Gold and silver nano particles

Accepted Manuscript Combined DFT/FTIR structural studies of monodispersed PVP/Gold and silver nano particles A.M. Abdelghany, M.Sh. Mekhail, E.M. Abdelrazek, M.M. Aboud PII:

S0925-8388(15)30037-2

DOI:

10.1016/j.jallcom.2015.05.262

Reference:

JALCOM 34531

To appear in:

Journal of Alloys and Compounds

Received Date: 9 January 2015 Revised Date:

13 May 2015

Accepted Date: 24 May 2015

Please cite this article as: A.M. Abdelghany, M.S. Mekhail, E.M. Abdelrazek, M.M. Aboud, Combined DFT/FTIR structural studies of monodispersed PVP/Gold and silver nano particles, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.05.262. 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.

ACCEPTED MANUSCRIPT Combined DFT/FTIR structural studies of monodispersed PVP/Gold and silver nano particles

A.M. Abdelghany1, M.Sh. Mekhail2, E.M. Abdelrazek2, M.M. Aboud2 Spectroscopy department, Physics Division, National Research Center, Dokki, 12311, Cairo, Egypt 2

Physics department, Faculty of Science, Mansoura University, 35516, Mansoura, Egypt

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Abstract

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Nano-particles of two Nobel metals, namely, (silver and gold) were prepared and used as a dopant in polyvinyl pyrrolidone (PVP) polymeric matrix by the

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simple casting technique. Prepared samples examined theoretically using density functional theory (DFT) and experimentally with Fourier transform infrared (FTIR) and (UV/Vis) spectroscopy. DFT calculations and FTIR experimental results shows the persistence of the characteristic bands of polymeric network in their positions while pyrrolidinone adsorbed both silver and gold colloid surfaces

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preferably via the non-bonding electrons of the carbonyl group. UV/Vis experimental data was employed to calculate the optical energy gap of pristine and doped samples. Optical band gap and particle size were calculated and is in

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agreement with the results obtained from TEM data. Transmission electron microscopy shows that the prepared silver and gold nanoparticles were mono

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dispersed within the polymeric matrix.

Keywords

PVP; Gold and Silver nanoparticles; DFT; band structure; FTIR; UV/Vis

Corresponding author: E-mail : [email protected] Tel. : +2 01221133152 Fax : +2 02 33370931 1

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1. Introduction

Nowadays, research on composite materials made of polymer and Nanometric metal particles has received considerable attention because of the unique properties. They exhibit as a result of the reduced filler dimension quantum size effects may arise and influence all physical properties of such materials [1]. The capping of

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nanoparticles with polymers such as polyvinylpyrrolidone (PVP) has identified as a viable method for producing nanoparticles of tunable morphologies and optical properties [2]. The growth of silver nanoparticles correlated with the surface interactions with PVP [3, 4]. Since PVP polymer is a large molecule, a need for a

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simplified mechanism for investigation the process of interaction between PVP and Nanometals. Wang et al. [5] has studied the interaction of silver colloids with PVP

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but further computational studies have never been reported thus far. By observing the interaction of pyrrolidinone and N-methyl-2-pyrrolidinone (monomers of PVP) with silver and gold nanoparticles, we hope to clarify the mechanism for the interaction of these metal nanoparticles with PVP. Neerish Revaprasadu et al [6] used

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Surface enhanced Raman spectroscopy (SERS) and density functional theory (DFT) for understanding the regioselective adsorption of pyrrolidinone on the surface of silver and gold colloids. The first investigated interaction is between the pyrrolidone group of PVP with silver and gold ions which followed by the reduction process and

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finally the growth of the nanoparticle, which predominantly depends on the ratio of the metal ion-to-PVP in solution.

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A combination of experimental results (FTIR) and (UV/Vis) and theoretical results obtained using Density Functional Theory (DFT) was used for understanding the complex interaction between synthesized nanoparticles and polymer chain. The aim of the present work is to prepare a new class of polymeric materials doped with nobel metal nanoparticles with unique optical properties and to correlate experimental (FTIR) results with theoretical approach (DFT) to understand the nature of interaction between polymeric material and dopant nanoparticles and extended to study the change in its physical parameters. 2

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2. Materials and method The studied PVP films filled with silver and gold were prepared by using casting method. A prepared Green–grey silver and deep red gold colloidal solution obtained from silver and gold nanoparticles respectively, (1mL) of silver and gold each mixed

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with aqueous solution of PVP (0.5gm of PVP dissolved in 50 mL of distilled water). Obtained solutions were casted to a glass Petri dish and dried in oven at T= 50 oC for 2 days to remove the solvent traces. After drying, the films peeled from Petri dishes and kept in vacuum desiccators until used in spectroscopic analysis. X-ray diffraction

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scans were obtained using PANalytical X‘Pert PRO XRD system using Cu Kα radiation (where, λ = 1.540 Å, the tube operated at 30 kV, the Bragg’s angle (2) in

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the range of (5–60). FT-IR absorption spectra carried out using the single beam Fourier transform-infrared spectrometer (Nicolet iS10, USA) in the spectral range of (500 – 4000 cm-1). UV/Vis absorption spectra were measured in the wavelength region of (190 – 900 nm) using spectrophotometer (UNICAM UV/Vis Spectrometer,

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Engla0nd) to study the change in structures of the samples due to adding the fillers and their optical properties. Transmission electron microscope (TEM), (JEOL-JEM2100, Japan) was used to study the size, shape and distribution of the nanoparticles

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within the polymeric matrix during preparation process.

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3. DFT calculations and models All calculations were carried out with Gaussian 03 programs [7] within the density functional theory (DFT) framework. Density functional calculations have been applied in many different studies [8–12], with a reasonable measure of agreement between the theoretical and experimental data. In this study the molecule–metal system structures of silver and gold were optimized using the Becke’s three parameter hybrid functional [13] with the Lee et al. [14] (B3LYP) correlation functional employed with the electron core potential basis set LANL2DZ developed by Hay and Wadt [15]. For Ag and Au the LANL2DZ set the electron core potential 3

ACCEPTED MANUSCRIPT simulates the 28 and 60 of their total 47 (Ag) and 79 (Au) electrons, respectively. For

both heavy elements, the remaining 19 electrons are described by all electron basis sets consisting of a (8s6p4d) set of primitive Gaussian type functions contracted to the [3s3p2d]. For C, N and O the LANL2DZ basis consists of a (10s5p) set contracted to the [3s2p] set, while, for H a (4s) set contracted to the [2s] basis set is

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used. Each stationary point has been characterized by harmonic frequency calculations at the same level of theory (B3LYP/LANL2DZ) and the FTIR have been identified.

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4. Results and discussion

4. 1.Expermental Fourier transform infrared analysis

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Fig. 1 shows FTIR absorbance spectra of pure PVP with Au/PVP and pure PVP with Ag/PVP Nano-composite films respectively recorded at room temperature in the region (4000–500 cm-1). The spectra exhibited characteristic bands of stretching and bending vibrations of the functional groups formed in the prepared films. FT-IR

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absorption bands positions and their assignment was listed in Table 1.

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Absorbance

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PVP PVP/Au PVP/Ag

4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber (cm )

Fig.1.FTIR absorption spectra of pure and doped PVP films.

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ACCEPTED MANUSCRIPT FTIR spectra shows a band about 1017 cm-1 assigned to CH2 rocking of PVP [16].

While a peak about 1225 cm-1 referred to twisting of CH2 of PVP [16].A band at about 3450 cm-1 [17]assigned to the stretching vibration of hydroxyl group (OH) of PVP which become boarder after adding silver or gold colloids. A bending vibration at 1629 cm-1 [18] of hydroxyl group confirms the presence of water. The band

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corresponding to CH2 asymmetric stretching vibration occurs at about 2950 cm-1and this band become broader after adding silver or gold colloids [19]. The band at 1446 cm-1is assigned to CH2 scissoring vibrations and its intensity increase with adding

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silver or gold.

Table (1) FTIR band assignment of different vibrational modes for prepared samples

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Band Assignments CH2 rock CH2 twist C-N stretching or C-O stretching CH2 scissor C=O CO2 CH2 asymmetric stretching O-H stretching

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Wavenumber (cm-1) 1017 1225 1286 1488-1446 1655 1629 2950 3450

Ref [30] [30] [24] [30] [19-22] [17] [18] [16]

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FTIR absorption spectra of PVP/Ag and PVP/Au composite materials show a shift in some in some vibrational modes and change in intensities of other bands compared

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with pristine polymeric films attributed to the complexation between polymeric matrix and nano particles. Furthermore, the vibrational band at about 1655 cm-1 corresponds to C=O stretching of PVP [20–23]. The present double bonds represent suitable sites for polarons and/or bipolarons [24].

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ACCEPTED MANUSCRIPT 4.2. Theoretical Fourier transform infrared analysis

DFT used for studying theoretically complex interaction between PVP and Silver and Gold nano colloids. Fig. 2 show possible probabilities of interaction between PVP with metal nanoparticles. The interaction between PVP and metal nanoparticles

nanoparticles by; a) Nonbonding electrons of carbonyl group. b) Adsorption of pyrrolidone via Nitrogen atom.

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c) Adsorption via both carbonyl group and Nitrogen atom.

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may carried by the adsorption of pyrrolidone ring on the surface of metal

Fig. 2 Possible modes of interaction between PVP and Silver and Gold nanoparticles at room temperature

Figs. 3, 4 shows optimized structure of four possible modes of interaction between PVP/Au and PVP/Ag with the obtained experimental and theoretical FTIR obtained from optimized structure of possible modes of interaction respectively.

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(b)

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(a)

(d)

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(c)

Theortical PVP+Au

(d)

(c)

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(b)

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Absorbance (arb.units)

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(a)

2

Exp.

0 4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber(Cm )

Fig. 3. Optimized structure of four possible interaction modes of PVP/Au with experimental and theoretical FTIR absorption spectra.

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(b)

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Theortical PVP +Ag

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Absorbance(arb.units)

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(d)

4

(a)

(a)

2

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0 4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumber(cm )

Fig. 4 Optimized structure of four possible interaction modes of PVP/Ag with experimental and theoretical FTIR absorption spectra. 8

ACCEPTED MANUSCRIPT Theoretical calculations show that silver and gold nanoparticle was stabilized by

chemical interaction with oxygen atom of pyrrolidone ring, while other suggested modes of interactions show low agreement with experimental data.

4. 3.UV-Vis absorption and optical properties calculations

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Fig. 5 shows UV/Vis absorption spectra of pure PVP and PVP/Au polymeric film. The absorption band observed at about 234 nm attributed to π→π* transition results from the presence of carbonyl groups (C=O) [25] supported by FTIR vibrational band at about 1655 cm

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. The UV/Vis spectrum of PVP/Au film figure 5-a shows

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absorption peak at 528 nm attributed to the surface Plasmon resonance phenomenon

Absorbance

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Absorbance

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of free electrons in the conduction bands of Au nanoparticles.

PVP/Ag

PVP/Au

200

300

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Pure PVP

400

500

600

700

800

Pure PVP

200

300

400

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Wavelenght (nm)

500

600

700

800

Wavelenght (nm)

(a)

(b)

Fig.5 UV/Vis absorption spectra of PVP and samples that filled with (a) Gold and (b) silver nanoparticles

UV/Vis absorption spectra of pure PVP and PVP/Ag polymeric film figure 5-b shows absorption peak at 441 nm attributed to the surface plasmon resonance phenomenon of free electrons in the conduction bands of Ag nanoparticles. [26]

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ACCEPTED MANUSCRIPT The direct method to investigate the band structure of materials by studying its

absorption spectra. Fundamental absorption refers to band-to-band or excitation transition. The fundamental absorption shows a sudden rise in absorption, known as absorption edge, which can be used to determine the optical band gap (Eg = ℎ/) where h is Planck’s constant. Absorption is expressed in terms of a coefficient

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 (absorption coefficient), the absorption coefficient  was calculated from the absorbance (A). Where  = 2.303 / and d is the sample thickness. Absorption follows [27]: ℎ = ℎ −  



For ℎ >  For ℎ < 

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ℎ = 0

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coefficient  for amorphous materials related to the energy of the incident photon as

Where  is the optical energy gap, ℎ is the energy of incident photon , is a constant and r is the exponent that takes the value 1, 2, 3, 1/2 and 3/2, depending on the nature of the electron transitions responsible for the optical absorption. The exponent r takes the value of 1/2 in case of direct electronic transition and 2 in

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case of indirect electronic transition. Davis and Mott [28, 29] reported that near fundamental band edge, both direct and indirect transitions occurs and can be observed by plotting (ℎ)2 and (ℎ)1/2 versus photon energy (ℎ).

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Fig.6 a and b shows the Davis and Mott plot of the (ℎ)2 and (ℎ) 1/2 as a

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function of photon energy (ℎ) for pure PVP, PVP/Ag and PVP/Au films.

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1.4x10

8

1.2x10

8

1.0x10

8

8.0x10

7

6.0x10

7

4.0x10

7

2.0x10

7

PVP PVP/Ag PVP/Au

120

100

80

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2 -1 2 ( α hν ) (cm eV)

1.6x10

140

PVP PVP/Ag PVP/Au

1/2 -1 1/2 ( α hν ) (cm eV)

1.8x10

60

20

0.0

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3

4

5

h ν (eV)

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-2.0x10

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0

3

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4

5

6

hν (eV)

(b)

Fig.6 a and b Davis and Mott plot of the ()2 and () 1/2as a function of photon energy

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() for pure PVP, PVP/Ag and PVP/Au films.

4. 4. X-Ray Diffraction Analysis (XRD)

X-ray pattern of pure PVP shows Two typical peaks at 2θ=10.9° and 21.4° were

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observed for PVP. [30]

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Fig.7a represent X-ray pattern of pure PVP and PVP/Ag, a peaks at 2θ values 39°and 43.4° corresponds to (111) and (200) planes of silver, respectively. Thus, the XRD spectrum confirmed the crystalline structure of silver nanoparticles. All the peaks in XRD pattern can be readily indexed to a face-centered cubic structure of silver. [31] The average crystalline size of Ag nanoparticle was estimated at 2θ values 39°and 43.4°using Debye–Scherrer diffraction formula [32] were 5.2 and 9.97nm, respectively. [32] =

 

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ACCEPTED MANUSCRIPT Where k = 0.9,  is X-ray wavelength and β is the half-width of the diffraction

While Fig.7b represent X-ray pattern of pure PVP and PVP/Au, there was a noticeable change in the intensity of XRD peaks after doping Gold nanoparticles, the intensity of

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peaks at 2θ = 10.9°,2θ = 21.4°was decreased after adding Au nanoparticles and no characteristic peak appear for Gold nanoparticles which refer to completely interaction

[200]

PVP/Ag

Pure PVP

20

30

40

2θ (degree)

(a)

50

60

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Intensity (a.u.)

Intensity (arb.unit)

[111]

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between PVP and Gold nanoparticles.

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PVP/Au

Pure PVP

20

30

40

50

60

2θ (degree)

(b)

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Fig.7a and b: X-ray diffraction of pure PVP and samples that filled with (a) Silver and (b) Gold nanoparticles

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4.5 Transmission electron microscopy (TEM) Fig.8a and b Show TEM images of the distribution and the morphology with the particle size histogram of Gold and silver NPs dispersed within PVP polymer respectively.

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ACCEPTED MANUSCRIPT It is clear from the histogram, gold and silver nanoparticles exhibit nearly spherical

shape with a particle distribution shown in the histogram Figure 8 (a,b). It should be taken into account that shape and size of the nanoparticles doesn't effect on the DFT

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calculation regime.

(a)

(b)

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Fig.8a and b: TEM image of the distribution and the morphology with the particle size

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histogram of gold (a) and silver (b) and NPs.

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Conclusions

Polyvinyl pyrrolidone (PVP) polymeric matrix doped with nano-particles of two nobel metals, namely, (silver and gold) were prepared via simple casting technique. Combined DFT – FTIR data were used for investigation of the type of

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interaction. Both DFT calculations and FTIR experimental results shows the persistence of the characteristic bands of polymeric network in their positions while pyrrolidinone adsorbed both silver and gold colloid surfaces preferably via the non-bonding electrons of the carbonyl group. UV/Vis absorbance spectra were

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employed to calculate the optical energy gap of pristine and doped samples. Optical band gap and particle size were calculated and is in agreement with the

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results obtained from TEM data. Transmission electron microscopy shows that the

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prepared silver and gold nanoparticles were dispersed within the polymeric matrix.

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ACCEPTED MANUSCRIPT Highlights

Nano-particles of two Nobel metals, namely, (silver and gold) were prepared. Polyvinyl pyrrolidone polymeric matrix doped with nobel metal were prepared via

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casting technique.

Prepared samples investigated via combined (DFT) and (FTIR).

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Transmission electron microscopy shows monodispersed nanoparticles.

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