Abstract This study quantifies NOx uptake efficiency and explores NOx binding mechanisms in calcium aluminate cementitious (CAC) materials. Comparison between unmodified and TiO2-modified CAC separates intrinsic NOx binding mechanisms from… Click to show full abstract
Abstract This study quantifies NOx uptake efficiency and explores NOx binding mechanisms in calcium aluminate cementitious (CAC) materials. Comparison between unmodified and TiO2-modified CAC separates intrinsic NOx binding mechanisms from those related to photocatalysis. Attributed to surface-related heterogeneous reactions, the NOx binding occurs in unmodified CAC at nitrite-to-nitrate ratio of 1: 1.3 and can be increased with surface area. The photocatalytic reactions in TiO2-modified CAC increase NOx uptake, and ~50% of converted NOx resists releasing back into the environment via dissolution. Compared to previously studied ordinary portland cement (OPC) materials, CAC increases NOx uptake capacity and demonstrates a more permanent NOx binding, potentially mitigating concerns related to the release of previously bound N-species in OPC. Examination of the interaction between NOx and a synthetic pure aluminum-bearing phase shows that the permanent NOx uptake in CAC could be largely attributed to the chemical binding of converted NOx within aluminum-bearing phases.
               
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