Engineering of antibacterial/recyclable difunctional nanoparticles via synergism of quaternary ammonia salt site and N-halamine sites on magnetic surface

A biocidal composite unit with improved synergism, using one cationic quaternary ammonia salt (QAS) site to attract electronegative bacteria to three highly biocidal N-halamine sites, was designed for the first time and attached onto surface of magnetic silica coated Fe 3 O 4 nanoparticles (silica@Fe 3 O 4 NPs) for superior biocidability, large killing area, and easy recyclability. Briefly, a compound containing one imide and two amide N H bonds, 2-(2,5-dioxoimidazolidin-4-yl)-N-(4-hydroxyphenyl)acetamide (DHPA), was prepared by amidation of hydantoin acetic acid with p-aminophenol. A biocidal precursor of one QAS site and three N-halamine sites was then constructed by alcoholysis of 3-triethoxysilylpropyl succinic anhydride with 2-(dimethylamino)ethan-1-ol to introduce a tertiary amine and subsequent esterification with DHPA to introduce three N H bonds. The triethoxysilyl groups in the precursor were hydrolyzed to silanol groups to condense with their counterparts on silica@Fe 3 O 4 NPs. The surface of resultant NPs carried units each contains one QAS site and three N-halamine sites after quaternization and chlorination. The biocidal surface showed superior biocidability against Escherichia coli and Staphylococcus aureus than reported systems due to the improved synergism between multiple antibacterial groups of different types and was stable towards quenching-chlorinating process and storage. The successful design opens insight in the syntheses of more powerful biocides.