Thermal treatment of graphitic carbon nitride (g-CN) in aqueous solutions of tetraethyl ammonium hydroxide at ∼100 °C yields transparent colloidal solutions retaining stability at a CN concentration of up to 50 g L−1 and upon dilution by a factor of 103. Atomic force microscopy showed that the major part of the CN particles in diluted colloidal solutions are characterized by a lateral size of around 30–50 nm and a thickness of 0.3–0.4 nm typical of a single CN layer. Besides, a small fraction of multi-layer 2–5 nm thick g-CN particles with a size of ∼60 nm is present in the solutions. Photoexcitation of the colloidal CN near the edge of the absorption band results in emission of strong broad-band photoluminescence with a maximum at 460–470 nm and a quantum yield of 45–50%.
