Keywords Biosynthesis · Silver nanoparticles · Montmorillonite · Tarragon · SEM Abbreviations Introduction XRD X-ray diffraction FTIR F ourier transform infrared spectroscopy Nanotechnology research and development has been an area TEM T ransmission electron microscopy of rapid growth worldwide . Silver nanoparticles (AgNPs) SPR Sur face plasmon resonance are one of the most extensively used varieties of NPs , E. coli Escherichia coli with a large number of applications. AgNPs are used as coat- S. aureus Staphylococcus aureus ing in solar energy absorption. Moreover, they are used as AgNPs Silver nanoparticles optical receptors, biological labels, and intercalating mate- UV–Vis Ultraviolet–visible rials for electrical batteries . So far, metals, such as Ag, FWHM F ull width half maxima Au, Pd, and CdS, have been used for synthesizing metal MBC Minimum bactericidal concentration NPs, Thus, the synthesis of Ag–NPs onto MMT supports MIC Minimum inhibitory concentration with swelling and ion exchange properties is a good way to control the particle size [4, 5]. AgNPs exhibit important chemical, physical, and biological characteristics among metal NPs  and have potential applications in antimicro- bial, anticancer, cosmetic, paint, food packing, and textile 1 3 Journal of Nanostructure in Chemistry (2018) 8:171–178 173 industries . Many techniques have been investigated for of 38 °C. AgNO (99.80%) was provided by Merck Co. synthesizing AgNPs, including physical, chemical, and, most Montmorillonite powder (MMT), used as the solid support, recently, biological methods . The chemical synthesis of was purchased from Fluka Chemical Co. 0.01 g of MMT NPs is rapid, but requires the use of toxic, hazardous chemi- powder was dispersed with vigorous stirring in certain cals such as sodium borohydride, hydrazine, hydroxylamine, amount of double-distilled water for 1 h. MMT suspension and ethanol . Additionally, with chemical synthesis, it is was added to 100 mL of 0.01 (mol/L) A gNO solutions for difficult to control the stability, growth, and aggregation of the synthesis of Ag/MMT nano composite. The mixture was particles, and capping agents are required for stabilization then added to 20 mL of A. dracunculus water extract at room of NP size . Recently, great attention has been directed temperature while sonicating and then vigorously stirred for towards plant extracts for NP , and Ag/nanocomposites 48 h. The color changed from yellow to dark brown at room synthesis . Use of biosynthetic green metal NPs is gain- temperature, and AgNPs were gradually obtained during the ing increasing approval owing to its simplicity, non-toxicity, reaction. and amenability to large-scale production . AgNP synthesis has been evaluated in different extracts, Purification of silver nanoparticles including Medicago sativa , Ulva flexuosa [ 14], Achil- lea biebersteinii , Moringa oleifera , Calendula To remove silver colloid residues, the solution was first officinalis [ 17], Peganum harmala , Green Tea , washed with double-distilled water via centrifugation for Pistacia atlantica , olive , Aloe vera , and Cori- 15 min at 4000 rpm, and then, washed three times with andrum Sativum . We developed a simple, rapid, and deionized water. After incubation at 65 °C for 2 h, the dried green method to synthesize AgNPs, using MMT and Tarra- powder of Ag–MMT-NPs was collected for further charac- gon leaf extract as both a reducing and capping agent under terization . In other previous similar investigations, the normal atmospheric conditions in the batch method in this maximum volume used for synthesis of AgNPs has been study. This method is easily adopted for large-scale synthesis 50 mL , but in our work the volume was increased to of NPs, without requiring any extra compounds or physical 2000 cc which resulted in synthesizing 2 g of silver nanopar- processes . ticles. due to this information, we can claim that this method Simple collection and widespread availability of Tarra- could be easily adopted for large-scale synthesis of NPs. gon, coupled with its remarkable biological activity, have led to its use as a medicine in many countries . Tarragon UV–Vis spectroscopy has been recently shown to have wide-ranging antimicro- bial activities . Based on some researchers, Tarragon Considering the UV–Vis spectrum of the reaction medium, has been shown to have antimicrobial activities against AgNP formation was monitored at a wavelength range of two bacteria Staphylococcus aureus and Escherichia coli 300–800 nm. A UV–Vis spectrophotometer (BioTek) was . The size of synthesized AgNPs with Tarragon extract used to record the spectra. The samples were appropriately is smaller as compared to the many earlier green synthesis diluted with water before each measurement. reports [1, 2]. Reaction of Tarragon extract with aqueous metal solution (AgNO ) yields only spherical nanoparticles. Fourier transform infrared (FTIR) spectroscopy The leaf extract and metal solution (A gNO ) concentrations were optimized to improve AgNP synthesis. AgNPs were For determining the functional groups in the synthesis of characterized by methods, including powder X-ray diffrac- AgNPs, spectroscopy analyses were performed to describe tion, UV–Vis spectroscopy, Transmission electron micros- the functional groups , bound distinctively to the surface copy, and Fourier transform infrared spectroscopy. The disk of AgNPs. Samples were prepared by vacuum-drying the diffusion method was applied to evaluate the antibacterial Tarragon extract before and after synthesis of AgNPs. After potential of AgNPs. mixing the dried samples with potassium bromide, they were pressed into a sheer slice. The samples were examined using an FTIR spectrometer (PerkinElmer, USA). Materials and methods X‑ray diffraction (XRD) Preparing of silver nanoparticles with Tarragon extract The crystal structure of AgNPs was determined and con- firmed via XRD analysis. After placing the air-dried NPs on Green A. dracunculus leaves were collected from north east an XRD grid, they were assessed in terms of AgNP forma- of Iran in May 2017. After washing the Tarragon leaves, tion, using an X-ray diffractometer (Cu Kα radiation, θ − 2θ they were dried under direct light for 3 days at a temperature configuration; PANalytical) with an X’Pert Pro generator 1 3 174 Journal of Nanostructure in Chemistry (2018) 8:171–178 (30 mA; 40 kV). For measuring the crystallite domain size, UV–Vis spectroscopy the XRD peak width was determined under the assumption that non-uniform strains are absent. UV–Vis spectroscopy is an efficient technique for NP anal- ysis, particularly for determining the stability of metal NPs Transmission electron microscopy (TEM) in aqueous solutions. Different concentration of AgNO (1, 2 and 3 mM) was reacted with the aqueous extract, and Morphological analysis of Ag–MMT-NPs was carried out on the spectra were recorded at a range of 350–850 nm ; a Zeiss EM 10C/CR TEM microscope (Zeiss, Germany) at then, the wavelength of maximum absorption was identi- 100 kV. The suspension was drop-casted on a carbon-coated fied. Biosynthesis of AgNPs by the Tarragon extract was copper grid and left to dry overnight at 25 °C. confirmed based on changes in color after the addition of AgNO (Fig. 1). Antibacterial activity Different concentrations of AgNO were used for opti- mization. The analysis showed a sharp plasmon resonance For determining the antibacterial activity of Ag–MMT-NPs, of 3 mM AgNO at nearly 437 nm (Fig. 2), consistent the agar disk diffusion method was applied, as previously with previous reports of peaks in the absorption spectrum reported . Briefly, AgNPs at 5, 0.5, and 0.05 μg/mL of 400–500 nm due to SPR in AgNPs [35, 36]. Without were used to prevent E. coli (ATCC 25922) and S. aureus any physical or chemical capping agents, the NPs were (ATCC 25923) growth. Bacterial cultures at a concentration dispersed. The Tarragon synthesized AgNPs were quite of 1.5 × 10 CFU/mL were inoculated with different concen- stable in the solution. trations of AgNPs . After incubating the culture plates at 37 °C for 24 h, the bacterial growth inhibition zone was measured in millimeters . For each bacterial strain, three independent experiments were performed. Results and discussion To investigate whether an aqueous extract of Tarragon can be used in the green synthesis of AgNPs, we combined the extract with 1, 2 and 3 mM of AgNO for 24 h. The slow change of color in the solution (from yellow to dark brown) was indicative of AgNP formation. The dark brown color might be related to the surface plasmon resonance (SPR) effect and AgNO reduction . Fig. 2 UV–Vis spectra of synthesized silver nanoparticles using Tar- ragon extract and AgNO Fig. 1 a Extract of Tarragon, b aqueous solutions of silver nitrate (AgNO ) and extract of Tarragon (Artemisia dracuncu- lus), c Ag–MMT-NPs after 24 h of incubation 1 3 Journal of Nanostructure in Chemistry (2018) 8:171–178 175 Fig. 3 XRD pattern of Ag–MMT-NPs, indicating crystal structure XRD analysis Fig. 4 a FTIR spectra of Tarragon extract, b Ag–MMT-NPs synthe- sized using the Tarragon extract Using the XRD pattern of synthesized Ag–MMT-NPs, the peaks were attributed to the crystalline planes of (>C=C), amines (=N–H), flavonoids, and amines (–NH ), Ag–MMT-NPs nanocomposite (Fig. 3). The peaks were which are all in the range of 800–3442/cm. The absorption very sharp, indicating the crystalline nature of synthesized band at 3396.66/cm in the spectrum might be attributed Ag–MMT-NPs . to the stretching vibrations of secondary amines of N–H The diffraction profile had intense peaks at 2θ of bond and bonded hydroxyl (–OH) groups of phenols and 38.14°, 46.2°, 64.51°, and 76.6°, corresponding to the carboxylic acids . Bonded hydroxyl (–OH) groups of (111), (200), (220), and (311) planes, respectively. The carboxylic acids and phenols could produce absorption mean particles size of AgNPs was evaluated using the bands at 3396.66/cm (Fig. 4a). In the AgNP spectrum, the Debye–Scherer Eq. (1): new band at 1607.23/cm might suggest a new C=O group (a ketone or an aldehyde) (Fig. 4b). FTIR spectroscopy d = , (1) cos was carried out to determine the potential biomolecules responsible for the reduction and capping of the AgNPs where λ denotes the X-ray wavelength (1.540560 Å), β rep- synthesized. The FTIR spectra of plant extract shows resents the width of XRD peak, θ shows the Bragg angle, absorption bands characteristics of functional groups such d refers to the size of particle, and K describes the Scherer as alcohol, phenol, amine, and carbonyl group. constant (0.9) . The average size of AgNPs was almost In this manner, they essentially act as a capping agent, 28 nm. providing stability and preventing agglomeration for AgNPs. This phenomenon has been observed in the green synthesis of AgNPs using other plant extracts . These findings FTIR analysis confirm that phenolic agents and proteins in the Tarragon (Artemisia dracunculus) extract are responsible for the In FTIR spectrum, the biomolecules resulting in A g reduction of AgNO . reduction and stabilization can be shown (Fig. 4). 3 FTIR spectroscopy was carried out to determine the potential biomolecules responsible for the reduction and TEM analysis capping of the AgNPs synthesized. The FTIR spectra of plant extract shows absorption bands characteristics of As shown in (Fig. 5a), the TEM image shows the average functional groups such as alcohol, phenol, amine and size was about 25.12 nm with interring particle distance carbonyl group. In FTIR absorption bands at 3396.66, (Fig. 5b). The AgNPs are quasi-spherical in shape and no 1625.75, and 1427.55/cm (Fig. 4a). The vibrational bands aggregation of AgNPs was observed. corresponded to bonds, such as alcohols (–O–H), alkenes 1 3 176 Journal of Nanostructure in Chemistry (2018) 8:171–178 Fig. 5 a TEM image of the synthesized Ag–MMT-NPs with Tarragon extract; b particle size distribution of biosynthesized Ag–MMT-NPs Fig. 6 Antibacterial activity of Ag–MMT-NPs against both a Gram-negative (E. coli) and b Gram-positive (S. aureus) in different solutions of nanoparticles without requiring any extra compounds or Antibacterial activity physical processes and have well-defined size and morphol- ogy. The green synthesis of Ag–MMT-NPs with the extract For evaluating the antibacterial activity of AgNPs, both is a more cost-effective and eco-friendly strategy, compared Gram-positive (S. aureus) and Gram-negative (E. coli) bac- to physical and chemical synthesis methods. Optimization teria were used (Fig. 6). The inhibition zone of Ag–MMT- of AgNO and Tarragon extract concentration was achieved NPs is listed in Table 1. to obtain large amount of AgNPs in batch process. UV–Vis, FTIR, TEM, and XRD studies were performed to confirm the Ag–MMT-NPs formation. For AgNPs, UV–Vis peak Conclusion was observed at 437 nm. The crystalline structure of synthe- sized Ag–MMT-NPs was revealed on XRD. The Ag–MMT- In the present research, a novel process was used for the NPs had an anisotropic nature and a quasi-spherical shape synthesis of Ag–MMT-NPs with Tarragon extract as a (average size around, 25.12 nm). reducing, nontoxic reagent and capping agent. Addition- ally, this method is easily adopted for the mass production 1 3 Journal of Nanostructure in Chemistry (2018) 8:171–178 177 Acknowledgements This work was supported by North Tehran branch and Shahr-e-Qods Branch of Islamic Azad University of Iran. We thank these two Universities for their kind Cooperation. Conflict of interests The authors declare that they have no conflict of interests. Open Access This article is distributed under the terms of the Crea- tive Commons Attribution 4.0 International License (http://creat iveco mmons.or g/licenses/b y/4.0/), which permits unrestricted use, distribu- tion, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. References 1. Ahmad, M., Ahmed, Sh, Ikram, S., Swami, B.L.: A review on plants extract mediated synthesis of silver nanoparticles for anti- microbial applications: a green expertise. J. 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