GO was synthesized from natural graphite
powder (325 mesh, GAK-2, Ukraine) by the method of Hum-mers and Offeman It was found that, prior to the GO
preparation according to ref 18, an additional graphite oxida-tion procedure was needed. Otherwise, incompletely oxidized
graphite-core/GO-shell particles were always observed in the
final product. The graphite powder (20 g) was put into an 80
°C solution of concentrated H2SO4(30 mL), K2S2O8(10 g), and
P2O5(10 g)