• A novel method for synthesizing graphene quantum dots (GQDs) from coal via chemical oxidation and exfoliation is presented.
• The synthesized GQDs show uniform size, high crystallinity, and strong photoluminescence, making them suitable for optoelectronic applications.
• The GQDs were successfully used as an electrochemical sensor for heavy metal ions with a low detection limit and high selectivity.
• This work offers a sustainable and cost-effective route to convert coal into high-value nanomaterials, promoting resource utilization.