The role of heteroatoms in iron-assisted graphitization of hard carbons derived from synthetic polymers: The special case of sulfur-doping

Three types of thermosetting heterocyclic phenolic resins (either oxygen-, nitrogen- or sulfur-doped) impregnated with FeCl3 were pyrolyzed in the temperature range of 750–1150 °C to study the influence of heteroatoms on the catalytic graphitization of non-graphitizing carbons. The thermal transformation from disordered to partly graphitized structures is strongly affected by the presence of sulfur and much less by nitrogen with respect to the oxygen-doped precursor. Sulfur totally blocks Fe-assisted catalytic graphitization but only up to a certain temperature. At ⁓1130 °C iron starts to catalyze the conversion of disordered carbon into a partly graphitized phase despite sulfur's presence. Nitrogen exhibits a similar impact to oxygen, and its presence neither significantly hinders nor enhances catalytic graphitization. However, the O-doped polymer is more prone to graphitization than its N-doped counterpart. An extensive discussion concerning sulfur's role in iron-assisted catalytic graphitization is presented herein.