Characterization and photocatalytic performance in air of cementitious materials containing TiO sub(2). Case study of formaldehyde removal

This article demonstrates that photocatalytically self-cleaning mortars and concretes can additionally contribute to the elimination of volatile organic compounds (VOC's) present in indoor and outdoor atmospheres. Formaldehyde was chosen as a representative VOC air pollutant. Titania (PC-105 from Millennium Chemicals) was added in a white Portland Cement (Societe Ciment Calcia) to prepare mortar samples according to a normalized methodology. A normalized steady-state was chosen after aging the samples for three months. The distribution of titania at the exposed surface of the mortar sample was quantitatively examined, using Raman spectroscopy mapping and diffuse reflectance spectroscopy. Interestingly, when varying the weight percentage of titania (with respect to the cement weight) between 0 and 10 wt%, it was demonstrated that the "occurrence rate" (or presence probability) of 100% in TiO sub(2) at the surface of the mortar was already reached at 5 wt% TiO sub(2). Direct linear correlation between UV-absorptance and Raman spectroscopy mapping spectroscopy was obtained. In parallel, the photocatalytic removal of formaldehyde, performed in a dynamic flow reactor with an in-line photoacoustic analytic spectrometer was established by the curve rate r = f(TiO sub(2) wt%). Since concretes and mortars are solids which can be considered as "breathing materials", which absorb and/or adsorb many compounds, it was carefully and quantitatively determined what part of formaldehyde was adsorbed and/or absorbed by the mortar, either in the dark or under UV. The real and true photocatalytic nature of the disappearance reaction relative to UV-irradiated TiO sub(2) let us conclude that, in addition to their photocatalytic self-cleaning properties, such cementitious materials can possibly contribute to the elimination of atmospheric VOC's which may come in contact with them.