Quantification of NOx uptake in plain and TiO2-doped cementitious materials

Abstract

This study brings new understanding of the interaction of nitrogen oxides (NOx) with cement-based materials, necessary for optimizing these materials for NOx sequestration. The masses of nitrites and nitrates produced through NOx uptake in cement-based materials are quantified for both plain portland cement pastes (OPC) and nano TiO2-doped OPC. Both nitrite and nitrate were bound within plain OPC, with a nitrite:nitrate ratio of 1:2. This intrinsic NOx sequestration capacity is attributed to the microstructural features and alkalinity of cement-based materials. The capacity is increased by 360%, with a lower nitrite:nitrate ratio of 1:1.3, in TiO2-doped OPC. The increase in NOx uptake and the change in nitrite:nitrate ratio is attributed to the microstructural differences and activation of photocatalytic reactions that are associated with TiO2 addition. Comparing NOx exposure with and without UV on TiO2-doped OPC shows that photocatalytic activities have greater influences on NOx uptake than microstructural differences induced by TiO2 addition.