Eco-Efficient Mortars with High-Content Construction, Waste-Derived Aggregates Functionalized via Nano-TiO2 for NOx Abatement

This study elucidates the photocatalytic NOx abatement efficacy of eco-efficient mortars incorporating construction waste-derived aggregates functionalized with nano-TiO2. The research findings demonstrate a positive correlation between NOx abatement efficiency and nano-TiO2 substitution ratio, with recycled glass sand (RG)-based panels exhibiting superior performance compared to standard sand and recycled clay brick sand (RCBS)-based counterparts. The employment of ultrasonic dispersion as a nano-TiO2 incorporation method yields enhanced abatement efficiency relative to direct mixing, attributable to improved photocatalyst dispersion and surface area accessibility. The loading capacity of nano-TiO2 on recycled aggregates is observed to be positively influenced by the concentration of nano-TiO2 solution, with recycled clay brick sand demonstrating the highest loading capacity. RG-RCBS panels are shown to exhibit higher NOx abatement efficiency than standard sand (SS)-RCBS panels, with an optimal substitution ratio of 40% glass sand identified for maximizing abatement efficacy in RG-RCBS systems. A decline in NOx abatement efficiency is observed with increasing NOx flow rate and concentration, attributable to reduced pollutant residence time and excess pollutant load exceeding the panels’ processing capacity. Prolonged curing time also results in diminished abatement efficiency, due to microstructural alterations within the mortar matrix and the accumulation of photocatalytic reaction byproducts. Collectively, these findings underscore the potential of recycled aggregate-based mortars, in conjunction with nano-TiO2, as a viable eco-efficient strategy for NOx abatement, highlighting the critical influence of material selection, photocatalyst loading, and operational parameters on system performance.