NO<sub>x</sub> uptake capacities and sequestration pathways by hydrated cementitious phases

This study seeks to quantify NOx sequestration by individual hydrated cementitious phases (C-S-H, AFm-SO4, and Ca (OH)2), establish a fundamental understanding of the reaction pathways, and reveal the effects of carbonation (CaCO3 and AFm-CO3). For uncarbonated phases, the highest NOx uptake was measured in C-S-H, with the produced nitrite/nitrate physically bound on solid surface. For AFm-SO4, an anion exchange process was observed, where nitrite/nitrate substitute for sulfate and form new AFm-NO2/NO3. Ca(OH)2 showed undetectable NOx uptake, which may be due to the relative low temperature and relative humidity. For carbonated phases, CaCO3 exhibited an improved NOx uptake compared to uncarbonated phases, with uptake capacity three times higher than that of C-S-H. The result of AFm-CO3 indicates that carbonation could potentially inhibit the anion exchange process that was observed in AFm-SO4. These findings provide guidelines for the rational design and optimization of cement-based materials for enhanced NOx sequestration.

本研究旨在量化单个水化胶凝相（C - S - H、AFm - SO₄和Ca(OH)₂）对氮氧化物的吸收，建立对反应途径的基本认识，并揭示碳化（CaCO₃和AFm - CO₃）的影响。对于未碳化的相，在C - S - H中测得的氮氧化物吸收量最高，生成的亚硝酸盐/硝酸盐物理吸附在固体表面。对于AFm - SO₄，观察到一种阴离子交换过程，即亚硝酸盐/硝酸盐取代硫酸盐并形成新的AFm - NO₂/NO₃。Ca(OH)₂显示出无法检测到的氮氧化物吸收，这可能是由于相对较低的温度和相对湿度。对于碳化相，与未碳化相相比，CaCO₃表现出更高的氮氧化物吸收量，其吸收能力是C - S - H的三倍。AFm - CO₃的结果表明，碳化可能会抑制在AFm - SO₄中观察到的阴离子交换过程。这些发现为合理设计和优化用于增强氮氧化物吸收的水泥基材料提供了指导方针。