Laser-Induced Graphene-PVA Composite as Robust Electrically

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Laser-Induced Graphene-PVA Composite as Robust Electrically Conductive Water Treatment Membranes Amit Kumar Thakur, Swatantra P. Singh, Maurício N. Kleinberg, Abhishek Gupta, and Christopher J. Arnusch ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b00510 • Publication Date (Web): 22 Feb 2019 Downloaded from http://pubs.acs.org on February 23, 2019

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ACS Applied Materials & Interfaces

Laser-Induced Graphene-PVA Composite as Robust Electrically Conductive Water Treatment Membranes Amit K. Thakur,† Swatantra P. Singh,†‡ Maurício Nunes Kleinberg, Abhishek Gupta and Christopher J. Arnusch* Department of Desalination and Water Treatment, Zuckerberg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede-Boqer Campus 84990, Israel ‡Center

for Environmental Science and Engineering (CESE), Indian Institute of Technology

Bombay, Powai, Mumbai 400076, India †Authors

with equal contribution

*Corresponding author: Dr. C. J. Arnusch, [email protected]

KEYWORDS: laser-induced graphene, poly (vinyl alcohol), surface modification, crosslinking, antifouling, ultrafiltration

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ABSTRACT: Graphene nanomaterials can feature both a superb electrical conductivity and unique physical properties such as an extreme surface wettability, which is potentially applicable for many purposes including water treatment. Laser-induced graphene (LIG) is an electrically conductive three-dimensional porous carbon material prepared by direct laser writing on various polymers in ambient conditions with a CO2 laser. Low fouling LIG coatings in water technology have been reported, however, the mechanical strength and the separation properties of LIG coated membranes are limited. Here we show mechanically robust electrically conductive LIGpoly(vinyl alcohol) (PVA) composite membranes with tailored separation properties suitable for ultrafiltration processes. PVA has outstanding chemical and physical stability with good filmforming properties and is a biocompatible and nontoxic polymer. Compared to LIG coated filters, the PVA-LIG composite membrane filters exhibited up to 63% increased bovine serum albumin rejection and up to ∼99.9% bacterial rejection, which corresponded well to the measured molecular weight cutoff ~ 90 kDa. Compared to LIG fabricated on a polymer membrane control, the composite membranes showed similarly excellent antifouling properties including low protein adsorption, and the anti-biofilm effects were more pronounced at lower PVA concentrations. Notably for the antibacterial capabilities, the LIG supporting layer maintained its electrical conductivity and a selected LIG-PVA composite used as electrodes showed complete elimination of mixed bacterial culture viability and indicated that the potent antimicrobial killing effects were maintained in the composite. This work demonstrates that the use of LIG for practical industrial filtration applications is possible.


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1. INTRODUCTION Graphene is an intriguing material and has received considerable attention in many applications because of its inimitable chemical, physical, electrical, and mechanical properties.1–4 Reports including graphene and its derivatives describe their utilization in energy, electronics and water applications.5–7 Laser-induced graphene (LIG) has emerged as an important and sustainable material due to its solvent and reagent free preparation and its potentially straightforward route to large-scale fabrication. The fabrication method has allowed the production of conformal 3D porous graphene structures in a single step and at quantities that permitted experimentation and development

in

a

variety

of

applications.

Its

electrical

properties,

flexibility,

hydrophilicity/hydrophobicity, antifouling and antibacterial properties, have been intensively exploited for various potential applications, such as supercapacitors,6 sensors,8 oxygen-evolution reaction,9 and heavy metal adsorption.10 Specifically, the antifouling and antimicrobial properties of LIG11–13 might be a viable solution for water treatment technology where fouling and resultant degradation of membranes is still a present challenge.14 Different from the uniform and defectfree surfaces of single layer graphene sheets made by chemical vapor deposition for example,15 the highly heterogeneous nanostructured 3D LIG network with variable wettability provides great opportunities for surface modification including imparting electrical conductivity. Recently, we and others have demonstrated a novel, cost-effective and scalable strategy to make LIG on a wide variety of carbon substrates, enabling graphene coatings on multiple commercial and tailor-made polymeric materials,12,16 and especially highly used polymers in water purification technology such as the polysulfone class of polymers.12 Since the discovery of LIG on commercial polyimide (PI) film in 2014,17 notable efforts have been made to alter the



chemical and physical properties of LIG by tuning the preparation methods or surface functionality. For example, the chemical composition of the LIG can be altered with polymer substrates that contain sulfur, or boron and metal doping of the substrates endowed LIG with varied surface chemistry and enhanced electrochemical properties.12,18,19 We recently demonstrated that LIG fabricated on porous poly(ether sulfone) ultrafiltration substrates resulted in surface electrochemical and electrical effects that led to highly antimicrobial and exceptional antifouling effects12 suitable for membrane water microfiltration. To increase the robustness of the surface and to tailor the separation ability, in the present study, we utilized poly(vinyl alcohol) (PVA) to generate a composite membrane from the highly porous electrically conductive LIG filters. PVA is highly used in membrane preparation due to its low toxicity, temperature stability, and good film-forming abilities.20 Its highly hydrophilic nature and good antifouling properties21–23 make PVA an ideal candidate for modification of surface properties of commercial membranes for ultrafiltration and nanofiltration applications.24,25 Herein, we fabricated a series of crosslinked LIG-PVA composite membranes via surface coating of PVA, and crosslinking with glutaraldehyde on the LIG support. These LIG membrane composites exhibited increased solute selectivity and permeability and were comparable to polymeric ultrafiltration membranes. The separation ability of the membranes could be tuned with increasing concentration amounts of PVA. The composite membrane exhibited complete inactivation of filtered bacteria and no surviving bacteria were seen on the surface. Such composite membranes that contain LIG potentially can be biofouling-resistant, highly efficient, and environmentally friendly water purification membranes.


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2. EXPERMENTAL SECTION 2.1 Chemicals and Materials. Ultrafiltration membranes polyethersulfone (PES) (UP 010P) with thickness 210 μm were purchased from Microdyn Nadir (Germany). Sodium chloride (NaCl, 99%), sodium phosphate dibasic heptahydrate (Na2HPO4·7H2O > 99%), monobasic potassium phosphate (KH2PO4, 99%), potassium chloride (KCl), acetone, hydrochloric acid (HCl) and glutaraldehyde (GA, 50 wt% in water) were obtained from Merck, (Israel). The dyes propidium iodide and SYTO 9 (LIVE/DEAD BacLight bacterial viability kit) were purchased from Thermo Fisher Scientific (Molecular Probes, USA). Poly (vinyl alcohol) (PVA, Mw 89000– 98000, 99+% hydrolyzed), and bovine serum albumin (BSA, ~ 66 kDa) were obtained from Sigma-Aldrich, (Israel). A Milli-Q ultrapure water purification system (Millipore, Billerica, MA, USA) was used for deionized (DI) water. All other chemicals were used without any further purification. 2.2. Fabrication of LIG-PVA Composite Membrane. LIG was generated on the surface of porous polyethersulfone membranes (UP 010) using a 10.6 μm carbon dioxide (CO2) laser cutting system (Universal VLS 3.50 Laser cutter platform). Settings of power (0.1% of full power 50 W), image density (1000 pulse per inch), and scan rate (25%) were used for all experiments under ambient conditions. LIG-PVA membranes were prepared by surface modification of the LIG filter by PVA as follows: A known amount of PVA (0.5, 1, 2, 3 and 4%, w/v) was dissolved in DI water at 80 °C with vigorous stirring for 4 h followed by cooling to room temperature. The LIG membrane support (5.5 cm X 5.5 cm) was fixed on a clean glass plate with cello tape, and 5 mL of the PVA aqueous solution was gently poured on top of the LIG substrate and allowed to contact for 10 min. Then, after removing the excess solution using a soft rubber roller, the resulting LIG substrates imbibed with PVA were dried at 50 °C in a



vacuum oven for 12 h. Afterward, the obtained PVA coated LIG substrates were then immersed into a crosslinking solution consisting of 5 wt% glutaraldehyde, 0.5% HCl and acetone for 12 h at 50 °C. Finally, the cross-linked membranes were thoroughly washed with acetone and dried in air at room temperature for 12 h before use and characterization. The membranes prepared with different PVA concentrations were designated as LIG-PVA-0.5, LIG-PVA-1, LIG-PVA-2, LIGPVA-3 and LIG-PVA-4 membranes, corresponding to the concentration of PVA in the coating solution, 0.5%, 1%, 2%, 3%, and 4%, respectively. The LIG support membranes were used as controls in this study. 2.3. Characterization and Measurements. Fourier transform infrared spectroscopy (FTIR; Vertex 70 spectrometer (Bruker Optics, Ettlingen) with a resolution of 4 cm−1 was used to chemically characterize the surface of the membranes. X-ray photoelectron spectroscopy (XPS) was performed on a PHI Quantera SXM scanning X-ray microprobe with a 200 μm beam size and 45° take off angle and calibrated using C 1s at 284.5 eV. A Renishaw Raman RE01 with a 633 nm laser was used for Raman measurements. The surface morphology of the composite membranes was observed by a scanning electron microscope (FEI Quanta 400 ESEM). Captive bubble contact angle measurements were performed with a OCA-15 contact angle analyser (DataPhysics, Filterstadt, Germany) as before.11 At least five contact angles at different locations on the surface were averaged. 2.4. Stability Tests of LIG and LIG-PVA Composite Membranes. To study the stability of the LIG and LIG-PVA membrane, the membranes were placed in beakers filled with water and sonicated at a frequency of 40 Hz for 30 min (MRC, Ultrasonic Cleaner). Pure water permeability and rejection of BSA was performed before and after sonication. For qualitative comparison of the durability of the LIG and the LIG-PVA-0.5 membrane, a tape-and-peel test


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was performed by applying and removing adhesive tape on top of the membrane surface and visually observing the amount of carbon removed (Movie S1, Supporting Information). For longer time stability testing, the LIG composite membrane with the least amount of PVA (LIGPVA-0.5) and the LIG support membrane were sequentially sonicated at r.t. for 30 min, then 2 h and finally 2 h at 50 °C and were visually inspected. 2.5. Performance Evaluation LIG-PVA Composite Membranes. Permeation and solute rejection was conducted using a dead-end stirred cell with volume capacity of 50 mL (Amicon UFSC05001 Millipore Co. Billerica, MA, USA) filtration system, pressurized with a nitrogen gas cylinder. Prior to measurements, samples were pre-compacted under 0.1 MPa for 30 min. Pure water permeability (PWP) (𝐽𝑤1 L m ―2 h ―2 bar ―1 abbreviated as LMH bar ―1) of membranes was evaluated by permeation tests with pure water. The rejection test (𝑅, %) of bovine serum albumin (BSA) protein (1.0 g/L in phosphate-buffered saline (PBS) solution, pH = 7.4) was evaluated by permeation test with BSA. All the experiments were performed at 25 ± 1 °C and a stirring speed of 500 rpm with a membrane area of 12.6 cm2. The water permeability ( 𝐽𝑤1) was measured using an electronic balance and calculated according to eq. 1: 𝐽𝑤1 =

𝑉 𝐴∆𝑡

(1)

where 𝑉, 𝐴 and 𝛥𝑡 represent the volume of permeated water, the membrane area and the permeation time, respectively. The BSA solution (1.0 g L-1 in PBS solution, pH = 7.4) was used to determine the rejection properties of membranes. The rejection ratio (𝑅) was determined using eq. 2:

(

𝑅= 1―

𝐶P 𝐶f

)

× 100

(2)



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where 𝐶p and 𝐶f are the solute concentrations of permeate and feed solutions, respectively. The concentration of the BSA in the feed and permeate solutions were measured using a UV-vis spectrometer (UV-2550, Shimadzu) at the wavelength of 280 nm. The molecular weight cut-off (MWCO) of the membranes was performed using gel permeation chromatography (GPC) (samples injection volume 25 μL, flow rate 0.5 mL min-1, 70 min runs in methanol:DI (20:80) as previously reported26 using polyethylene glycol (PEG) with the molecular weight of 35, 100, 200 and 400 kDa. Briefly, the rejection experiments were conducted at rt, using an Amicon 8010 stirred dead-end filtration cell (300 rpm) at 0.1 MPa. 2.6. BSA Fouling of LIG-PVA Composite Membranes. BSA (15 mL, 1 g L-1 PBS, pH 7.4) was added to a dead-end stirred cell containing a membrane used for pure water flux (active area of ~12.6 cm2) and a pressure of 0.1 MPa with a 500 rpm stir rate was applied. The permeate was collected and the flux (𝐽𝑠) was recorded. After that, the used membranes were cleaned with DI water for 30 min. The pure water flux of the cleaned membranes (𝐽𝑤2) was measured again at 0.1 MPa. The total flux decline ratio (FDR) and flux recovery ratio (FRR) were calculated using the following expressions:

(

FDR = 1 ―

FRR =

( ) 𝐽𝑤2 𝐽𝑤1

𝐽𝑠

)

𝐽𝑤1

× 100%

(3)

× 100%

(4)

A membrane with lower FDR and higher FRR implies better antifouling properties. For the static adsorption test, each 2 cm × 2 cm membrane sample was soaked in PBS solution for 1 h, and then transferred into a solution of BSA (1.0 g L ―1 PBS, pH = 7.4) for 24 h with continuous


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shaking. After adsorption, the BSA concentration was quantified by UV spectrophotometer at a wavelength of 280 nm. The adsorbed amount of BSA was calculated in accordance with eq. 5: Adsorbed BSA =

(𝐶0 ― 𝐶𝑒) × 𝑉

(5)

𝐴

where, 𝐶0 is the initial concentration of the BSA solution 𝐶𝑒 is the equilibrium concentration of BSA, 𝑉 is the volume of the added solution (mL), and A is the area of the membranes (cm2). 2.7. Biofilm Growth Experiments. Biofilm growth experiments were performed as described in detail elsewhere using mixed bacterial culture from a sample of secondary treated wastewater.11,12,27 2.8. Antibacterial Activity of LIG-PVA Composite Membranes. These experiments were performed as described in detail.12 Briefly, 15 mL of mixed bacterial culture suspension (∼106 CFU mL−1 in 0.9% NaCl solution) was passed through the filtration unit containing the stacked membranes at a flow rate of ca. 500 L m−2 h−1 at rt using 0, 1.5, 2.0 and 2.5 V. The bacteria CFU were enumerated using the plate counting method for the feed and the permeate solutions.

3. RESULTS AND DISCUSSION 3.1. Characterization of the LIG-PVA Composite Membranes. In the present study, a twostep strategy was used for the design and fabrication of LIG-PVA composite membranes (Figure 1). Firstly, the fabrication of LIG on commercial PES polymer membrane substrates was performed using a CO2 laser in an ambient atmosphere as before.12 This was followed by PVA surface coating and crosslinking with glutaraldehyde (see materials and methods). SEM images indicated that the LIG has a 3D porous structure and was characteristic of LIG previously reported having a broad distribution of pore sizes (Figure 1b).



Figure 1. (a) LIG is generated on UP 010 membranes using a 10.6 m CO2 laser; (b) SEM images of the as prepared LIG including cross-section (inset); (c) Preparation method for LIGPVA-4 membrane showing excess PVA solution removal with a rubber roller; (d) SEM images of LIG-PVA-4, including cross-section (inset).

The surface morphology of the composite membranes at high and low magnification is shown in Figure 2 and Figure S1, respectively. Coating with higher concentrations of PVA results first in the smaller pores to be filled in, and at the highest concentrations the very large pores are filled (Figure 2a-f), resulting in a reduction in pore size. Only the SEM image of the membrane made with the highest concentration of PVA (LIG-PVA-4) (Figures 1d and 2f) clearly showed a uniformly coated layer of PVA on the LIG substrate, with the LIG structure almost completely covered and no visible pores or pinholes were observed. Indeed the smoother covering of the


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PVA layer compared to the highly porous LIG substrate control can also be seen upon inspection of the cross-section SEM images (Figure 1b and 1d).

Figure 2. Surface SEM images of (a) LIG (b) LIG-PVA-0.5 (c) LIG-PVA-1 (d) LIG-PVA-2 (e) LIG-PVA-3 and (f) LIG-PVA-4 membranes.

Fourier transform infrared spectroscopy spectra of the LIG-PVA-4 membrane also indicated a complete covering and showed PVA adsorption bands at 3300−3400 cm−1, and ~2925 cm−1 associated with the stretching vibration of the hydroxyl (−OH) groups, and the CH asymmetric stretching vibration, respectively (Figure S2).28,29 In addition, the band observed at 1050-1140 cm−1 could indicate the formation of C−O−C groups by glutaraldehyde cross-linking.28,30 Raman spectra showed the typical D, G and 2D bands corresponding to the LIG. In general, as the amount of PVA increased, the 2D bands disappeared, and indicated that the covering amount of PVA on the membranes had increased (Figure 3a). Contact angle analysis was performed to



determine the surface wettability of the LIG-PVA composite membranes (Figure 3b), and showed that as the amount of PVA increased, the hydrophilicity of the surface increased.24 The contact angles of LIG-PVA-0.5, LIG-PVA-1, LIG-PVA-2, LIG-PVA-3 and LIG-PVA-4 were 38.9°, 35.7°, 32.4°, 30.3° and 28.4°, respectively.

Figure 3. Raman spectra (a) and water contact angle (b) of the LIG-PVA composite membranes.

3.2. Mechanical Stability of the LIG and LIG-PVA Composite Membranes. To investigate the mechanical stability of the LIG and LIG-PVA composite membrane, we exposed LIG and the LIG-PVA-0.5 membrane to ultrasonic agitation for 30 min in water (Figure S3). The LIG substrate showed the loss of LIG in contrast to the LIG-PVA-0.5 membrane, which did not exhibit any signs of disintegration or loss of LIG or PVA. For longer term stability tests, the LIG and LIG-PVA-0.5 membranes were subjected to 4.5 h ultrasonic agitation, including 2 hours at 50 °C. Again, the LIG membrane was significantly damaged, compared to the undamaged LIG composite membrane (Figure S3). After 1 h ultrasonic agitation of the LIG-PVA-0.5 and the LIG-PVA-4 membranes, the permeability and rejection differences between the membranes before or after treatment were 400 kDa. Accordingly, with a mixed culture of bacteria (~106 CFU mL-1), the highest removal of ~99.9% was seen with LIG-PVA-4 followed by LIG-PVA-3 (99.1%), LIG-



PVA-2 (98.5%), LIG-PVA-1 (72.5%) and LIG-PVA-0.5 (38.5%) (Figure 5d), an improved rejection over the previously reported LIG filter (see Table S1).12

Figure 4. Performance parameters for LIG-PVA composite membranes, (a) Pure water permeability (left axis) and BSA rejection (right axis); (b) Rejection of various PEG compounds with the LIG-PVA composite membranes.

3.4. Antifouling Performance of the Membranes. To evaluate the antifouling ability of the LIG-PVA composite membranes, protein fouling, flux decline and recovery testing were performed using BSA as a model foulant in a dead-end filtration system. Filtration of BSA solution resulted in flux decreases for the composite membranes, indicating BSA accumulation in the pores and on the surface of the membranes (Figure 5a).7,31,32 The LIG-PVA-0.5 approximately lost 36% of its initial flux due to the fouling and the LIG composite membranes with a higher content of PVA (1-4%) exhibited lower flux declines, with LIG-PVA-4 losing ~19% of its original flux from filtration of the BSA solution. The decrease in flux decline is most likely due to the enhanced hydrophilicity from the addition of PVA and is directly related to the amount of PVA contained within the LIG composites, which might prevent BSA adsorption. A


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hydrophilic surface is likely to form a hydrated layer that resists foulants.33 Also, the higher rejection of the LIG-PVA-4 membranes might prevent BSA from penetrating into the membrane causing less pore blocking.

Figure 5. (a) BSA permeability: Aqueous feed solution (1.0 g L-1) (b) Flux recovery ratio; (c) BSA static adsorption; (d) Bacterial cells removal for the different membranes.

The degree of irreversible membrane fouling is evident by the amount of flux recovery (FRR). The flux returned to ∼73, 78, 82, 87, and ~92% of the original flux for LIG-PVA-0.5, LIG-PVA1, LIG-PVA-2, LIG-PVA-3 and LIG-PVA-4, respectively, after gentle cleaning of the BSAfouled membrane surfaces with DI water (Figure 5b). Compared to the LIG-PVA-0.5 membrane, the greater FRR values of the LIG-PVA-4, membrane indicated a greater cleaning efficiency with increased PVA concentration. In addition to the dynamic fouling measurements, the static



protein adsorption test was performed to estimate the surface susceptibility to organic foulants. The protein adsorption slightly decreased (Figure 5c) from 5.0% to 3.3%, as the amount of PVA increased. Thus the properties of the polymer used in the LIG composite affect the fouling resistance of the membrane. 3.5. Biofilm Growth and Adhesion Analysis. We examined the biofouling of LIG-PVA composite membranes along with an LIG control surface with a mixed bacterial culture containing a variety of Gram positive and Gram negative species.27 The quantitative biovolume and average thickness for live and dead cells is shown in Figure 6.

Figure 6. Biofilm growth on the LIG as fabricated on the UP 010 support, and the series of LIGPVA composite membranes.

The LIG-PVA-0.5, LIG-PVA-1 membrane showed almost no biofilm formation similarly to the LIG control. The composite membranes made with increased PVA concentrations resulted in increased biofilm growth. Since the unique structure of LIG including its 3D texture, nanofibers and micropores was shown to be a contributing factor for the biofilm resistance, the coating of PVA on top of the LIG support might have eliminated this effect, allowing more biofilm growth


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on LIG-PVA membranes, and again underlining the importance of the polymer in the composite formation.11,13 SEM images were obtained after fixation of the biofilm (Figure 7), which showed that the LIG support membrane and LIG-PVA-0.5 membrane had the least amount of bacterial cells on the surface (Figure 7a-b), whereas, substantially more cells could be seen on the LIGPVA-1, LIG-PVA-2 and LIG-PVA-4, respectively (Figure 7c-e).

Figure 7. SEM images showing biofilm extent on different surfaces after biofilm growth experiments: (a) LIG, (b) LIG-PVA-0.5, (c) LIG-PVA-1, (d) LIG-PVA-2, (e) LIG-PVA-3, and (f) LIG-PVA-4 membranes.

Thus in addition to the material used in an LIG composite, the resulting composite structure might also be an important factor in the design of functional electrically conductive LIG composite membrane with antifouling properties. 3.6. Electrical Effects of LIG-PVA Composite Membranes: Bacteria Inactivation. Since the LIG-PVA-0.5 membrane had the highest surface electrical conductivity, was the most resistant to biofilm growth and had the highest pure water permeability in comparison to the other LIG



composite membranes, it was investigated for bacterial inhibition with applied voltages in filtration mode. Carbon threads were connected to two membranes and protected with epoxy glue and these were stacked in a dead-end filtration membrane flow-through system design as described earlier.12 In this configuration, ~106 cfu mL-1 were filtered through the LIG-PVA-0.5 membranes at ~500 LMH and resulted in ~6 log inhibition at 2.5 V, and around ~3 log inhibition at 2 V (Figure 8) in the permeate. Without the applied voltage, ~39% bacterial removal was seen (Figure S4), whereas at 2.5V, complete disinfection was seen. The electrical conductivity of the LIG-PVA-0.5 surface was measured to be ca. 5% less than the parent LIG surface and thus the mechanism of voltage dependent antimicrobial action was probably similar to previously reports.11,12,34 Briefly, both electrical and chemical effects might play a role. A rapid physical destruction of the bacteria or direct oxidation of bacterial components might occur as bacteria contact the electrode surface. Chemical effects include the electrochemical generation of species toxic to bacteria such as hydrogen peroxide, which might exist at high concentrations very near the electrode surface.


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Figure 8. Effect of applied voltage on bacterial cell viability with two LIG-PVA-0.5 membranes stacked in the dead end filtration mode using a mixed bacterial culture suspension (∼106 CFU mL−1 in 0.9% NaCl solution) at a flow rate of ∼500 L m−2 h−1. 4. CONCLUSIONS Here we demonstrated functional LIG-PVA composite membranes fabricated on LIG membrane supports by coating of PVA and crosslinking. The LIG composite membranes greatly improve the mechanical robustness of the LIG and as the PVA concentration increased, the protein and bacterial rejection also increased. The composite membranes also were resistant to fouling and had good FRR, but as the concentration of PVA increased, the water flux significantly decreased and the surfaces were more susceptible to biofilm growth. An antibacterial activity effect was observed with applied voltage and was seen in filtration mode. The polymer component (PVA) of the composite determines the extent of the antifouling effect although advantages of PVA might include that it is a water soluble polymer with many hydroxyl functionalities available to be cross-linked in three-dimensional networks or possibly grafted with functional groups. These might offer another handle to vary the surface properties and functionality of the composite membrane. Composite membranes including LIG might broaden the application of LIG in various water treatment processes. ASSOCIATED CONTENT Supporting Information LIG membrane performance, SEM image at low magnification, FTIR spectra, stability test and percentage removal of bacterial cells by LIG-PVA-0.5 membrane. AUTHOR INFORMATION Corresponding Author



*E-mail: [email protected]. ORCID iD Amit K. Thakur: 0000-0003-1409-6202 Swatantra P. Singh: 0000-0003-1898-3378 Maurício Nunes Kleinberg: 0000-0002-4883-3867 Abhishek Gupta: 0000-0002-2908-2121 Christopher J. Arnusch: 0000-0002-1462-1081 Conflicts of Interest B.G. Negev Technologies and Applications Ltd., the technology transfer company of BenGurion University (BGU) owns intellectual property rights to the processes and materials presented herein. Those rights are under an "option to license" agreement with a start-up company. A future License Agreement, if executed, might include certain payments to C.J.A. and allocation of certain amount of shares all such subject to the Intellectual Property Bylaws and Regulations of BGU. ACKNOWLEDGMENTS We are grateful to the Planning and Budgeting Committee (Council for Higher Education of Israel, Budget No. 6402479000) and United States-Israel Binational Science Foundation (BSF Grant No. 2014233) for financial support. C.J.A. wishes to thank the Canadian Associates of Ben Gurion University (CABGU) Quebec region for support. REFERENCES (1)

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Graphical Abstract


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Laser-Induced Graphene-PVA Composite as Robust Electrically

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