Antibacterial Properties Of Magnetic Nanomaterials

With the fast development of society and gradual improvement of people' living standard,healthy living environment has attracted more and more attentions from the public.Controlling and eliminating harmful bacteria are closely related to human health.Hence,researches on antibacterial agents are of very important significance.Antibacterial agents include mostly inorganic,organic and natural antibacterial agents,and the conventional antibacterial agents are mainly organic antibacterial agents.To our disappointment,organic antibacterial agents had some shortcomings,such as instability,short life,polluting environment,and their antibacterial activity keep better just in the short time,etc.For this reason,the researchers gradually turn their attentions to inorganic antibacterial agents which not only hold better antibacterial activity,but also have low toxicity,higher environment stability and little environmental pollution,etc.Monodisperse submicron CoFe2O4 spheres were prepared by solvothermal method.Polydopamine-coated silica@CoFe2O4 composite particles were synthesized by combination of sol–gel process and in situ self-polymerization method,in which tetraethyl orthosilicate(TEOS)and dopamine were used as the precursor for silica and polydopamine(PDA),respectively.The PDA@SiO2@CoFe2O4 composites had a multilayer core–shell structure with PDA as the outermost layer shell.Then,numerous of silver nanoparticles were assembled on the surface of PDA@SiO2@CoFe2O4 via the reduction of Ag+ by the surface PDA on the composites.The morphology,structure,and composition of the composites are characterized by transmission electron microscopy(TEM),X-ray powder diffraction(XRD),X-ray photoelectron spectrometry(XPS),vibrating sample magnetometry(VSM)and inductively coupled plasma optical emission spectrometry(ICP-OES).Antibacterial experiments indicated that the as-prepared composites could restrict up to 92% Escherichia coli(E.coli)and Staphylococcus aureus(S.aureas)at 0.6 mg/ml Ag.In addition,the composites showed a strong magnetic response to an externally applied magnetic field.Recently,worldwide research hotspot on the synthesis and photocatalytic bactericidal activity of magnetic photocatalysts has been pursued.However,the conventional sol-gel method for preparing TiO2-basd magnetic photocatalysts requires high-temperature calcination to crystallize amorphous TiO2 shell,which can transform the superparamagnetic Fe3O4 to antiferromagnetic ?-Fe2O3.Hence,we adopted a mild liquid-phase deposition(LPD)procedure to directly deposit anatase TiO2 on SiO2@Fe3O4 cores to obtain core-shell TiO2@SiO2@Fe3O4 magnetic antibacterial.To enhance its photocatalytic antibacterial efficiency,highly dispersed Au nanoparticles(NPs)were strongly immobilized on its surface to form Au/TiO2@SiO2@Fe3O4 composites via seed-mediated growth procedure.The 3 nm colloid Au seeds absorbed on TiO2@SiO2@Fe3O4 served as a nucleation site for the further growth of Au NPs overlayer.The morphology,structure,composition and magnetism of the resulting composites were characterized in detail and their antibacterial activity was evaluated by against Escherichia coli(E.coli)in both light and dark conditions.In comparison to TiO2@SiO2@Fe3O4,Au/TiO2@SiO2@Fe3O4 exhibited higher antibacterial activity under visible light irradiation.This enhanced photocatalytic antibacterial effect caused by the Au NPs attached on the TiO2 may be attributed to their surface plasmon resonance(SPR)whereby electrons are injected from the Au particles into the conduction band of Ti O2.In addition,the superparamagnetic composites could be easily separated and recycled from the treated solution using an external magnet.