Humidity Effect on the Photocatalytic Activity of Sustainable Cement-Based Composites

Introduction: In this study, a side-by-side comparison was performed to examine the effects of nano-TiO2 (nT) on the photocatalytic activity of Portland cement (PC) mixtures and its effectiveness compared to similar replacement percentages of micro-TiO2 (mT), both of which were 100% anatase. Methods: Cement paste specimens were prepared by progressive cement replacement with nT or mT. To simulate the effect of humidity in different seasons, the PC specimens were subjected to different moisture conditions, including normal conditions with 50% Relative Humidity (RH), saturated conditions with 100% RH, and oven-drying conditions with 0% RH. Their photochemical reaction (i.e., gas removal ability) with TiO2 was evaluated and compared with the control specimens. Furthermore, the self-cleaning ability of the mixtures was examined by applying a drop of methylene blue dye to the specimen surface; differences in dye discolouration with time under different illuminations were noticed. Results and Conclusion: This paper describes the results of an attempt to understand the effect of humidity on the photocatalytic performance of PC composites that incorporate TiO2. The results show that PC mixtures modified with nano titanium are more effective in hot and dry conditions. In contrast, micro titanium mixtures appear to be favourable for wet conditions. Furthermore, the particle size (micro versus nano), matrix voids and absorption values of the cement-TiO2 composite were identified as the key factors affecting the photocatalytic performance.