Photocatalytic Degradation of Gaseous Formaldehyde Using TiO₂ Film

The photocatalytic degradation of gaseous formaldehydea major cause of sick building syndromewas studied using a TiO2 thin film. TiO2 thin films have many unique photoinduced properties, for example, self-cleaning, anti-fouling, and anti-bacterial functions. UV illumination of the TiO2 thin film placed in a gaseous formaldehyde/air environment resulted in the total mineralization of formaldehyde to CO2 and H2O. We invoked a Langmuir−Hinshelwood kinetic model to analyze the dependence of reaction rates on the concentration of formaldehyde. In addition, the overall decomposition rate constant for formaldehyde was comparable to that of acetaldehyde (a standard test reactant) for initial concentrations of up to 1000 ppmv. However, the apparent adsorption constant Kapp of formaldehyde onto TiO2 was ca. 2.5 times larger than that of acetaldehyde. Thus in the low concentration regime, the reactivity of formaldehyde appeared to be greater than that of acetaldehyde. In like manner, a dark adsorption experiment also showed the high adsorption capacity of TiO2 for formaldehyde. Therefore, we conclude that TiO2 serves as both a good adsorbent and a photocatalyst for the elimination of gaseous formaldehyde.

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