## 3 Results and Discussion
### Optical Properties  
The optical properties of the synthesized photocatalysts were characterized using UV-Vis spectroscopy, covering a spectrum range from 220 to 850 nm (Figure 6a). Both the individual components, porous g-C\({}_{3}\)N\({}_{4}\) and CdS, and their composite demonstrated  
Figure 5: XPS elemental analysis spectrum of (**a**) CdS/g-C\({}_{3}\)N\({}_{4}\)-2 composite and (**b**) partial enlargement; XPS fine spectrum of (**c**) C, (**d**) N, (**e**) Cd, and (**f**) S.  
substantial light absorption within the visible spectrum. Specifically, the peak absorption for porous g-C\({}_{3}\)N\({}_{4}\) was recorded near 525 nm, while CdS exhibited its maximum around 600 nm. The CdS/g-C\({}_{3}\)N\({}_{4}\)-2 composite showed an even further red-shifted absorption edge at 620 nm, indicating enhanced visible light absorption ascribed to the synergistic interaction of CdS and g-C\({}_{3}\)N\({}_{4}\). The UV-Vis DRS data provided critical insights into the optical characteristics of the photocatalysts, enabling the application of the Tauc approach to determine their bandgap energies (Figure 6b). The bandgap energies (\(E_{g}\)) were determined according to the following equation: \(\Delta nv=k\big{(}nv-E_{g}\big{)}^{1/n}\). Where \(\alpha\) denotes the absorption coefficient, \(h\) stands for [PERSON]'s constant, \(v\) indicates the light frequency, \(E_{g}\) is the bandgap energy, and \(k\) is a constant. The parameter \(n\) defines the type of electronic transition in the semiconductor. The bandgap energies of the materials were evaluated by extrapolating the linear region of the Tauc plot until it met the photon energy axis (\(hv\)). The bandgap width relationship was as follows: CdS/g-C\({}_{3}\)N\({}_{4}\)-2 \(<\) CdS \(<\) porous g-C\({}_{3}\)N\({}_{4}\). This trend arises from the robust electron coupling of CdS with g-C\({}_{3}\)N\({}_{4}\), which modifies the composite's electronic properties. Such coupling promotes the flow of photogenerated electrons originating in the lower-energy molecular orbitals of CdS to the higher-energy CB of g-C\({}_{3}\)N\({}_{4}\), effectively narrowing the effective bandgap and improving visible light absorption [36]. Thus, such improved light-harvesting ability directly correlates with the observed increase in photocatalytic activity, as more charge carriers are available for initiating degradation reactions. Photoluminescence (PL) spectra (Figure 7) were used to study charge recombination dynamics within both the CdS/g-C\({}_{3}\)N\({}_{4}\)-2 composite and pure porous g-C\({}_{3}\)N\({}_{4}\) under 350 nm excitation. Consistent with prior findings on CdS nanomaterials, pristine CdS displayed a distinct PL emission peak within the 450-500 nm range under UV excitation [37; 38], indicative of photogenerated electron (e\({}^{-}\)) and hole (h\({}^{+}\)) recombination within CdS structures. Conversely, pure porous g-C\({}_{3}\)N\({}_{4}\) showed a pronounced emission peak around 550 nm, implying substantial recombination of photo-induced charge entities. In contrast, the significantly lower PL intensity observed for CdS/g-C\({}_{3}\)N\({}_{4}\)-2 as opposed to pure CdS and g-C\({}_{3}\)N\({}_{4}\) (Figure 7) indicates suppressed e\({}^{-}\)-h\({}^{+}\) recombination. This suppression is attributed to the heterojunction formation between CdS and g-C\({}_{3}\)N\({}_{4}\)[39]. The integration of CdS induces changes in the band structure of g-C\({}_{3}\)N\({}_{4}\). Specifically, the CB edge of CdS resides at a slightly reduced energy level as opposed to g-C\({}_{3}\)N\({}_{4}\), while the valence band (VB) edge remains at a higher energy level.