Transition-metal-ion-mediated polymerization of dopamine: Mussel-inspired approach for the facile synthesis of robust transition-metal nanoparticle-graphene hybrids

Inspired by the high transition-metal-ion content in mussel glues, and the cross-linking and mechanical reinforcement effects of some transition-metal ions in mussel threads, high concentrations of nickel(II), cobalt(II), and manganese(II) ions have been purposely introduced into the reaction system for dopamine polymerization. Kinetics studies were conducted for the Ni ²⁺-dopamine system to investigate the polymerization mechanism. The results show that the Ni²⁺ ions could accelerate the assembly of dopamine oligomers in the polymerization process. Spectroscopic and electron microscopic studies reveal that the Ni²⁺ ions are chelated with polydopamine (PDA) units, forming homogeneous Ni²⁺-PDA complexes. This facile one-pot approach is utilized to construct transition-metal-ion-PDA complex thin coatings on graphene oxide, which can be carbonized to produce robust hybrid nanosheets with well-dispersed metallic nickel/metallic cobalt/manganese(II) oxide nanoparticles embedded in PDA-derived thin graphitic carbon layers. The nickel-graphene hybrid prepared by using this approach shows good catalytic properties and recyclability for the reduction of p-nitrophenol. Metal mediation: Transition-metal-ion-mediated polymerization of dopamine has been developed to construct transition-metal-ion-polydopamine (PDA) complex bulk materials or thin coatings on graphene oxide (GO), leading to robust hybrids with well-dispersed metallic nanoparticles (MNPs) embedded in PDA-derived thin graphitic carbon layers (see figure; CPDA=carbonized PDA, G=graphene).