Bridging Gaps in the Synthesis of g-CN/WO3–x for Photocatalytic H2O2 Generation: Insights into S-Scheme Heterojunction and Plasmon-Induced Hot Electrons

This study presents a systematic design for fabricating g-CN/WO_3-x S-scheme heterojunctions with plasmonic features (localized surface plasmon resonance (LSPR) and hot electrons) to achieve superb photocatalytic H₂O₂ production activity. To optimize the synthesis, a rational approach is employed to how synthesis parameters influence the emergence of LSPR and hot electrons in WO_3-x and their effect on the heterojunction's performance. As a result of such a comprehensive strategy, the developed synthesis methodology effectively bridges gaps in the literature, addressing underexplored strategies for improving photocatalytic efficiency for the controlled synthesis of the g-CN/WO_3-x heterojunction. The plasmonic characteristics attributed to oxygen deficiency in WO₃ (WO_3-x) and g-CN/WO_3-x and interactions of g-CN and WO_3-x at the atomic level are further corroborated through a comprehensive analysis employing X-ray photoelectron spectroscopy (XPS), solid-state nuclear magnetic resonance (ssNMR), and electron paramagnetic resonance (EPR). Thanks to the presence of WO_3-x, the light-harvesting ability of g-CN/WO_3-x heterojunctions spans from the visible to near-infrared region. Moreover, the generation of hot electrons on the surface of WO_3-x mitigates electron-hole recombination in the binary heterojunction. Consequently, the g-CN/WO_3-x S-scheme heterojunctions synthesized with the optimal recipe provided a superior photocatalytic H₂O₂ generation rate of 1349.70 μmol·L^-1 in 10% (v/v) aqueous methanol solution within 90 min, which is 2.36 and 7.17 times greater than that of pristine g-CN and WO_3-x, respectively, superior to other similar photocatalysts tested in photocatalytic H₂O₂ production. The superb photocatalytic activity of the g-CN/WO_3-x heterojunction is attributed to the synergistic effects aroused in the S-scheme heterojunction, promoting efficient charge separation with enhanced redox potentials and plasmon-induced hot electrons that both accelerate reactions through the photothermal effect and serve as additional reducing species. This research broadens the perspective toward constructing nonmetallic plasmonic S-scheme heterojunctions for fields utilizing LSPR phenomena, such as photocatalysis, photonics, and biomedicine.