Carbon-Negative Nano-TiO2-Modified Photocatalytic Cementitious Composites: Removal of Airborne Pollutants (NOx and O3) and Its Impact on CO2 Footprint

This study explores the development and performance of photocatalytic cementitious composites modified with nano-TiO2 to address urban air quality and sustainability challenges. Nine mortar series were prepared, incorporating binders with varying carbon footprints and mass contents across different series. The interplay between the fundamental (abrasion resistance) and functional (air purification efficiency) properties of the composites’ surfaces and interfaces was investigated. The photocatalytic removal of airborne pollutants, specifically nitrogen oxides (NOx) and ozone (O3), was evaluated under simulated environmental conditions. The variations in binder composition influenced the composites’ overall initial carbon footprint and air purification efficiency. The assessment revealed a possible net decrease in carbon emissions over the life cycle of the composite due to the removal of ozone (greenhouse gas) and its precursor—NOx, highlighting the potential of photocatalytic cementitious composites for dual environmental benefits in an urban environment, emphasizing the critical role of surface and interface engineering in achieving carbon-negative composites.