1.Nanosilver what is?
Silver (Ag) has long been known as a metal that can keep food spoiled due to its antibacterial activity. This metal can release Ag + ions that inactivate microorganisms by destroying the cell membrane and the microbial’s ability to duplicate DNA. Silver nanoparticles are silver particles at nanometer size. Antibacterial silver nanoparticles by releasing Ag + ions, silver particles when at 1-10nm nanoscale can directly affect the cell membrane of bacteria by altering the osmotic pressure. results in cell death
Not only effective in the field of disinfection, nano-sized silver is also known to be an excellent catalyst for many chemical reactions. Especially organic fusion and has grown rapidly over the years, thanks to its unique properties such as selectivity, durability of the catalyst and its reusability in reactors. chemical application. Thus, silver nanoparticles have been exploited for a wide range of capacities, such as the reduction reactions of nitro ring compounds, carbonyl compounds, and deminization. Especially its applicability in industry, because pharmaceutical industries have produced the famous water pollutant 4-nitrophenol, which is a serious environmental pollutant. Therefore, there are many reports on the use of nanosilver as catalyst for 4-nitrophenol reduction in water and many related kinetic studies. From the perspective of organic synthesis, this reaction is quite simple and represents many similar organic fusion reactions.
– Pharmaceutical (mouthwash, throat spray, body deodorant spray from nano silver material)
– Cosmetic chemistry (Acne cream, cleanser, fabric softener … contains nanosilver)
– Livestock (nanosilver replaces antibiotics in prevention and treatment of livestock diseases)
– Aquatic products (nanoSilver-silvering and feeding help prevent and treat aquatic diseases, especially shrimp, fish, snails …)
– Rubber (antibacterial latex)
– Environment treatment
– Reaction catalyst
– Antibacterial nanosilver paint
– Antibacterial silver nano-fabric
3. Synthetic method
- Top-down method by physics
The principle of this method is from large metal, then converting it into nanoscale particles by fabrication techniques such as cutting, grinding, grinding … This method can produce nanoparticles with size from 10 – 100 nm.
However, the top-down method is not really effective. One of the problems is uniformity of the grain surface structure. This problem affects the physical and chemical properties of nanostructured particles due to the ratio of large surface area to volume. Despite this problem, this method can be chosen when fabricating a large number of silver nanoparticles. One of its applications is in the electronics industry, when nanoscale structures are cut using laser techniques.
Ion Ag + under the action of a physical agent. Under the effect of commonly used agents such as heat, electromagnetic waves (UV rays, microwaves, lasers, gamma, …), ultrasonic waves, Ag + ions are transformed into atomic silver.
Under the effect of physical agents, there are many processes of conversion of solvents or of substances dissolved or dissolved inside the solvent, to produce chemical radicals that reduce Ag + ions into atomic silver. form nano.
- A bottom-up method by chemistry or biology
The principle of this approach is to build from atoms, molecules or from molecular chains. One of the typical bottom-up synthesis methods is the synthesis of nanoparticles from the colloidal system.
This method uses chemical agents to reduce Ag + ions to Ag metal atoms, in the presence of electrostatic or surface protection agents, to prevent cluster agglomeration of needle particles. silver type, to maintain the silver particles at the nanoscale. The basic principle of the method is shown through the following equation:
Ag + + X -> Ag -> nano Ag.
In this method, Ag + ions under the effect of reducing agent X will reduce Ag + ions to Ag metal atoms, then these metal atoms adsorb Ag + ions and Ag + deionization reaction by X reducing agent. increasing the size of silver metal particles, in the presence of protective agents will form silver particles of nano size.
The commonly used reducing agents are: Sodium Borohydride (NaBH4), Ethylene Glycol, Sodium citrate, Acid ascorbic, …. Surface protection agents such as: TSC, PVP (Polyvinylpyrrolidone), CTAB (Cetrimonium bromide), SDS (Sodium dodecyl sulfate),….
4. Method measured the size of nanosilver particles
* DLS (Dynamic Light Scattering) method
– Measurement principle: Based on Mie scattering and Fraunhofer diffraction. The device is based on a light source, a solid diode laser at a wavelength of 650 nm that shines through the sample cell. At an angle of 900 and 1270 relative to the transmission of the light source is a sensor that records the signal of light intensity. When a laser beam hits the nanoparticles, the Brown thermal motion nanoparticles cause a fluctuation in the intensity of the scattered light that is recorded by the sensor. The intensity of the scattered light and the oscillation frequency depend on the nanoparticle’s motion velocity. Smaller particles will move faster under the action of Brown motion.
– Measurement results: Based on the changes in scattered light intensity and recorded frequency, through the Stokes-Einstein equation:
* Method TEM (Transmission electron microscopy)
– Measuring Principle: Similar to conventional optical microscopes, but the light source is no longer visible but is replaced by an electron emitting source. The sample is vacuum-aspirated, electrons are accelerated with voltages of about 80kV – 200kV, through the magnetic lenses and scattered by the sample. The image recorder and viewer is a fluorescent screen, when an electron hits the screen, the fluorescent material will glow and the image is recorded.
– Measurement results: Measured results are real images of silver nanoparticles, with high accuracy, but depending on different imaging regions on the technician’s specimen.
5. Determination of Ag + residue in nanosilver
According to the European Pharmacopoeia standard
– Take 0.5g of sample to test, add 5ml of anhydrous Ethanol and shake for 1 minute (the purpose is to transfer all Ag + ions from water into ethanol). Then filter the solution (in this solution contain Ag + ions if any), test the solution above with 2 ml of concentrated HCl. If no white precipitate occurs, the sample is of satisfactory quality.
Conventional rapid qualitative with a sample of 15000 ppm
– Take 0.1g of sample (total Ag concentration is 15000 ppm), add 15g of distilled water to the sample and shake well until the silver nano solution is completely dispersed (theoretical total Ag concentration is 100ppm). Take 5 ml of the above solution to test with 2 ml of 8M NaCl solution. If no white precipitate occurs, the sample is qualified.
– Theoretical basis:
AgCl <=> Ag + + Cl–
The equilibrium constant Ksp = [Ag +]. [Cl-] = 1.77 x 10-10 (at 250C)
After taking 5 ml of diluted solution to test with 2 ml of 8M NaCl solution. Obtained a solution of about 7ml of solution, with a total Ag concentration of 71ppm (0.66mM), and Cl- concentration of 2.3M. In order not to appear white precipitate [Ag +]. [Cl-] ≤ 1.77 x 10-10
=> [Ag +] ≤ = = 0.77 x 10-10 M = 0.77 x 10-6 mM
The total Ag content in the sample is 0.66mM
=> ion content Ag + ≤ 1.17 x 10-4%
6. Nanosilver reliability
The durability of silver nanoparticles can be studied by accelerating the aging rate of products by temperature.
– Theoretical basis:
AgNP → Agmicro
– From the Arrhenius equation, an increase in temperature increases the value of the reaction rate constant k:
That is, when increasing by 1000C, the reaction speed increases by about 3640 times.
– Proceed to boil the sample at 1300C for 1 day. Then sensory observations, quantification and evaluation. The evaluation results are similar to storing samples at 300C for about 10 years (1×3640).
– This is true for the case where Ea does not change significantly in the survey temperature range.