Immobilizing silver nanoparticles onto the surface of magnetic silica composite to prepare magnetic disinfectant with enhanced stability and antibacterial activity

In this article, silver nanoparticles inlaid Fe3O4–SiO2 magnetic composite (Fe3O4–SiO2–Ag) was successfully synthesized and its potential application as an antibacterial material in water disinfection was investigated. Silver nanoparticles, with diameter of about 10 nm, were anchored homogeneously and tightly onto the silica coat of Fe3O4–SiO2 magnetic nanoparticles, which increased the antibacterial abilities by avoiding the aggregation of Ag nanoparticles. The minimum inhibitory concentrations of Fe3O4–SiO2–Ag magnetic composite to Escherichia coli and Staphylococcus aureus were 15.625 mg L−1 and 31.25 mg L−1, respectively, and the minimum bactericidal concentrations were 250 mg L−1 and 500 mg L−1, respectively. In inactivation experiment, 150 mg L−1 of Fe3O4–SiO2–Ag disinfectant in 150 mL of normal saline solution could kill 99.9% of the tested bacteria within 60 min. Paper disk diffusion assay also showed excellent antibacterial abilities to both E. coli and S. aureus. The silica coat not only acted as a supporting matrix, but also enhanced the stability of the disinfectant. The obtained Fe3O4–SiO2–Ag composite has a high magnetic saturation value of 75 emu g−1, which indicates that the composite can be recovered from water solution for reuse through magnetic separation and the waste and possible contamination of disinfectant to environment are avoided.