Magnesium hydroxide is a kind of inorganic weak alkali products, because of its strong buffer performance, high activity and adsorption capacity and non-corrosive, non-toxic, harmless and many other unique properties, so it is known as “green neutralizer”, “environmentally friendly flame retardant” and “third kind of alkali”, it is one of the most popular and respected products in the process of implementing sustainable development strategy, protecting the environment and beneficial ecological development. Therefore, it is called “green neutralizer”, “environmentally friendly flame retardant” and “the third alkali”, and is one of the products that are highly favored and respected in the process of implementing the strategy of sustainable development, protecting the environment and benefiting the ecological development.
The preparation methods of nano magnesium hydroxide mainly include the following:
1, Magnesite calcination method: Magnesite and anthracite or coke are calcined in a vertical kiln, generating magnesium oxide and carbon dioxide. Bitter earth powder is mixed into slurry with water and then reacted with hydrochloric acid of specified concentration to prepare magnesium chloride solution, and then reacted with ammonia of certain concentration, and the product is washed, settled, filtered and separated, dried and crushed to get magnesium hydroxide product.
2, Dolomite calcination method: dolomite was calcined at 950°C for 2.5 hours and then digested at 70°C for 50 minutes. The molar ratio of hydrochloric acid dosage to calcium ions in primary acid leaching is 2:1, and the molar ratio of sulfuric acid dosage to magnesium ions in secondary acid leaching is 1:1. The pH value of the solution in the precipitation process is 11, and flaky magnesium hydroxide with general purity and dispersion can be obtained under these process conditions.
3, Liquid phase precipitation method: there are two sources of raw materials, one is magnesite, dolomite, serpentine, etc. After acid digestion or other methods of treatment, magnesium salts are obtained, and magnesium hydroxide is prepared by precipitation reaction with alkali; the other is magnesium salts obtained from seawater, saline lake water, and well brine and alkali are used in the precipitation reaction for the preparation of magnesium hydroxide The other one is to prepare magnesium hydroxide by precipitation reaction with alkali from seawater and brine.
4, Double-drop addition-reverse precipitation method: magnesium chloride and ammonia were used as raw materials, and the optimized process conditions were a reaction temperature of 60°C, a reaction time of 75 min, an aging temperature of 20°C, an aging time of 3 h, an ammonia-to-magnesium molar ratio of 1.7, and an initial concentration of Mg2+ of 1.7 mol/L. Through the combination of double-drop addition and reverse precipitation, magnesium hydroxide with an average particle size of 60 nm was prepared, which was small, uniform and well dispersed.
5, Liquid-phase alkalolysis: Using hexaammine magnesium chloride as the precursor, liquid-phase alkalolysis was used to convert hexaammine magnesium chloride into high-purity nano-magnesium hydroxide. To a dilute alkaline solution stronger than ammonia add hexaammonia magnesium chloride solid particles for alkalolysis, after aging add dispersant for surface treatment, the obtained suspension will be filtered and washed until the chloride ions can not be detected, the obtained filter cake after drying to obtain high-purity magnesium hydroxide nanoparticles.
Antimicrobial properties of nano magnesium hydroxide and its applications:
Antibacterial properties: nano magnesium hydroxide has significant antibacterial activity against a variety of bacteria such as Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. Studies have shown that the bactericidal effect of nano magnesium hydroxide on Gram-positive bacteria is significantly stronger than that of Gram-negative bacteria. Its antibacterial mechanism is mainly through the cytophagy a dissociation mechanism, that is, magnesium hydroxide nanoparticles into the cell interior to release a large number of OH–, destroying the neutral environment in the cell, leading to bacterial death.
Antibacterial mechanism: The antibacterial mechanism of nano magnesium hydroxide is mainly through its high specific surface area and alkaline environment, releasing OH– and Mg2+, destroying the bacterial cell membranes and intracellular protein structure, thus achieving antibacterial effect. In addition, the sterilization process of nano magnesium hydroxide does not depend on light source and can be carried out in the dark.
APPLICATIONS: nano magnesium hydroxide has been applied to prepare antibacterial paper and PVDF/magnesium hydroxide blended film. Experiments have shown that paper samples with 3 wt% magnesium hydroxide nanoparticles added can achieve 100% sterilization against E. coli in 18 hours. The preparation of the co-blended membrane, on the other hand, improved the membrane pore structure and permeability performance, which has a wide range of application prospects.
In summary, nanoparticles of magnesium hydroxide not only have a variety of preparation methods, but also have significant antimicrobial properties and broad application prospects.