Currently, the synthesis of active photocatalysts for the evolution of hydrogen, including photocatalysts based on graphite-like carbon nitride, is an acute issue. In this review, a comprehensive analysis of the state-of-the-art studies of graphic carbon nitride as a photocatalyst for hydrogen production under visible light is presented. In this review, various approaches to the synthesis of photocatalysts based on g-C₃N₄ reported in the literature were considered, including various methods for modifying and improving the structural and photocatalytic properties of this material. A thorough analysis of the literature has shown that the most commonly used methods for improving g-C₃N₄ properties are alterations of textural characteristics by introducing templates, pore formers or pre-treatment method, doping with heteroatoms, modification with metals, and the creation of composite photocatalysts. Next, the authors considered their own detailed study on the synthesis of graphitic carbon nitride with different pre-treatments and respective photocatalysts that demonstrate high efficiency and stability in photocatalytic production of hydrogen. Particular attention was paid to describing the effect of the state of the platinum cocatalyst on the activity of the resulting photocatalyst. The decisive factors leading to the creation of active materials were discussed.

Two types of photocatalysts, 1%Pt/Cd_1−xZn_xS/g-C₃N₄ (x = 0.2–0.3) and Cd_1−xZn_xS/1%Pt/g-C₃N₄ (x = 0.2–0.3), were synthesized by varying the deposition order of platinum, and a solid solution of cadmium and zinc sulfides onto the surface of g-C₃N₄. The characterization of photocatalysts showed that, for 1%Pt/Cd_1−xZn_xS/g-C₃N₄, small platinum particles were deposited onto a solid solution of cadmium and zinc sulfides; in the case of Cd_1−xZn_xS/1%Pt/g-C₃N₄, enlarged platinum clusters were located on the surface of graphitic carbon nitride. Based on the structure of the photocatalysts, we assumed that, in the first case, type II heterojunctions and, in the latter case, S-scheme heterojunctions were realized. The activity of the synthesized samples was tested in hydrogen evolution from triethanolamine (TEOA) basic solution under visible light (λ = 450 nm). A remarkable increase in hydrogen evolution rate compared to single-phase platinized 1%Pt/Cd_1−xZn_xS photocatalysts was observed only in the case of ternary photocatalysts with platinum located on the g-C₃N₄ surface, Cd_1−xZn_xS/1%Pt/g-C₃N₄. Thus, we proved using kinetic experiments and characterization techniques that, for composite photocatalysts based on Cd_1−xZn_xS and g-C₃N₄, the formation of the S-scheme mechanism is more favorable than that for type II heterojunction. The highest activity, 2.5 mmol H₂ g⁻¹ h⁻¹, with an apparent quantum efficiency equal to 6.0% at a wavelength of 450 nm was achieved by sample 20% Cd_0.8Zn_0.2S/1% Pt/g-C₃N₄.

A series of CuO_x–TiO₂ photocatalysts were prepared using fresh and thermally activated Evonik Aeroxide P25 titanium dioxide. The photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, XANES, diffuse reflectance spectroscopy, and N₂ adsorption technique. Photocatalytic activity of the samples was tested in hydrogen production from aqueous-alcoholic solutions of methylene blue under UV radiation (λ = 386 nm). It was found for the first time the synergistic effect of hydrogen production from two substrates—dye and ethanol. The maximum hydrogen production rate in the system water–ethanol–methylene blue was 1 μmol min⁻¹, which is 25 times higher than a value measured in a 10% solution of ethanol in water. The thermal activation of titania also leads to a change in the rate of hydrogen production. The highest catalytic activity was observed for a CuO_x–TiO₂ photocatalyst based on titania thermally-activated at 600 °C in air. A mechanism of the photocatalytic reaction is discussed.