Rapid green synthesis of silver nanoparticles and nanorods using Piper nigrum extract

Accepted Manuscript Rapid green synthesis of silver nanoparticles and nanorods using Piper nigrum extract Bandita Mohapatra, Sini Kuriakose, Satyabrata Mohapatra PII: DOI: Reference:

S0925-8388(15)00674-X http://dx.doi.org/10.1016/j.jallcom.2015.02.206 JALCOM 33601

To appear in:

Journal of Alloys and Compounds

Received Date: Revised Date: Accepted Date:

8 February 2015 27 February 2015 28 February 2015

Please cite this article as: B. Mohapatra, S. Kuriakose, S. Mohapatra, Rapid green synthesis of silver nanoparticles and nanorods using Piper nigrum extract, Journal of Alloys and Compounds (2015), doi: http://dx.doi.org/10.1016/ j.jallcom.2015.02.206

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Rapid green synthesis of silver nanoparticles and nanorods using Piper nigrum extract Bandita Mohapatra,1 Sini Kuriakose,1,2 and Satyabrata Mohapatra1,2* 1

Multifunctional Nanomaterials Laboratory, School of Basic and Applied Sciences, Guru

Gobind Singh Indraprastha University, Dwarka, New Delhi 110078, India 2

School of Basic and Applied Sciences, Guru Gobind Singh Indraprastha University,

Dwarka, New Delhi 110078, India

*Corresponding Author:

Dr. Satyabrata Mohapatra Assistant Professor, Nanoscience and Technology, School of Basic and Applied Sciences, Guru Gobind Singh Indraprastha University Dwarka, New Delhi 110078, India Phone: +91 11 25302414 E-mail: [email protected]

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Abstract

We report sun light driven rapid green synthesis of stable aqueous dispersions of silver nanoparticles and nanorods at room temperature using photoreduction of silver ions with

Piper nigrum extract. Silver nanoparticles were formed within 3 minutes of sun light irradiation following addition of Piper nigrum extract to the AgNO3 solution. The effects of AgNO3 concentration and irradiation time on the formation and plasmonic properties of biosynthesized

silver

nanoparticles

were

studied

using

UV-visible

absorption

spectroscopy. The morphology and structure of silver nanoparticles were well characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). The size of Ag nanoparticles increased with increase in irradiation time, leading to the formation of anisotropic nanostructures. Increasing the AgNO3 concentration resulted in the formation of Ag nanorods. UV-visible absorption studies revealed the presence of surface plasmon resonance (SPR) peaks which red shift and broaden with increasing AgNO3 concentration. We have demonstrated a facile, energy efficient and rapid green synthetic route to synthesize stable aqueous dispersions of silver nanoparticles and nanorods.

Keywords: Biosynthesis, Silver Nanoparticles, Nanorods, Surface plasmon resonance

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1. Introduction Metal nanoparticles have gained ever increasing interest due to their unique optical, magnetic and catalytic properties, which can be tuned by controlling their size, shape and chemical composition [1]. Noble metal nanoparticles, gold and silver nanoparticles in particular, exhibit strong localized surface plasmon resonance (LSPR) absorption of visible light and find applications in plasmonics [2], catalysis [3,4], surface enhanced Raman spectroscopy [5-7], biodiagnostics [8], nanophotonics [9] and optical biosensing [10].

Various physical and chemical methods have been used to synthesize gold and silver nanoparticles [11-28]. Wet chemical synthesis is a robust route to large scale synthesis of silver nanoparticles of tunable shape and size, through careful optimization of synthesis conditions. However, wet chemical methods use toxic chemicals which are hazardous for the environment and usually lead to toxic chemicals adsorbed on the surface of synthesized silver nanoparticles, making them unsuitable for biomedical applications because of the adverse side effects. On the other hand physical methods are very expensive and cumbersome for large scale production of nanoparticles. Due to this development of environmentally benign, energy efficient, facile and rapid green synthesis method avoiding toxic and hazardous chemicals has attracted significant research interests. Biosynthesis of silver nanoparticles using various plants or microorganisms is a promising method. Among the different biosynthesis methods, plant mediated synthesis of silver nanoparticles is relatively simple and inexpensive method as it avoids the cumbersome process of maintaining cell cultures needed for microorganisms [29]. Plant extracts containing biomolecules viz. vitamins, polysaccharides, proteins, amino acids, enzymes, and organic acids can act as both reducing as well as capping agent in the green synthesis of silver nanoparticles. Various groups have used different plant extracts

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and living plants for extra- and intra-cellular biosynthesis of silver nanoparticles. Leaf extracts of Mangifera indica [30], Murraya Koenigii [31], Azadirachta indica [32, 33],

Cinnamon camphora [34], Aloe vera [35], Emblica officinalis [36], Chenopodium album [37], Rosa rugosa [38], Cochlospermum gossypium [39], Citrus limon [40], Ocimum

sanctum [41], Capsicum annuum L. [42], seed extract of Jatropha curcas [43] and flower extract of Saraca indica [44] have been used for biosynthesis of silver nanoparticles. However, little progress has been made on the rapid biosynthesis of stable dispersions of Ag nanoparticles with controlled shape using plant extracts. Piper nigrum (black pepper) is a commonly used spice which provides natural nutritional and medicinal benefits due to its analgesic, antipyretic, anti-inflammatory and antimicrobial properties.

In this paper, we report biosynthesis of stable dispersions of silver nanoparticles and nanorods by a facile, energy efficient and rapid green synthetic method involving sun light driven photoreduction of silver ions with aqueous Piper nigrum extract. The effects of Ag concentration and irradiation time on the structural, optical and plasmonic properties of the biosynthesized Ag nanoparticles and nanorods have been investigated. We have demonstrated that photoreduction-assisted biosynthesis using Piper nigrum extract can be used to rapidly synthesize stable aqueous dispersions of silver nanoparticles and nanorods with strong plasmonic response.

2. Experimental Materials

Piper nigrum seeds and AgNO3 were used as the starting materials for green synthesis of Ag nanoparticles and nanorods. Dry Piper nigrum seeds were purchased from Dwarka, while AgNO3 was purchased from Merck, India. The chemical used was of analytical grade and was used as received without any purification. Double distilled water was used

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as the solvent in the experiments.

Synthesis of dispersions of silver nanoparticles

Piper nigrum seeds were crushed to powder form using pestle mortar and boiled in 100 mL double distilled water. The resulting solution was allowed to cool down and then filtered using filter paper followed by centrifugation at low speed. The supernatant was collected and diluted with double distilled water and then used as the reducing and capping agent for the synthesis of Ag nanoparticles. In a typical synthesis, different amounts of aqueous 10 mM AgNO3 solution were added into glass vials with aqueous solutions of the Piper nigrum extract at room temperature to reach different AgNO3 concentrations. The samples prepared with different AgNO3 concentrations of 0.625 mM, 1.25 mM and 2.5 mM are hereafter referred to as G3, G2 and G1, respectively. One set of samples were covered and kept as the reference samples. These samples were initially transparent but slowly changed into very faint yellowish color after 2 h. All the other solutions were irradiated with sun light at room temperature for different durations of time varying from 5 to 20 minutes. Within few (2-3) minutes following sun light exposure the color of these solutions changed from faint yellow to brownish color depending on the starting AgNO3 concentration. The color of these solutions changed to stronger brownish colors with increase in sun light irradiation time to 20 minutes. The schematic representation of the biosynthesis of silver nanoparticles is shown in Figure 1.

Characterization The morphology of the synthesized Ag nanoparticles coated onto chemically cleaned Si(100) substrates with native oxide was studied using Park Systems XE-70 atomic force microscope. The structural properties of the synthesized Ag nanoparticle dispersions coated on to Si substrates were studied by X-ray diffraction (XRD). The optical properties

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of as-synthesized Ag nanoparticle dispersions were characterized by UV-visible absorption spectroscopy. The absorption spectra were recorded in the wavelength range of 300 – 800 nm using HITACHI U3300 spectrophotometer with double distilled water as the reference medium.

3. Results and Discussion Figures 2(a), (c) and (e) show the AFM images of the biosynthesized silver nanoparticles in the samples G3, G2 and G1, respectively. The presence of Ag nanostructures can be seen in all the samples. AFM image of the sample G3, prepared with lowest Ag concentration of 0.625 mM, shows the presence of nearly spherical Ag nanoparticles in addition to few aggregates. Increasing the Ag concentration to 1.25 mM (sample G2) resulted in the formation of large number of Ag nanorods with aspect ratio up to 6 in addition to nearly spherical Ag nanoparticles. Further increase in Ag concentration to 2.5 mM (sample G1) led to the formation of a high density of nanorod like structures with reduced aspect ratio. It is interesting to see that these rod-like nanostructures are made up on Ag nanoparticles and are formed by oriented attachment of Ag nanoparticles. Figures 2(b), (d) and (f) show the 3D AFM images of the samples G3, G2 and G1, respectively. The size (width and length) distribution histograms of Ag nanostructures in the samples G3, G2 and G1 are shown in Figures 3 (a, b), (c, d) and (e, f), respectively. The average width, length and aspect ratio of Ag nanoparticles in sample G3 were estimated to be 23.8 nm, 29.4 nm and 1.22, respectively. The average width of Ag nanoparticles decreased to 17.2 nm, while the length of Ag nanoparticles varied from 10150 nm in case of sample G2. The aspect ratio of Ag nanoparticles varied from 1 to 6 in this sample. The average width and aspect ratio of Ag nanoparticles increased to 32.2 nm and 1.83, respectively as the AgNO3 concentration is increased to 2.5 mM. The

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formation of Ag nanorods of varying aspect ratio by controlling silver ion concentration in the solution is really interesting.

In order to understand the kinetics of formation of Ag nanoparticles and the effects of sun light irradiation time on the shape anisotropy of Ag nanoparticles and their plasmonic properties, sample G3 prepared with the lowest AgNO3 concentration of 0.625 mM was irradiated for different durations of time (0, 5, 10 and 20 minutes) and studied by AFM and UV-visible absorption spectroscopy. In Figure 4 we show the AFM images of the sample G3 before and after sun light irradiation for 10 minutes and 20 minutes. The corresponding 3D AFM images are also shown in Figures 4 (b), (d) and (f). The presence of small Ag nanoparticles can be clearly seen in the unirradiated sample. Sun light irradiation for 10 minutes resulted in an appreciable increase in number density and size of Ag nanoparticles. Further increase in the irradiation time led to growth as well as formation of larger aggregates of Ag nanoparticles. The corresponding size (width, length) distribution histograms of Ag nanoparticles in these samples are shown in Figure 5. The average width of Ag nanoparticles increased from 18.7 to 32.6 nm, while the average aspect ratio slightly increased from 1.15 to 1.19 with increase in irradiation time. Figure 6 shows the XRD pattern from sample G3. The presence of distinct peaks at 38.11o and 44.34o corresponding to the (111) and (200) reflections, respectively confirms the FCC structure (JCPDS card no. 04-0783) of biosynthesized Ag nanoparticles.

Figure 7 (a) shows the optical absorption spectra of as-synthesized samples G3, G2 and G1 prepared with varying AgNO3 concentrations of 0.625, 1.25 and 2.5 mM, respectively and irradiated with sun light for 5 minutes. The presence of an asymmetric broad peak around 453 nm can be clearly seen in these samples which correspond to the characteristic SPR absorption of Ag nanoparticles. Increase in AgNO3 concentration

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resulted in a small red shift (453 – 458 nm) and broadening of the SPR peak. The optical images of vials with these samples are shown in Figure 7 (b). It can be seen that the color of the Ag nanoparticle dispersion changes from light yellow to brownish color as the AgNO3 concentration is increased. The yellowish color also confirms the presence of Ag nanoparticles in the synthesized dispersions. In order to understand the evolution of plasmonic response of Ag nanoparticles with change in AgNO3 concentration, the absorption spectra were background subtracted (Figure 8(a)) and the SPR peaks were deconvoluted into two peaks (peak 1 and peak 2). The deconvoluted absorption spectra for samples G1, G2 and G3 are shown in Figure 8 (b), (c) and (d), respectively. The presence of two distinct peaks also confirms the shape anisotropy clearly seen in the AFM images (Figure 2). It is well known that Ag nanorods exhibit two distinct SPR absorption bands. The variation of the SPR peak positions with AgNO3 concentration is shown in Figure 8 (e). Peak 1 red shifted from 396 nm to 408 nm, while the Peak 2 showed a red shift of 24 nm (from 474 to 498 nm) as AgNO3 concentration is increased from 0.625 to 2.5 mM. The FWHM of Peak 1 showed a regular increase, while that of Peak 2 initially increased and then showed a decrease with increase in AgNO3 concentration (as shown in Figure 8 (f)).

The optical absorption spectra revealing the temporal evolution of the plasmonic response of Ag nanoparticles in sample G3 upon sun light irradiation for different durations of time are shown in Figure 9 (a). The unirradiated sample shows a broad SPR peak at 450 nm, confirming the presence of Ag nanoparticles. It can be clearly seen that sun light irradiation for 5 minutes resulted in a small red shift of SPR peak to 453 nm along with significant increase in the intensity while it showed a small decrease in intensity as the irradiation time is increased to 20 minutes. From the AFM images it is clear that the size of Ag nanoparticles increases from 18.7 to 32.6 nm and the Ag

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nanoparticles exhibit increased aggregation with increase in irradiation time (Figure 4). The shape anisotropy does not show appreciable change with time. Hence, the observed evolution of plasmonic response of Ag nanoparticles with irradiation time is mainly due to the growth in size and increased number density of Ag nanoparticles, which aggregate for longer irradiation time.

The formation of Ag nanoparticles and nanorods by Piper nigrum extract assisted photoreduction of silver ions can be understood as follows. Piper nigrum extract contains different biomolecules such as vitamins, polysaccharides, amino acids, alkaloids, and proteins [45]. Piperine is the main alkaloidal constituent of Piper nigrum leading to analgesic, antipyretic, anti-inflammatory activities. The biomolecules present in Piper

nigrum extract act as reducing agents, capping agents and scaffolds leading to the formation of Ag nanoparticles. Sun light assisted photoreduction favors highly enhanced formation and growth of Ag nanoparticles, which combine by oriented attachment resulting in the formation of Ag nanorods at higher AgNO3 concentrations. The biomolecules act as efficient capping agents leading to the highly stable aqueous dispersions of Ag nanoparticles and nanorods. We have demonstrated a simple, energy efficient and environmentally benign route to rapid biosynthesis of stable dispersions of high concentration of biocompatible Ag nanoparticles and nanorods with strong plasmonic response enabling diverse applications in nanobiotechnology.

4. Conclusions We have successfully synthesized highly stable aqueous dispersions of silver nanoparticles in the size range of 10-60 nm and silver nanorods with aspect ratio varying up to 6 by a facile, rapid, inexpensive and ecofriendly method involving photoreduction of silver ions with aqueous Piper nigrum extract. The effects of AgNO3 concentration and

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sun light irradiation time on the formation of Ag nanostructures and the evolution of plasmonic response of Ag nanoparticle dispersions were investigated. Increase in AgNO3 concentration resulted in the formation of Ag nanorods with aspect ratio up to 6. We have demonstrated a simple and energy efficient way to rapid biosynthesis of highly stable dispersions of Ag nanorods and nanoparticles with strong plasmonic response for diverse applications in nanobiotechnology.

Acknowledgement SM is grateful to Department of Science and Technology (DST), New Delhi for providing AFM and XRD facilities under Nano Mission program. JS is thankful to UGC, New Delhi for providing Maulana Azad National Fellowship. SK is thankful to Guru Gobind Singh Indraprastha University, New Delhi for providing IPR Fellowship.

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List of Figures and Figure Captions

Figure 1: Schematic representation of biosynthesis of silver nanoparticles using Piper

nigrum extract.

Figure 2: AFM images of as-synthesized Ag nanoparticles in 5 minutes sun light irradiated samples (a) G3, (c) G2 and (e) G1, prepared with different AgNO3 concentrations, (b, d, f) corresponding 3D AFM images the samples.

Figure 3: Size (width, length) distribution histograms of Ag nanoparticles in 5 minutes sun light irradiated samples (a, b) G3, (c, d) G2 and (e, f) G1, prepared with different AgNO3 concentrations.

Figure 4: AFM images of Ag nanoparticles in as-synthesized sample G3 (a) unirradiated and irradiated with sun light for (c) 10 minutes and (e) 20 minutes. (b, d, f) corresponding 3D AFM images of Ag nanoparticles in biosynthesized samples.

Figure 5: Size distributions of Ag nanoparticles in as-synthesized sample G3 (a, b) unirradiated, and irradiated with sun light for (c, d) 10 minutes and (e, f) 20 minutes.

Figure 6: Typical XRD pattern of synthesized Ag nanoparticles in sample G3.

Figure 7: (a) Optical absorption spectra of samples G3, G2 and G1, prepared with different AgNO3 concentrations, (b) Photographs of vials with the above Ag nanoparticle samples G3, G2 and G1.

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Figure 8: Deconvoluted optical absorption spectra of samples (b) G3, (c) G2 and (d) G1, after background subtraction, Variation of (e) SPR peak positions, and (f) FWHM of the deconvoluted peaks (peak 1 and peak 2) with AgNO3 concentration.

Figure 9: Optical absorption spectra of sample G3 (a) unirradiated, and irradiated with sun light for different durations of time, (b) Photographs of vials with the above Ag nanoparticle dispersions.

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Figure 1

Powdered, boiled in double distilled water

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Highlights

• • • •

Silver nanorods were synthesized by photoreduction using Piper nigrum extract. The morphological and structural properties were studied by XRD and AFM. Silver nanoparticles were formed at lower AgNO3 concentration. Increase in AgNO3 concentration resulted in formation of silver nanorods.

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