A bacterial removing effect of ultrafine ferrite particles prepared by chemical coprecipitation has been investigated. The ten kinds of ferrite nanoparticles were tested, and CdFe2O4, CuFe2O4, ZnFe2O4, Ca0.5Zn0.5Fe2O4 and Ni0.5Zn0.5Fe2O4 showed the effects to reduce bacterial titers of L. pneumophila, S. aureus, P. aeruginosa, B. subtilis and E. cob. in the liquid culture. The crystal structure of ZnFe2O4, Ca0.5Zn0.5Fe2O4 and Ni0.5Zn0.5Fe2O4 analized by XRD method was the spinel structure, while CdFe2O4 and CuFe2O4 are composed of the spinel structure and small amounts of byproducts. These ferrite particles shared common physical properties, ie, average size of ferrite particles with bacterial removing effects was uniformly less than 15 nm, specific surface area was more than 140m2/g, saturation magnetization was less than 0.35 T and coercivity was less than 6.4kA/m.
