## 2 Results and Discussions
### Photocatalytic Efficiency (PE) Results
#### 2.1.3 UV-Vis by Immersing Pollution  
Figure 5 presents the PE results obtained from UV-Vis. The PE values and their respective standard deviations are provided in the Supplementary Materials (Table S3). The UV-Vis absorption spectra of the RhB solution, both before (dark conditions) and after irradiation, are also presented in Figures S1 and S2 of the Supplementary Materials. Additionally, efficiency monitoring during the adsorption-desorption equilibrium (dark conditions) is shown in Figure S5. By the end of the 24 h period, the variation observed was minimal, indicating that the system had reached adsorption equilibrium. The PE results showed a trend that was consistent with the results obtained by the other two techniques and highlighted the improved self-cleaning performance of the TiO\({}_{2}\)-coated samples. Similarly, the reference samples showed consistently lower PE. Contrary to the PE calculation using the other two techniques, the gray substrate showed a slightly higher efficiency than the white substrate in this technique. Some factors, such as the differences in texture and porosity between the white and gray substrates and their adsorption capacity, as well as the distribution and retention of the pollutant, may have influenced these results. Therefore, a further analysis was needed to understand these phenomena. The values measured by UV-Vis were 4.6% (G_T16) and 2.8% (W_T16), significantly lower than those obtained by the other two methods, representing a reduction of approximately 85-90%. This difference in performance can be partially explained by the accumulation of adsorbed pollutants and dye degradation products on the surface of the samples. This accumulation can temporarily block the photocatalytic particles, partially inactivating the reaction sites and hindering the photocatalytic process. It is predicted that the removal of degradation by-products from the surface over prolonged irradiation periods would restore the activity of TiO\({}_{2}\) nanoparticles, potentially enhancing the degradation of pollutants [32; 33]. Future studies should explore longer irradiation intervals to further investigate this phenomenon and determine whether prolonged exposure affects photocatalytic performance. Another relevant factor influencing adsorption was the inherently low adsorption capacity of cement-based materials, which was particularly evident during the initial equilibrium phase in the dark. This phenomenon, as reported by [PERSON] et al. (2021) [32], is closely related  
Figure 5: Photocatalytic efficiency measured using UV-Vis. to the microstructural characteristics of the cementitious substrate and can be attributed to the continuous microstructural changes in cementitious materials due to the hydration process over time. As hydration progresses, the progressive transformation of capillary pores into finer gel pores leads to a decrease in overall porosity and total pore volume. In addition, this densification of the microstructure reduces the ability of the material to retain and adsorb external molecules, further reducing its hygroscopic behavior [34]. As photocatalysts occurs predominantly on the surface of the material, low adsorption of the pollutant reduces its concentration at the material-liquid interface, limiting the efficiency of the photocatalytic reaction. Furthermore, as the UV-Vis method measures the concentration of the pollutant in the solution, low adsorption can make degradation detection difficult since a significant part of the pollutant may remain in the solution without effectively interacting with the catalyst. Additionally, the light transmittance of the beaker glass may reduce the photocatalytic efficiency by limiting the amount of UV light reaching the functionalized surface. The PE values obtained through colorimetry showed greater dye degradation than those measured by UV-Vis spectrophotometry over the same period. This may indicate that the comparison times between techniques may vary due to differences in the processes evaluated by each method.