Carbon quantum dots hydrothermally synthesized from chitin

Abstract

A simple hydrothermal treatment of chitin in dilute nitric acid (0.5–2.0 wt %) at 180°C for up to 3 h, which provides the dissolution of up to 50% of the polysaccharide and the formation of nanosized carbon quantum dots (C-dots), is proposed. Aqueous solutions of C-dot dispersions have high dispersion stability. Under illumination with a luminescent lamp, the solutions exhibit bright luminescence, the characteristic feature of which is a change in color with variation in the excitation wavelength. According to high-resolution transmission electron microscopy, the C-dots have a crystalline structure. It is specified that the proposed mechanisms of the hydrothermal carbonization of carbohydrates assume the formation of only an amorphous coal-like product. The example of the hydrothermal treatment of a sucrose solution shows that, along with the formation of a solid precipitate of spherical carbon microparticles that is described in the literature, the formation of a luminescent crystalline product occurs. This fact suggests that the carbonization mechanism is more complicated than what has been assumed.