Rheological behaviour, mechanical performance, and NOx removal of photocatalytic mortar with combined clay brick sands-based and recycled glass-based nano-TiO₂ composite photocatalysts

Herein, we prepared composite photocatalysts (CP) by loading nano-TiO₂ (NT) on recycled clay brick sands (RCBS) and recycled glass (RG). CPs are denoted as NT@RCBS and NT@RG, respectively. The NT@RG was used to partially replace NT@RCBS and the combined CPs were then used to replace common river sand (RS) in photocatalytic mortar. Micrographs coupled EDS exhibit both NT@RCBS and NT@RG successfully carry NT on their surfaces; whilst the amount of carrying is measured by analytical balance as 0.0048 g per gram of RCBS and 0.0013 g per gram of RG. Once some NT@RCBS is replaced by NT@RG, the rheological behaviour is improved due to the smooth surface of the latter. However, compressive strength is not evidently lifted by NT@RG because the weak bonding between NT@RG and surrounding cementitious materials even though NT@RG relative to NT@RCBS has a higher hardness. However, the NT@RG by 25% weight replacement over NT@RCBS contributes to an enhanced NOx removal since a mutual promotion effect that NT@RCBS receives enough refracted light to activate photocatalysts in deep pores while NT@RG obtains enough room to accommodate final products caused by photocatalysis and enhances the anti-abrasion capacity. Finally, the combined use of NT@RCBS and NT@RG increases NOx removal by ~18.8%; and at the same saves NT usage by ~80% relative to the traditional NT (5% NT by wt. of cement) intermixing approach. Thereby, this study provides a cost saving approach to by construction wastes prepare environmentally friendly photocatalytic mortar with higher photocatalytic efficiency.