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The formation process of titania based nanorods during hydrothermal synthesis starting from an amorphous TiO₂·nH₂O gel has been investigated. Sodium tri-titanate (Na₂Ti₃O₇) particles with a rodlike morphology were prepared by a simple hydrothermal process in the presence of a concentrated NaOH aqueous solution. The ion exchange reaction of the synthesized Na₂Ti₃O₇ nanorods with HCl under ultrasonic treatment promotes a complete sodium substitution and the formation of H₂Ti₃O₇ nanorods. Low-temperature annealing of the as-produced nanorods of Na₂Ti₃O₇ and H₂Ti₃O₇ leads to a loss of the layered crystal structure and the formation of nanorods of condensed framework phasessodium hexa-titanate (Na₂Ti₆O₁₃) and metastable TiO₂-B phases, respectively. These transformations proceed without a significant change in particle morphology. The nanostructures were investigated by scanning …