Introduction
General information about electrochemical properties of nanoparticles
Nanoparticles represent a very small unit with dimensions measured in nanometers and exist in the natural world or created by man. Due to their submicroscopic size, they have special material characteristics and the manmade nanoparticles have varied applications in medicine, engineering, catalysis, and environmental improvement. The electrochemical properties of nanoparticles are different to that of the bulk metal. For instance, a gold electrode is not electro catalytically active for carbon monoxide oxidation unlike the gold nanoparticles deposited on the entire gold conductive support. The overpotential for the electrochemical reduction is decreased at the electrode surfaces having gold or platinum nanoparticles. Therefore, the electrocatalytic activity of the electrodes modified with the metallic nanoparticles depends on the size of the nanoparticles (Luis, Liz-Marzán, Prashant & Kamat, n.d)
Specific information about silver nanoparticle
The synthesis of the silver nanoparticles can be through spontaneous reduction of silver nitrate in an amino silica-coated electrode or by solution synthesis. Silver nanoparticles electrodes have a difference in their electrochemical properties in comparison to the regular electrodes. Silver nanoparticle electrodes show higher redox currents density with a narrow half-peak potential width. Therefore, silver nanoparticles made from amino silica matrix can act as the reference electrode. Another property is their ability to sense changes in the humidity level when fitted with a humidity sensor (Jiang, Liu & Li, 2004).
Background
Zhou, Rees & Compton (2011), did a study on the electrochemical detection of silver nanoparticles and realized that the methods used for effective detection of the nanoparticles is limited. The use of nanoparticles in various goods and industrial purposes continues to increase despite the limited detection methods. The study was helpful in developing a method that assessed the presence and the properties of the particles in a given sample of the electrochemical responses produced by the particles colliding with an electrode. The method allows easy identification, quantification and characterizing of the particles in a sample. The results of the research showed that the direct electro-oxidation of the silver nanoparticles colliding with an electrode can be both viable and quantitative. The method can also be used for the characterization and identification of the silver nanoparticles.
Another research by Geagea, Aubert, Banet & Sanson (2014) involved the signal enhancement of the electrochemical biosensors through a direct electrochemical oxidation of the silver nanoparticle label having a zwitterionic polymer. The study was aimed at developing a new versatile label for the electrochemical biosensors based on zwitterionic polymer having silver nanoparticles coating. The results of the study showed that the silver nanoparticle coating provides a high colloidal stability and contributes to the enhancement of the signal. Its electrochemical oxidation provides an easy sensing process. The method offers a new solution to the detection of biological marker traces directly in the biological media.
Current problems/challenges
The use of silver nanoparticles made by electrochemical reduction proves to possess significant antibacterial properties as well as having various applications. However, there are some few challenges in their use. Some limited and well-controlled investigations show potential toxicities of the silver nanoparticle (Ji et. al., 2007). In addition, the methods used in the synthesis of the silver nanoparticles of various shapes and sizes are in the development stages thereby having problems. Among them are challenges in the stability and aggregation of the nanoparticles, control of the crystal growth, morphology, size distribution, and difficulty in control of the synthesis process.
The importance of the problem
The presence of toxic substances in the use of silver nanoparticles is a health hazard to the user. The nanoparticles find applications in many consumer products, hence risky to their health. The challenges experienced in the synthesis of the silver nanoparticles might cause other unprecedented problems in their use. Lack of stability and aggregation of the nanoparticles may make them change to a different substance. Moreover, the limited control of the synthesis process is likely to affect the expected final products.
The main goal of the research is to investigate the electrochemical properties silver nanoparticle made using amino silica coating from a direct reduction reaction using cyclic voltammetry.
General objectives and goals for the research work
The principal goal of the research is to examine the electrochemical properties of the silver nanoparticle using cyclic voltammetry. The specific objectives are;
- To find out whether nanocomposite coating has thesame redox property as the silver nanoparticles made from a solution
- To assesstheimpact of silver nanoparticles and hydrolyzed amino silica on electron diffusivity of the amino silica coating
Method and Strategy
The research will involve the fabrication of the metal silica electrode using a method that does not involve many steps from the need of both reduction and immobilization of the metallic nanoparticles. The simple method employed uses one-step approach in the synthesis of amino silica materials with non-mobile silver nanoparticles distributed at a nanometer scale. The research will examine the electrochemical properties of the nano mixture coating produced from the spontaneous reduction of silver metal. In addition, the proposed method will also help in the examination of the effects of silver nanoparticles on electron transfer within the coating in a solution (Choi & Luo, 2011).
Experiments proposed
Among the proposed experiments is the preparation of silver nanoparticle covered with silica gel. The experiment involves the use of fluorine coated with tin oxide glass as the working electrode. It will be cleaned with acetone and methanol and then dried under compressed air. The surface will then be treated with oxygen plasma cleaner, and then dipped in methanol to form a coating. The resulting electrode should have a brownish yellow color which is an indication of the presence of the silver nanoparticles within the film. The experiment can be monitored by the use of Ultraviolet and Visible spectroscopy using silver nitrate methanol solution at every fifteen minutes interval (Choi & Luo, 2011).
The electrochemical measurements will be done by use of Cyclic Voltammetry set at a scan rate of 50 milliVolts per second. The working electrode used in the experiment is nanocomposite coated fluorine glass electrode coated with tin oxide. The reference electrode in use for the experiment is silver wire coated with silver chloride and the counter electrode is platinum foil. The electrolyte that will be used is phosphate buffer that can have chloride ions (Choi & Luo, 2011).
Justification
The use of a mixture of the solution and gel materials as an immobilization matrix in various applications has been proved to have some limitations. Among them is the reduced electrical conductivity arising from the intrinsic property of silica. Therefore, it is necessary that researchers in this field develop a better material. In overcoming the shortcomings, the research dwells much on creating a nanocomposite material using the solution and gel mixture method having metallic components. The method uses both the metal and silica. The two components have to work together in order to demonstrate the desired properties. Therefore, it is possible to create materials having improved electrochemical properties by simply treating an amino silica-coated electrode with silver nitrate solution (Armelao, Bottaro & Campostrini et al., 2007).
Expected outcomes
After the experimental activities, the results should show that silver nanoparticles are slowly generated inside the amino silica film when dipped in silver nitrate solution. The UV/ Vis spectroscopy absorbance measurements are expected to show an increase at 400 nm due to the increase in the concentration of the silver nanoparticles.
The cyclic voltammetry measurement of the coating in the phosphate buffer should show that the nanocomposite film reports a very sharp redox current with a narrow voltage range versus the reference electrode. It is expected that the high surface area to volume ratio of the nanoparticles will exhibit a high peak current with a narrow peak width. The silver wire working electrode is expected to show a broader redox peak in the phosphate solution. The peak should be asymmetrical and the peak to peak separation distance greater than the cyclic voltammogram (CV) graph of silver nanoparticle coating (Parang et. al., 2012).
Another expectation is that silver nanoparticles within the amino silica film should improve the electrotransfer rate as an indication of the small difference in the oxidation and reduction potential.
It is expected that the pure amino silica and nanocomposite films will show a high diffusion rate of the ferricyanide at the electrode. The overall redox current of the nanocomposite film is expected to be lower than that of the pure amino silica film due to the pores occupied by the silver nanoparticles.
Figure 1: The cyclic voltammogram (CV) of silver nanoparticle coated with a nanocomposite film of amino silica.
Potential problems
In the course of the research process, some results may not exhibit the expected results due to differences in the working conditions. The results might have a variation from the theoretical due to the technicalities of the entire process. Another major problem is the lack of standard and up to date instruments for the measurement of the oxidation and the reduction electrode potentials. It gives results that are not a true reflection of the research work. Another problem to encounter is a constrained budget, thereby making it a challenge to acquire all the necessary materials.
Alternative strategies
An alternative method of the synthesis of the silver nanoparticle composite material is the use of molybdenum trioxide modified with silver nanoparticle. The process enhances the electrochemical properties of the electrode. The molybdenum nanorods are prepared by use of a hydrothermal process involving the coating of the trioxide with silver nanoparticles as the electrode material (Xu, Cao & Zhang, 2014).
Techniques
The principle technique to be used in the research is cyclic voltammetry in the investigation of the electrochemical properties of the silver nanoparticle. In addition, Ultraviolet and Visible Spectroscopy serves will help in monitoring the formation of silver nanoparticles within the amino silica matrix at 400 nanometers.
Timelines
| Task/Duration | Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 |
| Selection of the research topic | ||||||
| Proposal writing | ||||||
| Proposal Approval and assembling of the research requirements | ||||||
| Conducting the actual research and data collection | ||||||
| Compilation of the final report having all the findings | ||||||
| Project presentation |
N.B.: The shaded regions show the duration under which the tasks will occur.
Conclusion
Cyclic voltammetry is useful in the investigation of the electrochemical properties of the silver nanoparticles through spontaneous reduction of silver nitrate in an amino silica coated electrode. The nanocomposite silver electrodes exhibit a higher redox current density and have a narrow half peak potential width.
References
- M. Brisard. Electrocatalysis: Proceedings of the International Symposium Volumes 2005- 2011 of Proceedings (Electrochemical Society) pp. 200-205 ISBN 1566774365, 9781566774369
Jeong, J.; Han, B.S.; Shin, J.H.; Sung, J.H.; Song, K.S. & Yu, I.J. Twenty-eight-day inhalation toxicity study of silver nanoparticles in Sprague Dawley rats. Inhal Toxicol, 2007; 19: 857-871
Ji, J.H.; Jung, J.H.; Kim, S.S.; Yoon, J.U.; Park, J.D.; Choi, B.S.; Chung, Y.H.; Kwon, I.H.;
- Armelao, G. Bottaro, R. Campostrini et al. Synthesis and structural evolution of mesoporous silica-silver nanocomposites, Nanotechnology, 2007;18(15) Article ID 155606, 8 pages
Luis M. Liz-Marzán, Prashant V. Kamat. Nanoscale Materials; pp. 25-27 ISBN 1402073666, 9781402073663
Parang Z, Keshavarz A, Farahi S, Elahi S, Ghoranneviss M, Nasseri A. Preparation And Investigation Of Optical, Thermal, And Electrochemical Properties Of Ag/Co Nanoparticles. Nano [serial online] April 2012; 7(2):1250006-1-1250006-9.
- Geagea, P.-H. Aubert, P. Banet & N. Sanson. Signal enhancement of electrochemical biosensors via direct electrochemical oxidation of silver nanoparticle labels coated with zwitterionic polymers: Journal of the Royal Society of Chemists 2014; 51, 402-405. DOI: 10.1039/c4cc07474b
Xu Y, Cao X, Zhang Y. Silver nanoparticle modified MoO3 with enhanced electrochemical properties for a lithium-ion battery. Canadian Journal of Chemistry [serial online]. January 2014; 92(1):16-18.
- J. Choi, U. Huh, and T. J. M. Luo. Spontaneous formation of silver nanoparticles in aminosilica: Journal of Sol-Gel Science and Technology, 2009; 51(1): 124–132.
Yong-Jae Choi and Tzy-Jiun M. Luo. Electrochemical Properties of Silver Nanoparticle Doped Aminosilica Nanocomposite. International Journal of Electrochemistry, 2011; Article ID 404937, 6 pages, doi:10.4061/2011/404937
- J. Jiang, C. Y. Liu, and Y. J. Li. Electrochemical studies of silver nanoparticles tethered on silica sphere, Chemistry Letters, 2004; 33(5): 498–499.
Zhou, Y.-G., Rees, N. V. and Compton, R. G. The Electrochemical Detection and Characterization of Silver Nanoparticles in Aqueous Solution: Angew. Chem. Int. Ed., 2011; 50: 4219–4221. doi: 10.1002/anie.201100885
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