Hollow flower-like titanium ferrocyanide structure for the highly efficient removal of radioactive cesium from water

The selective removal of Cs-137 from contaminated seawater or radioactive liquid waste remains a challenge due to the presence of high concentrations of competing ions, such as K+, Na+, Mg2+, and Ca2+. Here, we report a simple synthetic strategy to prepare hollow flower-like titanium ferrocyanide (hf-TiFC) for the removal of Cs-137 from water with enhanced Cs adsorption properties compared with conventional Cs adsorbents such as zeolites and crystalline silicotitanate (CST). hf-TiFC composed of 2-dimensional TiFC flakes was fabricated using a TiO2 sacrificial template via a simple reaction with potassium ferrocyanide (FC) based on the Kirkendall-type diffusion method under acidic conditions. The resulting hf-TiFC shows much faster Cs adsorption kinetics than the granular form of TiFC (g-TiFC) due to the lack of resistance against intracrystalline diffusion of Cs and a maximum adsorption capacity (454.54 mg/g) 3-fold higher than that of g-TiFC because of the increased effective surface area of hf-TiFC. Moreover, hf-TiFC also has better Cs adsorption kinetics, capacity and selectivity of Cs than do well-known Cs adsorbents such as chabazite (CHA) and protonated CST (HCST). In radioactive tests, even the low concentration of hf-TiFC (0.1 g/L) exhibited excellent removal performances in simulated seawater and nuclear liquid waste at pH 1 and 5.7 M Na+ with a high removal efficiency exceeding 99.1% at an initial Cs-137 specific activity of approximately 110 Bq/g.