RuO₂ Nanoparticle-Embedded Graphitic Carbon\nNitride for Efficient Photocatalytic H₂ Evolution

Abstract

Ruthenium\noxide nanoparticles (NPs) with an average diameter of\n3.5 ± 1.4 nm, embedded in graphitic carbon nitride (RuO₂/g-C₃N₄), were successfully prepared using\na modified wet impregnation method. The RuO₂/g-C₃N₄ nanocomposites were employed as photocatalysts in H₂ evolution with triethanolamine (TEOA) in aqueous media under\nirradiation with an LED lamp. When a small amount of the RuO₂ NPs (RuO₂: 0.62 wt %) was encapsulated in g-C₃N₄, the H₂ evolution rate per catalyst weight\n(3070 μmol h^–1 g^–1) under\nbasic pH conditions was remarkably improved, compared to the case\nwith the pristine g-C₃N₄. Mechanistic insights\ninto the H₂ evolution were obtained by the kinetic analysis\nof RuO₂/g-C₃N₄ with a series of alkanolamines\nas substrates and by X-ray photoelectron spectroscopy measurements.\nThe results revealed that the RuO₂ NPs embedded in g-C₃N₄ functioned as efficient oxidation sites for\nconverting alkanolamines into the corresponding aldehydes rather than\nas H₂ evolution sites. The H₂ evolution rates\nexhibited a saturation behavior dependent on the TEOA concentrations,\nsuggesting the equilibrium adsorption of the hydroxyl group of TEOA\non the RuO₂ surface. Conversely, the H₂ evolution\non the surface of g-C₃N₄ under basic conditions\nwas considered to be the rate-determining step as evidenced by the\nkinetic isotope effects exhibited in D₂O. These results\ndemonstrate that the RuO₂/g-C₃N₄ nanocomposites\ncan serve as an effective photocatalyst for H₂ evolution\nin tandem with selective substrate oxidations.