Effect of potassium on the structure, characteristics and Cs sorption ability of porous materials in the system Na2O–B2O3–SiO2–GeO2

Abstract

Functional porous materials actively used as sorbents and membranes have complex microstructural morphologies that satisfy different requirements for industrial or medical purposes. In order to apply porous membranes, the sizes, shapes and orientations of their pores, along with their densities, surface-to-volume ratios and spatial distributions, need to be carefully considered. Thus, the possibility to alter the properties of porous materials during the production process via their structural alteration becomes a priority. For example, improved production methods can help to enhance the performance of sorbents used in waste treatment. This paper presents the results of a study of the structure and physico-chemical properties of glasses of the Na₂O/K₂O–B₂O₃–SiO₂–GeO₂ system and porous glasses obtained from them. Changes in the structure of the initial glasses when sodium is replaced with potassium at constant ratios of glass-forming cations were estimated based on the results of Raman spectroscopy. At a ratio of K₂O/Na₂O contents of about 0.6, nonlinear dependencies of the density and temperature of the glass transition on the size of the alkaline cation are characterized by kinks. The characteristics of seven porous materials were determined according to the method of low-temperature adsorption–desorption of nitrogen. It is demonstrated that the microstructure of a porous material depends on the composition and structure of the initial glass. The results of the sorption of cesium from the solution correlate well with changes in the structure of the initial glasses when replacing sodium with potassium. The volume of micropores is shown to increase with an increase in the number of coordinated germanium atoms in the glass ^[6]Ge, while the specific surface area and volume of mesopores depend more on the ratio of ^[4]B and ^[3]B in the composition of borate superstructural groupings. As a result, the porous glass in which sodium oxide is completely replaced by potassium oxide has optimal characteristics regarding Cs sorption and stability.