Chemical synthesis of Fe3O4–graphene oxide nanohybrids as building blocks for magnetic and conductive membranes

•Fe3O4 nanocrystals are uniformly grown on graphene oxide (GO) at high density.•GO sheets act as physical substrate and surfactants for the growth of Fe3O4.•The saturation magnetization of the Fe3O4–GO hybrids is controlled.•Conductive membrane is formed by filtration of Fe3O4–GO suspension. We have developed a facile and scalable method for synthesising superparamagnetic Fe3O4 nanocrystals (NCs) anchored on graphene oxide (GO) sheets by a co-precipitation reaction. As-synthesized Fe3O4–GO nanohybrids (NHs) were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, transmission electron microscopy, and vibrating sample magnetometer. Fe3O4 NCs with a narrow size distribution (4.5±0.6nm) were uniformly decorated over GO surface at high density. The GO sheets act as two-dimensional substrates and surfactants for the growth and adhesion of Fe3O4 NCs. Structural changes induced in the GO due to Fe3O4 decoration were clearly observed using Raman spectroscopy. The magnetic properties of Fe3O4–GO NHs could be tuned by varying Fe3O4 content and a saturation magnetization as high as 39.2emug−1 was achieved. Fe3O4–GO NHs in their colloidal suspension were used as building blocks to fabricate magnetic and electrically conductive membranes by a vacuum-assisted assembly process.