Comparative Evaluation of Photocatalytic Efficiency Measurement Techniques Through Rhodamine B Degradation in TiO2-Based Cementitious Materials

Self-cleaning cementitious materials, particularly with TiO2-based photocatalytic coatings, offer significant benefits by reducing surface deterioration and maintenance requirements, even in harsh urban environments. Despite the growing interest in self-cleaning cementitious materials, an international standard test method to calculate their efficiency has not yet been established for this specific type of substrate. The objective of this study was to evaluate and compare three different techniques for assessing the photocatalytic efficiency (PE) of cementitious materials coated with TiO2: (i) spectrophotometric colorimetry (SPC); (ii) digital image processing-based colorimetry (DIP); and (iii) UV-Vis spectrophotometry (UV-Vis). Rhodamine B (RhB) was used as a model pollutant, and the photocatalytic efficiency was monitored under UV-Vis light. The results showed that each method has distinct advantages and specific challenges. SPC proved to be a practical and efficient approach, similarly to DIP, which was also accessible, providing reliable and accurate measurements. UV-Vis stood out for its precision but required careful application on cement-based substrates due to their unique porosity and adsorption characteristics. These results underscore the complementary potential of these techniques and highlight the importance of developing standardized protocols that integrate their strengths to facilitate the wider adoption of self-cleaning materials.