Formation of N-heterocyclic carbon quantum dots and their energy- and electron-transfer properties in photocatalysis

Nitrogen heterocyclic carbon quantum dots (NHCQDs) as a novel type of nitrogen-doped carbon-based quantum dots have been successfully synthesized for the first time via a facile and green molecular fusion hydrothermal approach using N-heterocyclic compound as the precursor. The hydrothermal synthesis of NHCQDs is accomplished by nitrifying with nitric acid and then hydrothermal treatment in alkaline aqueous solution. It can be found that the NHCQDs have a uniform distribution without apparent aggregation and particle size of 2–4 nm from the transmission electron microscopy (TEM) image of NHCQDs. The photoluminescent quantum yield of NHCQDs has been measured to be 44% under 360 nm light excitation by using quinine sulphate as a standard. The as-prepared NHCQDs show a downconversion and upconversion photoluminescent behavior, which can be applied in metal-free photocatalytic system as universal energy- and electron-transfer components under visible light.