A New Strategy for the Synthesis of Highly Active Catalysts Based on g-C3N4 for Photocatalytic Production of Hydrogen under Visible Light

Abstract

Materials based on graphite-like carbon nitride g‑C₃N₄ were synthesized by heat treatment of a mixture of melamine and urea, and the effect of synthesis conditions on the photocatalytic activity of the samples was studied at various melamine : urea ratios. Platinum (1 wt %) was deposited on the surface of the synthesized g‑C₃N₄ samples as a cocatalyst. The produced photocatalysts were characterized by X-ray powder diffraction analysis, diffuse reflectance UV-Vis spectroscopy, and low-temperature nitrogen adsorption. Photocatalytic activity was determined in the reaction of hydrogen evolution from an aqueous solution of triethanolamine (10 vol %) upon irradiation with visible light (λ = 425 nm). Optimal conditions for the synthesis of the photocatalyst 1% Pt/g-C₃N₄ were found, which was obtained by calcination of a mixture of melamine and urea (1 : 3) and ensured an H₂ evolution rate of 5.0 mmol g^–1 h^–1 at an apparent quantum efficiency of 2.5%. The developed synthetic approach produces highly active catalysts because, during the synthesis, an intermediate supramolecular complex melamine–cyanuric acid is formed, which, upon further heating, is converted into g-C₃N₄ characterized by a high specific surface area exceeding 100 m² g^–1.