Phase Transition between Nanostructures of Titanate and Titanium Dioxides via Simple Wet-Chemical Reactions

Abstract

Titanate nanofibers of various sizes and layered structure were prepared from inorganic titanium compounds by hydrothermal reactions. These fibers are different from "refractory" mineral substances because of their dimension, morphology, and significant large ratio of surface to volume, and, surprisingly, they are highly reactive. We found, for the first time, that phase transitions from the titanate nanostructures to TiO(2) polymorphs take place readily in simple wet-chemical processes at temperatures close to ambient temperature. In acidic aqueous dispersions, the fibers transform to anatase and rutile nanoparticles, respectively, but via different mechanisms. The titanate fibers prepared at lower hydrothermal temperatures transform to TiO(2) polymorphs at correspondingly lower temperatures because they are thinner, possess a larger surface area and more defects, and possess a less rigid crystal structure, resulting in lower stability. The transformations are reversible: in this case, the obtained TiO(2) nanocrystals reacted with concentrate NaOH solution, yielding hollow titanate nanotubes. Consequently, there are reversible transformation pathways for transitions between the titanates and the titanium dioxide polymorphs, via wet-chemical reactions at moderate temperatures. The significance of these findings arises because such transitions can be engineered to produce numerous delicate nanostructures under moderate conditions. To demonstrate the commercial application potential of these processes, we also report titanate and TiO(2) nanostructures synthesized directly from rutile minerals and industrial-grade rutiles by a new scheme of hydrometallurgical reactions.

Synthesis and characterisation of clay-supported titania photocatalysts

“…The most attractive process for the synthesis of TiO 2 nanoparticles is the solgel method [7][8][9][10][11][12][13][14][15][16][17][18][19]. This process involves the hydrolysis and polycondensation of a metal alkoxide Ti(OR) 4 (R=alkyl groups) precursor and subsequent formation of a gel, which after heat treatment results in a three dimensional crystalline network of linked TiO 6 octahedra [20][21][22].…”

Interaction of sodium titanate nanotubes with organic acids and base: chemical, structural and morphological stabilities

“…Similar behavior was also observed by other authors. [20][21][22]29 Nevertheless, in the diffractograms of the Figure 3. TEM imagens of a) Na-TiNT, b) Na-TiNT+PPH1, c) Na-TiNT+BA1, d) Na-TiNT+AN1, e) Na-TiNT+BA2 and f) Na-TiNT+PPH3.…”

“…16 In view of the many technological applications of the titanate nanotubes, understanding their chemical, structural and morphological stabilities in several media and their thermal stabilities under several kinds of treatments is an important issue. [18][19][20][21][22][23][24] Furthermore, the knowledge of the surface properties of such nanostructured materials is a key point for understanding their reactivity, and potentializing their technological applications. In this work we have focused our investigation on the stability of sodium titanate nanotubes in aqueous solutions of organic base and organic acids and on the characterization of the interaction products.…”

“…Zhu et al 20 reported that a phase transition from titanate nanofibers to TiO 2 polymorphs takes place in acid conditions at temperatures close to ambient. However, the phase obtained depends on the acid concentration.…”

Memristive Behavior of NAOH-Immersed Titania Nanostructures

“…Most have reported growing TiO 2 nanostructures using NaOH solution by a hydrothermal method where a high temperature is required for the process (Shao, Sun, Gao, Yang, & Luo, 2011;Xie, Wang, & Zhou, 2012;Zhu et al, 2005). However, in this work, we attempt to grow TiO 2 nanostructures at low temperature.…”