Photolytic and Photocatalytic Destruction of Formaldehyde in Aqueous Media

Abstract

Formaldehyde (HCHO) was decomposed in UV‐irradiated aqueous suspensions of titanium dioxide. Initial HCHO levels in the range 60–1000 ppm, a nominal dose of 1 g/liter, and a medium‐pressure Hg lamp were employed in these experiments. Chemical oxygen demand measurements of the solution before and after photocatalytic treatment revealed the mineralization of HCHO to be complete only for the lower end (<100 ppm) of the concentration range. Direct ultraviolet photolysis of HCHO also occurred, but this pathway had an initial lag unlike the photocatalytic route. In the presence of and ultraviolet irradiation, the direct photolysis route was bypassed and the reaction proceeded dominantly by the photocatalytic route. The kinetics of the photocatalytic oxidation of HCHO were analyzed using several models. The effect of addition to the system was also probed as well as the homogeneous ultraviolet approach for the treatment of HCHO. The latter exhibited the fastest kinetics for the destruction of HCHO. Finally, the long‐term stability and photocatalytic activity of were monitored with two substrates, namely, HCHO and trichloroethylene in two different media: viz. pristine water and a “real‐life” water sample with bicarbonate alkalinity. No degradation in the photocatalyst performance was noted over ten repeat use cycles in either case.