PVA nanoparticles via photo- and chemical reduction methods for antibacterial study

Accepted Manuscript Title: Synthesis and characterization of Ago /PVA nanoparticles via photo- and chemical reduction methods for antibacterial study Author: Ibraheem Othman Ali PII: DOI: Reference:

S0927-7757(13)00643-2 http://dx.doi.org/doi:10.1016/j.colsurfa.2013.08.032 COLSUA 18603

To appear in:

Colloids and Surfaces A: Physicochem. Eng. Aspects

Received date: Revised date: Accepted date:

14-6-2013 11-8-2013 12-8-2013

Please cite this article as: I.O. Ali, Synthesis and characterization of Ago /PVA nanoparticles via photo- and chemical reduction methods for antibacterial study, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2013), http://dx.doi.org/10.1016/j.colsurfa.2013.08.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Synthesis and characterization of Ago/PVA nanoparticles via photo- and chemical reduction methods for antibacterial study Ibraheem Othman Ali Department of Chemistry, Faculty of Science, Al-Azhar University, Nasr City 11884, Cairo, Egypt

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Abstract

Silver nanoparticles were synthesized using two different reduction methods, namely,

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chemical reduction using hydrazine hydrate, and UV irradiation in the presence of polyvinyl alcohol (PVA) as a stabilizing agent. The successful incorporation of silver

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nanoparticles in a PVA matrix was confirmed by UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron

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microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy. XPS studies reveal that the Ag3d states convert from Ag2O to Ago by reduction with hydrazine and

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UV irradiation. TEM results indicate that silver nanoparticles of spherical shape were formed following reduction by UV irradiation and yielded an average diameter from 13

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to 26 nm. On the other hand, nanorods with an average length of 130 nm and diameter of

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25 nm were produced following reduction by hydrazine hydrate. Measurements of optical spectra show that the surface plasmon resonance was localized around 425 nm, and

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confirmed the growth of Ag nanoclusters when reduced by hydrazine. XRD demonstrated that the colloidal nanoparticles were restricted to only authentic silver. These nanoparticles show promising antibacterial properties towards E. Coli. Keywords: Ag nanoparticles; PVA; XRD; UV irradiation; antibacterial. * Corresponding author. Tel.: +202 22629357/8; fax: +202 22629356. E-mail address: [email protected] (I. Othman).

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1. Introduction Nanocomposites formed by silver nanoparticles (NPs) embedded in polymer matrices with tunable particle size, shape, population and dispersity may possess high catalytic activity [1], large non-linear optical effects [2] unusual electronic properties [3] and can

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be used for sensor fabrication [4] and sunlight control [5].

Many synthetic strategies have been employed in order to synthesize silver

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nanoparticles and/or nanocomposites including usage of strong reducing agents in water [6,7], organic solvents [8], wet chemical synthesis [9,10], hydrazine hydrate,

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formaldehyde and glucose [11–13] . Moreover, some additives, such as, sodium dodecyle sulfate [11], tri-sodium citrate [12, 13], hydrothermal [14], ultraviolet irradiation

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photoreduction [15] and electrochemical deposition [16] have been used as well for the synthesis of silver nanoparticles.

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The polymers can act as reducing and/or capping agents and thus prevent particle growth. Many polymers have been used as NPs supporting media, e.g., poly vinyl alcohol

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[17], poly acrylic acid [18], poly arylesters [19], poly acrylonitrile [20] and poly vinyl

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pyrrolidone [21]. The properties of the resulting materials were dependent upon the

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particle size distribution, filling fraction and the dispersion medium. Polyvinyl alcohol (PVA) possesses excellent film forming, emulsifying, and adhesive properties. Coating of particle surfaces with PVA prevents their agglomeration, giving rise to monodispersed particles. Fabrication and characterization of silver-polyvinyl alcohol nanocomposites have already been reported by Mbhele et al. [22]. Recent developments have shown improvements in sensitivity of optical sensors based on metal nanoparticles arrays and single nanoparticles [23]. Localized surface plasmon resonance sensors attempt to detect molecular binding events and changes in molecular conformation. Silver have been used for its antimicrobial properties since ancient times: Alexander the Great refused to drink water which had not been stored in silver vessels, and Paracelcus claimed the beneficial properties of silver towards health [24]. When penicillin was discovered and the era of the antibiotics began, the use of silver for its 2 Page 2 of 29

antimicrobial properties decreased [25]. Since biocide-resistant strains have emerged, the interest in using silver as an antimicrobial agent has risen again [26]. However, antimicrobial agents based on ionic silver (e.g., silver nitrate) have one major drawback: they are easily inactivated by complexation and precipitation and thus have a limited

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usefulness [27]. Zerovalent silver nanoparticles were considered as a valuable alternative for ionic silver. Due to their large specific surface-to-volume ratio, nanoparticles have

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different properties than bulk material [28,29]. It has been that silver nanoparticles are antimicrobial towards a broad spectrum of Gram-negative and Gram-positive bacteria

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[30,31]. Furthermore, silver nanoparticles show antifungal [32] and antiviral activity [33, 34]. Besides their antimicrobial properties, silver nanoparticles can be used for their

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catalytic, conductive, and optical features [35-37].

In this work, Ag/PVA nanocomposites were prepared using two reduction methods;

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chemical reduction with hydrazine hydrate as well as UV-photoirradiations. The structural properties of the nanocomposites produced well as the influence of interaction

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between polymer chains and synthesized Ag nanoparticles while using the reduction

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methods as well as in their absence were investigated. Transmission electron microscopy

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(TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), FTIR and UV–visible measurements were combined to characterise the obtained Ag nanocomposites and to elucidate their structure and their growth mechanism. Furthermore, the silver nanoparticles were tested for their antimicrobial properties. 2. Experimental 2.1. Materials

All chemicals and reagents used were of analytical grade. Distillated water was used throughout the work. Silver nitrate (Merck), poly vinyl alcohol (Fluka, PVA; MW 125,000), hydrazine hydrate (HH 88% solution, Kanto Chemical Co. Ltd.) were adopted for this work.

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2.1.1. Synthesis of Ag/PVA composites (without reduction) A simple one step reaction of AgNO3 with PVA molecules was used to prepare Ag nanoparticles embedded in PVA molecules. As described earlier [38,39], dispersed PVA molecules serve as an Ag+→Ag reductant as well as a template. No other additive was

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used either to promote the reaction or to seed a topotactic growth in small Ag-particles. Adding a freshly prepared cold aqueousAgNO3 solution (0.01 M, 10 mL) drop by drop

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into an aqueous PVA solution in a beaker (here PVA dispersed in water at 0.2 g in 25 mL, mass percent of AgNO3 to PVA at 1:10) over a magnetic stirring at 60ºC performs

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the Ag+→Ag reaction in templates of PVA molecules. The byproduct nitric acid is evaporated. This interaction can be schematically represented as shown in Scheme 1. The

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Ag-particles disperse with the aid of PVA molecules in situ forming nanocolloids. Average color turns gradually yellow from being achromatic in the beginning due to the

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high silver concentrations [39]. Later, the film was prepared by evaporating off the solvent at 80 ºC. After finishing the reaction and removal of the supernatant, samples of

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Ag/PVA-air.

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200–300 μm thickness are formed after drying at 80ºC; these samples are designated as

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2.1.2. Synthesis of Ag/PVA composites by reduction with hydrazine Aqueous solutions of silver nitrate and PVA were mixed with an initial mass percent of AgNO3 and PVA at 1:10 and well stirred. Dilute aqueous solutions of hydrazine hydrate were separately prepared and were introduced to the Ag/PVA solution in appropriate quantities (1:1 with respect to silver nitrate) by a syringe. When the first drop of silver nitrate and PVA/HH solution was added, the mixture turned yellow immediately. Continuing the injection, the solution became opaque gradually. On finishing the injection, the solution turned turbid with a gray color due to reduction of Ag+ to Ag0 [6, 40]. Stirring was continued under an inert atmosphere (N2 gas) at room temperature for another 30 min. The aliquots were then checked for their absorption spectra to ascertain the formation of silver nanoparticles. Later, 200–300 μm thickness samples were produced after drying at 80ºC; these samples are designated as Ag/PVA-HH. 4 Page 4 of 29

2.1.3. Synthesis of Ag/PVA composites using UV-photoirradiation Aqueous solutions of silver nitrate and PVA were mixed with an initial mass percent of AgNO3 and PVA as 1:10 and well stirred. The resulting solution mixture was then irradiated under UV-light, which was generated by a high-pressure mercury lamp (365

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nm and 100 W) for 30 min. The UV-irradiation was carried out in a quartz cell (28 mm diameter and 200 mm height). The color of the resulting solution changed to grey after 30

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min UV-irradiation indicating the appearance of Ag nanoparticles. Stirring was continued under inert atmosphere (N2 gas) at room temperature for another 30 min. The aliquots

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were then checked for their absorption spectra to ascertain the formation of silver nanoparticles. After finishing the reaction, an appropriate cut off filter was placed in the

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front of the reactor to remove the portion of the UV radiation. Samples of 200–300 μm thickness were produced after drying at 80ºC; these samples are designated as Ag/PVA-

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UV.

2.2. Anti-microbial screening

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The anti-bacterial activity of the synthesized compounds was tested against two Gram-

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negative bacteria: Escherichia coli NCTC 10416, Pseudomonas aeruginosa NCIB 9016,

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and two Gram-positive bacteria: Bacillus subtilis NCIB 3610, Staphylococcus aureus NCTC 7447, and fungi namely Candida albicans IMRU 3669 using nutrient agar medium.

The sterilized (autoclaved at 120°C for 30 min) medium (40-50°C) was incubated (1ml/100 ml of medium) with the suspension (105 cfu ml-1) of the micro-organism (matched to McFarland barium sulphate standard) and poured into a petridish to give a depth of 3-4 mm. The paper impregnated with the test compounds (µg/ml-1 in methanol) was placed on the solidified medium. The plates were pre-incubated for 1h at room temperature and incubated at 37°C for 24 and 48 hrs. for anti-bacterial and anti-fungal activities, respectively. Ampicillin (mg/disc) was used as standard for antibacterial and anti-fungal. The observed zone of inhibition is presented in (Table 1). 5 Page 5 of 29

2.2. Physico-chemical characterizations X-ray diffraction (XRD) data of the samples were measured at room temperature by using a Philips diffractometer (type PW 3710). The patterns were run with Ni-filtered copper radiation (λ = 1.5404 Å) at 30 kV and 10 mA with a scanning speed of 2θ =

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2.5º/min.

The Fourier transform infrared (FT-IR) spectra were recorded on a Perkin Elmer

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Spectrometer (RXI FT-IR) system, single beam with a resolution of 2 cm-1. The samples were ground with KBr (1:100) as a tablet and mounted to the sample holder in the cavity

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of the spectrometer. The measurements were recorded at room temperature in the region 4000-400 cm-1.

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The size, morphology, and surface topology of Ag-particles were studied with transmission electron microscope (TEM) using a JEOL-JEM 1010 electron microscopes

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films after ultramicrotoming with Leica EM UC6 ultramicrotome. X-ray photoelectron spectroscopy (XPS) measurements were obtained on a KRATOS-

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AXIS 165 instrument equipped with dual aluminum–magnesium anodes using MgKα

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radiation as the X-ray source at a power of 150 W (accelerating voltage 12 kV, current 6

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mA) in a vacuum of 8.0 × 10-8 mPa. The measured samples were prepared by dropping the concentrated Ag colloidal solution (derived from centrifugation and redispersion of the as-formed silver colloidal solution) on freshly cleaved HOPG and drying at room temperature.

The optical characterization of Ag colloids in water and the Ag-PVA nanocomposite films were carried out using a Perkin–Elmer Lambda 35 spectrophotometer, employed in the wavelength range of 190–900 nm with the resolution of 0.5 nm. 3. Results and discussion 3.1. XRD Fig. 1 displays the XRD patterns of Ag/PVA-air, Ag/PVA-HH and Ag/PVA-UV samples. The XRD for all samples exhibited a strong and a broad diffraction peak located at 2θ = 19.99° and a shoulder at 2θ = 22.85° assigned to the (1 1 0) reflection; correlated to 6 Page 6 of 29

intermolecular interference between PVA chains in the direction of the intermolecular hydrogen bonding [41], and to the reflection from the plane (2 0 0) respectively. Additionally, it was noted that the intensity of the diffraction peak at 2θ = 19.99° decreased suddenly when exposed to UV irradiation due to a decrease in the number of

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PVA chains as a result of degradation. This indicates that the crystalline phase of the PVA polymer is suppressed. The changes to the pattern implies a break in intermolecular

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hydrogen bonding due to the UV irradiation and thus affecting the original crystalline domains of PVA causing a free motion of its molecular chains.

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On the other hand, the appearance of peaks in the Ag/PVA-HH and Ag/PVA-UV samples at 2θ = 38, 44.06, 64.42 and 77.28 are generated after doping, which may be assigned to

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the face-centred-cubic (fcc) structure of embedded Ag metal particles corresponding to h k l parameters (1 1 1), (2 0 0) (2 2 0) and (311) respectively [39,42,43]. However, the

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Ag/PVA-air sample did not show any peaks related to Ago. In addition, there are no other significant diffraction peaks except those of nano-silver indicating that the as-prepared

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procedure a good way to obtain superfine pure silver. However, the Ag/PVA-air sample

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was uniformly dispersed with a narrow size distribution within the PVA matrix as will be

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corroborated by UV–vis spectroscopy and TEM measurements. 3.2. UV–Vis spectroscopy study

Fig. 2 shows the UV-vis spectra of the Ag/PVA-air, Ag/PVA-HH and Ag/PVA-UV samples. It can be seen that the pure PVA solution exhibits an absorption peak at 279 nm. The physical properties of PVA are dependent on its preparation method (hydrolysis, or partial hydrolysis of polyvinyl acetate). Thus the absorption band at 279 nm may be assigned to a →* transition. This transition is related to the carbonyl groups (C=O) associated with ethylene unsaturated bonds (=C=C=) of the type (–CH=CH–)CO. The existence of carbonyl functionalities is probably due to residual acetate groups remaining after the manufacture of PVA from the hydrolysis of polyvinyl acetate or oxidation during manufacturing and processing [44,45]. 7 Page 7 of 29

UV-vis spectra of the Ag/PVA-air sample showed a decrease of the absorbance band at 280 nm without any peaks related to a surface plasmon resonance. However, the Ag/PVA-UV sample prepared by UV irradiation indicates a turbid deep yellow colloidal solution and thus indicates broad absorption peaks at 514 and 383 nm due to the surface

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plasmon resonance of Ag NPs [46-48]. Similarly, photoluminescence studies on silver nanoparticles showed a characteristic [49] emission peak at 515 nm due to silver

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nanoparticles of dimension less than 10 nm. Accordingly, the 514 nm band is therefore assigned to a surface plasmon resonance band. The absorption pattern of the Ag/PVA-HH

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sample showed a broad band at 425 nm with a shoulder at 382 nm, indicating a broad particle size distribution. The position of the plasmon absorption band depends on

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particle size, aspect ratio and diameter of the nanorods or nanowires. The broad shape of the absorption band in this case is indicative of the presence of both spheres and rods as

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reported in Ag/PVA-HH sample and as will be confirmed by the TEM results. 3.3. X-ray photoelectron spectra

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XPS analysis of elemental Ag atoms was carried out to confirm the interaction between

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Ag and the polymeric stabilizer PVA. In general, the binding energy of Ag3d is very

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sensitive to the chemical environment around Ag, particularly to the electron-donating ability of polymeric ligands. Fig. 3 showed the XPS spectra of Ag/PVA-air, Ag/PVA-HH and Ag/PVA-UV samples. No peaks of other elements except Ag, O and C with a small peak of N1S in Ag/PVA-HH and Ag/PVA-UV samples are observed on the spectra, indicating the high purity of the product. Neat cotton showed XPS signals at binding energy (BE) of 285.08 and 532.08 eV which are attributed to C1s and O1s respectively. The curve-fitted XPS spectra of Ag3d peaks from Ag/PVA are shown in Fig. 4. XPS of Ag/PVA-air showed binding energy peaks at 367.68 and 376.78 eV for Ag3d5/2 and Ag 3d3/2, respectively. Silver nanoparticle formation as silver oxide (Ag2O) has been identified by the O 1s state centered at 532 eV at the initial stage of the oxidation [50-53]. These binding energy values are shifted to the lower energy region (366.06 eV for Ag 3d5/2 and 372.69 eV for Ag3d3/2, respectively) in Ag/PVA-HH and Ag/PVA-UV samples due 8 Page 8 of 29

to metallic silver [54-56]. The shift of binding energy indicates that electrons are inclined to transfer from the carbonyl groups of PVA to the Ag ions. This suggests that silver oxide present in the Ag/PVA-air sample is converted into metallic Ag when the solution of consistent with XRD analyses and UV-vis spectroscopy. 3.4. FT-IR spectra

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AgNO3/PVA was either reduced by hydrazine hydrate or by UV irradiation. This result is

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Fig. 5 displays the FT-IR spectra of Ag/PVA-air, Ag/PVA-HH, Ag/PVA-UV samples together with the pure PVA sample. The FT-IR spectrum of pure PVA showed a broad

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band at 3402 cm-1 corresponding to O-H stretching vibrations of the PVA hydroxyl groups. The band at 1718 cm-1 corresponds to the C=O stretching of the PVA acetate

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group. The backbone aliphatic C–H stretching vibrations result in bands at 2928 and 2910 cm-1. The strong absorption peak at 1094 cm-1 is assigned to the C–O in stretching mode

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for PVA and the band observed at 1332 cm-1 is assigned to the coupling of O-H vibrations with the C-H wagging vibrations appearing at 1442 cm-1 (CH-OH).The bands

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at 608 and 844 cm-1 indicate the out of plane vibrations of O-H and C-H in PVA.

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Change in the FT-IR spectrum of the Ag/PVA nanocomposite was observed for the

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band peaking at 1332 cm-1, in comparison with band at 1442 cm-1, which indicates the decoupling between O-H and C-H vibrations due to bonding interaction between O-H and silver nanoparticles [22]. Another change in the FT-IR spectrum of the Ag/PVA nanocomposite was observed for the band peaking at 1144 cm-1 which occurs as a result of a symmetric C–C stretching mode that corresponds to the crystalline regions in PVA [57]. A small decrease in the band intensity at 1144 cm-1 was observed upon incorporation of the Ag nanofiller in the PVA matrix indicating the decrease of the crystalline phase content. Some other smaller bands at 1740, 1400, 1250, 1100 and 1039 cm-1 were also observed for to nitrate impurities. 3.5. Transmission electron microscopy (TEM) analysis Fig. 6 shows the TEM images for Ag/PVA-air, Ag/PVA-HH and Ag/PVA-UV samples. The TEM images for Ag/PVA-air and Ag/PVA-UV show spherical Ag nanoparticles within 9 Page 9 of 29

the polymeric matrix. The nanoparticles were well separated from each other. The particle diameter of from the Ag/PVA-air sample was 21 nm, while the Ag/PVA-UV sample showed two different sizes: 26 nm and 13 nm. The particle size distribution is broad and hence the half width of the surface plasmon absorption band is relatively large. On the

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other hand the Ag-PVA-HH sample exhibited circular structures with diameters about 47 nm and silver nanorods with uniform diameters of 25nm, and length of 156nm. The

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coagulation of the embedded Ag nanoparticles is associated with the aggregation of the colloids onto the reaction vial walls [9].These results were in a good agreement with

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those obtained from the UV–vis absorption spectra and XRD investigations. 3.6. Biological activity

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All the synthesized compounds were tested against antibacterial activity in vitro using the paper disc diffusion technique [58-62]. The tested micro-organism strains were:

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(Gram-negative bacteria: Escherichia coli NCTC 10416, Pseudomonas aeruginosa NCIB 9016, and Gram-positive bacteria: Bacillus subtilis NCIB 3610, Staphylococcus aureus

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NCTC 7447); the results of antimicrobial activity values given in Table 1. From Table 1,

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it has been clarified that: (i) all the synthesized materials showed weak activity against

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the Gram positive strain except Ag/PVA-HH, which exhibited moderate activity against B. subtil. (ii) Also, against E. Coli bacteria strain, most of the synthesized composites lose their activity, except materials Ag/PVA-HH which showed weak activity. In contrary, Ag/PVA-HH showed a loss in activity against P. aeruginosa, but the remaining members exhibited weak activity

In the vitro antifungal studies, all synthesized composites were tested against Candida albicans IMRU 3669, Aspergillus and Risops, the antifungal and the activity is presented in Table 1. In general, all the synthesized composites displayed exerted inactivation in vitro antifungal activity against the tested organism. 3.6. The chemical adsorption mechanism Molecular structure of PVA is shown in formula (1): 10 Page 10 of 29

CH2

(1)

CH OH n

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It is well known that Ag+ has sp hybrid orbitals, which can accept lone pairs of electrons from the hydroxyl oxygen atom of PVA to form a coordination bond. In addition,

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because sp hybrid orbitals usually form a linear coordinative bond, Ag+ forms a complex with PVA. When drying this complex at 80ºC in air a yellowish film is obtained and may

CH2

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be by the following mechanism Eq. (2). CH

+ Ag+

CH

n

drying at 80ºC

Ag

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OH

(i)

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CH2

CH2

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2

n

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HO

(ii)

(2)

Ag2O

HO CH

n

Eq. (2) was confirmed by XPS revealing peaks at 367.68 and 376.78eV suggesting the formation of Ag(I) nanoparticles. That Ag+ will form oxides (Ag2O) after drying at 80C has been identified by the O 1s state centered at 532eV at the initial stage of the oxidation [50-53].

On the other hand, when hydrazine hydrate is added to the complex of Ag+/PVA, this will reduced to Ag0/PVA [6]. Finally, Ag0 was dried under flow N2 at 80 ºC to get a grey dry film according to eq. (3):

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CH2

CH

CH HO n

HO n

+ N2 H4 . H 2O

drying at 80 C

Ag0

Ag

+ N2 + n H2O

(3)

HO CH2

CH n

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HO CH2

Ag

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CH2

CH

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n

According to the previous report some organic compounds like ethylene glycol [63],

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2,7-dihydroxynapthalene (2,7-DHN) [64], poly(vinyl) alcohol (PVA) [65] can accelerate the reduction process by sharing their hydroxyl group in presence of some kind of

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irradiation process. In this work, when the Ag+/PVA complex is photoirradiation by UV for 30 min, the hydroxyl groups present in PVA produce hydrated electrons which act as

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reducing agents to reduce Ag+ to Ag(0), which continues to grow on the PVA chain.

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From spectroscopic studies it has been proved that photolysis of hydroxylic compounds

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generates hydrated electrons [66–68]. The UV-photoirradiation of Ag salt itself did not produce Ag nanoparticles in the absence of PVA. Therefore, we believe that PVA acts both as a reducing agent and a template for the growth of Ag nanoparticles. The proposed reaction mechanism involved in the synthesis of Ag/PVA nanocomposite coating is given by eq.4.

3PVA + 3AgNO3 + h  [PVA-PVA-PVA]+ NO3- + 3Ag + 2HNO3

(4)

These equations (3, 4) were confirmed by XPS in forming the peaks at 366.06 and 372.69 eV confirming the existence of Ag0. 4. Conclusions In this study the Ag/PVA nanocomposites were synthesized via hydrazine hydrate or UV irradiation followed by solvent evaporation. XRD and TEM measurements revealed that Ag nanoparticles are in the nanometer size domain (26 nm). The UV–Vis absorption 12 Page 12 of 29

spectra of the prepared materials showed surface plasmon absorption (at 382 and 425 nm) confirming the presence of silver nanoparticles. XPS revealed that the coordination of Ag+ ions within PVA was via Ag2O formation that eventually changed into Ag0 after reduction. FT-IR measurements indicated that an interaction between Ag nanoparticles

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and OH groups of PVA existed suggesting Ag2O formation initially. Reduction of PVA/Ag using UV is accompanied by oxidation in the PVA backbone producing more

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carbonyl groups from the oxidation of OH, this assumption is supported by an increase of the νC=O band at 1720 cm-1 in the PVA/AgUV spectrum. Ag/PVA nanoparticles can be

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used as antibacterial materials. References

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diffraction standard-international centre for diffraction data, Swarthmore, PA, [44] R. Jayasekara, I. Harding, I. Bowater, G.B.Y. Christie, G.T. Lonergan, Preparation, surface modification and characterisation of solution cast starch PVA blended films, Polym. Test. 23 (2004) 17. [45] A.M. Whelan, M.E. Brennan, W.J. Blau, J.M. Kelly, Enhanced Third-Order Optical Nonlinearity of Silver Nanoparticles with a Tunable Surface Plasmon Resonance, J. Nanosci. Nanotech. 4 (2004) 66. [46] T. Itakura, K. Torigoe, K. Esumi, Preparation and Characterization of Ultrafine Metal Particles in Ethanol by UV Irradiation Using a Photoinitiator, Langmuir 11 (1995) 4129

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Arylimino-3-

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[64] A. Henglein, Radiolytic Preparation of Ultrafine Colloidal Gold Particles in Aqueous Solution:  Optical Spectrum, Controlled Growth, and Some Chemical Reactions, Langmuir 15 (1999) 6738. [65] P. Aniali, P.Tarasankar, Silver nanoparticle aggregate formation by a photochemical method and its application to SERS analysis J. Raman Spectrosc. 30 (1999) 199. [66] S. Tomoo., N. Maeda, H. Ohkoshi, Y. Yonezawa, Photochemical Formation of Colloidal Silver in the Presence of Benzophenone, Bull. Chem. Soc. Jpn. 67 (1994) 3165. 19 Page 19 of 29

[67] S. Kundu, L. Peng, H. Liang, A New Route to Obtain High-Yield Multiple-Shaped Gold Nanoparticles in Aqueous Solution using Microwave Irradiation, Inorg. Chem. 47 (2008) 6344. Figure Captions

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Fig.1: XRD patterns of Ag/PVA prepared by reduction or without reduction.

Fig. 2: UV-vis spectra of pure PVA and Ag/PVA prepared by reduction or without

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reduction..

Fig. 3: XPS patterns of Ag/PVA prepared by reduction or without reduction.

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Fig.4. Curve-fitted XPS spectra of Ag/PVA prepared by reduction or without reduction.. Fig.5: FT-IR absorbance spectra of pure PVA and Ag/PVA prepared by reduction or

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without reduction.

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Fig. 6: TEM images of Ag/PVA prepared by reduction or without reduction.

20 Page 20 of 29

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Fig.1

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Intensity (arb. units)

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Ag-UV

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Ag-HH

4

20

Without red.

40 2θ/degree

60

80

21 Page 21 of 29

cr us

425

278

382

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Fig.2

an 514

Ag/PVA-UV

322

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d

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383 280 320

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279

Absorbance

258

Ag/PVA-HH

250 300

Ag/PVA-air

PVA 400

500

600

700

nm

22 Page 22 of 29

Fig. 3 C1s

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6.0 5.0

O1s

3.0 Ag-UV

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2.0

N1s

1.0

Ag-HH

N1s

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1.0

d

3.0

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0.0

C1s

O1s

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4.0

Account X 105

Ag3d

an

0.0

2.0

cr

4.0

Ag3d

5.0

C1s

4.0

3.0

2.0

O1s

Ag-air

Ag3d

1.0

0.0

1200

1000

800

600

400

200

0.0

Binding Energy (eV)

23 Page 23 of 29

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Fig.4 0.42

cr

366.09

0.4

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Ag/PVA-HH

366.72

0.34

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372.69

0.3

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0.26

Ag/PVA-UV

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Account X 103

0.36 0.38

an

0.38

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18.0

367.68 376.68

14.0

Ag/PVA-air

10.0 6.0

362 365

370

375

380

Binding Energy (eV)

24 Page 24 of 29

4000

3500

3000

2500

922

PVA

2000

1500 1094

1442

862 752 603

1058

Ag/PVA-air

1000

608

1332 944

1144

1232

476

1702 1652 1522 1462

3316 3878 3792

Ag/PVA-UV 522

766

958

1143

1458

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1720

cr

3404 3316 3174

3694

2908

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M

2865

1730

d

2924

te

3438

3840 3744

Absorbance

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856 718 604

1652

2872

484

1686 1524 1462 1424 1338 1148 1062 986

1742

2926

3838 3746 3618 3558 3482 3426

Ag/PVA-HH.

844

1718 1572

2352

2928

3402

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Fig. 5

500

Wavenumbers/cm-1

25

Page 25 of 29

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Fig. 6

26 Page 26 of 29

Table1: Anti-microbial activity of the synthesized Ag/PVA nanoparticles

Staphylococcus aurea

+

+

+

Gram positive

E.coli

+

_

_

Negative

B.subtil

++

+

+

cr

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Ag/PVA-HH Ag/PVA-air Ag/PVA-UV Gram stain

Psdoum

_

+

+

Negative

Candida alb.

_

_

_

Unicellular fungi

Asp.

+

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Organism

_

Filamentus fungi

Risop

_

_

_

Filamentus fungi

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M

_

Positive

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(-) Inactive (8 mm), weak activity (8-12 mm), moderate activity (12-15 mm), strong activity (>15).

27 Page 27 of 29

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cr

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382 425

an M d te Ac ce p

Organism

Ag/PVA Gram stain

Staphylococcus aurea

+

Gram positive

E.coli

+

Negative

B.subtil

++

Positive

Psdoum

_

Negative

Candida alb.

_

Unicellular fungi

Asp.

+

Filamentus fungi

Risop

_

Filamentus fungi

28 Page 28 of 29

Ac ce p

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M

an

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●Silver nanoparticles were synthesized using two different reduction methods. ●XPS analysis reveals that the Ag3d states convert from Ag2O to Ago by reduction with hydrazine and UV irradiation. ●The antibacterial properties of these nano particles show promising results on E. coli. cultures.

29 Page 29 of 29