Larger Effect of Sintering Temperature Than Particle Size on the Photocatalytic Activity of Anatase TiO₂

Abstract

Photocatalytic activity of anatase TiO2 that increases with the increase of its synthesis temperature has been widely reported, but the reason for that remains incompletely understood. In this work, the positive effect of synthesis temperature, presumably due to the growth of particle size, has been examined. Three series of anatase samples with various particle sizes were prepared from the hydrolysis of TiOSO4 in water at 150 °C, followed by calcinations in air. The particle size of TiO2, estimated by X-ray diffraction and N2 adsorption, increased with the increase of the hydrothermal time, calcination time, and calcination temperature. For phenol photodegradation in aerated aqueous suspension, three series of the catalysts showed different correlation between the activity and particle size of TiO2. However, with the same amount of Ag+ adsorbed on the oxide surface for phenol photodegradation in a N2-purged aqueous suspension, those catalysts showed activities all increasing with the particle size of TiO2, whereas at given particle size, the thermally treated TiO2 was much more active than the hydrothermally treated one. These observations are discussed in terms of the solid crystallinity, surface area, exposed facets, surface hydroxyl groups, and light absorption. But, there only appears a positive correlation between the particle size, calcination temperature, and the number of surface defects, as revealed by photoluminescence spectroscopy. The increase of surface defects may facilitate separation of the photogenerated charges, consequently improving the efficiency for phenol degradation at the solid–liquid interface.

Photodegradation of phenol by N-Doped TiO2 anatase/rutile nanorods assembled microsphere under UV and visible light irradiation

“…5(b), the TiO 2 powder that was calcined at 800 C exhibited severe aggregation phenomenon, which led to the formation of large TiO 2 particles and reduction in surface area. The same phenomenon can also be found elsewhere in previous studies [25,30,37]. The reduction in surface area was proven by the BET analysis, as shown in Table 1.…”

“…According to Table 1, the average crystallite sizes of anatase and rutile increased as the calcination temperature increased. Similar trends can also be found elsewhere [37]. The lowest average size of anatase crystallite was estimated at 4.3 nm, which was prepared at 75 C. As the calcination temperature increased to 200, 400, and 600 C, the average crystallite size increased to 5.7, 9.4, and 49.4 nm, respectively.…”

“…In addition, as the calcination temperature increased up to 800 C, a reduction of absorption in visible region was observed. Possible explanation for this reduction has a direct relation with crystallite phase transition and loss of specific surface area [25,37,46]. It had been proven from the XRD analysis; that a complete phase transition from anatase to rutile occurred at 800 C as shown in Fig.…”

Understanding charge transfer processes on metal oxides: a laser-flash-photolysis study

“…Recent research indicates that charge carrier lifetimes in TiO2 depend on the particle size. 2 Smaller TiO2 particles show shorter lifetimes than larger ones. A possible explanation is the negative effect of surface recombination.…”

Structural characterization of N-doped anatase–rutile mixed phase TiO2 nanorods assembled microspheres synthesized by simple sol–gel method

“…Compared to rutile and brookite, anatase had shown the highest photocatalytic activity in the degradation of various organic pollutants in wastewater treatment. Most of the previous studies have focused on the preparation of single-phase TiO 2 nanostructures [1][2][3][4][5]. In addition, a recent study revealed that the combination of anatase-rutile mixed phase exhibited excellent photocatalytic activity compared to its single constituents [6][7][8][9][10].…”