Influence of Precursor Structure on the Formation of Active Carbon Deposition Sites and Helical Graphite Cones Growth Mechanism

Graphite cones (GCs) have large aspect ratios and high mechanical properties, which have attracted much attention due to their similarity to carbon nanotubes and vapor-grown carbon fibers. Currently, there have been some preparation methods and growth mechanisms for GCs. Still, the growth conditions of GCs have not been explored from the perspective of the molecular structure of the precursor. Therefore, this paper is based on the in situ preparation of helical graphite cones (HGCs) using different precursors of polyimide (PI) graphite fibers (GFs) doped with polycyclic aromatic hydrocarbons (PAH). By varying the type of precursor of PI fibers, it can be found that HGCs appeared on GFs with pyromellitic dianhydride/4, 4′-oxidiamine (PMDA/ODA), and biphenyl tetracarboxylic dianhydride/4, 4′-oxidiamine (BPDA/ODA) as precursors, but there is no growth of HGCs on GFs with biphenyl tetracarboxylic dianhydride/p-phenylenediamine (BPDA/PDA) as precursors. Based on this phenomenon, it can be further discovered that the growth of HGCs is related to the ether-oxygen bonds in the ODA. The ether-oxygen bonds broken during heat treatment provide active carbon deposition sites, which is a key factor for the growth of HGCs, thus producing many HGCs. The discovery at the molecular structure level significantly impacts the future preparation of HGCs and the improvement of their growth mechanisms.