Studying the effective parameters in the synthesis of silver nanoparticles by reverse microemulsion method

Doctoral dissertation in the field

Chemical engineering

Abstract

Study of effective parameters in the synthesis of silver nanoparticles by reverse microemulsion method

Metal silver nanoparticles are of interest due to their use as catalysts, antimicrobial agents and use in biosensors. The practical use of silver nanoparticles is highly dependent on the size distribution and structure of these particles. There are several methods for the synthesis of silver nanoparticles, such as chemical reduction of silver ions in a solution, photocatalytic reduction, use of microwave waves, and biochemical reduction. Meanwhile, there is special attention to the synthesis of silver particles using precipitation in reverse microemulsion. The reason for this issue is the possibility of controlling the size distribution and morphology of particles in this method. Several researches have been conducted on the synthesis of silver nanoparticles by microemulsion method. However, investigating the effect of some important parameters such as surfactants and additives on the size distribution and morphology of synthesized silver particles requires more studies. This research examines the effect of surfactants, concentration of reactants and additives on morphology and size distribution of silver nanoparticles obtained by inverse microemulsion method. In addition, the modeling of the deposition process of nanoparticles is done based on the mass balance equations and their solution by finite difference method, and the important parameters of the average size of the synthetic particles have been calculated. Optimizing the kinetic coefficients of the process was done by minimizing the difference between the average particle size measured in the laboratory and the average particle size calculated by the model. This model can be used in dynamic process control. The results show that the smallest particle size is related to the surfactant Span 80 and polyethylene glycol 1000. The addition of aniline decreases the average particle size and increases the hexagonal morphology of silver particles. Meanwhile, the use of sodium citrate and polyvinyl pyrrolidine increases the average size of the particles. Optimum kinetic coefficients indicate the high dependence of nucleation on supersaturation. Also, the number of atoms required to form a nano silver particle (Ncrit) was calculated as 5.

Key words: inverse emulsion, average particle size, modeling, morphology, silver nanoparticles.

1-1-silver metal

1-1-1-Physical and chemical properties of silver

Silver in pure form The metal is shiny and relatively soft. This metal is somewhat harder than gold and becomes shiny after polishing. This metal element has the highest conductivity in heat and electricity.

Although among the noble metals, silver is considered chemically active metal, but it should be noted that compared to non-noble elements, it does not have a significant level of reactivity. This element does not oxidize as easily as iron, but it reacts with sulfur and forms a cloudy compound (Lide, 1994). Silver cannot react with non-oxidizing acids such as hydrochloric and sulfuric acids or strong bases such as sodium hydroxide, but oxidizing acids such as nitric acid or concentrated sulfuric acid dissolve it and form monovalent silver (Ag+). This ion, which is present in all simple and soluble compounds of silver, is almost easily reduced to silver metal by using organic reducing agents such as those seen in silver mirrors (Lide, 1994). and in terms of abundance in the earth's crust, it has taken the 63rd place. Sometimes it is found as a free element, but in most places silver is found as minerals containing silver compounds, such as argentite with the chemical composition of Ag2S and serargirite with the chemical composition of AgCl. About 75% of silver produced in the world is actually a by-product of the extraction of other metals (Lide, 1994). The most important compounds of silver in terms of application are:

Silver nitrate: colorless compound, very soluble, toxic and easily reduced to metallic silver. This compound is used in the preparation of silver compounds and various inks.

Silver chloride: It is a white compound and insoluble in water, but it dissolves in ammonium hydroxide and forms Ag(NH3)2- complex. This compound is used as an ionization detector.

Silver bromide: a light yellow insoluble compound that is more insoluble than AgCl and is more used in photography.

Silver iodide: a yellow insoluble compound that is more insoluble than AgBr and is used for cloud fertility.

Silver sulfide: the most insoluble silver salt with a black color and is the main component of silverware darkening materials.

Silver oxide: it is the most stable form of silver (Ag2O) and has a color It is gray and is used in glass and ceramic industries. It is also one of the few conductive oxides that are used in fuel cells.

1-1-3-Usages of silver nanoparticles

Silver nanoparticles have significant antibacterial properties. This property has been proven for all kinds of bacteria, fungi and viruses (Sadeghi et al., 2012). Therefore, silver nanoparticles are widely used in the manufacture of medical equipment. For example, we can mention all kinds of wound adhesives, skin improvers, artificial teeth and bone coverings. Among its other uses, we can mention the manufacture of lotions, toothpaste, toys, antibacterial paints, air and water filters, and food preservatives. The suitable properties of silver nanoparticles make it possible to use fluorescence and make various sensors capable of working in living cells and ammonia concentration sensors, making images of cancer cells and biosensors used for plant pests and nuclear waste. Also, the high surface-to-volume ratio of silver nanoparticles is the best property for using it as a catalyst. Based on this, silver nanoparticles and its nanocomposites are a suitable choice as catalysts for benzene oxidation, phenol processing and carbon monoxide oxidation (Tolaymat et al., 2010).

1-1-4-common compounds in the synthesis of silver nanoparticles

Studies show that most methods of silver nanoparticle synthesis are based on the use of silver salts to produce Silver ions are nanoparticles with the ability to be regenerated and precipitated. Figure 1-1 shows the types of salts used in the production of silver nanoparticles. According to Figure 1-1, silver nitrate is the most used in the synthesis of nanoparticles, and the reason is the high chemical stability of this compound compared to other salts (Tolaymat et al., 2010). The solvents used are often used to dissolve metal salts. In the synthesis of silver nanoparticles, approximately 80% of the processing is done with water. But recently the use of organic solvents that are safe for the environment has been expanded and the reason for this is the large amount of contaminated waste in water-based processes as a solvent. microemulsion method

By

EHSAN NOURAFKAN

Production of silver-nanopraticles is important due to the use of these particles as antibacterial agents, biosensors, and catalysts. Applications of silver nanoparticles depend on their morphology and size distribution. Methods of chemical reduction of silver ions in solution, photocatalysis, microwaves and biochemical reduction are used in research and industry to form silver nanoparticles. However, precipitation in inverse microemulsions may be used to synthesize the nanosilvers. The advantage of this method is a better control of nanoparticles size and morphology. Numerous researches have been reported about the synthesis of nanosilver through the microemulsion method. However, effects of some parameters such as surfactants and additives on size distribution and morphology of nanoparticles are not fully investigated. The present research studies the effects of type of surfactants, concentration of reactants and additives on morphology and size distribution of silver nanoparticles synthesized through the microemulsion method. Additionally, modeling of process based on mass balances and the model solution through finite difference method were developed in the present study.