Photocatalytic paints based on titanium dioxide (TiO2) nanoparticles represent a promising treatment technology for cleaning the air at our dwellings. A few studies have shown that instead of elimination of harmful indoor air pollutants the production of carbonyl compounds occurs from the photocatalytic paints.

Gligorovski (a corresponding author of the contribution) and his coworkers published an article in Environmental Science & Technology focused on photocatalytic paints based on titanium dioxide (TiO2) which represent a promising remediation technology for cleaning the air at our homes. The photocatalytic paints are typically used to eliminate the gas-phase pollutants, like nitrogen oxides (NOx) and volatile organic compounds (VOCs) in particular the harmful aldehydes, formaldehyde and acetaldehyde. However, few studies have shown that instead of elimination of these harmful pollutants the emission of carbonyl compounds occurs during the irradiation of the photocatalytic paints. The main source of such carbonyls was assumed to be the photoinduced decomposition of paint binders, without performing further investigations.

The authors report unexpectedly high levels of volatile organic compounds (VOCs) released by photocatalytic paints. The concentrations of the VOCs were measured continuously and on-line with the state of the art PTR-ToF-MS (Proton Transfer Reaction-Time of Flight-Mass Spectrometry) coupled to a flow tube photoreactor. The authors describe a detailed reaction mechanism responsible for the production of harmful indoor air pollutants. The produced hydroxyl radicals (OH) upon activation of TiO2, react with the organic constituents of the paint leading to generation of formaldehyde and acetaldehyde, among the others. It is demonstrated that the quantity of TiO2 embedded in the paint and the constituent of the binder are of paramount importance with respect to the formation of these harmful indoor air pollutants.

Finally, the obtained laboratory results are rescaled to real-life scenario to determine the implications induced by these paints to indoor air quality.

The photocatalytic paints represent an important source of formaldehyde, acetaldehyde and other carbonyls. In addition to these harmful carbonyl compounds an important number of saturated and unsaturated carboxylic acids (C2, C3, C4 and C5), alkenes (C3, C4, C5 and C6) and saturated and unsaturated cyclic compounds, were observed suggesting that this remediation technology must be well optimized prior to be launched on the market and used in our dwellings.

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Paper info: A. Gandolfo, S. Marque, B. Temime-Roussel, R. Gemayel, H. Wortham, D. Truffier-Boutry, V. Bartolomei, S. Gligorovski, Unexpectedly high levels of organic compounds released by indoor photocatalytic paints, Environ. Sci. Technol., 2018, 52, 11328-11337.