Photocatalytic cement exposed to nitrogen oxides: Effect of oxidation and binding

The photocatalytic oxidation and binding capacity of cement containing titanium dioxide nanoparticles under nitric oxide and nitrogen dioxide gas exposures were examined experimentally both in the presence and absence of ultraviolet (UV) light, to examine independently the contributions of photocatalysis and potential additional mechanisms for binding of nitrogen oxides (NOx) inherent in cement-based materials. The overall, photocatalytic efficiency was similar for both gas exposures, with faster initial rates of initial NO binding for higher water-to-cement ratio pastes, due to higher surface area. In the absence of UV light, greater binding of NO2 gas was found compared to NO gas, perhaps due to the greater polarity of the NO2 molecule, although further examination of this phenomenon is warranted. Overall, these experiments show not only the fact that cementitious materials can be tailored to decrease NOx levels through photocatalysis but also the fact that Portland cements possess the inherent ability to bind NOx, and in particular NO2.