Chitosan immobilized porous polyolefin as sustainable and efficient antibacterial membranes

Research Article pubs.acs.org/journal/ascecg Chitosan Immobilized Porous Polyolefin As Sustainable and Efficient Antibacterial Membranes Prasanna Kumar S Mural,† Banothu Kumar,‡ Giridhar Madras,‡ and Suryasarathi Bose*,§ † Center for Nano Science and Engineering, ‡Department of Chemical Engineering, and §Department of Materials Engineering, Indian Institute of Science, Bangalore-560012, Karnataka, India S Supporting Information * ABSTRACT: Polyolefinic membranes have attracted a great deal of interest owing to their ease of processing and chemical inertness In this study, porous polyolefin membranes were derived by selectively etching PEO from PE/PEO (polyethylene/poly(ethylene oxide)) blends The hydrophobic polyolefin (low density polyethylene) was treated with UV-ozone followed by dip coating in chitosan acetate solution to obtain a hydrophilic-antibacterial surface The chitosan immobilized PE membranes were further characterized by Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscope (XPS) It was found that surface grafting of chitosan onto PE membranes enhanced the surface roughness and the concentration of nitrogen (or amine) scaled with increasing concentration of chitosan (0.25 to 2% wt/vol), as inferred from Kjeldahl nitrogen analysis The pure water flux was almost similar for chitosan immobilized PE membranes as compared to membranes without chitosan The bacterial population, substantially reduced for membranes with higher concentration of chitosan For instance, 90 and 94% reduction in Escherichia coli (E coli) and Staphylococcus aureus (S aureus) colony forming unit respectively was observed with 2% wt/vol of chitosan This study opens new avenues in designing polyolefinic based antibacterial membranes for water purification KEYWORDS: PE/PEO blends, Chitosan, UV-ozone, Antibacterial membrane ■ INTRODUCTION There is a great need for the development of water treatment technologies.1 Water purification by polymeric membranes is preferred due to their low/no thermal inputs and low cost Among other conventional techniques, polymeric membranes designed using melt blending of polymers and selectively etching out one of the phases to create a porous structure has gained a lot of attention recently.2 Commercially available membranes are made of materials such as Teflon, cellulose acetate, polyacrylonitrile, polyvinylidene fluoride, polyvinyl chloride, polyamides, etc.3,4 In this context, polyolefin based membranes are preferred due to their good chemical resistance, low cost, and ease of processability.5,6 Melt blending of polymer may lead to heterogeneous morphologies.7,8 In this case, selective etching of one of the phases can lead to membranes with controlled porosity The bacteria form a biofilm on the surface that leads to increase in resistance over a period of time This can be avoided by incorporating bactericidal agents or surface coating/modification to render an antimicrobial surface In our previous studies, we have reported antibacterial effects by incorporating various antibacterial agents5,6,9 as the surface modification/coating is governed by the stability and adhesiveness property of the membranes In this context, controlling the reaction parameters that develop different functional moieties on the surface can be an effective alternative to develop an antibacterial surface © 2015 American Chemical Society Various surface modification techniques are available such as chemical modification using acid/base,10 grafting polymer chains on the surface, UV, or plasma treatment.11−20 It has also been reported that a further addition of a layer of polymer chains on the surface of the membrane will offer additional resistance to water flow But the conversion of hydrophobic surface to hydrophilic surface will tend to reduce the resistance, fouling, and membrane performances over a period of time.21,22 The presence of functional moieties such as phenolic, amine groups, etc., can render antibacterial activity to the surface Further modification of the surface that can react with antibacterial moieties can be done by plasma treatment, UVozone treatment, etc The plasma treatment has been reported to be an expensive technique and is difficult to implement in the existing manufacturing lines For modification of inert surfaces like polyolefins, UV treatment can also be employed with relatively mild surface treatment.23 It has been reported that the porous membranes find application in blood oxygenator, membrane distillation, water purification, etc Generally these porous membranes are prepared from Teflon, PVDF, etc For applications such as water purification, membranes prepared from polyolefins are Received: August 21, 2015 Revised: November 30, 2015 Published: December 8, 2015 862 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering Initially, chitosan of different concentrations (0.25, 0.75, and 2.0% wt/ vol) was dissolved in 1% wt/vol acetic acid solution Porous PE substrates were initially functionalized by UV-ozone treatment at 35 °C for 20 These functionalized porous substrates were immediately immersed in the chitosan solution for with stirring to obtain the chitosan coated substrate The resultant substrate was washed several times with distilled water to neutralize the pH The neutralized chitosan coated substrate was then dried at 25 °C for 12 h prior to further characterization The washing and sonication followed by vacuum drying at 25 °C was repeated until constant weight of the sample was obtained Characterization Technique Surface modification of chitosan on porous substrate was further characterized using spectroscopic techniques The chemical composition of coated and uncoated porous substrate was assessed by FTIR using the Attenuated Total Reflection (ATR) mode and X-ray photoelectron spectroscope (XPS) The ATR spectra were recorded on a PerkinElmer Frontier in the range of 4000 to 650 cm−1 with 128 scans XPS measurements were performed by using Al monochromatic source (Kratos Analytical instrument) Further, the presence of chitosan on membrane surface was confirmed by immersing substrates in 0.01% wt/vol of Amido black aqueous solution for 12 h The excess of amido black was removed by thoroughly washing with distilled water The state of dispersion and distribution of chitosan on the membrane surface was evaluated using optical microscope Further, the surface roughness of the membrane was measured by noncontact optical profilometer (Talysurf CCI, Hobson) to obtain the average roughness (Ra) Three samples were tested to get average Ra The quantitative amount of chitosan on the membrane was determined by Kjeldahl nitrogen analysis, as described in the literature.16 Typically, membranes of specific size were digested in the presence of concentrated sulfuric acid and copper sulfate for h The color change to dark black indicates the digestion This is followed by addition of few drops of hydrogen peroxide and the substrates were heated until the solution become colorless The obtained solution was distilled in Kjeldahl setup with 40% wt/vol of sodium hydroxide solution The ammonium ions are distilled in the form of ammonia gas which was subsequently trapped in HCl solution The amount of ammonia is determined by titration against 0.01 N NaOH solution The amount of chitosan on the substrate was calculated by preferred due to their low cost, because they are chemically inert and they have good mechanical strength, antidegradation, and physical/chemical stability.24 But due to their hydrophobic nature, they tend to foul over a period of time Fouling augments the resistance resulting in higher pumping cost It is envisaged that fouling can be suppressed21 by modifying the surface Chitosan is a hydrophilic polymer used to inhibit biofouling.25−28 It is nontoxic and biocompatible and possesses inherent antimicrobial properties.29 On the other hand, polyethylene (PE) is nonpolar and chemically inert Various techniques like plasma, UV-ozone, etc., have been employed to modify the surface of PE.30 The present study investigates the application of PE membrane derived from PE/PEO blends We present the first demonstration of surface coating of chitosan on the PE membranes for water purification and antibacterial surface and to reduce the biofouling Chitosan was covalently coated on the PE membranes by UV-ozone treatment followed by dip coating in chitosan solution Chitosan coated PE membranes were found to exhibit marginal resistance to intrinsic water permeability with enhanced reduction of the bacterial population Our results highlight the potential of chitosan coating on PE membranes for bacterial population reduction and water permeation The concentration of the chitosan (0.25, 0.75, and 2.0% wt/vol) was varied in this study to assess the effect of chitosan concentration on the antibacterial properties of the membrane The surface coating of chitosan was analyzed using spectroscopic techniques like FTIR and XPS Further the state of chitosan distribution on the PE membrane surface was assessed by EDAX mapping and amide black staining experiments Surface and the cross-sectional morphology of the membranes were investigated by FESEM and optical profilometer The chitosan coated and untreated PE membranes were further characterized for water flux using a crossflow setup The bacterial population reduction of the chitosan coated surface was studied using E coli and S aureus as a Gram-negative and Gram-positive model bacteria In addition, simple dip coating can provide a platform for chitosan coating as the antibacterial membrane functional moiety for a wide range of applications ■ amount of chitosan (μg/mm 2) ⎡ (V M − V2M 2) ⎤ =⎢ 1 ⎥ × mol wt of chitosan ⎣ ⎦ 1000 (1) V1 and M1 are volume (mL) and concentration (M) of HCl solution, similarly V2 and M2 are volume (mL) and concentration (M) of NaOH solution, and (V1M1 − V2M2) represents moles of nitrogen present The membrane morphology was assessed using Field Emission-Scanning Electron Microscope (FESEM), Carl Zeiss at accelerating voltage of kV Membrane Performance Membrane performance was analyzed by pure water flux across the membrane (permeate flux) as a function of pressure (pressure range of 17.2−68.9 KPa) using a cross-flow filtration setup Permeate flux was recorded after h of steady state ensuring that the difference between two consecutive flux readings not exceed more than 10% Further to check for consistency, the flux of at least three samples was recorded prior to reporting the values Permeate flux was calculated by EXPERIMENTAL SECTION Materials Low density polyethylene (LDPE) of 25 g/10 melt flow index and poly(ethylene oxide) (PEO) of viscosity average molecular weight (Mv) of ca 400 000, melting temperature (Tm) of 65 °C with hydroxyl terminated group were procured from SigmaAldrich Chitosan from shrimp shells with a degree of deacetylation of 78% and molecular weight of ca 1450 kDa was obtained from Himedia Laboratories Pvt Ltd All other reagents and solvents were of analytical grade and used as such Preparation of Blends Blends of PE/PEO with 90 wt % PE and 10 wt % PEO were utilized in the present study for membrane preparation The blends of PE/PEO were melt mixed at 150 °C and 60 rpm for 20 under nitrogen gas using Polylab, Thermo Haake Minilab II Typically, PE/PEO blends with cc was mixed by a batch mixer with a recirculation chamber (which ensures the homogeneous mixing of PE/PEO) Before melt mixing PE and PEO, they were vacuum-dried for 12 h (PE at 50 °C and PEO at room temperature) to ensure that the traces of moisture were eliminated The samples for membrane applications were obtained by hot pressing PE/PEO blends at 150 °C for The hot pressed PE/PEO samples were made porous by selectively etching out the PEO phase in distilled water (for 24 h with constant stirring at room temperature) Chitosan Immobilized Porous PE Membrane Surface coating on porous PE substrate was done by dipping it in chitosan solution J = W /(At ) (2) In eq 2, W is the volume of water (L) permeated in time t (s) across the membrane active area A (m2) Antibacterial Performance Antibacterial performance of the membrane was assessed by E coli (E coli) of MG1655 strain as a Gram-negative and S aureus as a Gram-positive model bacterium Initially, culture from the stock was cultured in Luria−Bertani broth (LB) at 37 °C for h (until mid log phase) The obtained culture was centrifuged to form pellets and nutrient from broth was removed by 863 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering Figure ATR-FTIR spectra of untreated polymer (a) PE (i) and chitosan (ii), PE after UV-ozone treatment (b), after chitosan coating PE membranes (c) with 0.25 wt/vol chitosan (i), 0.75 wt/vol chitosan (ii), and wt/vol chitosan (iii) Magnified spectra of represent the expanded spectra of PE membranes coated with wt/vol chitosan (d) with peaks assigned and that of 1151 cm−1 arising from asymmetric stretching of the C−O−C bridge is well evident The peaks at 1070 and 1031 cm−1 further confirm the saccharine structure of chitosan.31 Figure 1b shows the FTIR of the UV treated PE, and this showed peak of carboxyl group (CO) at 1730 cm−1, shoulder at 1410 cm−1, and hydroxyl group (OH) group broad 3000− 3700 cm−1 This confirms that the UV-ozone treatment led to the carboxyl acid group in PE membranes Figure 1c and d shows the FTIR spectra of chitosan immobilized PE which showed distinct characteristic peaks, corresponding to primary and secondary amine of chitosan at 1650 and 1550 cm−1 respectively A new peak at 1737 cm−1 is evident which corresponds to CO stretch of the ester group.32 Hence, from FTIR, it is evident that coated membranes contain both characteristic peaks of PE and chitosan, with the formation of new ester linkage Thus, from FTIR, we can conclude that chitosan was successfully coated onto PE token membranes Further complete etching of PEO phase was ensured by taking the IR spectra of PE membranes as shown in Figure S1 From Figure S1 it is evident that no peaks of PEO were observed washing with phosphate buffered saline (PBS) Thus, obtained pellets were resuspended in PBS (of pH 7.4) for required final concentration of cells of ∼107−108 CFU/mL The three replicates were performed before reporting the antibacterial activity The membranes of specific dimensions were immersed in the PBS culture The suspended membranes were incubated at 37 °C for h After h, the supernatant of 100 μL was used for plating on the nutrient agar after suitable dilution After 12 h of incubation colonies formed were counted ■ RESULTS AND DISCUSSION Characterizing Chitosan Immobilized PE Membranes FITR The surface grafting of chitosan upon UV-ozone treatment was characterized by FTIR Figure 1a shows the FTIR spectra of untreated PE and chitosan Untreated PE membranes showed absorption peaks at 2920 and 2850 cm−1 corresponding to C−H stretching of methylene The peaks at 1464 and 720 cm−1 can be attributed to C−H bending and C− H rocking of methylene group, respectively The untreated chitosan exhibited a distinct absorption peak at 1650 cm−1 which is attributed to N−H bending of amide I and the peak at 1585 cm−1 due to C−C stretching (in-ring) of the aromatic ring The peak corresponding to 1381 cm−1 is due to amide III 864 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering XPS Further evidence of chitosan immobilization onto PE is based on XPS, as shown in Figure 2a, which reveals no traces of Scheme Proposed Mechanism of UV-Ozone Treatment, Possible Products of UV-Ozone Treatment (a) and Possible Chitosan Coating on PE Membranes via Ester Linkage (b) et al.16 for plasma treated PE films Further, neutralization of these chitosan coated PE membrane can lead to regeneration of NH2 group which is very important from antibacterial point of view and will be discussed in detail later Kjeldahl Nitrogen Analysis To obtain a quantitative picture, the concentration of nitrogen present on PE was assessed using Kjeldahl nitrogen analysis Both, the UV-ozone treated and untreated PE membranes were dipped in chitosan solution of varying concentration followed by repeated washing and sonication to remove the unbound chitosan Subsequently, the membranes were neutralized For the present study, chitosan of 0.25, 0.75, and 2.0% wt/vol chitosan was dissolved in acetic acid and used for nitrogen analysis The untreated PE membranes were free of chitosan whereas, for the UV-ozone treated samples the concentration of nitrogen scaled with increasing concentration of chitosan (see Figure 3) For instance, PE membranes which were subjected to 0.25% wt/ Figure Wide XPS spectra (a) of PE (i) before coating with chitosan and (ii) after coating with wt/vol chitosan N-1s scan (b) of PE (i) before coating with chitosan and (ii) after coating with wt/vol chitosan nitrogen on neat PE However, chitosan coated membranes exhibited a peak of N-1s (see Figure 2a and b) From XPS, the mass % and the atomic % of nitrogen was estimated to be 1.90 and 1.64% respectively, for 2% wt/vol chitosan coated membranes Further N-1s peak exhibited a binding energy of 402.8 eV and no such peak was observed for untreated PE membranes This suggests that elemental nitrogen is present only on treated PE membranes, which is arising from chitosan present on the surface A possible mechanism of grafting chitosan on PE can be explained, as shown in Scheme When subjected to UV-ozone treatment, the PE chains undergo chain scission and rearrangement to form carboxylic group, as shown in Scheme 1a This carboxylic group can react with the ester linkage of chitosan Both NH2 and OH groups of chitosan have equal probabilities to react, however, due to acidic media the carboxylic group is protonated Thus, the protonated carboxyl moieties will react with the hydroxyl group of chitosan to form ester linkage It is envisaged that formation of amide linkage is hindered in the presence of acidic media Thus, the proposed mechanism is in line with FTIR wherein the peak at 1737 cm−1 arising due to CO stretch of ester group confirms the grafting of chitosan onto PE Similar observations have been reported by Theapsak Figure Amount of chitosan coated on PE membranes obtained using Kjeldahl nitrogen analysis of treated and untreated PE 865 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering vol of chitosan coating exhibited weight of 13 ± 0.5 μg·mm−2 of chitosan, whereas the 2.0% wt/vol chitosan coated membranes exhibited weight of 32.7 ± 0.7 μg·mm−2 of chitosan This clearly suggests that UV-ozone treatment enhances the interaction between the membranes and chitosan Staining of Chitosan In order to understand the distribution and chitosan coverage on the porous PE membranes, the samples were stained with amide black It is envisaged that amide black interacts with the amine groups of chitosan and gets adsorbed on the surface Figure shows the The process of grafting chitosan on PE surface is carried out in a liquid media As soon as the media is separated, chitosan tend to phase separate in air as it tries to undergo shape relaxation resulting in a spherical shape in air It is important to note that the dispersion of chitosan is strongly contingent on the availability of functional moieties on the PE surface and also on the chitosan concentration The solution with 2.0% wt/vol chitosan exhibits slightly higher viscosity due to higher molecular weight of chitosan The higher molecular weight of chitosan tends to form aggregated structures resulting in a nonuniform distribution of droplets over the surface Surface Optical Profiles Figure shows the surface optical profiles acquired using an optical profilometer that reflects the surface roughness of untreated and 2.0% wt/vol chitosan coated PE membranes The untreated PE membranes exhibited a roughness (Ra) of ca 16.0 ± 3.8 μm and the membrane with wt/vol chitosan exhibited a Ra of ca 23.1 ± 3.2 μm This indicates an increase in surface roughness upon immobilizing chitosan These results clearly hint at the fact that the presence of chitosan is mainly on the PE surface and not in the pores This will help in retaining the pure water flux even after chitosan immobilization and will be discussed subsequently Designer Porous Membranes through Selective Etching of PEO from PE/PEO Blends: Morphology Figure shows the SEM micrographs of the surface and cross-section of PE membranes before and after chitosan coating PE/PEO blends are immiscible,2,5,6,33 wherein PEO is dispersed in the PE matrix as observed from the SEM micrographs The average droplet size of PEO in the blends is ca 1.13 μm with a polydispersity index of 1.10.5,6 Interestingly, after chitosan immobilization, the pore diameter was similar Thus, it can be concluded that chitosan is only coated on the membrane surface and this is also supported by surface staining experiments and optical profilometry as well In order to validate the hypothesis proposed earlier in context to the distribution of chitosan on the surface, EDAX mapping was carried out Figure shows the EDAX one to one surface mapping of the membrane coated with 2.0% wt/vol chitosan Figure 7a represents the surface morphology of the PE membrane, and Figure 7b and c represents the one to one mapping of C-1s (carbon) and N-1s (nitrogen), respectively It is evident that Figure Optical microscopic images of untreated PE (a), 0.25% wt/ vol chitosan coated PE (b), 0.75% wt/vol chitosan coated PE (c), and 2.0% wt/vol chitosan coated PE (d) optical microscopic images of untreated PE membranes and membranes coated with chitosan From Figure 4a, it is evident that untreated PE membrane does not exhibit any color However, membranes with chitosan immobilized on the surface show dark patches due to adsorption of amide black on the surface This phenomenon is consistent with increasing chitosan concentration This analysis clearly shows that chitosan is well distributed on the surface of the membrane which also suggests that UV-ozone treatment actually assists in generating free radicals on the surface that facilitate in chitosan immobilization Similar observations have been reported in literature.16 Figure Surface and roughness profile of untreated PE (a) and 2.0% wt/vol chitosan (b) obtained by optical profilometer (Ra indicates the roughness value of whole scanned surface) 866 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering Scheme Typical Cross Flow Test Cell for Estimating the Transmembrane Flux As a Function of Pressure Figure SEM micrograph of surface topology of untreated PE membrane (a) and across the surface (b) and PE membranes after 2.0% wt/vol chitosan on the surface (c) and across the surface (d) from nitrogen mapping, which is attributed to the presence of amine, that the chitosan is present on the surface of the membrane Further, the distribution of N-1s suggests uniform coating of chitosan on the surface and this observation supports the staining experiments as well EDAX spectra also revealed the atomic concentration of C and N to be 71.77 and 28.23%, respectively (and weight % of C and N to be 68.55 and 31.45%, respectively) Further traces of N-1s are absent in EDAX spectra of untreated PE membranes, as shown in Figure S2 confirming the absence of nitrogen on the surface Thus, the presence of nitrogen on the chitosan coated surface arises would arise from chitosan present on the surface Hence, the presence of chitosan on the PE surface can be confirmed Membrane Performance The membrane performance was evaluated by estimating the trans-membrane flux as a function of pressure using an indigenously developed cross-flow setup as shown in Scheme Figure illustrates the flux at various pressures for membranes with varying chitosan coating It is Figure Flux measurement at various trans membrane pressure for PE membranes observed that as pressure increases, flux increases for membranes From Figure 8, it is evident that the flux did not vary significantly with the coating of chitosan on PE membranes However, a decreased flux was noted for the highest concentrations of chitosan i.e at 2% wt/vol, which presumably could be attributed to the resistance offered by excess of chitosan Interestingly, in 0.75% wt/vol chitosan coated PE membranes, the flux increased from 4062 ± 266 to 4749 ± 252 L m−2 h−1 This increase in flux with respect to Figure SEM micrograph of wt/vol chitosan coated PE membrane (a), C-1s mapping on the surface (b), N-1s mapping on the surface (c), and EDAX spectra of the surface (d) 867 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering unmodified PE membrane is ascribed to the hydrophilic chitosan coating on a rather hydrophobic PE membrane Chanachai et al.34 reported a similar effect where an increase in hydrophilicity of the surface led to a decrease in repulsive forces between hydrophobic membrane and water Further, hydrophilicity facilitates in enhanced diffusion and thus increases the flux.35 But higher concentration of chitosan decreased the flux due to a thicker layer of chitosan which presumably blocked the pores and offered additional resistance to flow Antibacterial Studies The antibacterial activity of the chitosan coated PE membranes was studied using E coli as Gram-negative and S aureus as Gram-positive bacteria (see Figures and 10) The antibacterial activity is expressed here in Figure 10 Total agar plate counts of E coli (i) and S aureus (ii) colonies after 12 h of inoculation of negative control (a) untreated PE (b), 0.25% wt/vol chitosan (c), 0.75% wt/vol chitosan (d), and 2.0% wt/vol chitosan (e) Figure 10i and ii, it is evident that the number of colonies decreases with increasing chitosan concentration which indicates that chitosan eventually inhibits the bacterial growth The decrease in colonies clearly indicates the antibacterial nature of the membranes The mechanism of bacterial population reduction upon chitosan coating could be due to the interaction of free NH2 group (of chitosan) with the phospholipids36−39 present in the bacterial cell membrane Second, it can be envisioned that protonated NH3+ groups of the chitosan can form a complex with the phosphate groups in phospholipid bilayer of bacterial cell membrane This complex might as well result in the disruption of osmotic balance further resulting in the release of intracellular electrolytes such as potassium ions, glucose, nucleic acid, etc., thus resulting in cell death Further, at pH 6.0 similar reductions in bacterial population were noted for E coli It was observed with increase in chitosan concentration, antibacterial property was found to increase as shown in Figure 9ii ■ SUMMARY In this study, we were able to immobilize chitosan on UVozone treated PE membranes which was further confirmed by FTIR, XPS, EDAX, Kjeldhal analysis, and amide black staining experiments Thus, the hydrophobic polyolefin was converted to hydrophilic and in addition, rendered an antibacterial surface The concentration of chitosan immobilization was optimized by varying the concentration of chitosan solution and through the flux measurements For instance, 32 μg mm−2 of chitosan was estimated when the PE membranes were treated with 2% wt/vol chitosan solution, however, the flux was reduced But, PE membranes with 0.75% wt/vol chitosan coating exhibited increase in flux from 4062 ± 266 to 4749 ± 252 L m−2 h−1 with respect to untreated PE membranes Intriguingly, with wt/vol of chitosan coating on the surface, the bacterial reduction efficiency of 90 and 94% for E coli and S aureus respectively was observed Thus, this study clearly demonstrates that chitosan coated sustainable antibacterial membranes can be derived by etching one of the phases from binary polyolefinic blends and can further be explored for water purification Figure Dependence of E coli and S aureus (CFU mL−1) on the chitosan coating on the membranes after h of inoculation at pH 7.4 (i) Dependence of E coli at pH 6.0 (ii) (of negative control (cells without membranes) (a) untreated PE membranes (positive control) (b), 0.25% wt/vol chitosan (c), 0.75% wt/vol chitosan (d), and 2.0% wt/vol chitosan (e)) terms of colony forming units per milliliter (CFU mL−1) Figure shows the colony count after h of inoculation From Figure 9i, it is evident that untreated PE membranes exhibited a colony count of 2.8 × 107 per mL whereas 2% wt/vol chitosan coated PE membranes showed a colony of 6.0 × 106 i.e., about 90% reduction in E coli is observed with respect to initial count Similarly a reduction from 4.7 × 107 to 1.7 × 107 i.e., about 94% reduction in S aureus is observed with respect to initial count Figure 10 exhibits agar plate counts of bacterial colonies after 12 h of inoculation of untreated and chitosan coated PE From ■ ASSOCIATED CONTENT S Supporting Information * The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.5b00912 868 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering ■ (14) Ulbricht, M.; Matuschewski, H.; Oechel, A.; Hicke, H.-G Photo-Induced Graft Polymerization Surface Modifications for the Preparation of Hydrophilic and Low-Proten-Adsorbing Ultrafiltration Membranes J Membr Sci 1996, 115, 31−47 (15) Revanur, R.; McCloskey, B.; Breitenkamp, K.; Freeman, B D.; Emrick, T Reactive Amphiphilic Graft Copolymer Coatings Applied to Poly (Vinylidene Fluoride) Ultrafiltration Membranes Macromolecules 2007, 40, 3624−3630 (16) Theapsak, S.; Watthanaphanit, A.; Rujiravanit, R Preparation of Chitosan-Coated Polyethylene Packaging Films by Dbd Plasma Treatment ACS Appl Mater Interfaces 2012, 4, 2474−2482 (17) Deng, J.; Wang, L.; Liu, L.; Yang, W Developments and New Applications of Uv-Induced Surface Graft Polymerizations Prog Polym Sci 2009, 34, 156−193 (18) Wolska, J.; Smolinska-Kempisty, K.; Bryjak, M.; Kujawski, W Polypropylene Membranes with the Double Sensitivity Effect J Appl Polym Sci 2015, 132, 1097−4628 (19) Yu, H.-Y.; Xie, Y.-J.; Hu, M.-X.; Wang, J.-L.; Wang, S.-Y.; Xu, Z.K Surface Modification of Polypropylene Microporous Membrane to Improve Its Antifouling Property in Mbr: Co Plasma Treatment J Membr Sci 2005, 254, 219−227 (20) Shim, J K.; Na, H S.; Lee, Y M.; Huh, H.; Nho, Y C Surface Modification of Polypropylene Membranes by Γ-Ray Induced Graft Copolymerization and Their Solute Permeation Characteristics J Membr Sci 2001, 190, 215−226 (21) Jiang, J.; Zhu, L.; Zhu, L.; Zhang, H.; Zhu, B.; Xu, Y Antifouling and Antimicrobial Polymer Membranes Based on Bioinspired Polydopamine and Strong Hydrogen-Bonded Poly (N-Vinyl Pyrrolidone) ACS Appl Mater Interfaces 2013, 5, 12895−12904 (22) Yu, H.-Y.; Xie, Y.-J.; Hu, M.-X.; Wang, J.-L.; Wang, S.-Y.; Xu, Z.K Surface Modification of Polypropylene Microporous Membrane to Improve Its Antifouling Property in Mbr: Co2 Plasma Treatment J Membr Sci 2005, 254, 219−227 (23) Morra, M.; Occhiello, E.; Garbassi, F Adhesion Improvement by Uv Grafting onto Polyolefin Surfaces J Adhes 1994, 46, 39−47 (24) Jiang, J.-H.; Zhu, L.-P.; Li, X.-L.; Xu, Y.-Y.; Zhu, B.-K Surface Modification of Pe Porous Membranes Based on the Strong Adhesion of Polydopamine and Covalent Immobilization of Heparin J Membr Sci 2010, 364, 194−202 (25) Musale, D A.; Kumar, A.; Pleizier, G Formation and Characterization of Poly(Acrylonitrile)/Chitosan Composite Ultrafiltration Membranes J Membr Sci 1999, 154, 163−173 (26) Aravind, U K.; Mathew, J.; Aravindakumar, C T Transport Studies of Bsa, Lysozyme and Ovalbumin through Chitosan/ Polystyrene Sulfonate Multilayer Membrane J Membr Sci 2007, 299, 146−155 (27) Boributh, S.; Chanachai, A.; Jiraratananon, R Modification of Pvdf Membrane by Chitosan Solution for Reducing Protein Fouling J Membr Sci 2009, 342, 97−104 (28) Sarkar, K.; Banerjee, S.; Kundu, P Removal of Anionic Dye in Acid Solution by Self Crosslinked Insoluble Dendronized Chitosan Hydrol.: Curr Res 2012, 3, 133 (29) Carlson, R P.; Taffs, R.; Davison, W M.; Stewart, P S AntiBiofilm Properties of Chitosan-Coated Surfaces J Biomater Sci., Polym Ed 2008, 19, 1035−46 (30) Desai, S M.; Singh, R., Surface Modification of Polyethylene In Long Term Properties of Polyolefins; Springer, 2004; pp 231−294 (31) Peniche, C.; Argüelles-Monal, W.; Davidenko, N.; Sastre, R.; Gallardo, A.; San Román, J Self-Curing Membranes of Chitosan/PAA IPNS Obtained by Radical Polymerization: Preparation, Characterization and Interpolymer Complexation Biomaterials 1999, 20, 1869− 1878 (32) Gonzalez, E.; Hicks, R F Surface Analysis of Polymers Treated by Remote Atmospheric Pressure Plasma Langmuir 2010, 26, 3710− 3719 (33) Mural, P K S.; Madras, G.; Bose, S Positive Temperature Coefficient and Structural Relaxations in Selectively Localized Mwnts in PE/PEO Blends RSC Adv 2014, 4, 4943−4954 Figure S1: FTIR spectra of PE membrane after etching PEO phase Figure S2: SEM micrograph and EDAX mapping of untreated PE membrane (PDF) AUTHOR INFORMATION Corresponding Author *E-mail address: sbose@materials.iisc.ernet.in Notes The authors declare no competing financial interest ■ ACKNOWLEDGMENTS The authors would like to acknowledge the Department of Science and Technology and INSA (India) for the financial support and CeNSE, IISc, for various characterization facilities In addition, the authors are grateful to Prof Jayant Modak for extending his facilities, IISc, for extending their help in antibacterial studies ■ REFERENCES (1) Pendergast, M M.; Hoek, E M V A Review of Water Treatment Membrane Nanotechnologies Energy Environ Sci 2011, 4, 1946− 1971 (2) Trifkovic, M.; Hedegaard, A.; Huston, K.; Sheikhzadeh, M.; Macosko, C W Porous Films Via PE/PEO Cocontinuous Blends Macromolecules 2012, 45, 6036−6044 (3) Geise, G M.; Lee, H.-S.; Miller, D J.; Freeman, B D.; McGrath, J E.; Paul, D R Water Purification by Membranes: The Role of Polymer Science J Polym Sci., Part B: Polym Phys 2010, 48, 1685− 1718 (4) Ulbricht, M Advanced Functional Polymer Membranes Polymer 2006, 47, 2217−2262 (5) Mural, P K S.; Banerjee, A.; Rana, M S.; Shukla, A.; Padmanabhan, B.; Bhadra, S.; Madras, G.; Bose, S Polyolefin Based Antibacterial Membranes Derived from PE/PEO Blends Compatibilized with Amine Terminated Graphene Oxide and Maleated PE J Mater Chem A 2014, 2, 17635−17648 (6) Mural, P K S.; Sharma, M.; Shukla, A.; Bhadra, S.; Padmanabhan, B.; Madras, G.; Bose, S Porous Membranes Designed from Bi-Phasic Polymeric Blends Containing Silver Decorated Reduced Graphene Oxide Synthesized Via a Facile One-Pot Approach RSC Adv 2015, 5, 32441−32451 (7) Han, M.; Lim, B.; Jung, H.; Hyun, J.; Kim, S.; Kim, W Reactive Blends of Poly (Butylene Terephthalate)/Polyamide-6 with Ethylene Glycidyl Methacrylate Korea-Australia Rheology Journal 2001, 169− 177 (8) Utracki, L A Polymer Blends Handbook; Kluwer Academic Publishers: Dordrecht, The Netherlands, 2002; Vol (9) Sharma, M.; Madras, G.; Bose, S Unique Nanoporous Antibacterial Membranes Derived through Crystallization Induced Phase Separation in PVDF/PMMA Blends J Mater Chem A 2015, 3, 5991−6003 (10) Rubira, A F.; da Costa, A C.; Galembeck, F.; Leite Escobar, N F.; da Silva, E C.; Vargas, H Polyethylene and Polypropylene Surface Modification by Impregnation with Manganese (Iv) Oxide Colloids Surf 1985, 15, 63−73 (11) Wavhal, D S.; Fisher, E R Membrane Surface Modification by Plasma-Induced Polymerization of Acrylamide for Improved Surface Properties and Reduced Protein Fouling Langmuir 2003, 19, 79−85 (12) McCloskey, B D.; Park, H B.; Ju, H.; Rowe, B W.; Miller, D J.; Freeman, B D A bioinspired fouling-resistant surface modification for water purification membranes J Membr Sci 2012, 413-414, 82−90 (13) Ulbricht, M.; Belfort, G Surface Modification of Ultrafiltration Membranes by Low Temperature Plasma Ii Graft Polymerization onto Polyacrylonitrile and Polysulfone J Membr Sci 1996, 111, 193− 215 869 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 Research Article ACS Sustainable Chemistry & Engineering (34) Chanachai, A.; Meksup, K.; Jiraratananon, R Coating of Hydrophobic Hollow Fiber Pvdf Membrane with Chitosan for Protection against Wetting and Flavor Loss in Osmotic Distillation Process Sep Purif Technol 2010, 72, 217−224 (35) Dickson, J M.; Childs, R F.; McCarry, B E.; Gagnon, D R Development of a Coating Technique for the Internal Structure of Polypropylene Microfiltration Membranes J Membr Sci 1998, 148, 25−36 (36) Palermo, E F.; Lee, D.-K.; Ramamoorthy, A.; Kuroda, K Role of Cationic Group Structure in Membrane Binding and Disruption by Amphiphilic Copolymers J Phys Chem B 2011, 115, 366−375 (37) Singh, S K.; Singh, M K.; Kulkarni, P P.; Sonkar, V K.; Grácio, J J A.; Dash, D Amine-Modified Graphene: Thrombo-Protective Safer Alternative to Graphene Oxide for Biomedical Applications ACS Nano 2012, 6, 2731−2740 (38) Kumar, S.; Raj, S.; Kolanthai, E.; Sood, A K.; Sampath, S.; Chatterjee, K Chemical Functionalization of Graphene to Augment Stem Cell Osteogenesis and Inhibit Biofilm Formation on Polymer Composites for Orthopedic Applications ACS Appl Mater Interfaces 2015, 7, 3237−3252 (39) Kumar, S.; Bose, S.; Chatterjee, K Amine-Functionalized Multiwall Carbon Nanotubes Impart Osteoinductive and Bactericidal Properties in Poly (E-Caprolactone) Composites RSC Adv 2014, 4, 19086−19098 870 DOI: 10.1021/acssuschemeng.5b00912 ACS Sustainable Chem Eng 2016, 4, 862−870 ... wt/vol chitosan (i), 0.75 wt/vol chitosan (ii), and wt/vol chitosan (iii) Magnified spectra of represent the expanded spectra of PE membranes coated with wt/vol chitosan (d) with peaks assigned and. .. of surface coating of chitosan on the PE membranes for water purification and antibacterial surface and to reduce the biofouling Chitosan was covalently coated on the PE membranes by UV-ozone... present study, chitosan of 0.25, 0.75, and 2.0% wt/vol chitosan was dissolved in acetic acid and used for nitrogen analysis The untreated PE membranes were free of chitosan whereas, for the UV-ozone