Fig. 2.

Crystal structure and optical properties of graphitic carbon nitride. a Schematic diagram of a perfect graphitic carbon nitride sheet constructed from melem units. b Experimental XRD pattern of the polymeric carbon nitride, revealing a graphitic structure with an interplanar stacking distance of aromatic units of 0.326 nm. c UV-visible diffuse reflectance spectrum and image (inset) of g-C₃N₄. Reprinted with permission from Ref. [5]. Copyright 2009 Nature Publishing Group. Representation of the β-C₃N₄ (d), α-C₃N₄ (e), graphite-C₃N₄ (f), pseudocubic-C₃N₄ (g), and cubic-C₃N₄ (h). The carbon and nitrogen atoms are depicted as gray and blue spheres, respectively, from Ref. [4]. Copyright 1996 American Association for the Advancement of Science. (Color figure online)