Synthesis of Calcium Manganese Oxide Films Using a Sol–Gel Method and Evaluation of Color and Photocatalytic Properties

Herein, for developing colored photocatalysts, calcium manganese oxide (Ca–Mn–O) film and powder samples are synthesized by a sol–gel method using acetylacetone (acac) or citric acid as a chelating agent, and their color and photocatalytic properties are evaluated. Thin‐film X‐ray diffraction experiments clarify the precipitation of Ca–Mn–O phases, such as Ca₃Mn₂O₇ (Ca/Mn = 1.5) and Ca₂MnO₄ (Ca/Mn = 2), in the film samples with drop‐cast coating. These films strongly absorb all visible light due to the interband transition between O 2p and Mn 3d orbitals, resulting in dark gray coloration. By testing photocatalytic activities using methylene blue dyes, it is revealed that the film sample (acac, 4‐drops) exhibits photocatalytic activities, which makes Ca–Mn–O films dual functional with photocatalytic functions and coloration.