CATALYTIC PROPERTIES OF SYNTHETIC HAUSMANNITE IN THE OZONE DECOMPOSITION REACTION

Abstract

Samples of IS-Mn and IIS-Mn were synthesized and characterized by X-ray diffraction, IR spectroscopy and pH-metry. The X-ray diffraction method revealed both samples to be crystalline and single-phase. IS-Mn sample contains a phase of gausmannite (Mn3O4) with the parameters of the crystal lattice of tetragonal symmetry and the crystallites sized 43 nm. IIS-Mn sample, obtained by calcination of Mn3O4 sample in air under the condition of 600 oC for 4 hours, contains a phase of bixbyite Mn2O3 with a cubic crystal lattice and the crystallites sized 66 nm. The spectra of the Mn3O4 and Mn2O3 samples are particularly different in the region of Mn-OH and Mn-O valence vibrations. For gausmannite, the absorption band for Mn2+ in Td-coordination at 631 cm-1 and the absorption band for Mn3+ in Oh-coordination at 523 and 407cm-1 were clearly shown. In the IR spectrum of bixbyite, several intense absorption bands were observed at 674; 658; 606 and 542 cm-1, which correlate with the literature data and correspond to the valence oscillations of Mn-O in Mn2O3. The pH measurement of the aqueous suspension of the synthesized samples showed that Mn3O4 forms an alkaline medium, and Mn2O3 –weakly acidic upon contact with water molecules. Testing of Mn3O4 and Mn2O3 samples in the ozone decomposition reaction at the initial concentration of 100 mg/m3 showed that the kinetic curves profiles were determined by the phase composition. The testing of the samples was completed and it was established that the same degree of ozone decomposition, namely 50%, was achieved. For hausmannite, the values of the ozone half-life (t1/2) and the amount of ozone (Qexp), which reacted at the end of the experiment, are greater than Mn2O3 sample. The presence of manganese in two oxidation states Mn2+ and Mn3+ in the Mn3O4 structure promotes the redox process, and the alkaline medium contributes to the radical-chain reaction, which affects values t1/2 of and Qexp, which reacted.