Functionalized graphene sheets coordinating metal cations

Interactions of metal cations such as Li+, Na+, K+, Mg2+, Ca2+, Sr2+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, and Zn2+ with ammonia-treated graphene sheets (G) and thermal stability of metal cations coordinated with oxygen- and nitrogen-containing functional groups on G were investigated by rinsing G coordinated with metal cations (G-Metal) in 2-propanol using sonication and by heating G-Metal at 773 K, respectively. Monovalent alkali metal cations, divalent alkaline-earth metal cations, divalent transition metal cations such as Mn2+, and the other metal cation such as Zn2+ were removed by rinsing because of either no interaction or weak interactions between metal cations and G including various thermally stable nitrogen- and oxygen-containing functional groups. Trivalent transition metal cations such as Cr3+ and Fe3+ were agglomerated by heat treatment at 773 K, whereas divalent transition metal cations such as Co2+, Ni2+, and Cu2+ remained without severe agglomeration. Phenanthroline-like groups on edges of graphene showed the strongest interaction with Ni2+ among all of investigated nitrogen- and oxygen-containing functional groups as results of density functional theory calculation. The thermal stability of NNi bonding was confirmed as above 873 K as results of heat treatment of a standard compound (Ni phthalocyanine) in a glass ampoule.