Nickel-supported carbon nitride photocatalyst combined with organic dye for visible-light-driven hydrogen evolution from water

Abstract

A noble-metal-free photocatalytic H₂ production system consisting of a Ni-based catalyst, visible-light-responsive organic dye, and graphitic carbon nitride (g-C₃N₄) as a support has been developed. Characterization by means of XAFS revealed that the deposition of a trinuclear Ni precursor complex, Ni(NiL₂)₂Cl₂ (L = β-mercaptoethylamine), on the g-C₃N₄ affords a monomeric Ni(II) species involving β-mercaptoethylamine and aqua ligands in an octahedral coordination geometry. Such a Ni species acts as a hydrogen production site from an aqueous solution without an electron relay reagent by combining with thiazole orange (TO) as a photosensitizer. The emission of the attached TO at around 550 nm decreases with increasing loading amount of Ni catalyst, suggesting electron transfer from TO to the Ni catalyst via the g-C₃N₄ support. Leaching and agglomeration of the active Ni catalyst and TO are not observed during the photocatalytic reaction. Moreover, the use of highly porous carbon nitride (nanoporous carbon nitride; nanoC₃N₄) is proven to significantly enhance the photocatalytic activity because of the high surface area due to the unique porous structure as well as high absorption and emission properties of TO associated with nanoC₃N₄.