Heterogeneous reaction of formaldehyde on the surface of TiO2 particles

Abstract

The heterogeneous reaction of formaldehyde (HCHO) on the surface of titanium dioxide (TiO2) was investigated in situ using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with ion chromatography (IC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Formate, dioxymethylene, methoxy, and polyoxymethylene were observed in the infrared spectra of TiO2 particles during the reaction. On the surface of TiO2, the adsorbed HCHO was first oxidized to dioxymethylene and further oxidized to formate. The effects of temperature and ultraviolet radiation (UV) on the reaction products and reactive uptake coefficients were studied, and the results indicate that the reaction rate can be accelerated at increasing temperatures as well as under UV. The heterogeneous reaction mechanisms of HCHO on the surface of TiO2 in the dark and under UV irradiation are proposed. Kinetic measurements show that formate formation on TiO2 is second order in HCHO concentration and the initial reactive uptake coefficients at room temperature calculated with the Brunauer-Emmett- Teller specific surface area are (0.5–5) × 10−8 ([HCHO]: 1 × 1013−2 × 1014 molecules/cm3). A linear function relationship exists between the uptake coefficient and the concentration. The apparent activation energy of the reaction was also determined.