Herein, we report a new synthesis route for generating porous on graphene with a scalable and controllable size of micron to submicron through the successive insertion of potassium atoms into interlayers of graphite at low temperature. Comprehensive studies such as physico-chemical analysis confirm that the as-obtained porous graphene has few layers with fewer defects. Further, the magnetically separable magnetite (Fe3O4)/porous graphene nanocomposites were synthesized through a facile, cost-effective hydrothermal process. The as-prepared nanocomposites were characterized by different analytical techniques. In the nanocomposites, superparamagnetic Fe3O4 nanoparticles with an average size of 30 nm nanoparticles uniformly dispersed on the porous graphene sheets, and they acted as mutual spacers in the nanocomposites to avoid aggregation of the magnetic nanoparticles and restacking of the porous graphene layers. In addition, Fe3O4/porous graphene nanocomposites possessed high adsorption capacities of dyes and heavy weight metal ions from wastewater. An organic dye methyl violet was used as an adsorbate for investigating the adsorption characteristics of the Fe3O4/porous graphene nanocomposites. Fe3O4/porous graphene exhibited rapid adsorption (5 min), high adsorption capacity (Q(o)-460 mg/g), easy separation and reuse owing to the high specific surface area with porous nature of graphene and high magnetic property of Fe3O4 nanoparticles. Also, the nanocomposite used as an ultrahigh performance of novel capacitive deionization electrodes (CDI) for removal of Pb2+ and Cu2+ ions at constant applied potential 1.2 V and constant flow rate 4 ml/min. The results indicate that the Fe3O4/graphene nanocomposites exhibit an ultrahigh electrosorption for Pb2+, Cu2+ and Cd2+ ions. The progress made so far will guide further development of graphene based nanostructures with porous and exploration of such porous nanomaterials in environmental remediation toward removal of organic and inorganic contaminants. (C) 2017 Elsevier B.V. All rights reserved.