Dual-Metalloporphyrin-SensitizedPhotocatalyst forEfficient Solar Hydrogen Production: Importance of Loading Order ofMetalloporphyrins

Abstract Photoinduced charge separation is crucial for converting solar energy to electrical and chemical energy. In this work, to improve the photoinduced charge separation efficiency at the photosensitizing dye–semiconductor interface, we synthesized two dual-porphyrin-sensitized Pt-loaded TiO2 nanoparticle photocatalysts (ZnP–Zr–SnP@Pt–TiO2 (DPSP) and SnP–Zr–ZnP@Pt–TiO2 (DPSP-r)) by reversing the loading order of two metalloporphyrin-photosensitizing dyes (SnP and ZnP = 5,10,15,20-tetrakis(p-carboxyphenyl)-porphyrinato-M; M = SnIVCl2, ZnII). The apparent quantum yield of the photocatalytic H2 production reaction over DPSP in a 500 mM l-ascorbic acid sacrificial electron donor aqueous solution (2.08%) was estimated to be approximately 10 times higher than that over DPSP-r (0.21%), indicating the importance of the loading order of the metalloporphyrin dye for efficient photoinduced charge separation. The barely emissive nature of the DPSP compounds and the redox potentials of ZnP and SnP suggested that the redox cascade structure of the dual-metalloporphyrin ZnP–Zr–SnP layer on the Pt–TiO2 nanoparticle surface plays a key role in photoinduced charge separation for photocatalytic H2 production. The combination of this dual-metalloporphyrin sensitization method and the versatility of the metalloporphyrin family promotes the development of highly active visible-light-driven photocatalysts.