Characterization of Cuban and Brazilian natural zeolites by photoacoustic spectroscopy and electron paramagnetic resonance

This report describes the photoacoustic and electron paramagnetic resonance investigations of Brazilian and Cuban zeolites. Photoacoustic optical absorption measurements indicate the presence of iron (Fe3+) ions with their respective transition bands for both zeolites. Two species of manganese (Mn2+ and Mn3+) were identified in the Cuban sample and the electronic transitions assigned. Iron and manganese ions were confirmed through nonradiative relaxation (tau) and characteristic diffusion (tau(beta)) times evaluation, whose values were found to be tau(BRA) = 5.40 ms, tau(CUB) = 4.60 ms, tau(beta BRA) = 387 mu s and tau(beta BRA) = 305 ms. Crystal field (Dq-(BRA)/Dq-(CUB) = 1048 cm(-1)/945 cm(-1)) plus Racah (B-(BRA)/B-(CUB) = 457 cm(-1)/813 cm(-1) and C-(BRA)/C-(CUB) = 3655 cm(-1)/2496 cm(-1)) parameters were assessed as well. Paramagnetic resonance corroborated Fe3+ ions present in the Brazilian zeolite occupying sites showing axial and/or rhombic symmetry distortions. For the Cuban sample, results reveal the characteristic hyperfine sextet lines of Mn2+ overlapping the Fe3+ line. Values of Lande factor and isotropic hyperfine splitting constant were found to be 2.0 and 9.7 mT, respectively. This tells us that the Mn2+ lies in octahedral symmetry probably replacing calcium ions and point towards an ionic bonding character of the Mn2+ and its surroundings.

Automated summary

This report describes the investigation of Brazilian and Cuban zeolites using photoacoustic and electron paramagnetic resonance techniques. The presence of iron and manganese ions in both zeolites was confirmed, and their electronic transitions were assigned. Crystal field parameters and Racah parameters were assessed. Paramagnetic resonance results confirmed the presence of Fe3+ ions in Brazilian zeolite and revealed the overlapping hyperfine structure of Mn2+ ions in the Cuban sample. The findings suggest that Mn2+ ions are in octahedral symmetry, likely replacing calcium ions and exhibiting an ionic bonding character.