Optical Properties and Photocatalytic Activity of Marokite-Type CaMn₂O₄

The optical properties and electronic structure of marokite-type CaMn₂O₄ are investigated by using UV−vis spectroscopy and the local-spin-density approximation plus the Hubbard-U (LSDA+U) method. Four absorption bands are observed at 638 nm (1.94 eV), 512 nm (2.42 eV), 377 nm (3.29 eV) and 248 nm (5.00 eV), which are ascribed to the charge transfer transitions O2p↑→Mn3d e_g↑, O2p↓→Mn3d e_g↑, Mn3d e_g↑→Mn3d t_2g ↓ and O2p↑→Mn3d t_2g↓, respectively. We further use CaMn₂O₄ as a photocatalyst to decompose an azo-dye acid orange 7 (AO7) under irradiation of visible light and find that the decomposition ratio of AO7 reaches 15.9% under the irradiation of visible light for two hours.