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.