Green Biosynthesis of Silver Nanoparticles using Aqueous Urginea Indica Bulbs

Mechanics, Materials Science & Engineering, May 2017 – ISSN 2412-5954

Green Biosynthesis of Silver Nanoparticles using Aqueous Urginea Indica Bulbs Extract and Their Catalytic Activity Towards 4-NP1 R. Manigandan1, S. Praveen kumar1, S. Munusamy1, T. Dhanasekaran1, A. Padmanaban1, K. Giribabu1, R. Suresh2, V. Narayanan1,a 1 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India 2 – SRM University, Bharathi Salai, Ramapuram, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.64.70.791 provided by Seo4U.link Keywords: Urginea indica, Ag0 Nps, 4-nitrophenol, aqueous, catalysts, reduction.

ABSTRACT. A simple, green method is described for the synthesis of silver nanoparticles by reaction of the aqueous solution of Urginea indica (U. I.) bulbs extract and AgNO3. In this process, colloidal metallic silver nanoparticles (Ag0 Nps) were of a particular interest due to its haunting physicochemical properties. The formation of Ag0 Nps nanoparticles was proved by the significant color change during the preparation. The formation process and color variations by the impact of pH and concentration of extract were analyzed by UV-VIS spectrophotometer. Functional groups present in the extract and Ag0 NPs was characterized by FT-IR spectroscopy. The crystal structure, lattice parameter and crystallite size of synthesized silver NPs was confirmed by X-ray diffraction technique. The X-ray diffraction analysis of the sample showed the formation of nanoparticles with cubic silver structure. Elemental composition and morphology of the metallic silver was widely investigated by FESEM-EDX.

Introduction. The unique physicochemical properties of nanomaterials are attractive for use in a variety of technologies due to the factors such as conductivity, magnetic property and optical sensitivity by the characteristics such as small size, shape, surface structure, chemical composition [1]. Modifying the properties of nanoscale materials generally involves control over the physicochemical features of the material. Noble metal nanostructures have concerned attention due to their extensive applicability in various domains [2].

A wide number of synthetic protocols such as electro-spinning method, micro-chemical method, chemical vapor deposition and hydrothermal method have been formulated for the preparation of Ag nanoparticles [3]. However, the synthesis of silver nanoparticles by the conventional methods has many limitations. Plants provide a better platform for nanoparticles synthesis as they are free from toxic chemicals as well as provide natural capping agents [4]. In this work, silver nanoparticles were synthesized using Urginea indica bulbs extract as both capping/reducing agents. This study particularly deals with the synthesis of Ag0 nanoparticles, involving green chemical reduction of their respective inorganic metal ions using water as a solvent. Urginea indica (Indian squill) is a commonly available plant and an excellent source of biomolecules such as polyphenols, flavonoids, quercetin and apigenin glycosides. It also contains trace metals as well as carbohydrates, protein and powerful antioxidants. Main objective of this present study is to synthesize Ag0 nanoparticles using aqueous Urginea indica extract as both capping/reducing agents and to reveal its excellent catalytic activity toward 4-NP. Experimental section 1

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mechanics, Materials Science & Engineering, May 2017 – ISSN 2412-5954

Materials. 4-Nitrophenol, sodium borohydride and silver nitrate were of analytical grade and used as obtained from SRL India. Bulbs of Urginea indica was collected from Tamilnadu, India.

Preparation of U.I. Extract and Preparation of Silver Nanoparticles. Extraction of dried and powdered plant (4.5 kg) of U. indica was done by cold extraction. U. indica bulbs extract is prepared by simple soaking of fine powdered material in the aqueous meduim and the homogenates are kept for 2 h at room temperature with shaking. Plant materials were cold extracted with distilled water and after that the fraction was evaporated to cum-like colloidal nature by roto-dryer at low temperature (40−50 °C) and dried crude extracts were stored in refrigerator. The crude extract was diluted at the further stage of preparation. Aliquots of an aqueous AgNO3 solution (10−3 M) are added to the reaction vessels containing plant extracts (10 % v/v) and the resulting mixtures were allowed to stand for 24 h at room temperature. The reduction of the Ag+ ions by plant extract in the solutions was monitored by sampling the aqueous component (3 mL) and measuring the UV/Vis spectrum of the solutions.

The pH of the solution was adjusted by NaOH. All samples were diluted three times with distilled water.

Fig. 1. visible observation of silver nanoparticles biosynthesis: 1:ratio of U. I. extract and 1 M AgNO3 solution at different time interval [i) 0 min, ii) 30 min, iii) 1h, iv)1d (colour change).

Catalytic Reduction of 4-nitrophenol. Silver nanoparticles aqueous suspension (5mL, 0.25 g/L) was added to NaBH4 aqueous solution (5 mL, 0.3 M) and the mixture was stirred for 10 min at room temperature. 4-nitrophenol (5 mL, 0.003 M) was then added to the mixture, which was stirred until the bright yellow gradually changed to colorless. The reaction progress was monitored by measuring UV-vis absorption spectra. To study the catalyst durability, the catalyst was centrifuged after reaction for 60 minutes and the clear supernatant liquid was decanted carefully.

Result and Discussions UV-Vis Spectral analysis. In order to understand such reaction path and the surface Plasmon resonance of Ag NPs was continuously monitored using UV-visible spectroscopy. Fig. 2 shows the UV–Vis absorption spectra of 1 × 10−3 M silver nitrate solution in extract obtained from different solvents a) Ethanol, b) Hexane, c) DMF and d) Ethyl acetate. Solvent also can reduce the silver ion to metallic NPs and forms bigger sized particle [5]. Due to the large aggregate, the sample doesn’t produce any SPR peaks. To avoid this self-reduction of Ag0 during the course of preparation, we have used water as the solvent.

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Mechanics, Materials Science & Engineering, May 2017 – ISSN 2412-5954

Fig. 2. UV–Vis absorption spectra recorded to the extract with 1 × 10−3 M silver nitrate solution in different solvents a) Ethanol, b) Hexane, c) DMF and d) Ethyl acetate.

Fig. 3. Visible photograph and UV–vis spectra recorded for different pH [6-10 (a-e)].

To examine the pH effects on the formation of silver nanoparticles were carried out. The colour of the mixture turned from colourless to yellow through the way of brownish yellow. In the present studies, silver NPs were synthesized by reacting various ratio of 0.001 M AgNO3 concentrations with fixed amount of obtained U. I. extract to monitor the excitation spectrum of Ag0 NPs. In UV–Vis spectrum, a strong broad peak located between 420 nm to 430 nm was observed (Fig. 4). The obtained peaks corresponds to the SPR of silver nanoparticles prepared using the extract supernatant.

According to the reports, UV-vis spectrum of Ag NPs synthesized in aqueous medium consists of a peak in the region of 410-450 nm that is characteristic of size effect, which makes surface Plasmon resonance band (SPR) particularly on the for Ag NPs [6].

To check the concentration effects, synthesis was carried out in the different ratio of silver nitrate and extract. The UV-Vis absorption spectra of Ag NPs, thus synthesized Ag NPs showed maximum absorbance at 422 nm, which increased with the time of growth of silver NPs with the biomass (Fig. 4i-iv). Observation of this peak is well-matched with the earlier reports for various metal nanoparticles with sizes ranging from 2 nm to 100 nm [7].

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Mechanics, Materials Science & Engineering, May 2017 – ISSN 2412-5954 d)

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Fig. 4. UV–vis spectra recorded for different concentration (a) 0.5 :1, (b) 1:1, (c) 1:2 (d) 1:3 [Extract:AgNO3 (1×10−3 M)] The samples were collected at different time intervals of growth.

FT-IR spectral analysis. Functional groups present in the extract were analyzed using FTIR spectroscopy. Fig. 5a shows the FTIR spectrum of U. I extract obtained in water and Fig. 5b for the silver NPs formed in extract. Spectrum evidences the presence of OH group, phenyl ring -CH group, amide and thio groups in the extract. The presence of biomolecules in the extract is act as the reducing as well as the stabilizing agents for efficient stabilization of nanoparticles. After the addition of Ag ions in extract for 24 h, we can see the absence of some peaks in the FTIR spectrum (Fig. 5b).

Fig. 5. FTIR spectra of a) U. I aqueous extract and b) Ag ions with the extract at 24h.

Fig. 6 XRD Pattern of Ag0 NPs.

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Mechanics, Materials Science & Engineering, May 2017 – ISSN 2412-5954

X-ray diffraction analysis. The XRD patterns of the Ag NPs are shown in Fig. 6. The XRD pattern shows four intense peaks in the whole spectrum of 2θ values ranging from 20 to 80. XRD spectra of pure crystalline silver structures and pure silver nitrate have been published by the Joint Committee on Powder Diffraction Standards (file nos. 04-0783 and 84-0713). The peaks at values of 37.84 Silver nanoparticles were synthesized from 1 mM silver nitrate-U. I. extract at room temperature. The samples were collected at 24th hour, sonicated, air-dried and XRD pattern was observed with position 37.84, 43.97, 64.25 and 77.19 corresponding to (1 1 1), (2 0 0), (2 2 0) and (311) planes of face centered cubic structure of metallic silver with space group of Fm-3m, respectively. The full width at half maximum (FWHM) values measured for (1 1 1), (2 0 0), (2 2 0) and (311) planes of reflection were used with the Scherrer equation to calculate the average crystallite size of the nanoparticles.

From these the average particle size was found to be around 25-30 nm.

Morphological analysis.

FESEM and EDAX. FESEM determinations of the above-mentioned sonicated sample showed the formation of nanoparticles, which were confirmed to be of silver by EDAX. As shown in Fig. 7, welldispersed nanoparticles could be seen in the samples treated with silver nitrate. The particle present in the image was well arranged with smaller size. The obtained images shows the spherical shaped particles with approximately 25 nm in scale EDAX analysis also showed a peak in the silver region, confirming the formation of silver nanoparticles (Fig. 7).

Fig. 7. FESEM and EDAX of the 1 × 10−3 M silver nitrate with U. I. extract showing with higher resolution (scale bar at 100 nm).

Catalytic reduction. The reduction reaction of 4-nitrophenol can be easily monitored by UV-vis spectroscopy as shown in Fig. 9. The decrease in the strong absorption peak at 400 nm can be readily monitored by UV-vis spectroscopy. It can be seen that the absorption associated with p-nitrophenol at 400 nm decreases with a concomitant increase of the absorption at 300 nm due to the paminophenol as the reduction reaction proceeded [8].

Fig. 9. a) Time-dependent UV-visible spectra, b) Plots of (At/A0) vs time and c) efficiency plot for the catalytic reduction of 4-NP.

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Mechanics, Materials Science & Engineering, May 2017 – ISSN 2412-5954

Summary. A simple one-pot green synthesis of stable silver nanoparticles using U. indica bulbs extract at room temperature was reported in this study. Synthesis was found to be efficient in terms of reaction time as well as stability of the synthesized nanoparticles which exclude external capping/reducing agents. Therefore, this reaction pathway satisfies all the conditions of a 100% green chemical process. The formations of Ag0 NPs by U. I. bulb extract with respect to the pH variation, concentration variation and time duration was examined.

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Cite the paper R. Manigandan, S. Praveen kumar, S. Munusamy, T. Dhanasekaran, A. Padmanaban, K. Giribabu, R. Suresh, V. Narayanan (2017). Green Biosynthesis of Silver Nanoparticles using Aqueous Urginea Indica Bulbs Extract and Their Catalytic Activity Towards 4-NP. Mechanics, Materials Science & Engineering, Vol 9. doi:10.2412/mmse.64.70.791

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