Nano-magnesium oxide has many optical, electrical, magnetic, thermal, chemical and mechanical properties that are different from ordinary magnesium oxide. It has become a new type of functional inorganic material, especially in the field of antibacterial materials that are closely related to human survival and health. It shows unique advantages, such as long-lasting antibacterial activity, low cost, not easy to change color, and no biological toxicity.
1, How is nanomagnesium oxide antibacterial?
A correct understanding of the antibacterial mechanism of magnesium oxide is of great significance for research on improving the antibacterial activity of materials. The two main antimicrobial mechanisms of magnesium oxide include oxidative damage by reactive oxygen species and mechanical damage by adsorption.
①Oxidative damage by reactive oxygen species (ROS)
When studying ceramic powders, the active oxygen oxidation damage mechanism of magnesium oxide was proposed, that is, the oxygen vacancies on the surface of nanometer magnesium oxide can catalyze the single-electron reduction reaction of dissolved oxygen in water to produce superoxide anion O2. Because O2 has strong oxidizing properties, it can destroy bacterial cell membrane protein peptide chains, thereby quickly eliminating bacteria.
Magnesium oxide easily hydrates in an aqueous solution to form magnesium hydroxide, which coats the particle surface with a layer of OH and makes it alkaline. O2 has high chemical stability and bactericidal ability in an alkaline environment. Compared with bulk magnesium oxide, nano-magnesium oxide has a large specific surface area and many surface oxygen defects. It is easily hydrated to form magnesium hydroxide and can produce a large amount of O2, so it has strong bactericidal ability. Studies have shown that magnesium hydroxide produced by hydration of magnesium oxide will increase the pH of the solution to about 10.5, while NaOH aqueous solution with the same pH has no bactericidal effect on Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus).
Nano magnesium oxide is good, indicating that a simple increase in pH cannot promote the improvement of antibacterial properties.
The mechanism of ROS oxidative damage is recognized by most researchers. When preparing nano-magnesium oxide antibacterial materials, its antibacterial ability can be enhanced by exposing the (111) crystal face rich in active oxygen on the surface, or by doping to increase the antibacterial properties of the magnesium oxide surface. The disadvantage is that it generates more oxygen vacancies, or improves the antibacterial performance of the material by compounding with different antibacterial components.
② Mechanical damage due to adsorption
There are a large number of lattice-localized hydroxyl groups, free hydroxyl groups, ions and other active sites on the surface of nano-magnesium oxide, which can be used for adsorption and surface reactions. In addition to ROS oxidative damage, the antibacterial effect of nanomagnesium oxide can also cause cell membrane damage due to the adsorption of particles to microorganisms. As the particle size decreases, the antibacterial effect becomes better.
In the absence of ROS, nano-magnesium oxide still has strong antibacterial properties against E.coli. Bacterial death should be due to the pH change of the cell membrane and the release of Mg2+ during the contact with nano-magnesium oxide, which leads to the rupture of the cell membrane, rather than lipid peroxidation. effect. The electron-dense black spots after nanomagnesium oxide acts on bacteria indicate that it can penetrate the cell membrane or cell wall and enter the cell. The smaller the magnesium oxide particle size, the more electron-dense black spots in the cytoplasm and the higher the antibacterial activity; the study also found that, Amorphous nano-magnesium oxide has no bactericidal ability.
The shape of E. coli is visibly distorted, and its cell wall and membrane are damaged.
The mechanical damage mechanism of adsorption is a complement to the oxidative damage mechanism of reactive oxygen species. 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 nanomagnesium oxide, the higher the antibacterial properties are. , therefore the antibacterial properties of magnesium oxide can be improved by reducing the particle size of magnesium oxide, increasing the specific surface area, enhancing adsorption, etc.
How to exert the antibacterial properties of nanomagnesium oxide?
At present, there are two main development paths for magnesium oxide antibacterial materials: one is to improve the antibacterial performance of nanomagnesium oxide through control of particle size, morphological characteristics, etc., such as scaly nanomagnesium oxide, which can effectively treat anthrax, staphylococcus, and Escherichia coli. etc. show strong antibacterial and sterilizing capabilities; the second is to develop new composite antibacterial materials through the combination of magnesium oxide and other antibacterial materials, such as activated carbon/magnesium oxide, metal oxide/magnesium oxide, bromine gas/magnesium oxide, etc.
In terms of application, there are mainly the following categories:
① Using paint as a carrier, by adding 2 to 5% of nano-magnesium oxide, the antibacterial, flame retardant and hydrophobic properties 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 ceramic surface and sintering, the flatness and antibacterial properties 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 the fabric can be improved, and the problem of bacterial and stain erosion of textiles can be solved.
In addition, nano-magnesium oxide was used to invent a bacteriostatic agent (preservative) that can be used in acidic beverages. It is non-toxic and has good antibacterial efficiency against common beverage microorganisms, especially against Candida tropicalis in acidic beverages. It has obvious 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.