## 2 Results and Discussions
### Comparative Analysis Between Different Techniques
Low adsorption can limit pollutant degradation and lead to the underestimation of photocatalytic efficiency, masking the actual efficiency of the material. As UV-Vis monitors chemical transformations, its results may not be temporally synchronized with those obtained by colorimetry and may require more time for detection. Another concern with this technique relates to potential difficulties and inaccuracies in testing due to the potential instability of photocatalytic coatings in long-term experiments. This issue is particularly relevant when samples remain immersed in the dye solution for long periods of time, as particle instability in the solution may affect degradation rates, thus affecting the accurate assessment of photocatalytic efficiency. This should be a focus of future work if this approach is to be incorporated into a comprehensive self-cleaning assessment methodology. In such cases, UV-Vis offers a more reliable alternative by measuring the absorbance of the dye solution, independent of the substrate color. This method directly quantifies the chemical degradation of the pollutant, ensuring accurate evaluation even when surface techniques fail. For darker surfaces, prioritizing solution-based measurements is essential to accurately assess photocatalytic activity without interference from optical challenges. The comparison between techniques for dye degradation analysis highlights the need for adapted approaches to address the unique challenges of different substrates. While the ISO 10678 standard provides a robust framework for evaluating photocatalytic efficiency, particularly for smooth, non-porous materials like ceramics, its methodology requires \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Technique** & \multicolumn{2}{c}{**Advantages**} & \multicolumn{2}{c}{**Limitations**} \\ \hline  & & & - & Requires specific and expensive equipment \\  & - & Practical and efficient & - & Difficulty detecting small variations at low \\  & - & Enables monitoring of esthetic & - & dye concentrations \\ SPC & - & Enables (visual aspects) & - & Sensitive to substrate characteristics \\  & & changes (visual aspects) & - & Monitors color changes, not exactly \\  & & & pollutant degradation \\ \hline  & - & Fast and affordable & - & Difficulty detecting small variations at low dye \\  & - & Enables monitoring of & & concentrations \\  & - &esthetic changes & - & Sensitive to substrate characteristics \\ DIP & - & Practical and efficient & - & Dependence on controlled conditions to \\  & - & Consistent and accurate results & & capture images \\  & & (pixel-by-pixel) & - & Monitors color changes, not exactly \\  & - & Does not require expensive & & pollutant degradation \\  & & laboratory equipment & & \\ \hline  & - & High sensitivity to small & - & May take longer to detect pollutant degradation \\  & & variations in concentration & - & May underestimate efficiency on cementitious \\  & - & Versatile for detecting colored & & substrates due to their specific characteristics \\ UV-Vis & & and colorless pollutants & - & Difficulty and inaccuracy in testing, caused by the \\  & - & Monitors chemical degradation & & possible instability of photocatalytic coatings in \\  & & of the pollutant & & long-term tests \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Main aspects of each technique. adjustments to effectively analyze cementitious surfaces, which are characterized by a higher porosity and complex pollutant interactions. One key aspect of comparison is the choice of model pollutants. The ISO standard typically utilizes Methylene Blue in solution, a widely recognized compound for its consistent optical properties and degradation behavior. In contrast, this study focused on Rhodamine B, applied either on the surface of the substrate or in the solution. This dye is commonly employed in academic research due to its distinct optical properties, although it is less standardized for real-world applications. The methods for measuring pollutant degradation also vary.