Structural characterization and magnetic behavior of nickel nanoparticles encapsulated in monolithic wood-derived porous carbon

We report a new environmentally friendly and simple method to produce monolithic magnetic composites C/Ni nanoparticles (NiNPs) consisting of highly porous carbon matrix and well-separated Ni nanoparticles covered by graphite-like shells. The method is based on the carbonization of wood with addition of nickel nitrate and wood decomposition product (tar) as a binder. The specific structural features and magnetic properties of the C/NiNPs composites are systematically investigated. We have demonstrated the change in average size of NiNPs from ~ 9 to ~ 18 nm and in their magnetic character from superparamagnetic to ferromagnetic behavior by changing the pyrolysis temperature. The macroscopic magnetization 3.5 emu/g (38 emu/g(Ni)) of the obtained porous monolithic nanocomposites with small amount of nickel (8.8 wt.%) in low magnetic field and their ferromagnetic behavior at room temperature make them ideal candidates for use in applications involving magnetic separation (heterogeneous catalysis, adsorption of contaminants in aqueous media, etc.). The resulting maximum magnetization 38 emu/g(Ni) of carbon-encapsulated NiNPs is comparable and even somewhat exceeds that of similar core–shell Ni nanoparticles obtained by other methods. The fundamental question arises whether it is possible to achieve the magnetization for carbon-encapsulated NiNPs as that in the bulk Ni.