Bimetallic Pt-IrO x /g-C 3 N 4 Photocatalysts for the Highly Efficient Overall Water Splitting under Visible Light.

Two series of bimetallic photocatalysts (0.5% Pt/0.01–0.5% IrO_x/g-C₃N₄ and 0.1% Pt/0.01–0.1% IrO_x/g-C₃N₄) were synthesized by the thermolysis of melamine cyanurate and a successive deposition of platinum and iridium labile complexes (Me₄N)₂[Pt₂(μ-OH)₂(NO₃)₈] and fac-[Ir(H₂O)₃(NO₂)₃. The synthesized photocatalysts were studied by a set of physicochemical analysis techniques. Platinum exists in two states, with up to 60% in metallic form and the rest in the Pt²⁺ state, while iridium is primarily oxidized to the Ir³⁺ state, which was determined by X-ray photoelectron spectroscopy (XPS). The specific surface area (S_BET), which is determined by low-temperature nitrogen adsorption, ranges from 80 to 100 m² g⁻¹ and the band gap energy (E_g) value is in the range of 2.75–2.80 eV as found by diffuse reflectance spectroscopy (DRS). The activity of the photocatalysts was tested in the photocatalytic production of hydrogen from ultrapure water under visible light (λ = 400 nm). It was found that the splitting of water occurs with the formation of the stochiometric amount of H₂O₂ as an oxidation product. Two photocatalysts 0.5% Pt/0.01% IrO_x/g-C₃N₄ and 0.1% Pt/0.01% IrO_x/g-C₃N₄ showed the highest activity at 100 μmol h⁻¹ g_cat⁻¹, which is among the highest in H₂ production published for such systems. [ABSTRACT FROM AUTHOR]