Mokhnatska L. Synthesis, structure and electrochemical properties of nanodispersed oxides and oxidhydroxides of iron.

The study is dedicated todetermine the patterns of synthesis influence on structural, magnetic, morphological, electric and photocatalytic properties of iron oxides and oxide-hydroxides and composite based on these materials, and carbon nanotubes with using the¬se obtained systems as a base of electric composition for electrochemical capacitors with pro¬ton electrolyte. The usage of partial charge theory allowed to predict conditions for ob¬taining Fe3O4 and -FeOОН phases by deposition method, moreover the experi¬men¬tal ve¬ri¬fication of obtained data was done. The superlinear behavior of frequency-depen¬dent spe¬cific electrical conductivity of ultrafine Fe3O4 and -FeOОН phases was analyzed. It was established that electrodes based on Fe3O4 and -FeOОН shows the maximum values of specific capacitance 32 and 80 F/g, respectively. The usage of obtained by the method of ultrasonic homogenization electrodes based on composite Fe3O4/carbon nano¬tu¬bes didn’t demonstrate prominent increase of specific capacitance, which didn’t exceed 40 F/g. The efficiency of using the ion exchange method to obtain complex iron and lithium oxides with spinel structure at temperature <120oC with usage of ultrafine -FeOОН as precursor. Main patterns of structural-morphological dependence and depen¬den¬ce of micro magnetic properties of LiFe5O8 on synthesis conditions were defined, as well as there was explained that Gileo-Isikawa model can’t be used for interpretation of Mosbauer spectra of these materials. It was defined that the increase in the molar concentration of iron-containing pre¬cur¬sor during -FeOОН synthesis by deposition method leads to the decrease in the average si¬ze of crystallites of the obtained material, which are characterized by frequency-activated po¬laron conductivity. The application of -FeOОНwith different crystallinity degree as a ba¬se for electrode composition demonstrated the increase in specific capaci¬tance under the con¬dition of agglomeration decreasing of -FeOОН particles, which have the “core-shell” structure. Moreover, the precursorconcentrationincreasing leads to the increase in¬near-surface defective layerthickness. The thickness of near-surface layer doesn’t depend on iron-containing component morphology for β-FeOOH/carbon nano¬tu¬bes composite ma¬te¬rials. The particles size decreasing leads to the increase in charge car¬riers scattering in¬flu¬ence on defects in near-surface layer in contrast to electrical con-ductivity increasing as a result of the increase of β-FeOOH nonstoichiometry and Fe2+ ions concentration. The ma¬xi¬mum value of specific capacitance for an electrode based on β-FeOOH is 84 F/g. For¬ma¬tion of composites with nanotubes leads to decreasing the value of specific capacitance due todecrease in trans¬por-tefficiency of charge carriers. It was established that -FeOОН / TiO2 composite ma¬terials demonstrate increased photocatalytic activity in pho¬to¬deg¬ra¬dation reaction of me¬thy¬lene blue dyecompared toundoped titanium dioxide that can beexplained by increase in the photogenerated current carrierslife time as a resultof elec¬trons and holesseparation by heterojunction field on the phase boundary. The structural evolution during heat treatment and phase stability of the obtained by the method of hydrothermal synthesis ultra fine β-FeOOH was analyzed. There was shown, that the usage ofcompatible hydrothermal method to obtain β-FeOOH/carbon nano¬tubes composite materials allows obtaining effective electrode material for hybrid capa¬citors with water electrolyte with increased value of specific capacitance up to 87 F/g com¬pared to 49 F/g for β-FeOOH without carbon component.