TEXTURAL AND STRUCTURAL CHARACTERISTICS OF MANGANESE OXIDES WITH THE BIRNESSITE STRUCTURE
The interaction of manganese chloride and potassium permanganate in an excess of alkali - sodium hydroxide synthesized manganese oxides with the birnessite structure. X-ray and thermogravimetric analysis, Raman spectroscopy, scanning electron microscopy, and low-temperature nitrogen adsorption have been used to study the textural and structural characteristics of the synthesized materials as a function of the thermal modification temperature and sample composition (salt-form, H-form). It is shown that samples in the salt-form are related to the hexagonal form of birnessite. Conversion to the H-form leads to the formation of a tetragonal form of birnessite. The form of adsorption-desorption isotherms corresponds to type IV for all samples. For salt-forms, the hysteresis loop corresponds to the H1 type, for H-forms, to the mixed H1/H2 type. An increase in the temperature of thermal modification leads to sintering and closing of some pores, as a result of which the value of the specific surface decreases from SBET = 136,30 m2/g for an air-dry sample to SBET = 122,32 m2/g (150 °С) and to SBET = 114,28 m2/g (360 °С), while the pore diameter increases from Ddes = 14,11 nm to Ddes = 14,36 nm and Ddes = 15,96 nm. Transfer to the H-form, regardless of the temperature of thermal modification, contributes to a decrease in the pore diameter from Ddes = 14,36 nm to Ddes = 12,65 (150 °С) and from Ddes = 15,96 nm to Ddes = 9,37 nm (360 °С). At the same time, the specific surface area SBET = 122,32 m2/g (150 °С) and SBET = 158,21 m2/g (360 °С). It has been established that the water content in the samples is closely related to the quantitative determination of the specific surface area: the more water, the greater the surface area. The results of the study of synthesis and operation conditions (acid treatment) for textural and structural characteristics are relevant in connection with the development of cathode materials for lithium batteries, new magnetic materials, ion sieves, molecular sieves and catalysts based on manganese oxide with birnessite structure.