Preparation Of Core-shell Ag@SiO₂ Nanoparticles Hydrosol With Enhanced Stability And Antibacterial Activity

Recently, as the people consciousness of environmental protection enhancement, as well as for its own security, a new type of non-toxic environmentally friendly antibacterial agent is becoming more and more urgent. Due to silver nanoparticles possess broad-spectrum antibacterial properties, durable antimicrobial properties and non-toxic characteristics, they are widely used in biomedical materials, water quality and air purifier, and other fields. However, oxidation and reunion of silver nanoparticles prrevented their application. The unique core-shell structural Ag@SiO2 nanoparticles not only could overcome the defect, but also could play a role of slow-release properties of silver nanoparticles. The core-shell structural nanoparticles are becoming an important research field of materials science.Researchers have explored a lot of preparation methods. However, most procedures obtained Ag@SiO2 core-shell nanoparticles only at relatively low concentrations and are not stable. In this paper, the preparation process of high concentrated core-shell Ag@SiO2 nanodispersion was studied. Foremore, the structural stability and long-term stability were investigated. Then Ag@SiO2 nanodispersion was added to coating, tested the antibacterial properties of coating and explored the key factors affecting antibacterial properties.1. The monodispersed core-shell Ag@SiO2 nanodispersion was prepared by sol-gel method. Firstly, the process conditions such as the concentration of reactants and stirring speed on the morphology and particle size of nanodispersion were explored. Secondly, the average silica shell thicknesses could be tuned by choosing the appropriate Ag precursor/TEOS molar ratio,which had a spherical silver core in a size range from 10-15 nm in diameter and a silica spacer with controlled thickness (5 nm, 10 nm and 15 nm,respectively). Finally, we prepared the highest concentration of 1728 ppm Ag nanoparticles of Ag@SiO2-NPs hydrosol by increasing the amount of AgNO3 and adjusting the factors such as reaction time, stirring rate etc. The average diameter of nanoparticles was 50 nm, starting from Ag core diameters of 20 nm and the silica shell thickness of 18 nm.2. The structural and storage stability of the Ag@SiO2-NPs hydrosol was investigated. As the extension of storage time, silver nanoparticles were released by silica shell hole, it appeared SiO2 shell, core-shell structure were destroyed, Ag content of nanodispersion were reduced. Storage for 3 months,the morphology and particle size of Ag@SiO2 nanodispersion weren’t obviously changed, the silver content reduced from 864 ppm to 706 ppm,which proved that it had good storage stability. The silica shell thickness (5 nm to 10 nm and 15 nm) effecting on the structure stability of the Ag@SiO2 nanodispersion were explored, it concluded that the thicker the silica shell was,the better structural stability the nanoparticle had.3. The antibacterial activities of the Nano-coating films with different Ag contents and different thickness of silica shell were measured. It was concluded that nano-coating with a silver concentration of 50 ppm had a distinct antibacterial activity. The Ag@SiO2 dispersions stored for 110 days possessed good antibacterial activity; the silica shell thickness didn’t affect the antibacterial property distinctively. Antibacterial effects of the Ag@SiO2-NPs hydrosol stored for 415 days was about 100%. Hence, the excellent long-term antibacterial property of the Ag@SiO2 nanodispersion was demonstrated.