Abstract:The changing law of molecular weight cut-off(MWCO) of polysulfone-Fe3O4 magnetic composite ultrafiltration membranes with magnetic field intensity was studied.In order to restrain Fe3O4 nanoparticles from agglomerating,the nanoparticles were packed by the coupling agent and were prepared by chemical co-precipitation.Composite membranes were prepared by the phase inversion process.Nanoparticles’ average diameter determined by Zeta potential instrument was 66.83 nm.Through infrared analysis,the coupling agent combins with the surface of particles.Uniform distribution of Fe3O4 nanoparticles,no agglomeration and narrow pore size distribution were obtained through scanning electron microscopy and determination of pore size distribution.The MWCO of composite membranes,in which MWCO of basement membrane is 20000,decrease from 19,800 of 0T to 15,000 of 0.4T.Then continuing to increase the magnetic intensity,there is no more changes happened.