Utilising ilmenite mud waste (R-MUD) for sustainable photocatalytic cement mortars.

Rising urban air pollution necessitates the development of innovative methods for removing harmful components, such as nitrogen oxides (NOx). Photocatalytically active layers on building facades are effective in reducing NOx; however, the production of nano-TiO₂-based photocatalysts and Portland cement is environmentally unsustainable. The use of supplementary cementitious materials, such as fly ash, might decrease the efficiency of the photocatalytic effect. This study investigated the use of R-MUD, a TiO₂ production by-product, as a partial substitute for cement in photocatalytic cement composites to enhance their sustainability. R-MUD exhibits photocatalytic properties owing to the residual TiO₂ in the rutile and anatase phases and demonstrates pozzolanic activity, enabling reduced cement usage. Tests showed that the addition of R-MUD maintained acceptable rheological properties and affected the photocatalytic activity and self-cleaning effects of cement mortars at an acceptable level. Microstructural analysis confirmed the presence of TiO₂ particles on the mortar surfaces, which actively contributed to NOx reduction. Furthermore, R-MUD increases the air content and surface voids, expanding the active surface area and potentially enhancing the photocatalytic efficiency. This approach leverages industrial waste to improve the environmental performance of cement composites while addressing air pollution challenges, thereby offering a sustainable solution for urban environments.