Silver Nanoparticles - Research Proposal Example

Experiment: Silver Nanoparticles FAISAL BINHUDAYB ID: 2130924 SEPTEMBER 30, 2015 Objective The objective of this lab experiment was to synthesize silver nanoparticles using a simple chemical reaction process which does not require heating or quenching, and analyzing the samples by UV-Vis spectra and light scattering to determine the size and optical properties of the silver nanoparticles. Introduction For the past few decades, it has been known that nanoparticles of metals, particularly noble metals such as silver and gold exhibit distinct chemical, biological and physical properties from their bulk counterparts (Solomon, Bahadory and Jeyarajasingam). Nanoparticles are made of several thousands of atoms of an element, and are very much small in size, ranging from 1 to 100 nm. They usually exhibit different properties from those of the bulk material at the macro-scale. Metals such as copper, gold and silver interact with light differently at nano-scale level, which in turn affect their appearance in terms of colour (Liu and Jiang). Silver nanoparticles have unique thermal, electrical and optical properties and have a wide range of applications, from photovoltaics to chemical sensors, biological and medical applications to electronics and plasminics. Nano-size particles with particle diameters less than 100 nm have found a wide range of applications in different fields. Control of size and shape of the nanoparticles is very essentially especially where a desire property of the nanoparticles is required. This has sparked an interest in studying this particular area for utilization of these optical properties exhibited by the nanoparticles of silver as functional components in a number of products and sensors. Usually, the nanoparticles range between 1 nm and 100 nm in size and are extremely efficient at light absorbing and scattering. Unlike many other dyes and pigments, the colour of silver nanoparticles depend on the size and shape of these nanoparticles (Solomon, Bahadory and Jeyarajasingam). These variance in colours is as a result of the surface plasmon resonance, because at a particular energy, free electrons of metals oscillate and absorb electromagnetic radiation (Liu and Jiang). The efficient interaction of nanoparticles of silver with light occurs due to a collective oscillation of conductive electrons on the surface of the metal when excited by a specific wavelength of light. Silver nanoparticles have numerous technological applications and are incorporated in design of a wide array of products based on their desirable optical, antibacterial and conductive properties. In optical applications, silver nanoparticles are utilized in efficient harvesting of light energy, and for enhanced optical spectroscopies such as surface-enhanced Raman scattering and metal-enhanced fluorescence. In conductive applications, nanoparticles of silver are utilized in conductive inks and incorporated in various composites to improve electrical and thermal conductivity (Solomon, Bahadory and Jeyarajasingam). Due to their antibacterial properties, silver nanoparticles are incorporated in plastics, cosmetics, wound dressings, footwear, apparel and paints. In diagnostic applications, nanoparticles of silver are used in several assays and biosensors where the materials of the nanoparticles can be applied as biological tags and used for quantitative detections (Welles). In this particular lab experiment, nanoparticles of silver, were chemically synthesized using a chemical reaction involving reduction of silver nitrate with sodium borohydride. Sodium borohydride is the reducing agent, reducing silver nitrate to stabilized silver nanoparticles. The samples were then analyzed by UV-Vis spectra. The light scattering experiment to compare particle size was not performed because the machine had a problem. Experimental procedure R\Please refer to the manual “Nano3702/8702: Frontiers of Nanotechnology GE, Experiment7: Silver Nanoparticles”. Preparation of solutions The following solutions were prepared as per the calculated proportions to make the silver nanoparticles for optical properties testing. Mass of sodium citrate (Na3C6H5O7) that was used: Molar mass = 294.1 g Mass of 500ml, 0.000375 M silver nitrate (AgNO3): Molar mass = 169.87 g Mass of 500 mL, 0.05 M hydrogen peroxide (H2O2): Molar mass = 34.0147 g Mass of 250 mL, 0.005 M sodium borohydride (NaBH4) Molar mass = 37.83 g Mass of 250 mL, 0.001 M potassium bromide (KBr) Molar mass = 119.002 g Analysis and Discussion of Results During the chemical reaction process, nanoparticles of silver are kept in suspension owing to the repulsive forces that exist between the particles due to adsorbed borohydride. This synthetic process produces fairly stable silver nanoparticles (Liu and Jiang). Excessive amount of sodium borohydride ensures that all the ionic silver is reduced to silver nanoparticles. Each solution had a unique wavelength that correspond to the maximum absorbance. A greater absorption was observed between a wavelength of 500 nm and 600 nm, with peak absorbance 0.678 and 1.371. The figure 1 below shows the UV-Vis spectrum of 7 vial solutions labeled A to G that were prepared. Figure 1: UV-Vis absorption spectra for the seven vial solutions prepared The table below gives a summary of the maximum peak and wavelength for each solution: Table 1: Summary of wavelength and peak absorbance for each of the seven solutions prepared during the experiment. Solution Wavelength (nm) Peak Abs. A 506.1 0.678 B 628.9 1.029 C 627.0 1.022 D 514.1 0.904 E 505.0 0.910 F 616.0 1.371 G 741.1 1.364 From the table above, solution G has the highest absorbance peak (1.364 at), while solution A has the lowest peak (0.678 at). The absorbance value is dependent on the particle size present in the solutions. The solutions of silver nanoparticles prepared had colour changes from colorless to a number of colors. These distinctive colors of colloid silver are due to a phenomenon referred to as plasmon absorbance. Oscillations are created in conduction electrons when an incident light is directed towards a surface with the silver nanoparticles, absorbing electromagnetic radiation. Each solution forms a unique spectrum based on the colour of colloid silver in the solution. The wavelength of the maximum plasmon absorption in a given solution can be used to show the size of particles in the solution. When the silver nanoparticles that produced the absorption spectra shown in figure 1 above are analyzed using TEM derived size distribution, it becomes possible to determine the size of the particles (Solomon, Bahadory and Jeyarajasingam). Unfortunately, it was not possible to obtain adsorption spectra because the machine in the lab was out of operation due to a breakdown, and therefore, comparison of particle sizes was not done in this experiment. Figure 2: A picture of different colors of various sizes of Ag particles taken during the experiment. Dynamic light scattering is a technique for measuring the effective size of nanoparticles in a solution. A lot of information can be obtained about the physical state of silver nanoparticles by analysis of the spectral properties of the metal solution because silver nanoparticles have very unique optical properties. The spectral response is a function of particle diameter. The figure below shows the extinction spectra expected with silver nanoparticles with diameters between 10 nm and 100 nm. The maximum optical density lies between 400 nm and 600 nm, similar to the range of wavelength for absorption of the particles in figure 1. Figure 3: Extinction spectra of nanoparticles of silver with diameters between 10nm and 100nm, concentration of 0.02 mg/ml. From figure 3 above, the maximum peak plasmon resonance broadens and moves to longer wavelengths as the diameters of the particles increases. This is the relationship between absorbance and the size of silver particles. Determining the molar extinction coefficient By plotting a graph of concentration of silver nanoparticles in various dilutions against their respective absorbance, and getting the slope of the best line of fit, the molar extinction coefficient can be obtained. However, this experiment was not performed in the lab due to technical problems developed by the spectrophotometer instrument. Therefore, we could not obtain results for this part. The literature value of molar extinction coefficient is = 4.28 10 -8 M-1 cm-1. If the slope of the graph of concentration of dilutions versus absorbance is given, the molar extinction coefficient is obtained as follows: Molar extinction coefficient, = Where: L = 1 cm Conclusions This experiment demonstrated formation of silver nanoparticles using a simple chemical reaction. The nanoparticle solutions prepared exhibited colour variations that depict a phenomenon known as plasmon absorbance, and the optical properties of the silver solution. The wavelength at which this absorbance takes place is an indication of particle size of the element. Most peak absorptions of the solutions occurred between 500 nm and 600 nm of wavelength. This optical spectrum of the nanoparticles is due to surface plasmon absorption. Characterization of metal nanoparticles is very important when it comes to its applications in various fields. Performing this lab experiment provided good knowledge of understanding part of the processes in nanotechnology. References Read More