Currently, nanosilver products (AgNPs) are well known for their effectiveness in killing bacteria and viruses to help prevent and treat aquatic diseases (Shrimp, fish, snail, frog, eel …). In addition, it is also used in a number of other fields such as antibacterial fabrics, antimicrobial paints, as a medicine to disinfect barns, for drinking, mixing food to prevent bacterial and viral diseases in livestock industry. , water treatment, wastewater, waste, rubber …
However, not all products are as true as its name suggests. Business units that defy to make a profit make fake silver products of poor quality to deceive consumers who are not familiar with nano silver. NanoCMM Technology would like to share some information to help you identify real AgNPs and counterfeit AgNPs.
1. What is Nanosilver?
- Nanosilver is denoted as nano Ag, not nano Ag + (Ag + is a silver salt, not silver).
- Size AgNPs: from 10-100 nm (read as nanometer, 1nm = 1 / billion of 1m)
2. Method of measuring particle size
There are two methods of measuring particle size: DLS (Dynamic Light Scattering) Method and TEM (Transmission Electron Microscope).
+ DLS method will capture the signal of the largest particles and use the relative calculation formula to give a relative particle size result.
+ TEM that selects different shooting areas will produce different results to get accurate results, they have to combine a lot of shooting areas (A billion images to have a relative result) if only 1 2 standard images are taken for size of the product is not objective, inaccurate.
3. Color of nanosilver and silver salt
AgNPs absorb photos at the 400-450 nm wavelength, because of the optical absorption at this wavelength, when diluted to about 10 ppm, it has a lemon yellow color (Figure 1). Silver ions are colorless and transparent like filtered water
Figure 1. Nanosilver solution diluted at 10 ppm lemon yellow color (top left)
For example: nanosilver bottles commonly found on the market are 500 ppm (Or 1000 ppm), then dilute 50 (or 100) times with water (1 liter dilute with 49 (or 99) liters of water will get 10 ppm solution) .
So ask the question, if someone makes the colors of AgNPs fake and similar, how to know?
To distinguish, you can use the following 2 ways:
Shine the laser light through, solid AgNPs will scatter the light to the human eye so you will see a clear ray of light. (Picture 2)
Figure 2: The left side is the real silver nano solution, so it has the ability to scatter light (red line due to light scattering of AgNPs particles to our eyes), the right (not AgNPs) is the yellow color. However, there are no metal particles, so it cannot scatter light.
Add concentrated HNO3 acid to a yellow silver nano solution (10 ppm AgNPs solution) and the solution will lose its yellow color. Reason:
Ag + HNO3 -> AgNO3 + NO2 + H2O
If a yellow color persists, the yellow color of the solution is not that of the AgNPs
Nanosilver products, how much is silver, how much is Ag + (silver salt)
Currently, on the market for sale of nano silver a lot, each place sells a different content and a different price such as 500 ppm, 1000 ppm … However, in 500, 1000 ppm, how much% is AgNPs, how many% are ions Silver Ag +.
At present, some inspection units such as SGS, Bureau Veritas, Mekong Lab … can only analyze total silver content including Ag content and Ag + silver ion content.
The pharmaceutical units checked the Ag and Ag + content by qualifying with NaCl (table salt) or HCl acid based on Ksp theory (Solubility product of AgCl) to determine relative content of Ag and Ag +.
Test method: Dilute a little salt in water and add AgNps solution of 500 ppm or 1000 ppm … If a lot of white precipitate occurs, the solution has a large Ag + content. Poor product quality. If no white precipitate occurs, the Ag + content is insignificantly low.
Instructions on how to test: 100 ml of nano silver using 3.5 grams of salt. For economical use, 10 ml of AgNPs 0.35 g of salt. Or take 10 ml of AgNPs mixed with 10 ml of seawater (relative)
In the case of no white precipitate, the AgNPs solution turns gray (or black) so that the solution is clear for about 10-12 hours and has a gray layer on the bottom. This proves that this product has poor durability in seawater, and may lose its effectiveness before any problems are resolved.
Is there any effect when using Ag + silver salt?
Daphaco has a product called Argyrol 1% (2000 ppm Ag + ions to be dropped into the eyes of a newborn).
So if products on the market like 500 ppm, 1000 ppm Ag + are used to splash the pond, it will also have a big impact. However, it is wasteful like throwing money through a window because Ag + splashed into the water will be precipitated by the following reactions:
Ion (Ag +) + ion (CO3) 2- -> Ag2CO3 (white or light yellow precipitate)
Ion (Ag +) + ion (Cl-) -> AgCl (white precipitate), if the environment is salt water, the reaction will be faster. The result is both loss of money and inefficiency.