Interlayer Palladium-Single-Atom-Coordinated Cyano-Group-Rich Graphitic Carbon Nitride for Enhanced Photocatalytic Hydrogen Production Performance
Miao Ren, Xueyan Zhang, Yunqing Liu, Guang Yang, Lang Qin, Jiaqi Meng, Yihang Guo, Yuxin Yang
Abstract
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/DN-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 cyano-group-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–N3 coordination in the Pd/DN-UCN heterojunctions is confirmed, in which one Pd atom coordinates with one N atom of the cyano group and two sp2-hybridized N atoms in the adjacent layer. The presence of cyano groups and Pd–N coordination in the Pd/DN-UCN induces a midgap state in the band structure of g-C3N4. At optimal Pd loading levels (0.16%), the synthesized 0.16%Pd/DN-UCN0.50 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/DN-UCN0.50 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/DN-UCN.