TiO2 functionalization for efficient NO x removal in photoactive cement

Commercial titania nanoparticles (P25 Evonic-Degussa) were modified with organic compounds oleic acid (OA), oleylamine (OM) and equimolar concentrations of both modifiers (OAOM) through a biphase toluene/water emulsion processing in order to be endowed with hydrophobic properties. Specific molar ratio 3 between modifier and titania powder was used. The modified and the initial P25 photocatalysts were embedded in cement matrix in low percentage loading (2.5, 1, 0.5%). The grafting of the modifier to the titania nanoparticles was verified by thermal gravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared spectroscopy (FT-IR). Light absorption measurements revealed that the energy band gap of the photocatalysts was lowered after the modification. The average size (nm) and polydisperse index of the initial and modified P25 were determined via dynamic light scattering (DLS). The photocatalytic activity of the photocatalysts alone and the composite cement specimens was evaluated via ISO standard NO x oxidation procedure. The photocatalytic cements containing modified P25 exhibited 2-5 times better NO x removal than those with non-modified P25 even for the lowest photocatalyst loading. The results were attributed to the hydrophobic properties of the modified titania and its behavior during the incorporation in the cement matrix. This conclusion was confirmed by the SEM/EDX analysis which demonstrated a gradual increase of hydrophobic photocatalyst from the bottom to the surface of the cement specimens.