Effect of calcination temperature on the photocatalytic activity and adhesion of TiO 2 films prepared by the P-25 powder-modified sol–gel method

Abstract

TiO 2 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 °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 °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 °C was approximately four times that of PPMSGF-50 at 600 °C after 10 h of photocatalytic oxidation. Increasing calcination temperature in the range between 500 and 700 °C caused a significantly increase in the diffusion of foreign metals (i.e. chromium, iron and manganese) from the stainless steel support to the TiO 2 film. It is believed that the enhancement of the photocatalytic activity at lower calcination temperatures (400–500 °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. Cr 3+) on the surface of the films.