Efficient nitrogen oxide (NOx) reduction of photocatalytic mortar prepared by nano-TiO₂ treated recycled clay brick sands and recycled glass sands and their synergistic effect

This study introduces an effective approach to tackle the environmental challenge posed by construction waste, employing photocatalysis with nano-titanium dioxide (TiO₂) to modify recycled clay brick sands (RCBS) and recycled glass sands (RGS). The primary objective of this research is to leverage the distinct characteristics of these recycled fine aggregates and enhance their efficacy in nitrogen oxide (NOx) reduction. Following modification with nano-TiO₂, the microstructure of RCBS underwent notable transformations, as evidenced by the presence of Ti–O bonds, which confirm the effective infiltration and adhesion of the catalyst. Conversely, RGS exhibited minimal surface alterations after treatment. When the modified aggregates were incorporated into the photocatalytic mortar, the study revealed that the 28-day compressive strength diminished with an increasing substitution rate of natural river sand, reaching a decrement of 24.94% at full substitution. Nevertheless, the NOx degradation efficiency improved with higher substitution rates, attaining 78.6 μmol/m²h at full substitution, which represents a 7.78-fold increase compared to a 25% substitution rate. Significantly, a synergistic effect was observed when NT-RCBS and NT-RGS were combined at an optimal mass ratio of 75:25. This combination resulted in a NOx degradation rate of 103 μmol/m²h, marking a 71.7% enhancement compared to the direct incorporation of TiO₂ at 2% by weight using what. Additionally, this approach reduced TiO₂ usage by 50%. This study not only advances sustainable construction practices by upcycling waste materials but also offers economic advantages through cost reduction. The findings underscore the potential of photocatalysis in modifying recycled aggregates for high-value applications, thereby contributing to environment and resource conservation. © The Author(s), under exclusive licence to RILEM 2025.