Engineering of Superparamagnetic Core-Shell Iron Oxide/ N‑Chloramine Nanoparticles for Water Purification Hai Haham, † Michal Natan, ‡ Ori Gutman, † Michal Kolitz-Domb, † Ehud Banin, ‡ and Shlomo Margel* ,† † Institute of Nanotechnology and Advanced Materials, Department of Chemistry, Bar-Ilan University, Ramat-Gan 5290002, Israel ‡ The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan 5290002, Israel ABSTRACT: In this study, we describe the synthesis and characterization of superparamagnetic core-shell iron oxide (IO)/N-halamine antibacterial nanoparticles (NPs). For this purpose, superparamagnetic IO core NPs were coated with cross-linked polymethacrylamide (PMAA) by surfactant-free dispersion copolymerization of methacrylamide and N,N- methylenebis(acrylamide) in an aqueous continuous phase. The effect of the polymerization process on the chemical composition, size, shape, crystallinity, and magnetic properties of the IO/PMAA NPs was elucidated. Conversion of the core-shell IO/PMAA NPs into their N-halamine form, IO/ PMAA-Cl, was accomplished using a chlorination reaction with sodium hypochlorite. The influence of chlorination on the shape, crystallinity, and magnetic properties of the IO/PMAA NPs was studied. The IO/PMAA-Cl NPs demonstrated excellent antibacterial activity against Gram-negative and Gram-positive bacteria. Finally, the chlorination recharging capabilities of the NPs and their potential for use in the purification of water containing bacteria were demonstrated with magnetic columns packed with the IO/PMAA-Cl NPs. KEYWORDS: N-halamine nanoparticles, polyamide nanoparticles, magnetic nanoparticles, iron oxide, polymethacrylamide nanoparticles, antibacterial properties 1. INTRODUCTION Core-shell structured nanoparticles (NPs) have attracted much attention because of their implantation in many applications such as adsorbents, 1-3 chemical sensors, 4 inks, 5 and catalysis. 6,7 The combined functionality of the core-shell structure allows a broad range of applications depending on the characteristics of the core and the shell. 8 Materials with a core consisting of iron-based magnetic NPs have been intensively studied to address many environmental issues. 9-11 Core-shell magnetic Fe/C NPs have shown efficiency in adsorption and magnetic removal of contaminants from aqueous or gaseous effluents. 12,13 In addition, γ-Fe 2 O 3 /Ag core-shell NPs showed efficiency against numerous bacterial strains and species of fungi in aqueous solution. 14 Iron oxide (IO) NPs, such as Fe 3 O 4 or γ-Fe 2 O 3 , represent a category of suitable candidates for many environmental remediation applications because of their unique magnetic (e.g., ferro-ferrimagnetism, and superparamagnetism) and biocompatible (e.g., biodegradable and nontoxic) properties. 10 IO nanomaterials have shown an excellent ability to remove heavy metal ions in water treatment processes. 15 Moreover, a combination of magnetic IO with organic antibacterial compounds in core-shell nanostructures demonstrated efficiency in water disinfection experiments. 16-18 Chloramine-derivatized N-halamine compounds have been researched for three decades, in which their antibacterial potential for a variety of applications has been shown. 19,20 N- Halamine materials are considered to be low-cost, safe for human use, and effective against a broad spectrum of microorganisms such as Gram-positive, Gram-negative, and multidrug resistant bacteria. 21,22 N-Halamine materials are stable upon being exposed to organic materials in contrast to commercially used sanitizers, such as household bleach. The key role for antibacterial activity of N-halamines involves the generation of reactive oxygen species (ROS) only upon exposure to bacteria. On the other hand, ROS are not generated upon exposure to water, revealing that the mode of action is target-specific. 23,24 Moreover, N-halamine antibacterial materials can be regenerated. N-Halamines are converted to amide-, imide-, or amino-containing molecules as they interact with the microorganism, which may be recycled into N- halamine structures through a simple chlorination treat- ment. 20,21,25 This study combines the advantages of IO NPs and N- halamine materials into bifunctional magnetic-antibacterial IO/N-halamine NPs. IO NPs were coated with polymethacry- lamide (PMAA) by an aqueous surfactant-free copolymeriza- tion of methacrylamide (MAA), a monomer containing a primary amide group, and N,N′-methylenebis(acrylamide) (MBAA), a cross-linker monomer containing a secondary Received: May 16, 2016 Accepted: June 27, 2016 Research Article www.acsami.org © XXXX American Chemical Society A DOI: 10.1021/acsami.6b05806 ACS Appl. Mater. Interfaces XXXX, XXX, XXX-XXX