-20

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Due to the presence of drag forces resulting from water permeation during membrane

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filtration, some microorganisms may still deposit on hydrophilic membranes.5, 21 Therefore, it is

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also desirable to impart strong antimicrobial properties to the membranes in order to inactivate

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deposited bacteria.

Recently, numerous studies have examined the effectiveness of silver

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nanoparticles (AgNPs) in mitigating membrane biofouling by taking advantage of their strong

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and broad-spectrum antimicrobial properties.22-34 Interestingly, Ag+ ions can be reduced by the

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catechol groups of PDA, resulting in the in situ formation of AgNPs on PDA-modified

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surfaces.15, 35 Furthermore, the O- and N-sites of PDA can serve as anchors for the AgNPs

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through metal coordination via charge-transfer.36, 37 Hence, the generation and immobilization of

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AgNPs on PDA-modified membranes can pave a new way to impart membranes with both anti-

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adhesive and antimicrobial properties simultaneously to mitigate membrane biofouling.

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In this paper, we show for the first time that the surface modifications with PDA and

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AgNPs formed in situ can reduce polysulfone membranes’ propensity to bacterial adhesion and

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growth. Specifically, PSU membranes were modified with a PDA film to enhance membrane

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hydrophilicity and reduce bacterial attachment.

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exposed to AgNO3 solutions to generate AgNPs in situ on the membrane surfaces, thus imparting

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the membranes with strong antimicrobial properties. This facile and scalable membrane surface

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modification method using bioinspired PDA and AgNO3 solutions to enhance membranes’

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bacterial anti-adhesive and antimicrobial properties simultaneously has great potential for

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membrane biofouling mitigation for water filtration processes.

The PDA-modified membranes were then

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Materials and Methods

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Polysulfone Membrane Fabrication. PSU microfiltration membranes were fabricated

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using the wet phase inversion process38 and were used as the base membranes for the preparation

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of PDA-modified membranes. The detailed procedure for membrane fabrication is provided in

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the Supporting Information (SI).

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Membrane Modification with Polydopamine. The modification of PSU membranes

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with PDA was performed using a custom-made polycarbonate flow cell. A PSU membrane was

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clamped tightly between the top and bottom plates of the flow cell with the active side of the

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membrane facing the cross flow channel (90 × 38 × 2 mm). Dopamine hydrochloride powder

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(0.1 g; Sigma-Aldrich) was dissolved in 100 mL of a 15 mM Trizma hydrochloride (≥ 99.0%;

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Sigma-Aldrich) buffer solution with pH adjusted to 8.5. The chemical structure of dopamine is

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presented in Figure S1. Under this condition, dopamine can be oxidized by oxygen and self-

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polymerize to form PDA.15 The PDA solution was circulated across the membrane surface using

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a peristaltic pump (Cole Parmer, Vernon Hills, IL) at a cross flow velocity of 2.2 mm/s for 6 h.

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Following that, the membrane surface was rinsed twice (10 min/rinse) with the buffer solution at

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the same cross flow velocity. Finally, the membrane was removed from the cross flow cell and

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rinsed under running DI water for 30 s.

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In situ Formation of AgNPs on Polydopamine-Modified Membranes. In order to

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generate AgNPs on the membrane surface, a PDA-modified membrane was allowed to float on a

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50 mM AgNO3 solution (pH unadjusted, volume 25 mL) contained in a petri dish, with the active

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side of the membrane contacting the solution. The petri dish was covered with a piece of

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alumina foil to prevent exposure to light. The exposure time to AgNO3 solution was varied (1

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min, 1 h, 2 h, 12 h, and 24 h) to investigate its effects on AgNP generation on the membranes.

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The membranes were then soaked in fresh DI water three times (at least 10 min for each soaking)

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before use. The membrane surface modification process is illustrated in Figure 1a.

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FIGURE 1 Membrane Characterization.

The water contact angle measurements of PSU and

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modified membranes were performed using the sessile drop method.39 X-ray photoelectron

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spectroscopy (XPS) analysis of the membranes was conducted with a PHI 5600 XPS system

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using Mg Kα X-rays to determine the elemental composition on the membrane surface. The

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membranes were also examined with Environmental scanning electron microscopy (SEM)

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imaging to determine the distribution and morphologies of the AgNPs on the membrane surfaces.

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Energy-dispersive X-ray (EDX) analyses were conducted to detect Ag in the membranes. The

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AgNP mass loadings of the modified membranes were determined by soaking the membrane

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samples in 3.5% HNO3 solution and measuring the dissolved Ag concentrations with an atomic

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absorbance spectrometer (AAS).25, 34 All details for these techniques are presented in the SI.

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Anti-Adhesive Properties of Membranes. The bacterial deposition experiments were

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performed with a direct microscopic observation membrane filtration system at room

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temperature. The bacteria strain used was Escherichia coli K12 MG 1655.21 The bacteria carry

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the antibiotic resistance gene and are labeled with the green fluorescent protein. The details for

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the preparation of bacterial suspensions are presented in the SI. The closed-loop membrane

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filtration system was coupled with an epifluorescence microscope that was used to observe the E.

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coli cell deposition on the membrane surface in real time. This system has been described in our

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previous study13 and also in the SI. The membrane was conditioned and equilibrated with a 10

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mM NaCl and pH 7.0 (adjusted with 0.15 mM NaHCO3) solution at a cross flow velocity of 10

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cm/s and permeate flux of 26 µm/s for 40–50 min. The E. coli cells were then injected into the

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pressurized membrane filtration system using a syringe pump to initiate bacterial deposition in

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the same solution chemistry and hydrodynamic conditions. Each deposition experiment was

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carried out for 20 min and the images of E. coli cells were acquired every 3 min. The deposition

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rate coefficient, kobs, was calculated by normalizing the rate of bacterial deposition to the product

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of membrane surface area and cell concentration in the feed solution (ca. 1.4 × 107 cells/L).5, 13

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The bacterial deposition experiments were conducted at least three times for each type of

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membrane.

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Antimicrobial Properties of Membranes. The antimicrobial properties of the modified

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membranes were assessed using the colony forming unit (CFU) counting method.34 Details are

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presented in the SI.

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Stability of AgNPs Immobilized on Membranes. In order to test the stability of the

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AgNPs that were immobilized on the membranes, a Ag leaching test was performed by filtering

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DI water through the membranes for 220–340 min at an average permeate flux of 34 µm/s and

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measuring the dissolved Ag concentration in the filtrate using inductively coupled plasma mass

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spectrometry (ICP-MS).

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evaluated after filtration. Details are provided in the SI.

Additionally, the membranes’ antimicrobial properties were re-

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Results and Discussion

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AgNP Mass Loading Increases with Exposure Time to AgNO3 Solutions.

The

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designations used in this paper are “PDA membranes” for membranes modified with PDA only

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and “PDA-t membranes” for PDA-modified membranes exposed to AgNO3 solutions for a

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duration of t min. The elemental composition of the membrane surfaces was analyzed by XPS

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(Figure 1b). The spectra of all the modified membranes showed similar signal intensities in the

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N(1s) region, all of which were higher than that of the base membrane. This observation

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confirmed the formation of a PDA film on all the modified membranes since nitrogen is present

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in PDA. All the modified membranes also exhibited a noticeably lower signal intensities in the

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S(2p) region compared to the base membrane, likely due to the sulfone groups in the base PSU

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membrane being suppressed by the PDA film.

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Strong signal intensities in the Ag(3d) region were clearly observed in the XPS spectra of

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all the PDA/Ag-modified membranes, except for the PDA-1 membrane in which the Ag

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concentration was probably too low to be detected. Secondary electron (SE) imaging in the

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Environmental SEM also revealed the presence of individual spherical AgNPs on the surface of

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the modified membranes (Figure 1a). In contrast, no detectable signal in the Ag(3d) region was

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observed for the PSU and PDA membranes (Figure 1b) and no AgNPs were found on both

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membranes. Additionally, the signal intensities in the Ag(3d) region for the PDA/Ag-modified

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membranes increased as the membrane exposure time was increased (Figure 1b). These findings

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indicated that the AgNP mass loading can be controlled by a simple variation of the exposure

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time to the AgNO3 solutions and potentially the concentrations of the AgNO3 solutions.

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Backscattered electron (BSE) SEM images in Figure 2a indicated that some of the pores

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of the PSU membrane appeared to be covered by the PDA film. Additionally, bright spots were

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detected in the images of the PDA/Ag-modified membranes. Through EDX analysis, the Ag

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signal on the bright spots was shown to be high while the Ag signal on the dark spots was almost

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undetectable (Figure S2), thus demonstrating the bright spots to be the locations of AgNPs. It is

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noteworthy that BSE imaging, which uses high energy electrons, is capable of detecting AgNPs

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that are underneath or inside the PDA film, unlike SE imaging which uses low energy electrons

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and can only provide images of AgNPs exposed on the membrane surface. The SEM image of

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PDA-720 (Figure 1a) appears to show fewer AgNPs than the BSE image (Figure 2a), which is

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consistent with AgNPs located both on the surface of and inside the PDA film.

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From the images in Figure 2a, the distribution of AgNPs on the modified membrane

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surfaces was shown to be homogeneous. Also, the AgNPs increased in size and number as a

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function of membrane exposure time to AgNO3 solutions. The AgNP mass loading of the

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membranes were determined by soaking the membranes in HNO3 solutions. AAS analysis of the

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acid solutions showed that the AgNP concentrations in the membranes increased as a function of

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exposure time to the AgNO3 solutions (graph in Figure 2a), which corroborated with the results

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from XPS and SEM analyses (Figures 1b and 2a, respectively). Specifically, the AgNP mass

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loading on the membrane surface increased dramatically within 60 min and increased slowly

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afterwards. It is speculated that most of the AgNPs nucleated quickly on the membrane surface

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because of the strong reducing catechol groups in PDA while the increase of AgNP mass after 60

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min might be due to slower post nucleation ripening mechanisms while Ag+ is further reduced.15

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FIGURE 2

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Surface Modifications Enhance Membrane Anti-Adhesive Properties. Water contact

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angle measurements on the membranes showed that surface modifications with PDA, as well as

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with PDA and AgNPs, reduced the membranes’ contact angles by ca. 50 % compared to that of

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the base membrane (Figure 2b) and thus effectively enhanced their hydrophilicity.40,

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Furthermore, the contact angles on the membranes that were modified with PDA and AgNPs

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were independent of the AgNP mass loadings, thus indicating that the enhanced hydrophilicity of

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the modified membranes can be attributed to the PDA films.

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During the bacterial deposition experiments, the hydraulic resistance of the PSU base

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membranes was determined to be 3.0 × 1011 m-1, while the hydraulic resistances of the PDA,

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PDA-1, PDA-60, and PDA-720 membranes were 9.6 × 1011 m-1, 1.0 × 1012 m-1, 9.8 × 1011 m-1,

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and 1.1 × 1012 m-1, respectively. The hydraulic resistances of all the modified membranes were

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ca. 3 times higher than that of the base membrane regardless of the Ag mass loadings. Hence,

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the major contributor to the increase in hydraulic resistance was the PDA film. The deposition

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experiments showed that PDA and PDA/AgNP modifications reduced the bacterial deposition

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kinetics on the membrane surface by ca. 60 % (Figure 2c). These results demonstrate that the

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PDA and PDA/AgNP modifications considerably enhanced the membrane’s resistance to

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bacterial adhesion. Additionally, the kobs values of the modified membranes were comparable

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and independent of the AgNP mass loadings. Since the hydrophilicity of all the modified

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membranes had increased considerably (Figure 2b), the enhanced bacterial anti-adhesive

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properties exhibited by the modified membranes is attributed to the hydrophilic PDA films.18 A

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slight increase in the Ag concentration of 0.85 µg/L in the circulated solution was detected at the

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end of a separate cross flow filtration experiment using a PDA-60 membrane. The leaching of

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Ag was investigated and will be discussed in a later section.

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In situ Generated AgNPs Inhibit Bacterial Growth on Membranes. Using the CFU-

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counting method, 257 CFUs were observed on the PDA membrane while only 4 CFUs were

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observed on the PDA-1 membrane (Figure 2d). No CFUs were observed on the PDA-60, PDA-

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120, PDA-720, and PDA-1440 membranes. The result indicated that the in situ formation of

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AgNPs by exposing the PDA membranes to AgNO3 solutions for 1 hour or longer can ensure the

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complete inactivation of bacteria cells. Despite the incomplete inactivation of E. coli cells, the

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PDA-1 membrane had a comparable antimicrobial effect (close to 99 %) with that in other two

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studies that used a similar method to evaluate the membrane’s antimicrobial properties.23, 34 In

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both studies,23, 34 0.9 wt. % AgNPs were embedded in the membrane matrix and their results

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showed that the AgNP-impregnated membranes had a 99 % reduction of E. coli cell growth.23, 34

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In comparison, the similar antimicrobial effect achieved with a lower AgNP weight percentage in

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our study (0.12 ± 0.02 wt. %) implied that the membrane’s antimicrobial properties are greatly

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dependent on the location of AgNPs in the membrane structure. Recent studies demonstrated

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that the direct contact or close proximity of bacteria to AgNPs immobilized on the membrane

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surface maximizes the exposure of the bacteria to AgNPs by increasing the lethal concentrations

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of free released Ag+ ions dissolved from AgNPs.42-45 In contrast, not all the AgNPs embedded in

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the membrane matrix can be exposed to the deposited bacteria and thus a higher amount of

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AgNPs is required to achieve the same antimicrobial effect of AgNPs immobilized on the

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membrane surface. Therefore, the in situ formation of AgNPs on the membrane through the

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reduction of Ag+ ions by PDA has proven to be an efficient method to impart the membranes

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with strong antimicrobial properties as this approach ensured that AgNPs generated on the PDA

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films will have maximum opportunities for contact with deposited bacteria.

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Stability of AgNPs Immobilized on Membranes. Ag leaching test was carried out to

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quantify the degree of Ag release during filtration of DI water. The Ag concentrations in the

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permeates for the PDA-1 and PDA-60 membranes were 0.29 ± 0.18 and 1.17 ± 0.60 µg/L,

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respectively. The average Ag concentrations in the permeates in the Ag leaching tests from the

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studies of Diagne et al.46 and Yin et al.33 on AgNP-nanocomposite membranes were 5 µg/L and

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1.06 µg/L, respectively. Therefore, the leaching Ag concentrations in our study were comparable

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to those of previous studies.33, 46 The concentrations of Ag in the permeates in our study were 2–

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3 orders of magnitude lower than the maximum contaminant limit of Ag in drinking water (i.e.,

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100 µg/L) established by the U.S. Environmental Protection Agency47 and also by the World

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Health Organization.48 Therefore, there will likely be no risk to health related to Ag ingestion if

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this PDA/AgNP membrane modification technique were to be applied to mitigate membrane

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biofouling for water filtration.

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Additionally, the antimicrobial properties of the PDA-1 and PDA-60 membranes were

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examined after prolonged filtration of DI water. Only 2 CFUs were observed on the PDA-1

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membrane surfaces while no CFUs were observed on the PDA-60 membrane surfaces. These

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results were comparable to that on the freshly prepared PDA-1 and PDA-60 membranes (4 and 0

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CFUs, respectively). Therefore, the dissolution and loss of AgNPs were low and the AgNPs

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immobilized on the membrane surface could impart the membrane with long-lasting

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antimicrobial properties.

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In summary, this study showed PSU membranes modified with PDA and AgNPs formed

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in situ had enhanced resistance to biofouling over the native PSU membranes. The PDA film

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was effective in reducing bacterial adhesion on the membrane surface while the AgNPs imparted

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antimicrobial properties. Hence, this novel surface modification technique paves a way to

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mitigating biofouling by enhancing the membrane’s anti-adhesive and antimicrobial properties,

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simultaneously.

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modification of existing membranes of different configurations (such as hollow fiber and spiral

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wound),49 as well as feed spacers in spiral wound membranes,50 that are already in use in water

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and wastewater treatment plants. This approach may also allow for the in situ regeneration of

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AgNPs after they have been depleted through dissolution, thus enabling the sustainable

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application of nanocomposite membranes for water treatment.

Additionally, this simple and efficient approach will enable the in situ

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Acknowledgments

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This work was funded by the National Science Foundation (CBET-1133559).

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acknowledges funding support from the Gordon Croft fellowship. We acknowledge Dr. Michael

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McCaffery and Anna Goodridge of the Integrated Imaging Center (JHU) for Environmental

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SEM imaging and additional microscopy, and Dr. Howard Fairbrother’s group from the

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Department of Chemistry (JHU) for XPS and contact angle measurements. We thank Dr.

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Qiaoying Wang and Xin Liu from the Department of Geography and Environmental Engineering

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(JHU) for the AAS and contact angle measurements. We also acknowledge Dr. Khanh An

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Huynh from the Environmental Protection Agency, Las Vegas, Nevada, for the ICP-MS

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measurements.

L.T.

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Supporting Information Available

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Additional figures, tables, and details for Materials and Methods are presented. This material is

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available free of charge via the Internet at http://pubs.acs.org.

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Notes

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The authors declare no competing financial interest.

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18. Miller, D. J.; Araujo, P. A.; Correia, P. B.; Ramsey, M. M.; Kruithof, J. C.; van Loosdrecht, M. C.; Freeman, B. D.; Paul, D. R.; Whiteley, M.; Vrouwenvelder, J. S., Short-term adhesion and long-term biofouling testing of polydopamine and poly(ethylene glycol) surface modifications of membranes and feed spacers for biofouling control. Water Res 2012, 46, (12), 3737-53. 19. Miller, D. J.; Paul, D. R.; Freeman, B. D., An improved method for surface modification of porous water purification membranes. Polymer 2014, 55, (6), 1375-1383. 20. McCloskey, B. D.; Park, H. B.; Ju, H.; Rowe, B. W.; Miller, D. J.; Chun, B. J.; Kin, K.; Freeman, B. D., Influence of polydopamine deposition conditions on pure water flux and foulant adhesion resistance of reverse osmosis, ultrafiltration, and microfiltration membranes. Polymer 2010, 51, (15), 3472-3485. 21. Adout, A.; Kang, S.; Asatekin, A.; Mayes, A. M.; Elimelech, M., Ultrafiltration Membranes Incorporating Amphiphilic Comb Copolymer Additives Prevent Irreversible Adhesion of Bacteria. Environmental science & technology 2010, 44, (7), 2406-2411. 22. Marambio-Jones, C.; Hoek, E. M. V., A review of the antibacterial effects of silver nanomaterials and potential implications for human health and the environment. J Nanopart Res 2010, 12, (5), 1531-1551. 23. Liu, Y. L.; Rosenfield, E.; Hu, M.; Mi, B. X., Direct observation of bacterial deposition on and detachment from nanocomposite membranes embedded with silver nanoparticles. Water Res 2013, 47, (9), 2949-2958. 24. Liu, X.; Qi, S. R.; Li, Y.; Yang, L.; Cao, B.; Tang, C. Y. Y., Synthesis and characterization of novel antibacterial silver nanocomposite nanofiltration and forward osmosis membranes based on layer-by-layer assembly. Water Res 2013, 47, (9), 3081-3092. 25. Ben-Sasson, M.; Lu, X.; Bar-Zeev, E.; Zodrow, K. R.; Nejati, S.; Qi, G.; Giannelis, E. P.; Elimelech, M., In situ formation of silver nanoparticles on thin-film composite reverse osmosis membranes for biofouling mitigation. Water Res 2014, 62, 260-70. 26. Cao, X. L.; Tang, M.; Liu, F.; Nie, Y. Y.; Zhao, C. S., Immobilization of silver nanoparticles onto sulfonated polyethersulfone membranes as antibacterial materials. Colloid Surface B 2010, 81, (2), 555-562. 27. Chou, W. L.; Yu, D. G.; Yang, M. C., The preparation and characterization of silverloading cellulose acetate hollow fiber membrane for water treatment. Polym Advan Technol 2005, 16, (8), 600-607. 28. Kim, E. S.; Hwang, G.; El-Din, M. G.; Liu, Y., Development of nanosilver and multiwalled carbon nanotubes thin-film nanocomposite membrane for enhanced water treatment. J Membrane Sci 2012, 394, 37-48. 29. Koseoglu-Imer, D. Y.; Kose, B.; Altinbas, M.; Koyuncu, I., The production of polysulfone (PS) membrane with silver nanoparticles (AgNP): Physical properties, filtration performances, and biofouling resistances of membranes. J Membrane Sci 2013, 428, 620-628. 30. Lee, S. Y.; Kim, H. J.; Patel, R.; Im, S. J.; Kim, J. H.; Min, B. R., Silver nanoparticles immobilized on thin film composite polyamide membrane: characterization, nanofiltration, antifouling properties. Polym Advan Technol 2007, 18, (7), 562-568. 31. Mauter, M. S.; Wang, Y.; Okemgbo, K. C.; Osuji, C. O.; Giannelis, E. P.; Elimelech, M., Antifouling Ultrafiltration Membranes via Post-Fabrication Grafting of Biocidal Nanomaterials. Acs Appl Mater Inter 2011, 3, (8), 2861-2868. 32. Rahaman, M. S.; Therien-Aubin, H.; Ben-Sasson, M.; Ober, C. K.; Nielsen, M.; Elimelech, M., Control of biofouling on reverse osmosis polyamide membranes modified with

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50. Vrouwenvelder, J. S.; von der Schulenburg, D. A. G.; Kruithof, J. C.; Johns, M. L.; van Loosdrecht, M. C. M., Biofouling of spiral-wound nanofiltration and reverse osmosis membranes: A feed spacer problem. Water Res 2009, 43, (3), 583-594.

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Page 15 of 17


430 431 (a) 432 433

Exposure to AgNO3 solution

Coating with PDA

434 435 436 437 438 Base Membrane PDA-Modified PDA/AgNP439 Surface Modified Surface Surface 440 Environmental SEM image of PDA-720 441 (b) 442 S(2p) x5 443 N(1s) Ag(3d) x5 444 445 446 PDA-720 447 PDA-120 448 449 PDA-60 450 PDA-1 451 452 PDA 453 454 Base 455 456 457 396 166 168 170 172 365 370 375 380 399 402 405 458 Binding Energy (eV) 459 460 461 Figure 1. (a) Schematic diagram of PDA modification and in situ formation of AgNPs on the 396

399

402

405

166

168

170

172

365

370

375

380 300000

200000

100000

0

-100000

462

membrane surface and environmental SEM image of PDA-720 membrane. White scale bar

463

represents 5 µm. (b) N(1s), S(2p), and Ag(3d) XP spectra of the surface of the base and modified

464

membranes.

465 466 467 468

15


472 473

Base Membrane

PDA-120

474 475 476

(b) 60 40 20 0

2

4

6

PD A A PD -1 A PD -60 APD 120 A72 0

471

80

se

470

Page 16 of 17

PD

(a)

Ba

469

Contact Angle (degrees)


50

477

(c) 40

10

400

PDA-60

20

25

1.6 16 1.2

12

0.8

8 4

0.4

0

0.0

0

5 10 15 20 Exposure Time (h)

25

300 200 100 0

2

4

6

A PD -1 A PD -60 APD 120 A PD -72 A- 0 14 40

490

15

PD

489

10

A

488

5

CFU

Mass Density (µg/cm2)

487

20

0

Weight Percentage (wt. %)

486

(d)

PDA-1440

PDA-1

5

20

4

0

3

A7

PD

se

484

491

2

Ba

483

485

1

A6

0

PD

482

A1

481

20

PD

480

30

PD

PDA-720

A

PDA Membrane

PD

479

kobs (µm/s)

478

492

Figure 2. (a) BSE SEM images of base and modified membranes and mass loadings of AgNPs

493

on modified membrane surfaces. Recording contrast and brightness levels where held constant

494

for all images in order to insure proper BSE intensity comparisons between samples. White

495

scale bars represent 2 µm. (b) Contact angle measurements of selected membranes. (c) Bacterial

496

deposition rate coefficients, kobs, for selected membranes obtained at 10 mM NaCl and pH 7.0. (d)

497

CFUs on base and modified membranes. The symbols

498

present on the membranes. Error bars in b, c, and d represent standard deviations.

16


indicate that no colony was

Page 17 of 17

499


TOC Art

500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516

Polysulfone Membrane

PDA-Modified Membrane

17


PDA/AgNPModified Membrane

Polysulfone Membranes Modified with Bioinspired Polydopamine and

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