Green Synthesis of Silver Nanoparticles from the Unexploited Weed Resources

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1 International Journal of Nanotechnology and Applications ISSN X Volume 4, Number 2 (2010), pp Research India Publications Green Synthesis of Silver Nanoparticles from the Unexploited Weed Resources N. Roy and A. Barik * Ecology Research Unit, Department of Zoology University of Burdwan, Burdwan , West Bengal, India * anandamaybarik@yahoo.co.in Abstract Green synthesis of nanoparticles is an emerging branch of nanotechnology. The bioreduction property of three aquatic weed leaves extracts such as Ipomoea aquatica (Convolvulaceae), Enhydra fluctuans (Asteraceae) and Ludwigia adscendens (Onagraceae) in the synthesis of silver nanoparticles was investigated by UV-Vis spectrophotometry, Scanning Electron Microscopy (SEM) and Thermal Gravimetric Analysis (TGA). Among the above three, I. aquatica was found to demonstrate strong potential for synthesis of silver nanoparticles by rapid reduction of silver ions (Ag + to Ag 0 ). This study may be used in the development of value-added products from the weed leaves for biomedical and nanotechnology based industries. Keywords: Ipomoea aquatica, Enhydra fluctuans, Ludwigia adscendens, nanoparticles, UV-Vis spectrophotometry, SEM and TGA. Introduction Synthesis of nanoparticles of different shapes and sizes is an emerging area of research due to their use in a variety of biological fields. To date, metallic nanoparticles are mostly prepared from nobel metals (i. e., Ag, Pt, Au and Pd) [1]. The use of metallic nanoparticles in the field of catalysis, optoelectronics, diagnostic biological problems and display devices uncovered many significant findings. Among the nobel metals, silver (Ag) is the metal of choice in the field of biological systems, living organisms and medicine [2]. There are various methods for nanoparticles formation such as sol-process, micelle, sol-gel process, chemical precipitation, hydrothermal method, pyrolysis, chemical vapour deposition, bio-based protocols etc [1]. Among the above, bio-based protocols are currently under exploitation because it is cost effective, eco-friendly and

2 96 N. Roy and A. Barik don t use any toxic chemicals in the synthesis of nanoparticles [3]. There are several reports on the synthesis and use of Helianthus annus, Basella alba, Oryza sativa, Saccharum officinarum, Sorghum bicolour, Zea mays [1], Azadirachta indica (Neem) [4], Medicago sativa (Alfa alfa) [5,6], Aloe vera [7], Emblica officinalis (Amla) [8], Capsicum annuum [9], Geranium sp. [10,11], Diopyros kaki [12], Magnolia kobus [13], Coriandrum sp.[14] nanoparticles in pharmaceutical and biological applications; but only a study relating to the synthesis of nanoparticles from weed (Parthenium) leaf extract was made [2]. Here in, as a preliminary work, we investigated the efficiency to reduce silver ions (Ag + ) as well as formation of silver-nanoparticles from the aqueous solution of AgNO 3 complex by extracts of Ipomoea aquatica (Water morning-glory : Convolvulaceae), Enhydra fluctuans (Enhydra : Asteraceae) and Ludwigia adscendens (Water primrose : Onagraceae) weed leaves. The weeds (i.e., I. aquatica, E. fluctuans and L. adscendens) are troublesome, creeping and decumbent, growing abundantly in marshy places and rice fields in India and elsewhere [15-17]. All the above weeds have some medicinal and nutritive value but they compete with rice plants for nourishment and thus disturb crop productions. Although I. aquatica, E. fluctuans and L. adscendens are considered as undesirable plant, but their use in biosynthesis of silver-nanoparticles will make them value-added weeds for nanotechnology based industries in future. Materials and methods Fresh leaves of I. aquatica, E. fluctuans and L. adscendens were harvested randomly from plants growing in rice fields adjacent to the University of Burdwan (23 16 N & E). Leaves were initially rinsed thrice in distilled water and dried on paper toweling, and samples (25g) of each kind of dried weed leaves were cut into fine pieces and boiled with 100 ml of sterile distilled water up to 5 minutes. The crude extracts were passed through Whatman No.41 filter paper and the filtrates were kept at 4 C for further use. Silver nitrate (AgNO 3 ) was of analytical grade (AR) and purchased from E. Marck (India). 5 ml of each weed leaf extract was added into the 50 ml aqueous solution of 1 mm AgNO 3, separately. The reduction of Ag + to Ag 0 was monitored by measuring the UV-Vis spectrum of each reaction mixture (silver nitrate solution + weed leaf extract) at different time intervals within the range of nm in the UV-Vis spectrophotometer (Chemito-2100), because it has already been reported that the absorption spectrum of aqueous AgNO 3 only solution exhibited λ max at about 220 nm where as silver nanoparticles λ max at about 430 nm [1]. All the three reaction mixtures prepared from the three weed leaves were kept for 7 days at room temperature for stabilization and subsequently they were centrifuged at 8000 rpm for 5 minutes and redispersed in distilled water. This procedure was repeated three times and the remnant pellets were dried and powdered for SEM and TGA. A thin film of each sample was prepared separately by dissolving a portion of each powder particles in sterile distilled water on a small glass cover slip (3x3 mm), and set on a copper stab for electron microscopy using Hitachi made Scanning Electron Microscope (SEM) (Model: S530 with IB2 ion cotter, Japan). A carefully

3 Green Synthesis of Silver Nanoparticles from the Unexploited Weed Resources 97 weighted quantity of the synthesized silver nanoparticle powder of each was subjected to TGA on a Parkin-Elmer Diamond TG/DTA instrument at heating rate of 10 C/min under nitrogen atmosphere. Results and Discussion All the three reaction mixtures demonstrated a gradual increase in colour development from water colour to almost yellowish brown and exhibited a strong absorbance between nm in UV-Vis spectral analysis at 2 nd and 3 rd h of the reactions as increase in absorbance exhibited by the synthesis of silver nanoparticles (Figure 1). Among the three reaction mixtures, the λ max with time intervals was highest, moderate and lowest in I. aquatica, E. fluctuans and L. adscendens, respectively (Figure 2). The formation of silver nanoparticles as well as their morphological dimensions in the SEM study demonstrated that the average size was from nm with inter-particle distance, where as the shapes were spherical and cubic in I. aquatica but only spherical in E. fluctuans and L. adscendens (Figure 3). TGA plots of the three nanoparticle powder showed steady weight loss with increasing temperature range of C (Figure 4). The weight loss of the nanoparticle powder due to desorption of bioorganic compounds in the Ag-NPs were 17.81, 8.26 and 7.86% in I. aquatica, E. fluctuans and L. adscendens, respectively. Not only the physicists and chemists, but also the biologists are highly interested in synthesizing nanoparticles of different shapes and sizes by employing bio-based synthesis of nanometals using plant leaf extracts and microorganisms (fungi and bacteria) [1,2, 4-14, 18-24]. The weeds belonging to the families such as convolvulaceae, asteraceae and onagraceae were selected, and reduction of silver ions (Ag + ) present in the aqueous solution of silver complex in the plant extract demonstrated that the change in colour was due to the formation of silver nanoparticles in the solutions which are correlated with the UV-Vis spectra [1,2]. The SEM and TGA also supported the formation of silver nanoparticles [1, 25, 26]. This green synthesis approach of silver nanoparticles from the weed leaves revealed that I. aquatica is the most promising among the three weeds. The size and shape of the silver nanoparticles of these three weeds are in good agreement with the silver nanoparticles synthesized from Diopyros kaki, Magnolia kobus etc. [12, 13]. Arangasamy and Munusamy (2008) demonstrated that Helianthus annus of Asteraceae was promising in development of nanoparticles among H. annus (Asteraceae), Besella alba (Basellaceae), Oryza sativa, Saccharum officinarum, Sorghum bicolour and Zea mays (Poaceae) [1] but our results exhibited better silver nanoparticles formation in I. aquatica of Convolvulaceae than E. flactuans (Asteraceae) and L. adscendens (Onagraceae). This findings support that several factors such as plant source, organic compounds in the crude leaf extract, the concentration of AgNO 3, the temperature and also the pigments in the leaf together determines the nanoparticles synthesis [1]. The ecofriendly green chemistry approach for the use of these weeds for synthesis of silver nanoparticles will increase their economic viability and sustainable management. However, applications of these weeds have the added advantage that these unwanted plants can be used by

4 98 N. Roy and A. Barik nanotechnology processing industries as well in bactericidal, wound healing and other medical and electronic applications min 60 min 120 min 180 min 240 min 300 min min 60 min 120 min 180 min 240 min 300 min Absorbance Absorbance Weavelength (nm) (a) Absorbance Weavelength (nm) 30 min 60 min 120 min 180 min 240 min 300 min (b) Weavelength (nm) (c) Figure 1: UV-Vis spectra recorded at different time intervals from aqueous solution of silver nitrate with weed leaf extracts: (a) I. aquatica, (b) E. fluctuans, (c) L. adscendens I. aquatica E. fluctuans L. adscendens 2.4 Absorbance Time (minute) Figure 2: The comparison of λ max values of three weed leaf extracts at different time intervals from the UV-Vis spectra.

5 Green Synthesis of Silver Nanoparticles from the Unexploited Weed Resources 99 (a) (a1) (b) (b1) (c) (c1) Figure 3: The SEM images of silver nanoparticles synthesized from the three weed leaf extracts I. aquatica (a & a1), E. fluctuans (b & b1) and L. adscendens (c & c1): a, b & c at 25.0 kv 10 k; a1, b1 & c1 at 25.0 kv 40 k. (a) (b)

6 100 N. Roy and A. Barik (c) Figure 4: The TGA of three weed leaf reduced silver nanoparticle powder: (a) I. aquatica, (b) E. fluctuans, (c) L. adscendens. References [1] Leela, A. and Vivekanandan, M. 2008, Tapping the unexploited plant resources for the synthesis of silver nanoparticles, African J. of Biotechnol., 7, pp [2] Parashar, V., Parashar, R., Sharma, B., Pandey, A. C. 2009, Parthenium leaf extract mediated synthesis of silver nanoparticles: a novel approach towards weed utilization Digest J. of Nanomaterials and Biostructures. 4, pp [3] Mohanpuria, P., Rana, N. K. and Yadav, S. K. 2008, Biosynthesis of nanoparticles: technological concepts and future applications J Nanopart. Res., 10, pp [4] Shankar, S.S., Rai, A., Ahmad, A. and Sastry, M. 2004, Rapid synthesis of Au, Ag, and bimetallic Au core-ag shell nanoparticles using Neem (Azadirachta indica) leaf broth, J. Colloid Interface Sci., 275, pp [5] Gardea-Torresdey, J. L., Gomez, E., Peralta-Videa, J., Parsons, J. G., Troiani, H. E. and Santiago, P. 2002, Formation and growth of Au nanoparticles inside live alfalfa plants Nano Lett., 2, pp [6] Gardea-Torresdey, J. L., Gomez, E., Peralta-Videa, J., Parsons, J. G., Troiani, H. E. and Santiago, P., 2003, Alfalfa sprouts: a natural source for the synthesis of silver nanoparticles, Langmuir, 19, pp [7] Chandran, S.P., Chaudhary, M., Pasricha, R., Ahmad, A. and Sastry, M. 2006, Synthesis of gold nanotriangles and silver nanoparticles using Aloe vera plant extract, Biotechnol. Prog., 22, pp [8] Amkamwar, B., Damle, C., Ahmad, A. and Sastry, M. 2005, Biosynthesis of gold and silver nanoparticles using Emblica officinalis fruit extract, their phase transfer and transmetallation in an organic solution, J. Nanosci. Nanotechnol., 5, pp [9] Li, S., Shen, Y., Xie, A., Yu, X., Qiu, L., Zhang, L. and Zhang, Q. 2007, Green synthesis of silver nanoparticles using Capsicum annuum L. extract, Green Chem., 9, pp [10] Shankar, S.S., Ahmad, A. and Sastry, M. 2003, Geranium leaf assisted biosynthesis of silver nanoparticles, Biotechnol. Prog., 19, pp

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