RuO2 Nanoparticle-Embedded Graphitic Carbon Nitride for Efficient Photocatalytic H2 Evolution

Abstract

Ruthenium oxide nanoparticles (NPs) with an average diameter of 3.5 ± 1.4 nm, embedded in graphitic carbon nitride (RuO2/g-C3N4), were successfully prepared using a modified wet impregnation method. The RuO2/g-C3N4 nanocomposites were employed as photocatalysts in H2 evolution with triethanolamine (TEOA) in aqueous media under irradiation 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 (3070 μmol h–1 g–1) under basic pH conditions was remarkably improved, compared to the case with the pristine g-C3N4. Mechanistic insights into the H2 evolution were obtained by the kinetic analysis of RuO2/g-C3N4 with a series of alkanolamines as substrates and by X-ray photoelectron spectroscopy measurements. The results revealed that the RuO2 NPs embedded in g-C3N4 functioned as efficient oxidation sites for converting alkanolamines into the corresponding aldehydes rather than as H2 evolution sites. The H2 evolution rates exhibited a saturation behavior dependent on the TEOA concentrations, suggesting the equilibrium adsorption of the hydroxyl group of TEOA on the RuO2 surface. Conversely, the H2 evolution on the surface of g-C3N4 under basic conditions was considered to be the rate-determining step as evidenced by the kinetic isotope effects exhibited in D2O. These results demonstrate that the RuO2/g-C3N4 nanocomposites can serve as an effective photocatalyst for H2 evolution in tandem with selective substrate oxidations.