Hydrothermal synthesis of titanate nanotubes from TiO₂ nanorods prepared: Via a molten salt flux method as an effective adsorbent for strontium ion recovery

Hydrated titanate nanotubes (TNTs) were hydrothermally synthesized at 160 °C over reaction times of 6-72 h from molten salt TiO₂ nanorods (NRs). Most of the TiO₂ NRs were transformed into tubular structure within 24-72 h. The samples synthesized over short reaction times (6-24 h) formed admixtures of TNT and untransformed TiO₂ NR residues. Strontium ion (Sr²⁺) adsorption by the as-prepared samples was quantified. The surface area of the TNTs increased the Sr²⁺ ion adsorption relative to that of the TiO₂ NRs. The mechanism underlying Sr²⁺ adsorption relied on an ion exchange reaction between Sr²⁺ ions in the stock solution and Na⁺ ions in an interlayer of the TNTs. TEM, EDAX, and XAFS analysis confirmed that Sr²⁺ adsorption and Na⁺ release occurred at the interlayer of the TNT-2D. The maximum adsorption capacity of the TNTs was calculated using the Langmuir equation. TNT (TNT-2D) sample synthesized over 48 h displayed the highest adsorption capacity (113.6 mg g^-1), with a Sr²⁺ uptake having a nearly 99% efficiency.