Photo-organometallic, Nanoparticle Nucleation on Graphene for Cascaded Doping

Controlling the doping levels in graphene by modifying the electric potential of interfaced nanostructures is important to understand "cascaded-doping"-based applications of graphene. However, graphene does not have active sites for nanoparticle attachment, and covalently adding functional groups on graphene disrupts its planar sp²-hybridization, affecting its cascaded doping. Here we show a hexahepto (η⁶) photo-organometallic chemistry to interface nanoparticles on graphene while retaining the sp²-hybridized state of carbon atoms. For testing cascaded doping with ethanol interaction, transition metal oxide nanoparticles (TMONs) (Cr₂O₃/CrO₃, MoO₃, and WO₃) are attached on graphene. Here, the transition metal forms six σ-bonds and π-back-bonds with the benzenoid rings of graphene, while its opposite face binds to three carbonyl groups, which enable nucleation and growth of TMONs. With a radius size ranging from 50 to 100 nm, the TMONs downshift the Fermi level of graphene (-250 mV; p-doping) via interfacial charge transfer. This is consistent with the blue shift of graphene's G and 2D Raman modes with a hole density of 3.78 × 10¹² cm^-2. With susceptibility to ethanol, CrO₃ nanoparticles on graphene enable cascaded doping from ethanol that adsorbs on CrO₃, leading to doping of graphene to increase the electrical resistance of the TMONs-graphene hybrid. This nanoparticle-on-graphene construct can have several applications in gas/vapor sensing, electrochemical catalysis, and high-energy-density supercapacitors.