Photodegradation of an azo pyridone dye using TiO2 films prepared by the spray pyrolysis method

In this study, the feasibility of preparing porous TiO2 films on a stainless steel substrate from a hydrothermally prepared colloidal TiO2 solution by the spray pyrolysis technique is presented. The prepared samples were annealed at different temperatures and characterized by the XPS, XRD and SEM techniques, porosimetry and specific surface area measurements. The photocatalytic activities of the resulting films were evaluated by measuring the degradation of an azo pyridone dye, used as model pollutant, under simulated sunlight conditions. The relationships between the structural and morphological characteristics of the TiO2 films and their photoactivity were observed. It was found that the photoactivity was markedly dependent on the annealing temperature. On increasing the calcination temperature from 500 °C to 700 °C, the crystallite size and the rutile content increased, whereas the specific surface area and the rate of photodegradation decreased. Calcination at 700 °C resulted in a completely loss of photoactivity, due to the partial transformation of anatase to rutile phase, the increased crystallite size and decreased specific surface area. Specific activity (per unit of mass and per unit of surface area) was lowered within thicker films, pointing out significance of transport phenomena through porous films (the transport of dye and the transmittance of light as immaterial reagent). Based on the obtained results, the spray pyrolysis method appears to be a good choice for the preparation of photocatalytically active TiO2 films for the removal of dye pollutants.

► TiO2 films were prepared by spray pyrolysis method and calcined at different temperature.
► Photodegradation of azo pyridone dye was tested.
► Photodegradation decrease with increase in rutile content and decrease in specific surface area.
► Difference in photoactivity between outer and inner parts becomes smaller at higher temperature.