It is very important to develop effective synthesis methods of G-SAMs with monodisperse metal atoms for exploring their basic properties and potential applications. A series of monodisperse atomic transition metals (such as Co,Ni,Cu) in nitrogen-doped graphene have been synthesized by a convenient, fast and general strategy.A two-second microwave heating of a mixture of graphene oxide and metal salts for amine functionalization.

  The simple step of microwave heating can induce the reduction of graphene oxide, the doping of nitrogen and the incorporation of metal atoms into the lattice of graphene. Rapid microwave technology can minimize metal diffusion and aggregation and ensure the dispersion of unique monometallic atoms in graphene lattice.

The researchers first mixed the metal salts with the solution of graphene oxide, and used the strong interaction between metal ions and amino groups to distribute metal ions uniformly on the surface of graphene oxide. The dried mixture was then placed in a domestic microwave oven and heated at 1000W for 2s. In the process of microwave heating, graphene is excited by absorbing microwave and producing high temperature in an instant. The reduction of graphene, the doping of nitrogen and the intercalation of metal atoms in the lattice of graphene are realized simultaneously by one step method.

                 Fig1.

The Raman spectrum（Raman）、XX-ray diffraction pattern （XRD）and XX-ray photoelectron spectroscopy（XPS）show that microwave treatment can effectively remove the oxygen-containing groups on the surface of graphene oxide. At the same time, the defects on graphene surface were reduced and nitrogen doping was realized.

Fig 2. Morphology and atomic structure characterization of cobalt monoatom supported on graphene

The spherical aberration correction electron microscope andXthe X-ray absorption fine structure spectrum （Fig2）show that the cobalt metal is uniformly distributed on the graphene substrate in the form of a single atom, and the valence state is% 1. It is found that the peripheral coordination environment of the graphene-loaded MN4C4-type single-atom (Nat. Caal., 2018, 1, 63) synthesized by the conventional thermal method is more disordered compared with the metal single-atom synthesized by the microwave method, and the defect degree is higher.

Fig 3. Atomic structure characterization of graphene supported nickel and copper monatomic atoms

In addition to the graphene loaded cobalt single atom, the researchers expanded the microwave heating method, successfully synthesized the graphene loaded nickel monoatomic and copper monoatomic (Fig.3), and proved the universality of the method.

Fig 4. Graphene-loaded cobalt atom as high-efficiency hydrogen evolution catalyst

Published in Advanced Materials, 2018,30, 1802146 SCI Impact Factor:21.95