Abstract :
Solar photocatalytic degradation of formaldehyde in the gaseous phase has been investigated. The tested photoreactor
is made of a borosilicate glass tube with the inner surface coated with a sol–gel TiO2 thin film. In a pseudo-firstorder
Langmuir–Hinshelwood (L–H) model, the maximum reaction rate constant obtained is 0.148 min 1 under an
exposure to sunlight with solar UVA irradiance of 1.56 mW/cm2. The solar photolysis effect is found to be negligible. It
is also found that the sol–gel TiO2 thin film has a lower apparent photonic efficiency of solar photocatalysis than a
Degussa P25 TiO2 coating. However, for the photonic efficiency taking into account the absorbed and scattered
photons only and, in other words, excluding the transmitted photons, the thin film has a higher value. Based on a total
of 28 measured data, an empirical-correlation equation has been developed to express the reactant residue with respect
to the solar UVA irradiance and exposure time. A reasonable agreement between the correlation and experimental data
is obtained. The findings of this investigation can be applied to design optimization of a honeycomb photoreactor made
up of TiO2-coated glass tubes or polygonal cells.
2004 Elsevier Ltd. All rights reserved
