Photocatalytic cementitious materials: Influence of the microstructure of cement paste on photocatalytic pollution degradation

Incorporation of nanophotocatalysts into cementitious materials is an important development in the field of photocatalytic pollution mitigation. In this study, the photocatalytic nitrogen oxides(NOx) conversion by titanium dioxide (TiO2) blended cement pastes was used as a standard process to evaluate the internal factors that may influence the depollution performance. The chemical composition and microstructure of the TiO2 modified cement pastes were characterized and analyzed. The active photocatalytic sites related to the surface area of TiO2 are the key factor in determining the photocatalytic activity. Ordinary Portland cement pastes showed lower photocatalytic activity than white cement pastes probably due to the influence of minor metallic components. X-ray diffraction and thermal gravity analysis demonstrated that TiO2 was chemically stable in the hydrated cement matrix. The NOx removal ability decreased with the increase of curing age. This could be attributed to the cement hydration products which filled up capillary pores forming diffusion barriers to both reactants and photons. It was also proved that surface carbonation could reduce the photocatalytic pollution removal efficiency after the hydration of cement.