## 3 Results and Discussion
### Photocatalytic Characterization

Table 1: Results of XPS study of the cocatalyst in 0.5% Pt/g-C\({}_{3}\)N\({}_{4}\) and 0.5% PtO/g-C\({}_{3}\)N\({}_{4}\). Figure 2: (**a**) XRD pattern of synthesized g-C\({}_{3}\)N\({}_{4}\), L\({}_{4}\)—average crystallite size in the plane of the layer calculated using the Scherrer equation; L\({}_{c}\)—average crystallite size in the direction perpendicular to the layer calculated using the Scherrer equation; (**b**) diffuse reflectance spectra of g-C\({}_{3}\)N\({}_{4}\), 0.5% Pt/g-C\({}_{3}\)N\({}_{4}\), and 0.5% PtO/g-C\({}_{3}\)N\({}_{4}\). platinum in the metallic state (Pt foil). Thus, the XPS and XAS studies establish that in the case of 0.5%Pt/g-C\({}_{3}\)N\({}_{4}\), the platinum nanoparticles are metallic and do not have a core-shell structure. At the same time, the spectrum of the Pt \(L_{3}\)-edge of 0.5% PtO/g-C\({}_{3}\)N\({}_{4}\) is similar to that of platinum oxide PtO; both have the peaks E, F, and G. In the case of 0.5% PtO/g-C\({}_{3}\)N\({}_{4}\), the XPS and XAS confirm that the platinum nanoparticles are completely oxidized and also do not have a core-level structure. A study of the optical properties of photocatalysts showed that the deposition of both Pt and PtO leads to an increase in absorption in the visible region, which contributes to an increase in the rate of photocatalytic reactions under the visible light irradiation (\(\lambda>380\) nm). It should be noted that after the modification of g-C\({}_{3}\)N\({}_{4}\) with occatalysts, there is no shift in the absorption edge of the samples obtained, since the structure of g-C\({}_{3}\)N\({}_{4}\) does not change after the deposition of Pt or PtO (Figure 2b). The morphology of the photocatalysts was studied via TEM (Figure 4). In the case of the PtO/g-C\({}_{3}\)N\({}_{4}\) photocatalyst, small single occatalyst particles of size 1-2 nm are evenly distributed over the g-C\({}_{3}\)N\({}_{4}\) surface (Figure 4a,c). When platinum is deposited in the metallic state, platinum agglomerates of about 10 nm in size, consisting of smaller particles, can be observed (Figure 4b,d). This observation agrees well with the results of the XPS study of different surface [Pt]/[C\({}_{3}\)N\({}_{4}\)] ratios. Thus, the methods used allow us to clarify the key features of the synthesized photocatalysts, which makes it possible to find the correlation between structure and photocatalytic properties. In summary, it can be concluded that photoconduction of Pt\({}^{+4}\) under UV light results in a uniform deposition of fine platinum oxide particles onto the g-C\({}_{3}\)N\({}_{4}\) surface. When platinum is reduced with a solution of NaBH\({}_{4}\), Pt\({}^{+4}\) is completely reduced to the metallic state; however, the occatalyst particles in this case are distributed unevenly, and form aggregates on the surface of the g-C\({}_{3}\)N\({}_{4}\). Figure 3: Pt _4f_ core-level spectra **(a)** and XANES Pt \(L_{3}\)-edge spectra **(b)** of 0.5%Pt/g-C\({}_{3}\)N\({}_{4}\), as well as XANES Pt \(L_{3}\)-edge spectra of references (Pt foil and PtO). The Pt _4f_ core-level spectrum is normalized to the integral intensity of the C\(1s\) core-level peak, which corresponded to the spectrum of g-C\({}_{3}\)N\({}_{4}\).