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One step green synthesis of hexagonal silver nanoparticles and their biological activity
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One step green synthesis of hexagonal silver nanoparticles and their biological activity Samy M. Shaban a,*, Ismail Aiad a, Mohamed M. El-Sukkary a, E.A. Soliman b, Moshira Y. El-Awady a a b
Petrochemical Department, Egyptian Petroleum Research Institute, Egypt Faculty of Science, Ain Shams University, Cairo, Egypt
A R T I C L E I N F O
Article history: Received 19 January 2014 Accepted 6 February 2014 Available online xxx Keywords: Photosynthesis Hexaonal shapes Zetapotential Biological activity
A B S T R A C T
Hexagonal and spherical silver nanoparticles were prepared by in situ and green synthesis using sun light as reducing agent with assistance newly prepared cationic surfactant which act also as capping agents. The silver nanoparticles formation was investigated using UV–vis spectrophotometer, transmission electron microscope (TEM), dynamic light scattering (DLS), energy dispersive X-ray (EDX) and FTIR. The results showed formation uniform, well arrangement hexagonal and spherical shapes. Increasing hydrophobic chain length increase the stability and amount of AgNPS. Both prepared surfactants and surfactants capping silver nanoparticles showed high antimicrobial activity against Gram-positive and Gram-negative bacteria. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Nanotechnology is a field of applied science, focused on the design, synthesis, characterization and application of materials and devices on the Nano scale, many techniques of synthesizing silver nanoparticles (AgNPs) have been investigated. Some of them are chemical reduction [1], electrochemical [2], photochemical reduction [3], microwave [4] microemulsion [5,6] and UVirradiation [7], and. Nowadays special focus on ‘‘green chemistry’’ by researchers because of increasing awareness about the environment. Utilization of nontoxic chemicals, environmentally benign solvents and renewable materials are some of the key issues that merit important consideration in a green synthesis strategy [8,9]. Silver nano-particles have attracted considerable attention because of their potential applications in various fields such as environmental friendly antimicrobial coatings [10], oxidative catalysis [11], nano electronics (single-electron transistors, electrical connects) [12], conductive coatings [13], biosensors [14,15], antibacterial activity [16]. The aim of the present work is to develop a simple and effective one-pot green approach toward the rapid synthesis and stabilization
* Corresponding author. Tel.: +20 127 679 2188; fax: +20 222 747 433. E-mail address: [email protected] (S.M. Shaban).
of AgNPs using Sun light as reducing agent with assistance of the used cationic surfactants in reduction process. The used surfactants act as stabilizing agent for the synthesized AgNPs. AgNPs with hexagonal shapes and others with spherical shapes were prepared in short reaction time 5 min as maximum depending on the used capping agents without using complicated systems and any other intermediate steps. 2. Materials and methods 2.1. Chemicals Silver nitrate (AgNO3, 99%), were provided from Sigma– Aldrich/Germany. The used cationic surfactants were prepared according to reference [17]. All glassware was washed in a mixture of distilled water and non-ionic detergent, followed by rinsing with distilled water and ethanol for many times to get rid of any remnants of non-ionic detergent then dried prior to use. 2.2. Synthesis 2.2.1. Preparation of cationic capping agents The used cationic capping agents were reported [17]. The chemical structure of prepared capping agents showed in Scheme 1.
http://dx.doi.org/10.1016/j.jiec.2014.02.019 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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Scheme 1. the chemical structure of prepared cationic capping agents.
2.2.2. Preparation of silver nanoparticles (AgNPs) In situ, facile and green synthesis of silver nanoparticles was prepared using sun light as reducing agent with assistance of prepared surfactants [18]. In a typical experiment, 10 mL of 2 mM aqueous solution of AgNO3 were mixed with 10 mL of 2 mM aqueous solution of prepared cationic surfactants then the solution was irradiated with sun light. It was noticed a very fast change in the color of the solution to different colors like yellows with its different ranges in a time of 5 min maximum depending on the used capping agents as shown in Scheme 2. 2.3. Characterization techniques of silver nanoparticles The formation of silver nanoparticles was confirmed by the following instrumentations: 2.3.1. Transmission electron microscope (TEM) A convenient way to produce good TEM samples is to use copper grids. A copper grid pre-covered with a very thin amorphous carbon film. To investigate the prepared AgNPs using TEM, small droplets of the liquid were placed on the carbon-coated grid. A photographic plate of the transmission electron microscopy employed on the present work to investigate the microstructure of the prepared samples. Nanoparticle size was determined by using TEM model ‘‘Jeol JeM – 2100 (Japan)’’ (Egyptian Petroleum Research Institute ‘‘EPRI’’). 2.3.2. UV–visible spectroscopy The photosynthesis of Ag nanoparticles was monitored periodically by a UV–visible spectrophotometer (Shimadzu, UV-2550,
Japan). For the analysis, 5 mL of 2 mM aqueous solution of silver nitrate were mixed with 5 mL of 2 mM of the used cationic surfactant then it irradiated by sun light, until color change, then the sample was put in a cuvette for measurement. 2.3.3. Dynamic light scattering (DLS) The hydrodynamic diameter and zeta potential of the same solution which used in TEM, UV–vis and EDX, was characterized by dynamic light scattering (DLS) using a Malvern Zetasizer Nano (Malvern Instruments Ltd., Worcestershire, UK). Each DLS measurement was run in triplicate using automated, optimal measurement time and laser attenuation settings. The recorded correlation functions and measured particles mobility’s were converted into size distributions and zeta potentials, respectively, using the Malvern Dispersion Software (V5.10, http://www.zetasizer.com/). 2.3.4. Energy dispersive X-ray (EDX) spectroscopy The energy-dispersive X-ray (EDX) spectroscopy was recorded with an EDX detector (Oxford LINKISIS 300) equipped on a Transmission electron microscope (TEM, Hitachi S-520) operated at 10 kV accelerating voltage. 2.3.5. Fourier transform infrared spectrometer (FTIR) FT-IR spectra was recorded using the obtained solid cationic surfactants capped silver nanoparticle after centrifugation and washings to remove the unassociated organic molecules. Spectra was recorded on an ATI Mattson Infinity Series TM, Bench top 961 controlled by win first TM V2.01 software (Egyptian Petroleum Research Institute ‘‘EPRI’’).
Scheme 2. In situ photo preparation of silver nanoparticles.
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2.4. Biological activity 2.4.1. Biological activity against a wide range of bacteria and fungi The antimicrobial activity of synthesized cationic surfactants and their silver nanoform was measured against a wide range of tested organisms comprising: (bacteria and fungi) 1. Source of microorganisms: The different species of tested organisms were obtained from the unit of operation development center, Egyptian petroleum research institute. 2. The media The following media used in the antimicrobial activity of synthesized products, the bacterial species grow on nutrient agar, while fungi mold grow on Czapek’s dox agar. (a) Nutrient agar Nutrient agar consists of beef extract (3.0 g/l); peptone (5.0 g/l), sodium chloride (3.0 g/l) and agar (20.0 g/l), then, complete the volume to one liter, heated the mixture until the boiling, and sterilize the media by autoclave. (b) Czapek’s Dox agar Czapek’s Dox agar consists of sucrose (20.0 g/l), sodium nitrate (2.0 g/l), magnesium sulfate (0.5 g/l), potassium Chloride (0.5 g/l), ferrous sulfate (0.01 g/l) and agar (20.0 g/l), then, complete the volume to one liter, heated the mixture until the boiling, and sterilize the media by autoclave. (c) Microorganisms The used microorganisms were Gram-positive bacteria (Bacillus pumilus and Micrococcus luteus), Gram-negative bacteria (Pseudomonas aeuroginosa and Sarcina lutea) and Fungi (Candida albicans and Penicillium chrysogenum). An assay was made to determine the ability of an antibiotic to kill or inhibit the growth of living microorganisms, the technique that used is filter-paper disk-agar diffusion (Kirby-Bauer) [19]. 1. Inoculate flask of melted agar medium with the organism to be tested. 2. Pour this inoculated medium into a Petri dish. 3. After the agar has solidified, a multilobed disk that impregnated with different antibiotics laid on top of agar. 4. The antibiotic in each lobe of disk diffuses into medium and if the organism is sensitive to a particular antibiotic, no growth occur in a large zone surrounding that lobe (clear zone). 5. The diameters of inhibition zones were measured after 24–48 h at 35–37 8C (for bacteria) and 3–4 days at 25–27 8C (for yeast and fungi) of incubation at 28 8C. 6. Measure each clear zone and compare between them to determine the antibiotic, which is more inhibitor.
3. Results and discussions Aqueous solution of AgNO3 was reduced under exposure to sun light as a gratis source of reducing agent with assistance of prepared cationic surfactants. This technique is simple and inexpensive without any surplus material. It was found that in the presence of prepared cationic surfactants, an aqueous solution of AgNO3 was reduced and color of solution was changed to different colors like yellows with its different range, depending on the used capping agent in a few minutes as 5 min maximum, as indicated in Fig. 1 and shown in Scheme 2 .The color changes implied the occurrence of Ag+ reduction to AgNPs [20]. In a control experiment, when the sample (aqueous solution of silver nitrate with capping agent) was stored in a vial wrapped with aluminum
Fig. 1. Colors(For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.) of prepared colloidal silver nanoparticles with different capping agents.
foil to exclude light, the solution did not change color or form any solid precipitate over longer period. When the silver nitrate solution exposed to sun light without capping agent, after long time exceed 2 months we notes very slight change in color with very small precipitate on wall of glass vial. 3.1. Formation mechanism of silver nanoparticles For the synthesis of AgNPs, the generally accepted mechanism suggests a two-step process, i.e. atom formation and then polymerization of the atoms. In the first step, a portion of metal ions in a solution reduced by a suitable reducing agent. The atoms thus produced act as nucleation centers and catalyze the reduction of the remaining metal ions present in the bulk solution. Subsequently, the atoms coalesce leading to the formation of metal clusters. The process stabilized by the interaction with the prepared capping agent so preventing further coalescence and aggregation [21,22]. When aqueous solutions subject to sun light irradiation (gradiolysis), it produces the following species [23]:
H2 O ! e aqu ;
H 3 Oþ ;
H2 ; H; OH;
H 2 O2
The solvated electrons and H. atoms are strong reducing agents: E0 0 + (H2 O=e aqu ) = 2.87 V (SHE) and E (H /H) = 2.3 V (SHE) and can reduce Ag+ ions to neutral Ag0 atoms:
0 Agþ þ e aqu ! Ag
The reduction of Ag+ ions is the main process for the formation of nanoparticles under g-radiolysis. So both oxidizing OH radicals and H produced in radiolysis of water should be scavenged and it can be done efficiently by capping agents to produce H2O, H2 and organic radical. Since the electrochemical potential of the organic radical is more positive than that of the Ag+/Ag0 system [24], reaction of organic radical obtained from capping agent with Ag+ ions is relatively slow. Thus, during the process of irradiation, Ag+ ions are primarily reduced by solvated electrons and give rise to Ag0. The growth of silver nanoparticles by reduction of Ag+ to Ag0 is stepwise [25]. These neutral Ag0 atoms at first dimerize when they encounter or associate with the excess Ag+ ions trapped in the individual loops of capping agent. From the above results, we can conclude that sun light act as reducing agent in the presence of prepared cationic surfactants, theses surfactants facilitating and increasing rate of silver nanoparticles formation in addition their role as capping agent.
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3.2. Confirmation of silver nanoparticle formation Stable silver nanoparticles were prepared. The shape and size distribution were characterized using TEM, SAED, UV, DLS, EDX and FTIR techniques as following 3.2.1. Transmission electron microscope (TEM) and selected area electron diffraction (SAED) The morphology of prepared silver nanoparticles (AgNPs) were investigated by transmission electron microscope (TEM) Fig. 2 and the selected area electron diffraction pattern (SAED) Fig. 3. TEM photographs indicate that the nanosilver solution consist of well dispersed agglomerates of spherical and cubic shapes nanoparticles depending on the hydrophobic chain length of the used capping agents. In this agglomeration, the formed nanoparticles are not fused, i.e. each particle keep a distance from surrounding other particles and these distance increase by increasing chain length, and this was confirmed also by zeta potential values indicated in Table 2. Fig. 2 shows TEM morphology of prepared silver nanoparticles capped with C10Dim, C12Dim and C16Dim. AgNPs capped by C10Dim have spherical shape some particles have hexagonal shape, AgNPs capped by C12Dim have hexagonal shape while AgNPs capped by C16Dim have spherical shape. We note also by increasing the alkyl chain length of prepared capping agent the dispersion between particles increase (aggregation decrease) which confirmed by zeta potential values indicated in Table 2. The selected area electron diffraction pattern of capped AgNPs (SAED) is shown in Fig. 3. Where when the electron diffraction is carried out on a limited number of crystals one observes some spots of diffraction distributed on concentric circles [26], indicating that the prepared silver nanoparticles are polycrystalline [27].
3.2.2. UV–vis spectroscopy UV–vis spectroscopy is quite sensitive to the formation of silver nanoparticles due to surface plasmon excitation [28]. Fig. 4 shows absorption spectra of AgNPs capped by prepared surfactants, which show absorption band at lmax 418, 412 and 420 nm for C10Dim, C12Dim and C16Dim, respectively which an indication on formation silver nanoparticles, due to surface plasmon resonance of colloidal silver nanoparticles [29,30]. Band at lmax range from 290 to 306 nm characteristic for the used capping agents, which matches with the band appeared for aqueous solution of the used capping agents alone. It is known that the amount and size of Ag nanoparticles are positively related with the adsorption peak intensity and the lmax on the UV–vis spectra [31–34], respectively. From Fig. 4, there are increasing in the intensity (absorbance), of the bands at lmax range from 412 to 420 nm with increasing hydrophobic chain length of the used capping agent, which give indication on increasing formation percent of silver nanoparticles. For example, C10Dim, C12Dim and C16Dim have lmax at 418, 412 and 420 nm respectively with absorbance intensity 0.49, 0.79 and 0.89 respectively. Fig. 4 shows very small shift in value of lmax of prepared silver nanoparticles by increasing hydrophobic chain length of capping agent, which indicate that the in situ photo-reduction using sun light as reducing agent in the presence of the used capping agent, give similar size distribution. 3.2.3. Dynamic light scattering (DLS) Dynamic light scattering technique (DLS) was performed to understand the size distribution of silver nanoparticles capped by prepared cationic surfactants and their stability by zeta potential values.
Fig. 2. TEM image of prepared silver nanoparticle capped by (A) (C10Dim), (B) (C12Dim) and (C) (C16Dim).
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Fig. 3. SAED image of prepared silver nanoparticles capped by (A) (C10Dim), (B) (C12Dim) and (C) (C16Dim).
Particle size distribution of silver nanoparticles in aqueous solution of capping agents are listed in Table 1 and shown in Fig. 5. which indicate that the in situ photo-reduction using sun light as reducing agent in the presence of capping agent, give similar size distribution, these results matches with data obtained from UV–vis spectroscopy as shown in Fig. 4. Stability of nanoparticles is crucially important for many applications and can be determined using zeta potential measurements [35]. Zeta potential is the net surface charge of the nanoparticles when they are inside a solution. The fact that
particles push each other and their agglomeration behavior depends on large negative or positive zeta potential. The zeta potential playing an important role limits in the stability of solutions is +30 mV or 30 mV. To regard the particles as stable, zeta potential should be either higher than +30 mV or lower than 30 mV [36]. By inspection data in Table 2, it was found that the zeta potential values of prepared silver nanoparticle encapsulated by the prepared cationic surfactants are greater than +30 mV, which be indication on high stability of prepared silver nanoparticles against agglomeration. High value of zeta potential indicate that the surface charge on nano-silver is high so the electrostatic repulsion between particles increase, keeping particles without agglomeration and stable for long time. The acquired positive charge of zeta potential is mainly due to the used capping agent is cationic surfactant (carry positive charge) [37], while zeta potential of silver nanoparticle prepared without using capping agent and after irradiation to sun light for 1 month was 0.386 mV. Also we found that zeta potential values of prepared silver nanoparticles are positively related with hydrophobic chain length of added capping agents, where by increase chain length of capping
Table 1 Size distribution of prepared silver nanoparticles using prepared capping agents. Capping agent
Distribution range Size
Maximum distribution range
Number (%)
Size (nm)
Number (%)
97 98.3 97.2
15–38 21–38 21–44
92.2 87.4 91.6
(nm)
Fig. 4. UV spectra of prepared silver nanoparticles using C10Bn, C12Bn and C16Bn as capping agent.
AgNPs capped by C10Dim AgNPs capped by C12 Dim AgNPs capped by C16Dim
15–50 18–50 18–50
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Fig. 5. Size distribution of silver nanoparticles using prepared capping agents determined by DLS.
agent, zeta potential increase, which be indication on increasing stability of prepared silver nanoparticle against agglomeration for example zeta potential of prepared silver nanoparticle capped by C10Dim, C12 Dim and C16 Dim are 34.1 10.4, 48.9 9.9 and 52 10.7 respectively. 3.2.4. Energy dispersive X-ray (EDX) EDX spectroscopy results confirmed the significant presence of pure 100% silver with no other contaminants. The optical absorption peak at 3 keV, is typical for the absorption of metallic silver nanocrystallites due to surface plasmon resonance [38]. Fig. 6 shows the EDX analysis of the AgNPs capped by the prepared cationic surfactants. The EDX spectrum showed a strong and typical optical absorption peak at approximately 3 keV, which was attributed to the SPR of the metallic Ag nanocrystals [38]. This result indicated that AgNPs were formed in the reaction medium. Beside of Ag there are others bands for C, O and Br elements peaks which appeared due to the scattering caused by the compounds that are bound to the surface of silver which indicating that the used cationic surfactants act as capping agents for silver nanoparticles.
Table 2 Zeta Potential and conductivity of prepared silver nanoparticle by dynamic light Scattering (DLS). Capping agent
Zeta potential (mV)
Conductivity (mS/cm)
No capping and irradiation for 1 month AgNPs Capped by C10Dim AgNPs Capped by C12Dim AgNPs Capped by C16Dim
0.386 34.1 10.4 48.9 9.95 52 10.7
1.64 0.183 0.169 0.152
3.2.5. FT-IR spectroscopy FT-IR spectroscopy is used in order to understand the role of prepared capping agent in the formation of silver nanoparticles and the chemical environment of the final product. In Fig. 7, all bands around 2926, 2853, 1500 and 1642 cm1 indicating the presence of capping agent with the nanoparticles. Bands at 2926 and 2853 cm1 corresponds to asymmetric and symmetric C–H stretching of alkyl chain of C12Dim. Band at 1642 cm1 correspond to Schiff base group (–C5 5N–). On comparing IR bands of silver nanoparticles capped by surfactants in Fig. 7 with IR bands of surfactant alone in Fig. 8, we notes that some bands maxima are little blue shifted and some bands are also little red shifted. These relatively small shifts are mostly due to the constraint of the capping molecular motion, which presumably resulted from the attachment on the nanoparticles surface [39]. Also we note increasing in the intensity of the band around 1375 cm1 by 50–80% than band of capping agents alone, which indicate presence co-ordination bond between CH2 of hydrophobic chain length of capping agent and silver nanoparticles surface. This co-ordination bond enhance role of capping agents chain lengths in shaping, sizing and distribution as indicated by both transmission electron microscope, UV–vis spectroscopy and dynamic light scattering. 3.3. Evaluation of the synthesized surfactants as antibacterial and antifungal We evaluated the prepared cationic surfactants and their capped form with silver nanoparticles as biocide against some pathogenic Gram-positive (B. pumilus and M. luteus) and Gramnegative (P. aeuroginosa and S. lutea) bacteria and also, some
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Fig. 6. EDX silver nanoparticles capped by prepared surfactants: (A) is C10Dim, (B) is C12Dim and (C) is C16Dim.
pathogenic fungi (C. albicans and P. chrysogenum). The aim of the formation silver nanoparticles capped by cationic compounds is to increase their potency against microorganisms. The results of antimicrobial activity are recorded in Table 3, indicating that the synthesized compounds have antimicrobial activity rang from a moderate to slight high effect on Gramnegative bacteria and from slight high to high on Gram- positive bacteria and very high effect on fungi compared to the drug reference used. The biological activities of surfactants often show a non-linear dependence on their chain length, where bactericides and fungicide activity increase by increasing hydrophobic chain length
[40], in our work the optimal alkyl chain length has been noted to be twelve carbon atoms, which has the maximum inhibition zone where compounds with twelve carbon chain higher than these with ten carbon atoms chain which higher than these of sixteen carbon atoms. These results are agreement with results obtained before [40–44], this behavior known by cut-off effect which observed for the first time more than 70 years ago, in which the activity increases progressively in a homologous series of compounds, with increasing chain length up to a critical point, beyond which the activity decreases [45]. Several theories have been postulated as to why this cut-off effect occurs, first have associated this cutoff with a limit in
Fig. 7. FTIR spectrum C12Dim capped silver nanoparticle.
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Fig. 8. IR spectrum of N-(3-((3,4-dimethoxybenzylidene)amino)propyl)-N,N-dimethyldodecan-1-ammonium (C12Dim).
Table 3 Antimicrobial activity of synthesized surfactants and their nano form against pathogenic bacteria and fungi. Inhibition zone diameter (mm) Pseudomonas aeuroginosa
Sarcina lutea
Bacillus pumilus
Micrococcus luteus
Candida albicans
Penicillium chrysogenum
Erythromycin
30
44
32
32
–
–
Metronidazole
–
–
–
–
27
25
C10Dim C12Dim C16Dim AgNPs capped by C10Dim AgNPs capped by C12Dim AgNPs capped by C16Dim
13 16 15 16 17 16
29 37 24 29 38 26
17 18 16 23 24 17
22 31 22 25 32 22
24 28 23 27 36 24
17 19 16 25 29 25
solubility, they proposed that as the alkyl chain increases, lipid solubility increases at a rate faster than the change in partition coefficient (lipid/aqueous) theory. At these higher chain length, partitioning is limited, making the concentration at the site of action insufficient to have a significant effect on the membrane of the cell wall [46] and hence according to this theory the activity of compounds should be ordered as follow C10? C12 ? C16 chain due to increase lipid solubility from C10 to C16. Other accounts attribute this cut-off to a decrease in perturbation of the membrane at higher chain lengths, proposing that the longer alkyl chain molecules better mimic molecules in the lipid bilayer, causing less of a disruption in the membrane [47]. Other theory based on critical micelle concentration (CMC), as surfactants chain length increase, their tendency toward micelle formation is greater, noted by the lower CMCs at higher chain lengths. This tendency to form micelles becomes greater than the tendency to move toward the interface (the membrane), and thus the concentration at the action site becomes decreased, also, as the size of the diffusing species increases from the size of a monomer to that of micelles, their diffusibility and permeation abilities will decrease, affecting their action on the microbial cell wall and hence according to this theory the activity of compounds should be ordered as follow C10? C12 ? C16. Other theory based on surface and thermodynamic properties surfactants which showed tendency of prepared compound
toward adsorption at the interfaces which facilitate their role of adsorption at the bacterial cell membrane, where increasing DGoads enhances the higher adsorptivity of prepared compound, from previous thermodynamic results DGoads increase by increasing chain length [17], and hence according to this theory the activity of compounds should be ordered as follow C16 ? C12 ? C10 chain. From that we can conclude that factors effects on cut-off point of homologous series of surfactants varying in chain length, are solubility, critical micelle concentration, (CMC), size of diffusing species and change in free energy of adsorption. Magnitude of these factors determines when cut-off occurs, according to data in Table 3, the cut-off was observed with surfactants with chain length (C16) for all prepared compounds. It was observed from data in Table 3, that biological activity (inhibition zone) of silver nanoparticle in capsulated with prepared cationic surfactants higher than corresponding prepared cationic surfactant, this can be attributed to silver nanoparticle alone has biological activity, so prepared surfactant capped silver nanoparticles have higher activity, this can be attributed to the higher surface area of prepared nanoparticles and the acquired positive charge of prepared silver nanoparticles (as indicated in zeta potential values in Table 2) in addition positive charge of cationic surfactants, where these positive charge facilitate adsorption at negative cell wall membrane of bacteria.
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4. Conclusion From the obtained results, we can conclude: In situ, facile and green synthesis of silver nano particles were developed using sun light as reducing agent with assistance of prepared surfactants. The prepared surfactants act as capping agents (DLS, EDX and FTIR). Increasing hydrophobic chain length of the capping agents, the stability of prepared AgNPs increase. Increasing hydrophobic chain length of the capping agents, the amount of AgNPs increase (Increasing absorbance in UV–vis spectra). Hexagonal AgNPs were prepared. The silver nanoparticles increase the biological activity of the capping agents.
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Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
One step green synthesis of hexagonal silver nanoparticles and their biological activity Samy M. Shaban a,*, Ismail Aiad a, Mohamed M. El-Sukkary a, E.A. Soliman b, Moshira Y. El-Awady a a b
Petrochemical Department, Egyptian Petroleum Research Institute, Egypt Faculty of Science, Ain Shams University, Cairo, Egypt
A R T I C L E I N F O
Article history: Received 19 January 2014 Accepted 6 February 2014 Available online xxx Keywords: Photosynthesis Hexaonal shapes Zetapotential Biological activity
A B S T R A C T
Hexagonal and spherical silver nanoparticles were prepared by in situ and green synthesis using sun light as reducing agent with assistance newly prepared cationic surfactant which act also as capping agents. The silver nanoparticles formation was investigated using UV–vis spectrophotometer, transmission electron microscope (TEM), dynamic light scattering (DLS), energy dispersive X-ray (EDX) and FTIR. The results showed formation uniform, well arrangement hexagonal and spherical shapes. Increasing hydrophobic chain length increase the stability and amount of AgNPS. Both prepared surfactants and surfactants capping silver nanoparticles showed high antimicrobial activity against Gram-positive and Gram-negative bacteria. ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Nanotechnology is a field of applied science, focused on the design, synthesis, characterization and application of materials and devices on the Nano scale, many techniques of synthesizing silver nanoparticles (AgNPs) have been investigated. Some of them are chemical reduction [1], electrochemical [2], photochemical reduction [3], microwave [4] microemulsion [5,6] and UVirradiation [7], and. Nowadays special focus on ‘‘green chemistry’’ by researchers because of increasing awareness about the environment. Utilization of nontoxic chemicals, environmentally benign solvents and renewable materials are some of the key issues that merit important consideration in a green synthesis strategy [8,9]. Silver nano-particles have attracted considerable attention because of their potential applications in various fields such as environmental friendly antimicrobial coatings [10], oxidative catalysis [11], nano electronics (single-electron transistors, electrical connects) [12], conductive coatings [13], biosensors [14,15], antibacterial activity [16]. The aim of the present work is to develop a simple and effective one-pot green approach toward the rapid synthesis and stabilization
* Corresponding author. Tel.: +20 127 679 2188; fax: +20 222 747 433. E-mail address: [email protected] (S.M. Shaban).
of AgNPs using Sun light as reducing agent with assistance of the used cationic surfactants in reduction process. The used surfactants act as stabilizing agent for the synthesized AgNPs. AgNPs with hexagonal shapes and others with spherical shapes were prepared in short reaction time 5 min as maximum depending on the used capping agents without using complicated systems and any other intermediate steps. 2. Materials and methods 2.1. Chemicals Silver nitrate (AgNO3, 99%), were provided from Sigma– Aldrich/Germany. The used cationic surfactants were prepared according to reference [17]. All glassware was washed in a mixture of distilled water and non-ionic detergent, followed by rinsing with distilled water and ethanol for many times to get rid of any remnants of non-ionic detergent then dried prior to use. 2.2. Synthesis 2.2.1. Preparation of cationic capping agents The used cationic capping agents were reported [17]. The chemical structure of prepared capping agents showed in Scheme 1.
http://dx.doi.org/10.1016/j.jiec.2014.02.019 1226-086X/ß 2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
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Scheme 1. the chemical structure of prepared cationic capping agents.
2.2.2. Preparation of silver nanoparticles (AgNPs) In situ, facile and green synthesis of silver nanoparticles was prepared using sun light as reducing agent with assistance of prepared surfactants [18]. In a typical experiment, 10 mL of 2 mM aqueous solution of AgNO3 were mixed with 10 mL of 2 mM aqueous solution of prepared cationic surfactants then the solution was irradiated with sun light. It was noticed a very fast change in the color of the solution to different colors like yellows with its different ranges in a time of 5 min maximum depending on the used capping agents as shown in Scheme 2. 2.3. Characterization techniques of silver nanoparticles The formation of silver nanoparticles was confirmed by the following instrumentations: 2.3.1. Transmission electron microscope (TEM) A convenient way to produce good TEM samples is to use copper grids. A copper grid pre-covered with a very thin amorphous carbon film. To investigate the prepared AgNPs using TEM, small droplets of the liquid were placed on the carbon-coated grid. A photographic plate of the transmission electron microscopy employed on the present work to investigate the microstructure of the prepared samples. Nanoparticle size was determined by using TEM model ‘‘Jeol JeM – 2100 (Japan)’’ (Egyptian Petroleum Research Institute ‘‘EPRI’’). 2.3.2. UV–visible spectroscopy The photosynthesis of Ag nanoparticles was monitored periodically by a UV–visible spectrophotometer (Shimadzu, UV-2550,
Japan). For the analysis, 5 mL of 2 mM aqueous solution of silver nitrate were mixed with 5 mL of 2 mM of the used cationic surfactant then it irradiated by sun light, until color change, then the sample was put in a cuvette for measurement. 2.3.3. Dynamic light scattering (DLS) The hydrodynamic diameter and zeta potential of the same solution which used in TEM, UV–vis and EDX, was characterized by dynamic light scattering (DLS) using a Malvern Zetasizer Nano (Malvern Instruments Ltd., Worcestershire, UK). Each DLS measurement was run in triplicate using automated, optimal measurement time and laser attenuation settings. The recorded correlation functions and measured particles mobility’s were converted into size distributions and zeta potentials, respectively, using the Malvern Dispersion Software (V5.10, http://www.zetasizer.com/). 2.3.4. Energy dispersive X-ray (EDX) spectroscopy The energy-dispersive X-ray (EDX) spectroscopy was recorded with an EDX detector (Oxford LINKISIS 300) equipped on a Transmission electron microscope (TEM, Hitachi S-520) operated at 10 kV accelerating voltage. 2.3.5. Fourier transform infrared spectrometer (FTIR) FT-IR spectra was recorded using the obtained solid cationic surfactants capped silver nanoparticle after centrifugation and washings to remove the unassociated organic molecules. Spectra was recorded on an ATI Mattson Infinity Series TM, Bench top 961 controlled by win first TM V2.01 software (Egyptian Petroleum Research Institute ‘‘EPRI’’).
Scheme 2. In situ photo preparation of silver nanoparticles.
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2.4. Biological activity 2.4.1. Biological activity against a wide range of bacteria and fungi The antimicrobial activity of synthesized cationic surfactants and their silver nanoform was measured against a wide range of tested organisms comprising: (bacteria and fungi) 1. Source of microorganisms: The different species of tested organisms were obtained from the unit of operation development center, Egyptian petroleum research institute. 2. The media The following media used in the antimicrobial activity of synthesized products, the bacterial species grow on nutrient agar, while fungi mold grow on Czapek’s dox agar. (a) Nutrient agar Nutrient agar consists of beef extract (3.0 g/l); peptone (5.0 g/l), sodium chloride (3.0 g/l) and agar (20.0 g/l), then, complete the volume to one liter, heated the mixture until the boiling, and sterilize the media by autoclave. (b) Czapek’s Dox agar Czapek’s Dox agar consists of sucrose (20.0 g/l), sodium nitrate (2.0 g/l), magnesium sulfate (0.5 g/l), potassium Chloride (0.5 g/l), ferrous sulfate (0.01 g/l) and agar (20.0 g/l), then, complete the volume to one liter, heated the mixture until the boiling, and sterilize the media by autoclave. (c) Microorganisms The used microorganisms were Gram-positive bacteria (Bacillus pumilus and Micrococcus luteus), Gram-negative bacteria (Pseudomonas aeuroginosa and Sarcina lutea) and Fungi (Candida albicans and Penicillium chrysogenum). An assay was made to determine the ability of an antibiotic to kill or inhibit the growth of living microorganisms, the technique that used is filter-paper disk-agar diffusion (Kirby-Bauer) [19]. 1. Inoculate flask of melted agar medium with the organism to be tested. 2. Pour this inoculated medium into a Petri dish. 3. After the agar has solidified, a multilobed disk that impregnated with different antibiotics laid on top of agar. 4. The antibiotic in each lobe of disk diffuses into medium and if the organism is sensitive to a particular antibiotic, no growth occur in a large zone surrounding that lobe (clear zone). 5. The diameters of inhibition zones were measured after 24–48 h at 35–37 8C (for bacteria) and 3–4 days at 25–27 8C (for yeast and fungi) of incubation at 28 8C. 6. Measure each clear zone and compare between them to determine the antibiotic, which is more inhibitor.
3. Results and discussions Aqueous solution of AgNO3 was reduced under exposure to sun light as a gratis source of reducing agent with assistance of prepared cationic surfactants. This technique is simple and inexpensive without any surplus material. It was found that in the presence of prepared cationic surfactants, an aqueous solution of AgNO3 was reduced and color of solution was changed to different colors like yellows with its different range, depending on the used capping agent in a few minutes as 5 min maximum, as indicated in Fig. 1 and shown in Scheme 2 .The color changes implied the occurrence of Ag+ reduction to AgNPs [20]. In a control experiment, when the sample (aqueous solution of silver nitrate with capping agent) was stored in a vial wrapped with aluminum
Fig. 1. Colors(For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.) of prepared colloidal silver nanoparticles with different capping agents.
foil to exclude light, the solution did not change color or form any solid precipitate over longer period. When the silver nitrate solution exposed to sun light without capping agent, after long time exceed 2 months we notes very slight change in color with very small precipitate on wall of glass vial. 3.1. Formation mechanism of silver nanoparticles For the synthesis of AgNPs, the generally accepted mechanism suggests a two-step process, i.e. atom formation and then polymerization of the atoms. In the first step, a portion of metal ions in a solution reduced by a suitable reducing agent. The atoms thus produced act as nucleation centers and catalyze the reduction of the remaining metal ions present in the bulk solution. Subsequently, the atoms coalesce leading to the formation of metal clusters. The process stabilized by the interaction with the prepared capping agent so preventing further coalescence and aggregation [21,22]. When aqueous solutions subject to sun light irradiation (gradiolysis), it produces the following species [23]:
H2 O ! e aqu ;
H 3 Oþ ;
H2 ; H; OH;
H 2 O2
The solvated electrons and H. atoms are strong reducing agents: E0 0 + (H2 O=e aqu ) = 2.87 V (SHE) and E (H /H) = 2.3 V (SHE) and can reduce Ag+ ions to neutral Ag0 atoms:
0 Agþ þ e aqu ! Ag
The reduction of Ag+ ions is the main process for the formation of nanoparticles under g-radiolysis. So both oxidizing OH radicals and H produced in radiolysis of water should be scavenged and it can be done efficiently by capping agents to produce H2O, H2 and organic radical. Since the electrochemical potential of the organic radical is more positive than that of the Ag+/Ag0 system [24], reaction of organic radical obtained from capping agent with Ag+ ions is relatively slow. Thus, during the process of irradiation, Ag+ ions are primarily reduced by solvated electrons and give rise to Ag0. The growth of silver nanoparticles by reduction of Ag+ to Ag0 is stepwise [25]. These neutral Ag0 atoms at first dimerize when they encounter or associate with the excess Ag+ ions trapped in the individual loops of capping agent. From the above results, we can conclude that sun light act as reducing agent in the presence of prepared cationic surfactants, theses surfactants facilitating and increasing rate of silver nanoparticles formation in addition their role as capping agent.
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3.2. Confirmation of silver nanoparticle formation Stable silver nanoparticles were prepared. The shape and size distribution were characterized using TEM, SAED, UV, DLS, EDX and FTIR techniques as following 3.2.1. Transmission electron microscope (TEM) and selected area electron diffraction (SAED) The morphology of prepared silver nanoparticles (AgNPs) were investigated by transmission electron microscope (TEM) Fig. 2 and the selected area electron diffraction pattern (SAED) Fig. 3. TEM photographs indicate that the nanosilver solution consist of well dispersed agglomerates of spherical and cubic shapes nanoparticles depending on the hydrophobic chain length of the used capping agents. In this agglomeration, the formed nanoparticles are not fused, i.e. each particle keep a distance from surrounding other particles and these distance increase by increasing chain length, and this was confirmed also by zeta potential values indicated in Table 2. Fig. 2 shows TEM morphology of prepared silver nanoparticles capped with C10Dim, C12Dim and C16Dim. AgNPs capped by C10Dim have spherical shape some particles have hexagonal shape, AgNPs capped by C12Dim have hexagonal shape while AgNPs capped by C16Dim have spherical shape. We note also by increasing the alkyl chain length of prepared capping agent the dispersion between particles increase (aggregation decrease) which confirmed by zeta potential values indicated in Table 2. The selected area electron diffraction pattern of capped AgNPs (SAED) is shown in Fig. 3. Where when the electron diffraction is carried out on a limited number of crystals one observes some spots of diffraction distributed on concentric circles [26], indicating that the prepared silver nanoparticles are polycrystalline [27].
3.2.2. UV–vis spectroscopy UV–vis spectroscopy is quite sensitive to the formation of silver nanoparticles due to surface plasmon excitation [28]. Fig. 4 shows absorption spectra of AgNPs capped by prepared surfactants, which show absorption band at lmax 418, 412 and 420 nm for C10Dim, C12Dim and C16Dim, respectively which an indication on formation silver nanoparticles, due to surface plasmon resonance of colloidal silver nanoparticles [29,30]. Band at lmax range from 290 to 306 nm characteristic for the used capping agents, which matches with the band appeared for aqueous solution of the used capping agents alone. It is known that the amount and size of Ag nanoparticles are positively related with the adsorption peak intensity and the lmax on the UV–vis spectra [31–34], respectively. From Fig. 4, there are increasing in the intensity (absorbance), of the bands at lmax range from 412 to 420 nm with increasing hydrophobic chain length of the used capping agent, which give indication on increasing formation percent of silver nanoparticles. For example, C10Dim, C12Dim and C16Dim have lmax at 418, 412 and 420 nm respectively with absorbance intensity 0.49, 0.79 and 0.89 respectively. Fig. 4 shows very small shift in value of lmax of prepared silver nanoparticles by increasing hydrophobic chain length of capping agent, which indicate that the in situ photo-reduction using sun light as reducing agent in the presence of the used capping agent, give similar size distribution. 3.2.3. Dynamic light scattering (DLS) Dynamic light scattering technique (DLS) was performed to understand the size distribution of silver nanoparticles capped by prepared cationic surfactants and their stability by zeta potential values.
Fig. 2. TEM image of prepared silver nanoparticle capped by (A) (C10Dim), (B) (C12Dim) and (C) (C16Dim).
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Fig. 3. SAED image of prepared silver nanoparticles capped by (A) (C10Dim), (B) (C12Dim) and (C) (C16Dim).
Particle size distribution of silver nanoparticles in aqueous solution of capping agents are listed in Table 1 and shown in Fig. 5. which indicate that the in situ photo-reduction using sun light as reducing agent in the presence of capping agent, give similar size distribution, these results matches with data obtained from UV–vis spectroscopy as shown in Fig. 4. Stability of nanoparticles is crucially important for many applications and can be determined using zeta potential measurements [35]. Zeta potential is the net surface charge of the nanoparticles when they are inside a solution. The fact that
particles push each other and their agglomeration behavior depends on large negative or positive zeta potential. The zeta potential playing an important role limits in the stability of solutions is +30 mV or 30 mV. To regard the particles as stable, zeta potential should be either higher than +30 mV or lower than 30 mV [36]. By inspection data in Table 2, it was found that the zeta potential values of prepared silver nanoparticle encapsulated by the prepared cationic surfactants are greater than +30 mV, which be indication on high stability of prepared silver nanoparticles against agglomeration. High value of zeta potential indicate that the surface charge on nano-silver is high so the electrostatic repulsion between particles increase, keeping particles without agglomeration and stable for long time. The acquired positive charge of zeta potential is mainly due to the used capping agent is cationic surfactant (carry positive charge) [37], while zeta potential of silver nanoparticle prepared without using capping agent and after irradiation to sun light for 1 month was 0.386 mV. Also we found that zeta potential values of prepared silver nanoparticles are positively related with hydrophobic chain length of added capping agents, where by increase chain length of capping
Table 1 Size distribution of prepared silver nanoparticles using prepared capping agents. Capping agent
Distribution range Size
Maximum distribution range
Number (%)
Size (nm)
Number (%)
97 98.3 97.2
15–38 21–38 21–44
92.2 87.4 91.6
(nm)
Fig. 4. UV spectra of prepared silver nanoparticles using C10Bn, C12Bn and C16Bn as capping agent.
AgNPs capped by C10Dim AgNPs capped by C12 Dim AgNPs capped by C16Dim
15–50 18–50 18–50
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Fig. 5. Size distribution of silver nanoparticles using prepared capping agents determined by DLS.
agent, zeta potential increase, which be indication on increasing stability of prepared silver nanoparticle against agglomeration for example zeta potential of prepared silver nanoparticle capped by C10Dim, C12 Dim and C16 Dim are 34.1 10.4, 48.9 9.9 and 52 10.7 respectively. 3.2.4. Energy dispersive X-ray (EDX) EDX spectroscopy results confirmed the significant presence of pure 100% silver with no other contaminants. The optical absorption peak at 3 keV, is typical for the absorption of metallic silver nanocrystallites due to surface plasmon resonance [38]. Fig. 6 shows the EDX analysis of the AgNPs capped by the prepared cationic surfactants. The EDX spectrum showed a strong and typical optical absorption peak at approximately 3 keV, which was attributed to the SPR of the metallic Ag nanocrystals [38]. This result indicated that AgNPs were formed in the reaction medium. Beside of Ag there are others bands for C, O and Br elements peaks which appeared due to the scattering caused by the compounds that are bound to the surface of silver which indicating that the used cationic surfactants act as capping agents for silver nanoparticles.
Table 2 Zeta Potential and conductivity of prepared silver nanoparticle by dynamic light Scattering (DLS). Capping agent
Zeta potential (mV)
Conductivity (mS/cm)
No capping and irradiation for 1 month AgNPs Capped by C10Dim AgNPs Capped by C12Dim AgNPs Capped by C16Dim
0.386 34.1 10.4 48.9 9.95 52 10.7
1.64 0.183 0.169 0.152
3.2.5. FT-IR spectroscopy FT-IR spectroscopy is used in order to understand the role of prepared capping agent in the formation of silver nanoparticles and the chemical environment of the final product. In Fig. 7, all bands around 2926, 2853, 1500 and 1642 cm1 indicating the presence of capping agent with the nanoparticles. Bands at 2926 and 2853 cm1 corresponds to asymmetric and symmetric C–H stretching of alkyl chain of C12Dim. Band at 1642 cm1 correspond to Schiff base group (–C5 5N–). On comparing IR bands of silver nanoparticles capped by surfactants in Fig. 7 with IR bands of surfactant alone in Fig. 8, we notes that some bands maxima are little blue shifted and some bands are also little red shifted. These relatively small shifts are mostly due to the constraint of the capping molecular motion, which presumably resulted from the attachment on the nanoparticles surface [39]. Also we note increasing in the intensity of the band around 1375 cm1 by 50–80% than band of capping agents alone, which indicate presence co-ordination bond between CH2 of hydrophobic chain length of capping agent and silver nanoparticles surface. This co-ordination bond enhance role of capping agents chain lengths in shaping, sizing and distribution as indicated by both transmission electron microscope, UV–vis spectroscopy and dynamic light scattering. 3.3. Evaluation of the synthesized surfactants as antibacterial and antifungal We evaluated the prepared cationic surfactants and their capped form with silver nanoparticles as biocide against some pathogenic Gram-positive (B. pumilus and M. luteus) and Gramnegative (P. aeuroginosa and S. lutea) bacteria and also, some
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Fig. 6. EDX silver nanoparticles capped by prepared surfactants: (A) is C10Dim, (B) is C12Dim and (C) is C16Dim.
pathogenic fungi (C. albicans and P. chrysogenum). The aim of the formation silver nanoparticles capped by cationic compounds is to increase their potency against microorganisms. The results of antimicrobial activity are recorded in Table 3, indicating that the synthesized compounds have antimicrobial activity rang from a moderate to slight high effect on Gramnegative bacteria and from slight high to high on Gram- positive bacteria and very high effect on fungi compared to the drug reference used. The biological activities of surfactants often show a non-linear dependence on their chain length, where bactericides and fungicide activity increase by increasing hydrophobic chain length
[40], in our work the optimal alkyl chain length has been noted to be twelve carbon atoms, which has the maximum inhibition zone where compounds with twelve carbon chain higher than these with ten carbon atoms chain which higher than these of sixteen carbon atoms. These results are agreement with results obtained before [40–44], this behavior known by cut-off effect which observed for the first time more than 70 years ago, in which the activity increases progressively in a homologous series of compounds, with increasing chain length up to a critical point, beyond which the activity decreases [45]. Several theories have been postulated as to why this cut-off effect occurs, first have associated this cutoff with a limit in
Fig. 7. FTIR spectrum C12Dim capped silver nanoparticle.
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Fig. 8. IR spectrum of N-(3-((3,4-dimethoxybenzylidene)amino)propyl)-N,N-dimethyldodecan-1-ammonium (C12Dim).
Table 3 Antimicrobial activity of synthesized surfactants and their nano form against pathogenic bacteria and fungi. Inhibition zone diameter (mm) Pseudomonas aeuroginosa
Sarcina lutea
Bacillus pumilus
Micrococcus luteus
Candida albicans
Penicillium chrysogenum
Erythromycin
30
44
32
32
–
–
Metronidazole
–
–
–
–
27
25
C10Dim C12Dim C16Dim AgNPs capped by C10Dim AgNPs capped by C12Dim AgNPs capped by C16Dim
13 16 15 16 17 16
29 37 24 29 38 26
17 18 16 23 24 17
22 31 22 25 32 22
24 28 23 27 36 24
17 19 16 25 29 25
solubility, they proposed that as the alkyl chain increases, lipid solubility increases at a rate faster than the change in partition coefficient (lipid/aqueous) theory. At these higher chain length, partitioning is limited, making the concentration at the site of action insufficient to have a significant effect on the membrane of the cell wall [46] and hence according to this theory the activity of compounds should be ordered as follow C10? C12 ? C16 chain due to increase lipid solubility from C10 to C16. Other accounts attribute this cut-off to a decrease in perturbation of the membrane at higher chain lengths, proposing that the longer alkyl chain molecules better mimic molecules in the lipid bilayer, causing less of a disruption in the membrane [47]. Other theory based on critical micelle concentration (CMC), as surfactants chain length increase, their tendency toward micelle formation is greater, noted by the lower CMCs at higher chain lengths. This tendency to form micelles becomes greater than the tendency to move toward the interface (the membrane), and thus the concentration at the action site becomes decreased, also, as the size of the diffusing species increases from the size of a monomer to that of micelles, their diffusibility and permeation abilities will decrease, affecting their action on the microbial cell wall and hence according to this theory the activity of compounds should be ordered as follow C10? C12 ? C16. Other theory based on surface and thermodynamic properties surfactants which showed tendency of prepared compound
toward adsorption at the interfaces which facilitate their role of adsorption at the bacterial cell membrane, where increasing DGoads enhances the higher adsorptivity of prepared compound, from previous thermodynamic results DGoads increase by increasing chain length [17], and hence according to this theory the activity of compounds should be ordered as follow C16 ? C12 ? C10 chain. From that we can conclude that factors effects on cut-off point of homologous series of surfactants varying in chain length, are solubility, critical micelle concentration, (CMC), size of diffusing species and change in free energy of adsorption. Magnitude of these factors determines when cut-off occurs, according to data in Table 3, the cut-off was observed with surfactants with chain length (C16) for all prepared compounds. It was observed from data in Table 3, that biological activity (inhibition zone) of silver nanoparticle in capsulated with prepared cationic surfactants higher than corresponding prepared cationic surfactant, this can be attributed to silver nanoparticle alone has biological activity, so prepared surfactant capped silver nanoparticles have higher activity, this can be attributed to the higher surface area of prepared nanoparticles and the acquired positive charge of prepared silver nanoparticles (as indicated in zeta potential values in Table 2) in addition positive charge of cationic surfactants, where these positive charge facilitate adsorption at negative cell wall membrane of bacteria.
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G Model
JIEC-1907; No. of Pages 9 S.M. Shaban et al. / Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
4. Conclusion From the obtained results, we can conclude: In situ, facile and green synthesis of silver nano particles were developed using sun light as reducing agent with assistance of prepared surfactants. The prepared surfactants act as capping agents (DLS, EDX and FTIR). Increasing hydrophobic chain length of the capping agents, the stability of prepared AgNPs increase. Increasing hydrophobic chain length of the capping agents, the amount of AgNPs increase (Increasing absorbance in UV–vis spectra). Hexagonal AgNPs were prepared. The silver nanoparticles increase the biological activity of the capping agents.
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Please cite this article in press as: S.M. Shaban, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2014.02.019