| Abstract
| - Titanate nanofibers of various sizes and layered structure were prepared from inorganic titaniumcompounds by hydrothermal reactions. These fibers are different from “refractory” mineral substancesbecause 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 nanostructuresto TiO2 polymorphs take place readily in simple wet-chemical processes at temperatures close to ambienttemperature. In acidic aqueous dispersions, the fibers transform to anatase and rutile nanoparticles,respectively, but via different mechanisms. The titanate fibers prepared at lower hydrothermal temperaturestransform to TiO2 polymorphs at correspondingly lower temperatures because they are thinner, possess alarger 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 TiO2 nanocrystals reacted with concentrateNaOH solution, yielding hollow titanate nanotubes. Consequently, there are reversible transformationpathways for transitions between the titanates and the titanium dioxide polymorphs, via wet-chemicalreactions at moderate temperatures. The significance of these findings arises because such transitionscan be engineered to produce numerous delicate nanostructures under moderate conditions. To demonstratethe commercial application potential of these processes, we also report titanate and TiO2 nanostructuressynthesized directly from rutile minerals and industrial-grade rutiles by a new scheme of hydrometallurgicalreactions.
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