In some embodiments, the present disclosure pertains to methods of making graphene quantum dots from a carbon source (e.g., coal, coke, and combinations thereof) by exposing the carbon source to an oxidant. In some embodiments, the methods of the present disclosure further comprise a step of separating the formed graphene quantum dots from the oxidant. In some embodiments, the methods of the present disclosure further comprise a step of reducing the formed graphene quantum dots. In some embodiments, the methods of the present disclosure further comprise a step of enhancing a quantum yield of the graphene quantum dots. In further embodiments, the methods of the present disclosure also include a step of controlling the diameter of the formed graphene quantum dots by selecting the carbon source. In some embodiments, the formed graphene quantum dots comprise oxygen addends or amorphous carbon addends on their edges.