Mesoporous silica microcapsule-supported Ag nanoparticles fabricated via nano-assembly and its antibacterial properties

A novel method was proposed to fabricate a mesoporous silica microcapsule with Ag nanoparticles (AgNPs) loaded onto the interior wall of a mesoporous silica shell. The mesoporous silica microcapsule-supported AgNPs (denoted as AgNPs@silica microcapsule) was fabricated via a two-step process: (i) Ag+ ions were adsorbed on the surface of monodisperse sulfonated polystyrene (PS) beads via electrostatic interaction, and then reduced and protected by polyvinylpyrrolidone (PVP) to obtain PS–Ag composite spheres. (ii) Silica colloids generated by the hydrolysis and polymerization of tetraethoxysilane (TEOS) were assembled on the PS–Ag composite spheres via hydrogen bond forces to form a silica shell, followed by the removal of the PS core and PVP through calcinations. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometery (XRD) were adopted to analyze the as-prepared AgNPs@silica microcapsule. Furthermore, the antibacterial properties of this unique structured material were investigated as well. The results show that the AgNPs, with the form of elementary substance, dispersely load onto the interior wall of silica shell, and the shell is composed of a single layer of interconnected silica particles and mesopores. This unique structure can effectively avoid the aggregation problem existing in traditional Ag colloid system and slowly release Ag+ ions, which will diffuse to the external medium through the mesopore channels in the shell, inducing antibacterial activity. The antibacterial activity against Escherichia coli (E. coli) can reach up to 99.8% and, more importantly, can maintain a high level for long periods over two months. The AgNPs@silica microcapsule can combine the advantages of high surface area materials and large-scale materials, achieving both high antibacterial activity and easy recycling characteristics, thus showing its great potential as an antimicrobial agent.