Low temperature synthesis of graphene-encapsulated copper nanoparticles from kraft lignin

The formation of graphene-encapsulated copper nanoparticles was investigated through carbonizing a mixture of kraft lignin and copper sulfate pentahydrate at the temperature up to 500 °C. The abrupt conversion of copper ions into its atoms occurred at 300 °C. The formation of graphene layers surrounding copper nanoparticles started as early as the heating temperature reached 400 °C. Most copper nanoparticles were covered with less than five graphene layers when the temperature reached 500 °C. The average diameter of graphene-encapsulated copper nanoparticles was 12.75 and 11.62 nm for temperature at 400 and 500 °C, respectively. The heating temperature had no significant effect on the size of graphene-encapsulated copper nanoparticles in the evaluated temperature range. It is believed that the formation of graphene-layered shell surrounding copper nanoparticles is based on the mechanism of self-limiting theory with solid carbon as the carbon source.