Hebei Messi Biology Co., Ltd. stated that nano magnesium oxide has become a new type of functional inorganic material because it has many optical, electrical, magnetic, thermal, chemical and mechanical properties that are different from ordinary magnesium oxide. Especially in the field of antibacterial materials that are closely related to human survival and health, it has shown unique advantages, such as long-lasting and broad-spectrum antibacterial activity, low cost, not easy to change color, and no biological toxicity.
1. How does nano magnesium oxide fight bacteria?
Correctly understanding the antibacterial mechanism of magnesium oxide is of great significance for improving the research on the antibacterial activity of materials. The two main antibacterial mechanisms of magnesium oxide include oxidative damage by reactive oxygen species and mechanical damage by adsorption.
- ① Oxidative damage by reactive oxygen species (ROS)
When studying ceramic powders, the reactive oxygen species (ROS) oxidative damage mechanism of magnesium oxide was proposed, that is, the oxygen vacancies on the surface of nano magnesium oxide can catalyze the single-electron reduction reaction of dissolved oxygen in water to produce superoxide anion free radicals O2–. Since O2- is highly oxidizing, it can destroy the protein peptide chains of bacterial cell membrane walls, thereby quickly killing bacteria.
Magnesium oxide is easily hydrated in aqueous solution to form magnesium hydroxide, so that the surface of the particles is coated with a layer of OH- and is alkaline. In an alkaline environment, O2- has high chemical stability and bactericidal ability. Compared with bulk magnesium oxide, nano-magnesium oxide has a large specific surface area and many surface oxygen defects. It is easy to hydrate to form magnesium hydroxide and can produce a large amount of O2-, thus having strong bactericidal ability. Studies have shown that magnesium hydroxide generated by hydration of magnesium oxide will increase the pH of the solution to about 10.5, while the bactericidal effect of sodium hydroxide aqueous solution with the same pH on Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus) is not as good as that of nano-magnesium oxide, indicating that a simple increase in pH cannot promote the improvement of antibacterial properties.
The ROS oxidative damage mechanism has been recognized by most researchers. When preparing nano-magnesium oxide antibacterial materials, its antibacterial ability can be enhanced by exposing the (111) crystal plane rich in active oxygen on the surface, or by increasing the defects on the surface of magnesium oxide by doping to produce more oxygen vacancies, or by compounding with different antibacterial components to improve the antibacterial properties of the material.
- ② Mechanical damage caused by adsorption
There are a large number of active sites such as crystal-bound hydroxyl groups, free hydroxyl groups and ion holes on the surface of nano-magnesium oxide, which can serve as adsorption and surface reaction centers. In addition to ROS oxidative damage, the antibacterial effect of nano-magnesium oxide can also cause cell membrane damage due to the adsorption of particles on microorganisms, and the antibacterial effect is better as the particle size decreases.
In the absence of ROS, nano-magnesium oxide still has strong antibacterial properties against E. coli. The death of bacteria should be due to the change in cell membrane pH and the release of Mg2+ during contact with nano-magnesium oxide, which leads to cell membrane rupture, rather than lipid peroxidation. The electron-dense black spots after the nano-magnesium oxide acts on the bacteria indicate that it can penetrate the cell membrane or cell wall to enter the cell. The smaller the particle size of the magnesium oxide, the more electron-dense black spots there are in the cytoplasm, and the higher the antibacterial activity. The study also found that amorphous nano-magnesium oxide has no bactericidal ability.
The mechanical damage mechanism of adsorption is a supplement to the oxidative damage mechanism of reactive oxygen. It can not only explain the problem that magnesium oxide still has good antibacterial properties in the absence of ROS, but also verify the mechanism that the smaller the particle size of nano-magnesium oxide, the higher the antibacterial performance. Therefore, the antibacterial performance of magnesium oxide can be improved by reducing the particle size of magnesium oxide, increasing the specific surface area, and enhancing the adsorption effect.
2. How to exert the antibacterial performance of nano-magnesium oxide?
At present, there are two main development paths for magnesium oxide antibacterial materials: one is to improve the antibacterial properties of nano magnesium oxide by controlling the particle size and morphological characteristics, such as flaky nano magnesium oxide powder, which shows strong antibacterial and bactericidal ability against anthrax, staphylococcus, Escherichia coli, etc.; the other is to develop new composite antibacterial materials by compounding magnesium oxide with other antibacterial materials, such as activated carbon/magnesium oxide, metal oxide/magnesium oxide and chlorine, bromine/magnesium oxide, etc.
In terms of application, there are mainly the following:
① Using paint as a carrier, by adding 2%-5% nano magnesium oxide, the antibacterial property, flame retardancy and hydrophobicity of the paint are improved.
② By adding nano magnesium oxide to plastics, the antibacterial rate of plastic products and the strength of plastics can be improved.
③ By spraying on the surface of ceramics and sintering, the flatness and antibacterial property of the ceramic surface are improved.
④ By adding nano magnesium oxide to fabric fibers, the flame retardancy, antibacterial property, hydrophobicity and wear resistance of fabrics can be improved, solving the problem of bacterial and stain erosion of textiles.
In addition, nano-magnesium oxide has been used to invent an antibacterial agent (preservative) that can be used in acidic beverages. It is non-toxic and has good antibacterial efficiency against common beverage microorganisms, especially against tropical Candida in acidic beverages. It also has a significant antibacterial effect, and the preparation method is simple and suitable for industrial production. Perhaps in the near future, we will be able to see nano-magnesium oxide in food formulas.