Engineering defects in graphitic carbon nitride photocatalysts

Graphitic carbon nitride (g-C₃N₄) has emerged as a promising metal-free photocatalyst. However, it continues to face significant challenges in achieving competitive activities both in laboratories and practical applications. Defect engineering is a versatile strategy to refine the intrinsic properties of semiconductor photocatalysts, modulating their electronic structure, charge dynamics and active surface sites. Given rapid advancements in this field, there is an urgent need to overview the progress in engineering of defects in g-C₃N₄, which is essential for a deeper understanding of the activity of this photocatalyst. This review focuses on the synthesis, characterization, and physiochemical properties of defect-engineered g-C₃N₄, including g-C₃N₄ with substitutional dopants, interstitial dopants, vacancies, functional groups and/or structural disorder. It also explores various applications of g-C₃N₄ materials with introduced defects for photocatalytic H₂ evolution, CO₂ reduction, N₂ fixation and organic transformations, along with the mechanisms underlying their performance at the molecular level. Finally, this review article presents a perspective on the design, synthesis and properties of defect-modified g-C₃N₄ photocatalysts.