Effect. of calcination temperature on the photocatalytic activity and adhesion of TiO2 films prepared by the P-25 powder-modified sol-gel method

TiO2 films on 304 stainless steel with optimum P-25 loading (PPMSGFs-50) were prepared by the P-25 powder-modified sol-gel method (PPMSGM) at calcination temperatures from 400 to 700 degrees C. The as-prepared PPMSGFs-50 were characterized by differential scanning colorimetry/thermogravimetric analyses (DSC/TGA), scanning electron microscopy (SEM), TEM/high-resolution transmission electron microscope (HR-TEM), X-ray diffraction (XRD), N-2 adsorption and X-ray photoelectron spectroscopy (XPS). Their adhesion properties were tested by the scratch test and cross-hatch adhesion test and their photocatalytic activities were evaluated using 4-CBA as a model organic contaminant in water. It was found that decreasing calcination temperature leads to a decrease in the critical loading, which has a detrimental effect on the mechanical stability of the films. On the other hand, decreasing calcination temperature leads to an enhancement of photocatalytic activity. The optimum calcination temperature is 500 degrees C under which both enhanced photocatalytic. activity and good adherence on the support could be obtained. The 4-CBA removal efficiency for PPMSGF-50 at 500 degrees C was approximately four times that of PPMSGF-50 at 600 degrees C after 10h of photocatalytic oxidation. Increasing calcination temperature in the range between 500 and 700 degrees C caused a significantly increase in the diffusion of foreign metals (i.e. chromium, iron and manganese) from the stainless steel support to the TiO2 film. It is believed that the enhancement of the photocatalytic activity at lower calcination temperatures (400-500 degrees C) is due to an increase in the amount of two type of crystallites exposed to the solid-liquid interface and decrease in foreign metal ion concentrations (i.e. Cr3+) on the surface of the films. (c) 2005 Elsevier B.V. All rights reserved.