Novel template-free procedure of polyacrylonitrile-derived carbon hollow spheres preparation in the presence of palladium

A novel preparation method of hollow carbon spheres (HCSs) was developed. For the first time, polyacrylonitrile-derived HCSs were obtained under IR heating of joint precursor of the polymer and palladium compound in the presence of alkali. The simultaneous carbonization of polyacrylonitrile and its chemical activation with KOH in the presence of forming palladium nanoparticles provide the production of multiple HCSs located on the surface of the highly-porous carbon support. According to the proposed HCS preparation mechanism, the presence of potassium hydroxide during PAN pyrolysis leads to changes in both the products of pyrolysis and their concentration, which provides to the formation of a large amount of HCSs on palladium nanoparticles. The obtained HCSs are characterized by an outer diameter of 40–500 nm and a wall thickness of 3–15 nm. TEM micrographs and analysis of structural characteristics showed that HCS walls consist of oxidized graphite with an interplanar distance of 3.96 Å. It was found that HCSs are non-uniform, some of them have thickly sites built by additional graphene sheets on the graphitic sphere walls.