Rapid and facile synthesis of high-color purity solid-state carbon dots with high yield using a direct heating method

Carbon dots (CDs) are renowned for their unique properties with numerous and growing applications in various fields and industries. Although several methods are available to prepare CDs, low conversion yield, tedious purification processes and poor color purity remain major drawbacks. To address these issues, a cooling stage for full protonation prior to direct heating has been developed. This innovative method produces high-color purity solid-state CDs with a conversion yield of up to 99.5% in less than 6 min. The CDs synthesized by this method exhibited a highly crystalline structure, as confirmed by HRTEM, Raman and XRD analyses. In addition, the emission profile of the CDs could be effectively tuned by reducing the amount of concentrated sulfuric acid, resulting in a shift of the emission from 484 to 650 nm. The high-color purity of the CDs is postulated to be due to the solvent cage effect. Overall, this study presents a simple, efficient and rapid method for the preparation of high-quality CDs with excellent color purity and crystallinity.