Solvated Electrons Generated on the Surface of Na-SPHI for Boosting Visible Light Photocatalytic Hydrogen Evolution with Ultra-High AQE.

Enhancing the utilization of visible-light-active semiconductors with an excellent apparent quantum efficiency (AQE) remains a significant and challenging goal in the realm of photocatalytic water splitting. In this study, a fully condensed sulfur-doped poly(heptazine imide) metalized with Na (Na-SPHI) is synthesized by an ionothermal method by using eutectic NaCl/LiCl mixture as the ionic solvent. Comprehensive characterizations of the obtained Na-SPHI reveal several advantageous features, including heightened light absorption, facilitated exciton dissociation, and expedited charge transfer. More importantly, solvated electron, powerful reducing agents, can be generated on the surface of Na-SPHI upon irradiation with visible light. Benefiting from above advantage, the Na-SPHI exhibits an excellent H2 evolution rate of 571.8 µmol·h-1 under visible light illumination and a super-high AQE of 61.7% at 420 nm. This research emphasizes the significance of the solvated electron on the surface of photocatalyst in overcoming the challenges associated with visible light-driven photocatalysis, showcasing its potential application in photocatalytic water splitting.

Optimizing the band structure of sponge-like S-doped poly(heptazine imide) with quantum confinement effect towards boosting visible-light photocatalytic H2 generation.

Simultaneously manipulating the nanostructure and band structure of semiconductors for boosting the photocatalytic performance of photocatalyts is highly desirable. Herein, a series of hierarchical sponge-like S-doped poly(heptazine imide) (HS-SPHI) assembled by ultrathin nanosheets were successfully fabricated via a facile bottom-up supramolecular preassembly approach using melamine (MA) and trithiocyanuric acid (TTCA) as precursors. Benefiting from the synergistic effect of the S-doping and their unique hierarchical porous structure coupled with quantum confinement effect, the as-obtained HS-SPHIs are endowed with extended visible-light response, improved charge separation efficiency, enlarged specific surface area, and enhanced thermodynamic driving force for water reduction. As a result, all the HS-SPHIs exhibit remarkable boosting visible-light (>420 nm) photocatalytic H2evolution (PHE). The maximum PHE rate achieved by HS-SPHI-650 can be up to 3584.2 µmol g-1h-1, with an apparent quantum efficiency (AQE) of 14.67 % at 420 nm, which is about 22.4 times than that of pristine bulk g-C3N4 (B-GCN). We believe that this work will provide a significant strategy for optimizing the band structure of PCN in order to improve its photocatalytic performance.