Controllable ionic liquid-assisted electrochemical exfoliation of carbon fibers for the green and large-scale preparation of functionalized graphene quantum dots endowed with multicolor emission and size tunability

Abstract

Graphene quantum dots (GQDs), a type of emerging luminescent quantum dot, have drawn remarkable attention owing to their numerous fascinating properties and wide range of potential applications. Despite the intensive research efforts devoted to GQD fabrication, the mass production of high-quality GQDs in a reproducible and eco-friendly manner still represents a great challenge. Hence, we introduce an environmentally friendly, fast and industrially promising method for generating GQDs in large scale via the ionic liquid (IL)-assisted controllable electrochemical exfoliation of carbon fibers. Interestingly, it is found that the size-dependent optical properties of the as-prepared GQDs can be adjusted by using IL electrolytes with different water contents. For example, volume ratios of H₂O/IL of 0%, 15% and 30% generate blue-emitting GQDs (B-GQDs), green-emitting GQDs (G-GQDs) and yellow-emitting GQDs (Y-GQDs), respectively. More interestingly, when pure IL is used as the electrolyte, IL-functionalized GQDs with blue photoluminescence emission (B-GQDs) are generated. These functionalized GQDs can effectively improve the electrochemiluminescence (ECL) performance of the system of Ru(bpy)₃²⁺–ECL. Furthermore, we have fabricated a well-designed ECL sensor with satisfactory sensitivity for the determination of pentachlorophenol (PCP). More importantly, this proposed green and large-scale approach provides a promising and extremely flexible platform for the preparation of GQDs with tunable photoluminescence.