Formation mechanism of fine anatase crystals from amorphous titania under hydrothermal conditions

Abstract

Crystallization of amorphous titania prepared by hydrolysis of ethoxide was accelerated even by a small amount of water in the vapor phase. The existence of water promoted the change of localized structure of the amorphous titania to anatase structure, which resulted in acceleration of anatase nucleation. The anatase crystals grew in steam by solid-state epitaxial growth, but stopped growing in a short time. The growth of anatase crystals under hydrothermal conditions could be divided into the following two stages: the first stage with fast growth rate by the solid-state epitaxial growth and the second stage with slow growth rate by the dissolution and deposition process.

Magnetic recyclable microcomposite silica-steel core with TiO2 nanocomposite shell photocatalysts for sustainable water purification

“…103,104,105,106 Additional factors, such as the precursors employed and reaction conditions can also influence TiO 2 crystal growth. 107,108 The predominance of anatase TiO 2 in the sol-gel coatings employed in the present study (only a small amount of rutile polymorph found in P25(5)) is consistent with previous sol-gel TiO 2 calcination studies carried out at below 700 °C, 45 and TiO 2 -P25 nanocomposite coatings deposited onto glass and flat steel substrates. 47,109 The high photocatalytic activity reported for P25 TiO 2 nanoparticles is understood to be due to a combination of a large anatase (more photocatalytically active) to rutile ratio plus an inherent grain boundary structure.…”

Synthesis of TiO2 (Anatase) by Sol–Gel Process Performed in Metal Chlorides Saturated Aqueous Solutions

“…Despite the fact that a mechanistic study was not performed here, it is possible that the metal cations favor the formation of OTi 3 groups (10, 11), which could favor the formation of the anatase phase, with a localized structure with four edges shared by TiO 6 octahedral units, rather than the amorphous phase, with only two shared edges (12,13).…”

A new experimental procedure to obtain titania powders as anatase phase by a sol-gel process

“…It is worth noting that the samples are crystalline as synthesized, without needing any previous or further treatment such as heating or hydrothermal aging, as observed for other sol-gel derived titania powders 7,8 . This phenomenon is probably related with the formation of TiO 3 groups, which could favour the formation of the anatase phase, with a localized structure with four edges shared by TiO 6 octahedral units, rather than the amorphous phase, with only two shared edges [9][10][11][12] . All peaks, including that one around 25°, confirm that anatase is the crystalline phase formed 7,8 .…”