One-step synthesis of monodisperse transition metal core-shell nanoparticles with solid solution shells

Methods of forming monodispersed core-shell nanoparticles are provided. A cobalt(II)-ligand component, a metal(II)-ligand component, an organic reducing agent, and a capping agent can be added to an organic solvent to form a reaction mixture. The reaction mixture is then heated to a dissolving temperature while under a gas (e.g., including methane) such that the reaction mixture becomes a reaction solution while stirring at the dissolving temperature. The reaction solution is then be heated to a reaction temperature (e.g., about 200° C. or more) while under the gas to form the core-shell nanoparticles, and the core-shell nanoparticles can be collected from the reaction solution.