Bottom-up analysis of X-ray diffraction reveals turbostratic melon-like structures in materials commonly assigned to g-C3N4

Graphitic (sp 2 -hybridized) carbon nitride (g-C 3 N 4 ) is one of the most widely investigated metal-free photocatalysts, yet the atomic structure of materials commonly assigned to g-C 3 N 4 after conventional thermopolymerization remains controversial. The lack of detailed analyses of their X-ray diffraction (XRD) patterns has led to multiple and often inconsistent structural interpretations. Moreover, possible stacking configurations, including turbostratic, AB, and ABC sequences, as well as the effects of planar and non-planar layers, have never been investigated systematically. Here, first-principles calculations combined with a bottom-up XRD methodology based on Debye's equation are used to calculate the diffraction fingerprints of the proposed structures and of the main condensation intermediates. This approach discriminates between competing structural models while accounting for crystallite size effects and turbostratic stacking, thereby establishing which structural information can be reliably extracted from XRD patterns. Application of the method to experimental materials synthesized under conventional thermopolymerization conditions demonstrates that the diffraction patterns commonly assigned to g-C 3 N 4 are instead more consistently explained by turbostratic melon-like structures. This interpretation is further supported by elemental analysis and is consistent with previous structural studies based on complementary characterization techniques.