Dynamic changes on the surface during the calcination of rapid heat treated TiO2 photocatalysts

Titanium dioxide photocatalysts were prepared by a newly developed synthesis method that involves rapid heating with short, medium and long exposures of the sol–gel prepared amorphous starting materials (RHSE, RHME and RHLE series) at different temperatures and calcination times. These materials were characterized by various methods, such as XRD, TEM, DRS, IR, nitrogen adsorption and XPS techniques. The detailed study of these catalysts revealed that at low calcination temperatures (e.g. 400 °C) the highest activity will be achieved if a long calcination (90–120 min) is applied because of the surface purification from the deposited organics. At higher temperatures (e.g. 550 °C) shorter calcination times (5–10 min) proved to be effective to achieve high UV activity. At this temperature an unidentified oxygen type was detected from the O1s XPS of the samples which seems to be related to the presence of Ti3+. At 600 °C both short (10 min) and medium calcination (30–90 min) times were found to be beneficial for the phenol degradation under UV irradiation due to the very effective sensitization (10 min of calcination) and surface OH-group preservation (60 min of calcination).

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► Rapid heat treatment results in high UV-activity photocatalysts.
► Surface purity determines the activity at 400 °C.
► Surface anchored species influences the measured photoactivity.
► High UV activity for short/medium calcination times at 550 and 600 °C.
► Special oxygen forms appear at the surface for the best catalysts.