(438e) Photocatalytic Concrete Slab for Passive NOx Pollution Control

NOx emissions have become a constraint for sustainable economic growth due to ozone non-attainment in many urban areas. Recent developments in Europe, Japan, Hong Kong, and US have demonstrated the interest in deploying the photocatalytic technology in environmental remediation. Under light illumination NOx will be oxidized to nitric acid, neutralized by the alkaline materials in concrete, and washed away by rain. Ozone can also be decomposed to oxygen over photocatalysts according to the literature. Thus the photocatalytic coating has potential to economically reduce nitrogen oxides (NOx) emissions at ambient conditions nearly maintenance-free.

We report here the application of photocatalytic coatings on a concrete slab to simulate road pavements for passive NOx pollution control. Catalysts tested include Degussa P-25 TiO2 and TiO2 - boosted with BaTiO3, Nd2O3, and Fe2O3. Both NO and NO2 oxidation including the effects of inlet NO concentration, residence time (5-20 min.), and humidity are investigated. The removal efficiencies are in the range of 86-93% from 200 ppb-2000 ppb NO. Relative Humidity (RH) is seen to have some beneficial effect at <35% RH while lowering NO conversion by ~10% at > 35% RH. The additives Nd2O3, Fe2O3, and BaTiO3 are observed to depress the NO2 generation while improving NO conversion. The overall environmental impacts of this technology including nitrite/nitrate formation and the possibility of generating partially oxidized NOy and VOC species are discussed. The impact of catalytic reactions on the mechanical strength of the concrete slab will be measured.