Dependence of Surface Properties and Sorption Capacity of Magnesium Silicates on Crystalline Structure and Synthesis Method

Abstract

Crystalline magnesium silicates with talc and saponite structures have been synthesized under hydrothermal conditions. Amorphous magnesium silicate has been obtained using the precipitation and sol−gel methods. The influence of the crystalline structure of magnesium silicates on their sorption capacity and surface properties has been studied. The samples have been examined using X-ray diffraction analysis, scanning electron microscopy with EDX analysis, and low-temperature nitrogen adsorption. The moisture absorption capacity of the samples and the functional composition of their surfaces have been investigated. The ability of the samples to remove an antibiotic, ciprofloxacin, from aqueous media has been studied, and adsorption isotherms have been constructed. The Langmuir, Freundlich, and hybrid Langmuir−Freundlich models have been used to approximate the obtained data. The contributions of different mechanisms to the adsorption of ciprofloxacin by the synthesized magnesium silicates have been evaluated. An analysis of the quantitative distribution of acidic and basic sites, as well as the sorption capacity of the samples, has revealed that, for the studied materials, the distribution of the active sites and the sorption capacity depend essentially on the degree of crystallinity of the samples, the structural ordering of their surfaces, and the method of their preparation. It has been found that a decrease in the crystallinity and the transition to amorphous forms, as well as the specific features of the synthesis method leading to the formation of a more developed and porous surface, contribute to an increase in the sorption capacity of the samples.