Synthesis and study silver nanoparticles by chemical method

In this paper, Ag nanoparticles with various sizes and forms are made by using reduction methods of Ag ions in aqueous solutions in the presence of strong reducing agents like hydrogen peroxide (NaBH4) with different concentrations of silver nitrate AgNO3 (1mM to 0.9mM) improving its effect on the stability of the nanoparticles. From the results, stability of the Ag nanoparticles is due to the ions of NaBH4 that surrounding the nanoparticles and decreased from aggregating as demonstrated by using UV-VIS spectra, Particle size analyzer (PSA) , Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) to determine their behavior as catalyst materials and analysis the kinetics of reactions.


Introduction
nanomaterials have received considerable consideration with the recognition of their dramatically altered material properties as compared to their bulk materials.As a result, the nanoparticles have wide applications in civil and manufacturing fields.For example, they are used as micro-electronic materials, bactericidal materials, catalyst materials and Magnetic materials of Recording.Also, they have possible applications in detection of DNA and photodetection [1].The change of bulk material to nanomaterials results in distinctive features that are controlled by two main issues.First issue represented by decreasing in size of the particles, while the second issue including the number of atoms at the surface is increases noticeably as compared with the number of atoms in the center of the crystal and the broadly nanomaterials using is silver nanoparticles (AgNPs) [2].Silver nanoparticles have attracted considerable interest because of their size and shape properties like optical, electrical, and magnetic properties beside to possible applications in a common of fields including plasmon, nanoelectronics, chemical sensing and composite materials, cosmetic products, and electronic components.So far, many Ag nanostructures have been successfully synthesized with various morphologies [3][4][5].Silver nanoparticles with different shapes, sizes and surface properties are created using a variety of methods because of the type of reducing and capping agents used to prevent their aggregation [6].Silver nanoparticles are often created by using silver nitrate dissolving in Distill Water (DW) with NaBH4 or citrate as reducing agents or as capping agents resulting mostly in negatively charged surfaces [7].In the past, a number of processes are used to form silver nanoparticles, consist of reduction method of Ag ions in aqueous solvent with or without surfactants, electro-chemical reduction, heat evaporation, thermal decomposition in aqueous solvents, as well as poly procedure like chemical and photo-reduction, and radiation chemical reduction.All these procedures of synthesis include reduction of noble metals in the presence or absence of surfactants that is essential in control the formation of metal colloids during agglomeration [8][9][10].The synthesis of silver nanoparticles is well documented and usually, the nanoparticles are obtained by bottom-up methods where atoms are self-assembly into nanoparticles [11].Therefore, chemical reduction route has been intensively used and many reducing agents have been tested such as trisodium citrate [12], ethylene glycol [13], or sodium borohydride [14].Besides, solution temperature, concentrations of the metal salt, reducing agent and reaction time also control particle size.Since, controlling size and shape of metal nanoparticles remains a challenge [15].This study concerns the formation of silver nanoparticles using chemical reduction reaction by changing the concentration of AgNO3 from 1mM to 0.9mM while the concentration of NaBH4 which is a strong reducing agent is kept constant.Then, the micrograph and average particle size of the Silver nanoparticles obtained from each sample was observed by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM) and Particle size analyzer (PSA).The absorbance of solution containing Ag nanoparticles was measured using UV -Vis absorption spectroscopy at room temperature in the wavelength ranging from 300 to 900 nm improving Ag nanoparticles stability with changing the AgNO3 concentration and keeping the concentration of reducing agent constant.

Experimental procedures Preparation silver nanoparticles (AgNPs) using various concentrations of AgNO3 and its effect on sodium borohydride as strong reducing agent
The synthesis of Ag nanoparticles, using reduction reaction, involved the reduction of AgNO3 by strong reducing agents such as NaBH4.In the first approach, a colloidal of 2 mM NaBH4 is formed by dissolving 0.0079 g of NaBH4 in 100 mL of Distill Water (DW) and 1 mM AgNO3 is formed dissolving 0.019 g of AgNO3 in new baker of 100 mL of Distill Water (DW).Then

UV-VIS spectra
Ag nanoparticles of different types were characterized by UV/Vis spectroscopy, as their Surface Plasmon Resonances (SPR) cause different peaks in their absorption spectra.The absorbance of UV-Vis spectra for various concentrations AgNO3 aqueous solution with reducing agents like sodium borohydride, is shown in Fig 1 .For the first approach, UV-visible absorption spectra shows a maximum of absorption peak at 407 nm with the average particle size from 25 to 200 nm with small spherical shapes when the concentration sodium borohydride 2mM and AgNO3 1mM, yellow silver nanoparticle solution was obtained which implies the effect of NaBH4 as reducing agent and its stability for more than one month.In Fig ( 4 b), the particle size analysis (PSA) shows silver nanoparticles diameter range from 50 to 50000 nm with mean diameter 366 nm when the concentrations of AgNO3 is decreased to 0.9 mM as compared to NaBH4 concentrations 2 mM and leads to reduction of Ag ions was not complete which results in aggregation of particles producing and a great quantity of Ag nanoclusters while a few quantity of nanoparticles were produced.

Conclusions
In summary, the results indicate that the particle size can be ranged from small size to bigger size depending on the concentration of reducing agent and AgNO3 which is a limiting feature in Ag nanoparticles stability.In addition, the stability of Ag nanoparticles results from the fact that Ag nanoparticles created from NaBH4 ions are surrounding the nanoparticles and preventing them from agglomerates while the excessive NaBH4 concentration leads to prevent the reduction of Ag ions which results in aggregation of the particles and a large amount of Ag nanoclusters are formed as improved in UV.Vis, SEM, TEM and particle size analysis (PSA).

Vol: 13
No:1 , January 2017 DOI : http://dx.doi.org/10.24237/djps.1301.139AP-ISSN: 2222-8373 E-ISSN: 2518-9255 the solutions are mixed collectively by adding 5.0 mL of 1mM AgNO3 drop-wise about 2 minutes to 30 mL of cold 2.0 mM NaBH4.The forming solution is regularly stirred.Then 5 minutes later, a yellow color colloidal of Ag nanoparticles is achieved.In the second approach of formation Ag nanoparticles, the concentration of AgNO3 is changed by decreasing to 0.90 mM, but the concentration of NaBH4 used is kept.A colloidal of AgNO3 is prepared dissolving 0.017g of AgNO3 in 100 mL of Distill Water (DW).Then 10 mL of 0.9 mM AgNO3 is added to 30 mL of 2 mM cold NaBH4.After 5 minutes with stable stirred, Ag nanoparticles of a darker yellow colloidal is formed.Characterization of prepared AgNPsThe synthesis of Ag nanoparticles is characterized by UV-Vis spectral analysis (SP8001, Metertech) and Particle size analyzer (PSA, NanoBrook 90Plus Particle Size Analyzer) to predict the size of the Ag nanoparticle and their stability.Scanning Electron Microscopy (SEM) was performed for studying the surface morphology and structure of silver nanoparticles and Transmission Electron Microscopy (TEM, EM208, Philips, Day Petronic Co., Tehran, Iran) to demonstrate the typical shape and size of AgNPs.

Fig 4 :
Fig 4: Particle Size of the Ag nanoparticles formation using 2 mM of NaBH4 with a) 1mM of AgNO3 and b) 0.9mM of AgNO3