| Summary: | Photocatalysts based on g-C<sub>3</sub>N<sub>4</sub> have been investigated in the CO<sub>2</sub> reduction reaction under visible light irradiation (λ = 397, 427, 452 nm). Photocatalysts were prepared by melamine calcination at 500–600 °C with further platinum deposition (0.1–1.0 wt.%). The effect of the preparation conditions of g-C<sub>3</sub>N<sub>4</sub> and the method of platinum deposition on the physicochemical properties and activity of photocatalysts was studied. The photocatalysts were investigated by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, X-ray diffraction, high resolution transmission electron microscopy, UV-Vis spectroscopy, and low temperature nitrogen adsorption techniques. It has been found that the efficiency of CO<sub>2</sub> reduction is governed by the surface area of g-C<sub>3</sub>N<sub>4</sub> and the presence of platinum in the metallic state, while the optimal content of platinum is 0.5 wt. %. The highest rate of CO<sub>2</sub> reduction achieved over Pt/g-C<sub>3</sub>N<sub>4</sub> photocatalyst is 13.2 µmol h<sup>−1</sup> g<sup>−1</sup> (397 nm), which exceeds the activity of pristine g-C<sub>3</sub>N<sub>4</sub> by 7 times. The most active photocatalysts was prepared by calcining melamine in air at 600 °C, followed by modification with platinum (0.5 wt.%).
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