Applications of the Photocatalytic Degradation of TiO2 Nanoparticles Under UV Radiation in the Development of Innovative Self-Cleaning Geopolymer Construction Materials

Geopolymer materials obtained through the alkaline activation of fly ash represent a promising alternative for reducing the environmental impact of the construction sector, which is currently dominated by cement use. This study aimed to develop self-cleaning geopolymer composites by incorporating TiO2 nanoparticles. Specimens containing 1%, 3%, and 4% TiO2 were prepared using alkaline solutions based on Na2SiO3 and NaOH (6 M or 8 M), at mass ratios of 1:1 and 2:1. The results indicate that the three analyzed factors—the NaOH solution concentration, the activator ratio, and the nanoparticle dosage—significantly influence density, mechanical strength, and water absorption. Increasing the NaOH concentration to 8 M led to slight densification, improved flexural and compressive strength, and reduced water absorption. Modifying the Na2SiO3:NaOH ratio produced similar densification effects but resulted in reductions in mechanical strengths. The addition of 1–3% TiO2 increased density and mechanical performance while reducing water absorption, whereas 4% TiO2 content had the opposite effect. Self-cleaning capacity was confirmed by up to ~90% degradation of Rhodamine B after five UV–artificial rain–drying cycles, compared to only 27.3% degradation for the control samples.