Recently, Chao Gao research group from Zhejiang University selected polyimide pyrolysis carbon (PPC) as the research subject. After establishing the relationship between material structure and product features, they found a simple and clean electrochemical method to convert carbon waste selectively to high-value nanometer pearl - graphene quantum dots and micron level graphene, which make it once again become a high performance element of the structure of carbon materials. Especially for the graphene quantum dots smaller than 10 nm in size, the carbon yield of the products derived from traditional carbon precursors, such as graphite, graphene, carbon nanotubes, coal, etc., is often low (lt;50%). This is because these carbon precursors are mostly layered or porous structures, and the interlayer and pore area will be affected by electrochemical bubbling, and the large carbon products that are not electrolyzed will be produced and fall into the electrolyte. These carbon products will not be further electrolyzed, thus resulting in the waste of carbon. In this paper, it was found that the carbon precursors with sp2 and sp3 double-continuous structures can achieve the high yield (98%) and high carbon yield (77.4%) of graphene quantum dots in 2 hours, which provides a prospect for the industrial application of graphene quantum dots. At the same time, it is proved that when the graphene quantum dots are used to disperse carbon nanotubes, the dispersion concentration of carbon nanotubes can reach 0.6mg/mL. And when the graphene quantum dots were used as nano-filler for supercapacitors, the mass specific capacity of pure graphene supercapacitors was increased by 79.4% by only adding 3% of the graphene quantum dots.

Figure 1. Waste carbon and waste carbon cycle diagram of polymer-based industry. (a) Industrial polyimide carbon paper; (b) Carbon waste from industrial production; (c) Rolls of carbon waste removed from B (d) Schematic diagram of waste carbon cycle.

The results were published in Nanoscale(DOI: 10.1039/ D0NR00725K) as A Polyimide - Pyrolyzed Carbon Waste Approach for the Scalable and Controlled Electrochemical Preparation of Size-Tunable Graphene.