Interlayer Palladium-Single-Atom-Coordinated Cyano-Group-Rich Graphitic Carbon Nitride for Enhanced Photocatalytic Hydrogen Production Performance

To improve the photocatalytic hydrogen evolution activity of palladium-assisted graphitic carbon nitride (g-C3N4), here, palladium-single-atom-coordinated cyano-group-rich g-C3N4 (Pd/D-N-UCN) are synthesized, and the synthesis process includes copolymerization of urea-derived supramolecular aggregates and NH4Cl followed by wet impregnation. By combining powerful characteristic results and theoretical calculations, the formation mechanism of Pd single atoms on the ultrathin, mesoporous cyanogroup-rich g-C3N4 nanosheets is proposed, highlighting that the Pd single atoms are firmly stabilized in the interlayers of g-C3N4 nanosheets caused by the combination of the physical confinement effect of ultrathin, mesoporous g-C3N4 nanosheets and coordination bonding of cyano groups with Pd atoms; additionally, Pd-N-3 coordination in the Pd/D-N-UCN heterojunctions is confirmed, in which one Pd atom coordinates with one N atom of the cyano group and two sp(2)-hybridized N atoms in the adjacent layer. The presence of cyano groups and Pd-N coordination in the Pd/D-N- UCN induces a midgap state in the band structure of g-C3N4. At optimal Pd loading levels (0.16%), the synthesized 0.16%Pd/D-N-UCN oso exhibits enhanced photocatalytic hydrogen production activity as compared to electrostatically stabilized Pd single atoms on the sixfold cavities of g-C3N4, and apparent quantum yield values at the stationary point of the 0.16%Pd/D-N-UCN o.so concentration (1.2 g L-1) can reach up to 14.6, 15.8, 4.69, and 3.05% under monochromatic light irradiation at 365, 400, 450, and 550 nm, respectively. The cooperation of significantly boosted transfer of photoexcited electrons to atomically dispersed Pd sites via as-built interlayer Pd-N coordination delivery channels and the maximal Pd atom utilization efficiency dominates the enhanced photocatalytic hydrogen evolution activity of Pd/D-N-UCN.

Automated summary

In this study, a palladium-single-atom-coordinated cyano-group-rich g-C3N4 (Pd/D-N-UCN) was synthesized to improve the photocatalytic hydrogen evolution activity. The formation mechanism of Pd single atoms on g-C3N4 nanosheets and the coordination bonding of cyano groups with Pd atoms were proposed. The synthesized 0.16%Pd/D-N-UCN exhibited enhanced photocatalytic hydrogen production activity compared to electrostatically stabilized Pd single atoms.