A process for making an iron oxide impregnated carbon nanotube membrane. In this template-free and binder-free process, iron oxide nanoparticles are homogeneously dispersed onto the surface of carbon nanotubes by wet impregnation. The amount of iron oxide nanoparticles loaded on the carbon nanotubes range from 0.25-80% by weight per total weight of the doped carbon nanotubes. The iron oxide doped carbon nanotubes are then pressed to form a carbon nanotube disc which is then sintered at high temperatures to form a mixed matrix membrane of iron oxide nanoparticles homogeneously dispersed across a carbon nanotube matrix. Methods of characterizing porosity, hydrophilicity and fouling potential of the carbon nanotube membrane are also described.