Microwave-assisted hydrothermal synthesis of manganate nanoflowers for selective retention of strontium

Abstract

An alternative microwave-assisted hydrothermal route for the preparation of manganate nanoflowers under basic conditions has been proposed in view of potential uses in selective retention of strontium from multicomponent aqueous streams. Based on the combination of such characterization techniques as Scanning and Transmission Electronic Microscopy, X-ray photoelectron spectroscopy, and X-ray Diffraction, as well as taking advantage of the computer-aided structure simulation, homogeneous nanoflower morphology possessing a layered structure and K⁺ compensating cations was evidenced as corresponding to the KMn₄O₈ chemical formula. The nanoflower sample was subsequently tested for the selective adsorption of strontium and cesium by measuring the individual adsorption isotherms from single-solute and multicomponent aqueous solutions. The material appeared selective towards strontium against cesium even in multicomponent solutions provided that the concentration of calcium remained low. This difference in the retention selectivity was rationalized based on the Density Functional Theory (DFT) calculations of the energy of adsorption and direct calorimetry measurements of the enthalpy of displacement for the individual cations.

Keywords: Adsorption selectivity; Cesium; Hydrothermal synthesis; Manganate nanoflowers; Microwave-assisted synthesis; Multicomponent aqueous solutions; Radioactive remediation; Strontium.