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 degree 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.