Regulating of MnO2 photocatalytic activity in degradation of organic dyes by polymorphic engineering

• Published in: Solid state sciences Vol. 132; p. 106997
• Main Authors: Belousov, Artem S., Suleimanov, Evgeny V., Parkhacheva, Alina A., Fukina, Diana G., Koryagin, Andrey V., Koroleva, Aleksandra V., Zhizhin, Evgeny V., Gorshkov, Alexey P.
• Format: Journal Article
• Language: English
• Published: Elsevier Masson SAS 01.10.2022
• Subjects: Dye degradation; Manganese dioxide; Photocatalyst; Polymorphs; Visible light; Manganese dioxide; Visible light; Dye degradation; Polymorphs; Photocatalyst
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/j.solidstatesciences.2022.106997

Different phase nanostructured MnO2, including α-, β-, γ-, and δ-MnO2, were prepared by a hydrothermal route. Their photocatalytic activities in the degradation of cationic (methylene blue) and anionic (methyl orange) dyes were compared for the first time. The as-prepared oxides were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and low-temperature nitrogen adsorption-desorption techniques. It was shown that the highest efficiency was achieved in the degradation of cationic methylene in the presence of the δ-MnO2 photocatalyst (conversion of methylene blue was 90.4% after 180 min). These results are explained by unique physicochemical properties of the δ-MnO2 polymorph. It was observed that there is a synergetic effect between various physicochemical properties of δ-MnO2 which allows to obtain the high photodegradation efficiency: high adsorption ability towards methylene blue, unique 2D morphology, lower Mn–O bond strength, and high surface Mn4+/Mn3+ molar ratio. The reaction mechanism as well as the main products of the methylene blue photooxidation process over δ-MnO2 were also investigated. [Display omitted] •The highest photodegradation rates in the presence of MnO2 were observed when methylene blue was used as amodel dye.•All the prepared polymorphs are characterized by a low adsorption capacity towards methyl orange and low photocatalytic activity.•The photoconversion of methylene blue after 180 min decreased in the following order: δ-MnO2 > α-MnO2 > γ-MnO2 > β-MnO2.•The excellent photocatalytic performance of δ-MnO2 is explained by a synergetic effect between physicochemical properties.