Concentration and Recovery of Dyes from Textile Wastewater Using a

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Environmental Processes

Concentration and Recovery of Dyes from Textile Wastewater using a Self-standing, Support-free Forward Osmosis Membrane Meng Li, Xi Wang, Cassandra J Porter, Wei Cheng, Xuan Zhang, Lianjun Wang, and Menachem Elimelech Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b00446 • Publication Date (Web): 25 Feb 2019 Downloaded from http://pubs.acs.org on February 25, 2019

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Environmental Science & Technology

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Concentration and Recovery of Dyes from

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Textile Wastewater using a Self-standing,

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Support-free Forward Osmosis Membrane

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Environmental Science & Technology 6 7 8 9

Meng Li,1 Xi Wang,2 Cassandra J. Porter,3 Wei Cheng,3 Xuan Zhang,1,3* Lianjun Wang,1 and Menachem Elimelech3*

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1) Key Laboratory of New Membrane Materials, Ministry of Industry and Information Technology; School of Environmental and Biological Engineering, Nanjing University of Science & Technology, Nanjing 210094, China 2) School of Chemical Engineering, Nanjing University of Science & Technology, Nanjing 210094, China 3) Department of Chemical and Environmental Engineering, Yale University, New Haven, CT 06520-8286, USA 13 14 15 16 17

*Corresponding Author:

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Xuan Zhang: [email protected];

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Menachem Elimelech: [email protected].

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ACS Paragon Plus Environment


ABSTRACT 21

Forward osmosis (FO) can potentially treat textile wastewaters with less fouling than pressure-

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driven membrane processes such as reverse osmosis and nanofiltration. However, conventional

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FO membranes with asymmetric architecture experience severe flux decline caused by internal

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concentration polarization and fouling as dye molecules accumulate on the membrane surface. In

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this study, we present a new strategy for concentrating dye by using a self-standing, support-free

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FO membrane with a symmetric structure. The membrane was fabricated by a facile solution-

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casting approach based on a poly(triazole-co-oxadiazole-co-hydrazine) (PTAODH) skeleton. Due

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to its dense architecture, ultra-smooth surface, and high negative surface charge, the PTAODH

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membrane exhibits excellent FO performance with minimal fouling, low reverse salt flux, and

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negligible dye passage to the draw solution side. Cleaning with a 40% alcohol solution, after

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achieving a concentration factor of ~10, resulted in high flux recovery ratio (98.7%) for the

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PTAODH membrane, whereas significant damage to the active layers of two commercial FO

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membranes was observed. Moreover, due to the existence of cytotoxic oxadiazole and triazole

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moieties in the polymer structure, our PTAODH membrane exhibited an outstanding antibacterial

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property with two model bacteria. Our results demonstrate the promising application of the

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symmetric PTAODH membrane for the concentration of textile wastewaters and its superior

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antifouling performance compared to state-of-the-art commercial FO membranes.

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INTRODUCTION 39

Increasing stressors on water resources and growing concerns over pollution of aquatic

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environments have revived an interest in achieving minimal or zero liquid discharge (ZLD) of

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industrial wastewaters. Therefore, developing efficient, low-cost technologies for wastewater

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treatment and reuse has become an important goal.1-3 Dyeing processes in the textile industry are

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characterized by high water consumption and extremely polluted effluents containing high

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concentrations of various dyes and salts.4,5 Through separation and concentration processes, useful

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resources like dyes could be recycled or reused, reducing the risk to the environment and increasing

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fresh water supply.4

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Conventional wastewater treatment processes, such as biological degradation,6 adsorption,7

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advanced oxidation,8 and coagulation-flocculation,9 are widely utilized in the textile industry.

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However, possible wastewater toxicity to essential microorganisms used in biological reactors,

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large quantities of chemicals needed for effective treatment, and toxic byproducts render the above

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treatment techniques quite challenging and unsustainable.

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Treating textile wastewaters by membrane-based technologies could potentially be simpler and

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more environmentally friendly compared to conventional processes.4,10-18 The first step in treating

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dye wastewaters via membrane processes is fractionation, whereby larger dye molecules are

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selectively retained in the concentrate while smaller salt ions pass through more easily. Recently,

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several efforts have been made to enable effective separation of inorganic components from textile

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wastewaters by using commercial10-13 or self-made NF membranes13-18 with loose structures.

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Following fractionation, retained solutions of valuable dyes undergo a concentration process

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for their recovery and reuse.13 However, most dye concentration processes experience severe

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fouling of membrane surfaces, particularly when conventional, pressure-driven membrane

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processes are used (e.g., ultrafiltration19 and nanofiltration20), which results in rapid flux decline,

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frequent chemical cleaning, and reduced membrane lifespan. Organic fouling, especially 3



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irreversible fouling caused by adsorption or deposition of dyes on the membrane surface,15 is

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affected by the intrinsic hydrophobicity21-23 and the surface morphology of the membranes.24,25

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Furthermore, thin-film composite polyamide nanofiltration membranes contain carboxyl groups,

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which have been shown to enhance organic fouling.26

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Biofouling is another major performance-limiting factor in nanofiltration,27-29 reverse

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osmosis,30-33 and forward osmosis.34,35 To mitigate biofilm formation, membrane surfaces have

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been grafted with biocidal nanomaterials,29-38 such as silver or copper nanoparticles30,32 and

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graphene oxide (GO) nanosheets.37 However, the added costs and steps during fabrication pose

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difficulties when manufacturing these hybrid membranes on larger scales, while the potential

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leaching of nanomaterials may further hinder their commercialization.29,30 Hence, membranes

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composed of an inherently bactericidal material could be a more commercially viable option.

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Recently, we have presented a proof-of-concept of a self-standing, support-free FO membrane

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using a novel poly(triazole-co-oxadiazole-co-hydrazine) (PTAODH) skeleton.39 Due to the

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symmetric structure of the membrane, no internal concentration polarization was observed when

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evaluating the FO membrane desalination performance. Uniquely, the membrane is extremely

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smooth, and due to its robustness there is no need for membrane backing or a support layer. Despite

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the initial promise, the use of this membrane in emerging FO applications has not previously been

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demonstrated.

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In this work, we systematically evaluate the use of the PTAODH thin film for dye

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concentration in forward osmosis. For comparison, both the PTAODH symmetric membrane and

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two commercially available asymmetric FO membranes were exposed to an artificial textile

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wastewater effluent in which Congo Red was used as a model dye. Analyses of dye concentration

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efficiency, membrane regeneration performance, fouling propensity, and anti-biofouling

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properties provide insights into the membrane separation and antifouling mechanisms. Our work

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highlights the potential application of the symmetric FO membranes for sustainable concentration 4


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and recovery of valuable dyes in the textile industry.

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MATERIALS AND METHODS 90

Materials and Chemicals. Polyoxadiazole-co-hydrazide (PODH) and polytriazole-co-

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oxadiazole-co-hydrazide were synthesized according to our previous report39 and used for the

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fabrication of the self-standing, support-free FO membrane. The polymeric membrane is

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composed of a random copolymer containing polytriazole, polyoxadiazole, and polyhydrazine

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moieties at a controlled proportion. PTAODH-1.0 was used in the current study, where 1.0 denotes

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the molar ratio of 4-aminobenzoic acid to the repeating unit of PODH during the synthesis.

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Commercially available cellulose triacetate FO membrane (HTI-CTA) was provided by Hydration

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Technology Innovations, and polyamide thin-film composite FO membrane (CSM-TFC) was

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provided by Toray Chemical Korea, Inc. Congo Red (CR) and sodium sulfate (Na2SO4) were

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procured from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Other reagents and

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solvents were used as received. Deionized (DI) water with a minimum resistance of 18 MΩ-cm

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(Millipore) was used throughout the work.

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Membrane Characterization. Morphologies of the self-standing, support-free membrane

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(PTAODH-1.0) as well as the commercial HTI-CTA and CSM-TFC membrane samples were

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studied by field emission scanning electron microscopy (FESEM, S-4800, Hitachi, Japan). All

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membrane samples were air-dried, fractured in liquid nitrogen, and sputter coated with gold prior

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to imaging. Surface roughness of all membranes was measured by an Atomic Force Microscope

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(AFM, Mutilmode8, Germany). At least three measurements were made at different locations for

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each membrane surface.

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Dye Concentration Process. In forward osmosis (FO) mode (active layer facing the feed

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solution), 200 mL of 1.0 g L-1 CR solution and 150 mL of 1.5 M Na2SO4 solution were used as

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feed solution and draw solution, respectively. The effective membrane area was 10 cm2, and the 5



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crossflow velocity was fixed at 10.4 cm s-1, as described elsewhere.39 Reverse salt (Na2SO4)

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concentration in the feed solution was measured by ion chromatography (Dionex ICS-2100, USA)

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in terms of SO42- ion content; dye concentration was measured using a UV/VIS spectrometer

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(Lambda 25, PerkinElmer, USA). Water weight loss of feed solution was recorded by a digital

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balance to determine the water recovery. The concentration process was stopped at a water

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recovery ratio of 90%, corresponding to a concentration factor (CF) of 10.

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Analogously, in pressure-retarded osmosis (PRO) mode (active layer facing the draw solution),

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the concentration process was the same as described above, except for the orientation of the active

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layer in the cell. Because PTAODH-1.0 is symmetric, the two modes, denoted as FO-TF and FO-

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BF, represent testing both sides of the membrane (top surface facing the feed, FO-TF, and bottom

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surface facing the feed, FO-BF).

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Membrane Cleaning Strategy. After the concentration stage (water recovery 90% or CF

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= 10), various solutions were used to clean the fouled FO membranes in the FO setup for 30

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minutes at room temperature. Pure water, 20%, 40%, 60%, and 80% alcohol solutions were used

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in the feed side, and DI water was used in the draw side. Crossflow velocity on both the draw and

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feed sides of the membrane was maintained at 10.4 cm s-1. The flux recovery ratio (FRR), used for

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evaluating the effectiveness of cleaning the membranes, was calculated by13

FRR 

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J w ,a J w,b

100%

(1)

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where Jw,b and Jw,a represent the water flux of the CR solution (1.0 g L-1) before fouling and after

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cleaning, respectively.

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Evaluation of Antibacterial Properties of FO Membranes. Antibacterial properties

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of PODH, PTAODH-1.0, HTI-CTA, and CSM-TFC FO membranes were tested against both

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Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by a viable cell counting method,

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as described elsewhere.37,38,40 For both bacteria types, each membrane (HTI-CTA, CSM-TFC, 6


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PODH, or PTAODH-1.0) with dimensions of 2.5 cm × 2.5 cm was installed in a sterile, specially

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designed frame with clamps so that only the active surface was exposed and bacterial suspensions

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could be contained within the frame. In this holder, the membrane top surfaces were sterilized for

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30 minutes under UV radiation prior to the antibacterial tests. To prepare bacterial suspensions, E.

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coli and S. aureus were grown overnight at 37oC in a Luria-Bertani (LB) medium. Cells were

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collected by centrifugation, washed three times using sterile saline solution (NaCl, 0.9% (w/v)),

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and diluted to the concentration of 1.0×108 colony-forming units per milliliter (CFU mL-1). A

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quantity of 1.0 mL of bacterial suspension was poured onto the sterilized membrane surface. After

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three hours of contact with the bacterial solution, the membrane was taken out and rinsed with a

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sterile saline solution (NaCl, 0.9% (w/v)) to remove unattached cells on the membrane surface. To

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detach the deposited cells, the membrane was mildly sonicated for five minutes in 10 mL of sterile

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saline solution. The solutions were incubated overnight at 37oC and diluted by 100 times before

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plating on the LB/Agar plates for plate counting.

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RESULTS AND DISCUSSION 150

Membrane Properties. From our proof-of-concept study to develop a symmetric, support-free

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membrane for FO,39 the best performing membrane in terms of water flux and salt retention,

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referred to as PTAODH-1.0, was chosen for the present investigation. The water flux, Jw, and

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reverse salt flux, Js, of the membrane were found to be 11.7±0.7 L m-2 h-1 and 27.5±2.1 mmol m-2

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h-1, respectively, when using 1.5 M Na2SO4 as the draw solution. Other physicochemical properties

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of the membrane, including mechanical robustness, were described in our recent proof-of-concept

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study.39

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The morphologies of the PTAODH-1.0 membrane as well as the two commercial membranes

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used for comparison (HTI-CTA and CSM-TFC) were studied by FESEM. As shown in Figures

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1A and 1B, the surface morphologies for both sides of the PTAODH-1.0 FO membrane are almost 7



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identical, and no visible pores were observed over the entire scanning area. In addition, the cross-

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section image of PTAODH-1.0 (Figure 1C) portrays its symmetric structure. In contrast, both HTI-

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CTA and CSM-TFC membranes exhibit typical asymmetric structures with a dense layer on top

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of a polyester support mesh, as shown in Figures 1F and 1I. The surface roughness of the

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membranes was analyzed using atomic force microscopy (AFM) (Figure S1 in Supporting

165

Information). The PTAODH-1.0 membrane is extremely smooth and exhibits a very small average

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plane roughness (Ra) of 0.66±0.08 and 0.69±0.17 nm on each side of the symmetric membrane.

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In contrast, much greater Ra values were found for both the HTI-CTA (top: 9.95±0.21 nm; bottom:

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12.6±0.28 nm) and CSM-TFC (top: 30.3±1.84 nm; bottom: 9.6±5.78 nm) membranes. The overall

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roughness can also be judged by inspecting the top or bottom surface in the SEM images (Figures

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1D, 1E, 1G, and 1H).

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Besides exhibiting smoothness on the nanoscale, the PTAODH-1.0 membrane is uniquely

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smoother than both the HTI-CTA and CSM-TFC membranes on the microscale owing to its

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robustness, which eliminates the need for a supportive membrane backing. As seen in Figures 1F

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and 1I, the mesh support backings produce a regular pattern of microscale peaks and valleys on

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both the top and bottom surfaces of the HTI-CTA and CSM-TFC membranes. Considering that

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bacteria and aggregates of highly concentrated dyes 41 fall within the microscale range as opposed

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to the nanoscale, perhaps microscale roughness may be more influential for both organic and

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biofouling. Studies have shown that areas with the greatest fouling propensity are often dead zones,

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especially in crossflow systems.42,43 Dead zones are caused more frequently by micro- and

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macroscale structures, such as the presence of spacers,44 than by nanoscale roughness. In the case

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of HTI-CTA and CSM-TFC membranes, such dead zones create near-stagnant flow, which

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decreases mixing, thereby increasing concentration polarization (CP) and rates of organic and bio-

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foulant deposition. Furthermore, such dead zones can also decrease the effectiveness of cleaning,

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since cleaning relies on not only the foulant’s solubility in the cleaning solution but also on shear

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forces. The positive impact of the extreme smoothness of the PTAODH-1.0 membrane at both the 8


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nano- and micro-scales is evident in the results of our dye concentration and membrane cleaning

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studies, discussed in the following sections.

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Figure 1

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Desalination performance in FO (feed solution facing membrane active layer) and PRO (feed

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solution facing membrane support layer) modes was investigated for all three types of membranes.

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As shown in Figure 2, for the PTAODH-1.0 membrane, Jw and Js were consistent at both

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orientations, which again is indicative of membrane symmetry. In contrast, both HTI-CTA and

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CSM-TFC membranes exhibited markedly different desalination behaviors depending on their

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orientation. The water flux for the HTI-CTA membrane in PRO mode (10.2±0.4 L m-2 h-1) was

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slightly greater than that in FO mode (8.5±0.2 L m-2 h-1), whereas much greater Jw was found for

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the CSM-TFC membrane in PRO mode (44.1±1.3 L m-2 h-1) than that in FO mode (21.0±2.5 L m-2

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h-1). These results are attributed to the different extents of internal concentration polarization (ICP)

200

in FO (dilutive ICP) and PRO (concentrative ICP) modes.45,46 Although the pure water

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permeability (A) value of our symmetric membrane (0.118 L m-2 h-1 bar-1) was lower than the

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commercial membranes (0.375 L m-2 h-1 bar-1for HTI-CTA39,47 and 4.192 L m-2 h-1 bar-1 for CSM-

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TFC

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performance of a membrane,50 was still quite acceptable. Specifically, the reverse flux selectivities

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of our symmetric membrane for FO-TF and FO-BF modes were 426.2±5.2 L mol-1 and 430.0±10.7

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L mol-1, respectively, higher than those of the HTI-CTA membrane (FO mode: 384.9±20.8 L mol-1;

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PRO mode: 397.8±22.0 L mol-1), but only slightly lower than those of the CSM-TFC membrane

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(FO mode: 501.4±19.6 L mol-1; PRO mode: 579.8±53.6 L mol-1) (Figure 2B). The above Jw/Js

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ratio of the PTAODH-1.0 membrane reflects a desalination efficiency comparable to that of the

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commercial membranes.

48,49),

its reverse flux selectivity (Jw/Js), an essential parameter representing the FO

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Figure 2

212 213 214

Dye Concentration Performance. High salinities of up to ~6% (approximately 60,000 mg

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L-1 TDS calculated as pure NaCl) in textile wastewaters present challenges for both conventional

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and membrane-based treatment technologies.12,19 In conventional treatment, such high salt content

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adversely impacts microorganisms that are used in biological reactors for degradation of dyes. For

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FO dye concentration, high-salinity feed decreases the osmotic pressure driving force between the

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feed and draw solution, thereby decreasing water flux. Therefore, separation of dyes from salt

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seems a necessary prerequisite before degradation or concentration and reuse of dye. However,

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state-of-the-art membranes still exhibit severe fouling caused by dye moleculeswhether treating

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dye/salt mixtures or pure dye solutions,10,13,14 as discussed earlier. Particularly for high water

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recovery ratios, frequent cleaning would be necessary to maintain the production rate, leading to

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high energy consumption.

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In contrast, PTAODH-1.0, a smooth, symmetric thin film, shows more promise for dye

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concentration. Under periodic supplement of Na2SO4 to keep a constant draw solution osmotic

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pressure, Jw remained relatively stable at 10.6±0.3 L m-2 h-1 over the entire concentration procedure

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until CF ~10 (Figure 3A), which is directly related to minimal fouling at the feed side as well as

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negligible ICP.39,51 Moreover, it was reported that membrane surface roughness can act as a

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structural template for initial layers of foulant.52 Our membrane with an ultra-smooth surface

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effectively prevents the adhesion of dye molecules, slowing fouling rates and extending membrane

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life.

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In marked contrast to the symmetric PTAODH-1.0 membrane, the HTI-CTA and CSM-TFC

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membranes, with their asymmetric structure, exhibited significant Jw decline both in the FO and

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PRO modes (Figures S2A, S3A, S4A, and S5A). Specifically, the Jw in FO decreased by 38.3% 10


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from 8.1 to 5.0 L m-2 h-1 and by 37.7% from 15.9 to 9.9 L m-2 h-1 for the HTI-CTA and CSM-TFC

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membranes, respectively, over the time taken to reach CF ~10. The severe flux decline observed

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for the commercial asymmetric FO membranes is attributed to significant fouling. With the more

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porous support mesh layer of the commercial membranes facing the dye solution in PRO mode,

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the Jw (PRO) suffered considerable flux decline due to accumulation of dye foulants in the porous

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support layer:53 by 57.7% from the initial 9.7 to 4.1 L m-2 h-1 (HTI-CTA) and by 87.5% from the

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initial 26.3 to 3.3 L m-2 h-1 (CSM-TFC). As evidenced by these results, the ultra-smooth PTAODH-

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1.0 membrane, consisting of a symmetric architecture without a backing layer, could eliminate

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ICP and minimize dye entrapment and cake layer formation during dye concentration.

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The PTAODH-1.0 membrane also showed robust performance, achieving 10-fold dye

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concentration within 18 hours (Figure 3D). In contrast, it took ~60% and ~40% more time for the

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HTI-CTA membrane in FO and PRO modes, respectively (Figures S2 and S3) to achieve 10-fold

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dye concentration. While the CSM-TFC membrane was able to achieve a 10-fold dye

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concentration within 14 hours, slightly better than the PTAODH-1.0 membrane, the severe fouling

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and need for chemical cleaning will be a major hindrance to practical application. Furthermore,

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future improvement of the PTAODH-1.0 membrane fabrication, for example by reducing

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membrane thickness and thus increasing water flux, could readily enhance the performance of the

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membrane.

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During the entire concentration process, all three membranes possessed rather high dye

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retention and salt rejection (Figures 3B-3C, S2B-S2C, S3B-S3C, S4B-S4C, and S5B-S5C).

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Specifically, the PTAODH-1.0 membrane only allows 0.37 mmol Na2SO4 to diffuse into the feed

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solution until the end of operation, due to its inherently low Js values (23.9±2.8 mmol m-2 h-1).

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Moreover, a tiny amount of the dye, linearly increasing over time, was found in the draw solution

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with a final concentration of merely 2.2×10-3 mmol L-1 (Figure 3C), matching the final dye

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concentration in the draw for both HTI-CTA and CSM-TFC membranes under FO operation mode.

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It is worth mentioning that the excellent retention of dye by the PTAODH-1.0 membrane is

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also evident in the overlap between empirical and calculated dye concentration values, as shown

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in Figure 3D. The actual concentration of CR was found to be 9.99 g L-1 when the CF reached ~10,

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which was slightly lower than the theoretical value of 10.06 g L-1. Such a small discrepancy is

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within the margin of error of our measurement method.

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Figure 3

268 269

Membrane Cleaning and Regeneration. As seen in Figure S6, the images of the three

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membrane types before and after the concentration process indicate differences in fouling

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propensity. A very light red color could be seen on the surface of PTAODH-1.0, suggesting only

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slight dye adsorption, while both the HTI-CTA and CSM-TFC membranes (PRO mode) developed

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deep red color due to significant adsorption and accumulation of dye molecules.

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In spite of insignificant fouling on the PTAODH-1.0 membrane during FO operation, a proper

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cleaning strategy is necessary to maintain membrane desalination performance. The PTAODH-

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1.0 membrane exhibits a relatively high FRR of 93±1.1% after rinsing with pure water, exceeding

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the FRR of the HTI-CTA (at 86.3% and 76.7% for FO and PRO modes, respectively) and the

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CSM-TFC (at 84.3% and 64.8% for FO and PRO modes, respectively) membranes (Figure 4A).

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However, in order to maximize the FRR, it is advantageous to use a cleaning solution that better

280

dissolves the foulant of interest without damaging the membrane. Because dye molecules are

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generally more soluble in organic solvents than in aqueous solution,13 alcohol solutions were

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employed here. As shown in Figure 4B, the FRR of the PTAODH-1.0 membrane considerably

283

increases to 96.6% and 98.7% with a negligible increase in Js by cleaning with 20% or 40% of

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ethanol/water solution, respectively, indicating the membrane good antifouling and solvent-

285

resistant properties. However, a sharp increase of Js up to 125.7 mmol m-2 h-1 was observed when 12


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cleaning with an 80% alcohol solution, which caused the FO performance to deteriorate. We

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attribute this phenomenon to the physical expansion of the interstitial spaces within the membrane

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matrix caused by excessive ethanol.13,52

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Based on the above results, a 40% alcohol solution was chosen as the optimal cleaning medium

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for comparing the performance of the three membrane types. As shown in Figure 4C, unlike the

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superb performance of the PTAODH-1.0 membrane, after cleaning in FO mode, the HTI-CTA

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membrane rejected Na2SO4 considerably less (Js increased to 75.2 mmol m-2 h-1) with an FRR of

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106.3%, while only a moderate FRR of 92.2% was found for CSM-TFC membrane. Several

294

studies suggest that cellulose triacetate could swell or even degrade in the presence of ethanol by

295

a Claisen condensation reaction.54,55 Other studies suggested variation of pore size and pore density

296

of the polyamide layer in TFC membranes due to the contact with ethanol, causing severe volume

297

expansion or curling of the polymer matrix.56-58 Thus, the poor regeneration of both the HTI-CTA

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and CSM-TFC membranes with alcohol solutions was probably due to the physical collapse of the

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active layer, which hinders thorough cleansing in commercial applications.

300 301

Figure 4

302 303

Membrane Antibacterial Property. The antibacterial property of the PTAODH-1.0

304

membrane was investigated using two model bacteria, E. coli (Gram-negative) and S. aureus

305

(Gram-positive). To better understand the antibacterial mechanism, PODH (the precursor of

306

PTAODH without 1,2,4-triazole moiety) as well as the commercial FO membranes were included

307

in the investigation. The results, presented as percent of colony-forming units (CFU) compared

308

the control after three hours contact time, are shown in Figure 5. Based on their biocompatible

309

chemical structure,59,60 both the HTI-CTA and CSM-TFC membranes exhibit negligible

310

antibacterial activity against both bacteria types. Although the triazole moiety was found to 13



311

comprise only ~10 mol% of the PTAODH-1.0 backbone (calculated from our previous study),39

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significantly low cell viabilities of 14.0±1.4% and 18.0±12.6% were achieved against E. coli and

313

S. aureus, respectively. It has been reported that the hydrophilicity of oxadiazole and triazole

314

groups could disrupt the normal metabolism of bacterial cells by inhibiting the production of lipids

315

necessary for cell-wall biosynthesis, thus inhibiting bacterial reproduction.61-65 The triazole moiety

316

was even revealed to have cytotoxicity that may cause a fast cell deactivation.61 Moreover, the

317

smooth surface of the PTAODH-1.0 membrane could also prevent bacterial adhesion, growth,

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proliferation, and subsequent formation of biofilm.66,67 Thus, both bacteriostatic/bactericidal

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mechanisms and morphology contribute to the outstanding antibacterial properties of our

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membrane PTAODH-1.0.

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Figure 5

322 323

ASSOCIATED CONTENT 324

Supporting Information Available: Supporting figures include AFM morphology of PTAODH-

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1.0, HTI-CTA, and CSM-TFC membranes (Figure S1); results of concentration experiment using

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HTI-CTA membrane (FO mode) (Figure S2); results of concentration experiment using HTI-CTA

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membrane (PRO mode) (Figure S3); results of concentration experiment using CSM-TFC

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membrane (FO mode) (Figure S4); results of concentration experiment using CSM-TFC

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membrane (PRO mode) (Figure S5); and images of all three membranes before dye concentration,

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after dye concentration, and after physical cleaning (Figure S6). This material is available free of

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charge via the internet at https://pubs.acs.org/.

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AUTHOR INFORMATION 333

Corresponding Author 14


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* Xuan Zhang: [email protected].

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* Menachem Elimelech: [email protected]. Notes

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The authors declare no competing financial interest. ACKNOWLEDGMENTS

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This work was supported by the National Natural Science Foundation of China (21774058,

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51778292), the Natural Science Foundation of Jiangsu Province (BK20180072), and the

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Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX18_0480).

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REFERENCES 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359

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(57)Geens, J.; Boussu, K.; Vandecasteele, C.; Van der Bruggen, B. Modelling of Solute Transport in Non-aqueous Nanofiltration. J. Membr. Sci. 2006, 281, 139-148. (58)Yang, X. J.; Livingston, A. G.; Freitas dos Santos, L. Experimental Observations of Nanofiltration with Organic Solvents. J. Membr. Sci. 2001, 190, 45-55. (59)Wang, J.; Wang, Z.; Wang, J. X.; Wang, S. C. Improving the Water Flux and Bio-fouling Resistance of Reverse Osmosis (RO) Membrane through Surface Modification by Zwitterionic Polymer. J. Membr. Sci. 2015, 493, 188-199. (60)Chang, Y.; Chen, S. F.; Yu, Q. M.; Zhang, Z.; Bernards, M.; Jiang, S. Y. Development of Biocompatible Interpenetrating Polymer Networks Containing a Sulfobetaine-Based Polymer and A Segmented Polyurethane for Protein Resistance. Biomacromolecules 2007, 8,122-127. (61)Suresh Kumar, G. V.; Rajendraprasad, Y.; Mallikarjuna, B. P.; Chandrashekar, S. M.; Kistayya, C. Synthesis of Some Novel 2-substituted-5-(isopropylthiazole) Clubbed 1,2,4-Triazole and 1,3,4-Oxadiazoles as Potential Antimicrobial and Antitubercular Agents. Eur. J. Med. Chem. 2010, 45, 2063-2074. (62)Singh, A. K.; Singh, P.; Mishra, S.; Shahi, V. K. Anti-biofouling Organic-inorganic Hybrid Membrane for Water Treatment. J. Mater. Chem. 2012, 22, 1834-1844. (63)Lopes, S. M. M.; Novais, J. S.; Costa, D. C. S.; Castro, H. C.; Figueiredo, A. M. S.; Ferreira, V. F.; Pinho E Melo, T. M. V. D.; da Silva, F. C. Hetero-Diels-Alder Reactions of Novel 3triazolyl-nitrosoalkenes as An Approach to Functionalized 1,2,3-Triazoles with Antibacterial Profile. Eur. J. Med. Chem. 2018, 143, 1010-1020. (64)Plech, T.; Kapron, B.; Penech, A.; Kosikowska, U. Search for Factors Affecting Antibacterial Activity and Toxicity of 1,2,4-Triazole-Ciprofloxacin Hybrids. Eur. J. Med. Chem. 2015, 97, 94103. (65)Singh, A. K.; Prakash, S.; Kulshrestha, V.; Shahi, V. K. Cross-Linked Hybrid Nanofiltration Membrane with Antibiofouling Properties and Self-Assembled Layered Morphology. ACS Appl. Mater. Interfaces 2012, 4, 1683-1692. (66)Mansouri, J.; Harrisson, S.; Chen, V. Strategies for Controlling Biofouling in Membrane Filtration Systems: Challenges and Opportunities. J. Mater. Chem. 2010, 20, 4567-4586. (67)Zhu, J. Y.; Wang, J.; Hou, J. W.; Zhang, Y. T.; Liu, J. D.; Van der Bruggen, B. Graphenebased Antimicrobial Polymeric Membranes: A Review. J. Mater. Chem. A. 2017, 5, 6776-6793.

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Figure 1. FESEM images of PTAODH-1.0 (top row), HTI-CTA (middle row), and CSM-TFC (bottom row) membranes: (A), (D), and (G) top surfaces; (B), (E), and (H) bottom surfaces; (C), (F), and (I) cross-sections.

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Figure 2. Performance of the PTAODH-1.0, commercial HTI-CTA, and commercial CSM-TFC membranes. (A) Water flux (Jw) and reverse salt flux (Js) for three membranes at different membrane orientations. For the symmetric PTAODH-1.0 membrane, FO-TF indicates that the top surface was facing the feed solution while FOBF indicates that the bottom surface was facing the feed solution. The asymmetric HTICTA and CSM-TFC membranes were evaluated in FO and PRO modes (feed solution facing the active layer and support layer, respectively). (B) Calculated reverse flux selectivities (Jw/Js) for the three types of membranes at the above membrane orientations. FO performance experiments were carried out with an effective membrane area of 10.0 cm2 and a crossflow velocity of 10.4 cm s-1, using 1.5 M Na2SO4 as a draw solution and DI water as feed solution. At least two parallel tests were conducted at 25oC for two hours, presented as average values with error bars. 22


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Figure 3. Dye concentration experiment using the PTAODH-1.0 membrane. Congo Red (CR) solution was used as the feed with an initial concentration of 1.0 g L-1. A constant draw solution concentration of 1.5 M Na2SO4 was maintained by adding salt as needed at every monitoring time. (A) Variation of water flux, Jw, with time. (B) Variation of Na2SO4 mass and concentration in feed with time due to reverse salt flux. (C) Variation of CR mass in draw solution with time. (D) Calculated and actual CR concentration in the feed and the corresponding FO concentration factor with time. The calculated CR concentration was obtained by the total mass balance of CR in the feed and the draw solution, assuming no adsorption of dye to the membrane.

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Figure 4. Comparison of membrane cleaning efficiency in terms of the flux recovery ratio (FRR) and variations in Js. (A) FRR and the variation of Js (ΔJs) for PTAODH1.0, HTI-CTA(FO), HTI-CTA(PRO), CSM-TFC(FO), and CSM-TFC(PRO) membranes after cleaning with pure water. (B) FRR and the variation of Js (ΔJs) for the PTAODH-1.0 FO membrane using pure water (PW) and various concentrations (%) of alcohol solutions. (C) FRR and the variation of Js (ΔJs) for the PTAODH-1.0, HTICTA(FO), HTI-CTA(PRO), CSM-TFC(FO), and CSM-TFC(PRO) membranes after washing with 40% alcohol solution. 24


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Figure 5. Antibacterial properties of PODH, PTAODH-1.0, HTI-CTA, and CSM-TFC membranes against E. coli and S. aureus. Membrane samples were cut to 2.5 cm × 2.5 cm squares and each contacted with 1.0 mL of bacterial solution (concentration of 1.0×108 CFU mL-1) for three hours. The membranes were taken out, rinsed with sterile saline solution (NaCl, 0.9% (w/v)) to remove unattached cells from the membrane surface, and each immersed in 10 mL of sterile saline solution to detach the deposited cells by mild sonication for five minutes. After cultivation overnight at 37oC, the solutions containing the detached cells were diluted and plated on LB/Agar plates for plate counting. The commercial HTI-CTA membrane was used as a control, and all results were normalized to the result of the HTI-CTA membrane. Four samples of each membrane type were tested against both species of bacteria. Error bars indicate the standard deviations from three independent replicates.

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Concentration and Recovery of Dyes from Textile Wastewater Using a

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