Facile Molecular-Level Refinements for Carbon Quantum Dots via Hydrogen-Bonding-Assisted Selective Isolation

A novel method for synthesizing and refining high-purity carbon quantum dots (CQDs) using citric acid and diethylenetriamine as precursors is presented, achieved through molecular-level control by exploiting the differences in hydrogen-bonding strength. This process involves precipitation using melamine, extraction into ethanol, and encapsulation with (3-aminopropyl)­triethoxysilane (APTES). The resulting APTES-encapsulated CQDs exhibited an enhanced color purity, higher photoluminescence quantum yield, and improved fluorescence stability over a broad pH range. Utilizing these well-defined high-purity CQDs with uniform surface states, it has been revealed that ferric ions are photochemically sensed through the inner filter effect (IFE) mechanism, while mercury ions are detected through the photoinduced electron transfer (PET) mechanism. The versatility of CQDs, coupled with our advanced refinement technology, is expected to contribute significantly to the development of advanced research applications, particularly in displays and sensors.