Investigation of cost effective CO2 adsorbent has been a long demanding task in the present scenario of global warming. The present work investigates the high pressure carbon dioxide capture capacity of low cost magnetite decorated functionalized graphite nanoplatelets novel nanocomposite. Graphite nanoplatelets were prepared by acid intercalation followed by thermal exfoliation. Functionalization of graphite nanoplatelets was done by treatment in acidic medium. Magnetite nanoparticles were decorated onto functionalized graphite nanoplatelets surface by a chemical method. Magnetite decorated functionalized graphite nanoplatelets nanocomposite was characterized by electron microscopy, X-ray powder diffraction pattern, surface area analysis, Raman spectroscopy and FTIR spectroscopy techniques. The carbon dioxide capture capacity was measured using high pressure Sieverts apparatus. Adsorption capacity was calculated using the gas equation and incorporating van der Waals corrections at three different temperatures (25, 50 and 100 °C). A large enhancement in carbon dioxide uptake capacity of 55%, 80%, and 90% at near 11.5 bar pressure for 100 °C, 50 °C and 25 °C, respectively, was achieved by decorating magnetite nanoparticles onto functionalized graphite nanoplatelet surface. © 2011 The Royal Society of Chemistry.