## 3 Results and Discussion
### Photocatalytic Tests  
After confirming the successful synthesis of the ZnO and g-C\({}_{3}\)N\({}_{4}\) in the composites by characterization, their combined photocatalytic potential was ascertained. For this purpose, experiments were conducted using UV radiation at 395 nm using a constant amount of catalyst (25 mg). First of all, the adsorption capacity of the composites for the removal of Rhodamine B was assessed. As shown in Figure 6a, the composite alone exhibited a negligible removal  
Figure 5: Morphological characterization of ZnO/g-C\({}_{3}\)N\({}_{4}\) composites: (**a,b**) SEM images with magnifications of \(\times\)50 and \(\times\)500, respectively; (**c**) Elemental mapping corresponding to the elements Zn, C and N.  
capacity, rapidly reaching an adsorption-desorption equilibrium with removal values below 3%. The photolysis control assay demonstrated that light exposure alone, without the presence of a catalyst, had no significant effect on Rhodamine B degradation, with removal rates below 1%. This confirmed that the dye was stable under irradiation in the absence of a catalyst, which is consistent with the findings reported by [PERSON] et al. [17]. When the photocatalytic activity was evaluated under the LED light source, it was observed that, operating at 395 nm, significant catalytic performance was obtained. After 90 min of treatment, 59% of the dye was degraded. This good catalytic activity presented by the composites was due to the fact that ZnO is a good photocatalyst between the wavelengths of UV (280 to 400 nm) and g-C\({}_{3}\)N\({}_{4}\) in visible (between 400-460 nm) light. As already  
Figure 6: Results of Rhodamine B degradation experiments using various treatments and conditions: (**a**) profiles of Rhodamine B removal in adsorption, photolysis, and photocatalyst; (**b**) profiles with/without H\({}_{2}\)O\({}_{2}\); (**c**) profiles of dye degradation obtained from different catalysts-H\({}_{2}\)O\({}_{2}\) molar ratio; (**e**) profiles of dye degradation during 4 successive cycles using photo-Fenton like with a catalyst-H\({}_{2}\)O\({}_{2}\) molar ratio of 1:15. Dashed lines depict the pseudo-first-order kinetic fitting for all experiments with a R\({}^{2}\) > 0.98. (**d,f**) Apparent pseudo-first-order constant (k) values for each cycle. pointed out in the introduction, several studies confirmed that the combination of both materials reduces the band gap energy in the ZnO/g-C\({}_{3}\)N\({}_{4}\) composites [18; 38]. The results of this study confirmed that, although the band gap was reduced, the catalytic activity of the composites was effectively maintained at 395 nm, highlighting their suitability for photocatalytic-driven applications. Several previous studies have demonstrated that H\({}_{2}\)O\({}_{2}\) is generated during photocatalytic treatment and plays a significant role in degradation processes [54; 55; 56; 57]. To confirm this phenomenon, the concentration of H\({}_{2}\)O\({}_{2}\) in the treated solution was measured at the end of the experiment, yielding a value of 2 mg/L. This result confirmed the in situ production of H\({}_{2}\)O\({}_{2}\) during the treatment. To better understand the mechanisms and species involved in the photocatalytic degradation process, a literature review was carried out. Based on several works, Equations (7)-(15) present the main reactions involved [17; 18; 38; 40; 54; 58; 59]. When the ZnO/g-C\({}_{3}\)N\({}_{4}\) composites were irradiated, both ZnO and g-C\({}_{3}\)N\({}_{4}\) simultaneously generated electron-hole pairs following Equation (7). The electrons jumped to their respective conduction bands, leaving holes in the valence band. These photogenerated holes reacted with water, producing the \(\cdot OH\) radical (Equations (8) and (9)). In the conduction band, the photogenerated electrons reacted with the O\({}_{2}\) adsorbed on the surface to give rise to the \(O_{2}^{-}\). radical (Equation (10)) and, on the other hand, to the generation of H\({}_{2}\)O\({}_{2}\) (Equation (11)).