Preparation And Antibacterial Character Of Polymeric Quaternary Ammonium Salts Grafted Fe₃O₄ Nanoparticles

magnetic nanoparticles with a diameter of 20nm were prepared by coprecipitation of Fe2+/Fe3+ in ammonia solutions and with oleic acid (OA) as the stabilizer. These magnetic nanoparticles were extracted into toluene from water by simply adding some salt as inducer, and then the Fe3O4 magnetic nanoparticles were functionalized with the silane coupling agent of 3-methacryloylpropyl trimethoxysilane (MPS) through ligand exchange method, which could provide double bonds on the surface of Fe3O4 nanoparticles.Three quaternary ammonium salt monomers were synthesized from dimethylaminoethyl methacrylate (DMAEMA) by quaternization with benzyl bromide (BB), methyl iodide (MI) and bromohexane(BH), respectively. And then, the monomers were copolymerized with MPS on the surface of Fe3O4 magnetic nanoparticles by free radical polymerization in ethanol at two different concentration of initiator. Finally, three kinds of polymeric quaternary ammonium salts grafted Fe3O4 nanoparticles (PQAC-Fe3O4) were obtained. The morphology and surface composition of nanoparticles was characterized by XRD, FT-IR, DLS, TEM and TGA.The in vitro antimicrobial activity of the PQAC-Fe3O4 nanoparticles was evaluated against E. coli, S. aureus and C. albicans by the the shake-flask method, it was found that PQAC-Fe3O4 nanoparticles showed a wide spectrum of high efficient antibacterial activity, and the biocidal efficiency coulde be achieved 90% witin 10 minutes. The biocidal efficiency increased with the increasing concentration of the PQAC-Fe3O4 nanoparticles used, possibly due to the more opportunities for contact between the nanoparticles and the microorganisms. Compared to the other two tested microorganisms, the PQAC-Fe3O4 nanoparticles were less toxic to the gram-negative bacterium E. coli, it possibly due to the mechanism which the PQAC-Fe3O4 nanoparticles operated. In addition, it was found that the different antibacterial efficiency of the three synthesized PQAC-Fe3O4 was influenced not only by their positive charge density and hydrophobicity but also their dispersibility in water and the length of the polymeric quaternary ammonium salts. The antimicrobial activity of the PQAC-Fe3O4 nanoparticles which exhibited a response to an external magnetic field retained 95% biocidal efficiency against E. coli after 10 cycles of repeated test.In conclusion, high antibacterial efficiency of the PQAC-Fe3O4 nanoparticles which exhibited a response to an external magnetic field was attributed to not only the quaternary group density but also the substitent chain of the quaternary group. As one kind of biocides with high microbial activity and be resuability in water, the PQAC-Fe3O4 nanoparticles would be advantageous as a new type of insoluble antimicrobial agent in water treatment.