Graphite functionalization by ball milling with sulfur

The present study reports on ball-milling of high-surface-area graphite in the presence of sulfur, mainly considering high graphite/sulfur (G/S) weight ratios. Graphitic crystallites after co-milling with sulfur maintain essentially unaltered crystalline order while exhibit heavily functionalized lateral edges, mainly by O=S=O and S=O groups. Solvent extraction procedures and thermogravimetric experiments show that co-milled graphite/sulfur samples contain two different kinds of sulfur: an extractable one being only physically adsorbed on graphite (exhibiting a higher thermal stability) and a non-extractable fraction chemically bonded to defective graphitic sites (exhibiting a lower thermal stability).The amount of sulfur covalently bonded to graphite crystallites increases with the co-milling time up to a limit value, which is in the range 3.0-3.5 wt% and is poorly dependent on the starting G/S ratio.