Regulation of Pd-doped graphitic carbon nitride Schottky heterojunctions with the template of two-dimensional supramolecular polymer as both light-sensitizer and photocatalyst to promote hydrogen evolution

Abstract

Carbon nitrides have attracted growing attention as the metal-free semiconductor photocatalysts with various advantages, but still suffering from the limited efficiency due to a quick recombination of photogenerated carriers and a scarcity of reactive sites. Here, we developed a templated synthetic method to construct Pd-doped carbon nitride Schottky junctions using a two-dimensional (2D) supramolecular polymer and well-dispersed palladium acetate as the precursors. After the self-assembling, heating, and calcination processes, the Pd(0) atoms and their nanoparticles (Pd⁽⁰⁾NPs) are inserted or doped in the porous graphitic carbon nitride (g-C₃N₄) nanosheets to produce g-C₃N₄/Pd_x heterojunctions. It is revealed that compositions, microstructure, and photocatalytic H₂ evolution rates of the g-C₃N₄/Pd_x heterojunctions can be regulated by the amount of palladium acetate added in the template of 2D polymers. The most efficient g-C₃N₄/Pd_1.2 Schottky junction gives a H₂ evolution rate of 468 μmol g^-1 h^-1; nearly 40 times higher as compared to that of the corresponding g-C₃N₄ nanosheets. Investigations on the structure and mechanism reveal that the porous design and Schottky junctions enhance significantly the light utilization and build-in electric field between Pd⁽⁰⁾NPs and g-C₃N₄ nanosheets, thus resulting in an enhanced separation and transfer efficiency of the photogenerated charge carriers.