Bridging Functional Groups Governing the Charge Transfer Dynamic in an Amorphous Carbon Nitride Allotropic Heterojunction toward Efficient Solar Hydrogen Evolution

Modulation of the charge transfer dynamic in amorphous carbon nitride allotropic heterojunctions by an alternation in bridging functional groups for the heptazine- and triazine-based fragments is demonstrated to boost the photocatalytic activity for hydrogen evolution. Pyrimidine-bridged and NH-bridged amorphous carbon nitride allotropic heterojunctions are synthesized by thermal polycondensation of a supramolecular complex. Due to the improved charge separation efficiency and visible-light harvesting ability, both allotropic heterojunctions present more than tenfold enhanced photocatalytic activities for hydrogen evolution compared to the conventional heptazine-based carbon nitride under visible-light illumination. Moreover, the photocatalytic activity of the NH-bridged carbon nitride allotropic heterojunction with type-II charge transfer dynamic is superior to the pyrimidine-bridged one with a Z-scheme characteristic. The findings in this study emphasize that the electronic structure at the heterojunction interface governed by the bridging group greatly influences the charge transfer dynamic and therefore is a crucial factor driving the photocatalytic activity of carbon nitride allotropic heterojunctions.