Controllable preparation and properties of mesoporous silica hollow microspheres inside-loaded Ag nanoparticles

• The mesoporous silica microspheres inside-loaded AgNPs are prepared controllably.
• The loading behavior of AgNPs on the negative curvature surface is studied.
• The assembly of silica colloids is studied from the perspective of adjusting porosity.
• The Ag release can be controlled by regulating AgNP loading and porosity of silica.

The novel mesoporous silica hollow microspheres inside-loaded Ag nanoparticles (MSMAs) were fabricated through successively assembling Ag nanoparticles (AgNPs) and silica nanoparticles on the polystyrene beads and followed by the calcinations to remove the organics. The dosage of AgNO3, polyvinylpyrrolidone (PVP), tetraethoxysilane (TEOS) and ammonia was investigated to explore the variation in the morphology of the MSMAs such as the AgNP loading amount and the porosity of silica shell. Moreover, the Ag release property and long-term antibacterial activity of as-prepared MSMAs were also studied. The results show that the loading amount of AgNPs can be regulated by controlling the dosage of PVP or AgNO3, while the size of the pore in silica shell is increased with TEOS dosage. Lowering the PVP/AgNO3 mole ratio (> 1.5) is favorable to obtain the MSMAs with high Ag loading density. High Ag loading amount as well as large pore size will increase the Ag+ ion release rate, leading to the more efficient diffusion of Ag+ ions from the interior of the silica hollow microsphere to the external medium through the pore channels in the shell. The long-term antibacterial activity is mainly determined by the Ag+ ion release rate, and the highest antibacterial activity can remain at a high level of up to 96% for long periods of six months.