Effect of free radicals and electric field on preparation of coal pitch-derived graphene using flash Joule heating

Most of the traditional graphene production processes were not only solvent-intensive but also time-and-energy-consuming. Flash Joule heating (FJH) is an efficient approach to green and scalable large-scale production of graphene. However, its reaction mechanism is not clear during the process of electric field and free radical on graphene generation. In this work, synthesis of coal pitch-based graphene by FJH under the coupling effect of temperature and electric field, and Raman spectroscopy and electron transient magnetic resonance were studied at different input energies. The results show that the input energy is positively correlated with the generated radicals and is beneficial for the quality improvement of graphene. In addition, the mechanism is explained using ReaxFF molecular dynamics and DFT calculations: Joule heat provides energy for the kinetics and thermodynamics of the reaction. High temperature (3000 K) can dissociate branch chains in coal tar molecules to generate highly reactive alkane and alkene radicals. Different cooling rates affect the quality of graphene generation. When the cooling rate is slow, the graphite microplates will grow in layers, and a multi-layer phenomenon will appear; when the cooling rate is fast, the generated graphene will be in a turbostratic order. At the same time, the DFT calculation shows that the coal tar molecules are ionized under the action of the electric field and are oriented and arranged to reduce the reaction potential barrier.