Layered ammonium vanadate nanobelt as efficient adsorbents for removal of Sr and Cs from contaminated water.

In this study, a layered ammonium vanadate (NHVO) nanobelt adsorbent was synthesized by a facile hydrothermal method to remove Sr and Cs from contaminated water. The NHVO nanobelt was texturally and morphologically characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman, thermogravimetric differential thermal analyzer (TG-DSC), Brunauer- Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS) both before and after adsorbing Sr and Cs. The results showed that the NHVO nanobelt exhibited the optimal morphological structure with a 2:1 ratio of NHVO:dipropylamine. In the lattice of the adsorbent, the horizontal distance between oxygen atoms was 0.55 nm, the vertical distance between vanadium was 0.35 nm, and the layer distance of the adsorbent was 0.931 nm. The structure characterization indicated the VO octahedron formed a basic framework through sharing connected vertices. Adsorption mechanism studies indicated that ion exchange was the main adsorption mechanism for removing Sr and Cs. Batch experiments revealed that the adsorption capacity for Sr was 192.52 mg/g under a pH of 2. Similarly, the adsorption capacity for Cs was 251.09 mg/g when the pH was 5. The adsorption kinetics and adsorption isotherms data were in accordance with the pseudo-second-order kinetic model and Langmuir model, respectively. Adsorption isotherms results also indicated that the adsorption of Sr and Cs was endothermic (ΔH = 3.6 kJ/mol, ΔH = 29.1 kJ/mol) and increased entropy (ΔS = 29.15 J/molK, ΔS = 160.38 J/molK). Finally, the structure of the adsorbent, the adsorption performance and mechanism, and the interpretation of selective adsorption were also calculated by DFT method at the molecular level and the results were consistent with the experimental data.