A Nanometric View into Strengthening Mechanisms of Iron Incorporation in Graphene-Based Nanocomposites

Abstract

Recent advances in the ability to synthesize metal-ion coagulated graphene oxide (GO) colloidal dispersions have provided new avenues for fabrication of GO based thin films and membranes. Additionally, new fabrication techniques have recently emerged that enable the ability to intercalate and reduce metal halides in bulk graphite crystals, leading to metal-based graphite intercalated compounds (GICs). To this end, a fundamental study on the interplay between composition, atomic-scale structure and mechanical properties of metal-GO as well as metal-GIC composite materials was carried out employing molecular dynamics (MD) simulations. Specifically, the transition metal iron (Fe) was considered in this study; MD investigations reveal that Fe ions act as strong cross-linkers between individual GO sheets, increasing elastic modulus as well as tensile strength of the Fe-GO composite. Investigations of Fe intercalated GIC (Fe-GIC) showed interesting trends in its mechanical properties due to bond formation between the intercalated Fe atoms and the ‘sandwiching’ graphene sheets. In particular, with increasing iron concentration, there is strengthening in the out-of-plane direction, while reduction in the in-plane direction of the Fe-GIC lattice. While the Fe-C bonding ensures out-of-plane strengthening, it is equally detrimental to the strength of the in-plane C-C bonds within the graphene sheets. Valuable lessons learned from this work provide important insights into the design and development of GO and GIC composites for targeted mechanical and chemical applications.