A new strategy for producing antibacterial textile surfaces using silver nanoparticles

Chemical Engineering Journal 228 (2013) 489–495

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A new strategy for producing antibacterial textile surfaces using silver nanoparticles Leyla Budama, Burçin Acar Çakır, Önder Topel ⇑, Numan Hoda ⇑ Department of Chemistry, Faculty of Sciences, Akdeniz University, 07058 Antalya, Turkey

g r a p h i c a l a b s t r a c t

 Ag nanoparticles were synthesized

Silver nanoparticles fabricated within reverse micelle cores and their UV–visible spectra depending on precursor ratios

within PS-b-PAA reverse micelle cores.  The size of Ag np is determined as 20 nm, which is independent of precursor ratio.  The copolymer solution containing nano-Ag has been coated onto textile fabrics.  A covalent bonding was determined between PS-b-PAA and fabric surface.  Long term antibacterial textile surfaces were obtained which have activity against E. coli and S. aureus.

a r t i c l e

i n f o

Article history: Received 14 January 2013 Received in revised form 30 April 2013 Accepted 8 May 2013 Available online 16 May 2013 Keywords: PS-b-PAA Self-assembling Reverse micelle Silver nanoparticle Antibacterial activity

Toluene 135 oC

1.AgNO3 2. N2H4

Absorbance (a.u)

h i g h l i g h t s

Silver ratio

PS - b - PAA 300

400

λ / nm

500

600

a b s t r a c t Silver nanoparticles have been fabricated within reverse micelle cores of polystyrene-block-polyacrylic acid (PS-b-PAA) copolymer synthesized by the atom transfer free radical polymerization (ATRP) method at various silver:copolymer ratios. The PS-b-PAA reverse micelles formed by dissolving the copolymer in toluene have been characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Silver nanoparticles synthesized within the micellar cores have been characterized by TEM and powder X-ray diffraction (XRD). It has been determined that crystal silver nanoparticles were formed at whole ratios. The average size of the silver nanoparticles was found to be independent of the silver precursor ratio and is around 20 nm for all ratios. The copolymer solution including silver nanoparticles has been coated onto textile fabrics for antibacterial activity. It has been determined that an esterification reaction takes place between corona (PAA) and hydroxyl groups on the textile surfaces which enhances the permanency of antibacterial activity of the fabrics. Significant antibacterial activity against gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) have been determined. The antibacterial activity is permanent up to five washings against E. coli and up to twenty washings against S. aureus. Ó 2013 Elsevier B.V. All rights reserved.

1. Introduction Bacterial infection is a potential risk to human life. Many antibacterial agents such as quaternary ammonium salts, phenols, peroxides and halogen-releasing compounds have been so far used ⇑ Corresponding authors. Tel.: +90 242 3102301; fax: +90 242 2278911. E-mail addresses: [email protected] (Ö. Topel), [email protected] (N. Hoda). 1385-8947/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2013.05.018

to decrease the risk of dermal, oral or breathing. Even if some of these agents are not possible to apply to foods, textiles, filters, etc. due to their toxicity and poor efficiency, silver or silver ions are known as powerful antibacterial agents because they are effective against 650 disease-causing organisms in the body, even at low concentrations [1–3] and relatively nontoxic for human cells [4]. Therefore, silver in various forms such as metallic, ionic and nanoparticle has attracted great interest for last two decades and are ideally suited for a wide range of applications in research and

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industrial applications. One of the applications of silver nanoparticles is to enhance antibacterial properties of textiles materials. All types of textiles, such as synthetic or natural fibers, have no resistance to bacteria and/or pathogens. Consequently, many works involving silver nanoparticles have been reported to enhance antibacterial activity of textile fabrics. For example, Duran et al. [5] incorporated silver nanoparticles synthesized by fungi on cotton fabrics, and demonstrated that they show good antibacterial activity against Staphylococcus aureus. Perelshtein et al. [6] deposited silver nanoparticles onto the surface of different fabrics (nylon, polyester and cotton) by ultrasound irradiation and they demonstrated that coated fabrics with nanosilver as an antibacterial agent had excellent antibacterial activity against Escherichia coli and S. aureus. The antibacterial efficacy of nanosized silver colloidal solutions on cellulose based and synthetic fabrics for S. aureus and klebsiella pneumoniae was investigated by Lee et al. [7] They found that the antibacterial treatment of the textile fabrics was easily achieved by padding them with nanosized silver colloidal solution and the antibacterial activity of the fabrics was maintained after many cycles of laundering. However, so far no method has been developed to give permanent antibacterial activity to the surfaces using silver or silver derivatives. To overcome this problem and develop an efficient method or at least to extend the permanency, many methods using silver nanoparticles have been proposed including pre-treatment of the textile surface, embedding nanoparticles on the fiber polymeric matrix and coating the surface with a thin film of polymer containing nanoparticles and even in situ production of silver nanoparticles on cotton fabric [8–17]. In this respect, Ibrahim et al. [9] and Dastjerdi et al. [10] were coated with antibacterial agents using trimethylol melamine (TMM) and polysiloxane crosslinkers on a cotton surface respectively. Gulrajani et al. used poly(vinyl pyrrolidone), PVP, to stabilize silver nanoparticles during the synthesis, which were then applied to a silk fabric surface by the exhaust method [11]. They investigated antibacterial activity against the gram-positive bacterium S. aureus on silk fabrics as well as the durability to washing. The others examples of enhanced antibacterial activity are connected with surface modification of the fabrics and subsequent coating by silver nanoparticle sols synthesized mostly by the sol– gel technique [13,15,16]. Many possible mechanisms have been proposed to describe the antibacterial activity of silver nanoparticles, including attachment to the cell membrane leading to decreasing membrane permeability and respiration and activity in the cell [18–30]. The general concensus is that the antibacterial activity is due to silver ions released from silver nanoparticles [25,26]. When elemental silver nanoparticles are in contact with water or dissolved oxygen, silver ions are released from the surface of nanoparticles in accordance with the following equation [30]:

O2 ðaqÞ þ 4Hþ þ 4Ag ! 4Agþ ðaqÞ þ 2H2 O

ð1Þ

According to Dastjerdi et al., silver ions might destroy and/or pass through the cell membrane, and bond to the –SH groups of cellular enzymes [10,27]. This causes a critical decrease in enzymatic activity which might change microorganism metabolism and inhibit their growth, lead to the death of the cell [27,28]. The silver ions might also catalyze the production of oxygen radicals, resulting in oxidation of the molecular structure of the living organism [27,29]. The radicals formed due to the binding of silver ions to the cell wall and enzyme proteins might also inhibit many processes in living cells [28,29]. Thus, developing a matrix providing a controlled release of silver ions is of great importance for long-term antibacterial activity. Silver ions shows antibacterial activity even at a concentration of 107 g/L, therefore the determination of the number of nanoparticles per unit area and the size of

silver nanoparticles in contact with water at this concentration are other issues to be solved to get improved antibacterial surfaces. In this study, to get long-term antibacterial activity, we have improved a new strategy by binding covalently the PS-b-PAA copolymer containing silver nanoparticles on the textile surface after we produced silver nanoparticles within reverse micelle cores of PS-b-PAA copolymer. This strategy provides more stable silver nanoparticles on the textile surface and a controlled release of silver ions from the micellar cores coated on textile surface. 2. Experimental 2.1. Materials Toluene (Merck) was distilled over calcium hydride, CaH2 (Fluka) under reduced pressure and stored in dark glass bottles. Silver nitrate, AgNO3, and hydrazine, N2H4, (Aldrich) were used as purchased. Lactose broth and agar agar (Merck) were used as purchased for antibacterial tests. All other reagents were purchased from commercial sources and were used after the usual drying and/or distillation without further purification. 2.2. Synthesis of polystyrene-block-poly(acrylic acid), PS-b-PAA copolymers The amphiphilic polystyrene-block-poly(acrylic acid) copolymer, PS-b-PAA, was synthesized by atom transfer radical polymerization (ATRP) as described in the literature [31,32]. Styrene (Merck) was purified by distilling under reduced pressure from CaH2 after passing through an alumina column. Tertiary butyl acrylate (tBA) (Aldrich) was purified by passing through a basic alumina column and then distilling under reduced pressure. The purified styrene and tBA were stored under nitrogen at 4 °C. Copper(I) bromide, CuBr, was purified according to a published procedure [31,32]. In the first step of the synthesis, the PS–Br macroinitiators were synthesized by using the purified styrene monomer, ethyl 2bromopropionate initiator, CuBr catalyst and PMDETA (N,N,N0 ,N00 ,N00 -pentamethyldiethylenetriamine) ligand by ATRP [31,32]. The synthesized PS–Br was characterized by NMR and GPC measurements. Then, the PS–Br chain was elongated with tBA polymerization by ATRP using the same reactants to form the PS-b-PtBA block copolymer. Finally, PS-b-PAA was obtained by hydrolysis of PS-b-PtBA. The degree of hydrolysis was controlled by FTIR measurements using the KBr pellet method before and after hydrolysis. The synthesized PS-b-PAA copolymer was characterized by GPC and NMR measurements. According to the GPC results, the molecular weight was found to be 14,550 g/mol with block weights, PS(10912)-b-PAA(3638). The PDI value was 1.31. By considering molecular weights of styrene and acrylic acid, it was found that the blocks of the copolymer consisted of 105 and 50 monomers for the hydrophobic PS block and the hydrophilic PAA block, respectively. 2.3. Preparing reverse micellar nanoreactors of PS-b-PAA block copolymer Reverse PS-b-PAA micellar templates were prepared by heating for 20 min at 135 °C after dissolving the copolymer in toluene. The reverse micelles were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. DLS measurements were performed with Malvern Zetasizer NANO ZS (Malvern Instruments Limited, UK) equipped with a 4mW He– Ne laser operating at a wavelength of 633 nm. A Zeiss Leo 906E TEM instrument was used to characterize the morphology of the

L. Budama et al. / Chemical Engineering Journal 228 (2013) 489–495

491

PS - b - PAA

Toluene 135oC

AgNO3

Ag+ + Ag+ Ag Ag+

N 2 H4

Scheme 1. Schematic presentation of synthesis of the Ag nanoparticles within micelle cores.

micelles. A drop of 1% (w/v) copolymer solution was placed on a carbon-coated copper grid and excess solution on the grid was removed using filter paper. After being dried at room temperature in air for 24 h, electron micrographs of the samples were obtained. 2.4. Fabrication of silver nanoparticles within reverse micelle templates Silver nitrate was loaded into the micellar solution with different silver:copolymer ratios. The solutions have been left for 2 days with vigorous stirring in a dark room to incorporate silver ions into the cores. Then, the silver ions in the cores were reduced to silver nanoparticles by hydrazine, N2H4. The whole process is summarized in Scheme 1. The micellar solutions incorporated with silver ions have turned to brownish red from colorless. Silver nanoparticle formation has been followed by Varian Cary 100 UV/vis spectrophotometer and the particles were characterized by XRD measurements using a Phillips X’Pert Pro diffractometer which records in the 2h range of 10–80° using Cu Ka radiation (k = 0.15406 nm). The size of the silver nanoparticles was characterized with a Zeiss Leo 906E TEM instrument by evaluating TEM images with Adobe Photoshop 7. A total of 200 particles were counted and averaged for corresponding particle sizes. 2.5. Coating silver nanoparticles onto textile samples The coating of silver nanoparticles onto textile fabrics was carried out as described before [33]. Briefly, cotton fabrics were washed in a water bath at 60 °C for 3 h after the samples had been washed in a washing machine without using detergent. The samples were then washed with cold deionized water and were dried in an oven at 60 °C overnight. The clean textile samples were cut into 1.5 cm  1.5 cm squares for antibacterial testing. The samples were stirred for 30 min in copolymer solution containing silver nanoparticles. After the wet samples were dried at room temperature, they were placed in an oven for 5 min at 135 °C for further binding of the nanoparticles onto the textile fabric surface [34]. The covalent binding of micelles of copolymer was investigated by means of FTIR measurements using a Bruker Tensor 27 FTIR spectrometry with the KBr pellet technique.

nanosilver coated fabrics [35]. In this method, a colony of E. coli or S. aureus was cultivated in 5 mL of LB culture. The inoculation medium was kept at 37 °C for 24 h. A 100 lL portion of these cultures was diluted to 50 mL liquid culture. These inoculums were incubated for 5.5 h (for E. coli) and 6 h (for S. aureus) at 37 °C and 200 rpm rotation [36]. A 1000 lL portion of the diluted inoculation was added to a tube and diluted by taking 1 mL from a tube and adding another 1 mL sequentially as if all inoculums were diluted to 104 M (3  104 CFU/mL). 100 lL of inoculum was applied to the LB-agar medium and dispersed. The coated and uncoated textile fabrics were wetted by sterile water to provide release of silver ions and then placed on these mediums and incubated at 37 °C for 12 h. The inhibition zone around cotton fabrics were photographed at the end of the incubation period. 3. Results and discussion 3.1. Synthesis of silver nanoparticles in PS-b-PAA reverse micelle cores The synthesized PS-b-PAA copolymer consists of a PS block with 105 monomer units and a PAA block with 50 monomer units. Several solvents with different polarity, such as toluene, THF, dioxane, DMF and diethyl ether, were tried to arrange spherical and monodisperse reverse micelles in solution as described before [33]. The best way to generate spherical reverse micelles was to heat the copolymer solution at 135 °C for 20 min after dissolved in toluene [33]. The spherical PS-b-PAA micelles are seen in Fig. 1. DLS results of micellar solution of PS-b-PAA in toluene are given in Fig. S1. After preparing the spherical reverse micelles, silver precursors were loaded in micellar solution with six different Ag:copolymer mol ratios (2:1, 3:1, 5:1, 10:1, 20:1 and 30:1) as seen Scheme 1. Silver ions attached the carboxylic groups in the micelle cores were

2.6. Antibacterial activity measurements of nanosilver coated textile samples The antibacterial activity of textile samples coated with nanosilver incorporated copolymer solution was investigated against facultative gram-negative E. coli (American Type Culture Collection, ATCC No.: 23282) and gram positive S. aureus (ATCC No.: 35696). Lactose broth (LB)-agar agar solid cultures were prepared after sterilization in an autoclave for 20 min at 120 °C. The solid culture was prepared by solving 7 g of agar agar and 9 g of LB in 500 mL of water and poured onto a plastic petri dish for gelation. The surface of textile samples was sterilized in a UV box for an hour. The disc diffusion method was used to investigate antibacterial activity of the

Fig. 1. TEM image of reverse micelles in PS(10912)-b-PAA(3638) solution in toluene prepared at 135 °C.

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L. Budama et al. / Chemical Engineering Journal 228 (2013) 489–495 Table 2 Average diameters of silver nanoparticles as determined in TEM images depending on silver:copolymer mol ratios.

Absorbance (a.u)

30:1

20:1

Before and after reduction of 5:1 Ag:PSPAA solution

10:1 5:1 3:1 2:1 300

350

400

450

500

550

600

650

700

λ / nm Fig. 2. UV/vis spectrum of silver nanoparticles depending on Ag:copolymer ratios. Inset: the pictures of silver incorporated PS-b-PAA copolymer solution after and before reduction.

Table 1 Surface plasmon resonances (SPR) of silver nanoparticles related to silver:copolymer ratio. Ag:copolymer ratios

Surface plasmon resonance peaks (nm)

(2:1) (3:1) (5:1) (10:1) (20:1) (30:1)

449 446 442 444 440 440

Average particle diameter (nm)

(2:1) (3:1) (5:1) (10:1) (20:1) (30:1)

22 ± 6 19 ± 8 18 ± 5 21 ± 7 22 ± 6 18 ± 5

Silver nanoparticle formation for all ratios was also confirmed by XRD measurements. The diffraction pattern overlaid for three higher silver:copolymer ratios is shown in Fig. 4. The diffraction peaks are consistent with the standard patterns of crystal silver (JCPDS file No. 04-0783) [37]. These peaks, indexed to the reflections of (1 1 1), (2 0 0), (2 2 0), (3 1 1) planes, indicate face centered-cubic silver (JCPDS file No. 04-0783) [37,38]. Silver nanoparticles have the same crystal structure for all ratios, as seen in Fig. 4. Furthermore, there is no extra peak in the diffraction pattern which suggests that only crystalline silver nanoparticles were formed. The mean diameter D of silver nanoparticles was also calculated using the Debye–Scherrer formula, [39]:

D¼

reduced to silver nanoparticles by N2H4 according to the following equation:

4Agþ þ N2 H4 ¡N2 þ 4AgðnpÞ þ 4Hþ

Ag:copolymer ratios

0:89k b cos h

ð3Þ

where k is the X-ray wavelength; b is the full peak width in radians at half-height and h is Bragg’s angle. The mean size of the nanoparticles is calculated as 20 ± 6, 16 ± 1 and 9 ± 1 for 10:1, 20:1 and 30:1 respectively. These values show quite good agreement with TEM results for the silver nanoparticles, especially for 10:1 and 20:1 ratios. The XRD size was estimated small for the 30:1 ratio which is most probably due to the broad diffraction peaks.

ð2Þ

Hydrazine reduces more homogenously without producing potentially hazardous chemicals. Formation of silver nanoparticles in the micellar cores was directly seen by a color change of the solution from colorless to brownish red. Nanoparticle formation was also confirmed by UV/vis spectra of solutions before and after. Fig. 2 shows that, for all ratios, the surface plasmon band is seen at 440–449 nm without any absorption shift. The values for all ratios are summarized in Table 1. It is well known that the absorption maximum of Ag nanoparticles depends on the particle size. Thus, the sizes of Ag nanoparticles for all ratios should be almost the same within the experimental limits, since there is no shift in absorption maxima obtained from the synthesized silver nanoparticles for all ratios. On the other hand, the absorbances increase regularly with increasing Ag:copolymer ratios which is due to the fact that the nanoparticle concentration is directly related to precursor ratio. Representative photos showing the color change after reduction in 5:1 silver:copolymer ratio can be seen in Fig. 2. To determine the size, size distribution and morphology of the Ag-nanoparticles, TEM measurements were performed. Fig. 3 shows the TEM images of silver nanoparticles depending on Ag:copolymer ratios. It is clear that silver nanoparticles are monodisperse and spherical. The calculated sizes of silver nanoparticles depending on different silver:copolymer ratios are tabulated in Table 2. The sizes of nanosilver particles are almost the same in experimental limits with 20 nm averaged size for all ratios which complement the spectrophotometric results. By combining the spectrophotometric and TEM measurements, it is obvious that nanoparticle size is independent of the Ag:copolymer ratio, but increase in the precursor amount probably affects the number of nanoparticles in the cores instead particle size.

3.2. Coating the nanosilver incorporated PS-PAA onto textile surface The PS-b-PAA micellar solution containing silver nanoparticles has been coated onto textile fabrics as described in Section 2.5. FTIR measurements with the KBr pellet technique were performed to understand if any covalent binding takes place between the copolymer and textile surface. The FTIR spectra are seen in Fig. S2. It was determined that covalent binding takes place between carboxylic acid groups of PAA chains and cellulosic hydroxyl groups on the textile surface as a result of our final heating process. All details for the bond formation were given in our previous paper and the Supplementary data [33]. Briefly, we proposed to compare the height ratios of the hydroxyl peaks to the reference peak at 900 cm1 in the FTIR spectra from the heated and unheated PS-b-PAA coated textile samples in order to investigate the existence of covalent binding. We found a decrease in the ratios of the hydroxyl peak to the reference peak after heating the PS-bPAA coated textile samples. The decrease in the ratio means that there is an absorbance decrease due to esterification of the hydroxyl group. Covalent bond formation leads to strong attachment of silver nanoparticles onto the textile surface and therefore their antibacterial durability should be higher than silver coated textile samples produced by other methods in the literature. 3.3. Antibacterial activity of the nanosilver coated textile samples The antibacterial activity of the textile fabrics coated with different silver ratios is seen in Tables 3 and 4 against E. coli and S. aureus, respectively. Tables 3 and 4 show both the change in antibacterial activity by increasing silver precursor ratio in the first

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Fig. 3. TEM images of silver nanoparticles synthesized in PS(10912)-b-PAA(3638) reverse micelle cores depending on Ag:copolymer ratios (scale bars = 200 nm).

111

Intensity a.u.

row, and the effect of coating with silver nanoparticles on antibacterial activity as well as the laundry performance of antibacterial activity for 30:1 ratio in the second row, against E. coli and S. aureus, respectively. The clear zones in the areas surrounding the surface of textile fabrics were observed, while there is no antibacterial activity around the bare fabrics, Tables 3 and 4. It is clear that the antibacterial activity is higher against E. coli than S. aureus for all ratios since there is a wider inhibition zone around the fabric. To test the permanency of antibacterial activity, the fabric was washed in an ordinary washing machine using ordinary detergent. It was observed to decrease the antibacterial activity against E. coli after the third washing for 10:1 and 20:1 ratios, whereas the fabric samples with 30:1 ratio still had antibacterial activity up to five washings. However, significant antibacterial activity was observed on the surface of fabric against S. aureus for all ratios even after 20 washings, Table 4. To be able to compare washing effects, the photos for only 30:1 ratios before and after washing are given in Tables 3 and 4. During the antibacterial studies, it was observed that the antibacterial activity was closely related to wetness of the coated fabrics because of their hydrophobic surface. Very low and/or no activity was observed when dry fabrics were tested, which suggests that the mechanism of antibac-

200

311

220

30:1 20:1 10:1 30

40

50

60

70

80

2θ (degree) Fig. 4. XRD pattern of silver nanoparticles synthesized in PS-b-PAA reverse micelle core with N2H4 for 10:1, 20:1 and 30:1 Ag:copolymer ratios.

terial activity should be based on silver ion release. Thus, silver ion release from the wet fabrics is higher than from dry fabrics. The reason for the different antibacterial activity of the textile surfaces that are produced, against E. coli and S. aureus is another issue to be investigated.

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Table 3 Antibacterial activity of silver nanoparticles against E. coli synthesized at different Ag:copolymer ratios (10:1, 20:1 and 30:1). First row: changes in antibacterial activity on increasing precursor ratio. Second row: the effect of coating with silver nanoparticle solution on antibacterial activity as well as the laundry performance of antibacterial activity for 30:1 ratio against E. coli.

10:1

20:1

30:1

Uncoated fabric

30:1

30:1 after 5 washing

Table 4 Antibacterial activity of silver nanoparticles against S. aureus synthesized at different Ag:copolymer ratios (10:1, 20:1 and 30:1). First row: changes in antibacterial activity caused by increasing precursor ratio. Second row: the effect of coating with silver nanoparticle solution on antibacterial activity as well as the laundry performance of antibacterial activity for 30:1 ratio against S. aureus.

10:1

20:1

30:1

Uncoated fabric

30:1

30:1 after 20 washing

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4. Conclusions Silver nanoparticles with mean size of 20 nm were synthesized in PS-b-PAA reverse micelle cores for different precursor ratios. It was found that nanoparticle size and morphology do not depend on the precursor ratio loaded in reverse micelle cores; but, the precursor amount might affect the number of nanoparticles in the cores. The silver nanoparticles have face-centered cubic crystal form for all ratios. The micellar solution containing silver nanoparticles was embedded onto textile surfaces to test for antibacterial activity. It was determined that the block copolymer containing nanosilver was bound covalently with surface groups on the surface of textile fabrics. In the antibacterial tests against gram-negative E. coli and gram-positive S. aureus, a clear inhibition zone was observed surrounding nanosilver coated textile fabrics, indicating that nanosilver coated textile fabrics showed significant antibacterial activity. The activity is maintained up to five washings against E. coli whereas it is up to 20 washings against S. aureus. As a result, it might be concluded that our new strategy provides both more stable silver nanoparticles on the surface of textile fabric and long term antibacterial activity due to a controlled release of silver ions the micellar cores to textile surface. Acknowledgements The authors would like to thank the Scientific and Technological Research Council of Turkey (TUBITAK) for supporting this work under the project of TBAG-108T806. The authors are grateful to Prof. Roy Johnston (Chemistry Department, University of Birmingham) for linguistic corrections and Prof. Dr. Ertug˘rul Arpaç (Akdeniz University) for his permission to use his laboratory facility. Medicine Faculty of Akdeniz University is acknowledged for TEM measurements. The authors also thank Hakan Er for invaluable technical assistance in TEM measurements. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.cej.2013.05.018. References [1] H.J. Jeon, S.C. Yi, S.G. Oh, Preparation and antibacterial effects of Ag–SiO2 thin films by sol–gel method, Biomaterials 24 (2003) 4921–4928. [2] S.H. Jeong, S.Y. Yeo, S.C. Yi, The effect of filler particle size on the antibacterial properties of compounded polymer/silver fibers, J. Mater. Sci. 40 (2005) 5407– 5411. [3] S.T. Dubas, P. Kumlangdudsana, P. Potiyaraj, Layer-by-layer deposition of antimicrobial silver nanoparticles on textile fibers, Colloids Surf. A 289 (2006) 105–109. [4] J.L. Clement, P.S. Jarrett, Antibacterial Silver, Met. Based Drugs 1 (1994) 467– 482. [5] N. Durán, P. Marcato, G.I.H. De Souza, O.L. Alves, E. Esposito, Antibacterial effect of silver nanoparticles produced by fungal process on textile fabrics and their effluent treatment, Biomed. Nanotechnol. 3 (2007) 203–208. [6] I. Perelshtein, G. Applerot, N. Perkas, G. Guibert, S. Mikhailov, A. Gedanken, Sonochemical coating of silver nanoparticles on textile fabrics (nylone, polyester and cotton) and their antibacterial activity, Nanotechnology 19 (2008) 1–6. [7] H.J. Lee, S.Y. Yeo, S.H. Jeong, Antibacterial effect of nanosized silver colloidal solution on textile fabrics, J. Mater. Sci. 38 (2003) 2199–2204. [8] D. Lee, R.E. Cohen, M.F. Rubner, Antibacterial properties of Ag nanoparticle loaded multilayers and formation of magnetically directed antibacterial microparticles, Langmuir 21 (2005) 9651–9659. [9] N.A. Ibrahim, A.A. Aly, M. Gouda, Enhancing the antibacterial properties of cotton fabric, J. Ind. Text. 37 (2008) 203–212.

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