Hydrogen-bonding-assisted charge transfer: significantly enhanced photocatalytic H2 evolution over g-C3N4 anchored with ferrocene-based hole relay

Abstract

Herein, a polymeric graphitic carbon nitride (for simplicity, g-C₃N₄) photocatalyst has been identified as a promising material for hydrogen production from water due to its comparatively low cost and facile modification of its electronic structure. However, to date, how to speed up the transfer rate of photogenerated charges, especially hole transfer rate, still remains a formidable challenge. Herein, a novel system of g-C₃N₄/1,1′-ferrocenedicarboxylic acid (FcDA) composites was developed for efficient visible light-driven H₂ evolution, in which the redox mediator FcDA served as hole-transport molecules and platinum (Pt) acted as an electron sink. The FcDA molecules are anchored onto g-C₃N₄ by hydrogen-bonding interactions between the carboxylic groups and amino groups as well as π–π interactions between aromatic FcDA and graphitic C₃N₄. The matched energy-levels between g-C₃N₄ and FcDA facilitate photogenerated hole transfer from the g-C₃N₄ valence band to FcDA that results in the formation of FcDA⁺ radicals, and thus, photoinduced electrons and holes are efficiently separated. Due to the additional charge separation pathway, enhanced hole transfer kinetics, and the extremely rapid intermolecular radical reactions, charge recombination is effectively suppressed; therefore, more electrons can be released for hydrogen production. Under optimal experimental conditions, the developed g-C₃N₄/FcDA composite with 4 wt% FcDA exhibits high water splitting activity with a H₂ evolution rate of up to 77.91 μmol h⁻¹, which is nearly 6 times that of bare g-C₃N₄ (13.18 μmol h⁻¹). Moreover, the obtained g-C₃N₄/FcDA photocatalyst displays excellent stability, and there is no obvious decrease in the H₂-production rate after five test cycles. Thus, we anticipate that our simple modification strategy will offer an avenue to merge the polymeric g-C₃N₄ photocatalyst with surface organometallic chemistry for high-efficiency solar-to-fuel conversion.