Defect-Regulated Two-Dimensional Superlattice of Holey g-C₃N₄-TiO₂ Nanohybrids: Contrasting Influence of Vacancy Content on Hybridization Impact and Photocatalyst Performance

Defect engineering provides an effective way to explore efficient nanostructured catalysts. Herein, we synthesize defect-regulated two-dimensional superlattices comprising interstratified holey g-C₃N₄ and TiO₂ monolayers with tailorable interfacial coupling. Using this interfacial-coupling-controlled hybrid system, a strong interdependence among vacancy content, performance, and interfacial coupling was elucidated, offering key insights for the design of high-performance catalysts. The defect-optimized g-C₃N₄-TiO₂ superlattice exhibited higher photocatalytic activity toward visible-light-induced N₂ fixation (∼1.06 mmol g^-1 h^-1) than defect-unoptimized and disorderly assembled g-C₃N₄-TiO₂ homologues. The high photocatalytic performance of g-C₃N₄-TiO₂ was attributed to the hybridization-induced defect creation, facilitated hydrogenation of adsorbed nitrogen, and improvement in N₂ adsorption and charge transport. A comparison of the defect-dependent photocatalytic activity of g-C₃N₄, g-C₃N₄ nanosheets, and g-C₃N₄-TiO₂ revealed the presence of optimal defect content for improving photocatalytic performance and the continuous increase of hybridization impact with the defect content. Sophisticated mutual influence among defect, electronic coupling, and photocatalytic ability underscores the importance of defect fine control in exploring high-performance hybrid photocatalysts. Along with the DFT calculation, the excellent photocatalyst performance of defect-optimized g-C₃N₄-TiO₂ can be ascribed to the promotion of the uphill *N hydrogenation step as well as to enhancement of N₂ adsorption, charge transfer kinetics, and mass transports.