Valorization of petroleum coke into high-quality few-layer graphene through liquid-phase exfoliation

Abstract

Abstract Low-value fuel-grade petroleum coke (petcoke), an abundant byproduct from petroleum refining operations, is traditionally used in low-value fuel and metallurgical applications owing to its high carbon content and ability to be used in the synthesis of advanced carbon materials. In this paper, we demonstrate a non-oxidation-based route for producing conductive few-layer graphene from petcoke through sequential isopropanol assisted pre-treatment, thermal desulfurization, and CO 2 assisted liquid phase exfoliation. Unlike conventional graphene synthesis processes using high temperature chemical vapor deposition, oxidation reduction-based Hummer’s type methods, or exfoliation from expensive graphite sources, our approach enables the conversion of inexpensive petcoke into graphene nanosheets using a scalable solvent assisted route. Thermal treatment increased the graphitization degree of petroleum coke to approximately 78%, demonstrating its potential as a precursor for advanced graphitic materials. The optimized CO₂-assisted liquid-phase exfoliation and centrifugation procedure achieved approximately 90% recovery of dispersed exfoliated carbon solids. Combined optical microscopy, Raman, TEM, HRTEM, AFM, and electrical analyses confirmed the formation of well-dispersed, conductive few-layer graphene nanosheets, with thicknesses corresponding to approximately 3–5 layers. The graphene dispersions display stability up to six months and can be transformed into conductive films with a maximum electrical conductivity of 872 S m⁻ 1 after thermal annealing. This work establishes petcoke as a promising low-cost carbon resource for sustainable graphene production and offers a practical route for transforming refinery waste into value-added materials for energy storage, conductive coatings, composites, and carbon-based technologies.