Effect of Thermal Treatment on the Photocatalytic Activity of TiO₂ Coatings for Photocatalytic Oxidation of Benzoic Acid

Abstract

The effects of thermal treatment on the properties and photoactivities of TiO2 catalysts supported on 316 stainless steel plates were examined. Degussa P-25 was immobilized on 316 stainless steel plates by electrophoretic deposition. These TiO2-coated plates were heated at 473, 673, and 873 K for 1 h. The photoactivities of these TiO2 coatings were determined based on the removal of benzoic acid as the model pollutant. In particular, the photoactivity decreased by 52% in the sample heated at 873 K compared with the unheated sample. The results of x-ray diffraction showed that the crystallinity and the crystallite sizes of the catalysts supported on the plates did not significantly vary with increasing temperature over the range examined. Negligible change in the catalyst phase (the anatase-to-rutile ratio) was indicated from x-ray diffraction and micro-Raman spectroscopy. However, it was found that the Brunauer–Emmett–Teller surface area of the scraped catalysts heated at 873 K decreased by nearly 13% compared with the unheated sample. In addition, scanning electron microscopy/energy dispersive x-ray and x-ray photoelectron spectroscopy analyses also detected the presence of Fe3+ ions at the surface of the supported catalysts heated at 873 K. The drop in surface area and the presence of Fe3+ ions at the catalyst surface, which were considered to function as electron–hole recombination centers, were possible factors leading to the drop in the photoactivity exhibited by the sample. A lower temperature for thermal treatment such as 473 K was proposed to ensure the coating stability and the catalyst photoactivity.

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

“…9 also shows that the amount of 4-CBA adsorbed on PPMSGF-50 films calcined at 550 • C is six times that of PPMSGF-50 films calcined at 600 • C. At the same time, the BET of PPMSGF-50 at 550 • C is 47.08 m 2 /g, approximately 1.5 times that of PPMSGF-50 calcined at 600 • C. Therefore, a remarkable increase in BET should be an important reason for the significant increase in the number of crystallites on which the 4-CBA can be adsorbed. As a result, the photocatalytic activity was significantly enhanced at 500 and 550 • C. In addition, previous studies have shown that transition metal ions function as electron-hole recombination centers, which lead to a decrease in photocatalytic activity [17,30,31]. Therefore, a remarkable decrease in the number of Cr 3+ on the surface of the films is most probably another important reason for the enhancement of photocatalytic activity at lower calcination temperatures.…”

Synthesis, characterization and activity of an immobilized photocatalyst: Natural porous diatomite supported titania nanoparticles

“…A common trend of increase in crystallite size both of anatase and rutile TiO 2 (see Table 2) occurs with the increase in calcination temperature for TiO 2 /diatomite composites, due to high frequency of aggregation and sintering among the grains. In this study, the rutile content in the supported catalysts can be calculated based on the intensities of the peaks for anatase and rutile in the XRD patterns as follows [28,29]:…”

Photoreduction of carbon dioxide in the presence of H2, H2O and CH4 over TiO2 and ZnO photocatalysts

“…This is important for the stainless steel mesh coating, since iron impurities caused by heating the steel could have a negative effect on the photocatalytic efficiency of the catalyst. It has been reported that Fe 3+ ions present in TiO 2 coated steel plates heated at 600°C and more, but not at lower temperatures (Chan et al, 2002).…”