Multifunctional flexible free-standing titanate nanobelt membranes as efficient sorbents for the removal of radioactive (90)Sr(2+) and (137)Cs(+) ions and oils

Abstract

For the increasing attention focused on saving endangered environments, there is a growing need for developing membrane materials able to perform complex functions such as removing radioactive pollutants and oil spills from water. A major challenge is the scalable fabrication of membranes with good mechanical and thermal stability, superior resistance to radiation, and excellent recyclability. In this study, we constructed a multifunctional flexible free-standing sodium titanate nanobelt (Na-TNB) membrane that was assembled as advanced radiation-tainted water treatment and oil uptake. We compared the adsorption behavior of (137)Cs(+) and (90)Sr(2+) on Na-TNB membranes under various environmental conditions. The maximum adsorption coefficient value (Kd) for Sr(2+) reaches 10(7) mL g(-1). The structural collapse of the exchange materials were confirmed by XRD, FTIR and XPS spectroscopy as well as Raman analysis. The adsorption mechanism of Na-TNB membrane is clarified by forming a stable solid with the radioactive cations permanently trapped inside. Besides, the engineered multilayer membrane is exceptionally capable in selectively and rapidly adsorbing oils up to 23 times the adsorbent weight when coated with a thin layer of hydrophobic molecules. This multifunctional membrane has exceptional potential as a suitable material for next generation water treatment and separation technologies.

Figure 1. Characterization of sodium titanate nanobelt (Na-TNB) membrane.

(a) The fabrication of Na-TNB membrane by vacuum filtration; photographs of the Na-TNBs membrane before (b) and after silicone coating (c) and their corresponding radionuclide removal and oil uptake studies, respectively; inset: water contact-angle measurement. (d) The flexible free-standing Na-TNBs membrane. (e) The Na-TNBs membrane with different diameter discs and (f) the stability of Na-TNBs membrane in solution. (g) The cross-sectional SEM image of Na-TNBs membrane and SEM (h) and TEM (i) images of Na-TNBs.

Figure 2

(a) Adsorption kinetic curves of Sr²⁺ and Cs⁺ onto Na-TNBs at 1.5 mmol L⁻¹ initial Cs⁺ or Sr²⁺ concentration (V/m = 800 mL/g). (b) The linear fit of experimental data obtained using the pseudo-second-order kinetic model. Adsorption isotherms of Sr²⁺ (c) and Cs⁺ (d) onto Na-TNBs. Symbols denote experimental data, the solid lines represent the Langmuir model simulation, and the dashed lines represent the Freundlich model. All adsorption isotherms were conducted at V/m = 800 mL/g and with different initial Cs⁺ or Sr²⁺ concentration ranging from 0.17 mmol L⁻¹ to 6.85 mmol L⁻¹.

Figure 3

(a) The effect of adsorbent contents on the adsorption of Cs⁺ and Sr²⁺ at 1.5 mmol L⁻¹ initial Cs⁺ or Sr²⁺ concentration and different V/m ranging from 400 mL/g to 4000 mL/g. (b) Recycling of Na-TNBs in the ion exchange of Cs⁺ and Sr²⁺ at 1.5 mmol L⁻¹ initial Cs⁺ or Sr²⁺ concentration and V/m = 800 mL/g.

Figure 4

XRD patterns (a) FTIR spectra (b) and Raman spectra (c) before and after the ion exchange with Sr²⁺, Cs⁺ and H⁺, and XPS spectra (d) before and after the ion exchange with Sr²⁺ and Cs⁺.

Figure 5

Schematic structural features of Na-TNBs before (a) and after ion exchange with Sr²⁺ and Cs⁺ ions (b). (c) The phase transition to the rutile in concentrate acid solution. And the rutile can be further used for the regeneration of the titanates through alkaline treatment and silicone coating for oil uptake.

Figure 6

(a) A layer of gasoline was absorbed by the modified TNB membrane in 15 s. The gasoline was labeled with Rhodamine B for clear presentation. (b) Absorption efficiency of modified TNB membrane for oils and organic liquids.