Carbon nitride polymorphs: materials of the future

The search for non-metal photocatalysts is of considerable scientific and practical interest due to the growing environmental concerns associated with photocatalysis. Among such materials, graphitic carbon nitride (g-C₃N₄) undoubtedly holds the highest priority. The focus on this material has diverted attention of researchers from other polymorphs of carbon nitride, the solid phases of which, namely α, β, cubic, and pseudocubic phases, behave similarly to diamond-like structures (diamond, silicon nitrides, boron nitrides). These phases hold a considerable potential due to their structural features, both in a pure state and in composites. Although research into carbon nitride started with attempts to obtain and theoretically investigate dense carbon nitride phases, currently these phases are still least explored in terms of practical applicability; these issues are addressed only in few studies. The main challenge here lies in creating the special conditions required for the formation of dense phases. This review critically examines the structure, synthesis methods, product yields, and morphology of both dense and layered polymorphs of carbon nitride. The evolution of synthetic approaches to dense carbon nitride polymorphs is demonstrated, and results of theoretical studies of the band structure, along with the approximations employed, are analyzed. This review consolidates the fragmentary data on various C₃N₄ polymorphs and highlights the diversity of factors influencing their structure and morphology. Data on the potential use of dense carbon nitride phases and their composites, including application as photocatalysts, are also presented.

The bibliography includes 144 references.