Effective retention of cesium ions from aqueous environment using morphologically modified kaolinite nanostructures: experimental and theoretical studies

Abstract

Kaolinite can undergo a controlled morphological modification process into exfoliated nanosilicate sheets (EXK) and silicate nanotubes (KNTs). The modified structures were assessed as potential effective adsorbents for the retention of Cs⁺ ions. The impact of the modification process on the retention properties was assessed based on conventional and advanced equilibrium studies, considering the related steric and energetic functions. The synthetic KNTs exhibit a retention capacity of 249.7 mg g⁻¹ as compared to EXK (199.8 mg g⁻¹), which is significantly higher than raw kaolinite (73.8 mg g⁻¹). The kinetic modeling demonstrates the high effectiveness of the pseudo-first-order kinetic model (R² > 0.9) to illustrate the sequestration reactions of Cs⁺ ions by K, EXK, and KNTs. The enhancement effect of the modification processes can be illustrated based on the statistical investigations. The presence of active and vacant receptors enhanced greatly from 19.4 mg g⁻¹ for KA to 40.8 mg g⁻¹ for EXK and 46.9 mg g⁻¹ for KNTs at 298 K. This validates the significant impact of the modification procedures on the specific surface area, reaction interface, and reacting chemical groups' exposure. This also appeared in the enhancement of the reactivity of their surfaces to be able to uptake 10 Cs⁺ ions by KNTs and 5 ions by EXK as compared to 4 ions by kaolinite. The thermodynamic and energetic parameters (Gaussian energy < 8.6 kJ mol⁻¹; uptake energy < 40 kJ mol⁻¹) show that the physical processes are dominant, which have spontaneous and exothermic properties. The synthetic EXK and KNT structures validate the high elimination performance of the retention of Cs⁺ either in the existence of additional anions or cations.